JP2005242171A - Polarizer protection film and polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizer protection film free from light escaping in a heat test and discoloration in a humidity test, also free from the occurrence of a crack after an endurance test, and having high durability, and to provide a polarizing plate. <P>SOLUTION: A thermoplastic resin film having a ratio (B)/(A)≥0.6 when assuming that tensile strength based on JIS K 7127 before and after a constant load tensile test defined as follows is (A) and (B), respectively, and having a haze value ≤5% is used as the polarizer protection film. The constant load tensile test is a test applying 9.8N constant load to the length direction of a test piece having 20mm width for 24 hours under a 23°C-50% RH condition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a film for protecting a polarizer of a polarizing plate used mainly in a highly durable thin liquid crystal display device (hereinafter abbreviated as “LCD”) and a polarizing plate using the same.

  LCDs are widely used in desktop electronic calculators, electronic watches, personal computers, word processors, liquid crystal televisions, automobile and machine instruments, and the like. In general, an LCD is configured by laminating a retardation film or a polarizing plate on a glass substrate of a liquid crystal cell in which an electrode enclosing liquid crystal molecules is incorporated.

  The polarizing plate used in the LCD is usually provided with a polarizer on both sides of a film-like polarizer formed by adsorbing iodine or a dichroic dye on a stretched and oriented polyvinyl alcohol (hereinafter abbreviated as “PVA”) film. A polarizer protective film for protection is laminated in a sandwich shape.

  Conventionally, a cellulose triacetate (hereinafter abbreviated as “TAC”) film has been frequently used as a polarizer protective film. However, since TAC has a moisture permeability higher than necessary, when a moisture resistance durability test of a polarizing plate using the TAC is performed, there is a problem that moisture penetrates into the polarizing plate and consequently the polarizer is faded. In addition, after the heat resistance durability test of the polarizing plate, when observed under crossed Nicols, there is a problem that the portion near the side of the polarizing plate loses light in a frame shape (contrast decreases), and the display characteristics such as visibility deteriorate. is there.

It is generally known that the reason why light leakage occurs in the heat durability test is that the photoelastic coefficient of TAC is large. More specifically, when a stress is applied to a transparent elastic body such as plastic, it temporarily becomes an optically anisotropic body,
Change in birefringence (Δn) = stress (σ) × photoelastic coefficient (c)
Resulting in an optical phase difference. Since the LCD is used as a display by controlling the polarization state of light, if the phase difference occurs in the material that composes the display, especially the material sandwiched between two polarizers, Such a phenomenon occurs.

  As an external stress applied to the LCD, there is a contraction stress of a polarizer. When the heat resistance durability test of the polarizing plate is performed, the moisture contained in the polarizer in the polarizing plate evaporates and the volume shrinks. Further, since the polarizer is oriented by uniaxial stretching, the polarizer contracts even when this orientation is relaxed. Birefringence occurs in the polarizer protective film due to the stress accompanying the shrinkage.

  When the photoelastic coefficient is large, the phase difference generated by the contraction stress becomes large, so it is preferable that the photoelastic coefficient is small. Conventionally, since a TAC film used as a polarizer protective film has a large photoelastic coefficient and easily generates birefringence, a material having a smaller photoelastic coefficient has been desired.

  In order to solve these problems, Patent Document 1 proposes a polarizing plate using a film made of a saturated norbornene resin, which is one of cyclic olefin resins, as a polarizer protective film. Cyclic olefin-based resins are suitable as optical films such as polarizer protective films and retardation films for LCDs because they are excellent in transparency, moisture resistance and heat resistance and have a small photoelastic coefficient.

  However, norbornene-based resins are very fragile, so that the film may be broken in the manufacturing process, and various obstacles such as poor productivity occur. In other words, norbornene-based resin has high absolute strength but low elongation at break, so when it is pulled while bending the film during production or stretched with tension to make the film slack, Is easy to break.

  As a method for improving the brittleness of a cyclic olefin-based resin, Patent Document 2 discloses a film formed by dissolving or dispersing a saturated norbornene resin and a rubber component in a solvent and then casting (casting). This is to improve the elongation by blending a rubber component with the saturated norbornene resin. However, the obtained film is inferior in optical characteristics such as parallel light transmittance and cannot be used as a polarizer protective film.

  Further, the present inventor conducted a durability test (after exposure to high temperature conditions, after the polarizing plate using a saturated norbornene-based resin film as a polarizer protective film was bonded to the glass substrate of the liquid crystal cell at room temperature. It was discovered that there is a problem that a crack occurs in the polarizer protective film on the surface in contact with air on the opposite side of the liquid crystal cell after the durability test. Such a crack occurs even if the residual stress of the film is small.

  Conventionally, it has been known that an injection-molded product made of a cyclic olefin-based resin containing a saturated norbornene-based resin generates cracks (Patent Document 3), which is cited as a cause of a large residual stress generated in the injection molding. In addition, it is not known that cracks occur in a polarizer protective film obtained by a production method having a small residual stress in molding such as extrusion molding.

Note that Patent Document 3 neither describes nor suggests the problem of cracks. As will be described later, in the research of the present inventor, it was found that in order to improve cracks, it is not sufficient to simply add rubber, and it is necessary to devise measures such as finely and uniformly finely dispersing rubber. .
JP-A-6-511117 JP-A-5-148413 Japanese Patent Laid-Open No. 11-178690

  In view of the above problems, the present invention provides a highly durable polarizer protective film and a polarizing plate that are free from light leakage in a heat resistance test and inferior in a moisture resistance test, and that do not generate cracks after the durability test. It is in.

  In order to solve the above problems, the present inventor has studied in detail the cause of the occurrence of such cracks in a polarizing plate using a cyclic olefin-based resin film containing a saturated norbornene-based resin as a polarizer protective film. As a result, it was found that the mechanical strength of the film was significantly lowered due to the shrinkage stress of the polarizer as described above. For this reason, in order to prevent generation | occurrence | production of a crack, it turned out that it is necessary to suppress the fall of the intensity | strength of a film.

  The contraction stress of the polarizer is very large. When the polarizer is left at 90 ° C. for a long time, for example, the contraction stress reaches 20-30 N per 20 mm width. If the contraction stress of the polarizer is large, the contraction stress of the polarizing plate increases. Therefore, it is preferable that the contraction stress is small in order to prevent the occurrence of cracks.

  Furthermore, when a tensile stress corresponding to these shrinkage stresses was applied to the film (constant load tensile test), it was found that the strength of the film was lowered before and after the stress depending on the time during which the stress was applied. Thus, it is thought that the main cause of a crack is that the intensity | strength of a film falls gradually by applying stress continuously. Of course, in such a test, the stress acting on the film is tensile, whereas the stress acting on the film actually used in the polarizing plate mainly acts as compression. However, the phenomenon that the strength decreases under stress is considered to occur in both compression and tension.

  It has been found that the phenomenon that the strength of the film is reduced as described above occurs even when the load is considerably low. For example, when a constant load tensile test is performed in the TD direction on a norbornene-based resin film formed by an extrusion film forming method, the strength decreases with a similar tendency within a load value range of 5 to 20N. discovered. It was also observed that the film was cracked during the test. From this, in order for cracks to occur in the film, (1) extremely fine cracks that are invisible in the film are generated (2) cracks grow to a visible level. In the case of a norbornene resin, the stress for causing the phenomena (1) and (2) is close, and it is considered that cracks are likely to occur even with a small stress. In order to suppress the occurrence of cracks in the polarizing plate, it is also important to suppress the shrinkage of the polarizer, but these are only prolonging the life, essentially reducing the strength of the polarizer protective film under stress. Recognizing that prevention is the most important thing.

The present invention has been made based on the above findings. That is, in the present invention, when the tensile strength based on JIS K 7127 before and after the constant load tensile test according to the following definition, which is composed of a thermoplastic resin film, is (A) and (B), respectively, the ratio (B) / A polarizer protective film having (A) of 0.6 or more and a haze value of 5% or less is a requirement.
Constant load tensile test: A constant load of 9.8 N is applied for 24 hours in the length direction of a 20 mm wide test piece under the conditions of 23 ° C.-50% RH.

  Further, the present invention is used by being bonded to at least one surface of the liquid crystal cell so that the polarizer protective film is positioned at least on the side not in contact with the liquid crystal cell when the polarizing plate is bonded to the liquid crystal cell. It is a polarizing plate characterized by the above-mentioned.

  In the present invention, the constant load tensile test is performed by applying a tensile load of 9.8 N in the length direction of a 20 mm wide film and leaving it at 23 ° C.-50% RH for 24 hours. Specifically, when the film to be subjected to the constant load tensile test is an extruded film, it is parallel (MD) and perpendicular (TD) to the extrusion direction, and when it is a cast film, the coating direction (MD) is 20 mm wide × long. A test is performed in a state where a weight corresponding to a load of 9.8 N is hung in the length direction of the cut film.

  Moreover, the tensile strength of a film is measured based on JISK7127 using a tensile tester. Specifically, a sample was cut out based on the test piece type 2, and a film after the above constant load tensile test and a film before the constant load tensile test having the same dimensions as this film were prepared. The tensile strength is the higher of the breaking strength and the yield strength when a tensile test is performed at a tensile speed of 13.3 mm / min under the condition of 50% RH.

  The polarizer protective film of the present invention has a tensile strength ratio (B) / (A) where (A) and (B) are the tensile strengths based on JIS K 7127 before and after the constant load tensile test, respectively. It is necessary to be 0.6 or more. In the case of an extruded film, it is necessary to perform measurement in both the extrusion direction of the film (MD) and at a right angle (TD), and the tensile strength ratio of both needs to satisfy the above conditions. In the case of an extruded film, even if the birefringence appears to be very small at first glance, there may be anisotropy when the tensile strength ratio is measured. Therefore, in order to suppress cracks, both tensile strength ratios must satisfy the above conditions.

  Such conditions were found as a result of many experiments conducted by the present inventors. When the tensile strength ratio (B) / (A) is less than 0.6, the durability test of polarizing plates (high temperature conditions) When the film is left under normal temperature after being exposed to the film, the film strength gradually decreases and it becomes difficult to suppress the occurrence of cracks when the film is stressed by the contraction stress of the polarizer. . The tensile strength ratio (B) / (A) is preferably 0.8 or more, more preferably 0.9 or more, and still more preferably 0.95 or more.

  Furthermore, the polarizer protective film of the present invention has a haze value of 5% or less. If it exceeds 5%, it may cause light leakage when used for a polarizer protective film. More preferably, it is 3% or less, more preferably 1% or less, and particularly preferably 0.5% or less. The polarizer protective film of the present invention preferably has a parallel light transmittance of 87% or more. If it is less than 87%, it becomes difficult to use it for the use of a polarizer protective film. Preferably it is 89% or more, More preferably, it is 90% or more.

The polarizer protective film of the present invention preferably has a moisture permeability of 300 g / m ² · 24 hr or less as measured according to JIS Z 0280. This is because if the moisture permeability exceeds 300 g / m ² · 24 hr, the resulting polarizing plate has poor moisture resistance and it is difficult to suppress discoloration in the moisture resistance test. If the moisture permeability is less than 20 g / m ² · 24 hr, when the polarizing plate is produced by laminating the film to the polarizer using an aqueous adhesive, the moisture in the adhesive is removed during the wet lamination drying process. In this case, the water content in the polarizing plate is increased, and the polarizing performance and durability of the polarizing plate are deteriorated.

  The resin composition constituting the polarizer protective film of the present invention is preferably composed of a thermoplastic transparent resin and a rubbery polymer. As this transparent resin, an amorphous olefin resin is preferable, a cyclic olefin resin represented by a norbornene resin, a polyvinyl acetal resin, an olefin-maleimide copolymer having a substituted and / or unsubstituted imide group in the side chain. Examples of the polymer include a norbornene resin and an olefin-maleimide copolymer that are excellent in transparency, moisture resistance, heat resistance, and low photoelastic coefficient.

（式中、Ａ，Ｂ，Ｘ，Ｙはそれぞれ独立に水素原子、炭素数１〜１０の炭化水素基及び、ハロゲン原子、アルコキシ基、水酸基、エステル基、シアノ基、アミド基、イミド基、シリル基からなる極性基よりなる群から選ばれる原子又は基を表し、ｍは０又は１を表す。） The norbornene-based resin is, for example, one obtained by polymerizing at least one norbornene-based monomer represented by the following general formula (1), or a copolymerizable monomer copolymerizable therewith. Those obtained by copolymerization are preferably used.

(In the formula, A, B, X, and Y are each independently a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, a halogen atom, an alkoxy group, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group, and a silyl group. And represents an atom or group selected from the group consisting of a polar group consisting of a group, and m represents 0 or 1.)

  The copolymerizable monomer that can be copolymerized with the norbornene monomer represented by the general formula (1) is not particularly limited, and examples thereof include a cyclic olefin monomer that does not have a norbornene skeleton. Examples of the cyclic olefin monomer having no norbornene skeleton include cyclooctadiene, cyclooctene, cyclohexene, cyclododecene, and cyclododecatriene.

  In the norbornene-based monomer or copolymerizable monomer, it is preferable to give a certain moisture permeability to the resin obtained by having a polar group other than a halogen atom in the monomer structure.

  A method for polymerizing the norbornene monomer represented by the general formula (1) or a norbornene monomer represented by the general formula (1) and a copolymerizable monomer copolymerizable therewith. As the copolymerization method, for example, conventionally known methods such as ring-opening metathesis polymerization and addition polymerization can be employed.

  When the norbornene-based resin has an unsaturated bond in the molecule, it is preferably saturated by hydrogenation, and the hydrogenation rate is preferably 95% or more, more preferably 99% or more. When the hydrogenation rate is less than 95%, the obtained polarizer protective film has poor light resistance and heat deterioration resistance.

  The number average molecular weight in terms of polystyrene of the norbornene-based resin is preferably 10,000 to 1,000,000. If it is less than 10,000, the mechanical strength of the obtained polarizer protective film may be insufficient. Conversely, if it exceeds 1,000,000, melt extrusion moldability may be significantly reduced. More preferably, it is 15,000 to 700,000.

  The norbornene resin preferably has a glass transition temperature of 70 to 180 ° C. It is because the heat resistance of the polarizer protective film obtained may be inferior that it is less than 70 degreeC, and shaping | molding may become difficult when it exceeds 180 degreeC.

  Examples of commercially available norbornene-based resins include “ZEONOR” series, “ZEONEX” series manufactured by ZEON Corporation, “Optretz” series manufactured by Hitachi Chemical Co., Ltd., and “ARTON” series manufactured by JSR Corporation. Can be mentioned. Among these, the “Arton” series having an appropriate moisture permeability necessary for producing a polarizing plate by wet lamination is particularly preferred because it has a polar group in the molecular skeleton.

The olefin-maleimide copolymer is a binary or more multi-component containing a repeating unit derived from at least one olefin and at least one repeating unit having a substituted and / or unsubstituted maleimide structure. A copolymer is preferred. Such an olefin-maleimide copolymer can be synthesized from an olefin and a maleimide compound by a known method. The synthesis method is described in, for example, JP-A-5-59193, JP-A-5-195801, JP-A-6-1336058 and JP-A-9-328523.

Examples of the olefin include linear alkene having about 4 to 8 carbon atoms and lower alkyl substituted products thereof, among which isobutene is preferable. These olefins may be used alone or in combination of two or more.

Examples of the maleimide compound include maleimide and N-substituted maleimide, and examples of the substituent include a linear or branched alkyl group having about 1 to 20 carbon atoms and an alicyclic alkyl group having about 4 to 10 carbon atoms. Of these, N-methylmaleimide is preferred. These maleimide compounds may be used alone or in combination of two or more.

Moreover, what is obtained by introducing a substituted and / or unsubstituted maleimide structure into a polymer having an olefin skeleton is also treated as an olefin-maleimide copolymer. As a method for introducing a substituted and / or unsubstituted imide group into such a side chain, any conventionally known method can be employed. For example, a method of polymerizing a monomer having the imide group, a method of polymerizing various monomers. Then, after forming a main chain, a method of introducing the imide group, a method of grafting a compound having the imide group to a side chain, and the like can be mentioned.

In the olefin-maleimide copolymer, the content of the repeating unit of olefin is not particularly limited, but is about 20 to 70 mol%, preferably 40 to 60 mol%, more preferably 45 to 55 mol% of the total repeating units. . The content of the maleimide structure repeating unit is about 30 to 80 mol%, preferably 40 to 60 mol%, more preferably 45 to 55 mol%.

The olefin-maleimide copolymer may contain a repeating unit of another vinyl monomer in the main chain in a proportion of 50 mol% or less. Other vinyl monomers include acrylic acid monomers such as methyl acrylate and butyl acrylate, methacrylic acid monomers such as methyl methacrylate and cyclohexyl methacrylate, and vinyl ester monomers such as vinyl acetate. And vinyl ether monomers such as methyl vinyl ether, acid anhydrides such as maleic anhydride, and styrene monomers such as styrene, α-methylstyrene, and p-methoxystyrene.

Furthermore, the resin having a substituted and / or unsubstituted imide group in the side chain may contain a thermoplastic resin having a substituted and / or unsubstituted phenyl group and a nitrile group in the side chain as necessary.

  The rubbery polymer preferably used in the present invention is preferably thermoplastic, and is preferably a polymer composed of a hard segment and a soft segment. Such a rubbery weight body is generally known as a thermoplastic elastomer, and is generally configured such that the glass transition temperature of the hard segment is not lower than room temperature and the glass transition temperature of the soft segment is not higher than room temperature. Yes. Such a rubbery polymer is not particularly limited, and for example, styrene-butadiene block copolymer, hydrogenated styrene-butadiene block copolymer, styrene-isoprene block copolymer, hydrogenated styrene-isoprene block copolymer. And aromatic vinyl-conjugated diene block copolymers such as low crystalline polybutadiene, ethylene-propylene elastomer, styrene grafted ethylene-propylene elastomer, polyester elastomer, and ethylene ionomer resin. These rubbery polymers may be modified with specific functional groups such as epoxy groups, carboxyl groups, hydroxyl groups, amino groups, acid anhydride groups, and oxazoline groups. Of these, styrene-based elastomers are preferred.

  The styrene-based elastomer is not particularly limited as long as it can improve physical properties such as tensile elastic modulus and tensile elongation without impairing the optical properties of the obtained polarizer protective film. For example, styrene segment and glass Examples thereof include a copolymer composed of segments having a transition temperature of 25 ° C. or lower. For example, a copolymer of styrene and a hydrocarbon such as butylene, isobutylene, propylene, isopropylene, or ethylene can be given. Of these, styrene-ethylene-butylene copolymer (SEBS) and styrene-ethylene-propylene copolymer are preferable. In particular, a styrene-ethylene-butylene copolymer having a styrene component of 25 to 50% by weight and a butylene component of 25 to 50% by weight is preferable because an optical film having both extremely high optical properties and physical properties can be obtained. .

  The difference in refractive index between the amorphous olefin resin and the rubber polymer is preferably 0.2 or less. When the difference in refractive index exceeds 0.2, the transparency and residual phase difference of the obtained polarizer protective film may be deteriorated or optical distortion or the like may easily occur. More preferably, the difference in refractive index is 0.1 or less, more preferably 0.05 or less, and particularly preferably 0.03 or less.

  The amorphous olefin resin composition preferably contains 5 to 40 parts by weight of a rubbery polymer with respect to 100 parts by weight of the amorphous olefin resin. If the rubbery polymer is less than 5 parts by weight, the effect of improving the sufficient physical properties of the obtained polarizer protective film cannot be obtained. Conversely, if the rubbery polymer exceeds 40 parts by weight, the resulting polarizer protective film is obtained. Inferior optical properties. More preferably, the rubbery polymer content is 10 to 30 parts by weight.

  The amorphous olefin-based resin composition may further contain a resin that functions as a compatibilizing agent (hereinafter abbreviated as “compatibility resin”). By containing such a compatibilizing resin, the compatibility between the amorphous olefin resin and the rubbery polymer is improved, the optical properties of the obtained polarizer protective film are improved, and the film tension in the present invention is improved. This is because the strength ratio (B) / (A) may be improved.

  As the compatibilizing resin, for example, when blended with a norbornene-based resin, a cyclic olefin-based oligomer is preferable because of excellent compatibility. The number average molecular weight of such a compatibilizing resin is preferably 300 to 10,000. If it is less than 300, problems such as bleeding out may occur. Conversely, if it exceeds 10,000, the effect of improving compatibility may not be obtained. More preferably, it is 500-5000, More preferably, it is 600-2000.

  The compatibilizing resin preferably has a refractive index difference of 0.2 or less from the norbornene-based resin. When it exceeds 0.2, the transparency of the obtained polarizer protective film may be inferior. More preferably, it is 0.1 or less. In addition, when such a compatibilizing resin is blended into a norbornene-based resin composition by a melt kneading method, it is preferable that a 2 wt% decomposition temperature in an air atmosphere is 230 ° C. or higher in thermogravimetric analysis. More preferably, it is 250 degreeC or more, More preferably, it is 270 degreeC or more.

  Among the compatibilized resins having such properties, commercially available products include, for example, the trade name “Escollet” manufactured by Tonex Co., Ltd., the product name “Clearon” manufactured by Yashara Chemical Co., Ltd., and the product name “Arakawa Chemical Co., Ltd.” Archon "and so on. Such a compatibilizing resin is preferably contained in an amount of 10 parts by weight or less with respect to 100 parts by weight of the norbornene resin and 5 to 40 parts by weight of the rubbery polymer.

  In the above amorphous olefin resin composition, 2,6-di-t-butyl-4-methylphenol, 2- (1-methylcyclohexyl)-is optionally added within the range not impairing the object of the present invention. Antioxidants such as 4,6 dimethylphenol, 2,2-methylene-bis- (4-ethyl-6-tert-butylphenol), tris (di-nonylphenyl phosphite); pt-butylphenyl salicylate, UV absorbers such as 2,2′-dihydroxy-4-methoxy-benzophenone and 2- (2′-dihydroxy-4′-m-octoxyphenyl) benzotriazole; lubricants such as paraffin phenos and hydrogenated oil; stearo You may contain antistatic agents, such as aditopropyldimethyl- (beta) -hydroxyethyl ammonium trate. The kind and amount of these additives are not particularly limited as long as the effects of the present invention are not impaired.

  In addition, the polarizer protective film of the present invention preferably has a tensile elastic modulus measured according to JIS K 7127 of 900 MPa or more. This is because, when the pressure is less than 900 MPa, when this is bonded to a film-like polarizer to form a polarizing plate, the contraction of the polarizer may not be suppressed. More preferably, it is 2000 MPa or more.

  In addition, the polarizer protective film of the present invention preferably has a tensile fracture elongation measured in accordance with JIS K 7127 of 4 to 40%. This is because if it is less than 4%, the film may be easily broken during the production of the polarizing plate. The tensile elongation at break is more preferably 6% or more, and further preferably 8% or more.

The polarizer protective film of the present invention preferably has a photoelastic coefficient of 10 × 10 ⁻¹² m ² / N or less. When the polarizer protective film of the present invention is used as a polarizer protective film on the liquid crystal panel side, various external forces such as the contraction stress of the polarizer, the stress due to the distortion at the time of bonding, the stress due to the distortion at the time of incorporation in the display, etc. Take it. In particular, the contraction stress of the polarizer is large. When the photoelastic coefficient exceeds 10 × 10 ⁻¹² m ² / N, the optical characteristics change greatly due to deformation due to external force, making it difficult to use for optical film applications. More preferably, it is 5 × 10 ⁻¹² m ² / N or less.

The thickness of the polarizer protective film of the present invention is not particularly limited, but when the average film thickness is 100 μm or less, it is preferable to satisfy the above-described optical characteristics and physical characteristics. Conventional optical films made of amorphous olefin resins such as saturated norbornene resins are very fragile when the average film thickness is 100 μm or less, and break even if they are bent slightly, making it difficult to manufacture. . More preferably, when the average film thickness is 50 μm or less, the above optical characteristics and physical characteristics are satisfied. When the average film thickness is 50 μm or less and satisfies the above-mentioned optical characteristics and physical characteristics, the cost can be greatly reduced, and it is extremely valuable. The lower limit of the average film thickness is not particularly limited, but considering the use as a polarizer protective film, the above optical characteristics and physical characteristics are preferably obtained when the average film thickness is preferably 25 μm or more, more preferably 20 μm or more. It is preferable to satisfy. In addition, it is preferable that the difference of the maximum value and minimum value when the thickness is measured with the width | variety effective as a film according to JISK7130 is 5 micrometers or less for the polarizer protective film of this invention.

  As a method for forming a film using the amorphous olefin resin composition, melt extrusion molding is preferred. In the present invention, in order to increase the tensile strength ratio (B) / (A) of the above-mentioned film, it is necessary that the amorphous olefin resin and the rubber polymer are finely and uniformly finely dispersed. Moreover, generally the transparency of a film is also improved by doing in this way. Amorphous olefinic resin and rubbery polymer are essentially incompatible, but by molding by the melt extrusion method, moderate shear stress is applied, and the rubbery polymer is in a matrix made of amorphous olefinic resin. Can be obtained, and the polarizer protective film of the present invention having both optical properties and physical properties can be obtained.

  As the melt extrusion method, a conventionally known method can be used, and examples thereof include a method of melt extrusion in a film form from a T die attached to a melt extruder, and cooling and solidifying the film while drawing it on a cooling roll.

  In addition, the film formed by the solution casting (casting) method has a poor compatibility with the amorphous olefin resin and the rubbery polymer, so it is difficult to finely and uniformly disperse the rubbery polymer. Not only is the transparency of the film lowered, but the tensile strength ratio (B) / (A) of the film is also lowered.

  Preparation of the amorphous olefin-based resin composition and film forming may be performed in a series of steps, or the amorphous olefin-based resin composition is once formed into a pellet and then formed into a film using this pellet. May be.

  The polarizer protective film of the present invention can be obtained by appropriately setting the raw materials and production conditions as described above. And the polarizing plate of this invention is obtained by bonding such a polarizer protective film on the single side | surface or both surfaces of a polarizer using an adhesive agent or an adhesive. In addition, when the polarizer protective film of this invention is bonded together on the single side | surface of a polarizer, you may bond the conventional polarizer protective film on the other surface of this polarizer.

  The polarizer may be a film having the function of a polarizer. For example, after adsorbing iodine to a PVA film, the PVA / iodine polarizer is uniaxially stretched in a boric acid bath, and the PVA film has two colors. Examples include PVA / dye-based polarizers which are obtained by diffusing and adsorbing highly direct dyes and then uniaxially stretching.

  As a method for bonding the polarizer protective film of the present invention to the polarizer, for example, wet lamination using a water-based adhesive that is widely used in general is employed. In consideration of the thickness after drying and the smoothness of coating, this type of wet lamination is used, for example, by diluting the adhesive with water to an appropriate concentration (for example, 0.01 to 50% by weight). After being prepared, it is applied onto a polarizer protective film by a known method (for example, gravure coater, micro gravure coater, etc.) or dropped, and then laminated while squeezing excess coating solution with a pair of rolls, hot air, etc. And drying and bonding.

In addition, when manufacturing by wet lamination, in order to evaporate the water | moisture content contained in an adhesive agent, moderate moisture permeability is requested | required of a polarizer protective film. Specifically, at least one side, preferably both sides of the polarizer protective film, needs to have a moisture permeability of 40 g / m ² · 24 hr or more as measured by JIS Z 0280.

  The adhesive is not particularly limited as long as it has transparency, and for example, urethane adhesives, acrylic adhesives, PVA adhesives, and the like are preferably used from the viewpoint of high adhesive performance and durability. In addition, when the polarizer protective film is bonded to the polarizer, the adhesive surface of the polarizer protective film is generally used for corona discharge treatment, ultraviolet irradiation treatment, primer treatment, etc. for the purpose of improving the adhesion of the film. It is preferable to perform a surface treatment.

  The polarizing plate of the present invention is used by being bonded to a glass substrate of a liquid crystal cell in which an electrode enclosing liquid crystal molecules is incorporated. At this time, when the polarizing plate is bonded to a liquid crystal cell, the polarizing plate of the present invention is used. The child protective film is bonded to at least one surface of the liquid crystal cell using an adhesive or a pressure-sensitive adhesive so as to be positioned at least outside the liquid crystal cell.

  Usually, the polarizer protective film is bonded to both surfaces of the polarizer, and in the case of a normal TN type liquid crystal, the polarizing plate is bonded to both surfaces of the liquid crystal cell. Therefore, four polarizer protective films are used. Of these, two are located on the liquid crystal cell side, one is located on the viewer side, and the other is located on the backlight side. Here, the generation of cracks is most problematic in the polarizer protective film located on the viewer side, and the polarizer protective film on the backlight side is also important because cracks are likely to occur. Therefore, when the polarizing plate is bonded to the liquid crystal cell, the polarizer protective film of the present invention needs to be bonded to at least one surface of the polarizer so that it is positioned at least on the side not in contact with the liquid crystal cell. Preferably, the polarizer protective film of the present invention is preferably used in which all the polarizer protective films are bonded to both sides of the polarizer.

  The surface of the polarizer protective film of the present invention comprises an inorganic compound, an organic silicone compound such as a silane coupling agent, an acrylic resin, a vinyl resin, a melamine resin, an epoxy resin, a fluorine resin, a silicone resin, or the like. A transparent hard coat layer may be formed. Examples of the means for forming the hard coat layer include known methods such as thermal curing, ultraviolet curing, electron beam curing, vacuum deposition, sputtering, and ion plating. By forming the hard coat layer in this manner, the scratch resistance, moisture resistance, chemical resistance, etc. of the polarizer protective film and the polarizing plate can be improved.

  The polarizer protective film of the present invention is designed so that the tensile strength ratio (B) / (A) of the film before and after the constant load tensile test is 0.6 or more, and the film is designed in this way. And even if the shrinkage stress of the PVA polarizer generated in the heat resistance test continues, the film can withstand destruction, and as a result, the occurrence of cracks in the film can be suppressed. Moreover, since the haze value is designed to be 5% or less, light leakage can be effectively suppressed.

Furthermore, when the water vapor transmission rate is designed to be 300 g / m ² · 24 hr or less, the amount of water that comes into contact with the PVA polarizer is reduced when the moisture resistance test is performed, so that hydrolysis of the polarizer is suppressed. It can be suppressed.

In addition, when the photoelastic coefficient is designed to be 10 × 10 ⁻¹² m ² / N or less, the occurrence of birefringence can be suppressed even if the shrinkage stress of the PVA polarizer generated in the heat test acts on the film. As a result, frame-like light leakage is suppressed.

  Hereinafter, the present invention will be described in more detail by giving specific examples of the present invention. The present invention is not limited to these examples.

  Saturated norbornene resin (“Arton G6810” manufactured by JSR, refractive index 1.52, glass transition temperature 164 ° C.) dried at 100 ° C. for 4 hours, and styrene elastomer (“Tuftec H1041” manufactured by Asahi Kasei), refractive index 1.51) is fed to a twin-screw melt extruder equipped with a T die at a weight ratio of 85:15 using a feeder, melted and mixed at a cylinder temperature of 270 ° C., and T adjusted to 270 ° C. I sent it to the die. Subsequently, the composition of the saturated norbornene resin is melt-extruded from a T-die, brought into contact with a cooling roll whose temperature is adjusted to 140 ° C., and wound into a roll after cooling. From the saturated norbornene-based resin composition, A polarizer protective film having a thickness of 40 μm, a width of 300 mm, and a length of 100 m was produced.

  On the other hand, a 75 μm-thick unstretched PVA film made of PVA having a polymerization degree of 2400 and a saponification degree of 99 mol% was washed with water at room temperature, and then stretched 5 times in the longitudinal direction. While maintaining the tension state of this film, it was immersed in a dyeing bath (an aqueous solution containing 0.5% by weight of iodine and 5% by weight of potassium iodide) to adsorb the dichroic dye. Thereafter, a crosslinking treatment (an aqueous solution containing 10% by weight of boric acid and 10% by weight of potassium iodide) was performed at 50 ° C. for 5 minutes, and this was dried at 70 ° C. for 5 minutes to obtain a moisture content of 8% by weight. An adjusted film-like polarizer was produced.

  The said polarizer protective film was cut out to A4 size, and the corona discharge process was performed to the single side | surface (adhesion surface side with a polarizer) of this film. On the other hand, an adhesive solution was prepared by diluting an aqueous urethane adhesive (EL-436A / B, manufactured by Toyo Morton Co., Ltd.) main agent / curing agent (mixing ratio 10/3) with water to 10 wt%. Next, this adhesive solution was applied to the corona discharge-treated surface of the polarizer protective film with a Mayer bar # 8. This was bonded to one side of the polarizer. Furthermore, this operation was performed also on the other surface of the polarizer, and the polarizer protective film was attached to both surfaces of the polarizer. This was held for 72 hours in a 45 ° C. constant temperature bath and dried and cured to prepare a polarizing plate.

Saturated norbornene resin (“Arton G6810” manufactured by JSR) dried at 100 ° C. for 4 hours, styrene elastomer (“Clayton G1652” manufactured by Kraton Polymer Co., Ltd., refractive index 1.52), and Tonex as a compatibilizing resin “Escollets 228F” manufactured by the company was used in the same manner as in Example 1 except that 86: 9.5: 4.5 was used in a weight ratio of 40 μm in thickness and 300 mm in effective width made of a saturated norbornene resin composition. A polarizer protective film having a length of 100 m was prepared.
Further, a polarizing plate was produced in the same manner as in Example 1 except that this polarizer protective film was used.

An alternating copolymer consisting of N-methylmaleimide and isobutene (hereinafter abbreviated as MeMI-IB copolymer; N-methylmaleimide content 50 mol%, refractive index 1.53, glass transition temperature 155 ° C.) at 100 ° C. A polarizer protective film having a thickness of 40 μm, an effective width of 300 mm, and a length of 100 m made of a thermoplastic resin composition having a substituted imide group in the side chain, in the same manner as in Example 1 except that a material dried for 4 hours was used. Was made.
Further, a polarizing plate was produced in the same manner as in Example 1 except that this polarizer protective film was used.

A MeMI-IB copolymer used in Example 3 and an acrylonitrile-styrene copolymer (hereinafter abbreviated as SAN; refractive index 1.57, glass transition temperature 105 ° C.) having an acrylonitrile content of 28% by weight; Was used in the same manner as in Example 1 except that it was used at a weight ratio of 80:20. Polarized light having a thickness of 40 μm, an effective width of 300 mm, and a length of 100 m made of a thermoplastic resin composition having a substituted imide group in the side chain. A child protective film was prepared.
Further, a polarizing plate was produced in the same manner as in Example 1 except that this polarizer protective film was used.

(Comparative Example 1)
A saturated norbornene-based resin (“Arton G6810” manufactured by JSR Co., Ltd.) dried at 100 ° C. for 4 hours is supplied to a twin-screw melt extruder equipped with a T die and melted and mixed at a cylinder temperature of 280 ° C. It was sent to a temperature-controlled T die. Subsequently, the saturated norbornene-based resin is melt-extruded from a T-die and brought into contact with a cooling roll whose temperature is adjusted to 140 ° C., so that the thickness of the saturated norbornene-based resin is 40 μm, the effective width is 300 mm, and the length is 100 m. A polarizer protective film was produced.
Further, a polarizing plate was produced in the same manner as in Example 1 except that this polarizer protective film was used.

(Comparative Example 2)
Saturated norbornene resin (“Arton G6810” manufactured by JSR Co., Ltd.) dried at 100 ° C. for 4 hours and styrene elastomer (“Tuftec H1041” manufactured by Asahi Kasei Co., Ltd., refractive index 1.51), weight of 85:15 The mixed resin is dissolved in chloroform so that the concentration of the mixed resin becomes 10% by weight, and the solution of the mixed resin is cast on a glass plate using a coating blade, and this solution is cast at 80 ° C. for 72 hours. After drying under reduced pressure, the cast film was peeled off from the glass plate to prepare a 40 μm thick polarizer protective film made of a saturated norbornene resin composition. In the obtained film, a saturated norbornene-based resin and a styrene-based elastomer were phase-separated to become a non-uniform and opaque film, and thus a polarizing plate was not prepared.

(Comparative Example 3)
The thickness of the saturated norbornene resin composition is 40 μm, the effective width is 300 mm, and the length is 100 m, except that the blending ratio of the saturated norbornene resin and the styrene elastomer is changed to 97: 3. A polarizer protective film was produced.
Further, a polarizing plate was produced in the same manner as in Example 1 except that this polarizer protective film was used.

(Comparative Example 4)
As the polarizer protective film, a TAC cast film (“Fujitack Clear” manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 40 μm was used. A polarizing plate was produced in the same manner as in Example 1 except that this polarizer protective film was used.

  About the polarizer protective film obtained by each comparative example except each said Example and the comparative example 2, the tensile strength ratio before and behind a creep test, parallel light transmittance, a photoelastic coefficient, and a water vapor transmission rate were measured with the following method. In addition, the state of occurrence of cracks after the heat resistance test, the state of fading after the moisture resistance durability test, and the state of light leakage after the heat resistance test were observed for the polarizing plate by the following methods.

(Measurement of tensile strength ratio)
In the case of an extruded film, the polarizer protective film obtained in each of the above Examples and Comparative Examples is used (MD) and perpendicular (TD) to the extrusion direction, and in the case of a cast film, the coating direction (MD). Then, cut into a width of 20 mm and a length of 250 mm, and using a tensile tester, this cut-out film was allowed to stand for 24 hours under conditions of 23 ° C.-50% RH with a weight corresponding to a load of 9.8 N suspended. Thus, a constant load tensile test was conducted.

  Next, for the polarizer protective film before the constant load tensile test and after the constant load tensile test (within 12 hours after the constant load tensile test), using a tensile tester (Tensilon UTA-500, manufactured by Orientec Corp.), JIS. Based on K7127, the tensile strength of the film was measured. In this case, the dimensions of the test pieces are all 20 mm wide × 150 mm long, measured at 23 ° C.-50% RH with a chuck distance of 100 mm and a tensile speed of 13.3 mm / min. The higher point strength was taken as the tensile strength. From these measured values, tensile strength ratio = tensile strength after constant load tensile test (B) / tensile strength before constant load tensile test (A) was calculated. In addition, the measurement was performed 5 by each sample and the average value was employ | adopted.

(Measurement of parallel light transmittance)
Using the polarizer protective film obtained in each of the above Examples and Comparative Examples, the total light transmittance and the diffuse transmission are based on JIS K 7105 and using a haze meter TC-H III DPK (manufactured by Tokyo Denshoku Co., Ltd.). Rate, and from these measurements,
Parallel light transmittance = total light transmittance−diffuse transmittance was calculated.

(Measurement of photoelastic coefficient)
In the case of an extruded film, the polarizer protective film obtained in each of the above Examples and Comparative Examples was cut out in a width of 10 mm and a length of 150 mm in the coating direction in the case of a cast film, and the length was cut. The phase difference is measured with a load of 0,400,800,1200,1600,2000 g in the vertical direction, and the photoelastic coefficient is calculated from the slope of the straight line obtained by the approximate calculation by the least square method. Calculated. The phase difference was measured at a measurement wavelength of 590 nm in the normal direction of the film using KOBRA-21ADH (manufactured by Oji Scientific Instruments).

(Measurement of moisture permeability)
Using the polarizer protective film obtained in each of the above Examples and Comparative Examples, moisture permeability was measured in accordance with JIS Z 0280 (Cup method).

(The occurrence of cracks after the heat test)
One side of the polarizing plate obtained in each of the above examples and comparative examples was subjected to corona discharge treatment, and a double-sided pressure-sensitive adhesive sheet (2006, manufactured by Soken Chemical Co., Ltd.) was bonded to the treated surface, and the absorption axis of the polarizer was on the side. It cut out to 160 mm x 90 mm so that it might become 45 degree | times, and this was affixed on the glass plate of thickness 1mm. The obtained glass plate with a polarizing plate was left in an oven at 90 ° C. for 500 hours and then left at room temperature for 1000 hours, and the occurrence of cracks was visually evaluated. The case where cracks were observed was marked with ×, and the case where cracks were not observed was marked with ○.

(Status of light leakage after heat test)
One side of the polarizing plate obtained in each of the above examples and comparative examples was subjected to corona discharge treatment, and a double-sided pressure-sensitive adhesive sheet (2006, manufactured by Soken Chemical Co., Ltd.) was bonded to the treated surface, and the absorption axis of the polarizer was on the side. It cut out to 150 mm x 150 mm so that it might become 45 degree | times, and this was affixed on the glass plate of thickness 1mm. The obtained glass plate with a polarizing plate was left in an oven at 80 ° C. for 500 hours to conduct a durability test. A commercially available polarizing plate ("UHLC2-5618" manufactured by Sanritz Co., Ltd.) is superimposed on the glass plate with the polarizing plate after the test so as to be crossed Nicol, and placed on the light box for observation, thereby eliminating light leakage in the front direction. Observed. The case where light omission was observed was marked with ×, and the case where light was not observed was marked with ○.

(Discoloration after moisture resistance durability test)
The polarizing plate-attached glass plate obtained in the same manner as described above was allowed to stand for 500 hours under the condition of 60 ° C.-95% RH, and then allowed to stand at room temperature for 1 hour, and the discoloration state was visually evaluated. The case where a fading color was observed was rated as x, and the case where a fading color was not observed was marked as ○.

(Evaluation results)
The evaluation results are summarized in Tables 1 and 2. As is clear from the evaluation results in Tables 1 and 2, cracks are generated in the heat resistance durability test when the tensile strength ratio (B) / (A) is small. From this, it can be seen that the decrease in tensile strength due to the continuous application of the load by the creep test greatly affects the generation of cracks.

Claims (8)

When the tensile strength based on JIS K 7127 before and after a constant load tensile test according to the following definition, which is made of a thermoplastic resin film, is (A) and (B), the ratio (B) / (A) is 0. A polarizer protective film characterized by having a haze value of 6% or more and 5% or less.
Constant load tensile test: 9. In the length direction of a test piece having a width of 20 mm under conditions of 23 ° C. and 50% RH. Add 8N constant load for 24 hours ^2. The polarizer protective film according to claim 1, wherein the moisture permeability is 300 g / m ² · 24 hr or less. The polarizer protective film according to claim 1, wherein the moisture permeability is 20 g / m ² · 24 hr or more. The polarizer protective film according to claim 1, wherein the photoelastic coefficient is 10 × 10 ⁻¹² m ² / N or less.   The polarizer protection according to any one of claims 1 to 4, comprising a cyclic olefin-based resin composition containing 100 parts by weight of a cyclic olefin-based resin and 1 to 40 parts by weight of a rubbery polymer. the film.   It consists of a thermoplastic resin which has a substituted and / or unsubstituted imide group in a side chain, The polarizer protective film of any one of Claims 1-4 characterized by the above-mentioned.   The polarizer protective film according to any one of claims 1 to 6, wherein the polarizer protective film is formed by an extrusion film forming method.   At least one surface of the liquid crystal cell so that the polarizer protective film according to any one of claims 1 to 7 is positioned at least on a side not in contact with the liquid crystal cell when the polarizing plate is bonded to the liquid crystal cell. A polarizing plate, which is used by being attached to a substrate.