JP2018128568A - Retardation film, production method of the same and display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film produced by at least uniaxially orienting a laminate having stacked layers of a layer made of a resin having positive birefringence and a layer made of a resin having negative birefringence, the retardation film having approximately ideal wavelength dispersion characteristics in a wide range, a low photo-elastic constant, high developability of birefringence, good adhesiveness between the resin having positive birefringence and the resin having negative birefringence, and excellent flexibility and processability.SOLUTION: A retardation film and a production method of the film are provided: the retardation film has such characteristics that: a resin having positive birefringence comprises a repeating unit represented by formula (A) below by 30 mol% or more and 99 mol% or less based on all repeating units; a resin having negative birefringence comprises a styrene resin; a thickness ratio of the resins having positive birefringence and negative birefringence is 1:1 to 2:1; and a relationship between an in-plane retardation R450 at a wavelength of 450 nm and an in-plane retardation R550 at a wavelength of 550 nm satisfies a predetermined range.SELECTED DRAWING: None

Description

  The present invention is a retardation film in which a laminate of a resin having a positive birefringence and a resin having a negative birefringence is oriented at least in a uniaxial direction, has a specific wavelength dispersion, and has a photoelastic constant. A retardation film having low flexibility and excellent workability, a method for producing the same, and a display device using the same.

In general, optical films, particularly retardation films, are used in displays such as liquid crystals and organic EL display devices, and have functions such as color compensation, viewing angle expansion, and antireflection. Optical properties required for the retardation film include a wavelength dispersion property ideally close to a wide band, a low photoelastic constant, and a high birefringence.
In recent years, these display devices have been proposed to be flexible, and retardation films are also required to have flexibility as well as optical performance.

  As the retardation film, λ / 4 plate and λ / 2 plate are known, and thermoplastic polymers such as polycarbonate, polyethersulfone, polysulfone and the like obtained by polycondensation of bisphenol A are used as the material. The λ / 4 plate and λ / 2 plate obtained by stretching films of these materials have the property that the phase difference increases as the wavelength becomes shorter. For this reason, there is a problem that the wavelengths that can function as the λ / 4 plate and the λ / 2 plate are limited to specific wavelengths.

  As a method for controlling the wavelength in a wide band, a method is known in which two or more specific birefringent films having different wavelength dependences of the retardation are laminated at a specific angle. (For example, refer to Patent Documents 1 to 4) In these cases, since a plurality of retardation films are used, a process of adjusting and bonding the angles is necessary, and there is a problem in productivity. Moreover, the performance fall by the angle shift | offset | difference accompanying a pasting or increase in thickness also becomes a problem.

  In recent years, as a method of broadening the band without laminating such lamination, a laminate is formed by co-extrusion of a resin having positive orientation birefringence and a resin having negative orientation birefringence, There is known a method of manufacturing a laminated phase difference plate having a wavelength dispersion characteristic ideally close to a wide band by stretching the laminated body in the same direction. (See Patent Document 5) Specifically, there is a case where a resin having a norbornene resin as a resin having positive birefringence and a styrene-maleic anhydride resin as a resin having negative birefringence are used. However, adhesion was inferior.

In addition, by stretching a polymer film composed of a polymer monomer unit having a positive refractive index anisotropy and a polymer monomer unit having a negative refractive index anisotropy, the wavelength is ideally close to a wide band. A method of manufacturing a laminated phase difference plate having dispersion characteristics is known. (See Patent Document 6) In this case, in order to create a film having optical properties and mechanical properties, the types of monomers that can be used are special and limited. Therefore, various physical properties such as optical properties and mechanical properties are well balanced. It was difficult to make a film.
Furthermore, these retardation films are very fragile, are difficult to handle, and do not have the bending resistance required for flexible displays.
So far, a retardation film in which a laminate of a resin having a positive birefringence and a resin having a negative birefringence is oriented at least in a uniaxial direction has a wavelength dispersion characteristic that is ideally close to a broadband, A retardation film having a low elastic constant, high birefringence, and excellent flexibility and workability has not been obtained.

JP-A-5-27118 JP-A-10-68816 JP-A-10-90521 JP-A-4-343303 JP 2002-107542 A International Publication No. 2000/026705 Pamphlet

  It is an object of the present invention to provide a retardation film in which a laminate comprising a layer made of a resin having a positive birefringence and a layer made of a resin having a negative birefringence is oriented at least in a uniaxial direction, and is ideal for a wide band. An object of the present invention is to provide a retardation film having a wavelength dispersion characteristic close to, low photoelastic constant, high expression of birefringence, and excellent flexibility and workability.

  As a result of diligent investigations to achieve such an object, the present inventors have found that a laminate in which a layer made of a resin having a positive birefringence and a layer made of a negative birefringence are laminated at least in a uniaxial direction. In the phase difference film, as the resin having positive birefringence, a resin having a specific amount of a structural unit represented by polycarbonate having isosorbide, inmannide, and isoidid skeleton, and a resin having negative birefringence is a resin containing a styrene resin. By using a retardation film, it has been found that it has wavelength dispersion characteristics ideally close to a wide band, low photoelastic constant, high birefringence, excellent flexibility and workability, and has reached the present invention. did.

負の複屈折を有する樹脂が、スチレン系樹脂を含有する樹脂であって、正の複屈折を有する樹脂及び負の複屈折を有する樹脂の厚み比が１：１〜２：１であって、波長４５０ｎｍにおける面内位相差値Ｒ４５０と波長５５０ｎｍにおける面内位相差値Ｒ５５０の関係が下記式（１）を満たすことを特徴とする位相差フィルム。
０．６０≦Ｒ４５０／Ｒ５５０≦０．９５ ・・・（１） That is, the present invention is achieved by the following configuration requirements.
1. A retardation film obtained by orienting a laminate in which a layer made of a resin having positive birefringence and a layer made of a resin having negative birefringence are laminated at least in a uniaxial direction, wherein the resin having positive birefringence is The repeating unit represented by the following formula (A) contains 30 mol% or more and 99 mol% or less based on all repeating units,

The resin having negative birefringence is a resin containing a styrenic resin, and the thickness ratio of the resin having positive birefringence and the resin having negative birefringence is 1: 1 to 2: 1, A retardation film, wherein a relationship between an in-plane retardation value R450 at a wavelength of 450 nm and an in-plane retardation value R550 at a wavelength of 550 nm satisfies the following formula (1).
0.60 ≦ R450 / R550 ≦ 0.95 (1)

負の複屈折を有する樹脂が、スチレン系樹脂を含有する樹脂であって、正の複屈折を有する樹脂及び負の複屈折を有する樹脂の厚み比が１：１〜２：１であって、波長４５０ｎｍにおける面内位相差値Ｒ４５０と波長５５０ｎｍにおける面内位相差値Ｒ５５０の関係が下記式（１）を満たすことを特徴とする位相差フィルムの製造方法。
０．６０≦Ｒ４５０／Ｒ５５０≦０．９５ ・・・（１）
７．前記１〜５のいずれかに記載の位相差フィルムを具備した液晶表示装置または有機ＥＬ表示装置。 2. The glass transition temperature (Tg) of the resin having positive birefringence is 100 ° C. or higher and 150 ° C. or lower, and the glass transition temperature (Tg) of the resin having negative birefringence is 100 ° C. or higher and 150 ° C. or lower. 2. The retardation film as described in 1 above.
3. 3. The retardation film as described in 1 or 2 above, wherein the resin having negative birefringence is a styrene-maleic anhydride copolymer resin.
4). 4. Retardation film in any one of said 1-3 whose photoelastic coefficient is 30 * 10 <^-12> Pa < ^{-1 >} or less. 4. The retardation film according to any one of 1 to 3, wherein the retardation is 135 nm or more and 155 nm or less and the thickness is 20 μm or more and 70 μm or less.
6). A laminate in which a layer made of a resin having positive birefringence (A layer) and a layer made of a resin having negative birefringence (B layer) are laminated and integrated by melt coextrusion molding is stretched at least in a uniaxial direction. A method for producing a retardation film, wherein the resin having positive birefringence includes a repeating unit represented by the following formula (A), containing 30 mol% or more and 99 mol% or less based on all repeating units,

The resin having negative birefringence is a resin containing a styrenic resin, and the thickness ratio of the resin having positive birefringence and the resin having negative birefringence is 1: 1 to 2: 1, A method for producing a retardation film, wherein a relationship between an in-plane retardation value R450 at a wavelength of 450 nm and an in-plane retardation value R550 at a wavelength of 550 nm satisfies the following formula (1).
0.60 ≦ R450 / R550 ≦ 0.95 (1)
7). The liquid crystal display device or organic electroluminescence display which comprised the retardation film in any one of said 1-5.

  The retardation film of the present invention is a retardation film obtained by stretching a laminate comprising a layer made of a resin having positive birefringence and a layer made of a resin having negative birefringence at least in a uniaxial direction. Ideally close to chromatic dispersion, low photoelastic constant, high birefringence, and excellent flexibility and workability.

The retardation film of the present invention is a laminate in which a layer made of a resin having a positive birefringence and a layer made of a resin having a negative birefringence are laminated, each component constituting each of the following, those components The blending ratio, adjustment method, etc. will be specifically described sequentially.
For convenience of explanation, the layer made of resin having positive birefringence is the A layer, the layer made of resin having negative birefringence is the B layer, the resin having positive birefringence is resin A, and the negative birefringence is made. The resin having this may be referred to as “resin B”.

<Resin having positive birefringence>
In the retardation film of the present invention, the resin having a positive birefringence (resin A) refers to a resin that has a maximum refractive index in the stretching direction when a film formed from the resin is stretched. A resin having birefringence is a resin containing a repeating unit represented by the following formula (A) in an amount of 30 mol% to 99 mol% based on all repeating units.

本発明の位相差フィルムにおいて、正の複屈折を有する具体的な樹脂としては、ポリカーボネート、ポリエステル、ポリエステルカーボネートが挙げられ、その中で、ポリカーボネートが好ましい。

In the retardation film of the present invention, specific resins having positive birefringence include polycarbonate, polyester, and polyester carbonate, and among them, polycarbonate is preferable.

(Repeating unit (A))
The formula (A) in the retardation film of the present invention is derived from an aliphatic diol having an ether group, and is a diol having an ether bond in a biomass resource and having a high heat resistance. preferable.
Examples of the formula (A) include repeating units (A1), (A2) and (A3) represented by the following formulas having a stereoisomer relationship.

これら（Ａ１）〜（Ａ３）は、糖質由来のエーテルジオールであり、自然界のバイオマスからも得られる物質で、再生可能資源と呼ばれるものの１つである。繰り返し単位（Ａ１）、（Ａ２）および（Ａ３）は、それぞれイソソルビド、イソマンニドおよびイソイディッドと呼ばれる。イソソルビドは、でんぷんから得られるＤーグルコースに水添した後、脱水を受けさせることにより得られる。その他のエーテルジオールについても、出発物質を除いて同様の反応により得られる。

These (A1) to (A3) are carbohydrate-derived ether diols, which are substances obtained from natural biomass, and are one of so-called renewable resources. The repeating units (A1), (A2) and (A3) are called isosorbide, isomannide and isoid, respectively. Isosorbide is obtained by hydrogenating D-glucose obtained from starch and then dehydrating it. Other ether diols can be obtained by the same reaction except for the starting materials.

  Among isosorbide, isomannide, and isoidide, a repeating unit derived from isosorbide (1,4; 3,6-dianhydro-D-sorbitol) is particularly preferable because of ease of production and heat resistance.

  The resin having positive birefringence used in the retardation film of the present invention is a structural unit represented by the above formula (A) from the viewpoint of enhancing the expression of birefringence and improving the flexibility and workability ( A). Based on all repeating units, the lower limit of the repeating unit (A) is 30 mol% or more, preferably 40 mol% or more, and particularly preferable from the viewpoint of adhesion with a resin having negative birefringence. Is 45 mol% or more.

Moreover, the upper limit of the ratio of a repeating unit (A) is 99 mol% or less on the basis of all the repeating units. Preferably, it is 90 mol% or less, More preferably, it is 85 mol% or less, More preferably, it is 75 mol% or less.
When the number of repeating units (A) represented by the above formula (A) is less than the lower limit based on all repeating units, sufficient flexibility cannot be obtained.

  In addition, when the number of repeating units (A) represented by the above formula (A) is larger than the upper limit on the basis of all repeating units, adhesion of the laminate with flexibility, workability, and negative birefringence resin Sex cannot be obtained.

(Repeating unit (B))
The resin having positive birefringence used for the retardation film of the present invention contains the above repeating unit (A), and preferably further contains the repeating unit (B), and is particularly a copolymer polycarbonate resin thereof. It is preferable. As a preferred embodiment of the repeating unit (B), the repeating unit (B-1) or (B-2) described later can be mentioned.

(Repeating unit (B-1))
As a preferable embodiment of the resin used for the retardation film of the present invention, the resin preferably contains the above repeating unit (A) and a repeating unit (B-1) represented by the following formula. The total of the repeating unit (A) and the repeating unit (B-1) is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% or more in all repeating units. preferable.

（式中、Ｗは、炭素数２〜３０のアルキレン基または炭素数６〜３０のシクロアルキレン基を示す。）
繰り返し単位（Ｂ−１）は、脂肪族ジオール化合物や脂環式ジオール化合物から誘導されるものである。前記脂肪族ジオール化合物は、直鎖脂肪族ジオール化合物が好ましい。好ましくは炭素原子数４〜２４、より好ましくは炭素原子数６〜２０、さらに好ましくは炭素原子数８〜１２の直鎖脂肪族ジオール化合物が使用される。

(In the formula, W represents an alkylene group having 2 to 30 carbon atoms or a cycloalkylene group having 6 to 30 carbon atoms.)
The repeating unit (B-1) is derived from an aliphatic diol compound or an alicyclic diol compound. The aliphatic diol compound is preferably a linear aliphatic diol compound. Preferably, a linear aliphatic diol compound having 4 to 24 carbon atoms, more preferably 6 to 20 carbon atoms, and still more preferably 8 to 12 carbon atoms is used.

The alicyclic diol compound is preferably an alicyclic diol compound having 6 to 24 carbon atoms, more preferably 6 to 20 carbon atoms.
Specific examples of the linear aliphatic diol compound include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1 , 7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 2-ethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,10- Examples include decanediol, 1,12-dodecanediol, hydrogenated dilinoleyl glycol, hydrogenated dioleyl glycol, and the like. Of these, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol are preferable, and 1,9-nonanediol, 1,10-decanediol, 1,12 are particularly preferable. -Dodecanediol is preferred. Of these, 1,9-nonanediol is most preferred.

  Specific examples of the alicyclic diol compound include 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, and cyclohexanediols such as 2-methyl-1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, cyclohexanedimethanols such as 1,4-cyclohexanedimethanol, norbornanedimethanol such as 2,3-norbornanedimethanol, 2,5-norbornanedimethanol Tricyclodecane dimethanol, pentacyclopentadecane dimethanol, 1,3-adamantanediol, 2,2-adamantanediol, decalin dimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 3 9- bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-spiro [5.5] undecane. Among these, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5. 5] Undecane is preferred.

  These aliphatic diol compounds and alicyclic diol compounds may be used alone or in combination of two or more. Moreover, it is preferable that the polycarbonate resin of this invention contains 1 or more types of the said repeating unit (A) and an alicyclic diol compound, or an aliphatic diol compound, respectively.

  As a combination of the repeating unit (A) and the repeating unit (B-1), isosorbide and 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5 .5] A combination of undecane, 1,4-cyclohexanedimethanol and 1,9-nonanediol is preferred, and isosorbide and 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8, A combination of 10-tetraoxaspiro [5.5] undecane is more preferable from the viewpoint of adhesion.

  In addition, the diol used in the retardation film of the present invention may be used in combination with an aromatic diol as long as the effects of the present invention are not impaired. As aromatic dihydroxy compounds, α, α′-bis (4-hydroxyphenyl) -m-diisopropylbenzene (bisphenol M), 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, 1,1- Bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 4,4′-dihydroxy-3,3′-dimethyldiphenyl sulfide, bisphenol A, 2 , 2-bis (4-hydroxy-3-methylphenyl) propane (bisphenol C), 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane (bisphenol AF) ) And 1,1-bis (4-hydroxyphenyl) decane.

(Repeating unit (B-2))
As a preferable embodiment of the resin used in the retardation film of the present invention, it is preferable to include the repeating unit (A) and the repeating unit (B-2) represented by the following formula (B-2). Among all repeating units, the total of repeating units (A) and repeating units (B-2) is 80 mol% or more, preferably 90 mol% or more, particularly a copolymer polycarbonate resin. Preferably mentioned.

（式中Ｘは、炭素数３〜２０のアルキレン基または炭素数３〜２０のシクロアルキレン基を表し、Ｒは炭素数１〜２０のアルキル基または炭素数３〜２０のシクロアルキル基を表し、ｍは１〜１０の整数を示す。）
繰り返し単位（Ｂ−２）は、側鎖アルキル基または側鎖シクロアルキル基を有する脂肪族ジオールから誘導される単位である。
繰り返し単位（Ｂ−２）は、炭素数の合計が４〜１２の範囲であることが好ましく、５〜１０の範囲であることがより好ましい。かかる範囲であると、ポリカーボネート樹脂のＨＤＴ（荷重たわみ温度）が高く保持される。

(In the formula, X represents an alkylene group having 3 to 20 carbon atoms or a cycloalkylene group having 3 to 20 carbon atoms, R represents an alkyl group having 1 to 20 carbon atoms or a cycloalkyl group having 3 to 20 carbon atoms, m represents an integer of 1 to 10.)
The repeating unit (B-2) is a unit derived from an aliphatic diol having a side chain alkyl group or a side chain cycloalkyl group.
The repeating unit (B-2) preferably has a total carbon number in the range of 4 to 12, more preferably in the range of 5 to 10. Within such a range, the HDT (deflection temperature under load) of the polycarbonate resin is kept high.

(composition)
The resin having positive birefringence used for the retardation film of the present invention needs to contain 30 mol% or more and 99 mol% or less of the repeating unit (A), and may further contain the repeating unit (B). preferable. The molar ratio (A) / (B) between the repeating unit (A) and the repeating unit (B) is 30/70 to 99/1. Preferably it is the range of 40 / 60-96 / 4, More preferably, it is the range of 50 / 50-95 / 5.
When the molar ratio of the repeating unit (A) to the repeating unit (B) is in the range of 30/70 to 99/1, the heat resistance is high, the melt viscosity is appropriate, and the moldability is improved. Excellent impact. Moreover, when it is set as the layer and laminated body which consist of resin of negative birefringence, it is excellent in interphase adhesiveness. The molar ratio of each repeating unit is measured and calculated by proton NMR of JNM-AL400 manufactured by JEOL Ltd.

(Method for producing resin having positive birefringence)
The resin having positive birefringence used in the retardation film of the present invention can be produced by a reaction means known per se, for example, in the case of polycarbonate, a method in which a carbonate precursor such as a carbonic acid diester is reacted with a diol component. . Next, basic means for these manufacturing methods will be briefly described.

  The transesterification reaction using a carbonic acid diester as a carbonate precursor is carried out by a method in which a predetermined proportion of a diol component is stirred with a carbonic acid diester under heating in an inert gas atmosphere to distill the resulting alcohol or phenol. The reaction temperature varies depending on the boiling point of the alcohol or phenol produced, but is usually in the range of 120 to 300 ° C. The reaction is completed while distilling off the alcohol or phenol produced under reduced pressure from the beginning. Moreover, you may add a terminal stopper, antioxidant, etc. as needed.

Examples of the carbonic acid diester used in the transesterification include esters such as an aryl group having 6 to 12 carbon atoms and an aralkyl group which may be substituted. Specific examples include diphenyl carbonate, ditolyl carbonate, bis (chlorophenyl) carbonate and m-cresyl carbonate. Of these, diphenyl carbonate is particularly preferred. The amount of diphenyl carbonate used is 1 mol in total for the dihydroxy compound.
Preferably it is 0.97-1.10 mol, More preferably, it is 1.00-1.06 mol.

  In the melt polymerization method, a polymerization catalyst can be used to increase the polymerization rate. Examples of the polymerization catalyst include alkali metal compounds, alkaline earth metal compounds, basic phosphorus compounds, metal compounds and the like. Among these, as a polymerization catalyst, an alkali metal or an alkaline earth metal is preferable. Of the alkali metal compounds, sodium hydroxide and sodium bicarbonate are particularly preferred. Of the alkaline earth metal compounds, calcium carbonate and barium stearate are particularly preferable.

The amount of these polymerization catalysts used is preferably 1 × 10 ⁻⁹ to 1 × 10 ⁻² equivalent, preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻⁵ equivalent, more preferably 1 × with ^respect to 1 mol of the diol component. It is selected in the range of 10 ⁻⁷ to 1 × 10 ⁻³ equivalents.

In addition, a catalyst deactivator can be added at a later stage of the reaction. As the catalyst deactivator to be used, a known catalyst deactivator is effectively used. Among them, sulfonic acid ammonium salt and phosphonium salt are preferable. Furthermore, salts of dodecylbenzenesulfonic acid such as tetrabutylphosphonium salt of dodecylbenzenesulfonic acid and salts of paratoluenesulfonic acid such as tetrabutylammonium salt of paratoluenesulfonic acid are preferable. Further, as esters of sulfonic acid, methyl benzenesulfonate, ethyl benzenesulfonate, butyl benzenesulfonate, octyl benzenesulfonate, phenyl benzenesulfonate, methyl paratoluenesulfonate, ethyl paratoluenesulfonate, butyl paratoluenesulfonate, Octyl paratoluenesulfonate, phenyl paratoluenesulfonate and the like are preferably used.
Among these, dodecylbenzenesulfonic acid tetrabutylphosphonium salt is most preferably used.

The amount of the catalyst deactivator used is preferably 0.5 to 50 mol per mol of the catalyst when at least one polymerization catalyst selected from alkali metal compounds and / or alkaline earth metal compounds is used. It can be used in a proportion, more preferably in a proportion of 0.5 to 10 mol, still more preferably in a proportion of 0.8 to 5 mol.

(Specific viscosity: η _SP )
The specific viscosity (η _SP ) of the resin A in the present invention is preferably 0.2 to 0.5, more preferably 0.22 to 0.49, and still more preferably 0.24 to 0.48. If the specific viscosity of the resin is less than 0.2, the strength decreases, and if it is greater than 0.5, the moldability deteriorates.
The specific viscosity of the resin A in the present invention was determined using an Ostwald viscometer from a solution obtained by dissolving 0.7 g of resin in 100 ml of methylene chloride at 20 ° C.
Specific viscosity (η _SP ) = (t−t ₀ ) / t ₀
[T ₀ is methylene chloride falling seconds, t is sample solution falling seconds]
For example, in the case of polycarbonate, the specific viscosity can be measured in the following manner. First, the polycarbonate resin is dissolved in 20 to 30 times the weight of methylene chloride, and the soluble component is collected by celite filtration, and then the solution is removed and dried sufficiently to obtain a solid component soluble in methylene chloride. Using a Ostwald viscometer, the specific viscosity at 20 ° C. is determined from a solution of 0.7 g of the solid dissolved in 100 ml of methylene chloride.

(Glass transition temperature: Tg)
The glass transition temperature (Tg) of the resin A used in the present invention is preferably 100 to 150 ° C, more preferably 105 to 140 ° C, and still more preferably 110 to 135 ° C. When the glass transition temperature (Tg) of the resin is low, the heat resistance stability is inferior, and the retardation value may change over time and affect display quality. Moreover, when the glass transition temperature (Tg) of resin is high, melt viscosity will become high, workability will fall, and it may affect the external appearance at the time of using a film.
The difference in glass transition temperature (Tg) between the resin having positive birefringence and the resin having negative birefringence is preferably 20 ° C. or less, more preferably 15 ° C. or less, and further preferably 10 ° C. or less. If the glass transition temperature (Tg) of the resin having positive birefringence and the resin having negative birefringence is higher than 20 ° C., it may be difficult to obtain a desired phase difference and wavelength dispersion characteristics.

<Resin having negative birefringence>
In the retardation film of the present invention, the resin having a negative birefringence (resin B) means that when a film formed from a resin having a negative birefringence is stretched, the refractive index in the direction orthogonal to the stretching direction is maximized. In the present invention, it is a resin containing a styrenic resin. Specific examples include styrene / maleic anhydride copolymers, styrene / maleimide copolymers, and copolymers containing nitrile units and styrene units. Examples of the styrenic compound constituting the styrenic unit include styrene, vinyltoluene, methoxystyrene, or unsubstituted or substituted styrenic compounds such as chlorostyrene and α-methylstyrene. In the present invention, the resin B is particularly preferably a styrene / maleic anhydride copolymer.
In the present invention, the resin B is a styrene-based resin from the viewpoint of improving the birefringence expression and the adhesiveness with the resin having a positive birefringence, and the ratio of the styrene resin is a resin having a negative birefringence. Preferably, it is 50 to 100% by weight, more preferably 70 to 100% by weight, based on the weight of the layer consisting of.
When the content of the styrenic resin in the B layer is less than 50% by weight, sufficient birefringence cannot be obtained, and it is difficult to obtain a desired retardation when the retardation film is obtained.

<Phase difference film>
(Layer structure of retardation film)
The layer structure of the retardation film of the present invention is composed of an A layer made of a resin having a positive birefringence and a B layer made of a resin having a negative birefringence, and the outermost layer on the front and back has a positive birefringence. It is preferable from the viewpoint of flexibility.
For example, when A1, A2, and A3 are layers made of resin A, and B1 and B2 are layers made of resin B, respectively, in the case of 2 types and 3 layers, it becomes A1 / B1 / A2 and 2 types and 5 layers. In this case, the layer configuration is A1 / B1 / A2 / B2 / A3, and (A1 + A2) / B1 and (A1 + A2 + A3) / (B1 + B2) preferably have a thickness ratio described later. That is, for each ratio, the ratio of the total thickness of the positive birefringence and the sum of the negative birefringence can be arbitrarily selected according to the desired wavelength dispersion characteristics, but is 1: 1 to 2: 1. Preferably, it is 1.05: 1 to 1.8: 1, more preferably 1.1: 1 to 1.6: 1. When the ratio of the thickness of the resin layer having positive birefringence to the thickness of the resin layer having negative birefringence is within this range, wavelength dispersion characteristics that are ideally close to a wide band can be obtained.

  The total thickness of the retardation film of the present invention (total of A layers + B layers) is preferably 20 μm to 100 μm, more preferably 20 μm to 70 μm, still more preferably 20 μm to 60 μm, particularly preferably. Is 20 μm or more and 50 μm or less. When the thickness exceeds 100 μm, the flexibility is remarkably deteriorated. Further, when incorporated in the device, the thickness of the entire device is increased. When the thickness is less than 20 μm, it is difficult to develop a desired phase difference after stretching.

<Formation method of retardation film>
As a method for producing the retardation film, a method in which a laminate obtained by laminating and integrating the A layer and the B layer by melt coextrusion molding is preferably stretched at least in a uniaxial direction.
In the coextrusion molding method, a resin having a positive birefringence and a resin layer having a negative birefringence are melted and the multilayered resin is brought into close contact with a roll for molding. Specifically, a laminated sheet extruded from a multi-manifold die or a feed block die is used with three cooling rolls that are in a positional relationship where the rotation center axes are parallel and on the same plane and are arranged close to each other. A method of forming and then taking up with a pair of take-up rolls is preferable. A 1st cooling roll and a 2nd cooling roll may be comprised with a metal roll or a metal elastic roll, and may comprise it combining a metal roll and a metal elastic roll.

(Stretching method)
As the stretching method, a known method such as lateral uniaxial stretching using a tenter or the like, simultaneous biaxial stretching in which longitudinal uniaxial and lateral uniaxial are combined, sequential biaxial stretching, oblique stretching, or the like can be used.
The method for producing the retardation film of the present invention is not particularly limited. However, both ends of the unstretched film are held with clips and guided to a tenter, the film is preheated at a predetermined temperature, stretched while being heated, and then heated. However, a method of relaxing is preferable.
Although the stretching conditions of the retardation film of the present invention are not particularly limited, it is preferably carried out under the following conditions.

The preheating temperature at the time of stretching the film is preferably (Tg−5 ° C.) or more and (Tg + 25 ° C.) or less, and (Tg ° C.) or more (Tg + 20), where Tg is the glass transition temperature of the higher resin A or resin B. ° C) or less, more preferably (Tg + 5 ° C) or more and (Tg + 15 ° C) or less.
When the preheating temperature at the time of stretching the film exceeds (Tg + 25 ° C.), it is difficult to develop a desired retardation. Moreover, when it is less than (Tg-5 degreeC), the effect of the desired preheating is not acquired but it fractures | ruptures at the time of extending | stretching.
The preheating temperature is appropriately adjusted in order to adjust the absolute value of the orientation angle. In order to set the average value of the orientation angles in the entire width direction to 0 °, it is preferable to increase the preheating temperature by about 5 ° C. from the stretching temperature.

  The stretching temperature for stretching the film is preferably (Tg-10 ° C) or more and (Tg + 20 ° C) or less, more preferably (Tg-5 ° C) or more and (Tg + 15 ° C) or less, and (Tg ° C) or more (Tg + 10 ° C) or less. Is more preferable. When the stretching temperature exceeds (Tg + 20 ° C.), it is difficult to develop a desired phase difference. When the stretching temperature is less than (Tg−10 ° C.), the film tends to break during stretching.

  The stretching ratio when stretching the film is preferably 1.5 times or more and 5.0 times or less, more preferably 1.7 times or more and 4.0 times or less, and further preferably 2.0 times or more and 3.0 times or less. . If the draw ratio exceeds 5.0 times, it will break at the time of drawing. When the draw ratio is less than 1.5 times, it is difficult to develop a desired phase difference.

The stretching speed at the time of stretching the film is a value obtained by dividing the stretching ratio by the time required for stretching, and is preferably 1.5 times / min to 10.0 times / min, and more preferably 2.0 times / min to 9.0. The ratio is more preferably twice / min or less, and further preferably 3.0 times / min or more and 8.0 times / min or less. When the stretching speed exceeds 10.0 times / minute, the film tends to break during stretching. When the stretching speed is less than 1.5 times, it is difficult to develop a desired phase difference.
By appropriately performing the relaxation treatment continuously performed in the stretching step, it is possible to set the heat shrinkage rate to a predetermined value or less and to further control the variation in the heat shrinkage rate and the orientation angle.

  The relaxation temperature when relaxing while heating after stretching is preferably 80 ° C. or higher (Tg + 10 ° C.), more preferably 90 ° C. or higher (Tg + 5 ° C.) and even more preferably 100 ° C. or higher (Tg ° C.). When the relaxation temperature exceeds (Tg + 10 ° C.), the orientation of the molecular chain due to stretching is disturbed, and the desired phase difference is lowered. In addition, variations in the thermal shrinkage rate and the orientation angle are likely to increase. When the relaxation temperature is less than 80 ° C., it is difficult to obtain a desired heat shrinkage rate. Further, the film is easily broken by the remaining heat shrinkage stress.

  The relaxation rate when relaxing while heating after stretching is preferably from 0.010 to 0.070, more preferably from 0.015 to 0.060, and even more preferably from 0.020 to 0.050. When the relaxation rate exceeds 0.070, the film breaks due to flapping of the film at the tenter exit. In addition, the variation of the heat shrinkage rate and the orientation angle is increased. When the relaxation rate is less than 0.010, a desired heat shrinkage rate cannot be obtained. Further, the film is easily broken by the remaining heat shrinkage stress.

  The relaxation rate when relaxing while heating after stretching is a value obtained by dividing the relaxation rate by the time required for relaxation, preferably 0.005 / min or more and 0.070 / min or less, and 0.007 or more and 0.050 or less. Is more preferably 0.010 or more and 0.040 or less. When the relaxation rate exceeds 0.070 / min, it is difficult to obtain a desired heat shrinkage rate. When the relaxation rate is less than 0.005 / min, the thermal shrinkage rate and the orientation angle vary greatly.

<Characteristics of retardation film>
(Birefringence)
The birefringence of the retardation film of the present invention is preferably 0.001 or more, more preferably 0.002 or more, and more preferably 0.003 or more. When the birefringence of the film is less than 0.001, it is difficult to reduce the thickness of the film.

(Photoelastic constant)
The phase element film of the present invention preferably has a photoelastic constant of 30 × 10 ⁻¹³ Pa ⁻¹ or less, more preferably 20 × 10 ⁻¹³ Pa ⁻¹ or less, and even more preferably 17 ×. It is 10 ⁻¹³ Pa ⁻¹ or less, more preferably 13 × 10 ⁻¹³ Pa ⁻¹ or less, and most preferably 10 × 10 ⁻¹³ Pa ⁻¹ or less.

(Wavelength dispersion)
The retardation film of the present invention exhibits reverse wavelength dispersibility that becomes smaller as the retardation in the film plane becomes shorter in the visible light region having a wavelength of 400 to 800 nm. Such a retardation film needs to satisfy the condition of the following formula (1).
0.60 ≦ R (450) / R (550) ≦ 0.95 (1)
It is preferable that the condition of the following formula (1-1) is satisfied.
0.70 ≦ R (450) / R (550) ≦ 0.94 (1-1)
More preferably, the condition of the following formula (1-2) is preferably satisfied.
0.80 ≦ R (450) / R (550) ≦ 0.90 (1-2)
Most preferably, the condition of the following formula (1-3) is preferably satisfied.
0.83 ≦ R (450) / R (550) ≦ 0.87 (1-3)
Here, the in-plane retardation value R is defined by the following equation, and is a characteristic that expresses a phase delay between the X direction of light transmitted through the film in the vertical direction and the vertical Y direction.
_{R = (n x -n y)} × d
Where _nx is the refractive index in the main stretching direction in the film plane, _ny is the refractive index in the direction perpendicular to the main stretching direction in the film plane, and d is the thickness of the film. Here, the main stretching direction means a stretching direction in the case of uniaxial stretching, and a direction in which the degree of orientation is increased in the case of biaxial stretching. Refers to the orientation direction.

(Pencil hardness)
The resin used in the retardation film of the present invention preferably has a pencil hardness of HB or higher. In terms of excellent scratch resistance, F or higher is more preferable, and H or higher is more preferable.

(Flexibility)
As for the flexibility of the retardation film of the present invention, the number of times of bending until breakage is preferably 40,000 times or more and less than 100,000 times, more preferably 100,000 times or more. It is preferable that the number of times of bending until breakage is 40,000 times or more and less than 100,000 times because it is excellent in repeated bending durability when incorporated in a flexible display.

(Breaking strength)
The breaking strength of the retardation film of the present invention is preferably 140 MPa or more. When the breaking strength is 140 MPa or more, it is preferable that workability is hardly impaired. Moreover, since it is excellent in repeated bending durability at the time of incorporating in a flexible display, it is preferable.

(Elongation at break)
The breaking elongation of the retardation film of the present invention is preferably 30% or more. When the elongation at break is 30% or more, it is preferable that the same breakage hardly occurs. Moreover, since it is excellent in repeated bending durability at the time of incorporating in a flexible display, it is preferable.

(Adhesion)
The retardation film of the present invention peels off when the adhesion evaluation described below is performed, but the degree to which roughening of the interface is recognized is preferable, and it is more preferable that the retardation film does not peel off. If peeling is easily observed in this evaluation, peeling may occur in an impact test or the like when incorporated in a device, which is not preferable.

(Saturated water absorption)
The saturated water absorption of the resin used for the retardation film of the present invention is preferably 3.3% or less, more preferably 2.2% or less, and further preferably 2.0% or less. When the saturated water absorption rate is higher than 3.3%, various physical properties such as dimensional change and warpage due to water absorption are remarkable in the molded product, which is not preferable.

The resin used for the retardation film of the present invention preferably satisfies the following formula (I) in terms of the relationship between the glass transition temperature (Tg ° C.) and the water absorption (Wa%). It is more preferable to satisfy a). When the following formula (I) is satisfied, the resin is excellent in heat resistance and has a low water absorption rate, which is preferable because it can suppress changes in physical properties and deformation in a humid heat environment. The upper limit of the TW value is not particularly limited, but 10 or less is sufficient.
1.6 ≦ TW value = Tg × 0.04-Wa (I)
2.6 ≦ TW value = Tg × 0.04−Wa (I−a)

<Additives etc. in retardation film>
Resin used in the retardation film of the present invention is a heat stabilizer, plasticizer, light stabilizer, polymerized metal deactivator, flame retardant, lubricant, antistatic agent, surfactant, as required and necessary. Additives such as antibacterial agents, ultraviolet absorbers, mold release agents and the like can be blended.
In addition, the resin used in the retardation film of the present invention may be used in combination with other resins as long as the effects of the present invention are not impaired. That is, the above-mentioned resin A and resin B may be used as a resin composition.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In the examples, “parts” means “parts by weight”.

<Resin production example 1>
441 parts of isosorbide (hereinafter abbreviated as ISS), 66 parts of 1,9-nonanediol (hereinafter abbreviated as ND), 750 parts of diphenyl carbonate (hereinafter abbreviated as DPC), and tetramethylammonium hydroxide 0.8 × 10 ⁻ as a catalyst ² parts and 0.6 × 10 ⁻⁴ parts of sodium hydroxide were heated to 180 ° C. in a nitrogen atmosphere and melted. Thereafter, the degree of vacuum was adjusted to 13.4 kPa over 30 minutes. Thereafter, the temperature was raised to 240 ° C. at a rate of 60 ° C./hr and maintained at that temperature for 10 minutes, and then the degree of vacuum was set to 133 Pa or less over 1 hour. The reaction was carried out with stirring for a total of 6 hours, discharged from the bottom of the reaction tank under nitrogen pressure, and cut with a pelletizer while cooling in a water tank to obtain copolymer polycarbonate resin pellets as resin A.

<Resin production example 2>
ISS 366 parts, 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro (5.5) undecane (hereinafter abbreviated as SPG) 219 parts, ND 33 parts Except for the use, the same operation as in Resin Production Example 1 was performed to obtain a copolymer polycarbonate resin.

<Resin production example 3>
Except for using ISS 366 parts, SPG 125 parts, and ND 83 parts, the same operation as in Resin Production Example 1 was performed to obtain a copolymer polycarbonate resin.

<Resin production example 4>
Except for using 250 parts of ISS and 247 parts of 1,4-cyclohexanedimethanol (hereinafter abbreviated as CHDM), the same operation as in Resin Production Example 1 was performed to obtain a copolymer polycarbonate resin.

<Resin production example 5>
Except for using 350 parts of ISS and 149 parts of CHDM, the same operation as in Resin Production Example 1 was performed to obtain a copolymer polycarbonate resin.

<Resin production example 6>
Except for using ISS 502 parts, the same operation as in Resin Production Example 1 was performed to obtain a polycarbonate resin.

<Resin Production Example 7>
Except for using 124 parts of ISS and 775 parts of SPG, the same operation as in Resin Production Example 1 was performed to obtain a polycarbonate resin.

<Resin production example 8>
9,9-bis (4-hydroxy-3-methylphenyl) fluorene (hereinafter abbreviated as BCF) 37.0 parts, 9-bis [4- (2-hydroxyethoxy) phenyl] fluorene (hereinafter abbreviated as BPEF) 34. 3 parts, SPG 65.5 parts, DPC 85.7 parts and tetramethylammonium hydroxide 3.6 × 10 ⁻³ parts and sodium hydrogen carbonate 1.6 × 10 ⁻⁴ parts as a catalyst were heated to 180 ° C. in a nitrogen atmosphere and melted. I let you. Thereafter, the degree of vacuum was adjusted to 13.4 kPa over 30 minutes. Thereafter, the temperature was raised to 260 ° C. at a rate of 20 ° C./hr, held at that temperature for 10 minutes, and then the degree of vacuum was set to 133 Pa or less over 1 hour. The reaction was carried out under stirring for a total of 6 hours.
After completion of the reaction, 1.5 times mole of the catalyst amount of tetrabutylphosphonium salt of dodecylbenzene sulfonate was added to deactivate the catalyst, and then discharged from the bottom of the reaction tank under nitrogen pressure and cooled in a water tank while being pelletized. To obtain copolymer polycarbonate resin pellets.

<Resin production example 9>
Except for using 51.9 parts of BCF and 77.5 parts of SPG, the same operation as in Resin Production Example 8 was performed to obtain an aliphatic aromatic polycarbonate copolymer.
Moreover, the evaluation method of the resin and film used in the Example is as follows.
1. Polymer composition ratio (NMR)
Measurement was performed by proton NMR of JNM-AL400 manufactured by JEOL Ltd., and the polymer composition ratio was calculated.
2. Photoelastic constant A test piece having a length of 50 mm and a width of 10 mm was cut out from the film, and the photoelastic constant was measured using Spectroellipometer M-220 manufactured by JASCO Corporation.
3. Retardation and wavelength dispersibility A test piece having a length of 50 mm and a width of 50 mm is cut out from the retardation film, and the central part thereof is measured using a Spectroellipometer M-220 manufactured by JASCO Corporation. It was measured.
4). Tg (glass transition temperature)
A 2910 type DSC manufactured by TA Instruments Japan Co., Ltd. was used, and 15 mg of the sample was measured in a 50 ml / min nitrogen atmosphere at a heating rate of 20 ° C./min.
5). Flexibility and adhesion Flex resistance was measured according to the MIT tester method described in JIS P8115. At that time, the measurement sample was cut with a length of 110 mm and a width of 10 mm so that the main orientation axis direction (main stretching direction) of the film was the longitudinal direction, the bending surface had a radius of curvature of 1 mm, and The speed was 100 times per minute. The number of times of bending until the break was repeated (number of folding times) was measured 10 times, and the average value was determined as follows.
“◎”: 100,000 times or more until the break “○”: 40,000 times or more until the break and less than 100,000 “△”: The number of times until the break is 30,000 or more and less than 40,000 “×” : Less than 30,000 times of bending until rupture Further, the fractured cross section of the sample after the rupture was visually confirmed, and delamination was determined as follows.
“◎”: No peeling.
“◯”: peeling, but rough interface is observed.
"X": It peels and a rough surface is not recognized.
6). Mechanical strength Workability was determined as follows by measuring the breaking strength and breaking elongation in the main orientation axis direction (main stretching direction) of the film according to JIS K7127 using Tensilon RTC-1210A manufactured by ORIENTEC.
“◯”: breaking strength of 140 MPa or more and breaking elongation of 30% or more “Δ”: satisfying either breaking strength of 140 MPa or more or breaking elongation of 30% or more “x”: breaking strength of less than 140 MPa and breaking elongation of 30% Less than 10 mm width and 200 mm length of sample at a temperature of 23 ° C. and a humidity of 65% RH, with a distance between chucks of 100 mm and a tensile speed of 5 mm / min. It calculated from the measurement result of the amount of elongation and the load required for the fracture.

[Example 1]
Using the resin prepared in Production Example 1 as the resin A and the resin B as the styrene / maleic anhydride copolymer “Dylark D332” (Nova Chemical Co., Tg = 131 ° C.), the thickness ratio of the layer A and the layer B Is 1.3: 1, and a laminate having an unstretched film thickness of 135 μm is prepared, and the film is horizontally stretched at a preheating temperature of 135 ° C., a stretching temperature of 130 ° C., and a stretching ratio of 3.0 times. Obtained.
When viewed in the thickness direction, layer A, layer B, and layer A are laminated in this order so as to have a thickness ratio of 0.65: 1: 0.65.
The laminate was produced according to the following method.
The first and second extruders A and B, the die, and the first to third rolls and the pair of take-up rolls are sequentially arranged, and two types and three layers are distributed, that is, the first layer, the second layer, The feed block of the third layer (A1 / B1 / A2) was arranged so that the resin having positive birefringence is on the surface layer side.

  Resin having positive birefringence is melted by a single screw extruder having a screw diameter of 40 mm, and resin having negative birefringence is melted by a single screw extruder having a screw diameter of 30 mm and laminated in three layers by a feed block method. The resin laminate is extruded through a die having a set temperature of 250 ° C., rolled with the first roll and the second roll, cooled with the third roll, and the take-up resin laminate is formed with a pair of take-up rolls. Produced. In addition, the surface temperature of the 1st cooling roll was 100 degreeC, the surface temperature of the 2nd cooling roll was 90 degreeC, and the surface temperature of the 3rd cooling roll was 120 degreeC. These temperatures are values obtained by actually measuring the surface temperature of each cooling roll.

[Example 2]
The same conditions as in Example 1 except that the ratio of the resin having positive birefringence and the resin having negative birefringence is 0.6: 1: 0.6, and the thickness of the unstretched film is 180 μm. A retardation film was obtained.

[Example 3]
The same conditions as in Example 1 except that the ratio of the resin having positive birefringence and the resin having negative birefringence is 0.75: 1: 0.75, and the thickness of the unstretched film is 105 μm. A retardation film was obtained.

[Example 4]
A retardation film was obtained under the same conditions as in Example 1 except that the resin prepared in Production Example 2 was used as the resin having positive birefringence.

[Example 5]
Using the resin prepared in Production Example 3 as a resin having positive birefringence, a retardation film was obtained under the same conditions as in Example 1 except that the preheating temperature was 125 ° C. and the stretching temperature was 120 ° C.

[Example 6]
A retardation film was obtained under the same conditions as in Example 1 except that the resin prepared in Production Example 4 was used as the resin having positive birefringence.

[Example 7]
A retardation film was obtained under the same conditions as in Example 1 except that the resin prepared in Production Example 5 was used as a resin having positive birefringence and the stretching temperature was 120 ° C.

[Example 8]
Other than using two types of five-layer distribution, that is, using a feed block of the first layer, the second layer, the third layer, the fourth layer, and the fifth layer (A1 / B1 / A2 / B2 / A3) Obtained a retardation film under the same conditions as in Example 1.
When viewed in the thickness direction, the layer A, the layer B, the layer A, the layer B, and the layer A have a thickness ratio of 0.43: 0.5: 0.43: 0.5: 0.43 in this order ( The resin A is laminated so that the resin B = 1.3: 1).

[Comparative Example 1]
Resin having positive birefringence using a trade name ARTON (manufactured by JSR) which is a polycycloolefin resin and a styrene / maleic anhydride copolymer “DAILARK D332” (manufactured by Nova Chemical Co., Tg = 131 ° C.) And a resin laminate having a ratio of a resin having negative birefringence of 1.8: 1 and an unstretched film thickness of 240 μm, a preheating temperature of 135 ° C., a stretching temperature of 130 ° C., and a stretching ratio of 3. A phase difference film was obtained under the same conditions as in Example 1 except that the film was stretched transversely at 0 times.

[Comparative Example 2]
A retardation film was obtained under the same conditions as in Comparative Example 1 except that ZEONOR (manufactured by Nippon Zeon Co., Ltd.) was used as the resin having positive birefringence.

[Comparative Example 3]
Using the resin prepared in Production Example 6 as a resin having positive birefringence, a retardation film was obtained under the same conditions as in Example 2 except that the preheating temperature was 185 ° C. and the stretching temperature was 180 ° C.

[Comparative Example 4]
Using the resin prepared in Production Example 8, a resin film having an unstretched film thickness of 165 μm is prepared, and the film is horizontally stretched at a preheating temperature of 145 ° C., a stretching temperature of 140 ° C., and a stretching ratio of 3.0 times. Obtained.

[Comparative Example 5]
Using the resin prepared in Production Example 9, a resin film having an unstretched film thickness of 165 μm is prepared, and the film is horizontally stretched at a preheating temperature of 145 ° C., a stretching temperature of 140 ° C., and a stretching ratio of 3.0 times. Obtained.
The unstretched film was produced according to the following method.
Melting with a single screw extruder with a screw diameter of 40 mm, extruding through a die with a set temperature of 250 ° C., rolling with a first roll and a second roll, forming a resin film while cooling with a third roll, A take-up unstretched film was produced by a take-up roll. In addition, the surface temperature of the 1st cooling roll was 100 degreeC, the surface temperature of the 2nd cooling roll was 90 degreeC, and the surface temperature of the 3rd cooling roll was 120 degreeC. These temperatures are values obtained by actually measuring the surface temperature of each cooling roll.

[Comparative Example 6]
A retardation film was obtained under the same conditions as in Comparative Example 7, except that the resin prepared in Production Example 7 was used as the resin having positive birefringence.

When a norbornene-based resin was used as a resin having positive birefringence from Comparative Example 1 or Comparative Example 2 in Table 2, birefringence development, flexibility, workability, and a laminate were tested for flexibility. Poor adhesion at time.
Further, from Comparative Example 3 in Table 2, when only isosorbide is used as the resin having positive birefringence, the flexibility, workability, and adhesion when the laminate is subjected to a flexibility test are also poor.

  The retardation film obtained by orienting at least uniaxially the laminate obtained by laminating the layer made of the resin having positive birefringence and the layer made of the resin having negative birefringence according to the present invention has a wavelength ideally close to a wide band. It has dispersion characteristics, low photoelastic constant, high expression of birefringence, good adhesion of resin having positive birefringence and resin having negative birefringence, and has flexibility and workability. Since it is excellent, it is extremely useful as a retardation film for liquid crystals, organic EL displays and the like. In particular, as a flexible display device, for example, it can be suitably used as an in-vehicle display such as a car navigation system, a television, a smartphone, a tablet terminal, a digital signage, or the like.

Claims (7)

A retardation film obtained by orienting a laminate in which a layer made of a resin having positive birefringence and a layer made of a resin having negative birefringence are laminated at least in a uniaxial direction, wherein the resin having positive birefringence is The repeating unit represented by the following formula (A) contains 30 mol% or more and 99 mol% or less based on all repeating units,

The resin having negative birefringence is a resin containing a styrenic resin, and the thickness ratio of the resin having positive birefringence and the resin having negative birefringence is 1: 1 to 2: 1, A retardation film, wherein a relationship between an in-plane retardation value R450 at a wavelength of 450 nm and an in-plane retardation value R550 at a wavelength of 550 nm satisfies the following formula (1).
0.60 ≦ R450 / R550 ≦ 0.95 (1)   The glass transition temperature (Tg) of the resin having positive birefringence is 100 ° C. or higher and 150 ° C. or lower, and the glass transition temperature (Tg) of the resin having negative birefringence is 100 ° C. or higher and 150 ° C. or lower. The retardation film according to claim 1.   The retardation film according to claim 1, wherein the resin having negative birefringence is a styrene-maleic anhydride copolymer resin. The retardation film according to claim 1, which has a photoelastic coefficient of 30 × 10 ⁻¹² Pa ⁻¹ or less.   The retardation film according to any one of claims 1 to 3, wherein the retardation is 135 nm or more and 155 nm or less and the thickness is 20 µm or more and 70 µm or less. A laminate in which a layer made of a resin having positive birefringence (A layer) and a layer made of a resin having negative birefringence (B layer) are laminated and integrated by melt coextrusion molding is stretched at least in a uniaxial direction. A method for producing a retardation film, wherein the resin having positive birefringence includes a repeating unit represented by the following formula (A), containing 30 mol% or more and 99 mol% or less based on all repeating units,

The resin having negative birefringence is a resin containing a styrenic resin, and the thickness ratio of the resin having positive birefringence and the resin having negative birefringence is 1: 1 to 2: 1, A method for producing a retardation film, wherein a relationship between an in-plane retardation value R450 at a wavelength of 450 nm and an in-plane retardation value R550 at a wavelength of 550 nm satisfies the following formula (1).
0.60 ≦ R450 / R550 ≦ 0.95 (1) A liquid crystal display device or an organic EL display device comprising the retardation film according to claim 1.