JP2013033237A - Optical isotropic protective film for polarizing film, and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective film for a polarizing film excellent in heat resistance, moisture resistance, scratch resistance, mechanical strength, adhesiveness to a polarizing film and optical anisotropy, and to provide a polarizing plate having the protective film.SOLUTION: An optical isotropic protective film for a polarizing film is provided, which is formed of an acrylic thermoplastic resin including: a first structural unit by 50 to 95 mass% comprising a methacrylic acid monomer and a methacrylate monomer; a second structural unit by 0.1 to 20 mass% comprising N-substituted maleimide compound having an N-substituted group consisting of an aryl group or an arylalkyl group; and a third structural unit by 0.1 to 49.9 mass% comprising a N-substituted maleimide compound having an N-substituted group consisting of an alkyl group or a cycloalkyl group.

Description

  The present invention relates to an optically isotropic polarizing film protective film and a polarizing plate.

  A liquid crystal display device is a film or plate made of transparent glass, resin, or the like, between a pair of opposing electrode plates, or an electrode plate having a counter electrode arranged in one sheet and a film or plate A liquid crystal cell in which liquid crystal molecules are sealed between transparent material plates and a polarized light that is arranged in a pair of orthogonal states and has a function of dividing incident light into two polarization components orthogonal to each other and allowing only one of them to pass A display device comprising a plate and a planar light source. As the structure, a liquid crystal cell disposed between orthogonal polarizing plates is further disposed on a surface light source.

  The display principle is that light emitted from a planar light source is passed through a polarizing plate to be polarized, a voltage corresponding to screen information is applied between the electrodes, the orientation of liquid crystal molecules is changed appropriately, and the polarizing plate is further By transmitting the light, it is displayed as a light transmittance, that is, a light shade.

  As a method for producing a polarizing film constituting a liquid crystal display device, first, generally, a polyvinyl alcohol having a certain saponification degree or more is dissolved in hot water to prepare a dope solution, and then a casting drum or stainless steel belt having a mirror surface. It is formed into a film by a solution casting method in which the solvent is dried after pouring over. Next, the film is stretched to maintain the stretched state, and then iodine or a dichroic dye is adsorbed, and further immersed in a boric acid solution and dried.

  This polarizing film is easily damaged, and particularly when the surface on the liquid crystal cell side is damaged, the phase of light is disturbed and information is deteriorated. Also, stretching is caused by moisture absorption from the outside, and the degree of polarization decreases. Furthermore, the heat resistance is insufficient with only the polarizing film, and the film strength cannot be maintained.

  Therefore, in an actual liquid crystal display device, the polarizing film is used as a polarizing plate to which a polarizing film protective film for protecting the surface is attached and scratch resistance is improved, and a certain degree of heat resistance and strength are imparted.

  As a polarizing film protective film, a triacetyl cellulose film is common. The triacetyl cellulose film is produced by a solution casting method after dissolving a triacetyl cellulose polymer in a solvent typified by methylene chloride to obtain a dope solution. Due to the characteristics of the solution casting method, the in-plane polymer chain orientation during drying is small, and the in-plane birefringence is small. The degree of in-plane birefringence is sealed between a pair of opposing electrode plates in the form of a plate, and the liquid crystal aligned perpendicular to the cell surface is transmitted by tilting horizontally by applying a voltage between the electrode plates. The vertical alignment method (hereinafter referred to as “VA method”) that controls the amount of light or the liquid crystal that is sealed between two opposing electrode plates in a pair of plates and aligned horizontally with respect to the cell surface is placed between the electrode plates. In conventional liquid crystal display methods, such as the Twisted Nematic method (hereinafter referred to as “TN method”), which controls the amount of transmitted light by rising vertically by applying a voltage of 1, it was necessary and sufficient.

  The VA system and the TN system are suitable for liquid crystal televisions for personal use, liquid crystal display devices for personal computers, and inexpensive liquid crystal display devices for mobile communication devices, respectively. Since these are mainly used indoors and were not intended to be used in extremely severe environments, triacetylcellulose is also used for the polarizing plates used from the viewpoint of scratch resistance, heat resistance, moisture resistance, etc. A film using a polarizing film protective film was sufficient.

  However, in recent years, in addition to the development of broadband communication networks such as ADSL and optical communication, the mobile communication technology has rapidly developed, and various electronic devices are required to have bidirectional display and input. It has become. In order to cope with both displays and inputs, a liquid crystal display device-integrated touch panel is rapidly spreading.

  A liquid crystal display integrated touch panel is a device with display and input functions. It displays image information received from the outside of the device on a liquid crystal display device, and is screen information displayed by the operator, such as pictures and pictograms. By touching a point or area with a hand or a pen, the touched screen information position is sensed and the operator's intention is output to the outside as an information signal.

  As a liquid crystal system used for a liquid crystal display device integrated touch panel, an In-Plane-Switching system (hereinafter referred to as “IPS system”) and a Ringe Field Switching (hereinafter referred to as “FFS system”) are often employed. These are systems in which liquid crystal molecules are enclosed between a single electrode plate on which a counter electrode for controlling liquid crystal is disposed and a film-like or plate-like transparent material plate, and the liquid crystal molecules rotate within the plane of the liquid crystal cell, or Image information is output as a change in the amount of transmitted light by rotating in a state inclined from the in-plane.

  The IPS method and the FFS method are methods in which the liquid crystal rotates in a plane as compared with the VA method and the TN method, and the inter-electrode distance is changed with respect to a partial change in cell thickness caused by a pressing load by a finger or a pen. Therefore, the rotation of the liquid crystal molecules does not change. In addition, the viewing angle is also wider than that of the VA system. For this reason, it is difficult to cause changes such as color bleeding on the display screen during pressurization, moire interference unevenness, etc., so-called high pressure resistance, and the angle of the LCD touch panel integrated in the hand frequently changes. Even in this case, there is an advantage that color change hardly occurs and visibility is high.

  A display device with a new type of liquid crystal display system incorporated in such a liquid crystal display integrated touch panel is frequently used outdoors with large humidity fluctuations. Heating occurs. Further, compared to a normal liquid crystal display device, there is a need for a strength that can be applied to a mechanical external force by a finger, a pen, or the like, or a weight reduction on the premise that it is used outdoors. Therefore, a polarizing plate used for a new type of liquid crystal display system is required to have a better balance between environmental resistance, heat resistance, thickness reduction and mechanical strength than conventional ones. In order to display content, lower birefringence than that of the prior art, so-called optical isotropy is required.

  However, the triacetyl cellulose polarizing film protective film that has been used to form a conventional polarizing plate has too high moisture permeability to be used in a new type of liquid crystal display system, and the polarizing film absorbs moisture under high humidity. Due to the large fluctuations in optical properties, low heat resistance, and low mechanical strength, it is necessary to increase the thickness of the polarizing film protective film in order to develop the necessary and sufficient strength for the polarizing plate itself. In addition, the optical isotropy was insufficient.

  Therefore, in order to improve the durability and heat resistance of the polarizing plate, it has been proposed to use a protective film other than the triacetyl cellulose film. For example, Patent Documents 1 and 2 disclose a norbornene-based resin polarizing film protective film, and water resistance and mechanical strength are improved. However, these are not always sufficient in terms of environmental resistance, such as whitening on the surface of the protective film caused by oil coming from fingers or the like. In addition, since the surface tension of norbornene resin and polarizing film is too different and the gas barrier is too high, adhesives for acrylic polarizing film or polyvinyl alcohol polarizing film are used on both sides of the polarizing film. When attached, the solvent of the adhesive is difficult to escape, and depending on the use conditions such as at high temperatures, there is a problem in adhesion such as partial peeling caused by the generated gas. Also, because it is a laminated film of various materials structurally, the refractive index of each layer is different, so optically, interference unevenness between layers tends to occur, and light transmittance decreases due to reflection between layers. There are challenges.

  Therefore, in Patent Document 3, a laminated film type polarizing film protective film produced by a melt coextrusion method of a norbornene resin and a polycarbonate resin, and a laminated film type polarizing film protection obtained by laminating a norbornene resin film and a polyethylene terephthalate film. A film has been proposed. Oil resistance is improved on the laminated polycarbonate surface and the laminated polyethylene terephthalate surface, but problems still remain in adhesion to the polarizing film, causing peeling when used under high temperature and high humidity, resulting in polarization leakage There is a problem. Moreover, since it is still a laminated film, the refractive index in each layer is different, so that interference unevenness is likely to occur, and there is a problem that the light transmittance is reduced due to reflection between layers.

  On the other hand, from the viewpoint of reducing the birefringence of the polarizing film protective film by making a laminated film, that is, improving the optical isotropy, in Patent Document 4, by laminating two kinds of materials having positive and negative photoelastic coefficients. A laminated film exhibiting optical isotropy has been proposed. Specifically, a laminated film combining a polycarbonate having a positive photoelastic coefficient and high heat resistance and a polymethylmethacrylate having a negative photoelastic coefficient and a high surface hardness and being hardly damaged, and a positive photoelastic coefficient. It is a laminated film combining polysulfone having high heat resistance and an ethylene-tetracyclododecene copolymer having a negative photoelastic coefficient and low hygroscopicity. However, the optical isotropy cannot be determined only by a simple combination discussion of positive and negative photoelastic coefficients. In actual hot-melt molded films, stress remains in various directions during molding, and in the simple melt coextrusion method, the linear expansion coefficient between different types of polymers differs from the melted state to solidify, so there is always a change from one to one. It leaves distortion. From these facts, only the technical information disclosed in Patent Document 4 in which suppression of orientation birefringence is not taken into consideration is produced by the solution casting method in the same manner as the triacetyl cellulose polarizing film protective film, and stress remains only in the thickness direction. It is difficult to obtain a laminated film having high optical isotropy unless the film is laminated. Further, since the film is still a laminated film, there is a problem that interference unevenness due to a difference in refractive index in each layer is likely to occur, and light transmittance is reduced due to interlayer reflection.

  On the other hand, the method described in Patent Document 5 is a method for producing Patent Document 4 by a melt molding method, and is capable of stress relaxation between a cyclic olefin polymer having a positive photoelastic coefficient and a negative polymethyl methacrylate. It was made with the agent layer in between. Further, by limiting the refractive index difference in each layer of the laminated film to a specific small range, reflection between layers and interference unevenness are suppressed. However, the suppression of reflection and interference unevenness, which is a problem inherent to the laminated film, is not necessarily sufficient for use in a new liquid crystal display system.

  Originally, the reason why the photoelastic coefficient proposed in Patent Document 4 and Patent Document 5 is a combination of transparent resins showing positive and negative is to reduce optical distortion as a molded body as much as possible, and an essential solution. As a countermeasure, both a photoelastic birefringence and an orientation birefringence are zero (or both are very close to zero compared to the transparent resin conventionally used for a polarizing film protective film), so-called “zero / zero polymer”. Ideally, a polarizing film protective film consisting of a single layer similar to the triacetyl cellulose protective film is produced using the above as a raw material. If it does so, the interlayer reflection and interference nonuniformity which are the subjects of a laminated film type polarizing film protective film can be solved.

  As a study of zero / zero polymers, Patent Document 6 discloses a polymer that can be used as a polarizing film protective film, and birefringence does not occur even if there is any external stress or residual strain due to hot melt molding. Therefore, it is extremely excellent as an optically isotropic material.

JP-A-6-511117 Japanese Patent Laid-Open No. 2002-249600 JP 2005-115085 A JP 2000-206303 A International Publication No. 2006/137427 JP 2006-308682 A

  However, the polymer described in Patent Document 6 has a glass transition temperature of 100 ° C. or less, is not sufficiently heat resistant to be used as a polarizing film protective film, and has a difference in surface tension with the polarizing film because it contains fluorine. It is large and there is a tendency that adhesion after pasting is not sufficient.

  That is, as a polarizing film protective film constituting a polarizing plate in the IPS method and the FFS method, which are frequently used for a liquid crystal display integrated touch panel that supports bidirectional display and input, heat resistance, moisture resistance, and scratch resistance required in recent years There is nothing that satisfies all of the properties, mechanical strength, adhesion to the polarizing film, and optical isotropy.

  Therefore, the present invention provides heat resistance, moisture resistance, scratch resistance, mechanical strength, adhesion to a polarizing film, optics, and the like used for a liquid crystal display device, particularly a liquid crystal display device whose liquid crystal method is an IPS method or an FFS method. An object of the present invention is to provide a polarizing film protective film having excellent directivity and a polarizing plate including the polarizing film protective film.

  As a result of intensive studies to solve the above problems, the present inventor has melt-thermoformed a specific acrylic thermoplastic resin, resulting in heat resistance, moisture resistance, scratch resistance, mechanical strength, polarizing film The inventors have found that a polarizing film protective film and a polarizing plate excellent in adhesion and optical isotropy can be obtained, and the present invention has been made based on this finding.

［式中、Ｒ^１は、水素原子、炭素数１〜１２のアルキル基、炭素数５〜１２のシクロアルキル基、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ａ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示す。
Ａ群：ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基及び炭素数１〜１２のアルキル基。］

［式中、Ｒ^２は、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ｂ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示し、Ｒ^３及びＲ^４はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。
Ｂ群：ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基、炭素数１〜１２のアルキル基及び炭素数７〜１４のアリールアルキル基。］

［式中、Ｒ^５は、水素原子、炭素数３〜１２のシクロアルキル基、炭素数１〜１２のアルキル基、又は、下記Ｃ群より選ばれる少なくとも一種の置換基を有する炭素数１〜１２のアルキル基、を示し、Ｒ^６及びＲ^７はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。
Ｃ群：ハロゲン原子、ヒドロキシル基、ニトロ基及び炭素数１〜１２のアルコキシ基。］
［２］アクリル系熱可塑性樹脂の光弾性係数の絶対値が、３．０×１０^−１２Ｐａ^−１以下である、［１］に記載の光学等方性偏光膜保護フィルム。
［３］アクリル系熱可塑性樹脂のハロゲン原子含有率が、アクリル系熱可塑性樹脂の総量基準で０．４７質量％未満である、［１］又は［２］に記載の光学等方性偏光膜保護フィルム。
［４］第二の構造単位の含有量の、第三の構造単位の含有量に対するモル比が０より大きく１５以下である、［１］〜［３］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［５］Ｒ^１が、メチル基又はベンジル基であり、Ｒ^２が、フェニル基又はＢ群より選ばれる少なくとも一種の置換基を有するフェニル基であり、Ｒ^５が、シクロヘキシル基である、［１］〜［４］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［６］アクリル系熱可塑性樹脂は、フィルム成形した場合の１００μｍ厚みにおける透湿度が、３〜１００ｇ／（ｍ^２・２４ｈｒ）である、［１］〜［５］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［７］アクリル系熱可塑性樹脂は、偏光膜との屈折率差が、±０．０４以内である、［１］〜［６］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［８］アクリル系熱可塑性樹脂は、フィルム成形した場合の延伸倍率（Ｓ）と、該延伸倍率での１００μｍ厚み換算複屈折（Δｎ（Ｓ））との最小二乗法近似直線関係式（ａ）における傾きαの値が、下記式（ｂ）を満たす樹脂である、［１］〜［７］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
Δｎ（Ｓ）＝α×Ｓ＋β （ａ）
−０．３０×１０^−５≦α≦０．３０×１０^−５ （ｂ）
［式中、βは定数であり、無延伸時の複屈折を示す。］
［９］アクリル系熱可塑性樹脂のガラス転移温度が１３０℃以上である、［１］〜［８］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［１０］表面の鉛筆硬度が３Ｈ以上である、［１］〜［９］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［１１］アクリル系熱可塑性樹脂は、フィルム成形した場合の面内方向の位相差Ｒｅの絶対値が、１００μｍ厚み換算で８．０ｎｍ以下となる樹脂である、［１］〜［１０］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［１２］アクリル系熱可塑性樹脂は、フィルム成形した場合の厚み方向の位相差Ｒｔｈの絶対値が１００μｍ厚み換算で、８．０ｎｍ以下となる樹脂である、［１］〜［１１］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［１３］厚みが１０〜３００μｍである、［１］〜［１２］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［１４］溶融押出成形及び／又は溶融二軸延伸成形により製造される、［１］〜［１３］のいずれか１つに記載の光学等方性偏光膜保護フィルム。
［１５］［１］〜［１４］のいずれか１つに記載の光学等方性偏光膜保護フィルムを備える、偏光板。
［１６］液晶の方式が横電界方式又は斜め電界方式である液晶表示装置に使用される、［１５］に記載の偏光板。
［１７］液晶の方式が横電界方式又は斜め電界方式である液晶表示一体型タッチパネルに使用される、［１５］に記載の偏光板。 That is, the present invention relates to the following.
[1] Acrylic having a first structural unit represented by the following formula (1), a second structural unit represented by the following formula (2), and a third structural unit represented by the following formula (3) The acrylic thermoplastic resin is formed from a thermoplastic resin, and the acrylic thermoplastic resin is 50 to 95% by mass of the first structural unit, 0.1 to 20% by mass of the second structural unit, and 0.1% An optically isotropic polarizing film protective film having ˜49.9% by mass of a third structural unit.

[Wherein, R ¹ represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or And an aryl group having 6 to 14 carbon atoms and having at least one substituent selected from the following group A.
Group A: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms. ]

[Wherein, R ² represents an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms having at least one substituent selected from the following group B: R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group B: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. ]

[Wherein, R ⁵ represents a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, or at least one substituent having at least one substituent selected from the following group C. R ⁶ and R ⁷ each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group C: a halogen atom, a hydroxyl group, a nitro group, and an alkoxy group having 1 to 12 carbon atoms. ]
[2] The optically isotropic polarizing film protective film according to [1], wherein the absolute value of the photoelastic coefficient of the acrylic thermoplastic resin is 3.0 × 10 ⁻¹² Pa ⁻¹ or less.
[3] Optical isotropic polarizing film protection according to [1] or [2], wherein the halogen atom content of the acrylic thermoplastic resin is less than 0.47% by mass based on the total amount of the acrylic thermoplastic resin. the film.
[4] The optical unit according to any one of [1] to [3], wherein the molar ratio of the content of the second structural unit to the content of the third structural unit is greater than 0 and 15 or less. Isotropic polarizing film protective film.
[5] R ¹ is a methyl group or a benzyl group, R ² is a phenyl group or a phenyl group having at least one substituent selected from group B, and R ⁵ is a cyclohexyl group. ] The optically isotropic polarizing film protective film as described in any one of [4].
[6] The acrylic thermoplastic resin according to any one of [1] to [5], wherein the moisture permeability at a thickness of 100 μm when the film is formed is 3 to 100 g / (m ² · 24 hr). Optical isotropic polarizing film protective film.
[7] The optically isotropic polarizing film protective film according to any one of [1] to [6], wherein the acrylic thermoplastic resin has a refractive index difference within ± 0.04 with respect to the polarizing film. .
[8] The acrylic thermoplastic resin is a least-squares approximate linear relational expression (a) between the draw ratio (S) when film-forming and 100 μm-thickness converted birefringence (Δn (S)) at the draw ratio. The optically isotropic polarizing film protective film according to any one of [1] to [7], wherein the value of the slope α is a resin that satisfies the following formula (b).
Δn (S) = α × S + β (a)
−0.30 × 10 ⁻⁵ ≦ α ≦ 0.30 × 10 ⁻⁵ (b)
[In the formula, β is a constant and indicates birefringence at the time of non-stretching. ]
[9] The optically isotropic polarizing film protective film according to any one of [1] to [8], wherein the glass transition temperature of the acrylic thermoplastic resin is 130 ° C. or higher.
[10] The optically isotropic polarizing film protective film according to any one of [1] to [9], wherein the surface has a pencil hardness of 3H or more.
[11] The acrylic thermoplastic resin is a resin in which the absolute value of the retardation Re in the in-plane direction when film-forming is 8.0 nm or less in terms of 100 μm thickness, any of [1] to [10] The optically isotropic polarizing film protective film as described in any one.
[12] Any one of [1] to [11], wherein the acrylic thermoplastic resin is a resin in which an absolute value of a retardation Rth in the thickness direction when a film is formed is 8.0 nm or less in terms of thickness of 100 μm. The optically isotropic polarizing film protective film as described in one.
[13] The optically isotropic polarizing film protective film according to any one of [1] to [12], having a thickness of 10 to 300 μm.
[14] The optically isotropic polarizing film protective film according to any one of [1] to [13], which is produced by melt extrusion molding and / or melt biaxial stretching.
[15] A polarizing plate comprising the optically isotropic polarizing film protective film according to any one of [1] to [14].
[16] The polarizing plate according to [15], which is used for a liquid crystal display device in which a liquid crystal method is a horizontal electric field method or an oblique electric field method.
[17] The polarizing plate according to [15], which is used for a liquid crystal display integrated touch panel in which a liquid crystal method is a horizontal electric field method or an oblique electric field method.

  ADVANTAGE OF THE INVENTION According to this invention, the polarizing film protective film excellent in heat resistance, moisture resistance, scratch resistance, mechanical strength, adhesiveness with a polarizing film, and optical isotropy can be provided. Moreover, the polarizing plate provided with the polarizing film protective film is excellent in heat resistance, moisture resistance, scratch resistance, mechanical strength and optical isotropy, and realizes good visibility and reliability of the liquid crystal display device.

It is a figure which shows typically the structure of a melt drawing apparatus. It is a schematic cross section of a resistive film type liquid crystal display device integrated touch panel. It is a schematic cross section of an electrostatic projection type liquid crystal display device integrated touch panel.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

[Acrylic thermoplastic resin]
The optically isotropic polarizing film protective film of the present embodiment is made of an acrylic thermoplastic resin. The acrylic thermoplastic resin has a first structural unit, a second structural unit, and a third structural unit. Hereinafter, each structural unit will be described.

(First structural unit)
The first structural unit is a structural unit represented by the following formula (1).

式中、Ｒ^１は、水素原子、炭素数１〜１２のアルキル基、炭素数５〜１２のシクロアルキル基、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ａ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示す。ここで、Ａ群は、ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基及び炭素数１〜１２のアルキル基からなる群である。

In the formula, R ¹ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or The C6-C14 aryl group which has at least 1 type of substituent chosen from the following A group is shown. Here, group A is a group consisting of a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms.

  In the present specification, the alkyl group may be linear or branched. Further, the alkyl group in the arylalkyl group and the alkyl group in the alkoxy group may be linear or branched.

Examples of the alkyl group having 1 to 12 carbon atoms in R ^1, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 12 carbon atoms in ^{R 1,} a methyl group, an ethyl group, n- propyl group, an isopropyl group, n- butyl group, an isobutyl group, t- butyl, 2-ethylhexyl, nonyl , Decanyl group, lauryl group, etc. Among these, in terms of further improving the transparency and weather resistance of acrylic thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl Group, isobutyl group, t-butyl group and 2-ethylhexyl group are preferable, and methyl group is more preferable.

Examples of the cycloalkyl group having 5 to 12 carbon atoms in R ¹ include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a tricyclodecyl group, a bicyclooctyl group, a tricyclododecyl group, an isobornyl group, and an adamantyl group. And tetracyclododecyl group. Among these, a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, a tricyclodecyl group, a bicyclooctyl group, a tricyclododecyl group, and an isobornyl group are preferable.

Examples of the arylalkyl group having 7 to 14 carbon atoms in R ¹ include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, 6-phenylhexyl group, and 8-phenyloctyl group. Among these, benzyl group, 1-phenylethyl group, 2-phenylethyl group, and 3-phenylpropyl group are preferable.

The aryl group having 6 to 14 carbon atoms in R ^1, a phenyl group, a naphthyl group, anthracenyl group and the like, among these, phenyl groups are preferred.

R ¹ may be an aryl group having 6 to 14 carbon atoms having a substituent, wherein the substituent is a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, or 1 carbon atom. A group selected from the group consisting of ˜12 alkyl groups (Group A).

In R ¹ , the aryl group having 6 to 14 carbon atoms having a substituent is preferably a phenyl group having a substituent. Examples of the aryl group having 6 to 14 carbon atoms having a substituent include 2,4,6-tribromophenyl group, 2-chlorophenyl group, 4-chlorophenyl group, 2-bromophenyl group, 4-bromophenyl group, 2-methylphenyl group, 4-methylphenyl group, 2-ethylphenyl group, 4-ethylphenyl group, 2-methoxyphenyl group, 4-methoxyphenyl group, 2-nitrophenyl group, 4-nitrophenyl group, 2, Examples include 4,6-trimethylphenyl group. Among these, 2,4,6-tribromophenyl group is preferable in terms of imparting flame retardancy.

  The content of the first structural unit is 50 to 95% by mass based on the total amount of the acrylic thermoplastic resin, preferably 60 to 92% by mass, more preferably 70 to 90% by mass, and still more preferably 79 to 90%. % By mass. When the content of the first structural unit is 50% by mass or more, high total light transmittance and environmental resistance are exhibited.

  The acrylic thermoplastic resin may contain only one kind of the first structural unit, or may contain two or more kinds of the first structural unit.

For example, the acrylic thermoplastic resin may have a structural unit in which R ¹ is an alkyl group and a structural unit in which R ¹ is an arylalkyl group or an aryl group. At this time, the content of the latter structural unit is preferably 0.1 to 10% by mass, more preferably 0.1 to 8% by mass, based on the total amount of the acrylic thermoplastic resin. More preferably, it is -6 mass%. According to the acrylic thermoplastic resin in this range, an effect of improving optical characteristics such as birefringence can be obtained without a large decrease in heat resistance.

  The first structural unit is formed from, for example, a first monomer selected from methacrylic acid monomers and methacrylic acid esters. The first monomer can be represented by the following formula (1-a).

式中、Ｒ^１は式（１）におけるＲ^１と同義である。

Wherein, ^{R 1} has the same meaning as ^{R 1} in Formula (1).

  Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate; methacrylic acid. Cyclopentyl, cyclohexyl methacrylate, cyclooctyl methacrylate, tricyclodecyl methacrylate, bicyclooctyl methacrylate, tricyclododecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 1-phenylethyl methacrylate, 2 methacrylates -Phenoxyethyl, 3-phenylpropyl methacrylate, 2,4,6-tribromophenyl methacrylate and the like. These first monomers may be used alone or in combination of two or more. Of the methacrylic acid esters, methyl methacrylate and benzyl methacrylate are preferred because the acrylic thermoplastic resin obtained has excellent transparency and weather resistance.

(Second structural unit)
The second structural unit is a structural unit represented by the following formula (2).

式中、Ｒ^２は、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基、又は、下記Ｂ群より選ばれる少なくとも一種の置換基を有する炭素数６〜１４のアリール基、を示し、Ｒ^３及びＲ^４はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。Ｂ群は、ハロゲン原子、ヒドロキシル基、ニトロ基、炭素数１〜１２のアルコキシ基、炭素数１〜１２のアルキル基及び炭素数７〜１４のアリールアルキル基からなる群である。

In the formula, R ² is an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms having at least one substituent selected from the following group B; R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms. Group B is a group consisting of a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms.

Examples of the arylalkyl group having 7 to 14 carbon atoms in R ² include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, 6-phenylhexyl group, and 8-phenyloctyl group. Of these, a benzyl group is preferred in terms of further improving optical properties such as heat resistance and low birefringence.

Examples of the aryl group having 6 to 14 carbon atoms in R ² include a phenyl group, a naphthyl group, and an anthracenyl group, and among these, optical characteristics such as heat resistance and low birefringence are further improved. In the formula, a phenyl group is preferred.

R ² may be an aryl group having 6 to 14 carbon atoms having a substituent, wherein the substituent is a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, or 1 carbon atom. A group selected from the group consisting of ˜12 alkyl groups and arylalkyl groups having 7 to 14 carbon atoms (Group B).

  Examples of the halogen atom as a substituent include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  As a C1-C12 alkoxy group as a substituent, a C1-C10 alkoxy group is preferable and a C1-C8 alkoxy group is more preferable. Moreover, as a C1-C12 alkoxy group as a substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, isobutyloxy group, t-butyloxy group, 2-ethylhexyl An oxy group, 1-decyloxy group, 1-dodecyloxy group, etc. are mentioned.

Examples of the alkyl group having 1 to 12 carbon atoms and the arylalkyl group having 7 to 14 carbon atoms as the substituent are exemplified as the alkyl group having 1 to 12 carbon atoms and the arylalkyl group having 7 to 14 carbon atoms in R ¹ . Groups are exemplified as well.

In R ² , the aryl group having 6 to 14 carbon atoms having a substituent is preferably a phenyl group having a substituent or a naphthyl group having a substituent. Examples of the aryl group having 6 to 14 carbon atoms having a substituent include 2,4,6-tribromophenyl group, 2-chlorophenyl group, 4-chlorophenyl group, 2-bromophenyl group, 4-bromophenyl group, 2-methylphenyl group, 4-methylphenyl group, 2-ethylphenyl group, 4-ethylphenyl group, 2-methoxyphenyl group, 4-methoxyphenyl group, 2-nitrophenyl group, 4-nitrophenyl group, 2, Examples include 4,6-trimethylphenyl group. Among these, 2,4,6-tribromophenyl group is preferable in that flame retardancy is imparted.

Examples of the alkyl group having 1 to 12 carbon atoms in R ³ and ^{R 4,} preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. Moreover, as a C1-C12 alkyl group in R < ³ > and R < ⁴ >, a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group , Nonyl group, decanyl group, lauryl group, etc. Among these, in terms of further improving the transparency and weather resistance of the acrylic thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, An n-butyl group, an isobutyl group, a t-butyl group and a 2-ethylhexyl group are preferable, and a methyl group is more preferable.

Examples of the aryl group having 6 to 14 carbon atoms in R ³ and R ⁴ include a phenyl group, a naphthyl group, and an anthracenyl group, and among these, optical characteristics such as heat resistance and low birefringence are further improved. In this respect, a phenyl group is preferred.

R ³ and R ⁴ are preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and more preferably a hydrogen atom.

  The content of the second structural unit is 0.1 to 49.9% by mass, preferably 0.1 to 35% by mass, more preferably 0.1 to 20% based on the total amount of the acrylic thermoplastic resin. It is 7 mass%, More preferably, it is 7-20 mass%. If the content of the second structural unit is within this range, the transparency of the resin is maintained, the yellowing does not occur, and the heat resistance is improved without impairing the environmental resistance.

  The acrylic thermoplastic resin may contain only one second structural unit, or may contain two or more second structural units.

  The second structural unit is formed from, for example, a second monomer selected from N-substituted maleimide compounds represented by the following formula (2-a).

^Wherein, R 2, ^{R 3} and ^{R 4} have the same meaning as ^R 2, ^{R 3} and ^{R 4} in each formula (2).

  As the second monomer, N-phenylmaleimide, N-benzylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, N- (4-bromophenyl) maleimide, N- ( 2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-methoxyphenyl) maleimide, N- (2-nitrophenyl) maleimide, N- (2,4,6-trimethylphenyl) maleimide N- (4-benzylphenyl) maleimide, N- (2,4,6-tribromophenyl) maleimide, N-naphthylmaleimide, N-anthracenylmaleimide, 3-methyl-1-phenyl-1H-pyrrole 2,5-dione, 3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1,3-diph Sulfonyl -1H- pyrrole-2,5-dione, 1,3,4-triphenyl -1H- pyrrole-2,5-dione, and the like. Of these second monomers, N-phenylmaleimide and N-benzylmaleimide are preferred because the acrylic thermoplastic resin has excellent heat resistance and optical properties such as birefringence. These second monomers may be used alone or in combination of two or more.

(Third structural unit)
The third structural unit is a structural unit represented by the following formula (3).

式中、Ｒ^５は、水素原子、炭素数３〜１２のシクロアルキル基、炭素数１〜１２のアルキル基、又は、下記Ｃ群より選ばれる少なくとも一種の置換基を有する炭素数１〜１２のアルキル基、を示し、Ｒ^６及びＲ^７はそれぞれ独立に、水素原子、炭素数１〜１２のアルキル基又は炭素数６〜１４のアリール基を示す。Ｃ群は、ハロゲン原子、ヒドロキシル基、ニトロ基及び炭素数１〜１２のアルコキシ基からなる群である。

In the formula, R ⁵ is a hydrogen atom, a C 3-12 cycloalkyl group, a C 1-12 alkyl group, or a C 1-12 having at least one substituent selected from the following group C. An alkyl group, and R ⁶ and R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms. Group C is a group consisting of a halogen atom, a hydroxyl group, a nitro group, and an alkoxy group having 1 to 12 carbon atoms.

Examples of the cycloalkyl group having 3 to 12 carbon atoms in R ⁵ include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a tricyclodecyl group, a bicyclooctyl group, a tricyclododecyl group, Isobornyl group, adamantyl group, tetracyclododecyl group, etc., among them, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group are preferred, and acrylic thermoplastic resin A cyclohexyl group is more preferable in terms of further improving optical properties such as weather resistance and transparency and imparting low water absorption to the acrylic thermoplastic resin.

The alkyl group having 1 to 12 carbon atoms in ^{R 5,} preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. The alkyl group having 1 to 12 carbon atoms in ^{R 5,} a methyl group, an ethyl group, n- propyl group, an isopropyl group, n- butyl group, an isobutyl group, t- butyl group, n- pentyl group, n- Hexyl group, n-octyl group, n-dodecyl group, n-octadecyl group, 2-ethylhexyl group, 1-decyl group, 1-dodecyl group, and the like. Among these, weather resistance of acrylic thermoplastic resin and A methyl group, an ethyl group, and an isopropyl group are preferable because optical properties such as transparency are further improved.

R ⁵ may be a C 1-12 alkyl group having a substituent, wherein the substituent is a group consisting of a halogen atom, a hydroxyl group, a nitro group and a C 1-12 alkoxy group ( Group C).

  Examples of the halogen atom as a substituent include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  As a C1-C12 alkoxy group as a substituent, a C1-C10 alkoxy group is preferable and a C1-C8 alkoxy group is more preferable. Moreover, as a C1-C12 alkoxy group as a substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, isobutyloxy group, t-butyloxy group, 2-ethylhexyl An oxy group, 1-decyloxy group, 1-dodecyloxy group, etc. are mentioned.

In R ⁵ , examples of the alkyl group having 1 to 12 carbon atoms having a substituent include a dichloromethyl group, a trichloromethyl group, a trifluoroethyl group, and a hydroxyethyl group, and among these, a trifluoroethyl group is preferable. It is.

Examples of the alkyl group having 1 to 12 carbon atoms in R ⁶ and ^{R 7,} preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 12 carbon atoms in ^{R 6} and ^{R 7,} methyl group, ethyl group, n- propyl group, an isopropyl group, n- butyl group, an isobutyl group, t- butyl group, a 2-ethylhexyl group , Nonyl group, decanyl group, lauryl group, etc. Among these, in terms of further improving the transparency and weather resistance of the acrylic thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, An n-butyl group, an isobutyl group, a t-butyl group and a 2-ethylhexyl group are preferable, and a methyl group is more preferable.

Examples of the aryl group having 6 to 14 carbon atoms in R ⁶ and R ⁷ include a phenyl group, a naphthyl group, and an anthracenyl group, and among these, optical characteristics such as heat resistance and low birefringence are further improved. In this respect, a phenyl group is preferred.

R ⁶ and R ⁷ are preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and more preferably a hydrogen atom.

  The content of the third structural unit is 0.1 to 49.9% by mass, preferably 0.1 to 35% by mass, more preferably 0.1 to 30%, based on the total amount of the acrylic thermoplastic resin. % By mass, more preferably 0.1 to 15% by mass. If content of a 3rd structural unit is this range, transparency will be maintained and low hygroscopicity will be exhibited.

  The acrylic thermoplastic resin may contain only one third structural unit, or may contain two or more third structural units.

  The third structural unit is formed of, for example, a third monomer selected from N-substituted maleimide compounds represented by the following formula (3-a).

^Wherein, R 5, ^{R 6} and ^{R 7} have the same meanings as ^R 5, ^{R 6} and ^{R 7} in each formula (3).

  Examples of the third monomer include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, N-isobutylmaleimide, and Ns-butyl. Maleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide, N-cyclo Propylmaleimide, N-cyclobutylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, N-cycloheptylmaleimide, N-cyclooctylmaleimide, 1-cyclohexyl-3-methyl-1-phenyl-1H-pyrrole-2,5 -Dione, 1-cyclohex 3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-diphenyl- 1H-pyrrole-2,5-dione and the like can be mentioned. These third monomers may be used alone or in combination of two or more. N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-cyclohexylmaleimide are preferable because of the excellent weather resistance of the acrylic thermoplastic resin, and low hygroscopicity that is recently required for optical materials is excellent. N-cyclohexylmaleimide is particularly preferred.

  In the acrylic thermoplastic resin, the total content of the second structural unit and the third structural unit is preferably 5 to 50% by mass based on the total amount of the acrylic thermoplastic resin. More preferably, it is 5-40 mass%, More preferably, it is 10-35 mass%, More preferably, it is 10-30 mass%, Most preferably, it is 15-30 mass%. When it is within this range, the acrylic thermoplastic resin has a more sufficient heat resistance improvement effect, and more preferable improvement effects in terms of weather resistance, low water absorption, and optical properties. In addition, when the content of the second structural unit and the content of the third structural unit exceeds 50% by mass, the reactivity of the monomer component is reduced during the polymerization reaction, and the monomer that remains unreacted The amount increases, and the physical properties of the acrylic thermoplastic resin may decrease.

In the acrylic thermoplastic resin, the molar ratio C ₂ / C ₃ between the content C ₂ of the _second structural unit and the content C ₃ of the third structural unit is desirably greater than 0 and 15 or less. From the viewpoint of optical characteristics (low birefringence, low photoelastic coefficient) described later, the molar ratio C ₂ / C ₃ is more preferably 10 or less. When the molar ratio C ₂ / C ₃ is in this range, the acrylic thermoplastic resin of the present embodiment exhibits much better optical characteristics.

  In the acrylic thermoplastic resin, the total content of the first structural unit, the second structural unit, and the third structural unit may be 80% by mass or more based on the total amount of the acrylic thermoplastic resin. . As a result, the acrylic thermoplastic resin exhibits better optical characteristics.

(Fourth structural unit)
The acrylic thermoplastic resin may further contain a structural unit other than the above. For example, the acrylic thermoplastic resin further has a structural unit derived from another monomer copolymerizable with the first, second, and third monomers as long as the object of the invention is not impaired. You may do it. Hereinafter, a structural unit other than the first, second, and third structural units in the acrylic resin is referred to as a fourth structural unit.

  Other monomers that can be copolymerized include aromatic vinyl; unsaturated nitrile; cyclohexyl group, benzyl group, or acrylic acid ester having an alkyl group having 1 to 18 carbon atoms; olefin; diene; vinyl ether; vinyl ester; Examples thereof include vinyl chloride; allyl ester or methallyl ester of saturated fatty acid monocarboxylic acid such as allyl propionate; polyvalent (meth) acrylate; polyvalent arylate; glycidyl compound; unsaturated carboxylic acid. The other monomer may be one or a combination of two or more selected from these groups.

  Examples of the aromatic vinyl include styrene, α-methylstyrene, divinylbenzene, and the like. Examples of the unsaturated nitrile include acrylonitrile, methacrylonitrile, ethacrylonitrile, phenylacrylonitrile and the like. Examples of the acrylic ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, and acrylic acid. Examples include octyl, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, cyclohexyl acrylate, and benzyl acrylate.

  Examples of the olefin include ethylene, propylene, isobutylene, diisobutylene and the like. Examples of the diene include butadiene and isoprene. Examples of the vinyl ether include methyl vinyl ether and butyl vinyl ether. Examples of the vinyl ester include vinyl acetate and vinyl propionate. Examples of the vinyl fluoride include vinylidene fluoride.

  Examples of the polyvalent (meth) acrylate include ethylene glycol (meth) acrylate, diethylene glycol (meth) acrylate, trimethylolpropane tri (meth) acrylate, hexanediol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, and dipenta Erythritol hexa (meth) acrylate, di (meth) acrylate of bisphenol A ethylene oxide or propylene oxide adduct, di (meth) acrylate of halogenated bisphenol A ethylene oxide or propylene oxide adduct, isocyanurate ethylene oxide or propylene Examples thereof include di- or tri (meth) acrylates of oxide adducts.

  Examples of the polyvalent arylate monomer include diallyl phthalate and triallyl isocyanurate. Examples of the glycidyl compound monomer include glycidyl (meth) acrylate and allyl glycidyl ether. Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and half-esterified products or anhydrides thereof.

  The content of the fourth structural unit in the acrylic thermoplastic resin is preferably 0.1 to 20% by mass, and preferably 0.1 to 15% by mass, based on the total amount of the acrylic thermoplastic resin. Is more preferable, and it is still more preferable that it is 0.1-10 mass%. When the content is in the above range, the hygroscopicity of the acrylic thermoplastic resin is further improved. From the viewpoint of weather resistance, the content is preferably less than 10% by mass, and more preferably less than 7% by mass.

  The acrylic thermoplastic resin may have only one kind of the fourth structural unit, or may have two or more kinds.

  An example of the fourth structural unit is a structural unit represented by the following formula (4).

In the formula, R ⁸ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R ⁹ represents a halogen atom, a hydroxyl group, a nitro group, an alkyl group having 1 to 12 carbon atoms or an alkoxy group having 1 to 12 carbon atoms. A represents an integer of 1 to 3.

Examples of the alkyl group having 1 to 12 carbon atoms in R ^8, preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms in R ⁹ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, 1- A decyl group, 1-dodecyl group, etc. are mentioned, Among these, a methyl group is suitable.

Examples of the halogen atom for R ⁹ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The alkyl group having 1 to 12 carbon atoms in ^{R 9,} preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms in R ⁹ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, 1- Decyl group, 1-dodecyl group and the like. Among these, in terms of further improving the transparency and weather resistance of the acrylic thermoplastic resin, methyl group, ethyl group, n-propyl group, isopropyl group, n- A butyl group, an isobutyl group, a t-butyl group, and a 2-ethylhexyl group are preferable, and a methyl group is more preferable.

Further, the alkoxy group having 1 to 12 carbon atoms in ^{R 9,} preferably an alkoxy group having 1 to 10 carbon atoms, more preferably an alkoxy group having 1 to 8 carbon atoms. Moreover, as a C1-C12 alkoxy group as a substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, isobutyloxy group, t-butyloxy group, 2-ethylhexyl Examples thereof include an oxy group, a 1-decyloxy group, and a 1-dodecyloxy group, and among these, a methoxy group is preferable.

  The structural unit represented by the formula (4) can be formed from, for example, a monomer represented by the following formula (4-a).

式中、Ｒ^８、Ｒ^９及びａはそれぞれ式（４）におけるＲ^８、Ｒ^９及びａと同義である。

^Wherein, R 8, ^{R 9} and a have the same meanings as ^R 8, ^{R 9} and a in each formula (4).

  Examples of the fourth monomer include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, and 2-methyl-4-chlorostyrene. 2,4,6-trimethylstyrene, α-methylstyrene, cis-β-methylstyrene, trans-β-methylstyrene, 4-methyl-α-methylstyrene, 4-fluoro-α-methylstyrene, 4-chloro -Α-methylstyrene, 4-bromo-α-methylstyrene, 4-t-butylstyrene, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2,4-difluorostyrene, 2-chlorostyrene, 3 -Chlorostyrene, 4-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene, 2-bromostyrene Down, 3-bromostyrene, 4-bromostyrene, 2,4-dibromostyrene, alpha-bromostyrene, beta-bromostyrene, 2-hydroxystyrene, 4-hydroxystyrene, and the like. These monomers may be used alone or in combination of two or more. From the point that it is excellent in copolymerizability with the first monomer, the second monomer and the third monomer constituting the acrylic thermoplastic resin, and the optical properties can be adjusted with a small amount of use. Styrene and α-methylstyrene are particularly preferred. These fourth monomers may be used alone or in combination of two or more.

  The acrylic thermoplastic resin according to the present embodiment may be composed of one kind of copolymer, or one or more kinds of the first structural unit, the second structural unit, and the third structural unit. It may be a blend of two or more copolymers having structural units. For example, the acrylic thermoplastic resin may be a resin composed of one kind of copolymer having a first structural unit, a second structural unit, and a third structural unit. Alternatively, the acrylic thermoplastic resin may be a blend composed of two or more types of copolymers having a first structural unit, a second structural unit, and / or a third structural unit. Alternatively, it may be a blend composed of a polymer having the first structural unit, a polymer having the second structural unit, and a polymer having the third structural unit. From the viewpoint of transparency and uniformity, the acrylic thermoplastic resin is a copolymer having the first structural unit, the second structural unit, and the third structural unit, or the first structural unit, It is preferably a blend composed of two or more kinds of copolymers having the second structural unit and / or the third structural unit. The first structural unit, the second structural unit, and the first structural unit A copolymer having three structural units is particularly preferred.

  The content of halogen atoms in the acrylic thermoplastic resin is preferably less than 0.47% by mass and more preferably 0.45% by mass or less based on the total amount of the acrylic thermoplastic resin. Because acrylic thermoplastic resin contains less than 0.47% by mass of halogen atoms, it is difficult to generate halogen gas even when acrylic thermoplastic resin is handled at high temperatures during melt molding, etc. Corrosion of equipment to be used and work environment deterioration are prevented. In addition, when the acrylic thermoplastic resin (or a molded product thereof) is discarded, there is an advantage that it is difficult to generate a halogen-based gas having a relatively large environmental load.

  It is preferable that the weight average molecular weight (Mw) of polymethylmethacrylate conversion by the GPC measuring method of an acrylic thermoplastic resin is 3000-1 million. If Mw is 3000 or more, an optically isotropic polarizing film protective film having a required strength can be obtained by molding. Moreover, if Mw is 1000000 or less, necessary and sufficient heat fluidity can be obtained at the time of various melt molding. Mw is more preferably 30,000 to 800,000, still more preferably 60000 to 600,000. Particularly preferably, it is 100,000 to 400,000.

  It is preferable that the molecular weight distribution (Mw / Mn) in terms of polymethyl methacrylate by GPC measurement method of the acrylic thermoplastic resin is 1-10. The acrylic thermoplastic resin can be polymerized by a living radical polymerization method, and the molecular weight distribution can be adjusted as necessary. From the viewpoint of adjusting the resin viscosity suitable for molding processing, the molecular weight distribution (Mw / Mn) is more preferably 1.1 to 7.0, further preferably 1.2 to 5.0, It can also be set to 1.5 to 4.0.

  The glass transition temperature (Tg) of the acrylic thermoplastic resin is preferably 120 ° C. or higher. When Tg is 120 ° C. or higher, the film has necessary and sufficient heat resistance as a recent liquid crystal display film molded body. Tg is preferably 130 ° C. or higher, more preferably 135 ° C. or higher. On the other hand, the upper limit of Tg is preferably 180 ° C. or lower.

(Optical characteristics of acrylic thermoplastic resin)
(I) Absolute value of photoelastic coefficient C The absolute value of the photoelastic coefficient C of the acrylic thermoplastic resin is preferably 3.0 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 2.0 ×. It is 10 <^-12> Pa < ^{-1 >} or less, More preferably, it is 1.0 * 10 <^-12> Pa <^-1> or less.

Here, the photoelastic coefficient is described in various documents (see, for example, Chemical Review, No. 39, 1998 (published by the Academic Publishing Center)), and is defined by the following formulas (ia) and (ib). It is what is done. As the value of photoelastic coefficient C _R is close to zero, it can be seen that change in birefringence due to an external force is small.

C _R = | Δn | / σ _R (i-1)
| Δn | = nx−ny (i−2)
Wherein, C _R photoelastic coefficient, sigma _R is tensile stress, | [Delta] n | is the absolute value of the birefringence, nx is the refractive index of stretching direction, ny is the refractive index of stretching direction perpendicular to the direction in the plane, the Each is shown.

  The photoelastic coefficient C of the acrylic thermoplastic resin is sufficiently small as compared with existing resins (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.). Therefore, since it does not cause birefringence due to external force (photoelasticity), it is difficult to undergo birefringence change. In addition, since birefringence caused by residual stress at the time of molding (photoelasticity) hardly occurs, the birefringence distribution in the molded body is also small.

(Ii) In-plane phase difference Re
The acrylic thermoplastic resin preferably has an absolute value of retardation Re in the in-plane direction of 8 nm or less when formed into a film. Here, the phase difference Re is a value obtained by converting a value measured as a film into a thickness of 100 μm.

  The absolute value of the phase difference Re is more preferably 6 nm or less, and further preferably 4 nm or less.

  In general, the absolute value of the phase difference Re is an index representing the magnitude of birefringence. The birefringence of the acrylic thermoplastic resin is sufficiently small compared to the birefringence when the existing resin (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.) is used. Suitable for applications requiring zero birefringence.

  On the other hand, when the absolute value of the in-plane phase difference Re exceeds 8 nm, it means that the refractive index anisotropy is high, and it cannot be used for applications requiring low birefringence or zero birefringence as an optical material. There is. Moreover, in order to improve the mechanical strength of an optical material (for example, a film, a sheet, etc.), it may be stretched. If the absolute value of the retardation in the in-plane direction after the stretching process exceeds 8 nm, No low birefringence or zero birefringence material is obtained as an optical material.

(Iii) Thickness direction retardation Rth
The acrylic thermoplastic resin preferably has an absolute value of the thickness direction retardation Rth of 8 nm or less when formed into a film. Here, the retardation Rth is a value obtained by converting a value measured as a film into a thickness of 100 μm.

  The absolute value of the phase difference Rth is more preferably 6 nm or less, and further preferably 4 nm or less.

  The retardation Rth in the thickness direction is an index that correlates with the viewing angle characteristics of a display device incorporating the optical film when an optical material, particularly an optical film is used. More specifically, the smaller the absolute value of the thickness direction retardation Rth, the better the viewing angle characteristics, and the smaller the change in the color tone of the display color depending on the viewing angle and the lower the contrast.

  The acrylic thermoplastic resin is an absolute value of the retardation Rth in the thickness direction when used as an optical film, compared to the case where an existing resin (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.) is used. Is very small.

(Iv) Total light transmittance The acrylic thermoplastic resin preferably has a total light transmittance of 85% or more, more preferably 88% or more, and more preferably 90% or more when film-formed. Further preferred. Here, the total light transmittance is a value obtained by converting to a thickness of 100 μm. When the total light transmittance is less than 85%, the transparency is lowered, and it may not be used for applications requiring high transparency.

  As described above, the acrylic thermoplastic resin has a sufficiently small photoelastic coefficient C (approximately zero), and an in-plane retardation Re and thickness direction as an optical film regardless of the presence or absence of stretching. The absolute value of the phase difference Rth is all small (approximately zero), and optically complete isotropic property that cannot be achieved by a conventionally known resin can be realized. Furthermore, the acrylic thermoplastic resin can simultaneously achieve high heat resistance.

[Method for producing acrylic thermoplastic resin]
The acrylic thermoplastic resin of this embodiment can be obtained by polymerizing a monomer group including a first monomer, a second monomer, and a third monomer. As a technique for obtaining an acrylic thermoplastic resin, for example, commonly used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, living radical polymerization, anionic polymerization, etc. can be used. Usually, radical polymerization without catalyst deashing is selected.

  In order to use an acrylic thermoplastic resin as an optical material, it is preferable to avoid the introduction of minute foreign matters and impurities as much as possible. From this viewpoint, radical cast polymerization or radical solution polymerization without using a suspending agent or an emulsifier should be used. desirable.

  Moreover, as a polymerization form, any of a batch polymerization method and a continuous polymerization method can be used, for example. The batch polymerization method is desirable from the viewpoint of simple polymerization operation, and the continuous polymerization method is desirably used from the viewpoint of obtaining a polymer having a more uniform composition.

  The temperature and polymerization time at the time of the polymerization reaction can be appropriately adjusted according to the type and ratio of the monomer used. For example, the polymerization temperature is generally 0 to 160 ° C., and the polymerization time is 0.5 to 24 hours. The polymerization temperature is preferably 80 to 160 ° C. and the polymerization time is 1 to 8 hours.

  At the time of radical polymerization reaction, a polymerization initiator is added as necessary. As the polymerization initiator, a general radical polymerization initiator can be used depending on the polymerization temperature. For example, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, Organic peroxides such as benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate; 2,2′-azobis (isobutyronitrile), 1,1′-azobis Examples include azo compounds such as (cyclohexanecarbonitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2′-azobisisobutyrate. These polymerization initiators may be used alone or in combination of two or more.

  The amount of the polymerization initiator used may be appropriately set according to the combination of the monomers and reaction conditions, and is not particularly limited, but is preferably used in the range of 0.005 to 5% by mass.

  As the molecular weight regulator used as necessary in the polymerization reaction, any one used in general radical polymerization may be used. Can be mentioned. These molecular weight regulators are added so that the degree of polymerization is controlled within a desired range.

  Examples of the polymerization solvent for radical solution polymerization include aromatic hydrocarbon solvents such as toluene, xylene, and ethylbenzene, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, and ether solvents such as tetrahydrofuran. These solvents may be used alone or in combination of two or more. A solvent having a boiling point of 50 to 200 ° C. is preferable in view of polymerization temperature, ease of handling, and ease of separation and removal of the resin and the solvent.

  In radical solution polymerization, the polymerization solution concentration (resin content concentration) is preferably 10 to 95% by mass or less. If it is 10 mass% or more, adjustment of molecular weight and molecular weight distribution is easy. If it is 95 mass% or less, a high molecular weight polymer can be obtained. Further, from the viewpoint of heat removal during polymerization, in order to make the viscosity of the reaction solution appropriate, it is more preferably 75% by mass or less, and further preferably 60% by mass or less.

  Further, from the viewpoint of appropriately maintaining the viscosity of the polymerization reaction solution, a polymerization solvent can be appropriately added during the polymerization. By appropriately maintaining the viscosity of the reaction solution, it is easy to control heat removal and suppress side reactions in the reaction solution. In particular, in the latter half of the polymerization reaction in which the viscosity increases, it is more preferable to add a polymerization solvent as appropriate and control it to be 50% by mass or less.

  The acrylic thermoplastic resin obtained by solution polymerization needs to be separated from the solvent and the remaining monomer, except when the solution is used as it is to form an optically isotropic polarizing film protective film by a solution casting method. Separation methods include devolatilization treatment that volatilizes the solvent and residual monomer by heating or depressurizing the solution, extraction and removal of the solvent and residual monomer in a poor solvent of the resin, etc. A known method can be used.

  In this embodiment, since the acrylic thermoplastic resin is used for a polarizing plate that is a precise optical application as an optical material, the smaller the number of foreign matters mixed in, the better. As a method of reducing the number of foreign substances, a method of filtering a polymerization solution or a melt with, for example, a leaf disk polymer filter having a filtration accuracy of 1.5 to 15 μm in a polymerization reaction step, a devolatilization treatment step, and a molding step Etc.

  In the present embodiment, a resin other than the thermal stabilizer, the ultraviolet absorber, and the optical isotropic resin is added to the acrylic thermoplastic resin within a range that does not affect the final optically isotropic polarizing film protective film. Can be added. The adding method is not particularly limited as long as it is a known method. For example, it can be added by a method of adding at the time of polymerization, a method of adding to the solution after polymerization, a method of adding the resin by melt kneading or the like, or a method of combining these.

[Optical isotropic polarizing film protective film]
The optically isotropic polarizing film protective film in the present embodiment is a film formed by molding an acrylic thermoplastic resin. A polarizing film having a polarizing function is bonded to both surfaces or one surface of the polarizing film with an adhesive or the like, and is used to protect the polarizing film by imparting form retention and scratch resistance to the polarizing film.

  Here, the polarizing film is a film having a function of dividing incident light into two polarization components orthogonal to each other, allowing only one of them to pass, and absorbing or reflecting the other component. If it is, it will not specifically limit, Any polarizing film can be used. Moreover, the manufacturing method is not specifically limited, A conventionally well-known method is applicable. For example, after immersing a polyvinyl alcohol film while maintaining a uniaxially stretched state in a solution containing higher-order iodine ions produced by overdissolving iodine in a potassium iodide solution, and stretching after adsorbing iodine, 1 A method for producing a polarizing film by immersing in a boric acid aqueous solution of 5% by mass to 5% by mass at a bath temperature of 20 to 70 ° C., or a bath temperature of a polyvinyl alcohol film in an aqueous boric acid solution of 1 to 5% by mass After dipping at a temperature of 20 to 40 ° C. and stretching about 3 to 7 times in the uniaxial direction, it is immersed in a 0.05 to 5% by mass dichroic dye aqueous solution at a temperature of 20 to 40 ° C. to adsorb the dye. Then, the method etc. which manufacture a polarizing film by drying at 80-100 degreeC and heat-setting are mentioned.

  Although the thickness of a polarizing film is not specifically limited, It is 10-50 micrometers or less. If it is 10 μm or more, it can be produced without breaking during stretching or immersion. Moreover, if it is 50 micrometers or less, final drying is easy and it can obtain a polarizing film with few dispersion | variation. More preferably, it is 15-45 micrometers or less.

The optically isotropic polarizing film protective film of this embodiment has an acrylic thermoplasticity whose photoelastic coefficient (C) is −3.0 × 10 ⁻¹² Pa ⁻¹ to + 3.0 × 10 ⁻¹² Pa ⁻¹ . It is desirable to consist of resin. The photoelastic coefficient (C) in this embodiment is a phase difference observed when polarized light is incident on a transparent material in which the magnitude and direction of the strain S corresponding to the external force σ changes when the external force σ is applied. It is a physical coefficient defined by the relational expression of R and external force δ, R = (C) × σ, and is a value specific to each transparent material. The absolute value of the photoelastic coefficient C is more preferably 2.0 × 10 ⁻¹² Pa ⁻¹ or less, and further preferably 1.0 × 10 ⁻¹² Pa ⁻¹ or less. Within this range, there is little occurrence of photoelastic birefringence due to a new external force, and no frame light leakage, which is a problem in the large screen FPD, occurs. In addition, in a polarizing plate integrated inner touch panel application, image color misregistration or the like does not occur when an external force such as a pen touch is applied.

Here, the photoelastic coefficient is described in various documents (see, for example, Chemical Review, No. 39, 1998 (published by the Academic Publishing Center)), and is defined by the following formulas (ia) and (ib). It is what is done. As the value of photoelastic coefficient C _R is close to zero, it can be seen that change in birefringence due to an external force is small.
C _R = | Δn | / σ _R (i-1)
| Δn | = nx−ny (i−2)
Wherein, C _R photoelastic coefficient, sigma _R is tensile stress, | [Delta] n | is the absolute value of the birefringence, nx is the refractive index of stretching direction, ny is the refractive index of stretching direction perpendicular to the direction in the plane, the Each is shown.

  The photoelastic coefficient C of the acrylic thermoplastic resin of this embodiment is sufficiently small as compared with existing resins (for example, PMMA, PC, triacetyl cellulose resin, cyclic olefin resin, etc.). Therefore, since it does not cause birefringence due to external force (photoelasticity), it is difficult to undergo birefringence change. In addition, since birefringence caused by residual stress at the time of molding (photoelasticity) hardly occurs, the birefringence distribution in the molded body is also small.

As for the optically isotropic polarizing film protective film of this embodiment, it is desirable that the moisture permeability of the acrylic thermoplastic resin at a thickness of 100 μm is 3 to 100 g / (m ² · 24 hr). If it is 3 g / (m ² · 24 hr) or more, the polarizing film adhesive can be sufficiently dried. Further, when the moisture permeability is 100 g / (m ² · 24 hr) or less, it is possible to prevent the polarization degree of the polarizing film from being lowered due to moisture absorption from the outside. More preferable moisture permeability is 5 to 90 g / (m ² · 24 hr). More preferably, it is 10-80 g / (m < ² > * 24 hr), Most preferably, it is 20-70 g / (m < ² > * 24 hr).

  In the optically isotropic polarizing film protective film of the present embodiment, it is desirable that the difference between the refractive index of the acrylic thermoplastic resin and the refractive index of the polarizing film to be bonded is within ± 0.04. If it is within ± 0.04, unnecessary reflection in each of the polarizing film and the polarizing film adhesive layer, the polarizing film adhesive layer and the polarizing film protective film can be prevented, and the total light transmittance is increased. Can be held. Preferably it is within ± 0.035, more preferably within ± 0.03.

The optically isotropic polarizing film protective film of the present embodiment has a stretching ratio (S) when an acrylic thermoplastic resin is formed into a film and a 100 μm-thickness converted birefringence (Δn (S)) at the stretching ratio. It is desirable that the slope α in the least squares approximate linear relationship (a) is made of an acrylic thermoplastic resin having a range of −0.30 × 10 ⁻⁵ ≦ α ≦ + 0.30 × 10 ⁻⁵ . When the optical isotropic polarizing film protective film is within this range, the optical isotropic polarizing film protective film after stretching is subjected to a stretching process for the purpose of increasing the strength of the optical isotropic polarizing film protective film. It is possible to keep the birefringence expressed by
Δn (S) = α × S + β (a)
−0.30 × 10 ⁻⁵ ≦ α ≦ 0.30 × 10 ⁻⁵ (b)
[In the formula, β is a constant and indicates birefringence at the time of non-stretching. ]

  As for the optically isotropic polarizing film protective film of this embodiment, it is desirable that the glass transition temperature of an acrylic thermoplastic resin is 130 degreeC or more. If it is 130 degreeC or more, it can endure use, without the thermal deformation of a polarizing film protective film also in the vicinity of the LED light source currently used frequently for the backlight. In addition, thermal deformation does not occur even when heat such as sunlight incident from the outside is applied during outdoor use. A preferable glass transition temperature is 135 ° C. or higher, and a more preferable glass transition temperature is 140 ° C. or higher. On the other hand, the upper limit of Tg is preferably 180 ° C.

  As for the optically isotropic polarizing film protective film of this embodiment, it is desirable that the surface pencil hardness is 3H or more. If the pencil height is 3H or more, it is possible to prevent the polarizing film from being damaged as a polarizing film protective film. The surface pencil hardness is preferably 4H or more, more preferably 5H or more.

  In the in-plane direction retardation (Re) and thickness direction retardation (Rth) in the optically isotropic polarizing film protective film of the present embodiment, the in-plane and thickness direction retardation of the polarizing film protective film The phase difference is caused by either or both of distortion caused by residual stress and distortion caused by external stress applied after molding. In the optically isotropic polarizing film protective film of this embodiment, it is desirable that the absolute value of the in-plane retardation (Re) in terms of 100 μm thickness when formed into a film is 8 nm or less. It is desirable that the optically isotropic polarizing film protective film of the present embodiment has an absolute value of a thickness direction retardation (Rth) of 8 nm or less when converted into a thickness of 100 μm when formed into a film.

  If the absolute value of the retardation in the in-plane direction is 8 nm or less and the absolute value of the retardation (Rth) in the thickness direction is 8 nm or less, an image with good contrast can be obtained without disturbing the polarization. More preferably, both Re and Rth are 6 nm or less, and more preferably 4 nm or less.

  Although the thickness of the optically isotropic polarizing film protective film in this embodiment is not specifically limited, Preferably it is 10-300 micrometers, More preferably, it is 15-80 micrometers, More preferably, it is 20-40 micrometers. If it is 10 μm or more, the scratching strength of the polarizing film can be sufficiently expressed, and if it is 300 μm or less, the necessary and sufficient total light transmittance can be maintained. In addition, the acrylic thermoplastic resin according to the present invention has extremely high optical isotropy, and has a characteristic that birefringence does not increase even when stretched to increase strength after being formed into a film or sheet. doing. Therefore, it is very suitable as a substrate for a coating type polarizing plate as disclosed in JP-A No. 03-54506, instead of the above-mentioned iodine-doped polyvinyl alcohol type polarizing plate. In general, a coating-type polarizing plate is a glass or transparent resin plate that has been rubbed in advance, and then coated with a dichroic dye to orient the dichroic dye in the rubbed direction to impart polarizing performance. In addition, by arbitrarily changing the rubbing direction, it is possible to produce a polarizing plate that is continuously patterned and has little polarization unevenness. On the other hand, when the acrylic thermoplastic resin according to the present embodiment is used as a transparent resin plate, after the dichroic dye is coated, it is possible to perform orientation imparting treatment of the dichroic dye by stretching as post-processing. Thus, a coating type polarizing plate can be produced more easily.

(Molding)
Molding in the present embodiment is a method of processing an acrylic thermoplastic resin into an optically isotropic polarizing film protective film, a melt hot press, a combination of a melt hot press and a hot melt stretching method, a melt extrusion method, and Combination of melt extrusion method and hot melt stretching method, injection molding method and combination of injection molding method and hot melt stretching method, solvent cast method, combination of solvent cast method and hot melt stretching method, strain relief processing after thermal annealing molding, etc. This is a known resin molding method. Preferable methods include a melt extrusion molding method from the viewpoint of productivity and press molding from the viewpoint of optical performance.

  The melt extrusion molding method in the present embodiment is a method in which an acrylic thermoplastic resin is supplied to an extruder using a supply device, melted by rotation of a screw under heating, sent out from the extruder, and passed through a heated channel. , A method for forming an extruded optically isotropic polarizing film protective film from a die such as a T-base.

  In the melt extrusion molding method, the die temperature at the time of extruding the acrylic thermoplastic resin is desirably set to be low within a range in which the melt does not solidify in order to suppress thermal decomposition of the composition. It is preferable to set as low as possible within the range. In addition, the acrylic thermoplastic resin extruded in a molten state from the die is cast on various cooling supports such as a mirror-like cooling roll or a mirror-like cooling belt installed directly under the die or on the side of the die. Cooled and solidified, and then wound with a take-up roll. At this time, it is preferable to transfer the resin melt-extruded from the T die before solidifying by natural heat dissipation, and the distance between the die and the support such as a cooling roll or a cooling belt should be about 1 mm or more and 300 mm or less. It is common. If it is this range, it will become easy to reduce extrusion distortion and to reduce the variation of the distortion which causes the optical and mechanical nonuniformity between products. Further, the configuration and temperature of the support such as the cooling roll and the cooling belt vary depending on the thickness.

  When the acrylic thermoplastic resin of the present embodiment is manufactured as a primary molded product in a plate shape with a thickness of 300 μm or more, it is sandwiched between two pairs of cooling rolls or cooling belts having an interval according to the required thickness of the primary molded product. Thus, it is preferable to simultaneously transfer and solidify the surfaces from both sides of the extruded primary molded product. By doing so, it becomes easy to obtain a plate-shaped primary molded product having a flat surface and a smooth surface, and a primary molded product having a high thickness accuracy can be easily manufactured. It is also possible if it is necessary to provide a so-called bank for collecting a molten resin liquid immediately before being sandwiched between a pair of cooling rolls or a cooling belt. In the production of a plate-shaped primary molded product within this thickness range, the temperature of the cooling roll and the cooling belt is preferably 120 to 160 ° C.

  On the other hand, when an acrylic thermoplastic resin is directly molded and manufactured as an optically isotropic polarizing film protective film having a thickness of 50 μm or less, it is preferable to transfer and cool and solidify on a single cooling roll or cooling belt. . With this configuration, it is easy to obtain an optically isotropic film with little thickness unevenness and a flat and smooth surface. The temperature of the cooling roll and the cooling belt at this time is preferably 30 to 120 ° C.

  The melt biaxial stretch molding means thinning the plate-shaped primary product having a thickness greater than 300 μm and an optically isotropic polarizing film protective film (hereinafter referred to as the original fabric) having a thickness of 300 μm or less, This is a method for obtaining an optically isotropic polarizing film protective film. FIG. 1 is a schematic view of the melt stretching apparatus 100 as viewed from the side and from above. First, the raw material unrolled from the raw material roll 105 is heated in the range of glass transition temperature +5 to + 25 ° C. in the longitudinal stretching chamber 108 in which the preheating roll 106 and the longitudinal stretching roll 107 are arranged, and the machine flow direction ( Thereafter, the film is longitudinally stretched in a range of 10 to 350% due to a difference in peripheral speed between a plurality of rolls arranged in the MD direction. Next, the raw material stretched in the MD direction passes through the tension control roll 109 and the take-up roll 110, chucks the end of the film with the clip 111 attached to the chain, and glass transition temperature + 5 ° C. to + 25 ° C. in the same manner as the longitudinal stretching. After being introduced into the stretching chamber 112 in the transverse direction kept underneath, the paper is stretched in the range of 10% to 350% in the direction perpendicular to the machine flow direction (hereinafter referred to as TD direction) by widening the clip interval. Then, the raw fabric stretched in the TD direction passes through the tension control roll 113, passes through the slitter 114, and is taken up by the product take-up roll 116 via the end take-up roll 115. In general, after stretching, it is more preferable to reduce the clip interval by 5% to 10% in the vicinity of the outlet in the transverse stretching chamber 112 maintained from the glass transition temperature −15 ° C. to the glass transition temperature + 5 ° C.

  The stretching of the sheet or film can be carried out continuously by extrusion molding and cast molding. For example, an unstretched film or sheet is longitudinally uniaxially stretched in the mechanical flow direction, transversely uniaxially stretched in a direction perpendicular to the mechanical flow direction, or a sequential biaxial stretching method of roll stretching and tenter stretching, A biaxially stretched film can be obtained by stretching by an axial stretching method, a biaxial stretching method by tubular stretching, or the like.

  The strength of the molded body can be improved by stretching. The draw ratio is 0.1% or more and 350% or less in at least one direction. Preferably, they are 0.2% or more and 320% or less, More preferably, they are 0.3% or more and 300% or less. By stretching in this range, a molded article having excellent optical properties such as strength, transparency and birefringence can be obtained.

(Post-processing of optically isotropic polarizing film protective film)
The optically isotropic polarizing film protective film of the present embodiment is hard-coated, anti-reflective, transparent conductive, antistatic, electromagnetic shielding, gas barrier, if necessary, before being attached to the polarizing plate. Surface treatment such as treatment can be performed and used for final applications. When such surface treatment is performed, an adhesive can be used together with so-called anchor coat treatment such as treatment by corona discharge or plasma discharge, or surface treatment by application of a primer having an epoxy group, isocyanate group or the like. And adhesion to various inorganic layers can be enhanced.

  Examples of the treatment for improving the adhesion with the polarizing film adhesive include corona treatment using a high-frequency transmitter and plasma treatment by glow discharge in the atmosphere. In any treatment, wettability deteriorates in minutes, so it is necessary to apply a polarizing film adhesive immediately after the treatment.

  Examples of the hard coat treatment include organic hard coat materials such as organic silicone, melamine, epoxy, acrylic, and urethane acrylate, and methods for applying a hard coat layer material such as an inorganic hard coat material such as silicon dioxide. It is done. Of these, urethane acrylate and polyfunctional acrylate hard coat materials are preferably used from the viewpoint of good adhesion and excellent productivity. Moreover, you may contain a well-known inorganic filler as needed. Furthermore, various additives such as an antioxidant, an ultraviolet absorber, a light stabilizer, an antistatic agent, a leveling agent, and an antifoaming agent can be blended. Inorganic fillers include titanium oxide, zirconium oxide, zinc oxide, tin oxide, cerium oxide, antimony pentoxide, tin-doped indium oxide (ITO), antimony-doped tin oxide (IZO), and aluminum-doped zinc oxide ( AZO) and fluorine-doped tin oxide (FTO). Antimony pentoxide, ITO, IZO, ATO, and FTO are particularly preferred because of their high transparency. The primary particle diameter of these fillers is usually 1 to 100 nm, and such a nano-size can exhibit sufficient transparency with respect to visible light, and preferably 1 to 30 nm. The thickness of the hard coat treatment layer is 0.005 to 1 μm. If it is 0.005 μm or more, scratch resistance is exhibited, and if it is 1 μm or less, sufficient transparency is exhibited, more preferably 0.01 μm to 0.5 μm.

Examples of the antireflection treatment include a low refractive index layer obtained by uniformly applying and drying a paint and a nano-shaped structure layer represented by a moth-eye structure. As a method of evenly applying the paint, polyester resin, acrylic resin, urethane resin, vinyl chloride resin, epoxy resin, melamine resin, fluororesin, silicone resin, butyral resin, phenol resin, acetic acid containing nano-sized hollow fine particles Examples thereof include a low refractive index layer made of a paint comprising a hydrolyzable organosilicon compound such as vinyl resin or alkoxysilane and a hydrolyzate thereof. Among these, a low refractive index layer composed of an acrylic resin, an epoxy resin, a urethane resin, a silicone resin, a hydrolyzable organic silicon compound, and a paint made of the hydrolyzate thereof is preferable because of the dispersibility of the hollow fine particles and the strength of the porous body. Particularly preferred is a low refractive index layer comprising a fluorine-containing hydrolyzable organosilicon compound. Specific examples include 3,3,3-trifluoropropyltrimethoxysilane, methyl-3,3,3-trifluoropropyl. Examples include dimethoxysilane, heptadecafluorodecylmethyldimethoxysilane, heptadecafluorodecyltrichlorosilane, heptadecafluorodecyltrimethoxysilane, and tridecafluorooctyltrimethoxysilane. Further, the hollow fine particles to be used are not particularly limited, but inorganic hollow fine particles are preferable, and silica-based hollow fine particles are particularly preferable. Examples of the inorganic compound constituting the inorganic hollow fine particles include SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , TiO ₂ , ZrO ₂ , SnO ₂ , Ce ₂ O ₃ , P ₂ O ₅ , Sb ₂ O ₃ , MoO _3. , can be exemplified _{ZnO 2, WO 3, TiO 2} -Al 2 O 3, TiO 2 -ZrO 2, In 2 O 3 -SnO 2, Sb 2 O 3 -SnO 2 or the like. Further, the outer shell of the hollow fine particles may be porous having pores, or may be one in which the pores are closed and the cavity is sealed against the outside of the outer shell. The outer shell preferably has a multilayer structure including an inner layer and an outer layer.

  The refractive index of these antireflection layers is 1.25 to 1.40. If it is 1.25 or more, sufficient layer strength will be obtained and it is preferable. Moreover, if it is 1.40 or less, there is a sufficient difference in refractive index from the optically isotropic polarizing film protective film, and the antireflection function is exhibited. The layer thickness is 0.005 to 1 μm. If it is 0.005 μm or more, the strength is sufficient, and if it is 1 μm or less, sufficient transparency is exhibited. More preferably, it is 0.10-0.40 micrometer, More preferably, it is 0.15-0.30 micrometer.

  The nano-shaped structure represented by the moth-eye structure is not particularly limited in refractive index as a material, has a periodic structure of 0.15 to 0.30 μm, and has an uneven structure with a length of 0.1 to 0.3 μm. Any structure can be used as long as it is a known one. As the nano-shaped structure layer, 0.30 to 0.80 μm is optically preferable. Further, these two antireflection treatment layers can be formed on the hard coat treatment layer.

  As the transparent conductive treatment, any conventionally known techniques such as vacuum deposition, sputtering, and ion plating can be used. From the viewpoint of film uniformity and adhesion of the thin film to the anchor coat layer, the sputtering method is used. The thin film formation is preferred. Further, the thin film material to be used is not particularly limited, for example, in addition to metal oxides such as indium oxide containing tin oxide and tin oxide containing antimony, gold, silver, platinum, palladium, copper, aluminum, Nickel, chromium, titanium, cobalt, tin, zinc, or alloys thereof are preferably used. Among them, indium oxide (ITO) containing tin oxide is preferable. The thickness of the transparent conductive layer to be formed cannot be generally described because the required conductivity varies depending on the application, but generally 0.01 to 0.1 μm is preferable from the viewpoint of maintaining transparency.

  A transparent conductive layer can also serve as the antistatic layer and electromagnetic wave shielding treatment. As the gas barrier layer, a hard coat layer and / or a transparent conductive layer hard coat layer can also serve as the function.

[Polarizer]
The polarizing plate in the present embodiment is obtained by bonding the optically isotropic polarizing film protective film in the present embodiment to one side or both sides of the polarizing film.

  The polarizing film and the optically isotropic polarizing film protective film may be used for producing the polarizing plate as they are, but in order to increase the adhesion between the polarizing film and the optically isotropic polarizing film protective film, The surface in contact with the adhesive may be subjected to corona discharge treatment or plasma treatment and then used for bonding.

  In bonding the optically isotropic polarizing film protective film to the polarizing film, an adhesive for polarizing film is used. As the polarizing film adhesive, water-based adhesives such as aqueous polyvinyl alcohol solutions, aqueous solutions such as polyvinyl alcohol and polyurethane resins, and solvent-based adhesives such as epoxy-based curing agents and UV-curable adhesives are used. As an adhesive for a polarizing film, a polarizing film and an optically isotropic polarizing film protective film can be bonded, and the optically isotropic polarizing film protective film and the polarizing film of this embodiment can be bonded. If it is, it will not specifically limit.

  The polarizing film adhesive is applied so that the thickness after drying is preferably 0.01 to 50 μm, more preferably 0.01 to 30 μm, and still more preferably 0.01 to 3 μm. Necessary and sufficient adhesive strength can be obtained if the thickness of the polarizing film adhesive after drying is 0.01 μm or more, delamination does not easily occur, and if it is 50 μm or less, necessary and sufficient total light transmittance is obtained.

  The refractive index of the polarizing film adhesive after drying is preferably between the refractive index of the polarizing film and the refractive index of the optically isotropic polarizing film protective film.

  The temperature at the time of application of the adhesive for the polarizing film and the bonding temperature are preferably 15 to 40 ° C. If the temperature is 15 ° C. or higher, the necessary and sufficient viscosity can be secured, and if it is 40 ° C. or lower, the time for bonding is secured. it can. Furthermore, when an ultraviolet curable adhesive is used as the adhesive for the polarizing film, an exposure process is performed after bonding to cure the adhesive. Although the exposure light source in this case is not specifically limited, Preferably it is an ultraviolet-ray and the exposure amount becomes like this. Preferably it is 1-2000 mJ.

The polarizing plate of the present embodiment is a polarizing plate that includes a structure typified below as a part thereof.
[1] Optical isotropic polarizing film protective film / polarizing film [2] Optical isotropic polarizing film protective film / polarizing film / polarizing film protective film [3] Optical isotropic polarizing film protective film / polarizing film / optical Isotropic polarizing film protective film [4] Optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / hard coat layer [5] Optical isotropic polarizing film protective film / polarizing film / optical Isotropic polarizing film protective film / antireflection layer [6] Optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / transparent conductive layer [7] Optical isotropic polarizing film protective film / polarized light Film / optical isotropic polarizing film protective film / antistatic layer [8] Optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / electromagnetic wave shielding layer [9] Optical isotropic polarized light Film protective film / polarizing film / optical isotropy Optical film protective film / gas barrier layer [10] Optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / hard coat layer / antireflection layer [11] Optical isotropic polarizing film protective film / Polarizing film / optical isotropic polarizing film protective film / hard coat layer / transparent conductive layer [12] optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / hard coat layer / transparent conductive Layer [13] Optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / hard coat layer / antistatic layer [14] Optical isotropic polarizing film protective film / polarizing film / optical isotropic Polarizing film protective film / hard coat layer / electromagnetic wave shielding layer [15] Optical isotropic polarizing film protective film / polarizing film / optical isotropic polarizing film protective film / hard coat layer / gas barrier layer [16 Polarizing film / optical isotropic polarizing film protective film / hard coat layer [17] Polarizing film / optical isotropic polarizing film protective film / antireflection layer [18] Polarizing film / optical isotropic polarizing film protective film / transparent conductive Layer [19] Polarizing film / optical isotropic polarizing film protective film / antistatic layer [20] Polarizing film / optical isotropic polarizing film protective film / electromagnetic wave shielding layer [21] Polarizing film / optical isotropic polarizing film Protective film / gas barrier layer [22] Polarizing film / optical isotropic polarizing film protective film / hard coat layer / antireflection layer [23] Polarizing film / optical isotropic polarizing film protective film / hard coat layer / transparent conductive layer [24] Polarizing film / optical isotropic polarizing film protective film / hard coat layer / transparent conductive layer [25] Polarizing film / optical isotropic polarizing film protective film / hard coat layer / antistatic layer [26] Polarizing film / Optical isotropic deviation Film protective film / hard coat layer / electromagnetic shielding treatment layer [27] polarizer / optically isotropic polarizing film-protecting film / hard coat layer / gas barrier layer

(Post-processing of polarizing plate)
The polarizing plate of the present embodiment is a hard coat treatment, an antireflection treatment, a transparent conductive treatment, an antistatic treatment, an electromagnetic wave shielding treatment, and a gas barrier treatment as necessary even after the polarizing film and the polarizing film protective film are bonded together. Etc. can be used for the final application. When such surface treatment is performed, so-called anchor coat treatment such as treatment by corona discharge or plasma discharge or surface treatment by application of a primer agent having an epoxy group, isocyanate group, etc. can be used as necessary. Can increase the sex.

[LCD touch panel]
The liquid crystal display device-integrated touch panel in the present embodiment refers to a liquid crystal display device and an operator's intention by touching a point or region such as a picture or pictogram which is screen information displayed by the operator with a hand or a pen. This is a combination with a touch panel that outputs information signals to the outside.

  The liquid crystal system in this embodiment is a lateral electric field system, which is a so-called IPS (in-plane switching) liquid crystal display device, which sandwiches a liquid crystal cell with a planar light source, a liquid crystal cell having an electrode plate with an electrode structure, and the like. Of the polarizing plates arranged in a pair of two orthogonal states, at least one is the polarizing plate of the present embodiment.

  The liquid crystal system in the present embodiment is an oblique electric field system, which is a so-called FFS (fringe field switching) system, and sandwiches a liquid crystal cell having a planar light source, an electrode plate having an electrode structure, and the liquid crystal cell. Of the polarizing plates arranged in a pair of two orthogonal states, at least one is the polarizing plate of the present embodiment.

  FIG. 2 shows a resistance film type polarizing plate integrated inner touch panel. In order to produce, first, a polarizing film adhesive prepared in advance is applied to the opposite surface of the optically isotropic support plate 12 provided with the transparent conductive film 11 to the transparent conductive film 11, and prepared in advance. The surface of the polarizing plate made of the polarizing film 13 having the polarizing film protective film 14 attached on one side is adhered to the opposite side of the polarizing film protective film 14 side. Next, a commercially available polarizing plate 5 composed of three layers of polarizing plate protective film / polarizer / polarizing plate protective film is prepared, and an IPS liquid crystal display element 6 is stacked thereon. Further, the optical glass 7 having the ITO transparent conductive film 8 applied thereon and a pattern formed as a resistance film type touch panel electrode is overlaid so that the ITO transparent conductive film 8 is on top. A polarizing plate integrated with the above-mentioned optical isotropic support plate with the spacer 9 interposed therebetween is overlaid so that the transparent conductive film 11 side is down, and the four corners are sealed with an epoxy adhesive 15. In this way, the resistance film type polarizing plate integrated inner touch panel 1 is manufactured.

  FIG. 3 shows an electrostatic projection type polarizing plate integrated inner touch panel. For the production, the polarizing film protective film 22 is bonded to the polarizing film 21 separately prepared above, and the optical isotropic support plate 20 is further bonded to the surface of the optical isotropic support plate. After the film adhesive is applied, an electrostatic projection ITO pattern 19 is pasted on the produced optical glass 18. Further, an adhesive for polarizing film is applied to a glass plate, and an IPS liquid crystal display element 17 (a commercially available polarizing plate 16 composed of three layers of polarizing plate protective film / polarizer / polarizing plate protective film is bonded to the opposite surface. ) After being attached on top, when sealed with an epoxy adhesive 23, the electrostatic projection type polarizing plate integrated inner touch panel 2 is produced.

  The optically isotropic polarizing film protective film of the present embodiment has a good polarizing function by being integrated with the polarizing film, has excellent properties such as heat resistance and surface hardness, and is peeled and deformed even in long-term use. , Polarization degree change and the like hardly occur, high reliability, and excellent durability. Moreover, since it is high-strength and excellent in mechanical durability, the liquid crystal display device and / or the liquid crystal display device-integrated touch panel of the present embodiment is also suitably used in applications that require high durability such as in-vehicle use. be able to.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  Hereinafter, the contents of the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited to the following Example.

[Analysis of acrylic thermoplastic resin composition]
Acrylic thermoplastic resin obtained by polymerization was dissolved in CDCl ₃ , and ¹ H-NMR, ¹³ C-NMR (measurement temperature: 40 ° C.) measurement was carried out using a DPX-400 apparatus manufactured by Bruker, Inc. The amounts of (i) the first structural unit, (ii) the second structural unit, (iii) the third structural unit, and (iv) the fourth structural unit were identified, and the composition was confirmed from the ratio. .

[Measurement of glass transition temperature of acrylic thermoplastic resin]
The glass transition temperature (Tg) of the acrylic thermoplastic resin obtained by polymerization is a differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer Japan Co., Ltd.), and α-alumina is used as a reference in a nitrogen gas atmosphere. Based on JIS-K-7121, it calculated by the midpoint method from the DSC curve obtained by heating about 10 mg of samples from normal temperature to 200 degreeC with the temperature increase rate of 10 degree-C / min.

[Weight average molecular weight measurement of acrylic thermoplastic resin]
The weight average molecular weight and the number average molecular weight of the acrylic thermoplastic resin obtained by polymerization were measured using a gel permeation chromatograph (HLC-8220 manufactured by Tosoh Corporation), the solvent was tetrahydrofuran, and the setting temperature was 40 ° C. Was calculated by standard PMMA conversion.

[Optical property evaluation of acrylic thermoplastic resin]
<Preparation of sample for optical evaluation of acrylic thermoplastic resin>
The acrylic thermoplastic resin obtained by polymerization was formed into a film by melt vacuum press molding. A Kapton sheet was placed on the iron plate, and a 150 μm-thick gold frame cut into a 15 cm square was placed thereon, and an acrylic thermoplastic resin was placed thereon. Furthermore, the Kapton sheet was stacked and the iron plate was arrange | positioned. Put it in a vacuum compression molding machine (SFV-30, manufactured by Shindo Metal Industry Co., Ltd.) while sandwiching it between the two metal plates, and start reducing pressure and reach 10 kPa. The temperature rose. Then, after maintaining at 260 ° C. for 5 minutes, compression was performed at a press pressure of 10 MPa for 5 minutes, and then cooling was started. When the temperature reached 50 ° C., the inside of the vacuum dryer was returned to atmospheric pressure, and a sample was taken out. The sample was then peeled once from the Kapton sheet, sandwiched again with a new Kapton sheet, held in a dryer filled with nitrogen and maintained at a temperature 10 ° C. above the glass transition temperature (Tg) for 8 hours.

<Measurement of photoelastic coefficient of acrylic thermoplastic resin>
A birefringence measuring apparatus described in detail in Polymer Engineering and Science 1999, 39, 2349-2357 was used. A film made of an acrylic thermoplastic resin (thickness: about 150 μm, width: 6 mm) that has been cured for 24 hours or more in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60%, and similarly installed in the constant temperature and humidity chamber A film was placed on a tensioning apparatus (manufactured by Imoto Seisakusho Co., Ltd.) so that the distance between chucks was 50 mm. Next, a laser beam path of a birefringence measuring apparatus (RETS-100 manufactured by Otsuka Electronics Co., Ltd.), which will be described later, is set to the center of the film, and a strain rate of 50% / min (between chucks: 50 mm, chuck moving speed: 5 mm / min). The birefringence was measured while applying an extensional stress. From the relationship between the absolute value of birefringence (| Δn |) and the extensional stress (σ _R ), the slope of the straight line was obtained by least square approximation, and the photoelastic coefficient (C _R ) was calculated. For the calculation, data with an extensional stress between 2.5 MPa ≦ σR ≦ 10 MPa was used.
C _R = | Δn | / σ _R
| Δn | = | nx−ny |
(C _R : photoelastic coefficient, σ _R : stretching stress, | Δn |: absolute value of birefringence, nx: refractive index in the stretching direction, ny: refractive index in the direction perpendicular to the stretching direction in the plane)

[Measurement of retardation of protective film for optically isotropic polarizing film]
<Extrusion of optically isotropic polarizing film protective film and preparation of measurement sample>
Acrylic thermoplastic resin melt-kneaded at 260 ° C. using a twin screw extruder is extruded from a T-table with a width of 45 cm adjusted to 255 ° C. and a slit interval of 2 mm at an extrusion speed of 180 kg / hr, and a mirror surface adjusted to 150 ° C. The surface of the surface transfer and take-up rolls were adjusted with a cooling roll to produce a roll plate sample having a thickness of 250 μm. Thereafter, the roll was loosened, and a punched sample was obtained with a Thomson blade so as to have a rectangular shape of 24 cm in the MD direction and 20 cm in the TD direction. Further, the sample was cut into a 4 cm square and divided into 30 measurement samples, and the thickness of each of the four corners and convenient 120 points was measured and averaged to obtain the total thickness of the optically isotropic polarizing film protective film.

<Measurement of birefringence and calculation of birefringence in terms of thickness>
The birefringence of the optically isotropic polarizing film protective film was measured by a rotating analyzer method using RETS-100 manufactured by Otsuka Electronics. The value of birefringence is a value of light having a wavelength of 550 nm. Birefringence (Δn) was calculated by the following formula. The obtained value was converted to a sheet thickness of 100 μm to obtain a measured value.
Δn = nx−ny
(Δn: birefringence, nx: refractive index in the stretching direction, ny: refractive index in the direction perpendicular to the stretching direction in the plane)

The absolute value (| Δn |) of birefringence (Δn) was determined as follows.
| Δn | = | nx−ny |

<Details of in-plane direction phase difference Re measurement>
Optical isotropic polarizing film protection in the wavelength range from 400 nm to 800 nm by rotating analyzer method using RETS-100 manufactured by Otsuka Electronics Co., Ltd. installed in a constant temperature and humidity chamber adjusted to 23 ° C. and humidity 60% A birefringence measurement of the film was performed. For 30 samples of 4 cm square, the in-plane retardation Re was measured at the center of the sample, and then the thickness of the center of the sample was measured to obtain the in-plane retardation Re converted to a thickness of 100 μm. . Subsequently, after converting into an absolute value, the average was taken, and it converted into the whole thickness calculated | required above again, and the absolute value of phase difference Re of the in-plane direction of an optically isotropic polarizing film protective film was calculated | required.
In addition, conversion from each thickness to 100 micrometers thickness was performed based on the following numerical formula.
The absolute value of birefringence (| Δn |) and the phase difference Re have the following relationship.
Re = | Δn | × d
(| Δn |: absolute value of birefringence, Re: phase difference, d: thickness of sample)

The absolute value (| Δn |) of birefringence is a value shown below.
| Δn | = | nx−ny |
(Nx: refractive index in the stretching direction, ny: refractive index in the direction perpendicular to the stretching direction in the plane)

<Details of thickness direction retardation Rth measurement>
Measurement of birefringence of an optically isotropic polarizing film protective film at a wavelength of 589 nm using a phase difference measuring device (KOBRA-21ADH) manufactured by Oji Scientific Instruments Co., Ltd. installed in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60% Carried out. The measurement is performed on 30 samples of 4 cm square, and the thickness direction retardation Rth is measured at the center of the sample, and then the thickness of the sample at the center is measured to obtain the thickness direction retardation Rth converted to a thickness of 100 μm. It was. Subsequently, after converting into an absolute value, the absolute value of the retardation Rth in the thickness direction of the optically isotropic polarizing film protective film was obtained by taking an average and converting it to the total thickness obtained above.
In addition, conversion from each thickness to 100 micrometers thickness was performed based on the following numerical formula.
The absolute value of birefringence (| Δn |) and the phase difference Rth have the following relationship.
Rth = | Δn | × d
(| Δn |: absolute value of birefringence, Rth: phase difference, d: thickness of sample)

The absolute value (| Δn |) of birefringence is a value shown below.
| Δn | = | (nx + ny) / 2−nz |
(Nx: refractive index in the stretching direction, ny: refractive index in the direction perpendicular to the stretching direction in the plane, nz: refractive index in the thickness direction perpendicular to the stretching direction out of the plane)

[Details of measurement of slope α of relational expression between strain and birefringence in optical isotropic polarizing film protective film]
An optically isotropic polarizing film protective film (thickness: about 800 μm, width: 40 mm) is stretched by uniaxial free stretching at a stretching temperature (Tg + 20) ° C. and a stretching speed (500 mm / min) using an Instron 10t tensile tester. An optically isotropic polarizing film protective film was formed. The draw ratio was drawn at 100%, 200%, and 300%. Subsequently, the birefringence of the obtained stretched optically isotropic polarizing film protective film was measured by the above-mentioned method, and the birefringence (Δn (S)) that was expressed when uniaxially stretched was determined.
Least square method approximate linear relational expression obtained by plotting the value of birefringence (Δn (S)) expressed in the obtained stretched optically isotropic polarizing film protective film against the stretch ratio (S) ( The value of slope α was obtained from A). It means that the smaller the value of the inclination α, the smaller the birefringence (Δn (S)) and its change.
Δn (S) = α × S + β (β is a constant: birefringence value when not stretched) (A)
Here, the birefringence is a value obtained by converting a measured value to a thickness of 100 μm.

The draw ratio (S) is a value represented by the following formula, where L _{0 is} the distance between chucks before stretching and L ₁ is the distance between chucks after stretching.

  In the optically isotropic polarizing film protective film that completely satisfies optical isotropy, both the in-plane retardation Re and the thickness direction retardation Rth are “zero”, and there is no variation in the retardation even in a large area sample.

[Surface hardness measurement of acrylic thermoplastic resin]
In accordance with JIS K5600-5-4, an electric pencil scratch hardness tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) was used, and the pencil hardness of the acrylic thermoplastic resin was measured at a load of 500 g.

[Measurement of refractive index of acrylic thermoplastic resin]
The refractive index of the acrylic thermoplastic resin is obtained by using a model 2010 prism coupler manufactured by Metricon Corporation installed in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60% using the above-described melt-formed film for photoelasticity measurement. It was. The sample used was one day and night cured in a constant temperature and humidity chamber adjusted to 23 ° C. and 60% humidity.

[Measurement of moisture permeability of acrylic thermoplastic resin]
Measurement was performed in a test condition of 40 ° C. and a humidity of 90% in 24 hours using a melt-formed film for photoelastic coefficient measurement by a method according to the MONCON method described in JIS K7129B. The unit of moisture permeability is g / (m ² · 24h). Measuring apparatus: PERMATRAN W3 / 33 type water vapor transmission tester manufactured by MOCON.

[Contrast evaluation under stress condition of protective film for optically isotropic polarizing film]
Two commercially available polarizing plates were prepared on the backlight, and installed in an orthogonal state with a space. Next, an optically isotropic polarizing film was put between them, and the state when rotated in the plane direction was observed. Thereafter, an optically isotropic polarizing film protective film stretched 10% in the longitudinal (MD) direction with a stress within the elastic range was sandwiched again and rotated in the same manner, and changes in brightness were visually evaluated.

  When rotating in the state before stretching, the brightness does not change at all, and when rotating in the stretched state, there is no change in brightness, and when rotating in the state before stretching, the brightness changes completely No, and a slight change in brightness when rotated in the stretched state is observed, and when rotated in the state before stretching, partial light and darkness that is considered to be derived from residual stress due to molding is seen and stretched △ If the partial light and darkness observed when viewed in the state is Δ, partial light and darkness considered to be derived from residual stress due to molding when rotated in the state before stretching, and the stretched state The case where the partial light and darkness observed when viewed in terms of was changed to x.

[Evaluation of interference fringes of optically isotropic polarizing film protective film]
An optically isotropic polarizing film protective film was placed on a black plate that did not allow light to pass through, and the surface was visually evaluated by illuminating with a three-wavelength fluorescent lamp (National: FL20SS / ENW / 18).
Interference fringes are not visible at all ◎, interference fringes are faintly visible ○, interference fringes are conspicuous Δ, interference fringes are conspicuous, and glare occurs ×.

[Preparation of polarizing film]
Add 1 L of distilled water to a 5 L stirrer glass separable flask immersed in a hot water bath. The separable flask is then cooled and the distilled water inside is brought to 4 ° C. Thereafter, polyvinyl alcohol (special grade manufactured by Wako Pure Chemical Industries) powder having an average polymerization degree of 1800 and a saponification degree of 99.9% is added while rotating the stirrer at a rotation speed of 150 rpm. After maintaining in this state for 30 minutes, the internal temperature of the separable flask is heated at a rate of 2 ° C./min while continuing to stir, and when the internal temperature reaches 95 ° C., the rotation speed of the stirrer is reduced to 80 prm for 3 hours. Continue stirring. After confirming that there was no cocoon-like undissolved polyvinyl alcohol, stirring was stopped while maintaining the temperature at 95 ° C., and bubbles of air entrained by stirring stopped losing. At the stage where bubbles are almost removed, an aspirator is connected to the separable flask, and the bubbles are completely degassed by slightly reducing the pressure.

  A smooth glass plate (length 45 cm, width 45 cm, thickness 3 mm), glass round bar (diameter 2.5 cm, length 60 cm), and Scotch tape (manufactured by 3M) were prepared. Next, the glass plate was thoroughly wiped with a Kimwipe dipped in acetone, and then a scotch tape was laminated on both ends of the glass plate to provide a spacer having a height of 1.3 mm. A completely defoamed polyvinyl alcohol solution was slowly dropped on the upper part of the glass plate with the spacers on the left and right, and then a glass rod was placed perpendicular to the left and right spacers and slowly pulled down to the lower side of the glass plate. Next, the glass plate was placed on a horizontal base, covered with a cover with a slight gap between it and the water was dried. One week later, a film of polyvinyl alcohol having a thickness of about 80 μm was obtained.

  Next, the polyvinyl alcohol film was stretched uniaxially 3 times with a stretching jig at room temperature, and then an aqueous solution containing iodine and potassium iodide (iodine / potassium iodide / water = 0.05 / 5/100). (Mass ratio)) was immersed for 60 seconds. Next, it was immersed in a 65 ° C. aqueous solution containing potassium iodide and boric acid (potassium iodide / boric acid / water = 2.5 / 7.5 / 100 (mass ratio)) for 300 seconds. After washing with pure water at 30 ° C. for 20 seconds, it was dried at 50 ° C. to obtain a polyvinyl alcohol polarizing film.

  It was 1.53 when the refractive index of the obtained polyvinyl-alcohol-type polarizing film was measured.

[Preparation of adhesive for polarizing film]
Water is added to 163-030545 (molecular weight: 22,000, saponification degree: 88 mol%) manufactured by Wako Pure Chemical Industries, Ltd., which is a polyvinyl alcohol resin, to prepare an aqueous solution with a solid content concentration of 7% by mass. did. On the other hand, 100 parts of WLS-201 (solid content concentration 35 mass%) manufactured by Dainippon Ink & Chemicals, which is a polyurethane resin, is added to CR- manufactured by Dainippon Ink & Co., which is a polyepoxy curing agent. 5 parts of 5 L (100% active ingredient product) were blended and diluted with water to prepare an aqueous solution having a solid content of 20% by mass. The obtained polyurethane resin aqueous solution and polyvinyl alcohol resin aqueous solution were mixed at a mass ratio of 1: 1 (solid content mass ratio of 80:20) to obtain a mixed adhesive having a solid content concentration of 15 mass%. Prepared.

[Preparation of polarizing plate]
The surface of the optically isotropic polarizing film protective film was treated with plasma treatment under atmospheric pressure, and then both surfaces of the polarizing film were immediately pasted with the adhesive for polarizing film. Then, it dried for one week at 40 degreeC.

[Polarizer wet heat test and peelability evaluation method]
After preparing the polarizing plate, four samples were cut out in a size of 10 cm in the stretching direction of the polarizing film and 8 cm in the direction perpendicular to the stretching direction. Next, the set of 4 plates is left in a constant temperature and constant temperature chamber adjusted to a temperature of 85 ° C and a humidity of 85% for 24 hours, and then left in a constant temperature and humidity chamber adjusted to 23 ° C and a humidity of 60% for 24 hours. Was repeated 20 times.

  A film that does not peel at the interface between the polarizing film and the optically isotropic protective film is ◎, a film that peels within 1 mm from the edge, a film that peels within 1 mm or more and less than 2 mm from the edge, but a polarizing plate In the case where there was no partial peeling at the center, Δ, peeling of 2 mm or more was observed, or when there was partial peeling at the center of the polarizing plate, x.

[Method of wet-heat test and surface hardness test of polarizing plate]
After producing the polarizing plate, the plate was allowed to stand for 24 hours in a constant temperature and constant temperature device adjusted to a temperature of 85 ° C. and a humidity of 85%, and then left for 24 hours in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60%. . Thereafter, the pencil hardness of the polarizing plate was measured according to JIS K5600.

[Polarizer wet heat test and bending test method]
After producing the polarizing plate, the plate was allowed to stand for 24 hours in a constant temperature and constant temperature device adjusted to a temperature of 85 ° C. and a humidity of 85%, and then left for 24 hours in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60%. . Thereafter, 20 test pieces having a size of 1 cm in width and 10 cm in length were cut out. Next, it was evaluated whether or not this test piece was broken by being wound around a glass rod having a diameter of 5 mm.

  The case where the number of broken films was 0 was rated as “◎”, the case where there were 1 broken film as “◯”, the case where 2 cracked films were as “Δ”, and the case where there were 3 or more cracked films as “×”.

[Production of display device and evaluation of display quality]
The liquid crystal panel was removed from the commercially available liquid crystal television, and then only the polarizing plate on the viewing side was peeled off from the liquid crystal cell, and the polarizing plate before the wet heat test and the polarizing plate after were displayed side by side. When Comparative Example 2 was set at 1 point, the display quality was deteriorated, but 2 points were better than the standard, and 3 points were not deteriorated at all.

[Example 1]
An acrylic thermoplastic resin was produced by the following method. Methyl methacrylate (Wako Pure Chemicals, hereinafter referred to as MMA) was distilled at a reduced pressure of 0.01 MPa and 40 ° C. to remove the inhibitor. Next, distilled methyl methacrylate 24.30 kg, phenylmaleimide 2.40 kg (Wako Pure Chemicals, hereinafter phMI), cyclomaleimide (Wako Pure Chemicals, hereinafter chMI) 3.30 kg, meta-xylene 20 kg (Wako Pure Chemicals, hereinafter mXy) ) Was weighed and added to a 50 L tank to obtain a mixed monomer solution. Subsequently, nitrogen was bubbled at a rate of 100 mL / min for 12 hours to remove dissolved oxygen. The mixed monomer solution was added to a 60 L reactor purged with nitrogen and the temperature was raised to 130 ° C. Next, polymerization was carried out by adding an initiator solution in which 0.06 kg of perbutyl O (Japanese oil) was dissolved in 6 kg of mXy at a rate of 1 kg / hour, and the reactor was cooled to 50 ° C. after 8 hours. .

Subsequently, 500 L of methanol was added to a 1 m ³ reactor, and the above polymerization solution was poured over 5 hours to precipitate a polymer. Thereafter, the mixture was further stirred for 2 hours and filtered under reduced pressure. 300 L of methanol was further poured into the methanol-containing polymer powder after filtration under reduced pressure and stirred again. Thereafter, filtration under reduced pressure was performed, and the methanol-containing powder was collected and dried in a 0.3 m ³ conical vacuum dryer under conditions of a degree of vacuum of 0.03 MPa and a temperature of 80 ° C. The powder after drying was pelletized with a twin-screw extruder at 250 ° C. to obtain a pellet-shaped acrylic thermoplastic resin.

When the composition of this acrylic thermoplastic resin was confirmed, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. . Further, when the glass transition temperature (hereinafter referred to as Tg) was measured, it was 135 ° C., the surface hardness was 4H, the moisture permeability was 20 g / (m ² · 24 hr), the refractive index was 1.50, and the weight average molecular weight (hereinafter Mw). Was 22.5. The photoelastic coefficient was + 0.4 × 10 ⁻¹² Pa ⁻¹ , 10,000, and α was + 0.03 × 10 ⁻⁵ .

  The optically isotropic polarizing film protective film was extruded from a T-table having a width of 45 cm and a slit interval of 280 μm adjusted to 255 ° C. at a extrusion speed of 180 kg / hr using a twin screw extruder at a temperature of 260 ° C. The sample was manufactured as a roll plate sample having a thickness of 250 μm by adjusting the speed of the surface transfer and take-up roll with a mirror-cooled roll adjusted to ° C. Next, a punched sample was obtained with a Thomson blade so as to have a rectangular shape of 24 cm in the 20 cm MD direction and 20 cm in the TD direction with the Thomson blade.

  The absolute value of the retardation (Re) in the in-plane direction of the optically isotropic polarizing film protective film was 2 nm, and the retardation (Rth) in the thickness direction was 3 nm. Next, contrast evaluation under stress was performed. The result was ○. From this, it can be seen that polarization leakage hardly causes a decrease in contrast even when distortion due to external force is applied. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

  A polarizing plate was prepared from the optically isotropic polarizing film protective film and a polarizing film having a refractive index of 1.53, and the adhesion after the wet heat test was evaluated. The result is ◯, indicating that the moisture permeability is appropriate, the polarizing film adhesive is dried well, and the polarizing film adhesive is hardly dissolved by the moisture transmission during the test. It was also found that a high surface hardness of 3H could be maintained after the wet heat test. Furthermore, the bending test result after the wet heat test is ◯, indicating that the necessary and sufficient strength can be maintained.

  A liquid crystal display device was assembled with the produced polarizing plate, and it was confirmed that the quality decline before and after the wet heat test was two points, which was superior to the conventional product although there was deterioration compared to before the test.

[Example 2]
Styrene (Wako Pure Chemical) was distilled at a reduced pressure of 0.01 MPa and 52 ° C. to remove the inhibitor. Next, distilled methyl methacrylate 21.72 kg, phenylmaleimide 2.18 kg (Wako Pure Chemicals special grade), cyclomaleimide 5.28 kg (Wako Pure Chemicals special grade), distilled styrene 0.78 kg (Wako Pure Chemicals special grade), meta-xylene 20 kg (Japanese sum) Polymerization was carried out in the same manner as in Example 1 except that the photo-pure drug special grade was used as a mixed monomer solution, to obtain a pellet-shaped acrylic thermoplastic resin.

When the composition of this acrylic thermoplastic resin was confirmed, the structural units derived from monomers of methyl methacrylate, phenylmaleimide, cyclomaleimide, and styrene were 72.5% by mass, 7.3% by mass, and 17. They were 6 mass% and 2.6 mass%. When the glass transition temperature was measured, it was 141 ° C., the surface hardness was 4H, the permeation humidity was 10 g / (m ² · 24 hr), the refractive index was 1.52, and the Mw was 150,000. The photoelastic coefficient was + 0.1 × 10 ⁻¹² Pa ⁻¹ and α was −0.2 × 10 ⁻⁵ .

  Subsequently, the obtained pellet-shaped acrylic thermoplastic resin was formed into a film by melt press molding. First, a Kapton sheet is placed on an iron plate, a 100 μm thick metal frame cut into a rectangle with a width of 30 cm and a length of 40 cm is placed thereon, an acrylic thermoplastic resin is placed there, and a Kapton sheet is further placed. An iron plate was placed. Put it in a vacuum compression molding machine (SFV-30, manufactured by Shindo Metal Industry Co., Ltd.) while sandwiching it between the two metal plates, and start reducing pressure and reach 10 kPa. The temperature rose. Thereafter, after maintaining at 260 ° C. for 5 minutes, compression was performed at a press pressure of 10 MPa for 5 minutes, and then cooling was started. When the temperature reached 50 ° C., the inside of the vacuum dryer was returned to atmospheric pressure, and a sample was taken out.

  After cutting into a length of 26 cm × width of 26 cm with a cutter, melt stretch molding was performed with a test biaxial stretching apparatus (Toyo Seiki Seisakusho). The stretching was performed at a stretching temperature of 150 ° C., a preheating time of 5 minutes, an initial chuck distance (25 cm in length and 25 cm in width), and a stretching speed of 25 cm / min in both length and width. The sample was then sandwiched between Kapton sheets and heated for 8 hours in a dryer filled with nitrogen and kept at a temperature 10 ° C. above the transition temperature. After cooling, it was punched with a Thomson blade so as to form a 24 cm rectangular shape with 20 cm with a Thomson blade to obtain an optically isotropic polarizing film protective film with a thickness of 33 μm.

  The absolute value of the retardation (Re) in the in-plane direction of the obtained isotropic polarizing film protective film was 6 nm, and the retardation (Rth) in the thickness direction was 5 nm. The result of the contrast test under stress was ◎. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

  A polarizing plate was prepared by bonding to a polarizing film having a refractive index of 1.53. Next, the adhesion after the wet heat test was evaluated. The result is ◎, indicating that the moisture permeability is appropriate, the polarizing film adhesive is dried well, and the polarizing film adhesive is hardly dissolved by the moisture transmission during the test. It was also found that a high surface hardness of 3H could be maintained after the wet heat test. Furthermore, it can be seen from the bending test after the wet heat test that the necessary and sufficient strength can be maintained.

  A liquid crystal display device was assembled with the produced polarizing plate, and deterioration in quality before and after the wet heat test was confirmed. The result was 2 points, and it was found that the product was superior to the conventional product although there was deterioration compared to before the test.

[Example 3]
Benzyl methacrylate (Wako Pure Chemicals special grade) was distilled at a reduced pressure of 0.01 MPa at 52 ° C. to remove the inhibitor. Distilled methyl methacrylate 24kg, Phenylmaleimide 2.40kg (Wako Pure Chemical), Cyclomaleimide 3.30kg (Wako Pure Chemical), Distilled benzyl methacrylate 0.30kg (Wako Pure Chemical), Metaxylene 20kg (Wako Pure Chemical) The mixture was polymerized in the same manner as in Example 1 except that the mixed monomer solution was used to obtain a pellet-shaped acrylic thermoplastic resin. When the composition of this acrylic thermoplastic resin was confirmed, the structural units derived from each monomer of methyl methacrylate, phenylmaleimide, cyclomaleimide, and benzyl methacrylate were 80.3% by mass and 7.9% by mass, respectively. 10.8% by mass and 1.0% by mass. When the glass transition temperature was measured, it was 139 ° C., the moisture permeability was 13 g / (m ² · 24 hr), the refractive index was 1.51, and Mw was 22 million. The photoelastic coefficient was + 0.7 × 10 ⁻¹² Pa ⁻¹ and α was −0.02 × 10 ⁻⁵ .

  As in Example 2, the optically isotropic polarizing film protective film has a Kapton sheet placed on an iron plate, and a gold frame with a thickness of 250 μm cut into a rectangle with a width of 30 cm and a length of 40 cm is placed on the Kapton sheet. An acrylic thermoplastic resin was placed, a kapton sheet was placed, and an iron plate was placed. Put it in a vacuum compression molding machine (SFV-30, manufactured by Shindo Metal Industry Co., Ltd.) while sandwiching it between the two metal plates, and start reducing pressure and reach 10 kPa. The temperature rose. Thereafter, after maintaining at 260 ° C. for 5 minutes, compression was performed at a press pressure of 10 MPa for 5 minutes, and then cooling was started. When the temperature reached 50 ° C., the inside of the vacuum dryer was returned to atmospheric pressure, and a sample was taken out.

  After cutting into a length of 26 cm × width of 26 cm with a cutter, melt stretch molding was performed with a test biaxial stretching apparatus (Toyo Seiki Seisakusho). The stretching was performed at a stretching temperature of 150 ° C., a preheating time of 5 minutes, an initial chuck distance (25 cm in length and 25 cm in width), and a stretching speed of 25 cm / min in both length and width. The sample was then sandwiched between Kapton sheets and heated for 8 hours in a dryer filled with nitrogen and kept at a temperature 10 ° C. above the transition temperature. After cooling, the film was punched with a Thomson blade so as to form a 24 cm rectangular shape with 20 cm with a Thomson blade, and an optically isotropic polarizing film protective film having a thickness of 80 μm was obtained.

  The obtained optically isotropic polarizing film protective film had an in-plane direction retardation (Re) absolute value of 2 nm and a thickness direction retardation (Rth) of 2 nm. The result of the contrast test under stress was ◎. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

  A polarizing plate was prepared by bonding to a polarizing film having a refractive index of 1.53. Next, the adhesion after the wet heat test was evaluated. The result was ○. It was also found that the surface hardness was 3H even after the wet heat test, and the necessary and sufficient strength could be maintained in the bending test after the wet heat test.

  A liquid crystal display device was assembled with the produced polarizing plate, and deterioration in quality before and after the wet heat test was confirmed. The result was 2 points, and it was found that the product was superior to the conventional product although there was deterioration compared to before the test.

[Example 4]
The roll-shaped optically isotropic polarizing film protective film having a thickness of 250 μm obtained in Example 1 was used as a raw material, and the film was thinned by sequentially stretching with the melt stretching apparatus 100 of FIG. First, the raw material unrolled from the raw material roll is heated to 150 ° C., stretched by 300% longitudinally due to the peripheral speed difference between the rolls arranged in the MD direction, and then heated in a horizontal stretching chamber heated to 150 ° C. Then, the film was stretched 300% in the TD direction. The film thickness after stretching was 33 μm. The optically isotropic polarizing film protective film was obtained by punching with a Thomson blade in the same manner as in Example 1. The absolute value of the in-plane retardation (Re) of the optically isotropic polarizing film protective film was 4 nm, and the retardation (Rth) in the thickness direction was 6 nm. The result of the contrast test under stress was ◎.

  A polarizing plate was prepared by bonding to a polarizing film having a refractive index of 1.53. Next, the adhesion after the wet heat test was evaluated. The result was ◎. The surface hardness was 3H after the wet heat test, and the bending test result after the wet heat test was ◎. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

  A liquid crystal display device was assembled with the produced polarizing plate, and deterioration in quality before and after the wet heat test was confirmed. The result was 2 points, and it was found that the product was superior to the conventional product although there was deterioration compared to before the test.

[Comparative Example 1]
When the glass transition temperature was measured for ZEONOR 480R (Nippon Zeon Corporation), it was 130 ° C., the surface hardness was HB, and the moisture permeability was 0.9 g / (m ² · 24 hr). Furthermore, the refractive index was 1.53. Further, the photoelastic coefficient was measured, and was + 5 × 10 ⁻¹² Pa ⁻¹ and α was + 0.60 × 10 ⁻⁵ . Mw was not measured.

  Molding was performed in the same manner as in Example 1 to produce a 100 μm plate. The absolute value of the in-plane retardation (Re) of this plate was 12 nm, and the thickness direction retardation (Rth) was 9 nm. The result of carrying out the contrast evaluation under stress was evaluated as x because strain was left from the center to both ends, and a partial change in brightness was observed. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

  A polarizing plate was prepared by bonding to a polarizing film having a refractive index of 1.53. Next, the adhesion after the wet heat test was evaluated. The result was x. It was found that since the moisture permeability was too low, the polarizing film adhesive was insufficiently dried and easily peeled off during the wet heat test. The surface hardness was HB without change from before the wet heat test. In addition, although some peeling was observed, no crack was observed in terms of bending strength.

  A liquid crystal display device was assembled with the produced polarizing plate, and deterioration in quality before and after the wet heat test was confirmed. There was light leakage due to peeling, and the result was 1 point.

[Comparative Example 2]
A commercially available triacetyl cellulose film (Fuji Film, F-TAC, 80 μm thickness) was prepared, and the photoelastic coefficient was measured. The glass transition temperature was 145 ° C., the surface hardness was H, the moisture permeability was 175 g / (m ² · 24 hr), and the refractive index was 1.48. The molecular weight could not be measured because the sample did not dissolve. The photoelastic coefficient was + 15 × 10 ⁻¹² Pa ⁻¹ . α was not measured.

  The absolute value of the retardation (Re) in the in-plane direction of this plate was 5 nm, and the retardation (Rth) in the thickness direction was 66 nm. The result of the contrast evaluation under stress was Δ. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

A polarizing plate was prepared by bonding to a polarizing film having a refractive index of 1.53. Next, the adhesion after the wet heat test was evaluated. The result was ○. Since the moisture permeability was high, drying of the polarizing film adhesive was insufficient. However, the surface hardness decreased from before the wet heat test and became HB. From this, it can be seen that the scratch resistance deteriorated by the wet heat test. Also, the bending strength decreased with Δ.
A liquid crystal display device was assembled with the produced polarizing plate, and deterioration in quality before and after the wet heat test was confirmed. Since it is standard, it was set to 1 point.

[Comparative Example 3]
Polymerization and the polymer were recovered in the same manner as in Example 1 using MMA alone as the monomer solution. The glass transition temperature was 110 ° C., the surface hardness was 2H, the moisture permeability was 16 g / (m ² · 24 hr), the refractive index was 1.49, and the Mw was 160,000. The photoelastic coefficient was −4.7 × 10 ⁻¹² Pa ⁻¹ and α was −0.3 × 10 ⁻⁵ .

  Next, using a twin-screw extruder as a polarizing film protective film, the resin melted and mixed at 240 ° C. was extruded from a T table (FIG. 2) having a width of 45 cm and a slit interval of 120 μm adjusted to 225 ° C. at an extrusion speed of 180 kg / hr. The sample was manufactured as a roll plate sample having a thickness of 100 μm by adjusting the speed of the surface transfer and winding rolls with a mirror-cooled roll adjusted to 130 ° C. Next, a punched sample was obtained with a Thomson blade so as to have a rectangular shape of 24 cm in the 20 cm MD direction and 20 cm in the TD direction with the Thomson blade. The absolute value of the in-plane direction retardation (Re) was 7 nm, and the thickness direction retardation (Rth) was 5 nm. The contrast evaluation result under stress was Δ. Regarding the interference fringe test, it was ◎ because it was not a laminated film.

  A polarizing plate was prepared from a polarizing film having a refractive index of 1.53, and the adhesion after the wet heat test was evaluated. The result is ◯, indicating that the moisture permeability is appropriate, the polarizing film adhesive is dried well, and the polarizing film adhesive is hardly dissolved by the moisture transmission during the test. Further, it was found that 2H and the value before evaluation could be maintained even after the wet heat test. On the other hand, the bending test result after the wet heat test is ◯, indicating that there is no necessary and sufficient strength.

  Since the strength was insufficient, a liquid crystal display device was not assembled.

[Comparative Example 4]
A three-layer extruded film was produced using the cyclic olefin resin of Comparative Example 1 and the polymethyl methacrylate of Comparative Example 3 (mass ratio was cyclic olefin resin: polymethyl methacrylate = 50: 50). The film configuration was polymethyl methacrylate / cyclic olefin resin / polymethacrylate, the thickness of each layer was 25 μm / 50 μm / 25 μm, and the total film thickness was 100 μm.

  The absolute value of the in-plane retardation (Re) of the optically isotropic polarizing film protective film was 5 nm, and the thickness direction retardation (Rth) was 4 nm. Next, contrast evaluation under stress was performed. The result was ○. It was x regarding the interference fringe test.

  A polarizing plate was prepared from a polarizing film having a refractive index of 1.53, and the adhesion after the wet heat test was evaluated. A result is (triangle | delta) and it turns out that drying of the adhesive agent for polarizing films is inadequate. It can be seen that 2H is obtained after the wet heat test and the bending test result after the wet heat test is Δ, indicating that the strength is not sufficient.

  A liquid crystal display device was assembled with the produced polarizing plate, and deterioration in quality before and after the wet heat test was confirmed. The result was 2 points.

  Table 1 summarizes the characteristics of Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4.

  From Table 1, the optically isotropic polarizing film protective film of the present invention has a good polarizing function by being integrated with a polarizing plate, is excellent in properties such as heat resistance and surface hardness, and peels off even when wet. It can be seen that it has high reliability and excellent mechanical durability.

  A liquid crystal display having reliability and good visibility by providing a polarizing plate provided with a polarizing film protective film excellent in heat resistance, moisture resistance, scratch resistance, mechanical strength, adhesion to the polarizing film and optical isotropy Realize the device.

  DESCRIPTION OF SYMBOLS 1 ... Resistance film type polarizing plate integrated inner touch panel, 2 ... Electrostatic projection type polarizing plate integrated inner touch panel, 5, 16 ... Polarizing plate, 6, 17 ... In-plane switching type liquid crystal display element, 7, 18 ... Optical glass 8 ... ITO transparent conductive film, 9 ... spacer, 11 ... transparent conductive film, 12, 20 ... optical isotropic support plate, 13, 21 ... polarizing film, 14, 22 ... polarizing film protective film, 15, 23 ... epoxy Adhesive, 19 ... ITO pattern, 100 ... melt stretcher, 105 ... raw roll, 106 ... preheated roll, 107 ... longitudinal roll, 108 ... longitudinal stretch chamber, 109 ... tension control roll, 110 ... take-off roll, 111 ... Clip, 112 ... transverse stretching chamber, 113 ... tension control roll, 114 ... slitter, 115 ... end take-up roll, 116 ... product take-up roll Le.

Claims (17)

Acrylic thermoplastic having a first structural unit represented by the following formula (1), a second structural unit represented by the following formula (2), and a third structural unit represented by the following formula (3) Formed from resin,
The acrylic thermoplastic resin is 50 to 95% by mass of the first structural unit, 0.1 to 20% by mass of the second structural unit, and 0.1 to 49.9% by mass. % Of the third structural unit, an optically isotropic polarizing film protective film.

[Wherein, R ¹ represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or And an aryl group having 6 to 14 carbon atoms and having at least one substituent selected from the following group A.
Group A: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms. ]

[Wherein, R ² represents an arylalkyl group having 7 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, or an aryl group having 6 to 14 carbon atoms having at least one substituent selected from the following group B: R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group B: a halogen atom, a hydroxyl group, a nitro group, an alkoxy group having 1 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, and an arylalkyl group having 7 to 14 carbon atoms. ]

[Wherein, R ⁵ represents a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, an alkyl group having 1 to 12 carbon atoms, or at least one substituent having at least one substituent selected from the following group C. R ⁶ and R ⁷ each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
Group C: a halogen atom, a hydroxyl group, a nitro group, and an alkoxy group having 1 to 12 carbon atoms. ] The optically isotropic polarizing film protective film according to claim 1, wherein an absolute value of a photoelastic coefficient of the acrylic thermoplastic resin is 3.0 × 10 ⁻¹² Pa ⁻¹ or less.   The optically isotropic polarizing film protective film according to claim 1 or 2, wherein a halogen atom content of the acrylic thermoplastic resin is less than 0.47% by mass based on the total amount of the acrylic thermoplastic resin.   The optically isotropic polarization according to any one of claims 1 to 3, wherein the molar ratio of the content of the second structural unit to the content of the third structural unit is greater than 0 and 15 or less. Membrane protective film. R ¹ is a methyl group or a benzyl group,
R ² is a phenyl group or a phenyl group having at least one substituent selected from the group B;
The optically isotropic polarizing film protective film according to claim 1, wherein R ⁵ is a cyclohexyl group. The optical isotropy according to any one of claims 1 to 5, wherein the acrylic thermoplastic resin has a moisture permeability of 3 to 100 g / (m ² · 24 hr) at a thickness of 100 µm when formed into a film. Polarizing film protective film.   The optically isotropic polarizing film protective film according to any one of claims 1 to 6, wherein the acrylic thermoplastic resin has a refractive index difference within ± 0.04 with respect to the polarizing film. The acrylic thermoplastic resin has a slope in the least squares approximate linear relationship (a) between the stretch ratio (S) when film-molded and the 100 μm-thickness converted birefringence (Δn (S)) at the stretch ratio. The optically isotropic polarizing film protective film of any one of Claims 1-7 whose value of (alpha) is resin which satisfy | fills following formula (b).
Δn (S) = α × S + β (a)
−0.30 × 10 ⁻⁵ ≦ α ≦ 0.30 × 10 ⁻⁵ (b)
[In the formula, β is a constant and indicates birefringence at the time of non-stretching. ]   The optically isotropic polarizing film protective film according to any one of claims 1 to 8, wherein a glass transition temperature of the acrylic thermoplastic resin is 130 ° C or higher.   The optically isotropic polarizing film protective film of any one of Claims 1-9 whose surface pencil hardness is 3H or more.   11. The acrylic thermoplastic resin according to claim 1, wherein the absolute value of the in-plane retardation Re when the film is formed is a resin that is 8.0 nm or less in terms of 100 μm thickness. The optically isotropic polarizing film protective film described.   12. The acrylic thermoplastic resin according to claim 1, wherein the acrylic thermoplastic resin is a resin having an absolute value of a retardation Rth in the thickness direction in the case of film formation of 8.0 nm or less in terms of 100 μm thickness. An optically isotropic polarizing film protective film.   The optically isotropic polarizing film protective film of any one of Claims 1-12 whose thickness is 10-300 micrometers.   The optically isotropic polarizing film protective film according to any one of claims 1 to 13, which is produced by melt extrusion molding and / or melt biaxial stretching.   A polarizing plate provided with the optically isotropic polarizing film protective film of any one of Claims 1-14.   The polarizing plate of Claim 15 used for the liquid crystal display device whose liquid crystal system is a horizontal electric field system or an oblique electric field system.   The polarizing plate of Claim 15 used for the liquid crystal display integrated touch panel whose liquid crystal system is a horizontal electric field system or an oblique electric field system.

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