CN112703435B

CN112703435B - Optical film, method for producing same, optical laminate, and liquid crystal display device

Info

Publication number: CN112703435B
Application number: CN201980059082.8A
Authority: CN
Inventors: 西冈宽哉; 须田和哉; 摺出寺浩成
Original assignee: Zeon Corp
Current assignee: Zeon Corp
Priority date: 2018-09-28
Filing date: 2019-09-20
Publication date: 2023-03-24
Anticipated expiration: 2039-09-20
Also published as: TWI808262B; KR20210070272A; WO2020066899A1; TW202016184A; JP7463965B2; JPWO2020066899A1; CN112703435A

Abstract

The invention provides an optical film which is formed by using a thermoplastic norbornene resin containing a norbornene polymer, wherein the glass transition temperature Tg of the thermoplastic norbornene resin satisfies the formula (1), and the birefringence Deltan shown when the thermoplastic norbornene resin is subjected to free end uniaxial stretching to 1.5 times at Tg +15 DEG C _R Satisfying the formula (2), the retardation Rth in the thickness direction of the optical film and the thickness d of the optical film satisfy the formula (3). (1) Tg not lower than 110 deg.C and (2) delta n _R ≥0.0025;(3)Rth/d≥3.5×10 ^‑3 。

Description

Optical film, method for producing same, optical laminate, and liquid crystal display device

Technical Field

The invention relates to an optical film, a method for manufacturing the same, an optical laminate and a liquid crystal display device.

Background

Conventionally, an optical film formed using a thermoplastic resin is known. For example, patent documents 1to 5 describe optical films formed using a thermoplastic norbornene resin.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2005-043740;

patent document 2: japanese patent laid-open publication No. 2006-235085;

patent document 3: japanese patent laid-open publication No. 2006-327112;

patent document 4: japanese patent laid-open No. 2008-114369;

patent document 5: japanese patent laid-open No. 2003-238705.

Disclosure of Invention

Problems to be solved by the invention

In recent years, optical films used in image display devices such as liquid crystal display devices are required to have excellent retardation properties, and particularly, films having excellent retardation Rth in the thickness direction are required to have excellent retardation properties. Specifically, the optical film is required to have a large retardation Rth in the thickness direction per thickness. As a method for obtaining an optical film having a large retardation Rth in the thickness direction per thickness using a conventional film made of a thermoplastic resin, a method of stretching at a high stretching ratio is considered. However, an optical film obtained by stretching at a high stretch ratio tends to have a reduced accuracy of orientation angle.

In addition, the image display device is sometimes used in various environments, for example, may be used in a high-temperature environment. Therefore, the optical film is required to have high heat resistance. Therefore, when attention is paid to the retardation Rth in the thickness direction, it is required to suppress the variation of the retardation Rth in the thickness direction even under a high temperature environment.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical film formed using a thermoplastic norbornene resin, having a large retardation Rth in the thickness direction per unit thickness, having high orientation angle accuracy, and capable of suppressing a change in retardation Rth in the thickness direction under a high temperature environment, a method for manufacturing the optical film, and an optical laminate and a liquid crystal display device including the optical film.

Means for solving the problems

The inventors have made intensive studies to solve the above problems. As a result, the inventors have found that a predetermined birefringence Δ n is exhibited by using a glass transition temperature Tg in a predetermined range and stretching the film under a predetermined condition _R The resin (4) as a thermoplastic norbornene resin enables to produce an optical film having a large retardation per thickness in the thickness direction, a high accuracy of orientation angle, and excellent heat resistance, and the present invention has been completed.

That is, the present invention includes the following.

[1] An optical film formed using a thermoplastic norbornene-based resin containing a norbornene-based polymer,

the glass transition temperature Tg of the thermoplastic norbornene resin satisfies the following formula (1),

when the thermoplastic norbornene resin is uniaxially stretched at Tg +15 ℃ by a free end of 1 minute to 1.5 times, the thermoplastic norbornene resin exhibits birefringence Δ n _R Satisfies the following formula (2),

the retardation Rth in the thickness direction of the optical film and the thickness d of the 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 according to item [1], wherein the norbornene-based polymer has a molecular weight distribution of 2.4 or less.

[3] The optical film according to [1] or [2], wherein the norbornene-based polymer is selected from a polymer of a monomer containing 25% by weight or more of a tetracyclododecene-based monomer and a hydride thereof,

the tetracyclododecene monomer is selected from tetracyclododecene and tetracyclododecene derivatives in which a ring of tetracyclododecene is substituted.

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

[5] The optical film according to any one of [1] to [4], wherein the in-plane retardation Re of the optical film is 40nm or more and 80nm or less.

[6] A method for producing an optical film according to any one of [1] to [5],

the production method comprises molding the thermoplastic norbornene resin by an extrusion molding method or a solution casting method.

[7] An optical laminate comprising a polarizing plate and the optical film according to any one of [1] to [5 ].

[8] A liquid crystal display device having the optical laminate according to [7 ].

Effects of the invention

According to the present invention, it is possible to provide an optical film which is formed using a thermoplastic norbornene resin, has a large retardation Rth in the thickness direction per thickness, has high alignment angle accuracy, and can suppress a change in the retardation Rth in the thickness direction under a high-temperature environment, a method for producing the optical film, and an optical laminate and a liquid crystal display device each including the optical film.

Detailed Description

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be modified and implemented as desired without departing from the scope and range of equivalents of the claims of the present invention.

In the following description, unless otherwise specified, the in-plane retardation Re of the film is a value represented by Re = (nx-ny) × d. 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 specified. Here, nx represents a refractive index in a direction showing a maximum refractive index among directions (in-plane directions) perpendicular to the thickness direction of the film. ny represents a refractive index in a direction orthogonal to the nx direction among the in-plane directions. nz represents a refractive index in the thickness direction. d represents the thickness of the film. Unless otherwise stated, the measurement wavelength was 550nm.

In the following description, a "long film" is a film having a length of 5 times or more, preferably 10 times or more, with respect to the width of the film, and more specifically, a film having a length of such a degree that the film can be stored or transported by being wound in a roll. The upper limit of the ratio of the length to the width of the film is not particularly limited, and may be 100000 times or less, for example.

In the following description, unless otherwise specified, "polarizing plate" includes not only a rigid member but also a member having flexibility such as a resin film.

[1. Summary of optical film ]

An optical film according to an embodiment of the present invention is a film formed using a thermoplastic norbornene-based resin. The thermoplastic norbornene-based resin includes a norbornene-based polymer. The optical film of the present embodiment satisfies the following first to third requirements.

First, the glass transition temperature Tg of the thermoplastic norbornene-based resin satisfies the following formula (1).

(1)Tg≥110℃

Second, evaluation of birefringence Δ n of thermoplastic norbornene-based resin _R Satisfies the following formula (2). Here, the evaluation of birefringence indicates: birefringence developed when a material is uniaxially stretched at a free end for 1 minute at a stretching temperature 15 ℃ higher than the glass transition temperature of the material by a factor of 1.5.

(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 of the present embodiment satisfying the first to third requirements has a large retardation Rth in the thickness direction per unit thickness d as expressed by the formula (3). In addition, the optical film can suppress variation in retardation Rth in the thickness direction under a high-temperature environment. Further, the optical film can realize a retardation Rth in the thickness direction larger than the thickness d as described above and high alignment angle accuracy.

[2. Thermoplastic norbornene resin ]

The thermoplastic norbornene-based resin is a thermoplastic resin containing a norbornene-based polymer. The norbornene-based polymer is a polymer having a structure obtained by polymerizing a norbornene-based monomer and, if necessary, further hydrogenating the resulting polymer. Therefore, the norbornene-based polymer generally includes at least one structure selected from a repeating structure obtained by polymerizing a norbornene-based monomer and a structure obtained by hydrogenating the repeating structure. In such norbornene-based polymers, for example: a ring-opening polymer of a norbornene monomer, a ring-opening copolymer of a norbornene monomer and an arbitrary monomer, and a hydrogenated product thereof; addition polymers of norbornene monomers, addition copolymers of norbornene monomers and optional monomers, and hydrogenated products thereof. The norbornene polymer contained in the thermoplastic norbornene resin may be one type, or two or more types.

The norbornene-based monomer is a monomer having a norbornene structure in a molecule. Examples of the norbornene-based monomer include: bicyclo [2.2.1]Hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ]Deca-3, 7-diene (common name: dicyclopentadiene), tetracyclo [4.4.0.1 ] ^2,5 .1 ^7,10 ]Norbornene-based monomers not having an aromatic ring structure, such as dodecene-3-ene (a common name: tetracyclododecene); norbornene monomers having an aromatic substituent such as 5-phenyl-2-norbornene, 5- (4-methylphenyl) -2-norbornene, 5- (1-naphthyl) -2-norbornene and 9- (2-norbornene-5-yl) -carbazole; 1, 4-methyl bridge-1, 4,4a,4b,5,8,8a, 9a-octahydrofluorene, 1, 4-methyl bridge-1, 4,4a, 9a-tetrahydrofluorene (commonly known as "methyl bridge tetrahydrofluorene"), 1, 4-methyl bridge-1, 4,4a, 9a-tetrahydrodibenzofuran, 1,4-Norbornene-based monomers comprising a norbornene ring structure and an aromatic ring structure in a polycyclic condensed structure, such as methano-1, 4,4a, 9a-tetrahydrocarbazole, 1, 4-methano-1, 4, 9a, 10-hexahydroanthracene, 1, 4-methano-1, 4,4a,9,10, 10a-hexahydrophenanthrene, etc.; and derivatives of these compounds (for example, compounds having a substituent on the ring).

Examples of the substituent include: alkyl groups such as methyl, ethyl, propyl, and isopropyl; an alkylene group; an alkenyl group; polar groups, and the like. Examples of the polar group include a heteroatom and an atomic group having a heteroatom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, a halogen atom, and the like. Specific examples of the polar group include: halogen groups such as fluoro, chloro, bromo, and iodo; a carboxyl group; a carbonyloxycarbonyl group; an epoxy group; a hydroxyl group; an oxy group; an alkoxy group; an ester group; a silanol group; a silyl group; an amino group; a nitrile group; a sulfonic acid group; a cyano group; an amide group; imide groups, and the like. The number of the substituents may be one or two or more. The two or more substituents may be the same or different. However, from the viewpoint of obtaining an optical film having low saturated water absorption and excellent moisture resistance, the norbornene-based monomer preferably has a small amount of polar groups, and more preferably has no polar groups.

The norbornene-based monomer may be used alone or in combination of two or more kinds thereof at an arbitrary ratio.

The specific kind and polymerization ratio of the norbornene monomer are desired to obtain the desired glass transition temperature Tg and the evaluation birefringence Δ n _R The thermoplastic norbornene resin (4) is selected. Generally, the glass transition temperature and the birefringence of a norbornene polymer depend on the kind and polymerization ratio of norbornene monomers as raw materials of the norbornene polymer. Therefore, by appropriately adjusting the kind and polymerization ratio of the norbornene monomer, the glass transition temperature Tg and the birefringence developing property of the norbornene polymer can be adjusted, and therefore the glass transition temperature Tg and the evaluation birefringence Δ n of the thermoplastic norbornene resin containing the norbornene polymer can be adjusted _R Adjusting to satisfy the formula (1) and the formula (2).

Easily obtaining glass transition temperature Tg and evaluating birefringence Deltan from increasing glass transition temperature and birefringence development of norbornene polymer _R From the viewpoint of a large thermoplastic norbornene-based resin, a tetracyclododecene-based monomer is preferably used as the norbornene-based monomer. Therefore, the norbornene-based polymer is preferably selected from polymers of monomers containing tetracyclododecene-based monomers and hydrides thereof. Such a norbornene-based polymer generally includes one or more structures selected from a repeating structure obtained by polymerizing a tetracyclododecene-based monomer and a structure obtained by hydrogenating the repeating structure (hereinafter, may be referred to as a "tetracyclododecene-based structure" as appropriate).

The tetracyclododecene-based monomer means a monomer selected from tetracyclododecene and tetracyclododecene derivatives. The tetracyclododecene derivative refers to a compound having a structure in which a substituent is bonded to the ring of tetracyclododecene. The number of the substituents may be one or two or more. The two or more substituents may be the same or different. As a preferred tetracyclododecene derivatives, can be cited for example 8-ethylene-four ring [4.4.0.1 ^2,5 .1 ^7,10 ]Dodec-3-ene (common name: ethylenetetracyclododecene), 8-ethyl-tetracyclo [4.4.0.1 ^2,5 .1 ^7,10 ]-dodec-3-ene, 8-ethoxycarbonyltetracyclo [4.4.0.1 ^2,5 .1 ^7,10 ]-3-dodecene, 8-methyl-8-methoxycarbonyltetracyclo [4.4.0.1 ² ^,5 .1 ^7,10 ]-3-dodecene and the like. The tetracyclododecene monomers may be used singly or in combination of two or more.

The proportion (polymerization ratio) of the tetracyclododecene monomer contained is preferably 25% by weight or more, more preferably 27% by weight or more, particularly preferably 29% by weight or more, preferably 60% by weight or less, more preferably 55% by weight or less, and particularly preferably 50% by weight or less, relative to 100% by weight of the total amount of monomers as raw materials of the norbornene-based polymer. In tetracyclododecene monomersWhen the polymerization ratio is in the above range, the glass transition temperature Tg and the evaluation birefringence Δ n of the thermoplastic norbornene-based resin can be easily adjusted because the glass transition temperature Tg and the birefringence development property of the norbornene-based polymer can be increased _R The control is in the range of formula (1) and formula (2).

In general, the ratio of a repeating structure (monomer unit) derived from a certain monomer in a norbornene-based polymer is equal to the ratio of the monomer in the whole monomers (polymerization ratio). Therefore, the proportion of the tetracyclododecene-based structure in the norbornene-based polymer is generally in accordance with the polymerization ratio of the tetracyclododecene-based monomer with respect to the total amount of the monomers. Therefore, the proportion of the tetracyclododecene-based structure with respect to 100% by weight of the norbornene-based polymer is preferably in the same range as the polymerization ratio of the tetracyclododecene-based monomer described above.

Further, from the viewpoints of increasing the glass transition temperature and birefringence developing property of the norbornene-based polymer, easily obtaining a thermoplastic norbornene-based resin having a high glass transition temperature Tg and a high evaluation birefringence Δ nR, it is preferable to use a dicyclopentadiene-based monomer as the norbornene-based monomer. Therefore, the norbornene-based polymer is preferably selected from a polymer of a monomer containing a dicyclopentadiene-based monomer and a hydride thereof. Such a norbornene-based polymer generally includes one or more structures selected from a repeating structure obtained by polymerizing a dicyclopentadiene-based monomer and a structure obtained by hydrogenating the repeating structure (hereinafter, may be referred to as a "dicyclopentadiene-based structure" as appropriate).

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

Relative to 100 wt% of the total amount of monomers used as raw materials of the norbornene polymerThe proportion (polymerization ratio) of the dicyclopentadiene monomer(s) is preferably 50% by weight or more, more preferably 55% by weight or more, particularly preferably 60% by weight or more, preferably 80% by weight or less, more preferably 75% by weight or less, and particularly preferably 70% by weight or less. When the polymerization ratio of the dicyclopentadiene monomer is in the above range, the glass transition temperature Tg and the evaluation birefringence Δ n of the thermoplastic norbornene resin can be easily adjusted because the glass transition temperature Tg and the birefringence development property of the norbornene polymer can be increased _R The control is in the range of formula (1) and formula (2).

In general, the proportion of the dicyclopentadiene-based structure in the norbornene-based polymer is in accordance with the polymerization ratio of the dicyclopentadiene-based monomer with respect to the total amount of the monomers. Therefore, the proportion of the dicyclopentadiene-based structure to 100% by weight of the norbornene-based polymer is preferably in the same range as the polymerization ratio of the dicyclopentadiene-based monomer.

In particular, when a tetracyclododecene-based monomer and a dicyclopentadiene-based monomer are used in combination as the norbornene-based monomer, the ratio of the amounts of these monomers is preferably within a predetermined range. Specifically, the amount of the dicyclopentadiene monomer is preferably 100 parts by weight or more, more preferably 150 parts by weight or more, particularly preferably 200 parts by weight or more, preferably 500 parts by weight or less, more preferably 450 parts by weight or less, and particularly preferably 400 parts by weight or less, based on 100 parts by weight of the tetracyclododecene monomer. Therefore, in the norbornene-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, particularly preferably 200 parts by weight or more, preferably 500 parts by weight or less, more preferably 450 parts by weight or less, and particularly preferably 400 parts by weight or less, based on 100 parts by weight of the tetracyclododecene-based structure. In the case where the amount ratio is within the above range, the glass transition temperature Tg and the birefringence developing property of the norbornene-based polymer can be increased, and therefore the glass transition temperature Tg and the evaluation birefringence Δ n of the thermoplastic norbornene-based resin can be easily adjusted _R The control is in the range of formula (1) and formula (2).

In use with norborneneIn the case of any monomer to be copolymerized with the monomer, the arbitrary monomer is selected so as to obtain a polymer having a desired glass transition temperature Tg and an evaluated birefringence Deltan _R The thermoplastic norbornene resin (4) is not limited in scope. Examples of the arbitrary monomer that can be ring-opening copolymerized with the norbornene-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. In addition, examples of the arbitrary monomer capable of addition copolymerization with the norbornene-based monomer include: alpha-olefins having 2 to 20 carbon atoms such as ethylene, propylene and 1-butene, and derivatives thereof; cycloolefins 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. Any monomer may be used alone or in combination of two or more.

The norbornene-based polymer preferably contains a hydride having a structure obtained by polymerizing a norbornene-based monomer and further hydrogenating the monomer. The hydride may be a hydride obtained by hydrogenating a non-aromatic unsaturated bond in the polymer, a hydride obtained by hydrogenating an aromatic unsaturated bond in the polymer, or a hydride obtained by hydrogenating both a non-aromatic unsaturated bond and an aromatic unsaturated bond in the polymer. Particularly preferred is a norbornene polymer obtained by hydrogenating both a non-aromatic unsaturated bond and an aromatic unsaturated bond in the polymer. By using the hydrogenated norbornene polymer in this manner, the appearance of retardation Rth in the thickness direction can be effectively improved, and the photoelastic coefficient can be reduced. Therefore, it is possible to achieve both a large retardation Rth in the thickness direction and a low photoelastic coefficient. Further, the properties of the optical film such as mechanical strength, moisture resistance, and heat resistance can be effectively improved in general.

The glass transition temperature of the norbornene-based polymer is preferably 110 ℃ or higher, more preferably 112 ℃ or higher, and particularly preferably 114 ℃ or higher. By using the norbornene-based polymer having a high glass transition temperature in this manner, the orientation relaxation of the norbornene-based polymer in a high-temperature environment can be suppressed. Therefore, the variation of the retardation Rth in the optical film thickness direction under a high temperature environment can be suppressed. In addition, in general, a film containing a norbornene polymer in which the type and polymerization ratio of the norbornene monomer are adjusted so as to have a glass transition temperature within the above range tends to have a large developing property of birefringence due to stretching, and thus the retardation Rth in the thickness direction of the optical film tends to be increased. The upper limit of the glass transition temperature of the norbornene-based polymer is not particularly limited, but is preferably 180 ℃ or lower, more preferably 170 ℃ or lower, and particularly preferably 160 ℃ or lower. When the glass transition temperature of the norbornene-based polymer is not more than the above upper limit, the retardation Rth in the thickness direction of the optical film is easily increased.

The glass transition temperature of the norbornene polymer can be measured using a differential scanning calorimeter under the condition of a temperature rise rate of 10 ℃/min in accordance with JIS K6911.

The glass transition temperature of the norbornene-based polymer can be adjusted by, for example, the kind and polymerization ratio of the norbornene-based monomer which is a raw material of the norbornene-based polymer.

The norbornene-based polymer preferably has a large birefringence. Therefore, the norbornene-based polymer preferably has a large evaluation birefringence. Specifically, the evaluation birefringence of the norbornene-based polymer is preferably 0.0025 or more, more preferably 0.0026 or more, and particularly preferably 0.0027 or more. By using the norbornene-based polymer having a large evaluation birefringence as described above, a large retardation can be exhibited even when the stretching ratio is low. Therefore, the optical film can exhibit a large retardation Rth in the thickness direction at a small stretching magnification, and therefore the orientation angle accuracy of the optical film can be effectively improved. The upper limit of the evaluation of birefringence of the norbornene-based polymer is not particularly limited, but is preferably 0.0050 or less, more preferably 0.0047 or less, and particularly preferably 0.0045 or less. When the evaluation birefringence of the norbornene-based polymer is not more than the above upper limit, the production of the norbornene-based polymer can be easily performed.

Evaluation of birefringence of norbornene polymer the birefringence can be measured by the following method.

The norbornene polymer is molded to obtain a sheet. The sheet was subjected to free-end uniaxial stretching. The free-end uniaxial stretching is stretching in one direction, and means stretching in which no constraining force is applied to the sheet in a direction other than the stretching direction. The stretching temperature of the free-end uniaxial stretching is a temperature 15 ℃ higher than the glass transition temperature of the norbornene-based polymer. The stretching time was 1 minute, and the stretching ratio in the free-end uniaxial stretching was 1.5 times. After stretching, the in-plane retardation at the center of the sheet was measured at a measurement wavelength of 550nm, and the in-plane retardation was divided by the thickness of the center of the sheet to obtain an evaluation birefringence.

The evaluation of the birefringence of the norbornene-based polymer can be adjusted by, for example, the type and polymerization ratio of the norbornene-based monomer which is a raw material of the norbornene-based polymer, and the molecular weight distribution of the norbornene-based polymer.

The weight average molecular weight Mw of the norbornene-based polymer is preferably 10000 to 100000, more preferably 15000 to 80000, and particularly preferably 20000 to 60000. In the case where the weight average molecular weight is in the above range, the mechanical strength and moldability of the optical film can be highly balanced.

The molecular weight distribution Mw/Mn of the norbornene-based polymer is preferably 2.4 or less, more preferably 2.35 or less, and particularly preferably 2.3 or less. When the molecular weight distribution Mw/Mn of the norbornene-based polymer is within the above range, the adhesive strength of the optical film can be improved, and thus delamination (delaminations) of the optical film can be suppressed. The molecular weight distribution refers to the ratio of the weight average molecular weight to the number average molecular weight, and is expressed as "weight average molecular weight Mw/number average molecular weight Mn". The lower limit of the molecular weight distribution of the norbornene-based polymer is usually 1.0 or more.

The weight average molecular weight and the number average molecular weight of the norbornene-based polymer can be measured by gel permeation chromatography using cyclohexane as an eluent in terms of polyisoprene. When the norbornene-based polymer is insoluble in cyclohexane, toluene may be used as an eluent in the gel permeation chromatography. When the eluent is toluene, the weight average molecular weight and the number average molecular weight can be determined in terms of polystyrene conversion.

The norbornene polymer preferably has a stress birefringence of 2350X 10 ^-12 Pa ^-1 Above, 2400 × 10 is more preferable ^-12 Pa ^-1 Above, 2550X 10 is particularly preferable ^-12 Pa ^-1 Above, preferably 3000 × 10 ^-12 Pa ^-1 Hereinafter, 2950 × 10 is more preferable ^-12 Pa ^-1 Hereinafter, 2800 × 10 is particularly preferable ^-12 Pa ^-1 The following. When the stress birefringence of the norbornene-based polymer is not less than the lower limit of the above range, the film containing the norbornene-based polymer tends to have a large developing property of birefringence by stretching, and therefore the retardation Rth in the thickness direction of the optical film tends to be increased. In addition, when the stress birefringence of the norbornene polymer is not more than the upper limit of the above range, it is easy to control the retardations Re and Rth of the optical film, and the in-plane variation of the retardation can be suppressed.

The stress birefringence of the norbornene polymer can be measured by the following method.

The norbornene polymer was formed into a sheet form to obtain a sheet. After both ends of the sheet are fixed by clips, a weight of a predetermined weight (for example, 160 g) is fixed to one clip. Next, the sheet is lifted up in an oven set to a predetermined temperature (for example, a temperature 5 ℃ higher than the glass transition temperature of the norbornene-based polymer) for a predetermined time (for example, 1 hour) from the other side clip to which the weight is not fixed, and then subjected to a stretching treatment. The sheet subjected to the stretching treatment was slowly cooled and returned to room temperature. Regarding this sheet, the in-plane retardation at the center of the sheet was measured at a measurement wavelength of 650nm, and the in-plane retardation was divided by the thickness of the center of the sheet to calculate the δ n value. Then, the stress birefringence can be determined by dividing the δ n value by the stress applied to the sheet (in the above case, the stress applied when a predetermined weight is fixed).

The stress birefringence of the norbornene-based polymer can be adjusted by the kind and polymerization ratio of the norbornene-based monomer which is a raw material of the norbornene-based polymer.

The norbornene-based polymer can be produced by a production method including, for example, the following steps: norbornene-based monomers and optional monomers to be used as needed are polymerized in the presence of a suitable catalyst. In addition, when the norbornene-based polymer is a hydrogenated product thereof, the method for producing the norbornene-based polymer may include the steps of: after the polymerization, the resulting polymer is contacted with hydrogen in the presence of a hydrogenation catalyst containing a transition metal such as nickel, palladium, or ruthenium, to hydrogenate the carbon-carbon unsaturated bond.

The proportion of the norbornene-based polymer contained in the thermoplastic norbornene-based resin is arbitrary within a range in which the thermoplastic norbornene-based resin satisfying the formulae (1) and (2) can be obtained. From the viewpoint of effectively utilizing the excellent characteristics of the norbornene-based polymer, the proportion of the norbornene-based polymer contained in the thermoplastic norbornene-based resin is preferably 80 to 100% by weight, more preferably 90 to 100% by weight, and particularly preferably 95 to 100% by weight.

The thermoplastic norbornene-based resin may contain any component other than the norbornene-based polymer. Examples of the optional components include an ultraviolet absorber, an antioxidant, a heat stabilizer, a light stabilizer, an antistatic agent, a dispersant, a chlorine scavenger, a flame retardant, a crystal nucleating agent, a reinforcing agent, an anti-blocking agent, an antifogging agent, a mold release agent, a pigment, an organic or inorganic filler, a neutralizing agent, a lubricant, a decomposition agent, a metal deactivator, an antifouling agent, and an antibacterial agent. Any of the components may be used alone or two or more of them may be used in combination at any ratio.

The thermoplastic norbornene-based resin has a glass transition temperature Tg satisfying the above formula (1). Specifically, the glass transition temperature Tg of the thermoplastic norbornene-based resin is usually 110 ℃ or higher, preferably 112 ℃ or higher, and particularly preferably 114 ℃ or higher. By using the thermoplastic norbornene-based resin having a high glass transition temperature Tg in this manner, the orientation relaxation of the norbornene-based polymer in a high-temperature environment can be suppressed. Therefore, the variation of the retardation Rth in the optical film thickness direction under a high temperature environment can be suppressed. In addition, in general, a film containing a thermoplastic norbornene resin having a glass transition temperature Tg in the above range tends to have a large developing property of birefringence due to stretching, and thus the retardation Rth in the thickness direction of the optical film tends to be increased. The upper limit of the glass transition temperature Tg of the thermoplastic norbornene-based resin is not particularly limited, but is preferably 180 ℃ or lower, more preferably 170 ℃ or lower, and particularly preferably 160 ℃ or lower. When the glass transition temperature Tg of the thermoplastic norbornene-based resin is not more than the upper limit, the retardation Rth in the thickness direction of the optical film is easily increased.

The glass transition temperature Tg of the thermoplastic norbornene resin can be measured using a differential scanning calorimeter under the condition of a temperature rise rate of 10 ℃/min in accordance with JIS K6911.

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

The thermoplastic norbornene resin has an evaluated birefringence [ Delta ] n satisfying the formula (2) _R . Specifically, evaluation of birefringence Δ n of thermoplastic norbornene resin _R Usually 0.0025 or more, preferably 0.0026 or more, and particularly preferably 0.0027 or more. By using the optical fiber having a large evaluation birefringence Deltan _R The thermoplastic norbornene resin (2) can exhibit a large retardation even when the stretching ratio is low. Therefore, the optical film can exhibit a large retardation Rth in the thickness direction at a small stretching magnification, and therefore the orientation angle accuracy of the optical film can be effectively improved. Evaluation of birefringence Deltan of thermoplastic norbornene resin _R The upper limit of (b) is not particularly limited, but is preferably 0.0050 or less, more preferably 0.0047 or less, and particularly preferably 0.0045 or less. Evaluation of birefringence Deltan in thermoplastic norbornene-based resin _R When the content is not more than the above upper limit, the thermoplastic norbornene resin can be easily produced.

Evaluation of birefringence Deltan of thermoplastic norbornene resin _R The measurement can be performed by the following method.

The thermoplastic norbornene resin was molded to obtain a sheet. The sheet was subjected to free-end uniaxial stretching. The stretching temperature of the free-end uniaxial stretching is a temperature 15 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin (i.e., tg +15 ℃). The stretching time was 1 minute, and the stretching ratio of the free-end uniaxial stretching was 1.5 times. After stretching, the in-plane retardation Re (a) at the center of the sheet was measured at a measurement wavelength of 550nm, and the in-plane retardation Re (a) was divided by the thickness T (a) at the center of the sheet to obtain the evaluation birefringence Δ n _R 。

Evaluation of birefringence Deltan of thermoplastic norbornene resin _R The molecular weight distribution of the norbornene-based polymer and the content of the norbornene-based polymer can be adjusted by, for example, the type and polymerization ratio of the norbornene-based monomer which is a raw material of the norbornene-based polymer, and the molecular weight distribution of the norbornene-based polymer.

Stress birefringence C of thermoplastic norbornene-based resin _R Preferably 2350X 10 ^-12 Pa ^-1 Above, 2400 × 10 is more preferable ^-12 Pa ^-1 Above, 2550X 10 is particularly preferable ^-12 Pa ^-1 Above, preferably 3000X 10 ^-12 Pa ^-1 Hereinafter, 2950 × 10 is more preferable ^-12 Pa ^-1 Hereinafter, 2800 × 10 is particularly preferable ^-12 Pa ^-1 The following. Stress birefringence C in thermoplastic norbornene-based resin _R When the lower limit value of the above range is not less than the lower limit value, the film containing the thermoplastic norbornene-based resin tends to have a large developing property of birefringence due to stretching, and therefore the retardation Rth in the thickness direction of the optical film tends to be increased. Further, stress birefringence C in thermoplastic norbornene-based resin _R When the retardation is not more than the upper limit of the above range, the retardation Re and Rth of the optical film can be easily controlled, and the in-plane variation of the retardation can be suppressed.

Stress birefringence C of thermoplastic norbornene-based resin _R The measurement can be performed by the following method.

The thermoplastic norbornene resin was molded into a sheet form to obtain a sheet. After both ends of the sheet are fixed by clips, a weight of a predetermined weight (for example, 160 g) is fixed to one clip. Next, the sheet is lifted up for a predetermined time (for example, 1 hour) from the clamp on the side to which the weight is not fixed in an oven set to a predetermined temperature (for example, a temperature 5 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin), and then subjected to a stretching treatment. The sheet subjected to the stretching treatment was slowly cooled and returned to room temperature. For this sheet, the in-plane retardation Re (b) at the center of the sheet was measured at a measurement wavelength of 650nm, and this in-plane retardation Re (b) was divided by the thickness T (b) [ mm ] of the center of the sheet]From this, the δ n value is calculated. Then, the stress birefringence C can be obtained by dividing the δ n value by the stress applied to the sheet (in the above case, the stress applied when a predetermined weight is fixed) _R 。

Stress birefringence C of thermoplastic norbornene-based resin _R The content can be adjusted by the type and polymerization ratio of the norbornene monomer as a raw material of the norbornene polymer and the content of the norbornene polymer.

[3. Characteristics of optical film ]

The optical film of the present embodiment is formed using the thermoplastic norbornene-based resin, and the retardation Rth in the thickness direction and the thickness d satisfy the formula (3). In detail, the ratio Rth/d is usually 3.5X 10 ^-3 Above, preferably 3.7 × 10 ^-3 Above, particularly preferably 4.0X 10 ^-3 As described above. In this manner, the optical film of the present embodiment can increase the retardation Rth in the thickness direction per unit thickness d. Therefore, it is possible to thin the thickness d and increase the retardation Rth in the thickness direction. The upper limit of the ratio Rth/d is not particularly limited, but is preferably 8.0X 10 from the viewpoint of effectively suppressing delamination of the optical film ^-3 Hereinafter, more preferably 6.0 × 10 ^-3 The following.

The glass transition temperature and the birefringence developing property of the norbornene-based polymer generally depend on the kind and polymerization ratio of the norbornene-based monomer as a material of the norbornene-based polymer. Thus, the borneol is containedGlass transition temperature Tg and evaluation of birefringence Deltan of thermoplastic norbornene resin of ethylenic Polymer _R There is a correlation with the kind and polymerization ratio of norbornene-based monomers as materials of the norbornene-based polymer. Therefore, the glass transition temperature Tg and the evaluation birefringence Deltan of the thermoplastic norbornene-based resin _R The type and polymerization ratio of norbornene monomers contained in the thermoplastic norbornene resin as a raw material of the norbornene polymer are generally reflected. According to the studies of the present inventors, it was revealed that the thermoplastic norbornene-based resin comprising the norbornene-based polymer using the norbornene-based monomer of which the kind and amount are such that the resin has the glass transition temperature Tg within the predetermined range and the evaluation birefringence Δ n is excellent in the development of retardation Rth in the thickness direction by stretching _R Is selected in the manner of (a). Therefore, the optical film having a high Rth/d as described above can be produced by using the thermoplastic norbornene-based resin containing the norbornene-based polymer as a stretched film.

The optical film of the present embodiment preferably has a small photoelastic coefficient. The specific photoelastic coefficient of the optical film is preferably 8Brewster or less, more preferably 7Brewster or less, and particularly preferably 6Brewster or less. Here, 1brewster =1 × 10 ^-13 cm ² And/dyn. When the photoelastic coefficient of the optical film is small, the optical film is less likely to change in optical characteristics such as warpage and retardation. Therefore, when the optical film is provided in the liquid crystal display device, the occurrence of light leakage due to warpage of the optical film can be suppressed. The light leakage is a phenomenon in which light to be shielded leaks from the screen and the screen becomes bright when the liquid crystal display device is set to a black display state. The lower limit of the photoelastic coefficient is not particularly limited, but is preferably 0.5Brewster or more, more preferably 1.0Brewster or more, and particularly preferably 1.5Brewster or more.

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

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

The optical film of the present embodiment can realize high orientation angle accuracy. Specifically, the optical film has a slow axis in an in-plane direction perpendicular to its thickness direction. Further, the optical film can suppress the deviation in the direction of the slow axis. Therefore, since the deviation of the orientation angle θ, which is the angle formed by the slow axis and a certain reference direction, can be suppressed, high orientation angle accuracy can be achieved. When the optical film having high alignment angle accuracy is provided in a liquid crystal display device, the display characteristics such as the luminance and contrast of a screen can be made uniform in a plane.

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

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

The absolute value of the angle formed by the slow axis of the optical film and a certain reference direction was measured as the orientation angle θ. The measurement was performed at a plurality of measurement positions at intervals of 50mm in the width direction and 10m in the longitudinal direction of the optical film. Then, from these measurement results, the standard deviation θ σ of the orientation angle θ can be calculated.

In general, an optical film can be produced using a thermoplastic norbornene resin as a stretched film. Further, since the thermoplastic norbornene resin is excellent in birefringence development, the stretching ratio required for developing a large retardation to the extent of satisfying the formula (3) is small. Therefore, when an optical film is produced by forming a stretched film using a thermoplastic norbornene resin, the stretching ratio can be reduced. By such a small stretching magnification, the optical film described above can achieve high orientation angle accuracy.

The optical film of the present embodiment is excellent in heat resistance. Specifically, the optical film can suppress variation in the thickness direction retardation Rth under a high temperature environment. The optical film having excellent heat resistance can be applied to a liquid crystal display device used in a high-temperature environment.

The heat resistance of the optical film can be evaluated by the rate of change in retardation Rth in the thickness direction obtained by a durability test in a 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 of storing the optical film at 85 ℃ for 500 hours. After the durability test, the retardation Rth1 in the thickness direction of the optical film was measured. Then, the change rate can be calculated by dividing the change amount Rth0-Rth1 of the retardation in the thickness direction of the optical film obtained by the durability test by the retardation Rth0 in the thickness direction of the optical film before the durability test. According to the optical film of the present embodiment, the change rate of the retardation Rth in the thickness direction can be preferably 3% or less.

The optical film contains a thermoplastic norbornene-based resin having a high glass transition temperature Tg. Therefore, even under a high-temperature environment, the norbornene-based polymer molecules contained in the thermoplastic norbornene-based resin are less likely to undergo orientation relaxation. Therefore, as described above, the variation in the retardation Rth in the thickness direction in the high-temperature environment can be suppressed.

The optical film of the present embodiment preferably has high moisture resistance. Therefore, the optical film is preferably capable of suppressing variation in retardation Rth in the thickness direction under a high humidity environment. The optical film having excellent moisture resistance can be applied to a liquid crystal display device used in a high-humidity environment.

The moisture resistance of the optical film can be evaluated by the change rate of retardation Rth in the thickness direction obtained by the durability test under a high humidity 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 of storing the optical film at 60 ℃ and a humidity of 90% for 500 hours. After the durability test, the retardation Rth2 in the thickness direction of the optical film was measured. Then, the change rate can be calculated by dividing the change amount Rth0-Rth2 of the retardation in the thickness direction of the optical film obtained by the durability test by the retardation Rth0 of the optical film before the durability test in the thickness direction. According to the present embodiment, the rate of change of the retardation Rth in the thickness direction can be preferably 3% or less.

The norbornene polymer is preferably excellent in moisture resistance, and therefore the optical film is easily inhibited from moisture intrusion. Therefore, even under a high humidity environment, the molecules of the norbornene-based polymer contained in the optical film are less likely to undergo orientation relaxation. Therefore, as described above, the variation in the retardation Rth in the thickness direction in a high humidity environment can be suppressed.

The optical film of the present embodiment preferably has low water absorption. For example, when the optical film is immersed in water at 23 ℃ for 24 hours, the water absorption ratio on a weight basis of the optical film is preferably 0% to 0.15%, more preferably 0% to 0.10%, and particularly preferably 0% to 0.05%. When the water absorption rate is low as described above, the optical film can have excellent moisture resistance as described above.

The optical film of the present embodiment is preferably capable of suppressing delamination. Therefore, when the optical film is bonded to a film such as a polarizing plate using an adhesive, the optical film can be hardly peeled. Since a conventional stretched film containing a norbornene polymer is generally likely to be delaminated, the optical film of the present embodiment can suppress delamination as one of the advantages of the optical film.

The in-plane retardation Re of the optical film of the present embodiment may be any value depending on the application of the optical film. When a specific range is shown, the in-plane retardation Re of the optical film is preferably 40nm or more, more preferably 45nm or more, particularly preferably 50nm or more, preferably 80nm or less, more preferably 75nm or less, and particularly preferably 70nm or less. When the in-plane retardation Re of the optical film is not less than the lower limit of the above range, the retardation can be easily developed well. In addition, when the in-plane retardation Re of the optical film is not more than the upper limit value of the above range, the variation of the retardation in the plane can be suppressed. The in-plane retardation Re can be appropriately selected within the above range according to the design of the image display device.

The retardation Rth in the thickness direction of the optical film of the present embodiment may be any value depending on the application of the optical film. When a specific range is shown, the retardation Rth in the thickness direction of the optical film is preferably 100nm or more, more preferably 120nm or more, particularly preferably 150nm or more, preferably 400nm or less, more preferably 380nm or less, and particularly preferably 360nm or less. When the retardation Rth in the thickness direction of the optical film is equal to or more than the lower limit value of the above range, the contrast of the image display device in the oblique direction can be improved. In addition, when the retardation Rth in the thickness direction of the optical film is not more than the upper limit value of the above range, the in-plane variation of the retardation Rth in the thickness direction and the orientation angle can be suppressed. The retardation Rth in the thickness direction can be appropriately selected within the above range according to the design of the image display device.

The optical film of the present embodiment preferably has a high total light transmittance. The specific total light transmittance of the optical film is preferably 85% to 100%, more preferably 87% to 100%, and particularly preferably 90% to 100%. The total light transmittance can be measured in a range of a wavelength of 400nm to 700nm using a commercially available spectrophotometer.

The optical film of the present embodiment is preferably low in haze from the viewpoint of improving the image clarity of a liquid crystal display device to which the laminate film is attached. The haze of the optical film is preferably 1% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less. The haze can be measured by using a haze meter according to JIS K7361-1997.

The optical film of the present embodiment is preferably thin. By using the thermoplastic norbornene resin, a large retardation Rth in the thickness direction can be obtained even when the optical film is thin. In addition, when the optical film is thin, the warp of the optical film can be suppressed, and thus, variations in optical characteristics such as retardation due to the warp can be reduced. Therefore, 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 120 μm or less, more preferably 100 μm or less, and particularly preferably 80 μm or less. The lower limit of the thickness d is not particularly limited, but is preferably 20 μm or more, more preferably 30 μm or more, and particularly preferably 40 μm or more, from the viewpoint of suppressing delamination.

[4. Method for producing optical film ]

The optical film can be produced by a production method including, for example, the following steps: a step of molding a thermoplastic norbornene resin to obtain a resin film; and stretching the resin film. In order to distinguish the resin film before stretching from the optical film obtained after stretching, the film may be hereinafter referred to as a "film before stretching" as appropriate.

In the step of molding the thermoplastic norbornene resin to obtain the film before stretching, the molding method is not limited. Examples of the molding method include an extrusion molding method, a solution casting method, and a blow molding (inflation) molding method. Among them, extrusion molding and solution casting are preferable, and extrusion molding is particularly preferable.

After preparing the film before stretching, a step of stretching the film before stretching is performed. The stretching can orient the molecules of the norbornene-based polymer in the film, and thus an optical film having the above optical characteristics can be obtained. The stretching conditions in the step of stretching the film before stretching can be arbitrarily set within a range in which a desired optical film can be obtained.

The stretching method of the film before stretching may be, for example, uniaxial stretching in which stretching is performed in 1 direction, or biaxial stretching in which stretching is performed in 2 directions which are not parallel. The biaxial stretching may be simultaneous biaxial stretching in which stretching in 2 directions is performed simultaneously, or sequential biaxial stretching in which stretching in one direction is performed and then stretching in the other direction is performed. Among these, biaxial stretching is preferable, and sequential biaxial stretching is more preferable, from the viewpoint of easy production of an optical film having a large retardation Rth in the thickness direction.

The stretching direction of the film before stretching can be arbitrarily set. For example, in the case of a film in which the film is long before stretching, the stretching direction may be the machine direction, the transverse direction, or the oblique direction. The longitudinal direction represents the longitudinal direction of the long film, the transverse direction represents the width direction of the long film, and the oblique direction represents a direction which is neither parallel nor perpendicular to the longitudinal direction of the long film.

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

The stretching temperature of the film before stretching is preferably Tg ℃ or higher, more preferably Tg +5 ℃ or higher, preferably Tg +40 ℃ or lower, and more preferably Tg +30 ℃ or lower. When the stretching temperature is in the above range, the thickness of the optical film is easily made uniform.

As described above, in the above-described production method, the optical film can be obtained by stretching the film before stretching, but the above-described production method may further include any step.

For example, the above-described manufacturing method may include a step of trimming the optical film, a step of performing surface treatment on the optical film, and the like.

[5. Optical layered body ]

An optical laminate according to an embodiment of the present invention includes the optical film and the polarizing plate. The optical film can be made thin even if the retardation Rth in the thickness direction is large, and therefore the optical laminate can be made thin or the warpage of the optical laminate can be suppressed. Further, the optical film has high orientation angle accuracy, and therefore, the optical characteristics of the optical laminate can be made uniform in the plane. Further, since the optical film has high heat resistance, the optical laminate can also have high heat resistance. Such an optical laminate can be preferably applied to an image display device such as a liquid crystal display device.

As the polarizing plate, for example, a film having a polarizer layer can be used. As the polarizer layer, for example, a polarizer layer obtained by appropriately treating a film of an appropriate polyvinyl alcohol in an appropriate order and manner can be used. Examples of the polyvinyl alcohol include polyvinyl alcohol and partially acetalized polyvinyl alcohol. Examples of the treatment of the film include dyeing treatment using a dichroic substance such as iodine or a dichroic dye, stretching treatment, and crosslinking treatment. The polarizer layer is a polarizer layer capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and a polarizer layer having an excellent degree of polarization is particularly preferable. The thickness of the polarizer layer is generally from 5 μm to 80 μm, but is not limited thereto.

The polarizing plate may have a protective film on one side or both sides of the polarizer layer for protecting the polarizer layer. As the protective film layer, any transparent film layer can be used. Among them, a resin film layer excellent in transparency, mechanical strength, thermal stability, moisture resistance and the like is preferable. Examples of such resins include acetic acid resins such as cellulose triacetate, polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, thermoplastic norbornene resins, (meth) acrylic resins, and the like. Among them, from the viewpoint of small birefringence, an acetic acid resin, a thermoplastic norbornene-based resin, and a (meth) acrylic resin are preferable, and from the viewpoint of transparency, low hygroscopicity, dimensional stability, lightweight property, and the like, a thermoplastic norbornene-based resin is particularly preferable.

The polarizing plate can be produced by laminating a polarizer layer and a protective film layer, for example. In the bonding, an adhesive may be used as needed.

The optical laminate may further comprise any of the components in combination with the optical film and the polarizer. For example, the optical laminate may have an adhesive layer for bonding the optical film and the polarizing plate.

The thickness of the optical laminate is not particularly limited, but is preferably 30 μm or more, more preferably 50 μm or more, preferably 150 μm or less, and more preferably 130 μm or less.

[6. Liquid Crystal display device ]

A liquid crystal display device according to an embodiment of the present invention includes the above optical laminate. As described above, since the optical film included in the optical laminate can be thin, the optical laminate is less likely to warp. Therefore, the occurrence of light leakage due to the change in the optical characteristics of the optical film at the warped portion can be suppressed. The above-described warpage is generally likely to occur at the corners of the screen of the liquid crystal display device, but in the liquid crystal display device of the present embodiment, such light leakage at the corners can be suppressed. Further, since the optical film can have high alignment angle accuracy, the liquid crystal display device of the present embodiment can make display characteristics such as luminance and contrast of a screen uniform in the plane of the screen. Further, since the optical film has high heat resistance, the liquid crystal display device of the present embodiment can suppress a change in display characteristics in a high-temperature environment.

In general, a liquid crystal display device includes a liquid crystal cell and an optical laminate on at least one side of the liquid crystal cell. Among them, the optical laminate is preferably formed by arranging the liquid crystal cell, the optical film, and the viewing-side polarizer in this order. In such a structure, the optical film can function as a viewing angle compensation film.

As the liquid crystal cell, for example, a liquid crystal cell of any mode such as an in-plane switching (IPS) mode, a Vertical Alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, a continuous fireworks alignment (CPA) mode, a Hybrid Alignment Nematic (HAN) mode, a Twisted Nematic (TN) mode, a Super Twisted Nematic (STN) mode, or an Optically Compensated Birefringence (OCB) mode can be used.

Examples

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples, and may be modified and implemented arbitrarily within the scope and range equivalent to the scope of the present invention.

In the following description, "%" and "part" representing amounts are based on weight unless otherwise specified. Unless otherwise stated, the following operations were carried out in an atmosphere at normal temperature and normal pressure.

[ measurement method and calculation method of physical Property value of Polymer ]

(method of measuring weight-average molecular weight Mw, number-average molecular weight Mn and molecular weight distribution Mw/Mn of Polymer)

The weight average molecular weight Mw and the number average molecular weight Mn of the polymer were determined as standard polyisoprene values by Gel Permeation Chromatography (GPC) using cyclohexane as an eluent.

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

The measurement was carried out using 3 TOSOH CORPORATION columns (TSKgelG 5000HXL, TSKgelG4000HXL, and TSKgelG2000 HXL) connected in series under conditions of a flow rate of 1.0 mL/min, a sample injection amount of 100. Mu.L, and a column temperature of 40 ℃.

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

(method of measuring glass transition temperature Tg)

The glass transition temperature Tg was measured using a differential scanning calorimeter ("DSC 6220SII" manufactured by Nano Technology Co. Ltd.) under a condition of a temperature rising rate of 10 ℃/min based on JIS K6911.

(evaluation of birefringence. DELTA.n) _R Method of measuring (1)

The resin was molded into a sheet shape of 50mm in width, 100mm in length and 100 μm in thickness to obtain a sample sheet. The sample sheet was subjected to free-end uniaxial stretching using a tensile tester (model 5564 manufactured by Instron Japan Company Limited) with a thermostatic bath. The stretching conditions are as follows.

Stretching temperature: tg +15 deg.C

Distance between the clips: 65mm

Stretching ratio: 1.5 times (stretching distance 32.5 mm)

Stretching time: 1 minute

Stretching speed: 32.5 mm/min

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

The measurement sample was measured using a phase difference meter (Axospectra, manufactured by Inc. "AXOSCAN") and an in-plane retardation Re (a) [ nm ] of the central portion of the measurement sample was measured at a measurement wavelength of 550nm]And (4) carrying out measurement. Further, the thickness T (a) of the central portion of the measurement sample is [ mm ]]And (4) carrying out measurement. Using these measured values Re (a) and T (a), the evaluation birefringence Δ n of the resin was calculated by the following formula (X1) _R 。

Δn _R ＝Re(a)×(1/T(a))×10 ^-6 (X1)

(stress birefringence C _R Method of measuring (2)

The resin was molded into a sheet shape of 35mm in length, 10mm in width and 1mm in thickness to obtain a sample sheet. After both ends of the sample sheet were fixed by clips, a weight of 160g was fixed to one side of the clip. Next, the sample sheet was lifted up for 1 hour from the other side clamp to which the weight was not fixed in an oven set at a temperature of Tg +5 ℃ of the resin, and subjected to a stretching treatment. Then, the sample sheet was slowly cooled and returned to room temperature to obtain a measurement sample.

The in-plane retardation Re (b) [ nm ] of the central portion of the measurement sample was measured at a measurement wavelength of 650nm using a birefringence meter ("WPA-100" manufactured by Photonic Lamp, inc.). The thickness T (b) [ mm ] of the central portion of the measurement sample was measured. Using these measured values Re (b) and T (b), the δ n value is calculated by the following formula (X2).

δn＝Re(b)×(1/T(b))×10 ^-6 (X2)

Using the δ n value and the stress F applied to the sample, the stress birefringence C was calculated by the following formula (X3) _R 。

C _R ＝δn/F (X3)

[ II. evaluation method of Properties of optical film ]

(method of measuring photoelastic coefficient of optical film)

(method of evaluating the precision of orientation Angle of optical film)

The absolute value of the angle formed by the slow axis of the optical film and the longitudinal direction was measured as the orientation angle θ. This measurement was performed using a polarization microscope ("BX 51" manufactured by Olympus Corporation). The measurement of the orientation angle θ was performed at a plurality of measurement positions at intervals of 50mm in the width direction and at intervals of 10m in the longitudinal direction of the optical film. The standard deviation θ σ of these measurement results was calculated as an evaluation index of the orientation angle accuracy. The smaller the standard deviation θ σ of the orientation angle θ, the smaller the deviation of the orientation angle θ, and the more preferable.

(method of evaluating delamination of optical film)

An unstretched film (a film having a thickness of 100 μm, a glass transition temperature of 160 ℃ C. Of the resin, and which was not subjected to stretching treatment) formed using a resin containing a norbornene-based polymer was prepared as an adherend (adherend). One surface of an optical film as a film to be measured and one surface of the unstretched film are subjected to corona treatment. An adhesive (UV adhesive CRB series manufactured by Toyochem co., ltd.) was attached to both of the corona-treated surface of the optical film and the corona-treated surface of the unstretched film. The surfaces to which the adhesive is applied are bonded to each other. Then, the adhesive was cured by ultraviolet irradiation using a stepless UV irradiation apparatus (manufactured by Heraeus ltd). For the above ultraviolet irradiation, a D-type lamp was used as a lamp device, and the peak illuminance was 100mW/cm ² And a cumulative light amount of 3000mJ/cm ² The conditions of (2) are carried out. Thus, a sample film having a layer structure of an unstretched film/adhesive layer/optical film was obtained.

The obtained sample film was subjected to a 90-degree peel test in accordance with the following procedure.

The sample film was cut to a width of 15mm to obtain a film sheet. The optical film side surface of the film sheet was bonded to the surface of a glass slide using an adhesive. At this time, a double-sided adhesive tape (manufactured by Nitto Denko Corporation, product number "CS 9621") was used as the adhesive. The unstretched film included in the film sheet was held between the tips of high-performance digital display type push-pull force meters (ZP-5N manufactured by IMADA co., ltd.), pulled at a speed of 300 mm/min in the normal direction of the surface of the slide glass, and the magnitude of the pulling force was measured and used as the peel strength. The peel strength was evaluated according to the following evaluation criteria.

Good: 1.0N/15mm or more.

Poor: less than 1.0N/15mm.

(methods of measuring retardation Rth, re and thickness d of optical film, and method of evaluating Rth/d)

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

The thickness d of the optical film was measured by a caliper (manufactured by Mitutoyo Corporation, "ID-C112 BS").

The measured retardation in the thickness direction Rth is divided by the thickness d to calculate Rth/d.

(evaluation method of the rate of change of retardation Rth in the thickness direction of the optical film after 500 hours at 85 ℃ C.)

Before the durability test described below, the retardation Rth0 in the thickness direction of the optical film was measured. Then, the optical film was subjected to a durability test in which the film was stored at 85 ℃ for 500 hours. 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 rate of change in retardation in the thickness direction of the optical film (Rth rate of change) by the durability test is calculated according to the following formula (X4).

Rate of change of Rth (%) = { (Rth 0-Rth 1)/Rth 0 }. Times 100 (X4)

The smaller the Rth variation ratio, the more excellent the heat resistance of the optical film. Therefore, the obtained Rth change rate was evaluated according to the following evaluation criteria.

Good: the Rth change rate is 3% or less.

Poor results: the rate of change of Rth is more than 3%.

(method of evaluating the rate of change of retardation Rth in the thickness direction of an optical film after 500 hours at 60 ℃ C. And humidity of 90%)

Before the durability test described below, the retardation Rth0 in the thickness direction of the optical film was measured. Then, the optical film was subjected to a durability test in which the film was stored at 60 ℃ and 90% humidity for 500 hours. After the durability test, the retardation Rth2 in the thickness direction of the optical film was measured. From these measured values Rth0 and Rth2, the rate of change in retardation in the thickness direction of the optical film (Rth rate of change) by the durability test is calculated according to the following formula (X5).

Rate of Rth variation (%) = { (Rth 0-Rth 2)/Rth 0} × 100 (X5)

The smaller the Rth variation ratio, the more excellent the heat resistance and moisture resistance of the optical film. Therefore, the obtained Rth change rate was evaluated according to the following evaluation criteria.

Good: the Rth change rate is 3% or less.

Poor: the rate of change of Rth is more than 3%.

(method of measuring Water absorption of optical film)

A part of the optical film was cut to prepare a test piece (size: 100 mm. Times.100 mm), and the weight w0 of the test piece was measured. Then, the test piece was immersed in water at 23 ℃ for 24 hours. After the immersion, the weight w1 of the test piece was measured. Then, the ratio (w 1-w 0)/w 0 of the weight w1-w0 of the test piece increased by the immersion to the weight w0 of the test piece before the immersion was calculated as the water absorption rate (%). The water absorption is preferably low.

[ III ] evaluation method of characteristics of liquid Crystal display device ]

(evaluation of Corner unevenness (Corner Mura))

The liquid crystal display device was subjected to a durability test in which the device was stored at 85 ℃ for 100 hours. Then, 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: no light leakage around the screen was found at all.

Poor: light leakage around the screen is significant.

[ example 1]

(1-1) production of Ring-opened Polymer:

in a glass reaction vessel inside which nitrogen substitution was performed, 200 parts by weight of dehydrated cyclohexane, 0.75mol% of 1-hexene, 0.15mol% of diisopropyl ether and 0.44mol% of triisobutyl aluminum were added to the reactor at room temperature relative to 100 parts by weight of the total of the following monomers, and mixed. Then, while maintaining the temperature at 45 ℃, 29 parts by weight of Tetracyclododecene (TCD), 68 parts by weight of dicyclopentadiene (DCPD), 3 parts by weight of Norbornene (NB) and 0.02mol% of tungsten hexachloride (0.65 wt% toluene solution) as monomers were simultaneously added continuously to the reactor over 2 hours to conduct polymerization. Subsequently, 0.2mol% of isopropyl alcohol was added to the polymerization solution to deactivate the polymerization catalyst, thereby terminating the polymerization reaction. In the above description, the amount represented by the unit "mol%" is a value in which the total amount of the monomers is 100 mol%. The weight-average molecular weight Mw of the resulting norbornene-based Ring-opened Polymer was 2.8X 10 ⁴ The molecular weight distribution (Mw/Mn) was 2.1. Further, the conversion of monomer to polymer was 100%.

(1-2) production of hydrogenated norbornene Polymer:

then, 300 parts of the reaction solution containing the ring-opened polymer obtained in the step (1-1) was transferred to an autoclave equipped with a stirrer, and 3 parts of a diatomaceous earth-supported nickel catalyst ("T8400 RL", manufactured by Nikkiso chemical Co., ltd., nickel supporting rate of 57%) was added to perform hydrogenation at 160 ℃ under a hydrogen pressure of 4.5MPa for 4 hours.

After the completion of the hydrogenation reaction, the resulting solution was subjected to pressure filtration (Fundaback Filter, manufactured by Shichuan Islands Seisakusho K.K.) at a pressure of 0.25MPa using RADIOLITE #500 as a Filter bed to remove the hydrogenation catalyst, thereby obtaining a colorless and transparent solution. The obtained solution was poured into a large amount of isopropyl alcohol to precipitate a norbornene-based polymer which is a hydride of the ring-opening polymer. After filtering the precipitated norbornene polymer, 2.0 parts of an antioxidant [ pentaerythritol-tetrakis [3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate ] in which 0.1 part of the antioxidant was dissolved was added to 100 parts of the norbornene polymer](product name "Irganox (registered trademark) 1010" manufactured by Ciba Specialty Chemicals Corporation)]In xylene solution. Then, the resulting mixture was dried for 6 hours by using a vacuum dryer (220 ℃ C., 1 Torr), to obtain a thermoplastic norbornene resin. The weight-average molecular weight of the norbornene-based polymer was 4.0X 10 ⁴ The molecular weight distribution Mw/Mn was 2.3.

The glass transition temperature Tg of the obtained thermoplastic norbornene resin was measured by the above-mentioned method, and the birefringence Δ n was evaluated _R And stress birefringence C _R . The glass transition temperature Tg of the thermoplastic norbornene resin was 110 ℃ C, and the birefringence Δ n was evaluated _R 0.0030, stress birefringence C _R Is 2600X 10 ^-12 Pa ^-1 。

(1-3) production of film before stretching:

the thermoplastic norbornene resin obtained in the above step (1-2) is fed into a twin-screw extruder and molded into a strand-shaped molded article by hot-melt extrusion molding. The molded article was cut with a pellet cutter (strand cutter) to obtain pellets of a thermoplastic norbornene resin.

The granules were dried at 100 ℃ for 5 hours. The pellets were then fed to an extruder by conventional methods and melted at 250 ℃. Then, the molten thermoplastic norbornene resin was discharged from the die onto a cooling drum to obtain a long film before stretching having a thickness of 110 μm.

(1-4) production of optical film:

a longitudinal drawing machine using a floating system between rolls was prepared. Using this longitudinal stretching machine, the film before stretching was stretched 1.26 times in the longitudinal direction to obtain an intermediate film. The stretching temperature of the above stretching using the longitudinal stretcher was 120 ℃ which is a temperature (Tg +10 ℃) 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin.

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

The optical film obtained was evaluated by the above-described method.

(1-5) production of optical laminate:

as a long raw material film, an unstretched polyvinyl alcohol film (vinylon film, average degree of polymerization of about 2400, degree of saponification of 99.9 mol%) having a thickness of 65 μm was prepared. The raw material film was subjected to a swelling treatment of immersing the film in pure water at 30 ℃ for 1 minute and a dyeing treatment of immersing the film in a dyeing solution (a dyeing solution containing iodine and potassium iodide at a molar ratio of 1: 23, a dyeing concentration of 1.2 mmol/L) at 32 ℃ for 2 minutes while continuously transporting the film in the longitudinal direction by a guide roller, so that iodine was adsorbed to the film. Then, the film was washed with a 3% aqueous solution of boric acid at 35 ℃ for 30 seconds. Then, the film was stretched to 6.0 times at 57 ℃ in an aqueous solution containing 3% boric acid and 5% potassium iodide. Then, the film was subjected to complementary color treatment in an aqueous solution containing 5% of potassium iodide and 1.0% of boric acid at 35 ℃. Then, the film was dried at 60 ℃ for 2 minutes to obtain a long polarizer layer having a thickness of 23 μm. The degree of polarization of the polarizer layer was measured using an ultraviolet-visible spectrophotometer ("V-7100" manufactured by JASCO Corporation), and it was 99.996%.

An acrylic resin ("sumiexiht 55X" manufactured by sumitomo chemical corporation) was supplied to a hot-melt extrusion film-forming machine equipped with a T-die. The acrylic resin was extruded from the T-die and formed into a film shape. Thus, a long protective film layer having a thickness of 40 μm and formed using an acrylic resin was obtained.

One side of the obtained protective film layer was subjected to corona treatment. Then, an ultraviolet-curable adhesive (Arkls KRX-7007, manufactured by ADEKA) was applied to the surface of the corona-treated protective film layer to form an adhesive layer. The polarizer layer and the protective film layer were laminated via the adhesive layer using a nip roll. Next, the adhesive layer was subjected to 750mJ/cm using a UV irradiation apparatus ² The adhesive layer is cured by ultraviolet irradiation. Thus, a long polarizing plate having a layer structure of a polarizer layer/an adhesive layer (thickness: 2 μm)/a protective film layer was obtained.

One side of the optical film is subjected to corona treatment. Then, an ultraviolet-curable adhesive (Arkls KRX-7007, manufactured by ADEKA) was applied to the surface of the optical film subjected to the corona treatment to form an adhesive layer. The polarizing plate and the optical film are bonded to each other via the adhesive layer by using a nip roll. Next, the adhesive layer was subjected to 750mJ/cm using a UV irradiation apparatus ² The adhesive layer is cured by ultraviolet irradiation. The lamination is performed such that the slow axis of the optical film and the absorption axis of the polarizer layer are perpendicular to each other when viewed in the thickness direction. Thus, a long optical laminate having a layer structure of optical film/adhesive layer/polarizer layer/adhesive layer/protective film layer was obtained.

(1-6) production of VA-type liquid Crystal display device:

a VA type liquid crystal display device (40-inch television "TH-40AX700" manufactured by Panasonic Corporation) was prepared. The liquid crystal display device has a polarizing plate attached to a viewing side of a glass surface of a liquid crystal cell. The polarizing plate on the viewing side is peeled from the liquid crystal display device. Then, the long optical laminate produced in the above-described steps (1 to 5) was cut into a size suitable for a liquid crystal display device, and the surface on the optical film side was bonded to the glass surface of the liquid crystal cell to produce a VA liquid crystal display device for testing. The lamination is performed so that the absorption axis direction of the polarizing plate on the viewing side originally included in the liquid crystal display device coincides with the absorption axis direction of the polarizer layer of the optical laminate newly laminated to the liquid crystal cell.

The obtained liquid crystal display device was evaluated by the above-described method.

[ example 2]

The combination of the monomers used in the above 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 Norbornene (NB).

In the above step (1-4), the longitudinal stretching magnification was changed to 1.28 times and the lateral stretching magnification was changed to 1.48 times. In the above-mentioned step (1-4), the stretching temperatures in the longitudinal direction and the transverse direction were changed to 122.5 ℃ which was a temperature 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin (Tg +10 ℃).

In addition to the above matters, the production and evaluation of the thermoplastic norbornene resin, the optical film, and the liquid crystal display device were performed in the same manner as in example 1.

[ example 3]

The combination of the monomers used in the above 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 Ethylenetetracyclododecene (ETD).

In the above step (1-4), the stretch ratio in the machine direction was changed to 1.27 times, and the stretch ratio in the transverse direction was changed to 1.44 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 124 ℃ which was a temperature 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene resin (Tg +10 ℃).

[ example 4]

The combination of the monomers used in the above 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 Ethylenetetracyclododecene (ETD).

In the above step (1-4), the stretch ratio in the machine direction was changed to 1.30 times and the stretch ratio in the transverse direction was changed to 1.50 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal direction and the stretching temperature in the transverse direction are changed to 125 ℃ which is a temperature (Tg +10 ℃) 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin.

[ example 5]

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

In the above step (1-4), the longitudinal stretch ratio was changed to 1.256. In the above-mentioned step (1-4), the stretching temperatures in the longitudinal and transverse directions were changed to 125.5 ℃ which was a temperature 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin (Tg +10 ℃).

Comparative example 1

The combination of the monomers used in the above 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 Norbornene (NB). Further, the polymerization temperature in the above step (1-1) was changed to 55 ℃.

In the above-mentioned step (1-4), the stretch ratio in the machine direction was changed to 1.25 times and the stretch ratio in the transverse direction was changed to 1.45 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal direction and the stretching temperature in the transverse direction are changed to 122 ℃, which is a temperature (Tg +10 ℃) 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin.

Comparative example 2

The combination of the monomers used in the above-mentioned 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 Ethylenetetracyclododecene (ETD).

In the above step (1-4), the longitudinal stretching magnification was changed to 1.35 times and the lateral stretching magnification was changed to 1.55 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal direction and the stretching temperature in the transverse direction are changed to 114 ℃, which is a temperature (Tg +10 ℃) 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin.

In the same manner as in example 1 except for the above matters, the thermoplastic norbornene resin, the optical film and the liquid crystal display device were manufactured and evaluated.

Comparative example 3

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

In the above step (1-4), the longitudinal stretching magnification was changed to 1.60 times and the lateral stretching magnification was changed to 1.80 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal direction and the stretching temperature in the transverse direction are changed to 138 ℃ which is a temperature (Tg +10 ℃) 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin.

Comparative example 4

In the above step (1-4), the stretch ratio in the machine direction was changed to 1.20 times, and the stretch ratio in the transverse direction was changed to 1.40 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal direction and the stretching temperature in the transverse direction are changed to 138 ℃ which is a temperature (Tg +10 ℃) 10 ℃ higher than the glass transition temperature Tg of the thermoplastic norbornene-based resin.

Comparative example 5

A ring-opened polymer was obtained in the same manner as in the step (1-1) in example 1, except that 50 parts by weight of Tetracyclododecene (TCD) and 50 parts by weight of 8-Methyltetracyclododecene (MTD) were used as monomers. The weight-average molecular weight Mw of the Ring-opened Polymer was 4.0X 10 ⁴ The molecular weight distribution Mw/Mn was 2.0. The conversion of monomer to polymer was 100%.

300 parts of the polymerization reaction solution containing the ring-opened polymer thus obtained was transferred to an autoclave equipped with a stirrer, and 3 parts of a diatomaceous earth-supported nickel catalyst ("T8400 RL", manufactured by Nikkiso Co., ltd., nickel supporting rate 57%) was added to perform hydrogenation reaction at a hydrogen pressure of 4.5MPa and a temperature of 160 ℃ for 4 hours.

After the completion of the hydrogenation reaction, the resulting solution was subjected to pressure filtration (Fundaback Filter, manufactured by Shichuan Islands Seisakusho K.K.) at a pressure of 0.25MPa using RADIOLITE #500 as a Filter bed to remove the hydrogenation catalyst, thereby obtaining a colorless and transparent solution. The resulting solution was poured into a large amount of isopropyl alcohol to precipitate the polymer. The precipitated polymer was filtered and dried for 6 hours using a vacuum dryer (220 ℃ C., 1 Torr), to obtain a hydrogenated product of the above ring-opened polymer. The hydride of the ring-opening polymer has a glass transition temperature Tg of 158 ℃.

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 t-butyl benzene and reacted at 140 ℃ for 6 hours. The resulting reaction product solution was poured into methanol to solidify the reaction product. The solidified product was dried for 6 hours using a vacuum drier (220 ℃ C., 1 Torr) to obtain a hydrogenated maleic acid-modified ring-opened polymer. Hereinafter, the maleic acid-modified ring-opening polymer hydride may be referred to as "polar COP". The maleic acid group content of the polar COP was 25 mol%.

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

In the above step (1-4), the longitudinal stretching magnification was changed to 1.62 times and the lateral stretching magnification was changed to 1.82 times. In the above-mentioned step (1-4), the stretching temperature in the longitudinal and transverse directions is changed to 180 ℃ which is 10 ℃ higher than the glass transition temperature Tg of the hydrogenated maleic acid-modified ring-opened polymer (Tg +10 ℃).

In addition to the above matters, the optical film and the liquid crystal display device were manufactured and evaluated in the same manner as in example 1.

[ results ]

The results of the above examples and comparative examples are shown in tables 1 and 2 below. In tables 1 and 2 below, the meanings of abbreviations are as follows.

"T" of monomer column: tetracyclododecene (TCD).

"D" of monomer column: dicyclopentadiene (DCPD).

"N" of monomer column: norbornene (NB).

"E" of monomer column: ethylene Tetracyclododecene (ETD).

"M" of the monomer column: methanetetrahydrofluorene (MTF).

Rth Rate of Change (85 ℃ C.): the rate of change of retardation in the thickness direction of the optical film was determined by a durability test conducted when the film was stored at 85 ℃ for 500 hours.

Rth Rate of change (90% at 60 ℃): the optical film was stored in an environment of 60 ℃ and 90% humidity for 500 hours, and the change rate of retardation in the thickness direction of the optical film was measured.

[ Table 1]

[ Table 1. Results of examples ]

[ Table 2]

[ Table 2. Results of comparative examples ]

Reference example 1 appropriateness of the method for measuring peeling Strength

An evaluation test was conducted on whether or not it can be considered that the method for measuring the peel strength used in the examples and comparative examples described above reflects the evaluation 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 application laid-open No. 2005-70140. The optical film obtained in example 1 of the present application was prepared as a film to be measured. One surface of the optical film was subjected to corona treatment, and the corona-treated surface was bonded to one surface of the polarizing film via an adhesive. The cellulose triacetate film was attached to the other surface of the polarizing film via an adhesive. Then, the adhesive was dried at 80 ℃ for 7 minutes to cure the adhesive, to obtain a sample film. The obtained sample film was subjected to the same 90-degree peel test as in the above (evaluation method of delamination of optical film). As a result, the same value of peel strength as that obtained in example 1 of the present application was obtained.

From the results, it was confirmed that the measurement results of the peel strength obtained by the method for measuring the peel strength used in the examples and comparative examples reflect the evaluation of the peel strength when the adherend is a polarizing plate.

Claims

1. An optical film formed using a thermoplastic norbornene-based resin containing a norbornene-based polymer,

the norbornene-based polymer is selected from the group consisting of a polymer of a monomer containing a dicyclopentadiene-based monomer in an amount of 100 parts by weight or more and 500 parts by weight or less relative to 100 parts by weight of a tetracyclododecene-based monomer and a hydride thereof,

the tetracyclododecene monomer is selected from tetracyclododecene and tetracyclododecene derivatives in which the ring of tetracyclododecene is bonded with a substituent,

the dicyclopentadiene monomer is selected from dicyclopentadiene and dicyclopentadiene derivatives in which a substituent is bonded to a ring of dicyclopentadiene,

the norbornene polymer has a molecular weight distribution of 2.4 or less,

a birefringence [ Delta ] n exhibited by the thermoplastic norbornene-based resin when the thermoplastic norbornene-based resin is subjected to a free-end uniaxial stretching at Tg +15 ℃ for 1 minute by a factor of 1.5 _R Satisfies the following formula (2),

the retardation Rth in the thickness direction of the optical film and the thickness d of the optical film satisfy the following formula (3),

(1)Tg≥110℃，

(2)0.0050≥Δn _R ≥0.0025，

(3)Rth/d≥3.5×10 ^-3 。

2. the optical film according to claim 1, wherein the optical film has a photoelastic coefficient of 8Brewster or less.

3. The optical film according to claim 1 or 2, wherein the in-plane retardation Re of the optical film is 40nm or more and 80nm or less.

4. A method for producing an optical film according to any one of claims 1to 3,

the production method comprises molding the thermoplastic norbornene-based resin by an extrusion molding method or a solution casting method.

5. An optical laminate comprising a polarizing plate and the optical film according to any one of claims 1to 3.

6. A liquid crystal display device having the optical laminate according to claim 5.