TWI885132B - Polarizing plate and its manufacturing method - Google Patents

Abstract

An object of the present invention is to provide a polarizing plate having good heat resistance.

The polarizing plate contains a polarizer, a first adhesive layer, and a first resin film in this order, wherein the polarizer and the first adhesive layer are in direct contact with each other, the luminous efficiency correction single transmittance is 45.5% or more, the content of the zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more, and the polarizer has a thickness of 10 μm or more.

Description

Polarizing plate and method for manufacturing the same

The present invention relates to a polarizing plate and a method for manufacturing the same.

As for polarizers, polyvinyl alcohol-based resin films that adsorb and orient iodine or dichroic pigments such as dichroic dyes are known. Patent documents 1 to 3 propose using zinc-containing polyvinyl alcohol-based resin films.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2003-29042

[Patent Document 2] Japanese Patent Publication No. 2004-61565

[Patent Document 3] Japanese Patent Publication No. 2014-102353

Polarizers are used as polarizing plates in image display devices. When image display devices are used for a long time at high temperatures, the optical properties of the polarizing plates may change. In particular, in polarizing plates with high transmittance such as organic EL applications, the amount of circular dichroism pigment in the polarizing plates is small, making it difficult to meet durability tests such as heat resistance. Therefore, the heat resistance of polarizing plates is required to be improved.

The purpose of the present invention is to provide a polarizing plate with good heat resistance.

The present invention provides the following polarizing plate and method for manufacturing the polarizing plate.

[1] A polarizing plate comprising a polarizer, a first adhesive layer, and a first resin film in sequence; wherein,

The aforementioned polarizer is in direct contact with the aforementioned first adhesive layer.

The photometrically corrected single body transmittance is above 45.5%,

The content of zinc element contained in the aforementioned polarizer and the adhesive layer directly contacting the aforementioned polarizer is 0.15 mass % or more,

The thickness of the polarizer is greater than 10 μm.

[2] The polarizing plate as described in [1], wherein the polarization degree of the optical correction is 94.0% or more.

[3] The polarizing plate as described in [1] or [2], wherein the content of zinc contained in the polarizer and the adhesive layer directly contacting the polarizer is 0.22 mass % or less.

[4] The polarizing plate as described in any one of [1] to [3], wherein the moisture permeability of the first resin film at a temperature of 40°C and a relative humidity of 90% RH is 100 g/m ² /24h or more.

[5] A polarizing plate as described in any one of [1] to [4], wherein the first adhesive layer contains a zinc element.

[6] A polarizing plate as described in any one of [1] to [5], wherein a second adhesive layer and a second resin film are provided in order from the side closer to the polarizer on the side opposite to the first resin film of the polarizer.

[7] The polarizing plate according to [6], wherein the moisture permeability of the second resin film at a temperature of 40°C and a relative humidity of 90% RH is 100 g/m ² /24h or more.

[8] The polarizing plate as described in [6] or [7], wherein the second adhesive layer contains a zinc element.

[9] A method for manufacturing a polarizing plate, which is a method for manufacturing a polarizing plate as described in any one of [1] to [8],

It has the steps of treating a polyvinyl alcohol resin film with a treatment solution containing zinc salt to produce a polarizer.

According to the present invention, a polarizing plate with good high-temperature durability can be provided.

1:Polarizing plate

10: Polarizer

101: First subsequent coating

102: 1st resin film

FIG1 is a schematic cross-sectional view showing a polarizing plate of one embodiment of the present invention.

FIG2 is a flow chart showing a method for manufacturing a polarizer according to one embodiment of the present invention.

[Polarizing plate]

FIG1 is a cross-sectional view schematically showing a polarizing plate of one embodiment of the present invention. The polarizing plate 1 comprises, in order: a polarizer 10, a first adhesive layer 101, and a first resin film 102. The polarizer 10 is in direct contact with the first adhesive layer 101. The transmittance (Ty) of the polarizing plate's photometric correction monomer is greater than 45.5%, and the content of the zinc element is greater than 0.15 mass%. The thickness of the polarizer is greater than 10 μm. When the transmittance (Ty) of the polarizing plate's photometric correction monomer is greater than 45.5%, it is easier to visually detect changes in optical properties compared to a polarizing plate whose photometric correction monomer transmittance (Ty) is less than 45.5%. According to the present invention, by setting the content of zinc element contained in the polarizing plate and the thickness of the polarizer to the above range, a polarizing plate can be provided, which is a polarizing plate with a light correction monomer transmittance (Ty) of 45.5% or more, and the polarizing plate has excellent heat resistance, and even when provided to a heat resistance test, the change of optical characteristics before and after the heat resistance test is suppressed.

The single transmittance (Ty) of the polarizing plate for photometric correction is preferably 46.0% or more, and more preferably 47.0% or more. The single transmittance (Ty) of the polarizing plate for photometric correction is usually less than 50%.

In this specification, the heat resistance test refers to a durability test of the heat resistance test performed according to the method described in the paragraph of the embodiment described later. In the case of the heat resistance test, the optical property of the polarizing plate that suppresses the change before and after the durability test can be listed as the luminance correction polarization degree (Py). The change rate (△Py) of the luminance correction polarization degree (Py) of the polarizing plate before and after the heat resistance test is, for example, 4.0% or less, preferably 3.5% or less, and more preferably 3.0% or less. According to the present invention, a polarizing plate with a change rate (△Py) within this range and showing excellent heat resistance can be obtained.

The polarization degree (Py) of the polarizing plate after light correction is preferably 92.0% or more, more preferably 93.0% or more, and even more preferably 94.0% or more. The polarization degree (Py) of the polarizing plate after light correction can be 99.9% or less, and in other types, it can be 99% or less, and can also be 98% or less.

In the polarizing plate, the content of zinc in the polarizing plate and the adhesive layer directly contacting the polarizing plate is 0.15 mass % or more. By making the content of zinc in the polarizing plate and the adhesive layer directly contacting the polarizing plate 0.15 mass % or more, a polarizing plate with good high temperature durability can be provided. The content of the zinc element is preferably 0.16 mass % or more, and more preferably 0.17 mass % or more. From the perspective of obtaining a polarizing plate with a desired hue, the content of the zinc element is preferably 0.22 mass % or less, and more preferably 0.20 mass % or less.

The total zinc content of the polarizer and the adhesive layer directly contacting the polarizer can be adjusted by adjusting the zinc content of the polarizer and the zinc content of the first adhesive layer and/or the second adhesive layer contacting the polarizer. In addition, the method for determining the zinc content of the polarizer and the adhesive layer directly contacting the polarizer is set according to the method described in the embodiment described below.

The monomer hue b value of the polarizing plate is, for example, greater than -1.0 and less than 4.0, preferably greater than -0.5 and less than 3.0, and more preferably greater than 0 and less than 2.0.

The absorbance A700 of the polarizing plate at a wavelength of 700nm is, for example, 0.5 to 3.0, preferably 0.7 to 2.0, and more preferably 0.9 to 1.5.

In this specification, the transmittance (Ty) of the photometric correction monomer, the photometric correction polarization (Py), the rate of change (△Py) of the photometric correction polarization (Py), the monomer hue b value, the absorbance A700 at a wavelength of 700nm, and the content of zinc in the polarizer and the adhesive layer directly contacting the polarizer are set to the values measured according to the measurement method described in the paragraph of the embodiment described later.

The first resin film is bonded to the surface of the polarizer via the first adhesive layer, for example. The polarizing plate may further include a second adhesive layer and a second resin film on the side opposite to the first resin film, starting from the side close to the polarizer. The second resin film is bonded to the surface of the polarizer via the second adhesive layer, for example. In a polarizing plate, when obtaining the "total zinc content of the polarizer and the adhesive layer directly in contact with the polarizer", the adhesive layer directly in contact with the polarizer is equivalent to the first adhesive layer. In addition, when the second adhesive layer is directly in contact with the polarizer, the adhesive layer directly in contact with the polarizer is also equivalent to the second adhesive layer. Hereinafter, the first resin film and the second resin film are collectively referred to as resin films, and the first adhesive layer and the second adhesive layer are collectively referred to as adhesive layers.

〈Polarizing film〉

The polarizer is an absorption-type polarizer that has the property of "absorbing linear polarization with a vibration plane parallel to its absorption axis and transmitting linear polarization with 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 dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film. Such a polarizer can be manufactured according to the manufacturing method of the polarizer described below.

The thickness of the polarizer is 10 μm or more. By making the thickness of the polarizer 10 μm or more, a polarizing plate with excellent heat resistance can be provided. The thickness of the polarizer is preferably 12 μm or more, and more preferably more than 15 μm. The thickness of the polarizer is preferably 50 μm or less, and more preferably 30 μm or less.

The thickness of the polarizer can be set to the above range by, for example, selecting a polyvinyl alcohol resin film, adjusting the stretching ratio, etc.

The adjustment of the zinc content in the polarizing plate is preferably implemented by adjusting the zinc content in the polarizer. The polarizer contained in the polarizing plate of the present invention usually contains zinc.

The content of zinc in the polarizer can be set to the above range by, for example, adjusting the concentration of zinc salt in the treatment solution for treating the polyvinyl alcohol resin film, the immersion time of the polyvinyl alcohol resin film in the treatment solution containing zinc salt, the temperature of the treatment solution, etc.

<Polarizing film manufacturing method>

Refer to the drawings to illustrate another method for manufacturing a polarizer of the present invention.

The manufacturing method shown in FIG. 2 is a method for manufacturing a polarizer including a polyvinyl alcohol-based resin, and may include the following steps:

The polyvinyl alcohol resin film is immersed in a dyeing tank containing a treatment solution containing a dichroic pigment to perform dyeing step S20, and

The membrane after the dyeing step is immersed in a crosslinking tank containing a treatment solution containing a crosslinking agent to perform a crosslinking step S30 of a crosslinking treatment.

The manufacturing method may further include other steps besides those described above, specifically, as shown in FIG. 2 , including: a swelling step S10 of immersing the polyvinyl alcohol-based resin film before the dyeing step S20 in a swelling tank containing a treatment solution containing water, a washing step S40 of immersing the film after the crosslinking step S30 in a washing tank, and a drying step S50 after the washing step S40. In addition, the polyvinyl alcohol-based resin film can be subjected to uniaxial stretching treatment (stretching step) at any one or more stages in the polarizer manufacturing process, and more specifically, can be subjected to uniaxial stretching treatment (stretching step) at any one or more stages from before the swelling step S10 to the crosslinking step S30.

In the manufacturing method, at least one of the treatment solutions for treating the polyvinyl alcohol resin film contains a zinc salt. Examples of treatment tanks containing the treatment solution include a swelling tank, a dyeing tank, a crosslinking tank, a cleaning tank, and a color-replenishing tank described later. The treatment tank containing the treatment solution containing the 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 crosslinking tank and the color-replenishing tank, and more preferably at least one selected from the last crosslinking tank and the color-replenishing tank when there are more than two crosslinking tanks. By immersing the polyvinyl alcohol resin film in the treatment solution containing the zinc salt, the obtained polarizer can contain the zinc element. The content of zinc in the polarizer can be set to the above range 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.

Zinc salts contained in the treatment solution include, for example: zinc chloride, zinc iodide and other zinc halides, or zinc sulfate, zinc acetate, zinc nitrate, etc. Among them, zinc nitrate is preferred in terms of low price. Zinc salts can be added to the treatment solution as zinc salt solutions.

The concentration of zinc salt in the treatment solution may vary for each treatment tank. Relative to 100 parts by mass of the treatment solution contained in the treatment tank, the concentration of zinc salt in the treatment solution is preferably 2 parts by mass or more and 10 parts by mass or less, and more preferably 3 parts by mass or more and 6 parts by mass or less.

The immersion time of the polyvinyl alcohol-based resin film in the treatment solution and the temperature of the treatment solution may vary depending on the treatment tank. The specific immersion time and the temperature of the treatment solution are described in the subsequent paragraphs for each step.

The various processing steps included in the manufacturing method of the present invention can be continuously implemented by continuously transporting the polyvinyl alcohol-based resin film as the raw material film along the film transport path of the polarizer manufacturing device. The film transport path is equipped with equipment (processing tank or furnace, etc.) for implementing the above-mentioned various processing steps according to the implementation order of the above-mentioned various processing steps.

In addition to the above-mentioned equipment, the film transport path can be constructed by placing guide rollers or rollers at appropriate positions. For example, guide rollers can be placed 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 film, and pulled out of the treatment tank. More specifically, by setting two or more guide rollers in each treatment tank and transporting the film along these guide rollers, the film can be immersed in each treatment tank.

The polyvinyl alcohol resin constituting the polyvinyl alcohol resin film of the raw material film can be a polyvinyl acetate resin that has been saponified. In addition to polyvinyl acetate which is a homopolymer of vinyl acetate, polyvinyl acetate resins can also be exemplified by copolymers of vinyl acetate and other monomers that can be copolymerized with vinyl acetate. Other monomers that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth)acrylamides having an ammonium group, and the like. The degree of saponification of the polyvinyl alcohol resin is generally about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. In this specification, the so-called "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acryloyl".

Polyvinyl alcohol resins can be modified, for example, polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes can also be used.

The average degree of polymerization of the polyvinyl alcohol resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and even more preferably 2,000 to 5,000. 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 less than 100, it is difficult to obtain better polarization performance, and when it exceeds 10,000, the film processability may be poor.

From the perspective of setting the thickness of the polarizer to be greater than 10μm, the thickness of the polyvinyl alcohol resin film is preferably greater than 20μm and less than 100μm, more preferably greater than 30μm and less than 80μm, and even more preferably greater than 40μm and less than 65μm.

The polyvinyl alcohol-based resin film of the raw material film can be prepared, for example, as a roll (roll) of an unstretched or stretched polyvinyl alcohol-based resin film in a long strip. In this case, the obtained polarizer is also a long strip. The following is a detailed description of each step.

(1) Swelling step S10

The swelling treatment in this step is a treatment that is carried out as needed for the purpose of removing impurities, removing plasticizers, imparting easy dyeing properties, and plasticizing the polyvinyl alcohol resin film as the raw material film. Specifically, it can be a treatment of immersing the polyvinyl alcohol resin film 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 also be subjected to uniaxial stretching treatment before the swelling treatment, during the swelling treatment, or before and during the swelling treatment.

The treatment liquid contained in the expansion tank may be water (e.g. 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 expansion tank may contain zinc salt.

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

(2) Staining step S20

The dyeing treatment in this step is a treatment for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol resin film. Specifically, the polyvinyl alcohol resin film can be immersed in a dyeing tank containing a treatment solution containing the dichroic dye. The film can be immersed in one dyeing tank or in two or more dyeing tanks in sequence. In order to improve the dyeability of the dichroic dye, the film provided to the dyeing step can be subjected to at least a certain degree of uniaxial stretching treatment. It is also possible to perform a uniaxial stretching treatment during the dyeing treatment to replace the uniaxial stretching treatment before the dyeing treatment, or to perform a uniaxial stretching treatment during the dyeing treatment in addition to the uniaxial stretching treatment before the dyeing treatment.

The dichroic pigment may be iodine or a dichroic organic dye. Specific examples of dichroic organic dyes include: Red BR, Red LR, Red R, Pink LB, Rubin 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, Supra Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. A dichroic pigment may be used alone or in combination of two or more.

In the case of using iodine as a dichroic pigment, the treatment solution contained in the dyeing tank can use an aqueous solution containing iodine and potassium iodide. Other iodides such as zinc iodide can be used instead of potassium iodide, or potassium iodide and other iodides can be used in combination. In addition, compounds other than iodides can coexist with, for example, boric acid, zinc chloride, cobalt chloride, etc. In the case of adding boric acid, the point of containing iodine is different from the crosslinking treatment described later. The content of iodine in the above aqueous solution is usually 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 usually more than 0.5 mass parts and less than 20 mass parts per 100 mass parts of water. As described above, the treatment solution contained in the dyeing tank can contain a zinc salt.

The temperature of the treatment liquid contained in the dyeing tank during the immersion of the film 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 film is usually above 30 seconds and below 600 seconds, and preferably above 60 seconds and below 300 seconds.

When a dichroic organic dye is used as a dichroic pigment, an aqueous solution containing the dichroic organic dye may 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 mass parts to 10 mass parts per 100 mass parts of water, preferably 1×10 ^-3 mass parts to 1 mass part. Dyeing auxiliary agents may coexist in the dyeing tank, for example, inorganic salts such as sodium sulfate or surfactants may be contained. Only one dichroic organic dye may be used alone, or two or more dichroic organic dyes may be used in combination. The temperature of the treatment solution contained in the dyeing tank during the immersion of the film is, for example, 20°C to 80°C, preferably 30°C to 70°C, and the immersion time of the film is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

(3) Cross-linking step S30

The crosslinking treatment of the polyvinyl alcohol resin film after the dyeing step with a crosslinking agent is a treatment for the purpose of water resistance or hue adjustment by crosslinking. Specifically, the film after the dyeing step can be immersed in a treatment liquid contained in a crosslinking tank containing a crosslinking agent.

The film can be immersed in one crosslinking tank or in two or more crosslinking tanks in sequence. During the crosslinking treatment, uniaxial stretching treatment can also be performed.

Examples of crosslinking agents include boric acid, glyoxal, and glutaraldehyde, and boric acid is preferably used. Two or more crosslinking agents may be used in combination. The content of boric acid in the treatment solution contained in the crosslinking tank is generally not less than 0.1 mass part and not more than 15 mass parts per 100 mass parts of water, and preferably not less than 1 mass part and not more than 10 mass parts. In the case where the dichroic pigment is iodine, the treatment solution contained in the crosslinking tank preferably contains iodide in addition to boric acid. The content of iodide in the treatment solution contained in the crosslinking tank is generally not less than 0.1 mass part and not more than 15 mass parts per 100 mass parts of water, and preferably not less than 5 mass parts and not more than 12 mass parts. Examples of iodides include potassium iodide, zinc iodide, and the like. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may coexist in the crosslinking tank. As described above, the treatment solution contained in the crosslinking tank may contain a zinc salt. When there are more than two crosslinking tanks, it is preferred that the treatment solution contained in the last crosslinking tank contains a zinc salt.

The temperature of the treatment solution contained in the crosslinking tank during membrane immersion is usually above 50°C and below 85°C, preferably above 50°C and below 70°C. The membrane immersion time is usually above 10 seconds and below 600 seconds, preferably above 20 seconds and below 300 seconds.

In the crosslinking step S30, there may be more than two crosslinking tanks. In this case, the composition and temperature of the treatment solution contained in each crosslinking tank may be the same or different. The treatment solution contained in the crosslinking tank may have a concentration or temperature of a crosslinking agent and iodide corresponding to the purpose of impregnating the polyvinyl alcohol resin film. The crosslinking treatment for water resistance due to crosslinking and the crosslinking treatment for hue adjustment (color correction) may be performed in multiple steps (e.g., multiple tanks).

Generally speaking, when both the crosslinking treatment for water resistance caused by crosslinking and the crosslinking treatment for hue adjustment (color correction) are performed, the tank for the crosslinking treatment for hue adjustment (color correction) (color correction tank) is arranged in the latter stage. The temperature of the treatment liquid contained in the color correction tank is, for example, 10°C to 55°C, preferably 20°C to 50°C. The content of the crosslinking agent in the treatment liquid contained in the color correction tank is, for example, 1 to 5 parts by mass per 100 parts by mass of water. The content of the iodide in the treatment liquid contained in the color correction tank is, for example, 3 to 30 parts by mass per 100 parts by mass of water. As described above, the treatment liquid contained in the color correction tank may contain a zinc salt.

As described above, when manufacturing the polarizer, the polyvinyl alcohol resin film is subjected to uniaxial stretching treatment in any one or more stages from before the swelling step S10 to the crosslinking step S30 (stretching step, Figure 2). From the viewpoint of improving the dyeability of the dichroic dye, the film provided to the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or preferably, the uniaxial stretching treatment is performed during the dyeing treatment instead of the uniaxial stretching treatment before the dyeing treatment, or the uniaxial stretching treatment is performed during the dyeing treatment in addition to the uniaxial stretching treatment before the dyeing treatment.

The uniaxial stretching treatment may be either dry stretching in the atmosphere or wet stretching in a tank, or both. The uniaxial stretching treatment may be inter-roll stretching, hot roll stretching, tenter stretching, etc., in which a speed difference is given between two rolls to perform longitudinal uniaxial stretching, preferably including inter-roll stretching. The stretching ratio based on the original film (the cumulative stretching ratio of such stretching when the stretching treatment is performed in more than two stages) is 3 times or more and 8 times or less. In order to provide good polarization characteristics, the stretching ratio is preferably set to 4 times or more, and more preferably to 5 times or more.

(4) Cleaning step S40

The cleaning treatment in this step is a treatment that is performed as needed to remove excess crosslinking agents and dichroic dyes attached to the polyvinyl alcohol resin film. The polyvinyl alcohol resin film after the crosslinking step is cleaned with a cleaning solution containing water. Specifically, the polyvinyl alcohol resin film after the crosslinking step can be immersed 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 treatment may be to use the cleaning liquid as a rinse agent to spray the polyvinyl alcohol resin film after the crosslinking step, or the above-mentioned immersion and spraying may be combined.

The cleaning liquid can be water (e.g. pure water) or an aqueous solution to which a water-soluble organic solvent such as alcohol is added. The temperature of the cleaning liquid can be, for example, above 5°C and below 40°C.

The cleaning step S40 is an optional step and can be omitted, or the cleaning process can be performed in the drying step S50 as described later. It is preferred to perform the drying step S50 on the membrane after the cleaning step S40.

(5) Drying step S50

The drying step S50 is an area for drying the polyvinyl alcohol resin film after the cleaning step S40. The polyvinyl alcohol resin film after the cleaning step S40 can be continuously transported and introduced into the drying step S50 for drying treatment, thereby obtaining a polarizer.

The drying process is performed using a film drying means (heating means). A preferred example of the drying means is a drying furnace. The drying furnace is preferably one that can control the temperature inside the furnace. For example, the drying furnace is a hot air oven that can increase the temperature inside the furnace by supplying hot air. In addition, the drying process according to the drying means can be a process in which the polyvinyl alcohol-based resin film after the cleaning step S40 is closely attached to one or more heating bodies having a convex surface, or a process in which a heater is used to heat the film.

The above-mentioned heating bodies include: rollers (such as guide rollers that also serve as hot rollers) that have a heat source inside (such as a heat medium such as warm water or an infrared heater) and can increase the surface temperature. The above-mentioned heaters include: infrared heaters, halogen heaters, plate heaters, etc.

The temperature of the drying process (e.g., the temperature inside the drying furnace, the surface temperature of the hot roller, etc.) is usually between 30°C and 100°C, preferably between 50°C and 90°C. There is no particular limitation on the drying time, for example, between 30 seconds and 600 seconds.

After the above steps, a polarizer with oriented dichroic pigment adsorbed on a uniaxially stretched polyvinyl alcohol resin film can be obtained.

The obtained polarizer can be directly transported to the subsequent polarizing plate manufacturing step (the step of laminating the thermoplastic resin film to one or both sides of the polarizer).

〈Resin film〉

The resin film may be a transparent resin film composed of a thermoplastic resin, for example, a polyolefin resin such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin (norbornene resin, etc.); a cellulose ester resin such as cellulose triacetate or cellulose diacetate; a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate; a polycarbonate resin; a (meth) acrylic resin such as polymethyl methacrylate resin; or a transparent resin film composed of a mixture or copolymer thereof.

The effect is particularly effective when the moisture permeability of either the first resin film or the second resin film (or preferably both) is 100 (g/m ² /24h) or more, and particularly 300 (g/m ² /24h) or more at a temperature of 40°C and a relative humidity of 90%RH. Although the high temperature durability of such a high moisture permeability film is easily reduced due to the inflow and outflow of water, by satisfying the elements of the present invention, higher high temperature durability can be imparted. Examples of resin films satisfying such moisture permeability include cellulose triacetate and the like. In addition, if the moisture permeability of the resin film at a temperature of 40°C and a relative humidity of 90%RH is 100 (g/ ^m2 /24h) or more, the resin film surface may also have a surface treatment layer such as a hard coating layer or an anti-reflection layer. When a resin film with such moisture permeability is used, the heat resistance of the polarizing plate tends to deteriorate, but the polarizing plate of the present invention has good durability.

Either or both of the first resin film and the second resin film may be a protective film having optical functions such as a phase difference film and a brightness enhancement film. For example, a phase difference film with an arbitrary phase difference value can be made by stretching a transparent resin film made of the above materials (uniaxial stretching or biaxial stretching, etc.) or forming a liquid crystal layer on the film.

On the surface of the resin film opposite to the polarizer, a surface treatment layer (coating layer) such as a hard coating layer, an anti-glare layer, an anti-reflection layer, an anti-static layer, or an anti-fouling layer can also be formed.

From the perspective of thinning the polarizing plate, the thickness of the resin film is preferably thinner, but if it is too thin, the strength will be reduced and the processability will tend to deteriorate. Therefore, it is preferably 5 to 150μm, more preferably 5 to 100μm, and even more preferably 10 to 60μm.

(followed by the agent layer)

Polarizing plates can be obtained by laminating (stacking) a resin film on one or both sides of a polarizer via an adhesive layer. The adhesive used for laminating the polarizer and the resin film can be listed as: UV-curable adhesives and other active energy ray-curable adhesives, or aqueous solutions of polyvinyl alcohol resins or aqueous solutions containing crosslinking agents, amine emulsion adhesives and other water-based adhesives. Adhesives containing zinc elements can also be used.

By applying a zinc-containing adhesive to the surface of the polarizer, the zinc in the polarizer can be inhibited from migrating from the polarizer to other layers, thereby inhibiting the reduction of high-temperature durability. Methods for making the adhesive contain zinc can be listed as follows: adding zinc salt when preparing the adhesive. Zinc salts can be zinc halides such as zinc chloride and zinc iodide, or zinc sulfate, zinc acetate, zinc nitrate, etc. The content of zinc in the adhesive is calculated in terms of solid content, and when the total amount of the adhesive is 100 parts by mass, it can be set to, for example, 0.1 parts by mass or more and 5 parts by mass or less.

In the case of laminating a resin film on both sides of the polarizer, the adhesives forming the two adhesive layers may be of the same type or different types. For example, in the case of laminating a resin film on both sides, a water-based adhesive may be used on one side, and an active energy ray-curable adhesive may be used on the other side. The UV-curable adhesive may be a mixture of a radically polymerizable (meth) acrylic compound and a photo-radical polymerization initiator, and a mixture of a cationic polymerizable epoxy compound and a photo-radical polymerization initiator. In addition, a cationic polymerizable epoxy compound and a radically polymerizable (meth) acrylic compound may be used in combination, and a photo-radical polymerization initiator and a photo-radical polymerization initiator may be used in combination as initiators.

When using an active energy ray-curable adhesive, the adhesive is cured by irradiating the active energy ray after bonding. The light source of the active energy ray is not particularly limited, but preferably active energy ray (ultraviolet ray) having a luminescence distribution below a wavelength of 400nm. Specifically, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halogen lamps, etc. can be preferably used.

In order to improve the adhesion between the polarizer and the resin film, before laminating the polarizer and the resin film, the laminating surface of the polarizer and/or the resin film can be subjected to surface treatments such as corona treatment, flame treatment, plasma treatment, UV irradiation treatment, primer coating treatment, and saponification treatment.

As described above, the polarizing plate of the present invention can also be produced by laminating a resin film to a polarizer that is a single-layer film via an adhesive layer, but it is not limited to this method. For example, as described in Japanese Patent Publication No. 2009-98653, it can also be produced by a method of applying a substrate film. As for obtaining a polarizing plate having a thin film polarizer (polarizer layer), the latter method is advantageous, and for example, it can include the following steps.

The resin layer forming step is to apply a coating liquid containing a polyvinyl alcohol-based resin on at least one side of the substrate film, and then form a polyvinyl alcohol-based resin layer by drying to obtain a laminated film;

The stretching step is to stretch the laminated film to obtain a stretched film;

The dyeing step is to dye the polyvinyl alcohol resin layer of the stretched film with a dichroic pigment to form a polarizer layer (equivalent to a polarizer), thereby obtaining a polarizing laminated film;

The first bonding step is to use an adhesive (first adhesive layer) to bond the resin film (first resin film) to the polarizer layer of the polarizing laminate film to obtain a bonded film;

The peeling step is to peel off the base film from the laminating film to obtain a polarizing plate with a single-sided resin film.

Zinc may be contained in at least one of the dyeing step and the first bonding step. When zinc is contained in the dyeing step, zinc may be contained in the polarizing plate by containing zinc salt in the treatment liquid containing the dichroic pigment. In addition, when zinc is contained in the first bonding step, zinc may be contained in the polarizing plate by containing zinc in the adhesive.

In the case of a double-sided laminated resin film of a polarizer layer (polarizer), a second bonding step is further included, which is to use an adhesive (second adhesive layer) to bond the second resin film to the polarizer surface of the polarizing plate with the first resin film attached to one side. In addition, the adhesive for bonding the second resin film may contain a zinc element.

In the above method of applying the substrate film, the dyeing step of the polarizing laminated film (for example, after the crosslinking step or the washing step in the dyeing step of the polarizing laminated film) can include a drying step. The polarizing laminated film, the polarizing plate with a thermoplastic resin film on one side, and the polarizing film contained in the polarizing plate with a thermoplastic resin film on both sides obtained by the second lamination step or the polarizing film separated therefrom also belong to the polarizing film of the present invention.

The polarizing plate can be used in a display device. The display device can be any device such as a liquid crystal display device, an organic EL display device, etc., preferably an organic EL display device. When assembled in a liquid crystal display device, it is preferably used on the viewing side of the liquid crystal light-emitting element. In addition, when assembled in an organic EL display device, a circular polarizing plate combined with a phase difference film and the polarizing plate of the present invention can also be used as an anti-reflection film.

The polarizing plate is suitable for a car display device, which sequentially comprises: a polarizing plate, a light-transmitting component attached to the surface of the first resin film side of the polarizing plate, and a display device attached to the surface of the second resin film side of the polarizing plate. The light-transmitting component can be a glass plate or a light-transmitting resin film, etc.

The following is an example to illustrate the present invention in more detail, but the present invention is not limited to these examples.

[Implementation example]

[Photometric correction single unit transmittance (Ty), photometric correction polarization (Py) and single unit hue b value]

For polarizing plates, a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation] is used to measure the MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm.

According to the following formula, the monomer transmittance and polarization degree at each wavelength are calculated:

Single body penetration rate (%) = (MD + TD) / 2

Polarization degree (%) = {(MD-TD)/(MD+TD)}×100.

The so-called "MD transmittance" refers to the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizer, and is represented by "MD" in the above formula. In addition, the so-called "TD transmittance" refers to the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the polarizer, and is represented by "TD" in the above formula.

The obtained single body transmittance and polarization degree are photometrically corrected using the 2-degree field of view (C light source) of JIS Z 8701:1999 "Color display method - XYZ color coordinate system and X10Y10Z10 color coordinate system", and the photometrically corrected single body transmittance (Ty) and photometrically corrected polarization degree (Py) are obtained.

Furthermore, according to the method described in International Publication No. 2016/117659, the spectral transmittance τ(λ) of the polarizing plates manufactured in the embodiments and comparative examples was measured by a spectrophotometer (V7100, JASCO Corporation), thereby obtaining the orthogonal spectral transmission spectrum, the monomer hue b value, and the value of A700 defined by the following formula.

A700=-Log ₁₀ {(T _MD,700 ×T _TD,700 )/10000}

In the above formula, T _MD,700 is the transmittance at a wavelength of 700 nm obtained when the polarizer is configured so that the absorption axis of the polarizer is orthogonal to the linear polarization of the measurement light.

T _TD,700 is the transmittance at a wavelength of 700nm obtained when the polarizing plate is configured so that the absorption axis of the polarizer is parallel to the linear polarization of the measured light. The units are all %.

[Heat resistance test]

A 40mm×40mm test piece was cut from the manufactured polarizing plate, and a 40mm×40mm alkali-free glass was bonded to both sides of the cut polarizing plate using a 25μm thick acrylic adhesive (pressure-sensitive adhesive) to prepare a sample. For each sample, the photometrically corrected single body transmittance (Ty), photometrically corrected polarization (Py), single body hue b value, and A700 were calculated based on the values measured according to the above method before being submitted to the heat resistance test.

Each sample was placed in an oven at 80°C for 500 hours for heat resistance test. For each sample, after the heat resistance test, the photometric correction polarization degree (Py) was measured according to the above method, and then the change rate of photometric correction polarization degree △Py[%] was calculated according to the following method.

The change rate △Py[%] is the change rate of the luminance-corrected polarization degree (Py) before and after the heat resistance test. When the luminance-corrected polarization degree (Py) before the durability test is P1 and the luminance-corrected polarization degree (Py) after the heat resistance test is P2, it is the value calculated by the following formula (1).

△Py={(P1-P2)/P1}×100 (1)

[Determination of zinc content]

The polarizing plate was immersed in dichloromethane for 30 minutes and ultrasonically treated. The resin film (cellulose triacetate film) on both sides of the polarizing plate was dissolved with dichloromethane, and the sample consisting of the polarizing plate and the adhesive layer in contact with the polarizing plate was taken out. 1g of the sample and 50ml of mannitol solution were placed in a 100ml container, and an electrode was placed and titrated with 0.1N NaOH. The primary and secondary endpoints of the analyzer were recorded, and the concentration was calculated using the following formula.

Zinc content in the polarizer and the adhesive layer in contact with the polarizer (mass %) = (0.1N NaOH dosage at the second end point [mL] - 0.1N NaOH dosage at the first end point [mL]) × 0.29749 × 0.1 × 0.5 / sample amount [g]

Analysis machine: Metrohom 736GP Titrino

Electrode: Combined pH Electrode (Metrohm cat.#6.0258.000)

Titration solution: 0.1N NaOH

Composition of mannitol solution: 500g mannitol, 3500g pure water

〈Preparation of adhesives〉

3.5 parts of Gohsefimer Z-200 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 0.12 parts of zinc chloride, and 0.89 parts of glyoxal were dissolved in 100 parts of water to prepare polyvinyl alcohol resin adhesive A.

<Implementation Example 1>

(Manufacturing of polarizer)

A transparent unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or more and a thickness of 45 μm was immersed in 30°C water (deionized water) for 2 minutes to swell it, and then immersed in a 30°C dyeing solution containing 0.45 mmol/L iodine, 2 parts by mass of potassium iodide, and 0.35 parts by mass of boric acid for 2 minutes to dye it. At this time, the film was stretched at a stretching ratio of 1.72 times and 1.54 times in the swelling and dyeing stages, respectively, and stretched so that the cumulative stretching ratio until the dyeing tank became 2.64 times. Next, it was immersed in a crosslinking solution at 56°C containing 7.9 parts by mass of potassium iodide and 4.3 parts by mass of boric acid for 30 seconds (crosslinking stage) to crosslink, and stretched at a stretching ratio of 2.2 times. Furthermore, it was immersed in a crosslinking solution at 40°C containing 10.6 parts by mass of potassium iodide, 5.0 parts by mass of zinc nitrate and 3.9 parts by mass of boric acid for 5 seconds (color-replenishing stage) to crosslink, and stretched. At this time, the total cumulative stretching ratio of swelling, dyeing, crosslinking, and color-replenishing stages became 5.9 times. After the crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 100°C to produce a polarizer. The thickness of the polarizer was 18μm.

(Manufacturing of polarizing plates)

Using the polyvinyl alcohol adhesive A prepared as above, a protective film was bonded to both sides of the polarizer. As the protective film, a cellulose triacetate film (KC4UAW, manufactured by Konica Minolta Co., Ltd., thickness 40μm, moisture permeability 800g/ ^m2 /24h at 40°C and relative humidity 90%RH) was used on one side of the polarizer, and a cellulose triacetate film (thickness 60μm, reflectivity 1%) treated with an anti-reflection (LR) surface was used on the other side. After applying the polyvinyl alcohol adhesive A on both sides of the polarizer, a roller was used for bonding, and the polarizing plate of Example 1 was manufactured by drying at 80°C for 5 minutes.

<Implementation Example 2>

(Manufacturing of polarizer)

The polarizer was manufactured in the same manner as in Example 1 except that the temperature of the crosslinking liquid in the crosslinking stage was changed from 56°C to 60°C and the boric acid concentration of the crosslinking liquid in the color correction stage was set to 3.0 parts by mass. The thickness of the polarizer was 18μm.

(Manufacturing of polarizing plates)

The polarizing plate of Example 2 is manufactured in the same manner as Example 1 except that the polarizing film manufactured above is used.

<Implementation Example 3>

(Manufacturing of polarizer)

The polarizer was manufactured in the same manner as in Example 1 except that the drying temperature of the polyvinyl alcohol film after crosslinking in Example 1 was changed from 100°C to 90°C and the boric acid concentration of the crosslinking solution in the color correction stage was set to 3.0 parts by mass. The thickness of the polarizer was 18μm.

(Manufacturing of polarizing plates)

The polarizing plate of Example 3 is manufactured in the same manner as Example 1, except that the polarizing film manufactured above is used.

<Implementation Example 4>

(Manufacturing of polarizer)

The polarizer was manufactured in the same manner as in Example 1 except that the transparent unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray) with a saponification degree of 99.9% or more and a thickness of 45 μm was replaced by a transparent unstretched polyvinyl alcohol film (PE-6000, manufactured by Kuraray) with a saponification degree of 99.9% or more and a thickness of 60 μm, and the boric acid concentration of the crosslinking liquid in the color correction stage was set to 3.0 parts by mass. The thickness of the polarizer was 23 μm.

(Manufacturing of polarizing plates)

The polarizing plate of Example 4 is manufactured in the same manner as Example 1, except that the polarizing film manufactured above is used.

<Comparative example 1>

(Manufacturing of polarizer)

Except for changing the zinc nitrate content of the crosslinking solution in the color correction stage in Example 1 from 5.0 parts to 3.0 parts, the rest is the same as Example 1 to manufacture the polarizer. The thickness of the polarizer is 18μm.

(Manufacturing of polarizing plates)

Except for using the polarizer manufactured as described above, the polarizer of Comparative Example 1 is manufactured in the same manner as in Example 1.

<Comparative example 2>

(Manufacturing of polarizer)

Except for changing the content of zinc nitrate in the crosslinking solution in the color-correcting stage in Example 1 from 5.0 parts to 0 parts, the rest is the same as Example 1 to manufacture the polarizer. The thickness of the polarizer is 18μm.

(Manufacturing of polarizing plates)

The polarizing plate of Comparative Example 1 is manufactured in the same manner as Example 1 except that the polarizing film manufactured above is used.

〈Experiment〉

For the polarizing plates of Examples 1 to 4 and Comparative Examples 1 to 2, the light-corrected monomer transmittance (Ty), light-corrected polarization (Py), monomer hue b value and A700 were measured in the above manner. In addition, for the obtained polarizing plates, the content of zinc element in the polarizer was measured in the above manner. Furthermore, for the obtained polarizing plates, the heat resistance test was performed and the change rate of light-corrected polarization △Py was calculated. The results are shown in Table 1.

[Table 1]

1:Polarizing plate

10: Polarizer

101: First subsequent coating

102: 1st resin film

Claims (8)

A polarizing plate, which sequentially comprises a polarizer, a first adhesive layer, and a first resin film; wherein the polarizer and the first adhesive layer are in direct contact, the transmittance of the light correction monomer is 45.5% or more, the total content of zinc element contained in the polarizer and the adhesive layer directly contacting the polarizer is 0.15 mass % or more and 0.22 mass % or less, and the thickness of the polarizer is 10 μm or more. The polarizing plate as described in claim 1, wherein the luminous intensity correction polarization degree is greater than 94.0%. The polarizing plate as claimed in claim 1 or 2, wherein the moisture permeability of the first resin film at a temperature of 40°C and a relative humidity of 90% RH is 100 g/m ² /24h or more. The polarizing plate as described in claim 1 or 2, wherein the first adhesive layer contains a zinc element. The polarizing plate as described in claim 1 or 2, wherein the side of the polarizer opposite to the first resin film is provided with a second adhesive layer and a second resin film in order from the side close to the polarizer. The polarizing plate as claimed in claim 5, wherein the moisture permeability of the second resin film at a temperature of 40°C and a relative humidity of 90% RH is 100 g/m ² /24h or more. The polarizing plate as described in claim 5, wherein the second adhesive layer contains a zinc element. A method for manufacturing a polarizing plate, which is a method for manufacturing a polarizing plate as described in any one of claims 1 to 7, comprising: treating a polyvinyl alcohol resin film with a treatment solution containing a zinc salt to manufacture a polarizing plate.

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