JP2005222075A - Polarizing plate protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a polarizing plate protective film in which curving becoming problematic when manufacturing a polarizing plate by sticking films of different rigidity on both surfaces of a polarizing film is suppressed. <P>SOLUTION: The polarizing plate 50 is made by sticking the polarizing plate protective film 51, a polarizing film 52, and a polarizing plate protective film of larger rigidity together. The curvature of the polarizing plate due to difference in rigidity and that of the polarizing plate protective film 51 offset each other by using the film 51 with a predetermined curvature as the polarizing plate protective film 51, and sticking it to the polarizing film 62 with the concave surface of the curvature of the film 51 faced to the polarizing film, and thus a polarizing plate 50 can be obtained of which the curving does not become problematic. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polarizing plate protective film.

  In recent years, the development of liquid crystal display devices used in personal computers, mobile phones, car navigation systems, flat-screen televisions, etc. has been remarkable, and their production volume has increased significantly. As a result, the production amount of polarizing plates, which are indispensable members for liquid crystal display devices, has increased, and the production and usage of polarizing plate protective films have also increased dramatically. A polarizing plate protective film is an optical application film that is applied to both surfaces of a polarizing film made of polyvinyl alcohol or the like to protect the polarizing plate and impart dimensional stability. As the polarizing plate protective film, a cellulose acetate film is preferably used because it is excellent in transparency, smoothness, and optical isotropy.

  The cellulose acetate film is produced by a solution casting method. Specifically, a dope prepared by dissolving cellulose acetate and various additives in a solvent is cast on a support having a smooth surface such as an endless drum or band, and then peeled off and further dried to obtain a product. The drying after peeling is generally performed by hot air drying while being conveyed through a pass roller. In the initial stage, drying is carried out using a tenter or the like while being conveyed in a substantially non-contact state. Continuously produced film is usually wound on a cylindrical core made of resin, metal, wood, cardboard, etc., wound up to a length of several hundred to several thousand meters depending on the application and equipment capacity, and then packed as appropriate Thus, a product form is obtained (see, for example, Non-Patent Document 1).

  In film formation of cellulose acetate film, it is necessary to solidify to some extent to have the cast film peeled off from the support, so that it has self-supporting properties, but the physical properties of the resulting film differ depending on the history until peeling. . Also, films having various different physical properties can be obtained depending on the conditions after peeling.

There are two main methods for giving the film on the support a self-supporting property.
(1) A method of drying by applying hot air to the dope on the support to lower the solvent content in the dope (dry stripping method).
(2) A method in which the dope on the support is cooled and gelled (cooling stripping method).
Each of the above two methods has advantages and disadvantages, and films actually produced by either method are commercially available as optical films such as a protective film for polarizing plates.

  In addition, due to differences in the film forming method, the completed films have different physical properties. The film of the dry stripping method is generally stripped on the support by lowering the residual solvent content to less than 60% to provide self-supporting properties. Since the drying time on the support is long, there is a difference in structure between the front and the back, but the initial drying is relatively slow, and the degree of crystallization is small and soft. As a measure of the firmness of the film, the tensile modulus in the casting direction (hereinafter simply referred to as “elastic modulus”) is approximately 4 GPa or less.

On the other hand, the film of the cooling stripping method has a residual solvent content of 60% or more, and is cooled and gelled in a state without self-supporting property at room temperature. Thereafter, both sides are dried in a substantially non-contact state by a tenter or the like. Since the drying time on the support is short, the structural difference between the front and back surfaces is small, and crystallization progresses because it is dried at a high speed from both sides at an early stage and is generally hard. The elastic modulus is approximately 4 GPa or more. Here, the residual solvent content is determined by the absolutely dry method. Specifically, the weight of the sampled film was precisely weighed (this value is A (g)), and then the weight after absolutely drying for 90 minutes in an atmosphere of 120 ° C. was reweighed again (this value was B (g) And the following formula.
Stripped residual solvent content (%) = (A−B) / A × 100
Japan Society for Invention and Innovation Public Technical Bulletin No. 2001-1745

  By the way, when a polarizing plate is manufactured by combining films having different physical properties, adverse effects may occur. In particular, it appears remarkably when a polarizing plate is produced by combining films having different elastic moduli. As shown in FIG. 5 (a), the polarizing plate 80 includes a polarizing plate protective film 81 for the front surface, a polarizing film 82, and a polarizing plate protective film 83 for the back surface, as shown in FIG. 5 (b). Paste to form. Then, due to the change over time, the polarizing plate 80 is curved (curled) with the surface on which the polarizing plate protective film 81 having a low elastic modulus is attached as shown in FIG. 5C, and the value of the product is significantly impaired. It was. Further, even if there is no difference in elastic modulus, when there is a difference in thickness between the polarizing plate protective films 81 and 83 attached to both surfaces of the polarizing plate, the same phenomenon appears due to the difference in rigidity of the entire base. The polarizing plate 80 is curved with the side to which the thin film 81 is attached as the inner side. This is due to the difference in rigidity, that is, the product of the film modulus of elasticity and the film thickness, so that when contraction force is generated mainly due to environmental changes (for example, due to changes in the size of the polarizing film), This is a phenomenon that occurs because the resistance force is different. In general, a polarizing film is produced by adsorbing a polarizing material such as iodine or a dichroic dye on a film such as polyvinyl alcohol and then stretching the film in the longitudinal direction. After producing a polarizing plate by sticking a protective film on both sides of the polarizing film thus manufactured using an adhesive, the polarizing film interior was caused mainly by residual stress during stretching mainly remaining in the polarizing film over time. A shrinkage stress in the stretching direction is generated. It is the function of the polarizing plate protective film to overcome this shrinkage stress and minimize the shrinkage as much as possible, but if there is a difference in the rigidity of the polarizing plate protective film attached to both sides, there is a slight difference in shrinkage between the front and back sides. Arise. That is, since the amount of shrinkage is slightly larger on the surface to which the polarizing plate protective film having a low rigidity is attached, the bending of the polarizing plate occurs with this surface as the inner side.

  As mentioned above, in recent years, the demand for polarizing plates has increased, and the supply and demand for polarizing plate protective films has become severe. It has become difficult to select and use films with small differences in rigidity on the front and back. Yes. Further, in recent years, an optical compensation film has often been attached to one surface of a polarizing film instead of a polarizing plate protective film. An optical compensation film is an optically anisotropic layer provided on a polarizing plate protective film. The birefringence of the liquid crystal eliminates the difficulty in viewing the liquid crystal panel from an angle. It is used as a mean. In general, the optical compensation film is often thicker than the polarizing plate protective film due to the fact that it has an optically anisotropic layer. When a polarizing plate protective film is stuck on the opposite surface of such an optical compensation film, it is unavoidable to stick a film with low rigidity. Increasing the thickness of the polarizing plate protective film so as to match the rigidity of the optical compensation film increases the thickness of the polarizing plate and thus the entire liquid crystal display device, thereby reducing the commercial value.

  An object of this invention is to provide the polarizing plate protective film which canceled the curl.

  The present inventor has found that the above problems can be solved by preliminarily bending a low-rigidity film and sticking it so as to cancel the above-described inconvenient curve when manufacturing a polarizing plate. Here, affixing so as to cancel the curve means that the film is affixed so that the inner surface faces the polarizing plate when the film is curved.

  Since the film produced by the dry stripping method is accelerated to dry on the support, the distribution in the thickness direction of the residual solvent of the film is large when the film is peeled off, and the surface in contact with the support surface when forming the film. However, there is more residual solvent than the opposite side. For this reason, the shrinkage in the drying process after peeling off is larger than the opposite surface when the film is formed, and the surface is curved with the surface inward. In general, an operation for removing or alleviating the curvature (referred to as curl control) is generally performed during the manufacturing process by the method described in Japanese Patent Publication No. 54-26582. In order to solve the above problems, by adjusting the curl control so that a predetermined curve remains, even if a polarizing plate is manufactured in combination with a highly rigid film, there is no inconvenient curl. Can be used for Here, “adjust curl control” includes the meaning of “no curl control operation”.

  The polarizing plate protective film of the present invention has a rigidity of 320 kPa · m or less and a curvature of 10 mm or more. It is performed by at least one of a method of drying after coating and a method of rapidly cooling after heating one side of the film. In the present invention, the rigidity is a value calculated as the product of the tensile elastic modulus (Pa) and the film thickness (m) in the casting direction of the film. As shown in FIG. 3, the curvature means that the film sample 60 is cut into a rectangle having a casting direction of 305 mm and a width direction of 254 mm, and a surface to be inside the curl is placed on a horizontal and flat base 61. The height of the four corners of the sample 60 that was cut when left standing in an atmosphere of 25 ° C. and 65% RH for 3 hours was raised from the table (in FIG. 3, the height h1 that is the front corner of the film sample 60) , H2 only).

  The polarizing plate protective film is preferably a cellulose acylate film. It is preferable that the difference in shrinkage between the front and back of the polarizing plate protective film is a minute amount.

  The polarizing plate of the present invention may use an optical compensation film instead of the polarizing plate film having high rigidity in the polarizing plate protective film. In the present invention, the optical compensation film means a film in which an optical anisotropic layer 71b is provided on a polarizing plate protective film 71a as shown in FIG.

  According to the polarizing plate protective film of the present invention, the rigidity is 320 kPa · m or less and the bendability is 10 mm or more. Since at least one of the method of drying after applying the solvent and the method of rapidly cooling after heating one surface of the film, the curling of the polarizing plate protective film can be suppressed.

[polymer]
The polymer used in the present invention is not particularly limited. However, it is preferable to use cellulose acylate, and it is particularly preferable to use cellulose triacetate (hereinafter referred to as TAC) having an acetylation degree of 59.0% to 62.5%. A polarizing plate protective film constituted by using a TAC film formed from TAC is excellent in the function of optical properties and the stability of dimensions.

[solvent]
Any known solvent can be used as a solvent for preparing the dope used in the present invention. In particular, halogenated hydrocarbons such as methylene chloride (dichloromethane), esters, ethers, alcohols and the like are preferably used, but are not limited thereto. It is also possible to prepare a dope from a solvent obtained by mixing a plurality of these solvents and form a film from the dope.

[Additive]
Any of known additives can be added to the dope. Examples of the additive include, but are not limited to, a plasticizer, an ultraviolet absorber, and a matting agent. In addition, talc or the like can be added to the dope as another additive. These additives can be mixed at the same time when the dope is prepared. Further, after the dope is prepared, it can be mixed in-line using a static mixer or the like when transferred.

[Preparation of dope]
After the polymer and additives described above are charged into the solvent described above, the dope is prepared by dissolving the polymer and additives by any known dissolution method. This dope generally removes foreign matters by filtration. For filtration, various known filter media such as filter paper, filter cloth, non-woven fabric, metal mesh, sintered metal, and perforated plate can be used. By filtering, foreign substances and undissolved substances in the dope can be removed, and defects due to foreign substances in the product film can be reduced.

  In addition, the dope once dissolved can be heated to further improve the solubility. For heating, there are a method of heating while stirring in a stationary tank, a method of heating while transferring the dope using various heat exchangers such as a multi-tube type, a jacket pipe with a static mixer, and the like. Moreover, it is also possible to heat to the temperature more than the boiling point of dope by providing a cooling process after a heating process, and pressurizing the inside of an apparatus. By performing these heat treatments, the fine undissolved material can be completely dissolved, and foreign matters on the film can be reduced and the filtration load can be reduced.

[Solution casting method]
FIG. 1 shows a schematic diagram of a film production line 10. The dope 12 charged in the mixing tank 11 is stirred by the stirring blade 13 and is uniformly prepared. The dope 12 is sent to the stock tank 15 by the pump 14. Impurities are removed from the stock tank 15 to the filtration devices 17, 18, and 19 by the pump 16, and the impurities are removed and sent to the casting die 20 at a constant flow rate. An ultraviolet absorbent tank 21 is connected to the upstream side of the casting die 20. An ultraviolet absorbent solution 22 is charged in the ultraviolet absorbent tank 21. The ultraviolet absorbent solution 22 is supplied into the dope 12 from the ultraviolet absorbent tank 21 by the pump 23 and is made uniform by the static mixer 24. The dope 12 is cast from the casting die 20 onto the belt 30 and is moved by the rotating rollers 31 and 32 that are rotationally driven by a driving device (not shown). 33 is formed.

  When the film 33 is peeled off from the belt 30, in the case of a dry peeling method, the dope 12 on the belt 30 is dried by applying hot air to reduce the residue of the peeling solvent to less than 60% and then peeled off. It is preferable to peel off onto the take-off roller 34. In this case, a relatively soft film 33 (elastic modulus is about 4 GPa or less) is obtained.

  In the case of the cooling stripping method, a dope is generally cast on a drum that allows the surface to be cooled by passing a refrigerant inside instead of the belt 30, and the stripping solvent residue is 60% or more. In a state where there is no support, the gel is cooled and gelled to give self-support, and then it is fed into the tenter dryer 35 and dried while holding both ends and applying tension. In this case, since the film 33 is dried from both sides at a high speed, a film 33 that is relatively hard (elastic modulus is about 4 GPa or more) is obtained.

  The film 33 is further dried in a drying zone 37 provided with a plurality of rollers 36, and then passes through a cooling zone 38 and is cooled to room temperature. The film 33 fed out from the cooling zone 38 is subjected to a desired curl by the curl control device 40 after being trimmed by the trim device 39 so that the widths thereof are uniform. In the present invention, if the curl (curvature) of the film is 10 mm or more, the step of curling by the curl control device 40 can be omitted. Finally, the film 33 is wound up by the winder 41.

  In order to give the film 33 curvature, it is easy to use the curvature that naturally occurs in the film forming process. Further, as shown in FIG. 1, the curl control device 40 can impart desired curvature. Here, as a method of curl control, a method of directly spraying steam, a method of spraying high-temperature and high-humidity hot air, a method of spraying organic solvent vapor (for example, dichloromethane, methanol, acetone, etc.), an organic solvent (for example, Examples thereof include a method of applying and drying after application of dichloromethane, methanol, acetone, etc., and a method of heating one side of the film and then rapidly cooling it, but is not limited to these methods.

  In the embodiment described above, the curvature of the film 33 is such that the surface that is in contact with the belt 30 at the time of casting is inward, but the surface that is inward at the time of bending is on the polarizing film side. If it is attached to the film, it does not matter which side of the film comes inward. When the film of the present invention was affixed to both sides of the polarizing film, the film was affixed so that the same side of the film faced the polarizing film, and the curvature of the film on both sides was canceled out, resulting in a result. The curvature of the polarizing plate is reduced. Therefore, the film of the present invention can be used without being combined with a film having a high rigidity, and does not adversely affect the flexibility in use.

  The film 33 formed by the method described above can be used as a polarizing plate protective film 51 as shown in FIG. As shown in FIG. 2 (a), the polarizing film 52 is sandwiched between the polarizing plate protective film 51 of the present invention and the rigid film 53 (see FIG. 2 (b)). Since the film has a curvature in a direction opposite to the direction in which the polarizing plate is intended to be curved in advance, the force resulting from the contraction of the polarizing film and the bending force of the film cancel each other, and the result is shown in FIG. As described above, the polarizing plate 50 is obtained so as not to be bent over time, or to an extent that does not hinder practical use. In general, the rigidity of the film obtained in the present invention is 320 kPa · m or less, and the rigidity of a film having a large rigidity combined with this film is 320 kPa · m or more. In addition, when the difference in stiffness between the two is 20 kPa · m or less, the problem of bending due to bonding is generally not a problem. Moreover, both are bonded and it is set as a polarizing film. Immediately after bonding, the film can be flat with no curvature, but due to the principle described above, the polarizing film has a shrinking force with time and the rigidity of the protective film on both sides is different. There is a slight difference in the amount of shrinkage, which causes the polarizing plate to bend. However, when the difference in stiffness is 200 kPa · m or more, the polarization of the polarizing plate is large even according to the present invention, and the effect of the present invention is not obtained.

  On the other hand, a polarizing plate can be produced by sticking the film of the present invention on both surfaces of the polarizing film depending on production and supply / demand. In this case, by combining the surfaces to be attached to the polarizing film of the film to be attached to both sides, the curvatures of the films disappear from each other, and as a result, a polarizing plate having no curvature is obtained. Thus, the film of the present invention can be used in combination with a film having high rigidity, or can be used in combination with the films of the present invention, and has flexibility in production and supply / demand.

  FIG. 4 shows another embodiment of the polarizing plate 70. The above-described film 33 is used as the polarizing plate protective film 71 a, an optically anisotropic layer 71 b in which discotic liquid crystal is aligned is formed on the film 71 a, and the optical compensation film 71 is formed on one surface of the polarizing film 72. . A polarizing plate protective film 73 is formed on the other surface of the polarizing film 72 using the film 33 described above. The film 33 according to the present invention can also be used as an optical functional film such as an antireflection film having an antiglare layer formed thereon. From these products, it is also possible to constitute a part of a liquid crystal display device.

  Examples and Comparative Examples are given below, but the present invention is not limited thereto. The description will be made in detail with respect to Experiment 1 according to the present invention, and with respect to Experiments 2 to 6 which are other examples and Experiments 7 to 10 which are comparative examples, the description of the same conditions as in Experiment 1 is omitted. .

[Experiment 1]
<Preparation of raw material dope>
(Preparation of fine particle dispersion a)
Silica (Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) 2.00% by weight
Cellulose acetate (acetylation degree 61.0%) 2.00% by weight
Triphenyl phosphate 0.16% by weight
Biphenyl diphenyl phosphate 0.08% by weight
Methylene chloride 88.10% by weight
7.66% by weight of methanol
A solution was prepared and dispersed with an attritor so that the volume average particle size was 0.5 μm. Here, the value measured with a particle size distribution measuring apparatus LA920 manufactured by Horiba, Ltd. was used as the volume average particle diameter.

(Preparation of raw material dope A)
Cellulose triacetate (acetylation degree 61.0%) 89.3% by weight
Triphenyl phosphate 7.1% by weight
Biphenyl diphenyl phosphate 3.6% by weight
92% by weight of dichloromethane for 100 parts by weight of solid content
8% by weight of methanol
The dope was prepared by appropriately adding a mixed solvent and stirring and dissolving. The solid content concentration of the dope was 18.5%. Furthermore, 6.5 parts by weight of the fine particle dispersion a is added to 100 parts by weight of the solid content of the dope, and the mixture is stirred and mixed. The mixture was filtered through a filter (Nippon Seisen Co., Ltd. 06N, nominal pore diameter 10 μm), and further filtered through a mesh filter (Nippon Pole Co., Ltd. RM, nominal pore diameter 45 μm).

(Preparation of UV absorber solution b)
2 (2′-Hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole 5.83% by weight
2 (2′-hydroxy-3 ′, 5′-di-tert-amylphenyl) benzotriazole 11.66% by weight
Cellulose acetate (acetylation degree 61.0%) 1.48% by weight
Triphenyl phosphate 0.12% by weight
Biphenyl diphenyl phosphate 0.06% by weight
Dichloromethane 74.38% by weight
Methanol 6.47% by weight
An ultraviolet absorber solution was prepared according to the above formulation and filtered through an Astropore 10 μm filter manufactured by Fuji Photo Film Co., Ltd.

  For the above-mentioned dope A, using a static mixer, adjusting the amount of the UV absorber solution b with respect to the solid content in the dope so that the value expressed by weight% is 1.04. Added and mixed in the piping path.

  The dope was cast using the film forming line 10 shown in FIG. 1 so that the average thickness of the wound film was 80 μm, dried with hot air until self-supporting, and peeled off as a film 33. Here, the peeled film was sampled and the residual solvent content was measured. The resulting stripped residual solvent content was 39%. This film 33 was introduced into a tenter 35 and dried while holding both ends and applying tension. Thereafter, the film was dried in the drying zone 37 and wound up. In the drying zone 13, the film surface temperature was heated to a maximum of 130 ° C. After that, after passing the cooling zone 38 to cool the film to room temperature, the edge cutting device 39 performs the edge cutting so that the product film width becomes 1340 mm, and the winder is provided with the FRP resin core having a diameter of 168 mm. 41 was wound up.

<Creation of polarizing film>
Kuraray PVA film (75 μm) was immersed in an aqueous solution of 0.3 g / L of iodine and 18.0 g / L of potassium iodide at 25 ° C., and further 80 g / L of boric acid, 30 g / L of potassium iodide, It was stretched 5.0 times in an aqueous solution of 10 g / L of ferrous chloride and 50 ° C. Dry at 60 ° C. for 5 minutes. A polarizing plate was prepared by attaching a cellulose acetate film subjected to saponification treatment using a 4% aqueous solution of PVA (PVA-117H manufactured by Kuraray Co., Ltd.) as an adhesive to the polarizing film thus prepared. The film produced by using the above method is attached on one side so that the surface in contact with the belt 30 at the time of casting is on the polarizing film side, and on the other side is TD80UF manufactured by Fuji Photo Film Co., Ltd. (Elastic modulus 4.1 GPa, thickness 80 μm, film rigidity 328 kPa · m) was pasted.

[Experiment 2]
In the production of the cellulose acetate film of Experiment 1, the solvent used for preparing the raw material dope A was 85% by weight of dichloromethane.
15% by weight of methanol
A polarizing plate was produced in the same manner as in Experiment 1, except that the stripped residual volatile content was 44%.

[Experiment 3]
A polarizing plate was produced in the same manner as in Experiment 2 except that the stripped residual solvent content was 31% in the production of the cellulose acetate film in Experiment 2.

[Experiment 7]
In the production of the cellulose acetate film in Experiment 1, a polarizing plate was produced in the same manner as in Experiment 1 except that curl control was performed immediately before the film being produced entered the cooling zone. Here, the curl control is performed by spraying steam at 120 ° C. in an amount of 1 kg / m ² on the surface side not in contact with the support at the time of casting while maintaining the film temperature at 95 ° C. while the film is conveyed. It carried out by conveying the zone which hold | maintained room temperature at 65 to 85 degreeC for 30 second or more.

[Experiment 4]
A polarizing plate was prepared in the same manner as in Experiment 3 except that curl control was performed in the same manner as in Experiment 7 except that the cellulose acetate film was formed in Experiment 3.

[Experiment 5]
A polarizing plate was produced in the same manner as in Experiment 1 except that the curl control was performed in the same manner as in Experiment 7 on the surface side that was in contact with the support during casting in the production of the cellulose acetate film in Experiment 8 described later.

[Experiment 6]
In Experiment 1, a polarizing plate was prepared in the same manner as in Experiment 1, except that a WV film (thickness 110 μm, elastic modulus 3.6 GPa, rigidity 396 kPa · m) manufactured by Fuji Photo Film Co., Ltd. was attached to the opposite surface instead of TD80UF. did.

[Experiment 8]
A polarizing plate was produced in the same manner as in Experiment 1 except that the drying temperature after peeling was set to a maximum of 80 ° C. in the production of the cellulose acetate film in Experiment 1.

[Experiment 9]
A polarizing plate was produced in the same manner as in Experiment 1 except that the film thickness was 30 μm.

[Experiment 10]
In Experiment 7, as in Experiment 6, a polarizing plate was produced in the same manner as in Comparative Example 1, except that a WV film manufactured by Fuji Photo Film Co., Ltd. was attached to the opposite surface instead of TD80UF.

<Evaluation of polarizing plate>
In each, the elastic modulus and self-curvability of the obtained film and the curvability that the polarizing plate develops over time were evaluated. As the elastic modulus of the film, a value obtained by pulling the film sample in the casting direction with Tensilon was used. The rigidity of the film was determined by the product of a value representing the thickness of the film in μm and a value representing the elastic modulus of the film measured above in GPa. The unit is kPa · m.

  Evaluation of the curvature of the film was performed as follows. The film is cut into a rectangle having a casting direction of 305 mm and a width direction of 254 mm. This is left on a horizontal and smooth table in an atmosphere of 25 ° C. and 65% RH so that the surface in contact with the support at the time of casting of the film faces up, and left for 3 hours. Since the film was curved and its four corners were lifted from the platform, the height of the lift was measured with a scale, and the value obtained by averaging the values of the four corners in mm was taken as the value of curvature. The curvature of the polarizing plate was measured as follows. A rectangular sample with a long side of 305 mm and a short side of 254 mm was prepared by cutting each side so as to form an angle of 45 degrees with respect to the film forming direction of the polarizing film. It is allowed to stand so that the inner surface of the curve faces up, and is conditioned for 48 hours in an atmosphere of 25 ° C. and 65% RH. Of the two diagonal lines of the conditioned sample, measure the height at which the two corners at the opposite ends of the diagonal line forming an angle close to the film-forming direction of the polarizing film are lifted from the table by bending. The curvature value was used. The obtained evaluation results are shown in Table 1.

  The practically acceptable curvature of the polarizing plate is 20 mm or less, preferably 15 mm or less, and more preferably 10 mm or less. In addition, from the present example, the curvature of the film (polarizing plate protective film) is 10 mm, preferably more than 20 mm, so that the bending property of the polarizing plate is improved, more preferably 30 mm or more, and most preferably 40 mm or more. Proven.

  However, when the difference in film rigidity exceeds 200 kPa · m, the difference is too large, so that the effect of the present invention cannot be exhibited. Further, when the difference in film rigidity is 20 kPa · m or less, the difference in rigidity is small and the bending property of the polarizing plate is not generally a problem, and a known method for manufacturing a polarizing plate can be applied.

  In comparison between Experiment 5 and Experiment 8, the only difference is the presence or absence of curl control, but the elastic modulus of the film is different. This is because the physical properties in the vicinity of the surface subjected to the curl control operation are changed by the curl control operation, and the rigidity is thereby lowered. Therefore, the curl control is a disadvantageous direction with respect to the physical properties, and works in the direction of reducing the effect of imparting the curvature. Thus, it is preferable to obtain a predetermined curvature without providing curl control. If the curvature of the film is too large, the film is likely to be broken or wrinkled during conveyance in the polarizing plate production process, which adversely affects the production efficiency. From this viewpoint, the curvature of the film is preferably 80 mm or less, and more preferably 65 mm or less.

It is the schematic of the film forming line which forms the polarizing plate protective film which concerns on this invention. It is sectional drawing which showed the layer structure of the polarizing plate which concerns on this invention. It is a schematic sectional drawing for demonstrating curvature. It is sectional drawing which showed the other layer structure of the polarizing plate which concerns on this invention. It is the schematic sectional drawing which showed one form of the polarizing plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Film forming line 12 Dope 30 Belt 33 Film 34 Stripping roller 40 Curl control apparatus 50, 70 Polarizing plate 51, 53, 73 Polarizing plate protective film 52, 72 Polarizing film 71 Optical compensation film

Claims (3)

The rigidity is 320 kPa · m or less,
And the curvature is 10 mm or more, the control of the curvature is a steam spraying method, a wet hot air spraying method, an organic solvent vapor spraying method, a method of drying after applying an organic solvent, after heating one side of the film A polarizing plate protective film, which is obtained by at least one of the rapid cooling methods.   The polarizing plate protective film according to claim 1, wherein the polarizing plate protective film is a cellulose acylate film. The polarizing plate protective film according to claim 1 or 2, wherein a difference in shrinkage between the front and back surfaces of the polarizing plate protective film is a minute amount.

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