CN115443425A

CN115443425A - Polarizing plate and method for manufacturing same

Info

Publication number: CN115443425A
Application number: CN202180030920.6A
Authority: CN
Inventors: 赵天熙; 崔允硕; 金孝东; 崔正宁
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-04-28
Filing date: 2021-03-23
Publication date: 2022-12-06
Also published as: KR20230002830A; JP2021173936A; WO2021220668A1; TW202146949A

Abstract

The invention provides a polarizing plate having excellent heat resistance. A polarizing plate comprising a polarizing plate, a 1 st adhesive layer and a 1 st resin film in this order, wherein the polarizing plate is in direct contact with the 1 st adhesive layer, the visibility-correcting monomer transmittance is 45.5% or more, the content of zinc element contained in the polarizing plate and the adhesive layer in direct contact with the polarizing plate is 0.15% by mass or more, and the thickness of the polarizing plate is 10 [ mu ] m or more.

Description

Polarizing plate and method for manufacturing same

Technical Field

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

Background

As a polarizing plate, a polyvinyl alcohol resin film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented is known. Patent documents 1 to 3 propose zinc-containing polyvinyl alcohol resin films as such polyvinyl alcohol resin films.

Documents of the prior art

Patent literature

Patent document 1: japanese patent laid-open No. 2003-29042

Patent document 2: japanese patent laid-open publication No. 2004-61565

Patent document 3: japanese patent laid-open publication No. 2014-102353

Disclosure of Invention

Problems to be solved by the invention

The polarizer is used as a polarizing plate in an image display device. When the image display device is used at a high temperature for a long time, the optical characteristics of the polarizing plate may change. In particular, in a polarizing plate having a high transmittance for organic EL applications, the amount of circular dichroic dye in the polarizer is small, and it is difficult to satisfy durability tests such as heat resistance. Therefore, improvement in heat resistance of the polarizing plate is required.

The invention aims to provide a polarizing plate having good heat resistance.

Means for solving the problems

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

[1] A polarizing plate comprising a polarizing plate, a 1 st adhesive layer and a 1 st resin film in this order,

the polarizing plate is in direct contact with the 1 st adhesive layer,

the visibility correction monomer transmittance of the polarizing plate is 45.5% or more,

the content of zinc element contained in the polarizing plate and the adhesive layer in direct contact with the polarizing plate is 0.15 mass% or more,

the thickness of the polarizing plate is 10 μm or more.

[2] The polarizing plate according to [1], wherein the visibility correction polarization degree is 94.0% or more.

[3] The polarizing plate according to any one of [1] and [2], wherein a content of the zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.22% by mass or less.

[4]According to [1]]～[3]The polarizing plate according to any one of the above, wherein the moisture permeability of the 1 st resin film is 100g/m at a temperature of 40 ℃ relative humidity 90% ² More than 24 h.

[5] The polarizing plate according to any one of [1] to [4], wherein the 1 st adhesive layer contains a zinc element.

[6] The polarizing plate according to any one of [1] to [5], further comprising a 2 nd adhesive layer and a 2 nd resin film in this order from a side close to the polarizer on a side opposite to the 1 st resin film of the polarizer.

[7]According to [6]The polarizing plate, wherein the 2 nd resin film has a moisture permeability of 100g/m as measured at a temperature of 40 ℃ relative humidity 90% ² More than 24 h.

[8] The polarizing plate according to any one of [6] and [7], wherein the 2 nd adhesive layer contains a zinc element.

[9] A method for producing the polarizing plate according to any one of [1] to [8],

the method comprises a step of processing a polyvinyl alcohol resin film with a processing liquid containing a zinc salt to produce a polarizing plate.

Effects of the invention

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

Drawings

Fig. 1 is a schematic cross-sectional view showing a polarizing plate according to an embodiment of the present invention.

Fig. 2 is a flowchart showing a method for manufacturing a polarizing plate according to an embodiment of the present invention.

Detailed Description

[ polarizing plate ]

Fig. 1 is a cross-sectional view schematically showing a polarizing plate according to an embodiment of the present invention. The polarizing plate 1 includes a polarizer 10, a 1 st adhesive layer 101, and a 1 st resin film 102 in this order. The polarizing plate 10 is in direct contact with the 1 st adhesive layer 101. The visibility-correcting monomer transmittance (Ty) of the polarizing plate is 45.5% or more, and the content of the zinc element is 0.15% by mass or more. The thickness of the polarizing plate is 10 μm or more. In the case where the visibility correcting monomer transmittance (Ty) of the polarizing plate is 45.5% or more, a change in optical characteristics is easily observed as compared with a polarizing plate in which the visibility correcting monomer transmittance (Ty) is less than 45.5%. According to the present invention, by setting the content of the zinc element contained in the polarizing plate and the thickness of the polarizer to the above ranges, it is possible to provide a polarizing plate having a visibility-correcting monomer transmittance (Ty) of 45.5% or more, which is excellent in heat resistance and in which the change in optical characteristics before and after a heat resistance test is suppressed even when the polarizing plate is subjected to the heat resistance test.

The visibility correction monomer transmittance (Ty) of the polarizing plate is preferably 46.0% or more, and more preferably 47.0% or more. The visibility correction monomer transmittance (Ty) of the polarizing plate is usually 50% or less.

In the present specification, the heat resistance test refers to a durability test of heat resistance tests performed according to the method described in the column of examples described later. In the case of a polarizing plate subjected to a heat resistance test, an example of optical characteristics in which a change before and after a durability test is suppressed is a visibility-corrected polarization degree (Py). The change rate (Δ Py) of the visibility-corrected 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 exhibiting excellent heat resistance with a change rate (Δ Py) in such a range can be obtained.

The visibility-corrected polarization degree (Py) of the polarizing plate is preferably 92.0% or more, more preferably 93.0% or more, and further preferably 94.0% or more. The visibility-corrected polarization degree (Py) of the polarizing plate may be 99.9% or less, or 99% or less, or 98% or less in another embodiment.

The content of zinc element in the polarizer and the adhesive layer in direct contact with the polarizer of the polarizing plate is 0.15 mass% or more. By setting the content of zinc element in the polarizer and the adhesive layer in direct contact with the polarizer to 0.15 mass% or more, a polarizing plate having 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. The content of the zinc element is preferably 0.22 mass% or less, and more preferably 0.20 mass% or less, from the viewpoint of obtaining a polarizing plate of a desired color tone.

The total content of the zinc element contained in the polarizing plate and the adhesive layer in direct contact with the polarizing plate can be adjusted by adjusting the content of the zinc element contained in the polarizing plate, the content of the zinc element in the 1 st adhesive layer and/or the 2 nd adhesive layer in contact with the polarizing plate, and the like. The content of zinc element contained in the polarizing plate and the adhesive layer in direct contact with the polarizing plate was measured by the method described in the examples described later.

The b value of the single color tone of the polarizing plate is, for example, from-1.0 to 4.0, preferably from-0.5 to 3.0, and more preferably from 0 to 2.0.

The absorbance a700 of the polarizing plate at a wavelength of 700nm is, for example, 0.5 or more and 3.0 or less, preferably 0.7 or more and 2.0 or less, and more preferably 0.9 or more and 1.5 or less.

In this specification, the visibility-correcting monomer transmittance (Ty), the visibility-correcting polarization degree (Py), and the rate of change (Δ Py) of the visibility-correcting polarization degree (Py), the monomer hue b value, the absorbance a700 at a wavelength of 700nm, and the content of the zinc element in the polarizing plate and the adhesive layer in direct contact with the polarizing plate were values measured according to the measurement methods described in the columns of examples described later.

The 1 st resin film is bonded to the surface of the polarizing plate via, for example, a 1 st adhesive layer.

The polarizing plate may further include a 2 nd adhesive layer and a 2 nd resin film in this order from the side close to the polarizer on the side opposite to the 1 st resin film. The 2 nd resin film is bonded to the surface of the polarizing plate via, for example, a 2 nd adhesive layer. In the polarizing plate, when "the total content of zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer" is determined, the 1 st adhesive layer corresponds to the adhesive layer in direct contact with the polarizer, and when the 2 nd adhesive layer is provided in direct contact with the polarizer, the 2 nd adhesive layer also corresponds to the adhesive layer in direct contact with the polarizer. Hereinafter, the 1 st resin film and the 2 nd resin film are also collectively referred to as resin films, and the 1 st adhesive layer and the 2 nd adhesive layer are also collectively referred to as adhesive layers.

< polarizing plate >

The polarizing plate is an absorption type polarizing plate having the following properties: linearly polarized light having a vibration plane parallel to the absorption axis thereof is absorbed, while linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis) is transmitted. The polarizing plate may be, for example, a polarizing plate in which a uniaxially stretched polyvinyl alcohol resin film is adsorbed and oriented with a dichroic dye, and such a polarizing plate may be produced by a method for producing a polarizing plate described later.

The thickness of the polarizing plate is 10 [ mu ] m or more. By setting the thickness of the polarizer to 10 μm or more, a polarizing plate having excellent resistance can be provided. The thickness of the polarizing plate is preferably 12 μm or more, and more preferably more than 15 μm. The thickness of the polarizing plate is preferably 50 μm or less, and more preferably 30 μm or less.

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

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

The content of the zinc element contained in the polarizing plate can be set to the content of the zinc element within the above range by adjusting, for example, the concentration of the zinc salt in the treatment liquid for treating the polyvinyl alcohol resin film, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, and the like.

< method for producing polarizing plate >

A method for manufacturing a polarizing plate according to another embodiment of the present invention will be described with reference to the drawings.

The manufacturing method shown in fig. 2 is a method for manufacturing a polarizing plate including a polyvinyl alcohol resin, and may include the steps of:

a dyeing step S20 of immersing the polyvinyl alcohol resin film in a dyeing bath containing a treatment liquid containing a dichroic dye to dye the polyvinyl alcohol resin film; and

and a crosslinking step S30 of immersing the film after the dyeing step in a crosslinking tank containing a treatment liquid containing a crosslinking agent to perform crosslinking treatment.

The production method may further include other steps than the above, and specifically, as shown in fig. 2, the steps include a swelling step S10 of immersing the polyvinyl alcohol resin film before the dyeing step S20 in a swelling tank containing a treatment liquid 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. The polyvinyl alcohol resin film is uniaxially stretched (stretched) at any 1 or more stages of the polarizing plate production process, more specifically, at any 1 or more stages from before the swelling process S10 to before the crosslinking process S30.

In the production method, at least 1 of the treatment liquids for treating the polyvinyl alcohol resin film contains a zinc salt. Examples of the treatment tank for containing the treatment liquid include a swelling tank, a dyeing tank, a crosslinking tank, a cleaning tank, and a color correction tank described later. The treatment tank containing the treatment liquid containing the zinc salt is preferably a treatment tank from the rear of the dyeing tank to the front of the washing tank, more preferably at least 1 selected from the crosslinking tank and the color correction tank, and even more preferably at least 1 selected from the last crosslinking tank and the color correction tank when the number of crosslinking tanks is 2 or more. The polyvinyl alcohol resin film is immersed in a treatment liquid containing a zinc salt, whereby the obtained polarizing plate can contain zinc. The content of the zinc element in the polarizing plate can be adjusted to the content of the zinc element within the above range by adjusting the concentration of the zinc salt in the treatment liquid, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, and the like.

Examples of the zinc salt contained in the treatment solution include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferable from the viewpoint of low cost. The zinc salt may be added to the treatment solution in the form of a zinc salt solution.

The concentration of the zinc salt in the treatment liquid may vary depending on the treatment bath, but 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, with respect to 100 parts by mass of the treatment liquid contained in the treatment bath.

The time for immersing the polyvinyl alcohol resin film in the treatment liquid and the temperature of the treatment liquid may be different for each treatment tank. Specific immersion time and treatment liquid temperature will be described in the following paragraphs with respect to each step.

The various treatment steps included in the production method of the present invention can be continuously performed by continuously conveying a polyvinyl alcohol resin film as a raw material film along a film conveying path of a polarizing plate production apparatus. The film transport path includes facilities (treatment tank, furnace, etc.) for performing the various treatment steps described above in the order of their implementation.

The film transport path may be constructed by arranging a guide roll, a nip roll, and the like at appropriate positions in addition to the above-described devices. For example, the guide rollers may be disposed before and after the respective treatment tanks and in the treatment tanks, whereby the film can be introduced into and immersed into and pulled out from the treatment tanks. More specifically, by providing 2 or more guide rollers in each processing tank and transporting the film along these guide rollers, the film can be immersed in each processing tank.

As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film as the raw material film, a polyvinyl alcohol resin obtained by saponifying a polyvinyl acetate resin can be used. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. 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. In the present specification, "(meth) acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth) acryloyl group".

The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like modified with aldehydes may be used.

The polyvinyl alcohol resin preferably has an average degree of polymerization of 100 or more and 10000 or less, more preferably 1500 or more and 8000 or less, and further preferably 2000 or more and 5000 or less. The average degree of polymerization of the polyvinyl alcohol resin can be determined in accordance with JIS K6726 (1994). If the average polymerization degree is less than 100, it is difficult to obtain preferable polarization performance, and if it exceeds 10000, film processability may be poor.

From the viewpoint of making the thickness of the polarizing plate 10 μm or more, the thickness of the polyvinyl alcohol-based resin film is preferably 20 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less, and still more preferably 40 μm or more and 65 μm or less.

The polyvinyl alcohol resin film as the raw material film may be prepared, for example, in the form of a long roll (wound product) of unstretched or stretched polyvinyl alcohol resin film. In this case, the polarizing plate is also obtained as a long strip. Hereinafter, each step will be described in detail.

(1) Swelling step S10

The swelling treatment in this step is a treatment which is carried out as needed for the purpose of removing foreign matter, removing a plasticizer, imparting easy dyeability, plasticizing the film, and the like of the polyvinyl alcohol resin film as a raw material film, and specifically, may be a treatment in which the polyvinyl alcohol resin film is immersed in a swelling tank containing a treatment liquid containing water. The film may be immersed in 1 swelling bath, or may be successively immersed in 2 or more swelling baths. The membrane may 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 swelling tank may be water (for example, 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.

The temperature of the treatment liquid contained in the swelling tank at the time of immersing the film is usually about 10 to 70 ℃, preferably about 15 to 50 ℃, and the time for immersing the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

(2) Dyeing step S20

The dyeing treatment in this step is a treatment for adsorbing and orienting the dichroic dye to the polyvinyl alcohol resin film, and specifically, may be a treatment for immersing the polyvinyl alcohol resin film in a dyeing bath containing a treatment liquid containing the dichroic dye. The membrane can be immersed in 1 staining tank, also can be sequentially immersed in more than 2 staining tanks. In order to improve the dyeability of the dichroic dye, the film to be subjected to the dyeing step may be subjected to uniaxial stretching treatment at least to some extent. Instead of the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment may be performed at the time of the dyeing treatment, or the uniaxial stretching treatment may be performed at the time of 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, rubine BL, purplish red GS, sky blue LG, lemon yellow, blue BR, blue 2R, dark blue 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. The dichroic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

In the case of using iodine as the dichroic dye, an aqueous solution containing iodine and potassium iodide may be used as the treatment liquid contained in the dyeing bath. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, a compound other than iodide, for example, boric acid, zinc chloride, cobalt chloride, or the like may be coexistent. The addition of boric acid differs from the crosslinking treatment described later in that iodine is contained. The content of iodine in the aqueous solution is usually 0.01 parts by mass or more and 1 part by mass or less per 100 parts by mass of water. The content of iodide such as potassium iodide is usually 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of water. As described above, the treatment solution contained in the dyeing bath may contain a zinc salt.

The temperature of the treatment liquid contained in the staining bath when the membrane is immersed is usually 10 ℃ to 45 ℃, preferably 10 ℃ to 40 ℃, more preferably 20 ℃ to 35 ℃, and the immersion time of the membrane is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

In the case of using a dichroic organic dye as the dichroic dye, an aqueous solution containing the dichroic organic dye may be used as the treatment liquid contained in the dyeing bath. The content of the dichroic organic dye in the aqueous solution is usually 1 × 10 per 100 parts by mass of water ^-4 At least 10 parts by mass, preferably 1X 10 parts by mass ^-3 The amount of the organic solvent is not less than 1 part by mass. The dyeing bath may contain a dyeing assistant and the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant and the like. The dichroic organic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds. The temperature of the treatment liquid contained in the staining bath when the membrane is immersed is, for example, 20 ℃ or more and 80 ℃, preferably 30 ℃ or more and 70 ℃ or less, and the immersion time of the membrane is usually 30 seconds or more and 600 seconds or less, preferably 60 seconds or more and 300 seconds or less.

(3) Crosslinking step S30

The crosslinking treatment for treating the polyvinyl alcohol resin film after the dyeing step with the crosslinking agent is a treatment for the purpose of water resistance, color tone adjustment, and the like by crosslinking, and specifically, may be a treatment in which the film after the dyeing step is immersed in a treatment liquid contained in a crosslinking tank containing the crosslinking agent.

The membrane may be immersed in 1 crosslinking bath, or may be successively immersed in 2 or more crosslinking baths. The crosslinking treatment may be conducted by uniaxial stretching treatment.

Examples of the crosslinking agent include boric acid, glyoxal, glutaraldehyde, and the like, and boric acid is preferably used. More than 2 kinds of crosslinking agents may be used in combination. The content of boric acid in the treatment liquid contained in the crosslinking tank is usually 0.1 part by mass or more and 15 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the crosslinking tank preferably contains an iodide in addition to boric acid. The content of the iodide in the treatment liquid contained in the crosslinking tank is usually 0.1 part by mass or more and 15 parts by mass or less, and preferably 5 parts by mass or more and 12 parts by mass or less per 100 parts by mass of water. Examples of the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like, may be allowed to coexist in the crosslinking tank. As described above, the treatment liquid contained in the crosslinking tank may contain a zinc salt. When 2 or more crosslinking chambers are present, the treatment liquid contained in the last crosslinking chamber preferably contains a zinc salt.

The temperature of the treatment liquid contained in the crosslinking tank when the membrane is immersed is usually 50 ℃ to 85 ℃, preferably 50 ℃ to 70 ℃, and the immersion time of the membrane is usually 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds.

In the crosslinking step S30, the crosslinking groove may be 2 grooves or more. In this case, the composition and temperature of the treatment liquid contained in each crosslinking vessel may be the same or different. The treatment liquid contained in the crosslinking tank may have a concentration and a temperature of the crosslinking agent, the iodide, and the like according to the purpose of impregnating the polyvinyl alcohol resin film. The crosslinking treatment for the water resistance by crosslinking and the crosslinking treatment for color tone adjustment (complementary color) may be performed in a plurality of steps (for example, a plurality of tanks), respectively.

In general, when both of the crosslinking treatment for the water resistance by crosslinking and the crosslinking treatment for the color tone adjustment (complementary color) are performed, a groove (complementary color groove) for performing the crosslinking treatment for the color tone adjustment (complementary color) is disposed at the subsequent stage. The temperature of the treatment liquid contained in the color correction tank is, for example, 10 ℃ or higher and 55 ℃ or lower, and preferably 20 ℃ or higher and 50 ℃ or lower. The content of the crosslinking agent in the treatment liquid contained in the color correction tank is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of the iodide in the treatment liquid contained in the color-complementing tank is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water. As described above, the treatment liquid contained in the complementary color tank may contain a zinc salt.

As described above, in the production of the polarizing plate, the polyvinyl alcohol resin film is uniaxially stretched at any 1 or 2 or more stages from the swelling step S10 to the crosslinking step S30 (stretching step, fig. 2). From the viewpoint of improving the dyeability of the dichroic dye, the film to be subjected to the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or is preferably subjected to uniaxial stretching treatment at the time of dyeing treatment instead of the uniaxial stretching treatment before dyeing treatment, or is subjected to uniaxial stretching treatment at the time of dyeing treatment in addition to the uniaxial stretching treatment before dyeing treatment.

The uniaxial stretching treatment may be either dry stretching in which stretching is performed in air or wet stretching in which stretching is performed in a tank, or both of them may be performed. The uniaxial stretching treatment may be inter-roll stretching, hot-roll stretching, tenter stretching or the like in which longitudinal uniaxial stretching is performed by providing a circumferential speed difference between 2 nip rolls, and preferably includes inter-roll stretching. The stretching ratio based on the raw material film (cumulative stretching ratio in the case of stretching treatment in 2 or more stages) is 3 to 8 times. The stretch ratio is preferably 4 times or more, and more preferably 5 times or more, in order to impart good polarization characteristics.

(4) Cleaning step S40

The cleaning treatment in this step is carried out as needed for the purpose of removing an excessive crosslinking agent, a dichroic dye, or other chemical agent attached to the polyvinyl alcohol resin film, and is a treatment of cleaning the polyvinyl alcohol resin film after the crosslinking step with a cleaning solution containing water. Specifically, the polyvinyl alcohol resin film after the crosslinking step may be immersed in a treatment liquid (cleaning liquid) contained in a cleaning tank. The membrane can be immersed in 1 cleaning tank, or can be sequentially immersed in more than 2 cleaning tanks. Alternatively, the cleaning treatment may be a treatment of spraying a cleaning liquid on the polyvinyl alcohol resin film after the crosslinking step, or a combination of the above-mentioned immersion and spraying.

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. The temperature of the cleaning liquid may be, for example, 5 ℃ to 40 ℃.

The cleaning step S40 is an arbitrary step, and may be omitted, or the cleaning process may be performed in the drying step S50 as described later. The film after the washing step S40 is preferably subjected to a drying step S50.

(5) Drying step S50

The drying step S50 is a region for drying the polyvinyl alcohol resin film after the washing step S40. The polyvinyl alcohol resin film after the washing step S40 is continuously conveyed, and the film is introduced into the drying step S50 to be dried, whereby a polarizing plate can be obtained.

The drying treatment can be performed using a drying mechanism (heating mechanism) of the film. A suitable example of a drying mechanism is a drying oven. The drying oven is preferably capable of controlling the temperature within the oven. The drying oven is, for example, a hot air oven capable of raising the temperature in the oven by supplying hot air or the like. The drying treatment by the drying means may be a treatment of adhering the polyvinyl alcohol resin film after the washing step S40 to 1 or 2 or more heating bodies having a convex curved surface, or a treatment of heating the film by using a heater.

Examples of the heating body include a roller (e.g., a guide roller serving also as a heat roller) having a heat source (e.g., a heat medium such as warm water or an infrared heater) therein and capable of increasing the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a plate heater.

The temperature of the drying treatment (e.g., the temperature in the drying furnace, the surface temperature of the heat roll, etc.) is usually 30 ℃ or higher and 100 ℃ or lower, and preferably 50 ℃ or higher and 90 ℃ or lower. The drying time is not particularly limited, and is, for example, 30 seconds to 600 seconds.

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

The obtained polarizer may be directly transferred to the subsequent polarizing plate production step (step of bonding a thermoplastic resin film to one or both surfaces of the polarizer), for example.

< resin film >

The resin film may be a polyolefin-based resin including a thermoplastic resin, for example, a chain polyolefin-based resin (such as a polypropylene-based resin) or a cyclic polyolefin-based resin (such as a norbornene-based resin); cellulose ester resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate-based resin; (meth) acrylic resins such as polymethyl methacrylate resins; or a mixture or copolymer thereof.

Either or preferably both of the 1 st resin film and the 2 nd resin film have a moisture permeability of 100 (g/m) in relative humidity 90% at a temperature of 40 ℃ and RH ² 24 h) or more, in particular 300 (g/m) ² /24 h) or more, particularly, the effect is exhibited. Such a film having high moisture permeability is likely to have low high-temperature durability due to the presence of moisture, but can provide high-temperature durability by satisfying the requirements of the present invention. Examples of the resin film satisfying such moisture permeability include triacetyl cellulose. The moisture permeability of the resin film was 100 (g/m) at a temperature of 40 ℃ and a relative humidity of 90% ² /24 h) or more, a surface treatment layer such as a hard coat layer or an antireflection layer may be provided on the surface of the resin film. If such a moisture-permeable resin film is used, the heat resistance of the polarizing plate tends to be deteriorated, but the polarizing plate of the present invention has good durability.

Either or both of the 1 st resin film and the 2 nd resin film may be a protective film having an optical function such as a retardation film or a brightness enhancement film. For example, a transparent resin film formed of the above-described material is stretched (uniaxially stretched, biaxially stretched, or the like), or a liquid crystal layer is formed on the film, whereby a retardation film to which an arbitrary retardation value is applied can be produced.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer may be formed on the surface of the resin film on the side opposite to the polarizing plate.

The thickness of the resin film is preferably small from the viewpoint of thinning the polarizing plate, but if too thin, the strength tends to be lowered and the processability tends to be poor, and therefore, it is preferably 5 to 150 μm, more preferably 5 to 100 μm, and still more preferably 10 to 60 μm.

(adhesive layer)

The polarizing plate can be obtained by laminating (laminating) a resin film on one or both surfaces of a polarizer via an adhesive layer. Examples of the adhesive used for bonding the polarizing plate and the resin film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol resin or a cross-linking agent mixed therein, and an aqueous adhesive such as a urethane emulsion adhesive. As the adhesive, an adhesive containing zinc element may be used.

By applying an adhesive containing a zinc element to the surface of the polarizing plate, the zinc element in the polarizing plate can be prevented from transferring from the polarizing plate to another layer, and the deterioration of high-temperature durability can be prevented. As a method of adding zinc to the adhesive, a method of adding zinc salt at the time of preparing the adhesive can be mentioned. As the zinc salt, zinc halide such as zinc chloride or zinc iodide, zinc sulfate, zinc acetate, zinc nitrate, or the like can be used. The content of zinc as the binder may be, for example, 0.1 part by mass or more and 5 parts by mass or less when the total amount of the binder is 100 parts by mass in terms of solid content.

When resin films are bonded to both surfaces of the polarizing plate, the adhesives forming the 2 adhesive layers may be of the same type or of different types. For example, when a resin film is laminated on both surfaces, one surface may be laminated with an aqueous adhesive, and the other surface may be laminated with an active energy ray-curable adhesive. The ultraviolet-curable adhesive may be a mixture of a radical-polymerizable (meth) acrylic compound and a photo radical polymerization initiator, a mixture of a cationically-polymerizable epoxy compound and a photo cationic polymerization initiator, or the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable (meth) acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used as initiators in combination.

In the case of using an active energy ray-curable adhesive, the adhesive is cured by irradiation with an active energy ray after bonding. The light source of the active energy ray is not particularly limited, and active energy rays (ultraviolet rays) having an emission distribution at a wavelength of 400nm or less are preferable, and 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, a microwave-excited mercury lamp, a metal halide lamp, or the like can be preferably used.

In order to improve the adhesion between the polarizing plate and the resin film, the surface of the polarizing plate and/or the resin film to be bonded may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, saponification treatment, or the like, before the polarizing plate and the resin film are bonded.

As described above, the polarizing plate of the present invention can be produced by laminating a resin film on a polarizing plate which is a single-layer film via an adhesive layer, but is not limited to this method. For example, the film can be produced by a method using a base film as described in japanese patent application laid-open No. 2009-98653. The latter method is advantageous for obtaining a polarizing plate having a film polarizer (polarizer layer), and may include, for example, the following steps.

A resin layer forming step of applying a coating liquid containing a polyvinyl alcohol resin to at least one surface of a base film and then drying the coating liquid to form a polyvinyl alcohol resin layer to obtain a laminated film,

a stretching step of stretching the laminated film to obtain a stretched film,

a dyeing step of dyeing the polyvinyl alcohol resin layer of the stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizing plate) to obtain a polarizing laminate film,

a 1 st bonding step of bonding a resin film (1 st resin film) to the polarizer layer of the polarizing laminate film with an adhesive (1 st adhesive layer) to obtain a bonded film,

and a peeling step of peeling and removing the base film from the adhesive film to obtain the polarizing plate with the resin film on one side.

Zinc may be contained in at least one of the dyeing step and the first bonding step 1. When zinc is contained in the dyeing step, zinc can be contained in the polarizing plate by adding zinc salt to the treatment liquid containing the dichroic dye. In the case where the zinc element is contained in the first bonding step 1, the zinc element can be contained in the polarizing plate by containing the zinc element in the adhesive.

When resin films are laminated on both surfaces of a polarizer layer (polarizer), the method further comprises a 2 nd bonding step of bonding a 2 nd resin film to the polarizer surface of the polarizer having the 1 st resin film on one surface thereof using an adhesive (2 nd adhesive layer). In addition, zinc element may be contained in the adhesive for bonding the 2 nd resin film.

In the above method using a base film, the dyeing step for obtaining the polarizing laminate film (for example, after the crosslinking step or after the washing step in the dyeing step for obtaining the polarizing laminate film) may include a drying step. The polarizing film of the present invention includes a polarizing plate including the polarizing laminate film, the polarizing plate having a thermoplastic resin film on one side, and the polarizing plate having a thermoplastic resin film on both sides obtained through the 2 nd bonding step, or a polarizing plate separated therefrom.

Polarizing plates may be used for the display device. The display device may be any device such as a liquid crystal display device or an organic EL display device, and is preferably an organic EL display device. When incorporated into a liquid crystal display device, the liquid crystal display device is preferably used on the viewing side of a liquid crystal light-emitting element. In addition, when incorporated into an organic EL display device, a circularly polarizing plate in which a retardation film is combined with the polarizing plate of the present invention may be used as the antireflection film.

The polarizing plate is suitable for an in-vehicle display device including a polarizing plate, a light-transmitting member bonded to a surface of the polarizing plate on the 1 st resin film side, and a display device bonded to a surface of the polarizing plate on the 2 nd resin film side in this order. The light-transmitting member may be a glass plate, a resin film having light-transmitting properties, or the like.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Examples

[ visibility-correcting monomer transmittance (Ty), visibility-correcting polarization degree (Py), and monomer hue b value ]

The polarizing plate was measured for MD transmittance and TD transmittance at a wavelength of 380 to 780nm using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO corporation),

based on the following formula:

monomer transmittance (%) = (MD + TD)/2

Degree of polarization (%) = { (MD-TD)/(MD + TD) } × 100

The monomer transmittance and the degree of polarization at each wavelength were calculated.

The "MD transmittance" is a transmittance when the direction of polarized light emitted from the glan thompson prism is parallel to the transmission axis of the polarizing plate, and is expressed as "MD" in the above formula. The "TD transmittance" is a transmittance when the direction of polarized light emitted from the glan thompson prism is perpendicular to the transmission axis of the polarizing plate, and is represented by "TD" in the above formula.

For the obtained monomer transmittance and polarization degree, the transmittance was measured by JIS Z8701: 1999 "color display method — 2 degree visual field (C light source) of XYZ color system and X10Y 10Z10 color system" to perform visibility correction, and obtain visibility correction single transmittance (Ty) and visibility correction polarization degree (Py).

Further, the spectral transmittance τ (λ) of the polarizing plates produced in examples and comparative examples was measured by a spectrophotometer (V7100, japan spectro corporation) based on the method described in international publication No. 2016/117659, and the orthogonal spectral transmittance spectrum was obtained to obtain the single color 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 The transmittance at a wavelength of 700nm, T, obtained when the polarizing plate was disposed in a state in which the absorption axis of the polarizer was orthogonal to the linearly polarized light of the measurement light _TD，700 The transmittance at a wavelength of 700nm obtained when the polarizing plate was disposed in a state where the absorption axis of the polarizer was parallel to the linearly polarized light of the measurement light, and the units of these were% in each case.

[ Heat resistance test ]

A40 mm × 40mm test piece was cut out from the produced polarizing plate, and 40mm × 40mm alkali-free glass was bonded to both sides of the cut-out polarizing plate using an acrylic adhesive having a thickness of 25 μm to prepare a sample. For each sample, before being subjected to the heat resistance test, the visibility-corrected monomer transmittance (Ty), the visibility-corrected polarization degree (Py), the monomer hue b value, and a700 were calculated based on the measured values according to the above-described method.

Each sample was subjected to a heat resistance test by placing it in an oven at 80 ℃ for 500 hours. For each sample, after being subjected to the heat resistance test, the visibility correction polarization degree (Py) was measured by the above method, and the change rate Δ Py [% ] of the visibility correction polarization degree was calculated by the following method.

The change rate Δ Py [% ] is a change rate of the visibility correction polarization degree (Py) before and after the heat resistance test, and is a value calculated from the following equation (1) when the visibility correction polarization degree (Py) before the durability test is P1 and the visibility correction polarization degree (Py) after the heat resistance test is P2.

ΔPy＝{(P1-P2)/P1}×100 (1)

[ measurement of content of Zinc element ]

The polarizing plate was immersed in methylene chloride for 30 minutes and subjected to ultrasonic treatment, and resin films (triacetyl cellulose films) on both sides of the polarizing plate were dissolved in methylene chloride, and a sample including the polarizing plate and the adhesive layer in contact with the polarizing plate was taken out. A sample 1g of the sample taken out and 50ml of a mannitol solution were placed in a 100ml container, and the mixture was placed on an electrode and titrated with 0.1N NaOH. The 1 st and 2 nd endpoints of the analyzer were recorded, and the concentration was calculated according to the following calculation formula.

Content (mass%) of zinc contained in polarizing plate and adhesive layer in contact with polarizing plate

= (amount of 0.1N NaOH used [ mL ] for 2 times end point to amount of 0.1N NaOH used [ mL ] for 1 time end point) X0.29749X 0.1X 0.5/sample amount [ g ]

An analysis instrument: methodom 736GP Titrino

An electrode: combined pH electrode (Metrohm cat. # 6.0258.000)

Titration solution: 0.1N NaOH

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

< preparation of adhesive >

Polyvinyl alcohol resin adhesive A was prepared by dissolving 3.5 parts of GOHSEFIMER Z-200 (manufactured by Nippon synthetic chemical Co., ltd.), 0.12 part of zinc chloride and 0.89 part of glyoxal in 100 parts of water.

< example 1>

(production of polarizing plate)

An unstretched transparent polyvinyl alcohol film (TS 4500, manufactured by Kuraray) having a saponification degree of 99.9% or more and a thickness of 45 μm was immersed in water (deionized water) at 30 ℃ for 2 minutes to swell the film, and then immersed in a dyeing solution at 30 ℃ containing 0.45mmol/L iodine, 2 parts by mass of potassium iodide, and 0.35 part by mass of boric acid for 2 minutes to dye the film. At this time, stretching was performed at a stretching ratio of 1.72 times and 1.54 times in the swelling and dyeing stages, respectively, and stretching was performed so that the cumulative stretching ratio up to the dyeing tank became 2.64 times. Next, a solution containing 7.9 parts by mass of potassium iodide and 4.3 parts by mass of boric acid was immersed in a crosslinking solution at 56 ℃ for 30 seconds (crosslinking stage) to crosslink the solution, and simultaneously, stretching was performed at a stretching ratio of 2.2 times. Further, a crosslinking solution 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 at 40 ℃ was immersed for 5 seconds (color-complementary stage) to crosslink the components, and simultaneously, stretching treatment was performed. At this time, the total cumulative draw ratio in the swelling, dyeing and crosslinking, complementary color stages was 5.9 times. After the crosslinking, the polyvinyl alcohol film was dried in an oven at 100 ℃ to produce a polarizing plate. The thickness of the polarizer was 18 μm.

(production of polarizing plate)

Using the polyvinyl alcohol adhesive a prepared above, protective films were attached to both surfaces of the polarizer. As the protective film, triacetyl cellulose film (KC 4UAW, manufactured by Konika Meinen Co., ltd., thickness 40 μm, temperature 40 ℃ relative humidity 90% RH) was used on one side of the polarizing plate ² /24 h), the other side was surface-treated with an anti-reflection (LR) triacetyl cellulose film (thickness 60 μm, reflectance 1%). For the lamination, the polarizing plate of example 1 was produced by applying the polyvinyl alcohol adhesive a to both sides of the polarizer, joining the two sides by nip rolls, and drying the two sides at 80 ℃ for 5 minutes.

< example 2>

(production of polarizing plate)

A polarizing plate was produced in the same manner as in example 1, except that in example 1, the temperature of the crosslinking liquid in the crosslinking stage was set to 60 ℃ instead of 56 ℃, and the boric acid concentration of the crosslinking liquid in the complementary color stage was set to 3.0 parts by mass. The thickness of the polarizer was 18 μm.

(production of polarizing plate)

Using the polarizer manufactured as described above, the polarizing plate of example 2 was manufactured in the same manner as in example 1.

< example 3>

(production of polarizing plate)

A polarizing plate was produced in the same manner as in example 1, except that the drying temperature of the polyvinyl alcohol film after crosslinking was set to 90 ℃ instead of 100 ℃ in example 1 and the boric acid concentration of the crosslinking liquid in the complementary color stage was set to 3.0 parts by mass. The thickness of the polarizer was 18 μm.

(production of polarizing plate)

Using the polarizing plate manufactured as described above, the polarizing plate of example 3 was manufactured in the same manner as in example 1.

< example 4>

(production of polarizing plate)

A polarizing plate was produced in the same manner as in example 1 except that in example 1, a transparent unstretched polyvinyl alcohol film (PE-6000, manufactured by Kuraray) having a saponification degree of 99.9% or more and a thickness of 60 μm was used instead of a transparent unstretched polyvinyl alcohol film (TS 4500, manufactured by Kuraray) having a saponification degree of 99.9% or more and a thickness of 45 μm, and the boric acid concentration of the crosslinking liquid in the complementary color stage was 3.0 parts by mass. The thickness of the polarizer was 23 μm.

(production of polarizing plate)

Using the polarizing plate manufactured as described above, the polarizing plate of example 4 was manufactured in the same manner as in example 1.

< comparative example 1>

(production of polarizing plate)

A polarizing plate was produced in the same manner as in example 1, except that in example 1, the content of zinc nitrate in the crosslinking liquid in the complementary color stage was 3.0 parts instead of 5.0 parts. The thickness of the polarizer was 18 μm.

(production of polarizing plate)

Using the polarizer manufactured as described above, the polarizing plate of comparative example 1 was manufactured in the same manner as in example 1.

< comparative example 2>

(production of polarizing plate)

A polarizing plate was produced in the same manner as in example 1, except that the amount of zinc nitrate in the crosslinking liquid in the complementary color stage was changed to 0 parts instead of 5.0 parts in example 1. The thickness of the polarizer was 18 μm.

(production of polarizing plate)

Using the polarizing plate manufactured as described above, the polarizing plate of comparative example 1 was manufactured in the same manner as in example 1.

< test >

For the polarizing plates of examples 1 to 4 and comparative examples 1 to 3, the visibility-correcting monomer transmittance (Ty), the visibility-correcting polarization degree (Py), the monomer hue b value, and a700 were measured as described above. In addition, with respect to the obtained polarizing plate, the content of zinc element of the polarizer was measured as described above. The polarizing plate thus obtained was subjected to a heat resistance test, and the change rate Δ Py of the visibility correction polarization degree was calculated. The results are shown in Table 1.

[ TABLE 1]

Description of the reference numerals

1 polarizing plate, 10 polarizing plates, 101 1 st adhesive layer, 102 1 st resin film.

Claims

1. A polarizing plate comprising a polarizing plate, a 1 st adhesive layer and a 1 st resin film in this order,

the polarizing plate is in direct contact with the 1 st adhesive layer,

the visibility-correcting monomer transmittance of the polarizing plate is 45.5% or more,

the total content of zinc element contained in the polarizing plate and the adhesive layer in direct contact with the polarizing plate is 0.15 mass% or more,

the thickness of the polarizing plate is 10 [ mu ] m or more.

2. The polarizing plate according to claim 1, wherein the visibility correction polarization degree is 94.0% or more.

3. The polarizing plate according to claim 1 or 2, wherein the total content of zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.22% by mass or less.

4. The polarizing plate according to any one of claims 1 to 3, wherein the temperature of the 1 st resin film is 40 ℃ relative humidity 90% RH and the moisture permeability is 100g/m ² More than 24 h.

5. The polarizing plate according to any one of claims 1 to 4, wherein the 1 st adhesive layer contains a zinc element.

6. The polarizing plate according to any one of claims 1 to 5, further comprising a 2 nd adhesive layer and a 2 nd resin film in this order from the side close to the polarizer on the side opposite to the 1 st resin film of the polarizer.

7. The polarizing plate according to claim 6, wherein the 2 nd resin film has a moisture permeability of 100g/m in terms of temperature 40 ℃ relative humidity 90% ² More than 24 h.

8. The polarizing plate according to claim 6 or 7, wherein the 2 nd adhesive layer contains a zinc element.

9. A method for producing the polarizing plate according to any one of claims 1 to 8,