JP2006337569A - Polarizer protecting film, and polarizing plate and liquid crystal display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizer protecting film having the function of a retardation film, easy to produce, excellent in moisture permeability, and having a sufficiently low photoelastic coefficient, and to provide a polarizing plate and a liquid crystal display device using the polarizer protecting film. <P>SOLUTION: The polarizer protecting film having the function of a retardation film comprises a thermoplastic resin including a glutarimide unit, a (meth)acrylic ester unit and an aromatic vinyl unit, wherein a retardation Rth in a thickness direction of the film is Rth<-20 nm. The polarizing plate and the liquid crystal display device using the polarizer protecting film are also provided. The polarizer protecting film is easy to produce, excels in moisture permeability, has a sufficiently low photoelastic coefficient, and is suitable for use as a polarizer protecting film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarizer protective film, a polarizing plate using the same, and a liquid crystal display device.

  The linear polarizing plate is a material having a function of transmitting only linearly polarized light having a specific vibration direction among light passing therethrough and shielding other linearly polarized light. For example, as one of components constituting a liquid crystal display device Widely used. As such a linearly polarizing plate, one having a configuration in which a polarizer film and a polarizer protective film are laminated is generally used.

  The polarizer film is a film having a function of transmitting only linearly polarized light having a specific vibration direction. For example, a polyvinyl alcohol (hereinafter referred to as PVA) film is stretched and dyed with iodine or a dichroic dye. The film is generally used.

  The polarizer protective film has a function of holding the polarizer film and imparting practical strength to the entire polarizing plate. For example, a triacetyl cellulose (hereinafter referred to as TAC) film is generally used. ing.

  In the polarizer protective film, a film having an unnecessary retardation is generally not preferable. This is because even if the polarizer film has a highly accurate linear polarization function, the retardation of the polarizer protective film and the optical axis shift give the elliptically polarized light to the linearly polarized light that has passed through the polarizer film. Because it will end up.

  The phase difference of the film is determined by taking the direction in which the in-plane refractive index is maximum as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the film as the Z axis, and the refractive indexes in the respective axial directions as nx, ny, When nz and the thickness of the film are d, the in-plane retardation Re = (nx−ny) × d and the thickness direction retardation Rth = {(nx + ny) / 2−nz} × d. The aforementioned TAC film basically has a small in-plane retardation. However, the TAC film is a film that easily generates a phase difference due to the action of external stress, and is a film that has a relatively large thickness direction retardation. For this reason, particularly in a large-sized liquid crystal display device, there is a problem that the contrast in the peripheral portion is lowered.

Attempts have been made to use a film material having a smaller photoelastic coefficient than the TAC film as a polarizer protective film. For example (see, for example, Patent Document 1), the moisture permeability at 80 ° C. and 90% RH is 20 g · mm / m ² · 24 hr or less and the photoelastic coefficient is 1 × 10 ⁻¹⁰ cm ² / N or less. A protective film is disclosed.

  On the other hand, the liquid crystal display device has a TN mode and an STN mode that have been conventionally used as a liquid crystal drive mode. However, due to the recent increase in the size of the liquid crystal screen, there is less light leakage and color change during black display. A liquid crystal display device having a high viewing angle characteristic is required, and a VA mode and an IPS mode have been developed. In particular, in the IPS mode, since the liquid crystal molecules have a homogeneous alignment substantially parallel to the substrate surface in the non-driven state, the light passes with almost no change in the polarization state, and as a result, polarizing plates are arranged above and below the substrate. Thus, almost complete black display is possible in the non-driven state.

  However, in the IPS mode, almost complete black display is possible in the normal direction of the panel, but when the panel is observed from a direction deviated from the normal direction, it is deviated from the optical axis direction of the polarizing plate arranged above and below the liquid crystal cell. In the direction, light leakage is unavoidable due to the characteristics of the polarizing plate. As a result, there is a problem that the viewing angle is narrowed.

  In order to solve this problem, a polarizing plate is used in which a geometrical axis shift of the polarizing plate generated when observed from an oblique direction is compensated by a retardation film. A polarizing plate capable of obtaining such an effect is disclosed (see Patent Document 2). Moreover, the optical film and polarizing optical film which improved this are disclosed (refer patent document 3).

However, in order to obtain the optical film as described above, it is necessary to control the refractive index in the three-dimensional direction. Especially for controlling the refractive index in the thickness direction, it is necessary to go through a complicated stretching process, which is costly. Further, when such a function of the optical film is integrated with the polarizer protective film, the polarizer is protected. There is a problem that the film having characteristics as a film (low moisture permeability, low photoelasticity, etc.) is limited.
JP-A-7-77608 JP-A-4-305602 JP-A-2005-31621

  The present invention has been made in view of the above problems of the prior art, and is a polarizer protective film that is easy to manufacture, has excellent moisture permeability, has a sufficiently small photoelastic coefficient, and has a retardation film function. And a polarizing plate and a liquid crystal display device using the same.

  The present invention provides a polarizer protective film that is easy to manufacture, has excellent moisture permeability, has a sufficiently small photoelastic coefficient, and has a retardation film function. This is based on the finding that it is extremely effective to use the following film.

  That is, the present invention comprises a thermoplastic resin containing repeating units represented by the following general formulas (1), (2), and (3), and the thickness direction retardation Rth of the film is Rth < The polarizer protective film characterized by being -20 nm, the polarizing plate using the same, and a liquid crystal display device were provided.

（ここで、Ｒ¹およびＲ²は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ³は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)

（ここで、Ｒ⁴およびＲ⁵は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ⁶は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)

（ここで、Ｒ⁷は、水素または炭素数１〜８のアルキル基を示し、Ｒ⁸は、炭素数６〜１０のアリール基を示す。）

(Here, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.)

  According to the present invention, it is possible to provide a polarizer protective film that is easy to manufacture, excellent in moisture permeability, has a sufficiently small photoelastic coefficient, and has a retardation film function. In addition, by using the polarizer protective film of the present invention, a large liquid crystal display device, particularly an IPS mode liquid crystal display device, suppresses light leakage due to the geometrical axis misalignment of the polarizing plate and realizes a good display. It becomes possible to do.

  The polarizer protective film of the present invention comprises a thermoplastic resin containing repeating units represented by the following general formulas (1), (2), and (3), and has a thickness direction retardation Rth of the film. Is characterized in that Rth <−20 nm.

（ここで、Ｒ¹およびＲ²は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ³は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)

（ここで、Ｒ⁴およびＲ⁵は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ⁶は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)

（ここで、Ｒ⁷は、水素または炭素数１〜８のアルキル基を示し、Ｒ⁸は、炭素数６〜１０のアリール基を示す。）
本発明で使用する熱可塑性樹脂を構成する、第一の構成単位は、下記一般式（１）で表される（以下、グルタルイミド単位と言うことがある）。

(Here, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.)
The first structural unit constituting the thermoplastic resin used in the present invention is represented by the following general formula (1) (hereinafter sometimes referred to as a glutarimide unit).

（ここで、Ｒ¹およびＲ²は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ³は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）
好ましいグルタルイミド単位としては、Ｒ¹、Ｒ²が水素またはメチル基であり、Ｒ³が水素、メチル基、またはシクロヘキシル基である。Ｒ¹がメチル基であり、Ｒ²が水素であり、Ｒ³がメチル基である場合が、特に好ましい。

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)
As a preferred glutarimide unit, R ¹ and R ² are hydrogen or a methyl group, and R ³ is hydrogen, a methyl group, or a cyclohexyl group. The case where R ¹ is a methyl group, R ² is hydrogen, and R ³ is a methyl group is particularly preferred.

The glutarimide unit may be a single type or may include a plurality of types in which R ¹ , R ² , and R ³ are different.

  The second structural unit constituting the thermoplastic resin used in the present invention is represented by the following general formula (2) (hereinafter referred to as (meth) acrylic acid ester or (meth) acrylic acid structural unit). is there).

（ここで、Ｒ⁴およびＲ⁵は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ⁶は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）
好ましい（メタ）アクリル酸エステル又は（メタ）アクリル酸構成単位としては、アクリル酸メチル、アクリル酸エチル、メタクリル酸メチル、メタクリル酸エチル等が挙げられる。これらの中でメタクリル酸メチルが特に好ましい。

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)
Preferable (meth) acrylic acid ester or (meth) acrylic acid structural unit includes methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and the like. Of these, methyl methacrylate is particularly preferred.

These second structural units may be of a single type, and may include a plurality of types in which R ⁴ , R ⁵ , and R ⁶ are different.

  The third structural unit constituting the thermoplastic resin of the present invention is represented by the following general formula (3) (hereinafter sometimes referred to as an aromatic vinyl unit).

（ここで、Ｒ⁷は、水素または炭素数１〜８のアルキル基を示し、Ｒ⁸は、炭素数６〜１０のアリール基を示す。）
好ましい芳香族ビニル構成単位としては、スチレン、α−メチルスチレン等が挙げられる。これらの中でスチレンが特に好ましい。

(Here, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.)
Preferred aromatic vinyl structural units include styrene, α-methylstyrene, and the like. Of these, styrene is particularly preferred.

These third structural units may be of a single type or may include a plurality of types in which R ⁷ and R ⁸ are different.

  The content of the glutarimide unit represented by the general formula (1) in the thermoplastic resin is preferably 20% by weight or more of the thermoplastic resin. The preferable content of the glutarimide unit is 20% to 95% by weight, more preferably 40 to 90% by weight, and still more preferably 50 to 80% by weight. When a glutarimide unit is smaller than this range, the heat resistance of the film obtained may be insufficient, or transparency may be impaired. On the other hand, if it exceeds this range, the heat resistance is unnecessarily increased and it becomes difficult to form a film, the mechanical strength of the resulting film becomes extremely brittle, and the transparency may be impaired.

  The content of the aromatic vinyl unit represented by the general formula (3) in the thermoplastic resin is preferably 10% by weight or more based on the total repeating unit of the thermoplastic resin. The preferred content of the aromatic vinyl unit is 10 to 50% by weight, more preferably 15 to 40% by weight, and still more preferably 20 to 40% by weight. When the aromatic vinyl unit is larger than this range, the heat resistance of the resulting film may be insufficient and the photoelastic coefficient may be increased. When the aromatic vinyl unit is smaller than this range, the mechanical strength of the film may be decreased. . Further, when the aromatic vinyl unit is out of this range, it is difficult to obtain a retardation value that satisfies the thickness direction retardation Rth <−20 nm.

  The polarizer protective film of the present invention has a thickness direction retardation Rth <−20 nm. The direction in which the in-plane refractive index is maximum is the X-axis, the direction perpendicular to the X-axis is the Y-axis, the thickness direction of the film is the Z-axis, and the refractive indexes in the respective axial directions are nx, ny, nz, and the film thickness. If the thickness is d, the in-plane retardation Re = (nx−ny) × d and the thickness direction retardation Rth = {(nx + ny) / 2−nz} × d. The polarizer protective film of the present invention has a thickness direction retardation Rth <−20 nm, preferably Rth <−50 nm. When a polarizer protective film having a retardation value larger than the above range is used as a polarizing plate, the function as a retardation film is not achieved, and problems such as light leakage occur in a liquid crystal display device.

  The thermoplastic resin used in the present invention may contain the fourth structural unit as long as the thickness direction retardation Rth <−20 nm of the film is satisfied. As the fourth structural unit, nitrile monomers such as acrylonitrile and methacrylonitrile, maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide can be used.

  The thermoplastic resin used in the present invention may be a linear (linear) polymer as long as the thickness direction retardation Rth <−20 nm of the film is satisfied, or a block polymer, a core-shell polymer, a branched polymer, a ladder polymer, and a crosslinked polymer. It does not matter. There is no problem even if the block polymer is A-B type, A-B-C type, A-B-A type, or any other type. There is no problem even if the core-shell polymer is composed of only one core and only one shell, or each layer is a multilayer.

  The thermoplastic resin used in the present invention is a resin having a unit that can be imidized in the same manner as the glutarimide resin described in U.S. Pat. No. 3,284,425, U.S. Pat. It is obtained by imidizing a resin having a unit capable of imidization with ammonia or a substituted amine, using a resin obtained using methyl methacrylate as a main raw material.

  The thermoplastic resin used in the present invention can be obtained, for example, by imidizing a copolymer of methyl methacrylate and styrene (hereinafter referred to as MS resin) by the above method. In the present invention, it is preferable to imidize MS resin having a styrene content of 10 wt% to 50 wt%, more preferably imidizing MS resin having a styrene content of 15 to 40 wt%, and a styrene content of 20 to 30 wt%. It is more preferred to imidize the% MS resin.

The thermoplastic resin used in the present invention preferably has a weight average molecular weight of 1 × 10 ⁴ to 5 × 10 ⁵ . If the weight average molecular weight is less than the above value, the mechanical strength in the case of film is insufficient, and if it is more than the above value, the viscosity at the time of melting may be high, and the productivity of the film may be reduced. is there.

  The glass transition temperature of the thermoplastic resin used in the present invention is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 130 ° C. or higher.

  If necessary, other thermoplastic resins can be added to the thermoplastic resin used in the present invention.

The thermoplastic resin used in the present invention preferably has a small photoelastic coefficient. The photoelastic coefficient of the thermoplastic resin used in the present invention is preferably 20 × 10 ⁻¹² m ² / N or less, more preferably 10 × 10 ⁻¹² m ² / N or less, and more preferably 5 × 10. More preferably, it is ^-12 m ² / N or less. When the absolute value of the photoelastic coefficient is larger than 20 × 10 ⁻¹² m ² / N, optical distortion occurs due to stress, and light leakage tends to occur. In particular, the tendency becomes remarkable in a high temperature and high humidity environment.

The photoelastic coefficient means that when an external force is applied to an isotropic solid to cause stress (ΔF), it temporarily exhibits optical anisotropy and exhibits birefringence (Δn). The ratio of stress to birefringence is called the photoelastic coefficient (c), and the following formula is given: c = Δn / ΔF
Indicated by

  As a method of forming the thermoplastic resin into the form of the polarizer protective film of the present invention, any conventionally known method can be used. Examples thereof include a solution casting method and a melt extrusion method. Any of them can be adopted. The solution casting method is suitable for the production of a film with little resin deterioration and good surface properties, and the melt molding method can obtain a film with high productivity. As a solvent for the solution casting method, methylene chloride or the like can be preferably used. Examples of the melt molding method include a melt extrusion method and an inflation method.

  The thickness of the polarizer protective film of the present invention is preferably 20 μm to 300 μm, more preferably 30 μm to 200 μm. More preferably, it is 40 μm to 100 μm. The thickness unevenness of the film is preferably 10% or less, more preferably 5% or less of the average thickness.

  The light transmittance of the polarizer protective film of the present invention is preferably 85% or more, more preferably 88% or more, and further preferably 90% or more. The turbidity of the film is preferably 2% or less, more preferably 1% or less, and still more preferably 0.5% or less.

  In the present specification, for convenience of explanation, a film after the thermoplastic resin is formed into a film and before being stretched may be referred to as a “raw material film”.

  The raw material film can be a polarizer protective film as it is without being stretched. However, in the production of the polarizer protective film of the present invention, after forming the film by the above-mentioned method, it is uniaxially stretched or biaxially stretched. It is preferable to manufacture a film having a predetermined thickness. By stretching, the mechanical properties of the film are further improved, and a specific retardation can be imparted. If an example of an embodiment is given, after manufacturing a 150-micrometer-thick raw material film by melt extrusion molding, a 40-micrometer-thick film can be manufactured by vertical and horizontal biaxial stretching.

  The film may be stretched continuously immediately after forming the raw material film. Here, the state of the “raw material film” may exist only momentarily. In the case where it exists only momentarily, that momentary state after the film is formed and then stretched is referred to as a raw material film. In addition, the raw material film only needs to be in a film shape sufficient to be stretched thereafter, and does not need to be in a complete film state. Of course, it does not have the performance as a completed film. Also good. Moreover, after shaping | molding a raw material film as needed, you may store or move a film once, and may extend a film after that. As a method of stretching the raw material film, any conventionally known stretching method can be adopted. Specifically, for example, there are longitudinal stretching using a roll or a hot stove, transverse stretching using a tenter, and sequential biaxial stretching in which these are sequentially combined. Moreover, the simultaneous biaxial stretching method of extending | stretching length and width simultaneously is also employable. You may employ | adopt the method of performing horizontal extending | stretching by a tenter after performing roll longitudinal stretching.

  The polarizer protective film of this invention can be made into a final product in the state of a uniaxially stretched film. Furthermore, it is good also as a biaxially stretched film by combining and extending | stretching a process. When biaxial stretching is performed, stretching conditions such as longitudinal stretching and transverse stretching temperatures and magnifications may be the same as necessary. Anisotropy may be imparted.

  The stretching temperature and stretching ratio of the film can be adjusted as appropriate using the obtained film's retardation, mechanical strength and surface properties, and thickness accuracy as indices. The range of the stretching temperature is preferably in the range of Tg-30 ° C to Tg + 30 ° C, where Tg is the glass transition temperature of the film obtained by the DSC method. More preferably, it is the range of Tg-20 degreeC-Tg + 20 degreeC. More preferably, it is the range of Tg or more and Tg + 20 degrees C or less. If the stretching temperature is too high, the thickness unevenness of the obtained film tends to increase, and it is difficult to develop a phase difference, and the mechanical properties such as elongation, tear propagation strength, and fatigue resistance are not sufficiently improved. It is easy to become. Moreover, the trouble that the film adheres to the roll is likely to occur. On the other hand, when the stretching temperature is too low, the turbidity of the stretched film tends to be high, and in the extreme case, it tends to cause problems in the process such as tearing or cracking of the film. The preferred draw ratio depends on the drawing temperature, but is selected in the range of 1.1 to 3 times. More preferably, it is 1.3 times to 2.5 times. More preferably, it is 1.5 times to 2.3 times.

  In addition, when forming into a film, it may contain a heat stabilizer, a UV absorber, a processability improver such as a lubricant, or a known additive such as a filler or other polymers as necessary. . In particular, a filler may be contained for the purpose of improving the slipperiness of the film. As the filler, inorganic or organic fine particles can be used. Examples of inorganic fine particles include metal oxide fine particles such as silicon dioxide, titanium dioxide, aluminum oxide and zirconium oxide, silicate fine particles such as calcined calcium silicate, hydrated calcium silicate, aluminum silicate and magnesium silicate, Calcium carbonate, talc, clay, calcined kaolin, calcium phosphate, and the like can be used. As the organic fine particles, resin fine particles such as silicon resin, fluorine resin, acrylic resin, and cross-linked styrene resin can be used.

  By incorporating an ultraviolet absorber into the polarizer protective film of the present invention, weather resistance is improved, and durability of a liquid crystal display device using the polarizer protective film of the present invention can be improved, which is preferable in practice. Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers such as 2- (2H-benzotriazol-2-yl) -p-cresol and 2-benzotriazol-2-yl-4,6-di-t-butylphenol, Triazine-based UV absorbers such as 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol, benzophenone-based UV absorbers such as octabenzone, etc. Benzoate light stabilizers such as 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate and bis (2,2,6,6-tetramethyl) Light stabilizers such as hindered amine light stabilizers such as -4-piperidyl) sebacate can also be used.

  The polarizer protective film of the present invention can be subjected to a surface treatment as necessary to improve adhesion with other materials. As the surface treatment method, any conventionally known method is possible. For example, electrical treatment such as corona discharge treatment and spark treatment, plasma treatment under low pressure or normal pressure, ultraviolet irradiation treatment in the presence or absence of ozone, acid treatment with chromic acid, alkali saponification treatment, flame treatment, And silane-based primer treatment or titanium-based primer treatment. By these methods, the surface tension of the film surface can be increased to 50 dyne / cm or more.

  Moreover, in order to improve affinity with an adhesive agent or an adhesive, an easily bonding layer can be provided in the single side | surface or both surfaces of a film. As a preferred easy-adhesion layer, a copolymer polyester, a urethane-modified one thereof, a copolymer polyester having a carboxyl group or a sulfonic acid group, a solution such as polyvinyl alcohol, or an aqueous dispersion was applied and dried. Layers can be used. Moreover, the method of providing a cellulose-ester resin etc. as an easily bonding layer, performing this for an alkali saponification process, and improving affinity can also be used.

  The polarizer protective film of the present invention can be subjected to a coating treatment such as a hard coat, an antiglare coat, a non-reflective coat, and other functional coats as necessary.

  The polarizer protective film of the present invention can be bonded to a polarizer film via an adhesive, integrated with the polarizer film through predetermined drying, and a polarizing plate can be produced. A known iodine-based or dye-based polarizer film can be used as the polarizer film. Examples of the adhesive include gelatin-based, vinyl-based latex-based, polyurethane-based, isocyanate-based, polyester-based, and epoxy-based adhesives in addition to water-based adhesives mainly composed of polyvinyl alcohol-based compounds. The adhesive may contain various crosslinking agents. In addition, a stabilizer such as a catalyst, a coupling agent, various tackifiers, an ultraviolet absorber, an antioxidant, a heat stabilizer, and a hydrolysis stabilizer can be added to the adhesive. The solid content of the adhesive is generally 10 to 50% by weight.

  A liquid crystal display device can be obtained by providing a polarizing plate using the polarizer protective film of the present invention on one side or both sides of a liquid crystal cell. The polarizing plate of the present invention can be used for various liquid crystal display devices, but the polarizer protective film of the present invention is particularly useful for an IPS mode liquid crystal display device because a negative thickness direction retardation value is obtained.

  JP-A-2005-31621 discloses a polarizing optical film (polarizing plate + optical film) suitable for the IPS mode. The direction in which the refractive index in the film plane is maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive indexes in the respective axial directions are nx, ny, nz, When the film thickness is d (nm), the Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is Nz ≦ 0.9, and the front phase difference Re = (nx−ny). ) In order to obtain an optical film in which xd is Re ≧ 80 nm, the film can be stretched uniaxially or biaxially in the plane direction and stretched in the thickness direction, or by heating with heat shrink film adhered There is a need for a method of stretching or / and shrinking the polymer film under the action of the shrinkage force. Each of these methods requires a complicated processing step, which causes a cost increase.

  In order to obtain a polarizing optical film suitable for the IPS mode as described above using the polarizer protective film of the present invention, it can be achieved by combining with a retardation film stretched uniaxially or anisotropically biaxially. For example, by laminating a retardation film obtained by uniaxially stretching a positive birefringent material on a polarizing plate using the polarizer protective film of the present invention in which a negative thickness direction retardation is expressed by isotropic biaxial stretching, Equivalent optical performance can be obtained.

  An IPS mode liquid crystal display device includes a pair of substrates sandwiching a liquid crystal layer, an electrode group formed on one of the pair of substrates, and a liquid crystal composition material layer having dielectric anisotropy sandwiched between the substrates. A liquid crystal comprising: an alignment control layer formed opposite to the pair of substrates for aligning a molecular arrangement of the liquid crystal composition material in a predetermined direction; and a driving means for applying a driving voltage to the electrode group Has a cell. The electrode group has an arrangement structure arranged so as to apply an electric field mainly parallel to the interface between the alignment control layer and the liquid crystal composition material layer.

  The polarizing optical film in which the polarizing plate of the present invention and a retardation film uniaxially or anisotropically biaxially stretched are laminated is disposed on the viewing side of the liquid crystal cell or on the opposite side (light incident side). The slow axis of the retardation film and the absorption axis of the polarizing plate of the present invention are arranged so as to be orthogonal or parallel. The polarizing optical film preferably has the retardation film side as the liquid crystal cell side. A polarizing plate is disposed on the opposite side of the liquid crystal cell on which the polarizing optical film is disposed. The absorption axis of the polarizing plate arranged on both sides of the liquid crystal cell and the absorption axis of the polarizing optical film (polarizing plate of the present invention) are arranged in an orthogonal state.

  When the polarizing optical film is arranged on the viewing side of the liquid crystal cell in the IPS mode, the liquid crystal cell on the opposite side (light incident side) to the viewing side is liquid crystal in the liquid crystal cell with no voltage applied. It is preferable to arrange the material so that the extraordinary refractive index direction of the substance and the absorption axis of the polarizing plate are in parallel.

  When the polarizing optical film is arranged on the light incident side of the IPS mode liquid crystal cell, a polarizing plate is arranged on the liquid crystal cell on the viewing side, and the abnormal light refractive index direction of the liquid crystal substance in the liquid crystal cell when no voltage is applied. And the polarizing optical film (polarizing plate of the present invention) are preferably arranged so that the absorption axes thereof are in an orthogonal state.

  The optical film and polarizing optical film of the present invention can be preferably used for forming various devices such as a reflective transflective liquid crystal display device. A reflective transflective liquid crystal display device or the like is suitably used as a portable information communication device or a personal computer. When forming a reflective transflective liquid crystal display device, the polarizing optical film according to the present invention is preferably disposed on the viewing side of the liquid crystal cell. The optical film and polarizing optical film of the present invention can be applied to other various liquid crystal display devices.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to this Example. In addition, each measuring method of the physical property measured in the following Examples and Comparative Examples is as follows.

(1) Quantification of imidation ratio Using the pellet of the product as it was, IR spectrum was measured at room temperature using TravelIR manufactured by SensIR Technologies. From the obtained spectrum, the absorption intensity (Abs _Ester) attributed to the ester carbonyl group of 1720 cm ^-1, the ratio of the absorption intensity assignable to an imide carbonyl group of 1660cm ^-1 (Abs _imide), the following equation 1 Was used to determine the imidization ratio (Im%).

（２）ガラス転移温度（Ｔｇ）
生成物１０ｍｇを用いて、示差走査熱量計（ＤＳＣ、株式会社島津製作所製ＤＳＣ−５０型）を用いて、窒素雰囲気下、昇温速度２０℃／ｍｉｎで測定し、中点法により決定した。

(2) Glass transition temperature (Tg)
Using 10 mg of the product, a differential scanning calorimeter (DSC, model DSC-50 manufactured by Shimadzu Corporation) was used and measured at a heating rate of 20 ° C./min in a nitrogen atmosphere and determined by the midpoint method.

(3) Styrene content Using a Varian NMR measuring apparatus Gemini-300, the styrene content was determined from the integral ratio of absorption derived from aromatic and absorption derived from aliphatic.

(4) Total light transmittance A test piece having a size of 50 mm × 50 mm was cut out from the film. This test piece was measured by the method described in 5.5 of JIS K7105-1981 at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5% using a turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. did.

(5) Turbidity Using the turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd., the test piece obtained in (4) was added to JIS K7105 at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5%. Measured accordingly.

(6) In-plane retardation Re and thickness direction retardation Rth
A 40 mm × 40 mm test piece was cut out from the film. Using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Co., Ltd.), the in-plane retardation Re was measured at a temperature of 23 ± 2 ° C. and a humidity of 50 ± 5% at a wavelength of 590 nm and an incident angle of 0 °. It was measured. The thickness d of the test piece measured using a digimatic indicator (manufactured by Mitutoyo Corporation), the refractive index n measured by an Abbe refractometer (manufactured by Atago Co., Ltd. 3T), the wavelength 590 nm measured by an automatic birefringence meter, and the surface A three-dimensional refractive index nx, ny, nz was determined from the inner phase difference Re and the phase difference value in the 40 ° tilt direction, and the thickness direction phase difference Rth = {(nx + ny) / 2−nz} × d was calculated.

(7) Photoelastic coefficient A test piece was cut out in a strip shape having a width of 15 mm and a length of 60 mm from the film, and the temperature was 23 ± 2 ° C. and the humidity was 50 ± using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Co., Ltd.). In 5%, it measured at wavelength 590nm. One side of the film was fixed, and the other side was subjected to birefringence measurement in a state where a load was applied every 100 gf from no load to 1000 gf, and the amount of change in birefringence due to unit stress was calculated from the obtained results.

Example 1
A commercially available MS resin (MS-600 manufactured by Nippon Steel Chemical Co., Ltd.) was used as an imidizing agent to produce an imidized resin. The extruder used was a meshing type co-rotating twin screw extruder having a diameter of 15 mm. The set temperature of each temperature control zone of the extruder was 230 ° C., the screw rotation speed was 300 rpm, MS resin was supplied at 1 kg / hr, and the amount of methylamine supplied was 30 parts by weight with respect to the MS resin. MS resin was introduced from the hopper, and the resin was melted and filled with a kneading block, and then methylamine was injected from the nozzle. A seal ring was placed at the end of the reaction zone to fill the resin. By-products after the reaction and excess methylamine were devolatilized by reducing the pressure at the vent port to -0.02 MPa. The resin that came out as a strand from a die provided at the exit of the extruder was cooled in a water tank and then pelletized with a pelletizer.

The obtained imidized resin was dissolved in methylene chloride (resin concentration 25 wt%), applied onto a PET film, and dried to prepare a cast film. This cast film was subjected to simultaneous biaxial stretching (biaxial stretching device X4HD manufactured by Toyo Seiki Co., Ltd.) at a stretching ratio of 2 times (longitudinal and lateral) and a temperature 20 ° C. higher than the glass transition temperature to prepare a biaxially stretched film. Table 1 shows the total light transmittance, turbidity, in-plane retardation, and thickness direction retardation of this biaxially stretched film. Moreover, it was 3 * 10 < ^-12 > m < ² > / N when the photoelastic coefficient of this biaxially stretched film was measured.

(Example 2)
Example except that Atrete MM-70 manufactured by Nippon A & L Co., Ltd. was used as the MS resin, the MS resin was supplied at 0.5 kg / hr, and the supply amount of methylamine was 40 parts by weight with respect to the MS resin. Resin was prepared as in 1. A biaxially stretched film was obtained in the same manner as in Example 1. Table 1 shows the total light transmittance, turbidity, in-plane retardation, and thickness direction retardation of this biaxially stretched film.

(Comparative Example 1)
Table 1 shows the total light transmittance, turbidity, in-plane retardation, and thickness direction retardation of a triacetyl cellulose (TAC) film manufactured by Fuji Photo Film Co., Ltd. When the photoelastic coefficient of this film was measured, it was 15 × 10 ⁻¹² m ² / N.

(Comparative Example 2)
Implemented except that MS-800 manufactured by Nippon Steel Chemical Co., Ltd. was used as the MS resin, the MS resin was supplied at 0.5 kg / hr, and the supply amount of methylamine was 40 parts by weight with respect to the MS resin. A resin was prepared as in Example 1. A biaxially stretched film was obtained in the same manner as in Example 1. Table 1 shows the total light transmittance, turbidity, in-plane retardation, and thickness direction retardation of this biaxially stretched film.

Claims (10)

It consists of a thermoplastic resin characterized by containing repeating units represented by the following general formulas (1), (2), and (3), and the thickness direction retardation Rth of the film is Rth <−20 nm. A polarizer protective film characterized by

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or an aryl group having 6 to 10 carbon atoms.)

(Here, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.) The polarizer protective film according to claim 1, wherein the polarizer protective film is stretched. The polarizer protective film according to claim 1, wherein the thermoplastic resin has a photoelastic coefficient of 10 × 10 ⁻¹² m ² / N or less. The glass transition temperature of a thermoplastic resin is 120 degreeC or more, The polarizer protective film as described in any one of Claims 1-3 characterized by the above-mentioned. The polarizing plate using the polarizer protective film as described in any one of Claims 1-4. A polarizing optical film, wherein the polarizing plate according to claim 5 and a retardation film are laminated. The polarizing optical film according to claim 6, wherein the retardation film is laminated so that the slow axis of the retardation film and the absorption axis of the polarizing plate are orthogonal or parallel to each other. A liquid crystal display device comprising the polarizing plate according to claim 5 or the polarizing optical film according to claim 6 or 7 laminated thereon. An IPS mode liquid crystal display device, wherein the polarizing optical film according to claim 6 or 7 is disposed on the cell substrate on the viewing side, and a polarizing plate is disposed on the cell substrate on the opposite side to the viewing side. In addition, the liquid crystal display device is characterized in that the abnormal light refractive index direction of the liquid crystal substance in the liquid crystal cell and the absorption axis of the polarizing plate are in a parallel state when no voltage is applied. An IPS mode liquid crystal display device, wherein a polarizing plate is disposed on the cell substrate on the viewing side, and the polarizing optical film according to claim 6 or 7 is disposed on the cell substrate on the opposite side to the viewing side. In addition, the liquid crystal display device is characterized in that the abnormal light refractive index direction of the liquid crystal substance in the liquid crystal cell and the absorption axis of the polarizing optical film are in an orthogonal state in a voltage-free state.