JP2009109870A - Optical compensation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensation film having superior optical characteristics, such as a large refractive index in the film thickness direction, a large in-plane phase difference, and small wavelength dependence, in particular, an optical compensation film for a liquid crystal display element. <P>SOLUTION: The film made of a β-substituted acrylate resin satisfies the relation nz>ny≥nx, wherein the three-dimensional refractive index of the film in the film in-plane lead axis direction is nx; the refractive index in the film in-plane direction orthogonal thereto is ny (when nx and ny are equal, it is an arbitrary orthogonal biaxial refractive index); and the refractive index in the perpendicular direction outside the film is nz. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical compensation film excellent in optical properties such as a large refractive index in the thickness direction of the film, a large in-plane retardation, and a small wavelength dependency, and more particularly to an optical compensation film for a liquid crystal display element. is there.

  Liquid crystal displays are widely used as the most important display devices in the multimedia society, from mobile phones to computer monitors, notebook computers, and televisions. Many optical films are used in liquid crystal displays to improve display characteristics. In particular, the retardation film plays a large role in improving contrast and compensating for color tone when viewed from the front or obliquely. As a conventional retardation film, polycarbonate or cyclic polyolefin is used, and these polymers are polymers having positive birefringence. Here, the sign of birefringence is defined as shown below.

  The optical anisotropy of the polymer film molecularly oriented by stretching or the like can be represented by a refractive index ellipsoid shown in FIG. Here, when the film is stretched, the refractive index in the fast axis direction in the film plane is nx, and the refractive index in the film in-plane direction orthogonal thereto is ny (where nx and ny are equal, any two orthogonal The refractive index in the vertical direction outside the film surface is denoted by nz. The fast axis is an axial direction having a low refractive index in the film plane.

  The negative birefringence means that the stretching direction is the fast axis direction, and the positive birefringence is that the direction perpendicular to the stretching direction is the fast axis direction.

  That is, the refractive index in the stretching axis direction is small in uniaxial stretching of a polymer having negative birefringence (fast axis: stretching direction), and the axis orthogonal to the stretching axis direction in uniaxial stretching of a polymer having positive birefringence. The refractive index in the direction is small (fast axis: direction orthogonal to the stretching direction).

  The in-plane retardation (Re) is expressed as a value obtained by multiplying the refractive index (ny) in the direction orthogonal to the fast axis direction minus the refractive index (nx) in the fast axis direction by the film thickness.

  Many polymers have positive birefringence. As a polymer having negative birefringence, there are acrylic resin and polystyrene. However, acrylic resin has low retardation and has insufficient characteristics as an optical compensation film. Polystyrene has a large photoelastic coefficient at room temperature and a phase difference that changes with a slight stress, such as a problem of stability of the phase difference, a problem of optical properties such as a large wavelength dependency of the phase difference, and low heat resistance. It is not used at present because of practical problems.

  A stretched polymer film exhibiting negative birefringence has a high refractive index in the thickness direction of the film and becomes an unprecedented optical compensation film. For example, super twisted nematic liquid crystal (STN-LCD) and vertical alignment liquid crystal (VA) -LCD), in-plane oriented liquid crystal (IPS-LCD), reflective liquid crystal display, transflective liquid crystal display, and other optical compensation films for compensating the viewing angle characteristics and optical compensation for compensating the viewing angle of polarizing plates. There is a strong market demand for an optical compensation film that is useful as a film and has negative birefringence. A method for producing a film has been proposed in which a polymer having positive birefringence is used to increase the refractive index in the thickness direction of the film. One is a treatment method in which a heat-shrinkable film is bonded to one side or both sides of a polymer film, the laminate is subjected to a heat stretching treatment, and a shrinkage force is applied in the thickness direction of the polymer film (see, for example, Patent Documents 1 to 3). ). In addition, a method of uniaxially stretching in a plane while applying an electric field to a polymer film has been proposed (see, for example, Patent Document 4). In addition, a retardation film composed of fine particles having negative optical anisotropy and a transparent polymer has been proposed (see, for example, Patent Document 5). Further, an optical compensation film or an optical compensation layer in which a liquid crystalline polymer film is applied and homeotropically oriented has been proposed (see, for example, Patent Document 6). Furthermore, optical compensation films coated with aromatic polymers such as polyvinyl naphthalene, polyvinyl biphenyl, and polyvinyl carbazole have been proposed (see, for example, Patent Documents 7 and 8).

Japanese Patent No. 2818983 JP 05-297223 A JP 05-323120 A Japanese Patent Laid-Open No. 06-088909 Japanese Patent Laid-Open No. 2005-156862 JP 2002-333524 A JP 2001-91746 A Japanese Patent Laid-Open No. 2006-221116

  However, the methods proposed in Patent Documents 1 to 4 have a problem that the manufacturing process is very complicated and the productivity is inferior. In addition, the control of the uniformity of the phase difference and the like is significantly more difficult than the control by the conventional stretching. When polycarbonate is used as the base film, the photoelastic constant at room temperature is large, and there is a problem in the stability of the phase difference, such as the phase difference being changed by a slight stress. Furthermore, there are problems such as the large wavelength dependence of the phase difference.

  Further, the retardation film obtained in Patent Document 5 is a retardation film having negative birefringence by adding fine particles having negative optical anisotropy, and from the viewpoint of simplification of the production method and economical efficiency. There is a need for a retardation film that does not require the addition of fine particles. The method described in Patent Document 6 has a problem that it is difficult to uniformly homeotropically align the liquid crystalline polymer. Further, the methods described in Patent Documents 7 and 8 have problems that the obtained film is easily broken and that the wavelength dispersion of retardation is large.

  Therefore, an object of the present invention is to provide an optical compensation film having excellent optical characteristics.

  As a result of intensive studies on the above problems, the inventors of the present invention are films made of a β-substituted acrylate ester resin, and the optical compensation film having a specific relationship with the three-dimensional refractive index of the film is the above. The present inventors have found that the problems are satisfied and have completed the present invention.

  That is, the present invention is a film made of a β-substituted acrylate resin, and the three-dimensional refractive index of the film is nx in the fast axis direction in the film plane, and in the in-plane direction perpendicular to the film. When the refractive index is ny (where nx and ny are equal, any biaxial refractive index orthogonal to each other) and the refractive index in the vertical direction outside the film surface is nz (thickness direction), nz> ny ≧ nx And the ratio of the phase difference measured at a wavelength of 450 nm to the phase difference measured at a wavelength of 550 nm (R450 / R550) is 1.1 or less.

  Hereinafter, the optical compensation film of the present invention will be described in detail.

  The optical compensation film of the present invention is a film made of a β-substituted acrylate ester resin, and the three-dimensional refractive index of the film is nx the refractive index in the fast axis direction in the film plane, and the film surface orthogonal to it. When the refractive index in the inward direction is ny (where nx and ny are equal, any biaxial refractive index orthogonal to each other) and the vertical refractive index outside the film surface is nz, nz> ny ≧ nx. It is an optical compensation film which has a relationship and the ratio (R450 / R550) of the retardation measured at a wavelength of 450 nm to the retardation measured at a wavelength of 550 nm is 1.1 or less. Here, the refractive index nx in the fast axis direction in the film plane is the refractive index in the axial direction having the lowest refractive index in the film plane. And these nx, ny, and nz can be calculated | required by using a sample inclination type | mold automatic birefringence meter, for example.

  In general, since the control of the three-dimensional refractive index of the film is performed by stretching the film, the manufacturing process and quality control are complicated, but the film made of β-substituted acrylate ester resin is unstretched. It exhibits a unique behavior that the refractive index in the film thickness direction increases.

  The wavelength dependence of the phase difference can be expressed as a ratio R450 / R550 of the phase difference (R450) measured at a wavelength of 450 nm and the phase difference (R550) measured at a wavelength of 550 nm. In the optical compensation film comprising the β-substituted acrylate ester resin of the present invention, the R450 / R550 is 1.1 or less, preferably 1.08 or less, particularly preferably 1.05 or less.

  The optical compensation film comprising the β-substituted acrylate resin of the present invention has an out-of-plane retardation (Rth) of −30 to −2000 nm represented by the following formula (1), where d is the thickness of the film. It is preferable that it is preferably −50 to −1000 nm, more preferably −100 to −500 nm.

Rth = [(nx + ny) / 2−nz] × d (1)
The thickness of the optical compensation film of the present invention is preferably 1 to 200 μm, particularly preferably 10 to 100 μm.

  Examples of the β-substituted acrylate resin in the present invention include polymers of β-substituted acrylate esters, and among them, a β-substituted acrylate residue unit represented by the general formula (a) is 50 mol% or more. 70 mol% or more, and in particular, it is preferably 80 mol% or more and 90 mol% or more because an optical compensation film having excellent heat resistance and mechanical properties is obtained.

（ここで、Ｒ₁は炭素数１〜４のアルキル基、ハロゲン基を示し、Ｒ_２は炭素数１〜１２の直鎖状、分岐状アルキル基又は環状アルキル基を示す。）
一般式（ａ）により示されるβ−置換アクリル酸エステル残基単位のＲ_１は炭素数１〜４のアルキル基、ハロゲン基であり、Ｒ_２は炭素数１〜１２の直鎖状、分岐状アルキル基又は環状アルキル基であり、フッ素，塩素などのハロゲン基、エーテル基、エステル基若しくはアミノ基で置換されていても良い。

(Here, R ₁ represents an alkyl group having 1 to 4 carbon atoms and a halogen group, and R ₂ represents a linear, branched alkyl group or cyclic alkyl group having 1 to 12 carbon atoms.)
R ₁ of the β-substituted acrylate residue unit represented by the general formula (a) is an alkyl group having 1 to 4 carbon atoms or a halogen group, and R ₂ is a linear or branched chain having 1 to 12 carbon atoms. An alkyl group or a cyclic alkyl group, which may be substituted with a halogen group such as fluorine or chlorine, an ether group, an ester group or an amino group.

Here, examples of the alkyl group having 1 to 4 carbon atoms in R ₁ include a methyl group, an ethyl group, a propyl group, and a butyl group. Examples of the halogen group include chlorine, fluorine, bromine, and iodine. It is done. Examples of the linear, branched or cyclic alkyl group having 1 to 12 carbon atoms in R ₂ include linear alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group and lauryl group. ; Branched alkyl groups such as isopropyl group, s-butyl group, isobutyl group, t-butyl group; cyclic alkyl groups such as cyclopentyl group, cyclohexyl group, etc. Among them, optically excellent balance of heat resistance and mechanical properties R ₁ is preferably a methyl group, and R ₂ is preferably an isopropyl group, a t-butyl group, or a cyclohexyl group because it is a compensation film.

  Here, the β-substituted acrylate residue unit represented by the general formula (a) specifically includes methyl crotonic acid residue, ethyl crotonic acid residue, propyl crotonic acid residue, and isopropyl crotonic acid residue. , Butyl crotonate residue, crotonate-s-butyl residue, isobutyl crotonate residue, tert-butyl crotonate residue, hexyl crotonate residue, octyl crotonate residue, lauryl crotonate residue, croton And crotonic acid ester residues such as cyclopentyl acid residue, cyclohexyl residue crotonic acid residue, chloroethyl crotonic acid residue, and crotonic acid-2-methoxyethyl residue, and the like. Particularly, isopropyl crotonic acid residue, crotonic acid-t- A butyl residue and a cyclohexyl crotonic acid residue are preferred.

  The β-substituted acrylate ester composed of 50 mol% or more of the β-substituted acrylate residue unit represented by the general formula (a), which is preferably used as the β-substituted acrylate resin in the present invention, has the general formula A resin comprising 50 mol% or more of the β-substituted acrylate residue unit represented by (a) and 50 mol% or less of the residue unit comprising a β-substituted acrylate ester and another copolymerizable monomer. Yes, as a residue unit comprising β-substituted acrylates and other copolymerizable monomers, for example, styrene residues such as styrene residues and α-methylstyrene residues; acrylic acid residues; Acrylic acid ester residues such as methyl acrylate residue, ethyl acrylate residue and butyl acrylate residue; methacrylic acid residue; methyl methacrylate residue, methacrylic acid residue Ethyl residues, mention may be made of one or more methacrylic acid esters residue such as butyl methacrylate residues.

The β-substituted acrylic ester resin in the present invention has a number average molecular weight (Mn) in terms of standard polystyrene obtained from an elution curve measured by gel permeation chromatography (hereinafter referred to as GPC). X10 ³ or more is preferable, and it is particularly preferably 2 × 10 ⁴ or more and 3 × 10 ⁵ or less because it becomes an optical compensation film having excellent mechanical properties and excellent moldability during film production. .

  In the present invention, the β-substituted acrylate ester resin may be produced by any method as long as the β-substituted acrylate ester resin is obtained. For example, β-substituted acrylate esters, Depending on the case, β-substituted acrylates and other copolymerizable monomers can be used in combination to carry out anionic polymerization or anionic copolymerization.

  Examples of the β-substituted acrylates include methyl crotonic acid, ethyl crotonic acid, propyl crotonic acid, isopropyl crotonic acid, butyl crotonic acid, crotonic acid-s-butyl, crotonic acid isobutyl, crotonic acid-t- Crotonates such as butyl, hexyl crotonate, octyl crotonate, lauryl crotonate, cyclopentyl crotonate, cyclohexyl crotonate, chloroethyl crotonate, and 2-methoxyethyl crotonate, and the like, and β-substituted acrylates Examples of other monomers copolymerizable with styrene include styrenes such as styrene and α-methylstyrene; acrylic acid; acrylic esters such as methyl acrylate, ethyl acrylate, and butyl acrylate; methacrylic acid; Methyl acid, methacryl Ethyl, can be given one or more methacrylic acid esters such as butyl methacrylate.

  Moreover, as an anionic polymerization method to be used, it can carry out by a well-known polymerization method, for example, any of a block polymerization method, a solution polymerization method, etc. are employable.

  Examples of the polymerization initiator used in the anionic polymerization method include organic lithium such as n-butyllithium, s-butyllithium, and t-butyllithium, and a Grignard reagent.

  And there is no restriction | limiting in particular as a solvent which can be used in a solution polymerization method, For example, aromatic solvents, such as benzene, toluene, xylene; Hexane; Cyclohexane; Dioxane; Tetrahydrofuran (THF); Acetone; A solvent is also mentioned.

  Moreover, it is preferable to perform polymerization temperature in the range of -78-150 degreeC generally when performing anionic polymerization.

  In the optical compensation film of the present invention (film (A)), the three-dimensional refractive index of the film is nx as the refractive index in the fast axis direction in the film plane, and ny (here, the refractive index in the film plane direction orthogonal thereto) Where nx and ny are equal, any biaxial refractive index orthogonal to each other), and when the refractive index in the vertical direction outside the film plane is nz, ny> nx ≧ nz, and the film thickness is d In this case, an optical compensation film (hereinafter referred to as film (C)) composed of a film (B) having an in-plane retardation (Re) of 50 nm or more measured at a wavelength of 550 nm represented by the following formula (2). be able to.

Re = (ny−nx) × d (2)
As the film (B), for example, a film having a three-dimensional refractive index of ny> nx ≧ nz can be obtained by uniaxially stretching a polymer having positive birefringence.

  The polymer of the film (B) is not particularly limited as long as it is a polymer having positive birefringence. Preferred examples from the viewpoint of heat resistance and transparency include polycarbonate resin, polyether sulfone resin, cyclic Examples thereof include polyolefin resins and N-substituted maleimide / olefin copolymers.

  The film in-plane retardation (Re) of the film (B) is preferably 50 nm or more, particularly preferably 100 nm or more, and further preferably 120 nm or more.

  In the film (C), the three-dimensional refractive index of the film is nx as the refractive index in the fast axis direction in the film plane, and ny (where nx and ny are equal) in the film in-plane direction perpendicular thereto. In this case, when the refractive index in the perpendicular direction outside the film plane is nz and the film thickness is d, the orientation parameter (Nz) represented by the following formula (3) is −0. .1 to 0.95 is preferable, and in particular, when a viewing angle compensation film for STN-LCD, IPS-LCD, reflective LCD, and transflective LCD is used, Nz is preferably 0.40 to 0.60. In particular, 0.45 to 0.55 is preferable. When a viewing angle compensation film for a polarizing plate is used, Nz is preferably −0.10 to 0.10, particularly −0.05 to 0.05, and more preferably 0. ~ 0.05 is preferred.

Nz = (ny−nz) / (ny−nx) (3)
Further, in the film (C), the in-plane retardation (Re) represented by the formula (2) is preferably from 50 to 500 nm, particularly preferably from 100 to 500 nm, and further from 130 to about 1/4 wavelength plate. In the case of 140 nm and a half-wave plate, 270 to 280 nm is preferable.

  There is no restriction | limiting in particular as a manufacturing method of the film which consists of (beta) -substituted acrylic ester resin in the optical compensation film of this invention, For example, it can manufacture by methods, such as a solution cast method and a melt cast method.

  The solution casting method is a method in which a solution obtained by dissolving a β-substituted acrylate ester resin in a solvent (hereinafter referred to as a dope) is cast on a support substrate, and then the solvent is removed by heating or the like to obtain a film. . In this case, as a method for casting the dope on the support substrate, for example, a T-die method, a doctor blade method, a bar coater method, a roll coater method, a lip coater method or the like is used. Examples of the support substrate used include a glass substrate; a metal substrate such as stainless steel or ferrotype; and a plastic substrate such as polyethylene terephthalate. The film made of the β-substituted acrylate ester resin thus obtained can be peeled off from the support substrate, and can be peeled off when a glass substrate or a plastic substrate is used as the support substrate. It can also be used as it is as a laminate.

  In the solution casting method, when forming a film having high transparency and excellent thickness accuracy and surface smoothness, the solution viscosity of the dope is a very important factor, and preferably 700 to 30000 cps. It is preferable that it is 1000-10000 cps. The melt casting method is a molding method in which a β-substituted acrylate resin is melted in an extruder and extruded from a slit of a T die into a film shape, and then cooled and cooled with a roll or air.

  The production method of the optical compensation film comprising the optical compensation film (film (A)) and the film (B) preferably used for the optical compensation film of the present invention is not particularly limited. For example, from a β-substituted acrylate ester resin A method of laminating an unstretched film and a uniaxially stretched film having a positive birefringence (hereinafter referred to as production method 1), a β-substituted acrylate resin based on a film having a positive birefringence It can manufacture by the method (henceforth manufacturing method 2) etc. which apply | coat to a uniaxially stretched film.

  Examples of the film having positive birefringence in Production Methods 1 and 2 include films made of polycarbonate resin, polyether sulfone resin, cyclic polyolefin resin, N-substituted maleimide / olefin copolymer, and the like. The film having positive birefringence is uniaxially stretched, for example, at a temperature of 150 to 200 ° C. and a stretching speed of 10 to 30 mm / min. A uniaxially stretched film that is stretched under conditions of a stretching ratio of 30 to 70% and has positive birefringence can be produced.

  In the production method 1, an optical compensation film can be produced by bonding a uniaxially stretched film having positive birefringence to an unstretched film made of a β-substituted acrylate resin. As a bonding method in this case, it can be manufactured, for example, by a continuous roll-to-roll process, and can be bonded using a known adhesive.

  In the production method 2, an optical compensation film can be produced by applying an unstretched film made of a β-substituted acrylate resin to a uniaxially stretched film having positive birefringence. In this case, the coating method is a method in which a solution (coating solution) in which a β-substituted acrylate ester resin is dissolved in a solvent is coated on the film, and then the solvent is removed by heating or the like. As a coating method at that time, for example, a doctor blade method, a bar coater method, a gravure coater method, a slot die coater method, a lip coater method, a comma coater method or the like is used. Industrially, the gravure coater method is generally used for thin film coating, and the comma coater method is generally used for thick film coating. In solution coating, in order to perform coating with high transparency and excellent thickness accuracy and surface smoothness, the coating solution viscosity is a very important factor, preferably 10 to 10000 cps, particularly 10 to 5000 cps. It is preferable. The coating thickness of the β-substituted acrylate resin in the present invention is determined by the retardation in the film thickness direction, preferably 1 to 200 μm, and particularly preferably 10 to 100 μm after drying. Further, the surface of the film (B) can be subjected to an easy adhesion treatment in advance.

  Moreover, it can also laminate | stack with the optical compensation films of this invention, or another optical compensation film.

  The optical compensation film of the present invention is preferably blended with a plasticizer because the optical compensation film is more excellent in elongation. The plasticizer is not particularly limited. For example, tricresyl phosphate, tri (2-ethylhexyl phosphate), trixylenyl phosphate, bisphenol A bis (diphenyl phosphate), triphenyl phosphate, 2-ethylhexyl diphenyl phosphate, cresyl Phosphate ester plasticizers such as diphenyl phosphate, tricresyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tris (butoxyethyl) phosphate; tributyl trimellitate, tri-normal hexyl trimellitate, tri (2-ethylhexyl) ) Trimerits such as trimellitate, tri-normal octyl trimellitate, tri-isooctyl trimellitate, tri-isodecyl trimellitate Ester plasticizers: tri (2-ethylhexyl) pyromellitate, tetrabutyl pyromellitate, tetra-normal hexyl pyromellitate, tetra (2-ethylhexyl) pyromellitate, tetra-normal octyl pyromellitate, tetra-isooctyl pyromellitate And pyromellitic acid ester plasticizers such as tetra-isodecyl pyromellitate.

  The optical compensation film of the present invention preferably contains an antioxidant in order to improve the thermal stability. Examples of the antioxidant include hindered phenol antioxidants, phosphorus antioxidants, and other antioxidants. These antioxidants may be used alone or in combination. And since an antioxidant effect | action improves synergistically, it is preferable to use together and use a hindered phenolic antioxidant and phosphorus antioxidant, for example, 100 weight part of hindered phenolic antioxidants in that case It is particularly preferable to use a phosphorous antioxidant mixed in an amount of 100 to 500 parts by weight. Moreover, as an addition amount of antioxidant, 0.01-10 weight part is preferable with respect to 100 weight part of (beta) -acrylic acid ester-type resin, and it is preferable that it is especially the range of 0.5-1 weight part.

  Furthermore, as an ultraviolet absorber, for example, an ultraviolet absorber such as benzotriazole, benzophenone, triazine, or benzoate may be blended as necessary.

  In the optical compensation film of the present invention, other polymers, surfactants, polymer electrolytes, conductive complexes, inorganic fillers, pigments, dyes, antistatic agents, antiblocking agents, lubricants, etc. are within the scope of the invention. May be blended.

  The optical compensation film of the present invention can be laminated with a polarizing plate and used as a circular or elliptical polarizing plate. Moreover, it is useful as an optical compensation film such as a viewing angle improving film or a color compensation film of a liquid crystal display element, and a circularly polarizing plate can also be used as an antireflection film. Furthermore, it can also be used as an optical compensation film that improves the viewing angle characteristics of a brightness enhancement film used in a liquid crystal display.

  According to the present invention, an optical compensation film effective for improving the contrast and viewing angle characteristics of a liquid crystal display, particularly an optical compensation having an optical compensation characteristic with an orientation parameter Nz calculated from a three-dimensional refractive index of −0.05 to 0.9. A film can be provided.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

~ Measurement of number average molecular weight ~
Using gel permeation chromatography (GPC) (trade name HLC-802A, manufactured by Tosoh Corporation), dimethylformamide (DMF) was used as a solvent to obtain a standard polystyrene equivalent value.

~ Measurement of glass transition temperature ~
A differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd., trade name DSC2000) was used and the temperature was 10 ° C / min. It measured at the temperature increase rate of.

~ Measurement of light transmittance ~
Based on JIS K 7361-1 (1997 edition), the light transmittance was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

~ Measurement of haze ~
Based on JIS K7136 (2000 version), the haze was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

~ Measurement of three-dimensional refractive index, out-of-plane retardation of film, in-plane retardation of film and orientation parameter ~
The three-dimensional refractive index was measured by changing the elevation angle using a sample tilt type automatic birefringence meter (trade name KOBRA-WR, manufactured by Oji Scientific Instruments). Furthermore, the out-of-plane retardation (Rth), in-plane retardation (Re), and orientation parameter (Nz) were calculated from the three-dimensional refractive index.

Synthesis Example 1 (Production Example of β-Substituted Acrylic Ester Resin (Crotonic Acid Ester Polymer))
In a 3 liter reactor, 524 g of crotonic acid-t-butyl and 5 g of s-butyllithium as a polymerization initiator and 1 L of THF were charged, and an anionic polymerization reaction was carried out at a polymerization temperature of -78 ° C. and a polymerization time of 3 hours. After the completion of the polymerization, the obtained solution was precipitated in methanol, and the obtained polymer was filtered and dried at 80 ° C. to obtain a crotonic acid-t-butyl polymer. The number average molecular weight of the obtained crotonic acid-t-butyl polymer was 40,000.

Example 1
The crotonic acid-t-butyl polymer obtained in Synthesis Example 1 was dissolved in toluene to form a 18% solution, and tris (100% by weight of crotonic acid-t-butyl polymer was used as a hindered phenol antioxidant. 2,5-di-tert-butylphenyl) phosphite 0.35 parts by weight and pentaerythritol-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) as a phosphorus-based antioxidant After adding 0.15 part by weight and 1 part by weight of 2- (2H-benzotriazol-2-yl) -p-cresol as an ultraviolet absorber, it is cast on a support substrate of a solution casting apparatus by a T-die method, After drying at 80 ° C., 120 ° C. and 150 ° C. for 15 minutes, a film having a width of 200 mm and a thickness of 44 μm was obtained.

  The obtained film had a light transmittance of 91% and a haze of 0.3, and the three-dimensional refractive index of the film was nx = 1.4885, ny = 1.4885, nz = 1.4901 (nz> ny = nx). there were. The obtained film had an in-plane retardation of 0 nm and an out-of-plane retardation of -70 nm. Further, the wavelength dependence (R450 / R550) of the retardation outside the film surface was 1.03.

  From these results, the obtained film was suitable for an optical compensation film because it had a large refractive index in the thickness direction and a small wavelength dependency.

Example 2
A film having a width of 200 mm and a thickness of 70 μm was obtained in the same manner as in Example 1. The obtained film had a light transmittance of 92% and a haze of 0.3, and the three-dimensional refractive index of the film was x = 1.4885, ny = 1.4885, and nz = 1.4901 (nz> ny = nx). there were. The obtained film had an in-plane retardation of 0 nm and an out-of-plane retardation of -112 nm. Moreover, the wavelength dependence (R450 / R550) of the retardation outside the film surface was 1.02.

  From these results, the obtained film was suitable for an optical compensation film because it had a large refractive index in the thickness direction and a small wavelength dependency.

Comparative Example 1
A methylene chloride solution containing 25% by weight of polycarbonate (trade name Panlite L1225, manufactured by Teijin Ltd.) and 75% by weight of methylene chloride was prepared, and the methylene chloride solution was cast on a PET film to volatilize the solvent. The film was obtained by solidifying and peeling. The peeled film thus obtained was further dried at 100 ° C. for 4 hours, from 110 ° C. to 130 ° C. at 10 ° C. intervals for 1 hour, respectively, and then dried at 120 ° C. for 4 hours in a vacuum drier for about 90 μm The film (henceforth a film (1)) which has thickness of this was obtained.

  The obtained film (1) had a glass transition temperature (Tg) of 150 ° C. The light transmittance was 90.0%, the haze was 0.6, and the three-dimensional refractive index of the film was nx = 1.5830, ny = 1.5830, and nz = 1.5830 (nz = ny = nx). The in-plane and out-of-plane retardation of the obtained film was 0 nm.

  From these results, the obtained film did not have a large refractive index in the thickness direction and was not suitable for an optical compensation film.

Example 3
The film obtained in Comparative Example 1 was cut into a square of 50 mm each, and the temperature was 170 ° C. and the stretching speed was 10 mm / min. With a biaxial stretching apparatus (manufactured by Imoto Seisakusho). Under the conditions, free-width uniaxial stretching was performed and stretching was + 50%. The stretched film (referred to as film 1 (a)) exhibited positive birefringence. The three-dimensional refractive index of the obtained film 1 (a) is nx = 1.5826, ny = 1.5842, nz = 1.5822 (ny>nx> nz), and the in-plane retardation (Re) is It was 125 nm.

  Furthermore, the film produced in Example 1 was bonded onto the stretched film 1 (a) to obtain an optical compensation film. The three-dimensional refractive index of the optical compensation film is nx = 1.5594, ny = 1.5607, nz = 1.5600, the in-plane retardation Re = (nx−ny) × d is 125 nm, and the orientation parameter Nz is 0. .5.

  From these results, the obtained film was suitable for an optical compensation film.

Example 4
The film obtained in Comparative Example 1 was cut into a square of 50 mm each, and the temperature was 170 ° C. and the stretching speed was 10 mm / min. With a biaxial stretching apparatus (manufactured by Imoto Seisakusho). The film was subjected to free width uniaxial stretching under the conditions of + 33% stretching. The stretched film (referred to as film 1 (b)) exhibited positive birefringence.

  The obtained film 1 (b) has a three-dimensional refractive index of nx = 1.5826, ny = 1.5839, nz = 1.5825 (ny> nx> nz), and the in-plane retardation (Re) of the film is It was 113 nm.

  Furthermore, the film produced in Example 2 was bonded onto the stretched film 1 (b) to obtain an optical compensation film. The three-dimensional refractive index of the optical compensation film is nx = 1.5362, ny = 1.5370, nz = 1.5370, the in-plane retardation Re = (nx−ny) × d is 112 nm, and the orientation parameter Nz is 0. Met.

Example 5
The crotonic acid ester copolymer obtained in Synthesis Example 1 was dissolved in DMF to form a 20% solution, which was used as a coating solution.

  The film obtained in Comparative Example 1 was cut into a square of 50 mm each, and the temperature was 170 ° C. and the stretching speed was 10 mm / min. With a biaxial stretching apparatus (manufactured by Imoto Seisakusho). Under the conditions, free-width uniaxial stretching was performed and stretching was + 50%. The stretched film (referred to as film 1 (a)) exhibited positive birefringence. The three-dimensional refractive index of the obtained film 1 (a) is nx = 1.5826, ny = 1.5842, nz = 1.5822 (ny> nx> nz), and the in-plane retardation (Re) is It was 125 nm.

  Furthermore, it applied so that the thickness after drying might be set to 40 micrometers by the doctor blade method using the coating solution on this stretched film 1 (a), and the optical compensation film was obtained. (Nx = 1.5594, ny = 1.5607, nz = 1.5600) In-plane retardation Re = (nx−ny) × d is 125 nm, and the orientation parameter Nz is 0.5. Films with similar properties could be obtained by coating.

Comparative Example 2
The film obtained in Comparative Example 1 was cut into a square of 50 mm, and the temperature was 165 ° C. and the stretching speed was 10 mm / min. Using a biaxial stretching apparatus (manufactured by Imoto Seisakusho). Under the conditions, free-width uniaxial stretching was performed and stretching was + 50%. The stretched film (referred to as film 1 (c)) exhibited positive birefringence, and the film in-plane retardation Re = (nx−ny) × d was 263 nm. The three-dimensional refractive index was nx = 1.5820, ny = 1.8551, nz = 1.5819 (nz <nx <ny), and the orientation parameter Nz was 1.02.

  From these results, the obtained film was not suitable for an optical compensation film.

Comparative Example 3
Under a nitrogen atmosphere, 9.0 g of poly (2-vinylnaphthalene) (Aldrich, weight average molecular weight: 175,000) was added to 49.6 g of methylene chloride using a small disper and dissolved at 2500 rpm for 1 hour at room temperature. did. The resulting polymer solution was filtered using a 25 μm filter. Next, this polymer solution was applied onto a 188 μm-thick PET film by a bar coater method, and then air-dried overnight under a nitrogen stream to produce a poly (2-vinylnaphthalene) film on the PET substrate. .

  A part of this poly (2-vinylnaphthalene) film was peeled off from the PET substrate, and the film thickness and optical properties were measured. The film thickness after drying was 58 μm. During peeling, the film was brittle and partially damaged.

  The three-dimensional refractive index of the obtained film was nx = 1.6557, ny = 1.6558, nz = 1.6578. The out-of-plane phase difference (Rth) was −120.2 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was 1.12.

  From these results, although the obtained film had a relationship of nz> ny ≧ nx, it was not suitable for an optical compensation film because of its large wavelength dependence.

Comparative Example 4
Using a small disper, add 13.2 g of poly (9-vinylcarbazole) (Aldrich, weight average molecular weight: about 1.1 million) to N-methyl-2-pyrrolidone (NMP) and dissolve at 6000 rpm for 1 hour at room temperature did. The resulting polymer solution was filtered using a 25 μm filter. Next, this polymer solution was applied onto a PET film having a thickness of 188 μm by the bar coater method, and then dried with hot air at 60 ° C. for 1 hour and at 100 ° C. for 15 minutes, so that the poly (9- Vinylcarbazole) film was prepared.

  A part of this poly (9-vinylcarbazole) film was peeled off from the PET substrate, and the film thickness and optical characteristics were measured. The film thickness after drying was 33 μm. During peeling, the film was brittle and partially damaged.

  The three-dimensional refractive index of the obtained film was nx = 1.68819, ny = 1.6820, and nz = 1.6926. The out-of-plane phase difference (Rth) was −350.0 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was 1.14.

  From these results, although the obtained film had a relationship of nz> ny ≧ nx, it was not suitable for an optical compensation film because of its large wavelength dependence.

Change in refractive index ellipsoid by stretching

Explanation of symbols

nx: Refractive index in the fast axis direction in the film plane.
ny: Refractive index in the film in-plane direction orthogonal to nx.
nz: The refractive index in the vertical direction outside the film surface.

Claims (13)

It is a film made of a β-substituted acrylate resin, and the three-dimensional refractive index of the film is nx as the refractive index in the fast axis direction in the film plane, and ny ( Here, when nx and ny are equal, the refractive index of any two axes orthogonal to each other), and when the refractive index in the vertical direction outside the film surface is nz, the relationship is nz> ny ≧ nx, measured at a wavelength of 450 nm. The optical compensation film, wherein the ratio of the retardation measured at a wavelength of 550 nm (R450 / R550) is 1.1 or less. 2. The optical compensation film according to claim 1, wherein the β-substituted acrylate resin is composed of 50 mol% or more of a β-substituted acrylate residue unit represented by the general formula (a).

(Here, R ₁ represents an alkyl group having 1 to 4 carbon atoms and a halogen group, and R ₂ represents a linear, branched alkyl group or cyclic alkyl group having 1 to 12 carbon atoms.) 3. The optical compensation film according to claim 1, wherein when the thickness of the film is d, an out-of-plane retardation (Rth) represented by the following formula (1) is −30 to −2000 nm.
Rth = [(nx + ny) / 2−nz] × d (1) The optical compensation film (A) according to any one of claims 1 to 3, and the three-dimensional refractive index of the film is nx the refractive index in the fast axis direction in the film plane, and the refractive index in the film in-plane direction perpendicular thereto Ny (where nx and ny are equal, any biaxial refractive index perpendicular to each other), and when the refractive index in the vertical direction outside the film plane is nz, there is a relationship of ny> nx ≧ nz, An optical compensation film comprising a film (B) having an in-plane retardation (Re) of 50 nm or more measured at a wavelength of 550 nm represented by the following formula (2) when the thickness of the film is d.
Re = (ny−nx) × d (2) The three-dimensional refractive index of the film is nx as the refractive index in the fast axis direction in the film plane, and ny as the refractive index in the film in-plane direction perpendicular thereto (where nx and ny are equal, any two axes perpendicular to each other) (Refractive index), when the refractive index in the vertical direction out of the film plane is nz and the film thickness is d, the orientation parameter (Nz) represented by the following formula (3) is −0.1 to 0.95, and The optical compensation film according to claim 4, wherein a film in-plane retardation (Re) represented by the formula (1) is 50 to 1000 nm.
Nz = (ny−nz) / (ny−nx) (3) 6. The optical compensation film according to claim 4, wherein the orientation parameter (Nz) is 0.40 to 0.60, and the in-plane retardation (Re) is 50 to 500 nm. 6. The optical compensation film according to claim 4, wherein the orientation parameter (Nz) is -0.05 to 0.05, and the in-plane retardation (Re) is 50 to 500 nm. The optical compensation film according to any one of claims 4 to 7, wherein the film (B) is a uniaxially stretched film having positive birefringence. The optical compensation according to any one of claims 4 to 8, wherein the film (B) is a film comprising a polycarbonate resin, a polyether sulfone resin, a cyclic polyolefin resin, or an N-substituted maleimide / olefin copolymer. the film. The film in-plane retardation (Re) of the film (A) measured at a wavelength of 550 nm represented by the above formula (2) when the thickness of the film (A) is d is less than 50 nm. The optical compensation film according to any one of 4 to 9. 11. The optical compensation film according to claim 4, wherein an unstretched film made of a β-substituted acrylate resin and a uniaxially stretched film having positive birefringence are bonded. Production method. The method for producing an optical compensation film according to claim 4, wherein a β-substituted acrylate resin is applied to a uniaxially stretched film having positive birefringence. A liquid crystal display element comprising the optical compensation film according to claim 1.

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