Polarizing plate and method for manufacturing the same

Abstract

The present invention provides a polarizing plate which does not change color even in a high temperature (105° C.) and long time (600 hours or more) durability test. The polarizing plate of the present invention has a monomer hue b value of 2.7 or more and an absorbance of 4.5 or less at a wavelength of 700 nm.

Description

Technical Field

[0001] The present invention relates to a polarizing plate and a method for manufacturing the same. Background Art

[0002] Patent Documents 1 and 2 propose polarizing films whose color tone changes little even after being heated at 120° C. for 100 hours.

[0003] Patent Document 3 discloses a polarizing film that can provide a polarizing plate having excellent durability in a heat cycle test and has an orthogonal color tone of neutral gray.

[0004] Patent Document 4 proposes an optical layered body which is excellent in the yellowing suppression effect even when exposed to a high temperature environment.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2004-226707

[0008] Patent Document 2: Japanese Patent Application Publication No. 2007-304626

[0009] Patent Document 3: Japanese Patent Application Publication No. 2013-148806

[0010] Patent Document 4: Japanese Patent Application Publication No. 2018-025765 Summary of the invention

[0011] Problems to be solved by the invention

[0012] The polarizing plates described in Patent Documents 1 to 4 may discolor in a durability test under more severe conditions, namely, a high temperature (eg, 105° C.) and a long time (eg, 600 hours or more).

[0013] An object of the present invention is to provide a polarizing plate which does not undergo discoloration even in a durability test at a high temperature (105° C.) and for a long period of time (600 hours or more).

[0014] Means used to solve problems

[0015] The present invention provides the following polarizing plate and a method for producing the same.

[0016] [1] A polarizing plate having a single-body color tone b value of 2.7 or more and an absorbance at a wavelength of 700 nm of 4.5 or less.

[0017] [2] The polarizing plate according to [1], comprising a polarizer and a first thermoplastic resin film bonded to one side of the polarizer via an adhesive.

[0018] [3] The polarizing plate according to [2], further comprising a second thermoplastic resin film, wherein the second thermoplastic resin film is bonded to the polarizer on the side opposite to the first thermoplastic resin film via an adhesive.

[0019] [4] The polarizing plate according to [2] or [3], wherein the adhesive is a water-based adhesive.

[0020] [5] The polarizing plate according to any one of [1] to [4], wherein the content of zinc in the polarizing plate is 150 ppm or more.

[0021] [6] An in-vehicle display device comprising the polarizing plate described in any one of [1] to [5].

[0022] [7] A method for producing a polarizing plate, which is the method for producing a polarizing plate described in [2],

[0023] The polarizer includes a polyvinyl alcohol-based resin film,

[0024] The manufacturing method includes a washing step in which the polyvinyl alcohol-based resin film is washed with a washing liquid and the washing is not carried out with a washing liquid having a temperature higher than 22° C.

[0025] [8] The method for producing a polarizing plate according to [7], further comprising a drying step of drying the polyvinyl alcohol-based resin film at a temperature of 96° C. or higher.

[0026] [9] The method for manufacturing a polarizing plate according to [7] or [8], further comprising a bonding step, in which the first thermoplastic resin film is bonded to one side of the polarizer via an adhesive, and the adhesive is dried at a temperature above 85°C.

[0027] Effects of the Invention

[0028] According to the present invention, a polarizing plate can be provided which does not undergo discoloration even in a durability test at a high temperature (105° C.) and for a long period of time (600 hours or more). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0030] Figure 2 This is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0031] Figure 3 It is a cross-sectional schematic diagram showing an example of the arrangement of an apparatus used in a polarizing plate production process.

[0032] Description of Reference Numerals

[0033] 10 polarizing plate, 11 first thermoplastic resin film, 12 polarizing plate, 13 second thermoplastic resin film, 110 raw material film of polyvinyl alcohol resin, 111 lead-out roller, 113 swelling tank, 115 dyeing tank, 117 cross-linking tank, 119 cleaning tank, 123 drying furnace, 127 winding roller, 130 polarizing plate. DETAILED DESCRIPTION

[0034] The following describes the embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to the following embodiments. In all the following drawings, the scales are appropriately adjusted to facilitate understanding of the components, and the scales of the components shown in the drawings are not necessarily consistent with the scales of the actual components.

[0035] <Polarizing plate>

[0036] The monomer tone b value of the polarizing plate of one embodiment of the present invention is 2.7 or more, and the absorbance at a wavelength of 700nm is 4.5 or less. For the polarizing plate, when the monomer tone b value is 2.7 or more, by setting the absorbance at a wavelength of 700nm to 4.5 or less, there is a tendency that it is not easy to discolor even in a durability test (hereinafter referred to as a durability test) at a high temperature (105°C) and a long time (more than 600 hours). In this specification, a durability test refers to a durability test performed in accordance with the method described in the first embodiment column described later. The so-called no discoloration means that no yellowing is observed when the polarizing plate is observed in accordance with the method described in the first embodiment column described later. The polarizing plate of the present invention preferably does not discolor until 1000 hours, more preferably until 1400 hours in the durability test.

[0037] Generally speaking, when the absorbance of the polarizing plate at a wavelength of 700 nm is high, it tends to be less likely to turn red, and when the monomer tone b value of the polarizing plate is low, it tends to be less likely to turn yellow. －The decomposition of polyvinyl alcohol and the polyeneization of the polarizer tend to cause a decrease in the absorbance at a wavelength of 700nm and an increase in the monomer tone b value. Therefore, it is believed that in order to suppress discoloration in the durability test of the polarizing plate, it is advantageous when the absorbance at a wavelength of 700nm of the polarizing plate is high and the monomer tone b value is low. However, unexpectedly, the inventors found that in a more severe durability test at high temperature (105°C) and for a long time (more than 600 hours), discoloration can be suppressed by setting the monomer tone b value of the polarizing plate to more than 2.7 and the absorbance at a wavelength of 700nm to less than 4.5. The polarizing plate having a monomer tone b value of more than 2.7 and an absorbance at a wavelength of 700nm of less than 4.5 is a new type of polarizing plate that has not been disclosed in Patent Documents 1 to 4.

[0038] The single-tone b value of the polarizing plate is preferably 2.9 or more, more preferably 3.1 or more, further preferably 3.3 or more, and particularly preferably 3.5 or more. The single-tone b value of the polarizing plate is usually 4.1 or less, for example, 3.9 or less.

[0039] The b value of the polarizing plate is the b value of the polarizing plate itself in the Lab color system. The b value is calculated using the following formula based on the tristimulus values ​​X, Y, and Z specified in JIS Z 8722:2009 "Color Measurement Methods - Reflected and Transmitted Object Color".

[0040] b value = 7.0 (Y - 0.847Z) / Y 1 / 2

[0041] The single-body color tone b value of the polarizing plate can be measured according to the measuring method described in the section of Examples described later.

[0042] The absorbance of the polarizing plate at a wavelength of 700 nm is preferably 4.4 or less, more preferably 4.3 or less. The absorbance of the polarizing plate at a wavelength of 700 nm is usually 3.9 or more, for example, 4.1 or more, or 4.2 or more.

[0043] The absorbance of the polarizing plate at a wavelength of 700 nm can be measured using an absorptiophotometer such as an ultraviolet-visible spectrophotometer, and calculated according to the following formula.

[0044] Absorbance at 700nm = -log[{TD transmittance at 700nm (%)} / 100]

[0045] The measurement is performed using polarized light parallel to the absorption axis direction of the polarizing plate as incident light. In this formula, the TD transmittance is the transmittance when the direction of polarized light emitted from the Glan-Thomson prism is orthogonal to the transmission axis of the polarizing plate.

[0046] The absorbance of the polarizing plate at a wavelength of 700 nm can be measured according to the measurement method described in the section of Examples described later.

[0047] The monomer hue b value and the absorbance at a wavelength of 700 nm within the above range can be obtained by the following operations, namely, adjusting the temperature of the cleaning liquid in the cleaning step in the polarizer manufacturing process described later, adjusting the drying temperature in the drying step, and adjusting the drying temperature of the adhesive used to bond the polarizer to the thermoplastic resin film.

[0048] The polarizing plate may contain zinc. When the polarizing plate contains zinc, the zinc is preferably contained in at least one of the polarizer and the adhesive. When the polarizing plate contains zinc, the content of zinc in the polarizing plate may be, for example, 150 ppm or more. When the content of zinc in the polarizing plate is 150 ppm or more, there is a tendency to easily suppress discoloration in a durability test. From the viewpoint of suppressing discoloration, the content of zinc in the polarizing plate is preferably 200 ppm or more, and more preferably 250 ppm or more. On the other hand, the content of zinc in the polarizing plate is generally 1000 ppm or less. The content of zinc is determined according to the determination method described in the embodiment column described later. The content of zinc in the polarizing plate can be set within the above range, for example, by adjusting the zinc concentration in the polarizer and / or the adhesive.

[0049] Figure 1 A polarizing plate 10 according to one embodiment of the present invention is shown. Figure 1 As shown in FIG. 1 , the polarizing plate 10 may include a polarizing plate 12 and a first thermoplastic resin film 11 bonded to one side of the polarizing plate 12 via an adhesive. Figure 2 As shown in the figure, the polarizing plate 10 may further include a second thermoplastic resin film 13, which is attached to the polarizer 12 on the side opposite to the first thermoplastic resin film 11 via an adhesive. Hereinafter, the first thermoplastic resin film and the second thermoplastic resin film are sometimes collectively referred to as a thermoplastic resin film. The polarizing plate may further include an adhesive layer, an optical functional layer, and a protective film described later on the side opposite to the polarizer side of the thermoplastic resin film.

[0050] The polarizing plate can be used in an image display device. The image display device can be any image display device such as a liquid crystal display device, an organic EL display device, but preferably a liquid crystal display device. The liquid crystal display device has a liquid crystal panel having a liquid crystal unit as an image display element, and a backlight. When constructing a liquid crystal display device, the polarizing plate can be used as a polarizing plate configured on the visible side, can also be used for a polarizing plate configured on the backlight side, and can also be used for a polarizing plate on both the visible side and the backlight side.

[0051] When the polarizing plate includes the first thermoplastic resin film and the second thermoplastic resin film, the polarizing plate can be attached to the image display device in such a manner that the first thermoplastic resin film is on the outside of the image display device. When the polarizing plate includes the first thermoplastic resin film and the second thermoplastic resin film, the polarizing plate is suitable for a vehicle-mounted display device including a light-transmitting member disposed on the first thermoplastic resin film side of the polarizing plate and a display device disposed on the second thermoplastic resin film side of the polarizing plate in this order. The light-transmitting member may be a glass plate, a light-transmitting resin film, or the like.

[0052] [Polarizing plate]

[0053] The polarizer is an absorption-type polarizer having the following properties, that is, absorbing linear polarized light having a vibration plane parallel to its absorption axis and transmitting linear polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). For example, the polarizer can be a polarizer in which a dichroic pigment such as iodine is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film.

[0054] The thickness of the polarizer is usually 65 μm or less, preferably 50 μm or less, more preferably 35 μm or less, and further preferably 30 μm or less. The thickness of the polarizer is usually 2 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. The thickness of the polarizer can be controlled, for example, by selecting a polyvinyl alcohol resin film, adjusting the stretching ratio, and the like.

[0055] Reference Figure 3 , an example of the polarizer manufacturing process is described. The polyvinyl alcohol resin film 110 as the raw material film rolled out from the lead-out roller 111 is then directed to the swelling tank 113 with water as the swelling bath, where it is immersed in the swelling bath (water) and subjected to swelling treatment (swelling process). The film subjected to swelling treatment is directed to the dyeing tank 115 with an aqueous solution containing iodine as the dyeing bath, where it is dyed and iodine is adsorbed (dyeing process). Thereafter, it is directed to the cross-linking tank 117 with an aqueous solution containing boric acid as the treatment bath, where the polyvinyl alcohol resin adsorbed with iodine is cross-linked using boric acid to fix the iodine (cross-linking process). The film is then cleaned in the cleaning tank 119 (cleaning process), and dried in the drying furnace 123 (drying process) to obtain the polarizer 130. The polarizer 130 is wound on the winding roller 127. The polyvinyl alcohol-based resin film is uniaxially stretched in any one or more stages of the polarizing plate production process, more specifically, in any one or more stages from before the swelling process to the cross-linking process.

[0056] Each treatment step can be continuously performed by continuously conveying the polyvinyl alcohol-based resin film as a raw material film along a film conveying path of the polarizing plate manufacturing apparatus. The film conveying path is equipped with equipment (treatment tank, furnace, etc.) for performing the above-mentioned various treatment steps in accordance with the respective execution order.

[0057] The film conveying path can be constructed by configuring guide rollers, clamping rollers, etc. at appropriate positions in addition to the above-mentioned equipment. For example, guide rollers can be configured before and after each treatment tank or in the treatment tank, thereby allowing the film to be introduced into the treatment tank, immersed in the treatment tank, and pulled out of the treatment tank. More specifically, the film can be immersed in each treatment tank by arranging two or more guide rollers in each treatment tank and conveying the film along these guide rollers.

[0058] As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, for example, a resin obtained by saponifying a polyvinyl acetate resin can be cited. As the polyvinyl acetate resin, in addition to polyvinyl acetate as a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable therewith can also be exemplified. As other monomers copolymerizable with vinyl acetate, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth) acrylamides having an ammonium group, etc. can be cited. The saponification degree of the polyvinyl alcohol resin is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The so-called "(meth) acrylic acid" in this specification refers to at least one selected from acrylic acid and methacrylic acid. The same is true for "(meth) acryloyl".

[0059] The polyvinyl alcohol-based resin may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may be used.

[0060] The average degree of polymerization of the polyvinyl alcohol resin is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol resin can be obtained according to JIS K 6726 (1994). When the average degree of polymerization is within the above range, there is a tendency for excellent polarization performance and film processability.

[0061] The thickness of the polyvinyl alcohol resin film as the raw material film may be, for example, 10 μm to 150 μm, preferably 15 μm to 100 μm, and more preferably 20 μm to 80 μm. The length in the width direction of the polyvinyl alcohol resin film as the raw material film may be, for example, 600 mm to 5000 mm.

[0062] The polyvinyl alcohol-based resin film as the raw material film can be prepared in the form of a roll (rolled product) of a long unstretched or stretched polyvinyl alcohol-based resin film, for example. In this case, the polarizing plate can also be obtained in the form of a long object.

[0063] (1) Swelling process

[0064] The swelling treatment in this step is a treatment performed as needed for the purpose of removing foreign matter, removing plasticizer, imparting easy dyeing properties, and plasticizing the film of the polyvinyl alcohol-based resin film as the raw material film. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film 110 is immersed in a swelling tank containing a treatment liquid containing water. The film can be immersed in one swelling tank or in two or more swelling tanks in sequence. The film can be subjected to uniaxial stretching treatment before the swelling treatment, during the swelling treatment, or before and during the swelling treatment.

[0065] The treatment liquid contained in the swelling tank may be water (eg, pure water), or an aqueous solution to which a water-soluble organic solvent such as alcohol is added. As described above, the treatment liquid contained in the swelling tank may contain a zinc salt.

[0066] The temperature of the treatment liquid contained in the swelling tank during immersion of the membrane is usually 10° C. to 70° C., preferably 15° C. to 50° C., and the membrane immersion time is usually 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds.

[0067] (2) Dyeing process

[0068] The dyeing process in this operation is a process for making the polyvinyl alcohol resin film adsorb dichroic pigments and orient them. Specifically, it can be a process in which the polyvinyl alcohol resin film is immersed in a dyeing tank that accommodates a treatment solution containing dichroic pigments. The film can be immersed in one dyeing tank or in two or more dyeing tanks successively. In order to improve the dyeability of the dichroic pigment, the film provided to the dyeing process can be subjected to at least a certain degree of uniaxial stretching. The uniaxial stretching process before the dyeing process can be replaced by the uniaxial stretching process during the dyeing process, or the uniaxial stretching process can be carried out during the dyeing process on the basis of the uniaxial stretching process before the dyeing process.

[0069] The dichroic pigment may be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include Red BR, Red LR, Red R, Pink LB, Rubine BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, SupraOrange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. The dichroic dye may be used alone or in combination of two or more.

[0070] When using iodine as a dichroic pigment, as a treatment solution contained in the dyeing tank, an aqueous solution containing iodine and potassium iodide can be used. It is also possible to replace potassium iodide and use other iodides such as zinc iodide, or potassium iodide and other iodides can be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., can also coexist. When adding boric acid, it is different from the cross-linking treatment described later in that it contains iodine. The content of iodine in the above-mentioned aqueous solution is generally more than 0.01 mass parts and less than 1 mass parts per 100 mass parts of water. In addition, the content of iodides such as potassium iodide is generally more than 0.5 mass parts and less than 20 mass parts per 100 mass parts of water.

[0071] The temperature of the treatment liquid contained in the dyeing tank when the membrane is immersed is usually above 10°C and below 45°C, preferably above 10°C and below 40°C, and more preferably above 20°C and below 35°C. The immersion time of the membrane can be, for example, above 20 seconds and below 600 seconds, and preferably above 20 seconds and below 300 seconds.

[0072] When a dichroic organic dye is used as the dichroic pigment, an aqueous solution containing the dichroic organic dye can be used as the treatment liquid contained in the dyeing tank. The content of the dichroic organic dye in the aqueous solution is usually 1×10-4 parts by mass or more and 10 parts by mass or less, preferably 1×10 -3 The dyeing tank may contain at least 1 part by mass and at most 1 part by mass. Dyeing aids and the like may also coexist in the dyeing tank, for example, inorganic salts such as sodium sulfate, surfactants, etc. The dichroic organic dye may be used alone or in combination of two or more. The temperature of the treatment liquid contained in the dyeing tank during the immersion of the film is, for example, above 20°C and below 80°C, preferably above 25°C and below 50°C, and the immersion time of the film is usually above 30 seconds and below 600 seconds, preferably above 60 seconds and below 300 seconds.

[0073] (3) Cross-linking process

[0074] The cross-linking treatment of the polyvinyl alcohol-based resin film after the dyeing process with a cross-linking agent is a treatment performed for the purpose of water resistance and color tone adjustment by cross-linking. Specifically, it can be a treatment in which the film after the dyeing process is immersed in a treatment liquid contained in a cross-linking tank containing a cross-linking agent. The film can be immersed in one cross-linking tank or in two or more cross-linking tanks in sequence. It is also possible to perform a uniaxial stretching treatment during the cross-linking treatment.

[0075] As cross-linking agent, boric acid, glyoxal, glutaraldehyde etc. can be mentioned, preferably boric acid is used. It is also possible to use more than two cross-linking agents. The content of boric acid in the treatment solution accommodated in the cross-linking tank is generally more than 0.1 mass part and less than 15 mass parts per 100 mass parts of water, preferably more than 1 mass part and less than 10 mass parts. When the dichroic pigment is iodine, the treatment solution accommodated in the cross-linking tank preferably also contains iodide on the basis of boric acid. The content of iodide in the treatment solution accommodated in the cross-linking tank is generally more than 0.1 mass part and less than 15 mass parts per 100 mass parts of water, preferably more than 5 mass parts and less than 12 mass parts. As iodide, potassium iodide, zinc iodide etc. can be mentioned. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate etc. can also be coexisted in the cross-linking tank.

[0076] The temperature of the treatment liquid contained in the crosslinking tank during immersion of the film is, for example, 30°C to 85°C, preferably 30°C to 60°C, and the immersion time of the film is, for example, 2 seconds to 600 seconds, preferably 2 seconds to 300 seconds.

[0077] In the cross-linking process, there may be more than two cross-linking tanks. In this case, the composition and temperature of the treatment solution contained in each cross-linking tank may be the same or different. The treatment solution contained in the cross-linking tank may have a concentration and temperature of a cross-linking agent and an iodide corresponding to the purpose of impregnating the polyvinyl alcohol-based resin film. It is also possible to perform a cross-linking treatment for water resistance by cross-linking and a cross-linking treatment for color tone adjustment (color correction) in multiple processes (e.g., multiple tanks).

[0078] Generally speaking, in the case of implementing both a cross-linking treatment for water resistance utilizing cross-linking and a cross-linking treatment for color tone adjustment (color correction), the tank (color correction tank) for implementing the cross-linking treatment for color tone adjustment (color correction) is arranged in the rear section. The temperature of the treatment liquid contained in the color correction tank is, for example, above 10°C and below 55°C, preferably above 20°C and below 50°C. The content of the cross-linking agent in the treatment liquid contained in the color correction tank is, for example, above 1 part by mass and below 5 parts by mass per 100 parts by mass of water. The content of iodide in the treatment liquid contained in the color correction tank is, for example, above 3 parts by mass and below 30 parts by mass per 100 parts by mass of water.

[0079] As mentioned above, when manufacturing polaroid, polyvinyl alcohol resin film is subjected to uniaxial stretching (stretching process) in any one or more stages from before swelling process to cross-linking process. From the viewpoint of improving the dyeability of dichroic pigment, the film provided to the dyeing process is preferably a film subjected to at least some degree of uniaxial stretching, or preferably, the uniaxial stretching before the dyeing process is replaced by the uniaxial stretching during the dyeing process, or, on the basis of the uniaxial stretching before the dyeing process, the uniaxial stretching during the dyeing process is also carried out.

[0080] The uniaxial stretching process can be any of the dry stretching for stretching in the air and the wet stretching for stretching in the groove, or both of them can be carried out. The uniaxial stretching process can be the roller-to-roll stretching, hot roller stretching, tenter stretching, etc. for longitudinal uniaxial stretching applied with a circumferential speed difference between two clamping rollers, but preferably includes roller-to-roll stretching. The stretching ratio (the cumulative stretching ratio thereof in the case of stretching treatment in more than two stages) based on the original material film is more than 3 times and about 8 times or less. In order to give good polarization characteristics, the stretching ratio is preferably set to more than 4 times, and more preferably set to more than 5 times.

[0081] (4) Cleaning process

[0082] The cleaning process in this process is a process implemented as needed for the purpose of removing excess cross-linking agents, dichroic pigments and other agents attached to the polyvinyl alcohol resin film, and is a process of cleaning the polyvinyl alcohol resin film after the cross-linking process using a cleaning solution containing water. Specifically, it can be a process of immersing the polyvinyl alcohol resin film after the cross-linking process in a treatment solution (cleaning solution) contained in a cleaning tank. The film can be immersed in one cleaning tank, or in two or more cleaning tanks in sequence. Alternatively, the cleaning process can also be a process of spraying the cleaning solution as a spray liquid onto the polyvinyl alcohol resin film after the cross-linking process, or the above-mentioned immersion process can be combined with the spraying process.

[0083] The cleaning liquid may be water (for example, pure water) or an aqueous solution to which a water-soluble organic solvent such as alcohol is added.

[0084] In the cleaning process, the temperature of the cleaning liquid used to clean the polyvinyl alcohol resin film after the cross-linking process can be, for example, above 2°C and below 40°C. From the viewpoint of obtaining the monomer hue b value and the absorbance at a wavelength of 700nm within the above-mentioned range, it is preferred not to use a cleaning liquid with a temperature higher than 22°C for cleaning.

[0085] When the polyvinyl alcohol-based resin film after the cross-linking step is immersed in a cleaning tank, the temperature of the cleaning liquid in the cleaning tank is preferably 2° C. to 22° C., more preferably 2° C. to 10° C. The time of immersion in the cleaning tank may be, for example, 10 seconds to 100 seconds, preferably 20 seconds to 80 seconds.

[0086] When the cleaning liquid is sprayed as a shower liquid onto the polyvinyl alcohol-based resin film after the crosslinking step, the temperature of the cleaning liquid may be the same temperature or different temperatures in the center and the both ends in the width direction of the polyvinyl alcohol-based resin film. However, from the viewpoint of the monomer color tone b value and the absorbance at a wavelength of 700 nm, it is preferably different temperatures, and it is more preferred that the temperature in the center is lower than the temperature at the both ends. From the viewpoint of the monomer color tone b value and the absorbance at a wavelength of 700 nm, the temperature of the cleaning liquid is preferably 2°C or more and 10°C or less in the center and 10°C or more and 22°C or less at the both ends, and it is more preferred that it is 3°C or more and 7°C or less in the center and 15°C or more and 22°C or less at the both ends.

[0087] (5) Drying process

[0088] The drying step is a region for drying the polyvinyl alcohol-based resin film after the washing step. The polyvinyl alcohol-based resin film after the washing step can be introduced into the drying step while being continuously conveyed, and a drying treatment can be performed, thereby obtaining a polarizing plate.

[0089] The drying treatment is carried out using a drying mechanism (heating mechanism) of the film. A suitable example of the drying mechanism is a drying furnace. The drying furnace is preferably capable of controlling the temperature in the furnace. The drying furnace is, for example, a hot air oven that can increase the temperature in the furnace by supplying hot air, etc. In addition, the drying treatment using the drying mechanism can also be a treatment in which the polyvinyl alcohol-based resin film after the cleaning step is closely attached to one or more heating bodies having a convex curved surface, or a treatment in which the film is heated using a heater.

[0090] The heating body includes a roller (e.g., a guide roller also serving as a heating roller) that has a heat source (e.g., a heat medium such as warm water, an infrared heater) inside and can increase the surface temperature. The heater includes an infrared heater, a halogen heater, a plate heater, and the like.

[0091] In the drying step, the temperature of the drying treatment (e.g., the temperature inside the drying furnace, the surface temperature of the hot roller, etc.) can be, for example, 30° C. or higher, and is preferably 96° C. or higher from the viewpoint of obtaining the monomer color tone b value and the absorbance at a wavelength of 700 nm within the above range. The temperature of the drying treatment is usually 100° C. or lower. The drying time is not particularly limited, and can be, for example, 30 seconds or more and 900 seconds or less, and is preferably 30 seconds or more and 60 seconds or less.

[0092] The drying process may be a single stage or may be divided into a plurality of stages, preferably divided into two or more stages and four or less stages. When the drying process is divided into a plurality of stages, from the viewpoint of the monomer hue b value and the absorbance at a wavelength of 700 nm, it is preferred that the drying temperature of at least one stage is 96° C. or higher. When the drying process is divided into a plurality of stages, the temperature of the drying treatment is preferably set so that the temperature of the subsequent stage becomes higher than that of the initial stage. When the drying process is divided into a plurality of stages, the drying time of each stage may be, for example, 10 seconds or more and 300 seconds or less, preferably 10 seconds or more and 20 seconds or less.

[0093] In the polarizer manufacturing process, at least one of the treatment solutions that the polyvinyl alcohol resin film is treated can contain zinc salt. As the treatment tank for accommodating the treatment solution, for example, a swelling tank, a dyeing tank, a cross-linking tank, a cleaning tank, a color-correcting tank, etc. can be cited. The treatment tank for accommodating the treatment solution containing zinc salt is preferably a treatment tank located after the dyeing tank and before the cleaning tank, more preferably at least one selected from the cross-linking tank and the color-correcting tank, and more preferably at least one selected from the last cross-linking tank and the color-correcting tank in the presence of more than two cross-linking tanks. By immersing the polyvinyl alcohol resin film in the treatment solution containing zinc salt, the resulting polarizer can be made to contain zinc element. For the content of zinc element in the polarizer, the content of zinc element in the above-mentioned range can be set by adjusting the concentration of zinc salt in the treatment solution, the immersion time of the polyvinyl alcohol resin film in the treatment solution containing zinc salt, the temperature of the treatment solution, etc.

[0094] As the zinc salt contained in the treatment solution, for example, zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, zinc nitrate, etc. can be cited. Among them, zinc nitrate is preferred from the aspect of minimizing the change in tension. The zinc salt can be added to the treatment solution in the form of a zinc salt solution.

[0095] The concentration of the zinc salt in the treatment liquid varies in each treatment tank, and may be, for example, 1 to 10 parts by mass, preferably 2 to 7 parts by mass, relative to 100 parts by mass of the treatment liquid contained in the treatment tank.

[0096] Through the above steps, a polarizing plate in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film can be obtained.

[0097] The obtained polarizing plate can be directly sent to the next polarizing plate production step (step of laminating a thermoplastic resin film to one side or both sides of the polarizing plate), for example.

[0098] [Thermoplastic resin film]

[0099] Thermoplastic resin films may be, for example, polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.), cyclic polyolefin resins (norbornene resins, etc.); cellulose ester resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resins; (meth) acrylic resins such as polymethyl methacrylate resins; or light-transmitting resin films such as mixtures and copolymers thereof. Thermoplastic resin films may be a single-layer structure formed of a resin layer containing one or more thermoplastic resins, or a multilayer structure in which a plurality of resin layers containing one or more thermoplastic resins are stacked.

[0100] The first thermoplastic resin film and the second thermoplastic resin film may be thermoplastic resin films of the same type or different types.

[0101] Examples of the linear polyolefin-based resin include homopolymers of linear olefins such as polyethylene resins and polypropylene resins, and copolymers containing two or more linear olefins.

[0102] Cyclic polyolefin resin is a general term for resins containing cyclic olefins as polymerized units, with norbornene, tetracyclododecene (also known as dimethyl octahydronaphthalene) or their derivatives as representative examples. Examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins and hydrogenated products thereof, addition polymers of cyclic olefins, copolymers of cyclic olefins with chain olefins such as ethylene and propylene or aromatic compounds having a vinyl group, and modified (co)polymers of these modified with unsaturated carboxylic acids or their derivatives.

[0103] Among them, it is preferable to use a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer as a cyclic olefin.

[0104] The cellulose ester resin is a resin in which at least a part of the hydroxyl groups in cellulose are esterified with acetic acid, and may be a mixed ester in which a part is esterified with acetic acid and a part is esterified with another acid. The cellulose ester resin is preferably an acetyl cellulose resin.

[0105] Examples of the acetyl cellulose-based resin include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.

[0106] The polyester resin is a resin other than the above-mentioned cellulose ester resin having an ester bond, and is generally a resin containing a polycondensate of a polycarboxylic acid or a derivative thereof and a polyol.

[0107] Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polycyclohexylene dimethylene naphthalate.

[0108] Among them, polyethylene terephthalate is preferably used from the viewpoints of mechanical properties, solvent resistance, scratch resistance, cost, etc. Polyethylene terephthalate refers to a resin in which 80 mol% or more of repeating units are composed of ethylene terephthalate, and may also contain constituent units derived from other copolymer components.

[0109] Examples of other copolymerization components include a dicarboxylic acid component and a diol component.

[0110] Examples of the dicarboxylic acid component include isophthalic acid, 4,4'-dicarboxybiphenyl, 4,4'-dicarboxybenzophenone, bis(4-carboxyphenyl)ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalate, and 1,4-dicarboxycyclohexane.

[0111] Examples of the diol component include propylene glycol, butylene glycol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol.

[0112] The dicarboxylic acid component and the diol component may be used in combination of two or more types, respectively, as necessary.

[0113] Furthermore, hydroxycarboxylic acids such as p-hydroxybenzoic acid, p-hydroxyethoxybenzoic acid, and β-hydroxyethoxybenzoic acid may be used in combination with the above-mentioned dicarboxylic acid components and diol components.

[0114] As other copolymerization components, a dicarboxylic acid component and / or a diol component having an amide bond, a urethane bond, an ether bond, a carbonate bond, or the like may be used in a small amount.

[0115] Polycarbonate resins are polyesters formed from carbonic acid and diols or bisphenols. Among them, aromatic polycarbonates having diphenylalkane in the molecular chain are preferably used from the viewpoints of heat resistance, weather resistance, and acid resistance.

[0116] Examples of the polycarbonate include polycarbonates derived from bisphenols such as 2,2-bis(4-hydroxyphenyl)propane (also known as bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)isobutane, and 1,1-bis(4-hydroxyphenyl)ethane.

[0117] The (meth)acrylic resin is a polymer containing a structural unit derived from a (meth)acrylic monomer, and examples of the (meth)acrylic monomer include methacrylate and acrylate.

[0118] Examples of the methacrylate include methyl methacrylate, ethyl methacrylate, n-, iso- or tert-butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate.

[0119] Examples of the acrylic acid ester include ethyl acrylate, n-, iso- or tert-butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate.

[0120] The thermoplastic resin film is preferably a cellulose ester resin film or a cyclic polyolefin resin film.

[0121] The thermoplastic resin film may contain additives as necessary, such as lubricants, anti-blocking agents, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, light stabilizers, impact resistance improvers, surfactants, and the like.

[0122] Examples of the ultraviolet absorber include salicylate compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex compounds.

[0123] Either or both of the first thermoplastic resin film and the second thermoplastic resin film may be a protective film having optical functions such as a phase difference film and a brightness enhancement film. For example, a transparent resin film containing the above materials may be stretched (uniaxially stretched or biaxially stretched, etc.), or a liquid crystal layer may be formed on the film, thereby producing a phase difference film having an optional phase difference value.

[0124] A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer or an antifouling layer may be formed on the surface of the thermoplastic resin film on the side opposite to the polarizer side.

[0125] From the viewpoint of thinning the polarizing plate, the thickness of the thermoplastic resin film is preferably thin. However, if it is too thin, the strength decreases and the processability tends to be poor. Therefore, it is preferably 5 μm to 150 μm, more preferably 5 μm to 100 μm, and further preferably 10 μm to 60 μm.

[0126] [Adhesive]

[0127] In order to bond the polarizer to the thermoplastic resin film, an adhesive can be used. The adhesive can be any material that exhibits adhesive strength to the polarizer and the thermoplastic resin film, and examples thereof include water-based adhesives obtained by dissolving or dispersing adhesive components in water, and curable adhesives containing active energy ray-curable compounds. Considering that the surface of the polarizing film is hydrophilic, the adhesive is preferably a water-based adhesive obtained by dissolving or dispersing adhesive components in water. From the viewpoint of being able to reduce the thickness of the cured adhesive, a water-based adhesive is also preferred. Among the adhesive components that are the main components of the water-based adhesive, there are polyvinyl alcohol-based resins, urethane resins, and the like.

[0128] When a polyvinyl alcohol resin is used as the main component of the water-based adhesive, the polyvinyl alcohol resin can be obtained by saponifying a polyvinyl acetate resin. As the polyvinyl acetate resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable therewith can be exemplified. As other monomers copolymerizable with vinyl acetate, for example, unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, acrylamides having an ammonium group, etc. can be cited.

[0129] The polyvinyl alcohol resin used in the adhesive preferably has an appropriate degree of polymerization. For example, when it is set as a 4 mass % concentration aqueous solution, the viscosity is more preferably in the range of 4 mPa·sec to 50 mPa·sec, and further preferably in the range of 6 mPa·sec to 30 mPa·sec.

[0130] The saponification degree of the polyvinyl alcohol resin used in the adhesive is not particularly limited, but is generally preferably 80 mol% or more, more preferably 90 mol% or more. If the saponification degree of the polyvinyl alcohol resin used in the adhesive is low, the water resistance of the adhesive tends to be insufficient.

[0131] The adhesive preferably uses a modified polyvinyl alcohol resin. Suitable modified polyvinyl alcohol resins include acetoacetyl-modified polyvinyl alcohol resins, anion-modified polyvinyl alcohol resins, cation-modified polyvinyl alcohol resins, etc. If such modified polyvinyl alcohol resins are used, it is easy to obtain an effect of improving the water resistance of the adhesive.

[0132] The polyvinyl alcohol resin modified by acetoacetyl group is a resin having an acetoacetyl group (CH3COCH2CO-) in addition to the hydroxyl group constituting the polyvinyl alcohol skeleton, and may also have other groups, such as acetyl group, etc. The acetoacetyl group typically exists in a state of replacing the hydrogen atom of the hydroxyl group constituting the polyvinyl alcohol. The polyvinyl alcohol resin modified by acetoacetyl group can be manufactured, for example, by a method of reacting polyvinyl alcohol with diketene. The polyvinyl alcohol resin modified by acetoacetyl group has an acetoacetyl group as a highly reactive functional group, and is therefore preferred in terms of improving the durability of the adhesive.

[0133] The content of acetoacetyl in the acetoacetyl-modified polyvinyl alcohol resin is not particularly limited as long as it is 0.1 mol% or more. The so-called acetoacetyl content mentioned here is the value expressed as % by the mole percentage of acetoacetyl relative to the total amount of hydroxyl, acetoacetyl, and other ester groups (acetyl groups, etc.) in the polyvinyl alcohol resin, sometimes referred to as "acetoacetylation degree". If the acetoacetylation degree of the polyvinyl alcohol resin is less than 0.1 mol%, the effect of improving the water resistance of the adhesive may not be sufficient. The acetoacetylation degree of the polyvinyl alcohol resin is preferably about 0.1 to 40 mol%, more preferably 1 to 20 mol%, and particularly preferably 2 to 7 mol%. If the acetoacetylation degree is greater than 40 mol%, the effect of improving water resistance becomes smaller.

[0134] The anion-modified polyvinyl alcohol resin is a resin that contains anionic groups, typically carboxyl groups (-COOH) or salts thereof, in addition to the hydroxyl groups constituting the polyvinyl alcohol skeleton, and may also have other groups, such as acetyl groups. The anion-modified polyvinyl alcohol resin can be produced, for example, by copolymerizing an unsaturated monomer having anionic groups (typically carboxyl groups) with vinyl acetate and then saponifying. On the other hand, the cation-modified polyvinyl alcohol resin is a resin that contains cationic groups, typically tertiary amino groups or quaternary ammonium groups, in addition to the hydroxyl groups constituting the polyvinyl alcohol skeleton, and may also have other groups, such as acetyl groups. The cation-modified polyvinyl alcohol resin can be produced, for example, by copolymerizing an unsaturated monomer having cationic groups (typically tertiary amino groups or quaternary ammonium groups) with vinyl acetate and then saponifying.

[0135] The adhesive may be an adhesive containing two or more of the above-mentioned modified polyvinyl alcohol-based resins, or an adhesive containing both an unmodified polyvinyl alcohol-based resin (specifically, a completely or partially saponified product of polyvinyl acetate) and the above-mentioned modified polyvinyl alcohol-based resin.

[0136] The polyvinyl alcohol resin constituting the adhesive can be appropriately selected from commercially available products for use. Specifically, for example, "PVA-117H" sold by Kuraray as a polyvinyl alcohol with a high saponification degree, "GOHSENOL NH-20" sold by Nippon Synthetic Chemical Industry (Strain), "GOHSEFIMER Z" series sold by Nippon Synthetic Chemical Industry (Strain) as a polyvinyl alcohol modified by acetoacetyl group, "KL-318" and "KM-118" sold by Kuraray as an anion-modified polyvinyl alcohol, "GOHSENAL T-330" sold by Nippon Synthetic Chemical Industry (Strain), "CM-318" sold by Kuraray as a cation-modified polyvinyl alcohol, and "GOHSEFIMER K-210" sold by Nippon Synthetic Chemical Industry (Strain) can be cited.

[0137] The concentration of the polyvinyl alcohol resin in the adhesive is not particularly limited, but because it is used in the form of an aqueous solution, it is preferably within the range of 1 mass part or more and 20 mass parts or less relative to 100 mass parts of water, wherein it is more preferably within the range of 1 mass part or more and 15 mass parts or less, further preferably within the range of 1 mass part or more and 10 mass parts or less, and particularly preferably within the range of 2 mass parts or more and 10 mass parts or less. If the concentration of the polyvinyl alcohol resin in the aqueous solution is too small, there is a tendency that the adhesion is easy to reduce. On the other hand, if its concentration is too large, there is a tendency that the optical properties of the resulting polarizing plate are easy to reduce. The water used in the adhesive can be pure water, ultrapure water, tap water, etc., and is not particularly limited. However, from the viewpoint of maintaining the uniformity and transparency of the formed adhesive, pure water or ultrapure water is preferred. In addition, alcohols such as methanol and ethanol can also be added to the adhesive aqueous solution.

[0138] A crosslinking agent may be contained in a water-based adhesive having a polyvinyl alcohol resin as a main component. The crosslinking agent may be any compound having a functional group reactive with the polyvinyl alcohol resin, and any crosslinking agent that has been used in polyvinyl alcohol adhesives may be used without particular limitation. Compounds that can be crosslinking agents are given according to their functional groups, such as isocyanate compounds having at least two isocyanate groups (-NCO) in the molecule; epoxy compounds having at least two epoxy groups (bridged -O-) in the molecule; mono- or di-aldehydes; organic titanium compounds; inorganic salts of divalent or trivalent metals such as magnesium, calcium, iron, nickel, zinc, and aluminum; metal salts of glyoxylic acid; hydroxymethyl melamine, etc.

[0139] Specific examples of the isocyanate compound serving as a crosslinking agent include toluene diisocyanate, hydrogenated toluene diisocyanate, an adduct of trimethylolpropane and toluene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, isophorone diisocyanate, ketone oxime blocked products thereof, and phenol blocked products thereof.

[0140] Specific examples of the epoxy compound serving as the crosslinking agent include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, di- or tri-glycidyl ether of glycerol, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diglycidyl amine, and a water-soluble polyamide epoxy resin obtained by reacting epichlorohydrin with a polyamide polyamine which is a reaction product of a polyalkylene polyamine and a dicarboxylic acid.

[0141] Specific examples of monoaldehydes serving as crosslinking agents include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and specific examples of dialdehydes include glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, maleic dialdehyde, phthalaldehyde, and the like.

[0142] As for the organic titanium compound that serves as a crosslinking agent, various organic titanium compounds are sold by Matsumoto Fine Chemical Co., Ltd. According to the company's homepage for organic titanium compounds (Internet <URL: http: / / www.m-chem.co.jp / products / products1.html>, searched on November 18, 2013), if the water-soluble organic titanium compounds that can be suitably used in the present invention are given in the order of their structural formula (original Japanese: indicative formula), chemical name used by the company, and trade name of the company, the organic titanium compounds shown below are available.

[0143] [(CH3)2CHO]2Ti[OCH2CH2N(CH2CH2OH)2]2: The chemical name used by the company is "di(triethanolamine)titanate diisopropyl ester", the company's trade name is "Orgatix TC-400",

[0144] (HO)2Ti[OCH(CH3)COO-]2(NH4 + )2: The chemical name used by the company is "titanium ammonium lactate" and the company's trade name is "Orgatix TC-300".

[0145] (HO)2Ti[OCH(CH3)COOH]2: The chemical name used by the company is “titanium lactate”; the company’s trade names are “Orgatix TC-310” and “Orgatix TC-315”.

[0146] The metal salt of glyoxylic acid is preferably an alkali metal salt or an alkaline earth metal salt, and examples thereof include sodium glyoxylate, potassium glyoxylate, magnesium glyoxylate, and calcium glyoxylate.

[0147] Among these crosslinking agents, epoxy compounds represented by the above-mentioned water-soluble polyamide epoxy resin, aldehydes, methylolmelamine, alkali metal or alkaline earth metal salts of glyoxylic acid, and the like can be preferably used.

[0148] The crosslinking agent is preferably dissolved in water together with the polyvinyl alcohol-based resin to form an adhesive. However, as described below, the amount of the crosslinking agent in the aqueous solution may be a trace amount, so as long as it has a solubility of, for example, at least about 0.1% by mass in water, it can be used as a crosslinking agent. Of course, a crosslinking agent having a solubility in water of a degree generally referred to as water-soluble is suitable as a crosslinking agent used in the present invention.

[0149] The amount of the crosslinking agent is an amount appropriately designed according to the type of the polyvinyl alcohol resin, and is generally 5 parts by mass or more and 60 parts by mass or less, preferably 10 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the polyvinyl alcohol resin. If the crosslinking agent is mixed within this range, good adhesion can be obtained. As mentioned above, in order to improve the durability of the adhesive, it is preferred to use a polyvinyl alcohol resin modified with acetoacetyl groups. In this case, it is also preferred to mix the crosslinking agent with 5 to 60 parts by mass, more preferably 10 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the polyvinyl alcohol resin. If the amount of the crosslinking agent is too much, the reaction of the crosslinking agent is promoted in a short time, and there is a tendency for the adhesive to gel in advance, as a result, the usable time becomes extremely short and industrial use becomes difficult.

[0150] For the water-based adhesive with polyvinyl alcohol resin as the main component, it is preferred to contain a zinc salt in addition to the cross-linking agent from the viewpoint of suppressing discoloration. As the zinc salt, for example, zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, zinc nitrate, etc. can be cited. Among them, zinc nitrate is preferred. The zinc salt can be added to the water-based adhesive with polyvinyl alcohol resin as the main component in the form of a zinc salt solution.

[0151] When a water-based adhesive having a polyvinyl alcohol-based resin as a main component contains a zinc salt, the content of the zinc salt may be, for example, 0.01 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of water, and is preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 2.5 parts by mass or less from the viewpoint of ensuring the durability of the adhesive.

[0152] The adhesive may contain conventionally known appropriate additives such as a silane coupling agent, a plasticizer, an antistatic agent, and fine particles, within a range that does not inhibit the effects of the present invention.

[0153] When a carbamate resin is used as the main component of a water-based adhesive, a mixture of a polyester ionomer carbamate resin and a compound having a glycidyloxy group can be cited as an example of a suitable adhesive. The polyester ionomer carbamate resin mentioned here is a carbamate resin having a polyester skeleton and into which a small amount of ionic components (hydrophilic components) are introduced. Since the ionomer carbamate resin is directly emulsified in water without using an emulsifier and becomes an emulsion, it can be suitably used in a water-based adhesive. The scheme of using a polyester ionomer carbamate resin in an adhesive for a polarizing film and a protective film is well known, for example, as recorded in Japanese Patent Gazette No. 2005-070140, Japanese Patent Gazette No. 4432487, and Japanese Patent Gazette No. 2005-208456.

[0154] Examples of the active energy ray-curable adhesive include ultraviolet-curable adhesives.

[0155] The ultraviolet curing adhesive may be a mixture of a radically polymerizable (meth) acrylic acid compound and a photoradical polymerization initiator, a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator, etc. In addition, a cationically polymerizable epoxy compound and a radically polymerizable (meth) acrylic acid compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

[0156] When thermoplastic resin films are laminated on both sides of the polarizer, the adhesives may be of the same type or of different types. For example, when thermoplastic resin films are laminated on both sides of the polarizer, one side may be laminated using a water-based adhesive and the other side may be laminated using an active energy ray-curable adhesive.

[0157] The thickness of the adhesive in the polarizing plate may be, for example, 0.001 μm to 10 μm, and is preferably 0.01 μm to 5 μm, more preferably 0.01 μm to 3 μm, and further preferably 0.02 μm to 2 μm from the viewpoint of adhesion and thin film formation.

[0158] [Adhesive layer]

[0159] In order to fit with the light-transmitting member and the image display element, the polarizing plate can have an adhesive layer on the outermost surface of either the first thermoplastic resin film side or the second thermoplastic resin film side. The adhesive layer can be formed by an adhesive composition with polymers such as (meth) acrylic resin, rubber polymer, urethane resin, ester resin, silicone resin, polyvinyl ether resin as the main component. Among them, it is suitable to be an adhesive composition with (meth) acrylic resin as the base polymer with excellent transparency, weather resistance, heat resistance, etc. The adhesive composition can be an active energy ray curing type or a thermosetting type.

[0160] As the (meth) acrylic resin (base polymer) used in the adhesive composition, for example, a polymer or copolymer using one or more of (meth) acrylic acid esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate as monomers can be suitably used. Preferably, a polar monomer is copolymerized with the base polymer. Examples of polar monomers include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, and the like, such as (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth) acrylamide, N,N-dimethylaminoethyl (meth) acrylate, and glycidyl (meth) acrylate.

[0161] The adhesive composition may contain only the above-mentioned base polymer, but usually also contains a crosslinking agent. Examples of the crosslinking agent include divalent or higher metal ions that form carboxylic acid metal salts with the carboxyl group; polyamine compounds that form amide bonds with the carboxyl group; polyepoxy compounds and polyols that form ester bonds with the carboxyl group; and polyisocyanate compounds that form amide bonds with the carboxyl group. Among them, polyisocyanate compounds are preferred.

[0162] The adhesive layer can be formed by the following methods, i.e., dissolving or dispersing the adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare an adhesive solution, and applying the solution directly to the target surface of the laminate to form an adhesive layer; forming an adhesive layer in a sheet form on a release film to which a demolding treatment has been applied, and transferring the sheet to the target surface of the polarizing plate.

[0163] The thickness of the adhesive layer is determined based on its adhesive strength, and can be, for example, in the range of 1 μm to 50 μm, preferably 2 μm to 40 μm, more preferably 3 μm to 30 μm, and further preferably 3 μm to 25 μm.

[0164] The polarizing plate may include the above-mentioned separator. The separator may be a film including polyethylene resins such as polyethylene, polypropylene resins such as polypropylene, polyester resins such as polyethylene terephthalate, etc. Among them, a stretched film of polyethylene terephthalate is preferred.

[0165] The adhesive layer may contain optional ingredients, glass fibers, glass beads, resin beads, fillers including metal powder and / or other inorganic powders; pigments; colorants; antioxidants; ultraviolet absorbers; antistatic agents, and the like.

[0166] [Optical functional layer]

[0167] The optical functional layer can be other optical functional films other than polarizers for imparting the desired optical function. A suitable example of an optical functional film is a phase difference film. As a phase difference film, for example, a film imparting a phase difference of λ / 2 (λ / 2 wavelength plate), a film imparting a phase difference of λ / 4 (λ / 4 wavelength plate) and a positive C plate can be cited. The optical functional film can include an orientation layer and a substrate, and can also have two or more liquid crystal layers, an orientation layer and a substrate, respectively.

[0168] Although the thermoplastic resin film may also serve as the phase difference film, a phase difference film may be laminated separately from these films.

[0169] Examples of the retardation film include a light-transmitting birefringent film formed of a stretched film of a thermoplastic resin; a film in which a discotic liquid crystal or a nematic liquid crystal is fixedly oriented; and a film in which the above-mentioned liquid crystal layer is formed on a base film.

[0170] The base film is usually a film made of a thermoplastic resin, and an example of the thermoplastic resin is a cellulose ester resin such as triacetyl cellulose.

[0171] Examples of other optically functional films (optical members) that may be included in the polarizing plate include a light-collecting plate, a brightness enhancement film, a reflective layer (reflective film), a semi-transmissive reflective layer (semi-transmissive reflective film), a light diffusion layer (light diffusion film), etc. These are generally provided when the polarizing plate is disposed on the back side (backlight side) of the liquid crystal cell.

[0172] [Protective film]

[0173] The polarizing plate may include a protective film for protecting its surface (typically, the surface of the thermoplastic resin film of the polarizing plate). The protective film is peeled off together with the adhesive layer it has after the polarizing plate is bonded to an image display device or other optical member.

[0174] The protective film is formed, for example, by a substrate film and an adhesive layer laminated thereon. The above description can be cited for the adhesive layer. The resin constituting the substrate film can be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, a polyester resin such as polyethylene terephthalate and polyethylene naphthalate, a thermoplastic resin such as a polycarbonate resin, etc. Polyester resins such as polyethylene terephthalate are preferred.

[0175] The thickness of the pellicle membrane is not particularly limited, but is preferably in the range of 20 μm to 200 μm. When the thickness of the base film is 20 μm or more, it tends to be easier to impart strength to the polarizing plate.

[0176] <Method for producing polarizing plate>

[0177] Another embodiment of the present invention is a method for manufacturing a polarizing plate having a polarizer and a first thermoplastic resin film bonded to one side thereof via an adhesive. The method for manufacturing a polarizing plate may include the above-mentioned polarizer manufacturing process. From the viewpoint of obtaining a monomer hue b value within the above-mentioned range and an absorbance at a wavelength of 700 nm, the method for manufacturing a polarizing plate preferably includes at least one of a washing process and a drying process, wherein the polyvinyl alcohol resin film is washed with water and not washed with a washing solution having a temperature higher than 22° C., and the polyvinyl alcohol resin film is dried at a temperature higher than 96° C. in the drying process.

[0178] The method for manufacturing the polarizer may further include a laminating step, in which the first thermoplastic resin film is laminated to one side of the polarizer via an adhesive, and the adhesive is dried at a temperature of 85°C or above. In the laminating step, the adhesive may be applied to either or both of the laminating surfaces of the polarizer and the first thermoplastic resin film, and the laminating surface of the other party may be laminated thereon, and the laminating may be performed by pressing from top to bottom using, for example, a laminating roller. Various coating methods such as a scraper, a winding rod, a die coater, a comma-shaped blade coater, and a grooved roller coater (Japanese original: グラビアコーター) may be used in the coating of the adhesive. In addition, the polarizer and the first thermoplastic resin film may be continuously supplied in a manner such that the laminating surfaces of the two are on the inner side, and the adhesive is cast therebetween.

[0179] After laminating the polarizer to the first thermoplastic resin film, the laminate comprising the polarizer, the adhesive and the first thermoplastic resin film is subjected to heat treatment, thereby drying the adhesive. As for the evaporation, curing and crosslinking of the solvent, since the reaction is advanced at different temperatures, it is preferred to heat the laminate continuously or in multiple stages in a slowly heated manner. As for the temperature of the heat treatment, from the viewpoint of obtaining the monomer tone b value within the above-mentioned range and the absorbance at a wavelength of 700nm, it is preferred to include a treatment at 85°C or above. The upper limit of the temperature of the heat treatment for drying the adhesive is usually below 100°C, preferably below 90°C. The solvent contained in the adhesive can be removed by heat treatment. In addition, when the adhesive is a curable adhesive, the heat treatment can be utilized to advance the curing and crosslinking reactions.

[0180] When an active energy ray-curable adhesive is used as the adhesive, the adhesive can be cured by irradiating the active energy ray after lamination. The light source of the active energy ray is not particularly limited, and preferably has an active energy ray (ultraviolet light) with a luminous distribution below a wavelength of 400 nm. Specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, etc. are preferably used.

[0181] In order to improve the adhesion between the polarizer and the thermoplastic resin film, the bonding surface of the polarizer and / or the thermoplastic resin film may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, saponification treatment, etc. before bonding the polarizer and the thermoplastic resin film.

[0182] When the polarizing plate includes a second thermoplastic resin film, the polarizing plate and the second thermoplastic resin film can be bonded together in the same manner as the bonding of the polarizing plate and the first thermoplastic resin film. The bonding of the polarizing plate and the second thermoplastic resin film can be performed before or after the bonding of the polarizing plate and the first thermoplastic resin film, or can be performed simultaneously with the bonding of the polarizing plate and the first thermoplastic resin film.

[0183] <Application of polarizing plates>

[0184] Polarizing plates can be used in mobile devices such as televisions, personal computers, mobile phones, and tablet terminals. In addition, polarizing plates can also suppress discoloration after high temperature (105°C) and long-term (600 hours or more) durability tests, so they are suitable for vehicle-mounted applications that are easily exposed to more severe temperature conditions. As vehicle-mounted applications, for example, image display devices used in navigation devices, speedometers, air-conditioning touch screens, reversing monitors (Japanese original: バックモニター) and rear-view monitors (Japanese original: リアモニター) can be cited.

[0185] Example

[0186] The present invention will be described in further detail below using Examples. "%" and "parts" in the examples are by mass % and by mass parts unless otherwise specified.

[0187] [Production Example 1: Preparation of Water-Based Adhesive (1)]

[0188] Acetoacetyl-modified polyvinyl alcohol (trade name "GOHSEFIMER Z-200", manufactured by Nippon Synthetic Chemical Industry Co., Ltd., viscosity of 4% aqueous solution = 12.4 mPa·sec, degree of saponification = 99.1 mol%) was dissolved in pure water to prepare a 10% aqueous solution. The obtained acetoacetyl-modified polyvinyl alcohol aqueous solution and sodium glyoxylate as a crosslinking agent were mixed so that the solid content mass ratio of the aqueous solution to the sodium glyoxylate was 1:0.1. Then, zinc nitrate and pure water were added in an amount of 1.5 parts of zinc nitrate and 2.5 parts of acetoacetyl-modified polyvinyl alcohol to 100 parts of water to prepare a water-based adhesive composition (1).

[0189] <Example 1>

[0190] A long polyvinyl alcohol (PVA) raw film (trade name "M6000" manufactured by Kuraray Co., Ltd., saponification degree 99.9 mol% or more) with a width of 3390 mm and a thickness of 60 μm was continuously conveyed while being unwound from a roll, and immersed in a swelling bath containing pure water at 28° C. for a residence time of 45 seconds (swelling process). Thereafter, the film pulled out from the swelling bath was immersed in a dyeing bath containing iodine at 30° C. with a potassium iodide / water ratio of 1.5 / 100 (mass ratio) for a residence time of 120 seconds (dyeing process). Then, the film pulled out from the dyeing bath is immersed in a first crosslinking bath at 30°C with a potassium iodide / boric acid / water ratio of 0.5 / 0.6 / 100 (mass ratio) for a residence time of 70 seconds, and then immersed in a second crosslinking bath at 60°C with a potassium iodide / boric acid / water ratio of 15 / 4.9 / 100 (mass ratio) for a residence time of 50 seconds (crosslinking process). Thereafter, the film is immersed in a cleaning bath containing pure water at 7°C for a residence time of 40 seconds. Subsequently, the central part is sprayed with water at a temperature of 5.3°C and the two end sides are sprayed with water at a temperature of 22°C, thereby cleaning (cleaning process). The obtained PVA is continuously dried under the following three-stage drying conditions of temperature and time (first stage: 75°C for 15 seconds, second stage: 85°C for 15 seconds, third stage: 96°C for 15 seconds) (drying process). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching was performed by roller stretching in a bath. The total stretching ratio based on the original film was set to 5.8 times. The thickness of the obtained polarizing plate was 25 μm.

[0191] For the polarizer obtained as described above, a thermoplastic resin film containing triacetyl cellulose as a protective film (trade name "KC4CT1W", manufactured by Konica Minolta) is bonded at a bonding temperature of 70°C via an aqueous adhesive composition (1), and then the aqueous adhesive is continuously dried under the following three-stage drying conditions of temperature and time (first stage: 60°C for 25 seconds, second stage: 85°C for 25 seconds, third stage: 90°C for 25 seconds) (bonding process). It should be noted that the aqueous adhesive is applied to one surface of the thermoplastic resin film with a thickness of 200nm. The zinc content of the obtained polarizing plate was measured, and the result was 280ppm. The measurement results of the monomer hue b value and the absorbance at a wavelength of 700nm and the durability test results are shown in Table 1.

[0192] <Comparative Example 1>

[0193] A polarizing plate of Comparative Example 1 was prepared in the same manner as in Example 1, except that the water temperature of the spray at both ends was set to 24°C in the cleaning step of Example 1 and the temperature of the third stage was set to 93°C in the drying step. The zinc content of the obtained polarizing plate was measured and found to be 280 ppm. The measurement results of the monomer color tone b value and the absorbance at a wavelength of 700 nm and the durability test results are shown in Table 1.

[0194] [Durability test]

[0195] The obtained polarizing plate was cut to prepare a durability test sample (size: 12 cm×30 cm). The durability test sample was subjected to an autoclave treatment [temperature 50° C., pressure 5 kg / cm 2 (490.3 kPa)] and then placed in an environment of 23°C and 55% relative humidity for 24 hours. A heating test was conducted in a heating environment of 105°C, and the color change before and after heating was visually confirmed. The time required for the color change to occur was measured.

[0196] [Measurement of Monomer Color Tone b Value and Absorbance at 700nm Wavelength]

[0197] The single-body color tone b value and the absorbance at a wavelength of 700 nm of the polarizing plate before the durability test were measured using a spectrophotometer ("V-7100" manufactured by JASCO Corporation).

[0198] [Determination of zinc content]

[0199] The zinc content in the polarizing plate was measured as follows.

[0200] Nitric acid was added to the accurately weighed polarizing plate, and the solution obtained by acid decomposition using a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General was used as the measurement solution. For zinc concentration, the zinc concentration of the measurement solution was quantified using an ICP emission spectrophotometer (5110ICP-OES) manufactured by Agilent Technology, and the zinc mass relative to the mass of the polarizing plate was calculated.

[0201] [Table 1]

[0202] Example 1 Comparative Example 1 Monochrome b 4.1 2.7 Absorbance at wavelength 700[nm] 4.4 4.6 Durability 1400 510

Claims

1. A polarizing plate having a single-body hue b value of 3.5 or more and an absorbance at a wavelength of 700 nm of 3.9 or more and 4.5 or less. 2 . The polarizing plate according to claim 1 , comprising a polarizer and a first thermoplastic resin film bonded to one side of the polarizer via an adhesive. 3 . The polarizing plate according to claim 2 , further comprising a second thermoplastic resin film, wherein the second thermoplastic resin film is bonded to the polarizer on a side opposite to the first thermoplastic resin film side via an adhesive.

4. The polarizing plate according to claim 2 or 3, wherein The adhesive is a water-based adhesive. 5 . The polarizing plate according to claim 1 , wherein a content of zinc element in the polarizing plate is 150 ppm or more. 6 . A vehicle-mounted display device comprising the polarizing plate according to claim 1 .

7. A method for manufacturing a polarizing plate, which is the method for manufacturing a polarizing plate according to claim 2, The polarizer includes a polyvinyl alcohol-based resin film, The manufacturing method comprises a cleaning step, In the cleaning step, the polyvinyl alcohol-based resin film is cleaned with a cleaning solution, and the cleaning solution is not cleaned with a temperature higher than 22° C. The temperature of the cleaning liquid in the center portion in the width direction of the polyvinyl alcohol-based resin film is lower than the temperature of the cleaning liquid in the both end portions.

8. The method for manufacturing a polarizing plate according to claim 7, further comprising a drying step, In the drying step, the polyvinyl alcohol-based resin film is dried at a temperature of 96° C. or higher.

9. The method for producing a polarizing plate according to claim 7 or 8, further comprising a laminating step, In the laminating step, the first thermoplastic resin film is laminated to one side of the polarizer via an adhesive, and the adhesive is dried at a temperature of 85° C. or higher.

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