TWI712496B - Polarizing plate - Google Patents

Abstract

The present invention is a polarizing plate, which is a polarizing plate formed by laminating a polarizing film layer and a cured material layer composed of a resin composition, characterized in that the thickness of the cured material layer is 10 μm or less, and the boric acid penetration Calculated as 2.25g/m ^{2 in terms of} boron atom. Below day, the hardened material layer is directly adjacent to at least one side of the polarizing film layer. Thereby, it is possible to provide a polarizing plate that can maintain the initial polarization performance and is excellent in moisture and heat resistance even if the thickness of the cured product layer composed of the resin composition laminated on the polarizing film layer is 10 μm or less.

Description

Polarizer

The present invention relates to a polarizing plate that is a thin film and has excellent moisture and heat resistance.

Polarizers with light transmission and shielding functions and liquid crystals that change the polarization state of light are the basic components of liquid crystal displays (LCD). The conventional polarizing plate is manufactured by attaching a protective film on one side or both sides of a polarizing film layer formed by dyeing and stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" is abbreviated as "PVA") .

For the aforementioned protective film, films such as triacetyl cellulose (TAC) have been widely used in the past. In recent years, with the development of liquid crystal displays in mobile devices, thin films are gradually required to be lighter. From this point of view, there are documents suggesting that no protective film is placed on the polarizing film layer, and a photocurable resin composition is formed on the surface of the polarizing film layer. The hardened layer of the polarizing plate. (For example, refer to Patent Documents 1 to 5, etc.). However, when used under high temperature and high humidity conditions, the polarization performance may be reduced, and a polarizing plate with excellent moisture and heat resistance is required.

Prior art literature Patent literature

Patent Document 1 JP 2013-513832 Publication

Patent Document 2 JP 2011-221185 A

Patent Document 3 Japanese Patent Laid-Open No. 11-030715

Patent Document 4 JP 2004-245924 A

Patent Document 5 JP 2007-334307 A

The present invention has been accomplished in order to solve the above-mentioned problems, and its object is to provide a polarizing plate that can maintain the initial polarization performance and is excellent in moisture and heat resistance even if the thickness of the cured layer composed of a resin composition laminated on the polarizing film layer is 10 μm or less .

In order to achieve the above-mentioned object, the inventors have repeatedly studied and reviewed and found that even if the thickness of the hardened layer is 10 μm, the penetration of boric acid is 2.25 g/m ² in terms of boron atoms. The hardened material of less than 1 day is laminated on the polarizing film layer to solve the above-mentioned problem. Based on this knowledge, the present invention was completed through repeated examinations.

That is, the present invention relates to: [1] A polarizing plate, which is a polarizing plate formed by laminating a polarizing film layer and a cured material layer composed of a resin composition, wherein the thickness of the cured material layer is 10 μm or less, and boric acid penetrates The permeability is 2.25g/m ² in terms of boron atom. Day or less, the hardened layer is directly adjacent to at least one side of the polarizing film layer; [2] The polarizing plate of [1] above, wherein there is no protective film layer on the hardened layer; [3] As in [1] ] Or the polarizing plate of [2], wherein the polarizing film layer on the side opposite to the side where the hardened layer is laminated does not have a protective film layer; [4] the polarizing plate of [1] or [2] above, The aforementioned resin composition is a photocurable resin composition; [5] The polarizing plate of the aforementioned [1] or [2], wherein the boric acid content in the aforementioned polarizing film layer is calculated in terms of boron atoms, relative to the polarizing film The layer is 1-8% by mass; [6] The polarizing plate as in [1] or [2], wherein the thickness of the aforementioned polarizing film layer is less than 20 μm; [7] The polarizing plate as in [1] or [2], wherein The overall thickness of the polarizing plate is 40μm or less; [8] The polarizing plate of [1] or [2] above, wherein the water vapor permeability of the hardened layer is 2500 g/m ² . day or less; [9] The polarizing plate of [1] or [2] above, wherein the layer structure is a two-layer structure of a polarizing film layer/the aforementioned cured layer, or the aforementioned cured layer/polarized film layer/the aforementioned cured layer The three-layer structure; [10] The polarizing plate as in [1] or [2] above, in which the total light transmittance is 40-45%, and the polarization degree is above 99.9%; [11] As in [1] or [2] ] Of the polarizing plate, in which the total light transmittance change after 48 hours of heat and humidity resistance test at 60°C and 90%RH is 1.5% or less, and the polarization degree is 99.9% or more.

According to the present invention, it is possible to provide a polarizing plate that can maintain initial polarization performance and is excellent in moisture and heat resistance even if the thickness of the cured product layer composed of a resin composition laminated on the polarizing film layer is 10 μm or less.

1‧‧‧Hardened layer

2‧‧‧TAC film

3‧‧‧Water permeability cup

4‧‧‧Pure water

5‧‧‧Closed container

6‧‧‧8% by mass boric acid aqueous solution at 60℃

7‧‧‧Sample water

8‧‧‧Taper

Fig. 1 is a schematic diagram of a method for measuring the penetration of boric acid in terms of boron atom.

The form used to implement the invention

The present invention is a polarizing plate, which is a polarizing plate formed by laminating a polarizing film layer and a cured material layer composed of a resin composition, characterized in that the thickness of the cured material layer is 10 μm or less, and the boric acid penetration Calculated as 2.25g/m ^{2 in terms of} boron atom. Below day, the hardened material layer is directly adjacent to at least one side of the polarizing film layer. The inventors of the present invention have found that even if the thickness of the cured product layer composed of a resin composition laminated on the polarizing film layer is 10 μm or less, the penetration of boric acid by the cured product layer is 2.25 g/m ² . A polarizing plate excellent in heat and humidity resistance can be obtained in less than day. That is, even if the polarizing plate of the present invention is a film, it has excellent moisture and heat resistance and can maintain the initial polarizing performance.

(Polarized film layer)

In the polarizing film layer of the present invention, a dichroic dye is adsorbed on a PVA film (typically, a uniaxially stretched PVA film). This kind of polarizing film layer can be stretched on a PVA film containing a dichroic dye in advance, or the PVA film can be stretched while adsorbing the dichroic dye, or after the PVA film is stretched to form a matrix, it can be adsorbed Dichroic pigments, etc.

The above-mentioned PVA can be used by making vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl tertiary carbonate, vinyl laurate, vinyl stearate, and benzoin Polyvinyl ester obtained by saponification of one or more types of vinyl esters such as vinyl acid esters and isopropenyl acetate. Among the above-mentioned vinyl esters, vinyl acetate is preferred from the viewpoints of ease of manufacture of PVA, ease of acquisition, and cost.

In addition, the above-mentioned PVA may be one obtained by converting vinyl ester units of a polyvinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and other monomers copolymerizable therewith into a vinyl alcohol unit. Other monomers that can be copolymerized with vinyl ester monomers include, for example, ethylene, propylene, 1-butene, isobutylene, and other α-olefins with 2 to 30 carbon atoms; (meth)acrylic acid or its salts; (methyl) ) Methyl acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, ( (Meth)acrylates such as tert-butyl meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; (Meth)acrylamide; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone ( (Meth)acrylamide, (meth)acrylamide propanesulfonic acid or its salt, (meth)acrylamide propyldimethylamine or its salt, N-methylol (meth)acrylamide or (Meth)acrylamide derivatives such as its derivatives; N-vinylamide such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether , Ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether , Vinyl ethers such as stearyl vinyl ether; vinyl cyanide such as (meth)acrylonitrile; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc.; allyl acetate , Allyl compounds such as allyl chloride; Maleic acid or its salts, esters or anhydrides; Iconic acid or its salts, esters or anhydrides; Vinyl silyl compounds such as vinyl trimethoxysilane; No Saturated sulfonic acid and so on. The said vinyl ester copolymer may have 1 type or 2 or more types of structural units derived from the said other monomer. This other monomer can be used by pre-existing it in the reaction vessel when supplying the vinyl ester monomer to the polymerization reaction, or adding it to the reaction vessel during the progress of the polymerization reaction. From the viewpoint of polarization performance, the content of units derived from other monomers is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 2 mol% or less.

The degree of polymerization of the above-mentioned PVA is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and more preferably in the range of 2,000 to 4,000. By setting the degree of polymerization to 1,500 or more, the durability of the polarizing film obtained by uniaxially stretching the film can be improved. On the other hand, by setting the degree of polymerization to 6,000 or less, it is possible to suppress an increase in the manufacturing cost, or poor passability during film formation. In addition, the degree of polymerization of PVA in this specification means the average degree of polymerization measured in accordance with the description of JIS K6726-1994.

From the viewpoint of the polarization performance of the polarizing film layer, the degree of saponification of the above-mentioned PVA is preferably 95 mol% or more, more preferably 98 mol% or more, more preferably 98.5 mol% or more, and 99.0 mol% or more. Ear% or more is particularly good. If the degree of saponification is less than 95 mol%, the PVA may easily dissolve during the manufacturing process of the polarizing film, and the dissociated PVA may adhere to the film, thereby reducing the polarization performance of the polarizing film. In addition, in this specification, the degree of saponification of PVA refers to the total moles of structural units (typically, vinyl ester units) and vinyl alcohol units possessed by PVA that can be converted into vinyl alcohol units by saponification. Number, the ratio of the number of moles of the vinyl alcohol unit (mole%). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The above-mentioned PVA film may contain a plasticizer. By making the PVA film contain a plasticizer, the usability or extensibility can be improved. As the plasticizer, polyhydric alcohols are suitably used. Specifically, ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like can be mentioned. One kind or two or more kinds of these plasticizers may be contained. From the viewpoint of improving the extensibility of the PVA film, glycerin is preferred among these.

The content of the plasticizer in the above-mentioned PVA film is preferably 1-20 parts by mass relative to 100 parts by mass of PVA, more preferably 3-17 parts by mass, and even more preferably 5-15 parts by mass. By making the content of the plasticizer more than 1 part by mass, the extensibility of the PVA film is further improved. On the other hand, by making the content of the plasticizer 20 parts by mass or less, it is possible to suppress the plasticizer from permeating out of the surface of the PVA film, thereby reducing the usability of the PVA film.

In the above-mentioned PVA film, processing stabilizers such as fillers, copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, etc. can be blended appropriately according to needs. Agents, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, release agents, mold release agents, reinforcing agents, crosslinking agents, antifungal agents, preservatives, crystallization rate retarders, etc. Of additives.

The thickness of the polarizing film layer in the present invention is preferably 20 μm or less. Generally, the thinner the polarizing film layer is, the easier it is to reduce the moisture and heat resistance. For this kind of polarizing film layer, the effect of the present invention can be more prominent. The thickness of the polarizing film layer is more preferably 15 μm or less, and more preferably 12 μm or less. On the other hand, when the thickness of the polarizing film layer is too thin, problems such as wrinkles or cracks are likely to occur during manufacturing. Therefore, the thickness of the polarizing film layer is preferably 1 μm or more, more preferably 2 μm or more, and 3 μm or more. More preferably, 5 μm or more is particularly preferred.

The boric acid content of the polarizing film layer in the present invention is calculated in terms of boron atoms, and is preferably 1 to 8% by mass relative to the polarizing film layer. When the content of boric acid is less than 1% by mass, the effect of improving heat and humidity resistance may decrease. The aforementioned boric acid content is more preferably 2% by mass or more. On the other hand, when the aforementioned boric acid content exceeds 8% by mass, the dimensional change of the polarizing film at high temperature may increase. The content of the aforementioned boric acid is more preferably 5% by mass or less.

As explained in the following examples, the content of boric acid in terms of boron atom can be prepared by dissolving the polarizing film in distilled water to make it 0.0005 mass% to prepare the sample to be tested, and the sample to be tested can be measured by ICP luminescence analysis The boron concentration in is calculated by the following formula (1).

[(X×10 ^-6 ×Y)/Z]×100 (1)

X: boron concentration of the sample to be tested [ppm]

Y: The mass of the sample to be tested in which the polarizing film is dissolved [g]

Z: The mass of the polarizing film [g]

(Method of manufacturing polarizing film)

The method at the time of manufacturing the polarizing film layer in this invention is not specifically limited. The polarizing film layer can be suitably manufactured through any combination of the steps of uniaxially stretching the PVA film, the step of adsorbing the dichroic dye, the step of treating with an aqueous boric acid solution, and the step of washing with water. After this manufacturing step, the total stretching ratio of the PVA film is preferably about 4 to 8 times. In addition, swelling treatment, fixation treatment, drying treatment, heat treatment, etc. can be further carried out as needed.

The above-mentioned swelling treatment can be performed by immersing the PVA film in water. When immersed in water, the temperature of the water is preferably in the range of 20-40°C, more preferably in the range of 22-38°C, and more preferably in the range of 25-35°C. In addition, the time for immersion in water is preferably within a range of 0.1 to 5 minutes, and more preferably within a range of 0.2 to 3 minutes. In addition, the water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

The step of uniaxially stretching the above-mentioned PVA film may be either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be performed in an aqueous solution containing boric acid, or may be performed in a dyeing bath or a fixed treatment bath described later. In the case of the dry stretching method, the uniaxial stretching treatment can be performed directly at room temperature, or the uniaxial stretching treatment can be performed while heating, or the PVA film after water absorption can be used and the uniaxial stretching treatment can be performed in the air. Among them, the wet stretching method is preferred, and it is more preferred to perform uniaxial stretching in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 15% by mass, and more preferably in the range of 1 to 7% by mass. In addition, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass. The stretching temperature during the uniaxial stretching treatment is preferably in the range of 30 to 90°C, more preferably in the range of 40 to 80°C, and particularly preferably in the range of 50 to 70°C. In addition, the stretching ratio (total stretching ratio of the raw material PVA film) during the uniaxial stretching treatment is preferably 4 to 8 times from the viewpoint of the polarization performance of the obtained polarizing film.

The step of adsorbing the above-mentioned dichroic dye may be at any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. It can be performed by immersing the PVA film in an aqueous solution containing a dichroic dye as a dye bath. The concentration of the dichroic dye in the aforementioned aqueous solution can be appropriately set in accordance with the type of the dichroic dye and the like, and may be set in the range of 0.001 to 2% by mass, for example. When an iodine-potassium iodide aqueous solution [an aqueous solution containing iodine (I ₂ ) and potassium iodide (KI)] is used as the aforementioned aqueous solution, the iodine-based dye can be efficiently adsorbed on the PVA film. The concentration of iodine (I ₂ ) in the aqueous solution is preferably 0.01 to 1% by mass, and the concentration of potassium iodide (KI) is preferably 0.01 to 50% by mass. From the viewpoint that the dichroic dye can be efficiently adsorbed on the PVA film, the temperature of the aqueous solution containing the dichroic dye is preferably 5 to 50°C during the dyeing process. The time for immersing the PVA film in the aforementioned aqueous solution is preferably 0.1 to 10 minutes.

Examples of the dichroic dye include iodine-based dye I ₃ ^- or I ₅ ^- . Examples of the relative cation include alkali metals such as potassium. An iodine-based dye can be obtained by, for example, contacting iodine (I ₂ ) with potassium iodide.

The step of treating with the above-mentioned boric acid aqueous solution can be performed by immersing the aforementioned PVA film in an aqueous solution containing a boric acid crosslinking agent. By performing such a treatment, when the wet stretching is performed at a higher temperature, the PVA in the film can be effectively prevented from dissolving into water. From this point of view, the step of treating with the aforementioned boric acid aqueous solution is preferably performed after the step of adsorbing the aforementioned dichroic dye. As the boric acid crosslinking agent, one kind or two or more kinds of boron compounds such as borates such as boric acid and borax can be used. The concentration of the aforementioned aqueous solution containing the boric acid crosslinking agent is preferably 1-15% by mass, and more preferably 2-7% by mass. The aqueous solution containing the boric acid crosslinking agent may also contain auxiliary agents such as potassium iodide. During the cross-linking treatment, the temperature of the aforementioned aqueous solution is preferably 20-50°C.

When manufacturing the polarizing film, in order to make the dichroic dye (iodine-based dye, etc.) adhere to the PVA film firmly, it is preferable to perform a fixing treatment after the uniaxial stretching treatment. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more types of boron compounds such as boric acid, borax, and the like can be suitably used. The concentration of the aforementioned boron compound is preferably 2-15% by mass, and the temperature of the fixing treatment liquid is preferably 15-60°C. In addition, iodine compounds or metal compounds can be added to the fixed treatment solution as needed.

As the step of the water washing treatment, the film is generally immersed in water, distilled water, pure water, or the like. At this time, from the viewpoint of improving the polarization performance, the aqueous solution used in the cleaning treatment preferably uses an iodide containing potassium iodide as an auxiliary agent, and the concentration of the iodide is preferably 0.5-10% by mass . In addition, the temperature of the aqueous solution during the washing treatment is generally 5 to 50°C, preferably 10 to 45°C, and more preferably 15 to 40°C. From an economic point of view, the temperature of the aqueous solution should not be too low. If the temperature of the aqueous solution is too high, the polarization performance may decrease.

In addition, drying treatment, heat treatment, etc. can also be performed after the above-mentioned washing treatment as needed. The conditions of the drying treatment are not particularly limited, and drying is preferably performed at 30 to 150°C. By drying at a temperature within the aforementioned range, it is easy to obtain a polarizing film having excellent dimensional stability. By performing the heat treatment after the drying treatment, a polarizing film with more excellent dimensional stability can be obtained. Here, the heat treatment refers to a process of further heating the polarizing film after the drying process with a moisture content of 5% or less to improve the dimensional stability of the polarizing film. The conditions of the heat treatment are not particularly limited, and the heat treatment is preferably performed at 60 to 150°C. If the heat treatment is performed at a temperature lower than 60°C, the dimensional stabilization effect caused by the heat treatment may be insufficient, and if the heat treatment is performed at a temperature higher than 150°C, there may be serious redness on the polarizing film. .

The polarizing film obtained by the above method is usually used by laminating an optically transparent and mechanically strong protective film on both sides or one side to make a polarizing plate. However, the polarizing plate of the present invention is designed as a cured product described later The layer is directly laminated on at least one surface of the polarizing film layer, and the other surface of the polarizing film layer and the form of not having a protective film layer on the hardened material layer. With this structure, the polarizer film can be made lighter and has the advantage of low cost. Examples of the protective film include cellulose acetate-based resin films such as triacetyl cellulose (TAC) and diacetyl cellulose; polyethylene terephthalate, polyethylene naphthalate, and poly(ethylene naphthalate). Polyester resin film such as butylene terephthalate; polycarbonate resin film.

(Hardened layer)

The hardened layer of the present invention satisfies a thickness of 10 μm or less, and the penetration of boric acid is 2.25 g/m ² in terms of boron atoms. less than day. In particular, the penetration of boric acid of the hardened layer is 2.25 g/m ² in terms of boron atoms. The day or less is important, and it is possible to provide a polarizing plate that can maintain the initial polarization performance and is excellent in moisture and heat resistance. The penetration of boric acid is more than 2.25g/m ² in terms of boron atom. In the case of day, the humidity and heat resistance of the polarizing plate cannot be sufficiently improved. From this point of view, the penetration of boric acid is 1.50 g/m ² in terms of boron atoms. Day or less is better, 1.00g/m ² . Less than day is better, 0.50g/m ² . Day or less is further preferred, 0.20g/m ² . Less than day is particularly good. On the other hand, the lower limit of the penetration of boric acid in terms of boron atoms in the cured layer is not particularly limited. If the penetration of boric acid in terms of boron atoms is too low, the flexibility of the cured layer tends to be lost. , So the penetration of boric acid is 0.02g/m ² in terms of boron atom. More than day is better, 0.05g/m ² . More than one day is better, 0.10g/m ² . More than day is more preferable.

As explained in the following examples, the penetration of boric acid (A) in terms of boron atom is obtained by fixing the hardened layer of the measurement object in a moisture-permeable cup filled with pure water and immersing it in 8% by mass at 60°C In the boric acid aqueous solution, the boron concentration in the moisture permeability cup before the start of the test and 24 hours after the test was analyzed by the ICP emission analysis method, and the concentration increase was calculated according to the following formula (2).

A={(a ₂₄ -a ₀ )×10 ^-6 ×M}/S (2)

A: Boric acid penetration rate in terms of boron atom [g/m ² ． day]

a ₂₄ : Boron concentration in sample water after 24 hours [ppm]

a ₀ : boron concentration in the sample water before the start of the test [ppm]

M: Weight of sample water [g]

S: The area of the hardened layer in contact with the boric acid aqueous solution (the penetration area of the moisture-permeable cup) [m ² ]

Furthermore, for the cured layer that is difficult to measure individually, it can be measured in the same manner as in the above formula (2) by using a multilayer film in which the cured layer is formed on a base film such as a triacetate cellulose (TAC) film. The boric acid penetration (A') of the entire multilayer film in terms of boron atoms is calculated by the following formula (3) in the cured product layer (q ₂ /l ₂ ).

1/A'=L/Q=l ₁ /q ₁ +l ₂ /q ₂ (3)

A': Permeability of boric acid in terms of boron atom conversion between the cured layer and the base film as a whole [g/m ² . day]

L: The overall thickness of the cured product layer and the base film [μm]

Q: The overall boric acid penetration coefficient of the cured layer and the base film [g. μm/m ² . day]

l ₁ : The film thickness of the base film [μm]

q ₁ : Boric acid penetration coefficient of the base film [g. μm/m ² . day]

l ₂ : The thickness of the hardened layer [μm]

q ₂ : Boric acid penetration coefficient of the hardened layer [g. μm/m ² . day]

As long as the penetration of boric acid meets the requirement of 2.25 g/m ² in terms of boron atom conversion for the aforementioned hardened layer. Below day, you can use thermoplastic resin composition, thermosetting resin composition, organic sol-gel method. Any resin composition such as an inorganic hybrid resin composition. When the polarizing film layer is heated rapidly, the polarization performance is likely to decrease, so it is preferable to use a photocurable resin composition that can be laminated with the polarizing film under mild conditions. Among them, it is a suitable embodiment that the photocurable resin composition is acrylic resin acrylate. Here, the acrylic resin acrylate includes the reaction of an acrylic resin obtained by copolymerizing an acrylic monomer having a functional group such as a carboxyl group, a glycidyl group, and a hydroxyl group, and an acrylate having a group reactive with these functional groups. And those who import double bonds (C=C). The weight average molecular weight of the acrylic resin acrylate is not particularly limited, but is preferably 62,000 or more, more preferably 65,000 or more, and more preferably 70,000 or more. On the other hand, the weight average molecular weight of acrylic resin acrylate is usually 1,000,000 or less.

In the present invention, it is important that the thickness of the cured product layer is 10 μm or less. When the thickness exceeds 10 μm, it is impossible to achieve sufficient thinning of a polarizing plate in which conventional protective films are laminated. From this point of view, the thickness of the cured product layer is preferably 8 μm or less, more preferably 7 μm or less, and even more preferably 6 μm or less. On the other hand, the lower limit of the thickness of the hardened layer is not necessarily limited. When the above-mentioned boric acid penetration in terms of boron atoms is achieved with a thin hardened layer, the flexibility of the hardened layer tends to be easily lost. Therefore, it is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more.

In the present invention, the water vapor permeability of the hardened layer is 2500 g/m ² . Day or less is preferred. The water vapor penetration in the aforementioned hardened layer exceeds 2500 g/m ² . In the case of day, problems such as poor appearance of the polarizing plate may occur. From this point of view, the water vapor permeability of the aforementioned hardened layer is 2000 g/m ² . Less than day is better, 900g/m ² . Day or less is further preferred. On the other hand, the water vapor permeability of the aforementioned hardened layer is usually 500 g/m ² . more than day.

As explained in the examples below, the water vapor permeability (B) of the cured product layer is determined in accordance with JIS Z-0208.

In addition, the cured product layer that is difficult to measure separately is a multilayer film formed on a base film such as a triacetate cellulose (TAC) film, and the total water vapor of the multilayer film is measured in accordance with JIS Z-0208 The permeability (B'), and the water vapor permeability (p ₂ /l ₂ ) of the hardened layer is calculated from the following formula (4).

1/B'=L/P=l ₁ /p ₁ +l ₂ /p ₂ (4)

B': Total water vapor permeability between the hardened layer and the base film [g/m ² . day]

L: The overall thickness of the cured product layer and the base film [μm]

P: The total water vapor transmission coefficient of the hardened layer and the base film [g. μm/m ² . day]

l ₁ : The film thickness of the base film [μm]

p ₁ : Water vapor transmission coefficient of the substrate film [g. μm/m ² . day]

l ₂ : The thickness of the hardened layer [μm]

p ₂ : Water vapor penetration coefficient of the hardened layer [g. μm/m ² . day]

(Polarizer)

In the polarizing plate of the present invention, the cured material layer is directly adjacent to at least one surface of the polarizing film layer. It is a suitable embodiment not to have a protective film layer on the hardened material layer, and it is also a suitable embodiment to have no protective film layer on the polarizing film layer on the side opposite to the side where the hardened material layer is laminated. As the layer structure of the polarizing plate of the present invention, it can be a two-layer structure of polarizing film layer/hardened material layer. However, by designing a three-layer structure of hardened material layer/polarizing film layer/hardened material layer, a more excellent Durability, while suppressing bending of the polarizing film, is preferable. In the case of a three-layer structure, the cured product layer laminated on one side of the polarizing film and the cured product layer laminated on the other side of the polarizing film may be different resin compositions.

In addition, the hardened layer in the present invention may be a single layer that satisfies the boric acid penetration and thickness in terms of boron atom, or may be a composition layer having a multilayer structure in which two or more hardened layers are stacked.

In the present invention, the adhesive force between the polarizing film layer and the cured material layer is preferably 0.06 N/mm or more. If the adhesive force is less than 0.06 N/mm, there is a risk of interlayer peeling during processing of the polarizer. From this point of view, the adhesive force is more preferably 0.08 N/mm or more, and more preferably 0.12 N/mm or more.

The overall thickness of the polarizing plate of the present invention, the thinner the polarizing film layer, the easier it is to reduce the humidity and heat resistance, and the effect of the present invention can be more prominently displayed in this polarizing film layer. Therefore, it is preferably 40μm or less, 35μm The following is more preferable, 30 μm or less is more preferable, and 25 μm or less is particularly preferable. On the other hand, if the overall thickness of the polarizing plate is thin, the mechanical strength is reduced, so 2 μm or more is preferable, and 5 μm or more is more preferable.

The total light transmittance of the polarizing plate of the present invention is preferably 40-45%. From the viewpoint of polarization performance, the total light transmittance is more preferably 41% or more, and more preferably 42% or more. On the other hand, from the viewpoint of the degree of polarization, the total light transmittance is preferably 44% or less. The total light transmittance can be measured by the method described later in the examples.

The degree of polarization of the polarizing plate of the present invention is preferably 99.9% or more. From the viewpoint of polarization performance, the degree of polarization is more preferably 99.92% or more, and more preferably 99.95% or more. The degree of polarization can be measured by the method described later in the examples.

The polarizing plate of the present invention, after being tested for 48 hours of heat and humidity resistance at 60°C and 90%RH, the total light transmittance is preferably less than 1.5%, and the polarization degree is more than 99.9%. good. It can be seen that the total light transmittance change of the polarizing plate after the humidity and heat resistance test is less than a certain value, and the degree of polarization is more than a certain value. Therefore, the polarizing plate of the present invention, even if it is a film, has excellent humidity and heat resistance and can Maintain the initial polarization performance. The amount of change in the aforementioned total light transmittance is more preferably 1.3% or less, and more preferably 1.1% or less. On the other hand, the amount of change in the aforementioned total light transmittance is usually 0.1% or more. In addition, the aforementioned degree of polarization is more preferably 99.92% or more, more preferably 99.95% or more, and particularly preferably 99.98% or more.

[Example]

The following examples illustrate the present invention in detail, but the present invention is not limited by these examples at all. In addition, the boric acid content of the polarizing film layer, the boric acid transmittance of the cured layer, the total light transmittance and polarization of the polarizing plate, and the humidity and heat resistance test used in the following examples and comparative examples were measured to The evaluation method is disclosed as follows.

[Boric acid content of polarizing film]

The mass Z (g) of the polarizing film was measured, and the polarizing film was dissolved in 20 mL of distilled water to become 0.0005 mass%. The aqueous solution in which the polarizing film is dissolved is used as the sample to be tested, and its mass Y (g) is measured. Then, a multi-element measurement type ICP emission analyzer (ICPE-9000) manufactured by Shimadzu Corporation was used to measure the boron concentration X (ppm) of the test sample. Then, the value is substituted into the following formula (1), and the calculated value is defined as the mass% of boric acid in the polarizing film layer.

Boric acid content of polarizing film (mass%)

[(X×10 ^-6 ×Y)/Z]×100 (1)

X: boron concentration of the sample to be tested [ppm]

Y: The mass of the sample to be tested with the polarizing film dissolved [g]

Z: The mass of the polarizing film [g]

[Permeability of boric acid in terms of boron atom in hardened layer]

In the present invention, as a method for measuring the penetration of boric acid in terms of boron atoms of the hardened layer, the hardened layer to be measured is fixed in a moisture-permeable cup pre-filled with pure water (fastening type, according to JIS Z- 0208), immersed in an 8% by mass boric acid aqueous solution at 60°C, and analyzed the contents of the cup before the start of the test and 24 hours after the test by the ICP emission analysis method (Shimadzu Multi-element ICP emission analyzer ICPE-9000) Based on the boron concentration of the sample water, the boric acid penetration (A) in terms of boron atom is calculated according to the following formula (2) from the increase in concentration (refer to Fig. 1).

A={(a ₂₄ -a ₀ )×10 ^-6 ×M}/S (2)

A: Boric acid penetration rate in terms of boron atom [g/m ² ． day]

a ₂₄ : Boron concentration in sample water after 24 hours [ppm]

a ₀ : boron concentration in the sample water before the start of the test [ppm]

M: Weight of sample water [g]

S: The area of the hardened layer in contact with the boric acid aqueous solution (the penetration area of the moisture-permeable cup) [m ² ]

In addition, the cured product layer of the resin composition that is difficult to measure individually is a multilayer in which a base film (such as a triacetate cellulose (TAC) film, etc.) with high penetration of boric acid in terms of boron atoms is used to form the cured product layer For the film, measure the boric acid penetration (A') of the entire cured layer and the base film in terms of boron atoms, and calculate the boric acid penetration of each cured layer in terms of boron atoms by calculating with the following formula (3) (q ₂ /l ₂ ).

1/A'=L/Q=l ₁ /q ₁ +l ₂ /q ₂ (3)

A': Permeability of boric acid in terms of boron atom conversion between the cured layer and the base film as a whole [g/m ² . day]

L: The overall thickness of the cured product layer and the base film [μm]

Q: The overall boric acid penetration coefficient of the cured layer and the base film [g. μm/m ² . day]

l ₁ : The film thickness of the base film [μm]

q ₁ : Boric acid penetration coefficient of the base film [g. μm/m ² . day]

l ₂ : The thickness of the hardened layer [μm]

q ₂ : Boric acid penetration coefficient of the hardened layer [g. μm/m ² . day]

[Water vapor penetration of hardened layer]

In the present invention, the measurement of the water vapor permeability of the cured product layer is carried out in accordance with JIS Z-0208. That is, the hardened layer to be measured is fixed in a moisture-permeable cup (fastened type) filled with calcium chloride, and the weight gain is measured every 24 hours under an environment of 40°C and 90%RH, and the water vapor penetration is calculated. Penetration (B).

Furthermore, regarding the cured product layer of the resin composition that is difficult to measure individually, a multilayer film in which the cured product layer is formed on a substrate film with high water vapor permeability (for example, a triacetate cellulose (TAC) film, etc.) is used. The total water vapor permeability (B') of the cured product layer and the base film was measured, and the water vapor permeability (p ₂ /l ₂ ) of each cured product layer was calculated by the following formula (4).

1/B'=L/P=l ₁ /p ₁ +l ₂ /p ₂ (4)

B': Total water vapor permeability between the hardened layer and the base film [g/m ² . day]

L: The total thickness of the cured product layer and the base film [μm]

P: The total water vapor transmission coefficient of the hardened layer and the base film [g. μm/m ² . day]

l ₁ : The film thickness of the base film [μm]

p ₁ : Water vapor transmission coefficient of the substrate film [g. μm/m ² . day]

l ₂ : The thickness of the hardened layer [μm]

p ₂ : Water vapor penetration coefficient of the hardened layer [g. μm/m ² . day]

[Total light transmittance and polarization degree of polarizing plate]

The central part of the polarizing plate obtained in the following examples or comparative examples in the width direction (TD), the polarizing plate length direction (MD) 2cm, the width direction (TD) 3cm, and the TD direction is the same and next to the MD direction. Two rectangular samples, using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation), in accordance with JIS Z 8722 (method for measuring object color), the visual sensitivity of C light source and 2° field of view in the visible light region Correction: measure the light transmittance when tilted 45° with respect to the longitudinal direction and the light transmittance when tilted -45° with respect to the sample, and determine the average value (%) as the total light transmittance of the polarizer rate. In addition, for this sample, the light transmittance T∥(%) in the parallel polarization state and the light transmittance T⊥(%) in the cross polarization state were measured in the same manner as above, and the polarization was obtained by the following formula (5) degree.

Polarization={(T∥-T⊥)/(T∥+T⊥)} ^1/2 ×100 (5)

[Moisture and heat resistance of polarizing plate]

The polarizing plate was fixed to a metal frame, and placed in a thermohygrostat (HUMIDIC CHAMBER IG400 manufactured by Yamato Science Co., Ltd.) at 60°C and 90% RH, and subjected to a 48-hour heat and humidity resistance test. After the test, the total was measured by the above method. The light transmittance and the degree of polarization are used as indicators of the heat and humidity resistance of the polarizing plate.

[Example 1] (Production of polarizing film)

Use 100 parts by mass of PVA (saponified product of copolymer of vinyl acetate and ethylene, average degree of polymerization 2,400, degree of saponification 99.4 mol%, content rate of ethylene unit 2.5 mol%), and 10 parts by mass of glycerin as a plasticizer , As a surfactant, a film-forming stock solution composed of 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate and water is used to form a film by casting to obtain a PVA film with a thickness of 30 μm. The film is subjected to a swelling step and a dyeing step , Cross-linking step, stretching step, fixing treatment step and drying step to produce a polarizing film.

That is, the above-mentioned PVA film is immersed in water at a temperature of 30°C for 1 minute, and during this period, it is uniaxially extended in the longitudinal direction (MD) to twice its original length (first-stage extension), and then the amount used is set to 0.03 iodine Mass% and 0.7% by mass of potassium iodide are mixed in water and immersed in a dyeing bath at a temperature of 32°C for 2 minutes. During this period, it extends uniaxially in the MD direction to 2.3 times the original length (Second stretch) ), and then immersed in a cross-linking bath containing boric acid at a concentration of 2.6% by mass and a temperature of 32°C for 2 minutes, during which time it stretched uniaxially in the longitudinal direction (MD) to 2.6 times the original length (third-stage stretch) , Further immersed in a boric acid/potassium iodide aqueous solution containing boric acid at a concentration of 2.8% by mass and potassium iodide at a concentration of 5% by mass, and a temperature of 57°C. During this period, it uniaxially extends in the length direction (MD) to 6 times the original length (Extension of the 4th paragraph) Then, the film was washed by immersing in a potassium iodide aqueous solution containing boric acid at a concentration of 1.5% by mass and potassium iodide at a concentration of 5% by mass and at a temperature of 22°C for 5 seconds. It was dried in a dryer at 40°C for 240 seconds to produce a polarizing film with a thickness of 12 μm.

(Making of polarizing plate)

As a resin composition, 20 g of an acrylic resin acrylate product manufactured by Hitachi Chemical Co., Ltd. named "HITAROID 7975 (weight average molecular weight: 80,000)" and a product named "IRGACURE 184" manufactured by Ciba specialty chemicals 1 -0.25 g of hydroxycyclohexyl phenone was weighed into a sample bottle, and after mixing, it was coated on the surface of a polarizing film layer with a thickness of 12 μm using a No. 13 bar coater. After the applied polarizing film layer was dried at 70°C for 1 minute, it was irradiated with a black light lamp so that the accumulated light amount became 400 mJ/cm ² to cure the resin composition. In addition, the same was applied to the opposite surface of the polarizing film layer to produce a polarizing plate having a cured product layer on one side with a thickness of 5.9 μm and a total thickness of 24 μm. Using the obtained polarizing plate, the total light transmittance and polarization degree were measured by the above-mentioned methods, and the humidity and heat resistance was evaluated. The results are shown in Table 1.

In addition, except for coating on one side of a cellulose triacetate (TAC) film, a TAC film laminated with a cured product layer was produced in the same manner as described above, and the water vapor permeability of the cured product layer was measured. And boric acid penetration. The results are shown in Table 1.

Comparative example 1

A polarizing plate was manufactured in the same manner as in Example 1, except that the photocurable resin composition was made of DIC Co., Ltd. product name "UNIDIC V-6841" of acrylic acid ester polymer and acrylic ester monomer mixture product. Using the obtained polarizing plate, the total light transmittance and the degree of polarization were measured, and the humidity and heat resistance was evaluated. The results are shown in Table 1.

In addition, except for coating on one side of a cellulose triacetate (TAC) film, a TAC film laminated with a cured product layer was produced in the same manner as described above, and the water vapor permeability of the cured product layer was measured. , Boric acid penetration. The results are shown in Table 1.

Comparative example 2

A polarizing plate was manufactured in the same manner as in Example 1 except that the photocurable resin composition was made of Hitachi Chemical Co., Ltd. product name "HITAROID 7988 (weight average molecular weight: 60000)" acrylic resin acrylate product. Using the obtained polarizing plate, the total light transmittance and the degree of polarization were measured, and the humidity and heat resistance was evaluated. The results are shown in Table 1.

In addition, except for coating on one side of a cellulose triacetate (TAC) film, a TAC film laminated with a cured product layer was produced in the same manner as described above, and the water vapor permeability of the cured product layer was measured. , Boric acid penetration. The results are shown in Table 1.

Comparative example 3

A polarizing plate was manufactured in the same manner as in Example 1 except that the photocurable resin composition was made of Hitachi Chemical Co., Ltd. product name "HITAROID 7975D (weight average molecular weight: 15000)" acrylic resin acrylate product. Using the obtained polarizing plate, the total light transmittance and the degree of polarization were measured, and the humidity and heat resistance was evaluated. The results are shown in Table 1.

In addition, except for coating on one side of a cellulose triacetate (TAC) film, a TAC film laminated with a cured product layer was produced in the same manner as described above, and the water vapor permeability of the cured product layer was measured. , Boric acid penetration. The results are shown in Table 1.

Comparative example 4

A polarizing plate was produced in the same manner as in Example 1, except that the acrylic polymer product of DIC Co., Ltd. product name "UNIDIC V-6840" was used for the photocurable resin composition. Using the obtained polarizing plate, the total light transmittance and the degree of polarization were measured, and the humidity and heat resistance was evaluated. The results are shown in Table 1.

In addition, except for coating on one side of a cellulose triacetate (TAC) film, a TAC film laminated with a cured product layer was produced in the same manner as described above, and the water vapor permeability of the cured product layer was measured. , Boric acid penetration. The results are shown in Table 1.

Claims (11)

A polarizing plate, which is a polarizing plate formed by laminating a polarizing film layer and a cured material layer composed of a resin composition, and the thickness of the cured material layer is 10 μm or less, and the penetration of boric acid is 2.25 g in terms of boron atom /m ² . Below day, the hardened layer is directly adjacent to at least one side of the polarizing film layer. The polarizing plate of claim 1, wherein there is no protective film layer on the hardened layer. The polarizing plate of claim 1 or 2, wherein the polarizing film layer on the side opposite to the side where the hardened layer is laminated does not have a protective film layer. The polarizing plate of claim 1 or 2, wherein the resin composition is a photocurable resin composition. For the polarizing plate of claim 1 or 2, wherein the content of boric acid in the polarizing film layer is 1-8% by mass relative to the polarizing film layer in terms of boron atoms. The polarizing plate of claim 1 or 2, wherein the thickness of the polarizing film layer is 20 μm or less. The polarizing plate of claim 1 or 2, wherein the overall thickness of the polarizing plate is 40 μm or less. For example, the polarizing plate of claim 1 or 2, wherein the water vapor permeability of the hardened layer is 2500 g/m ² . less than day. Such as the polarizing plate of claim 1 or 2, wherein the layer structure is a two-layer structure of polarizing film layer/the hardened layer, or a three-layer structure of hardened layer/polarizing film/the hardened layer. For example, the polarizing plate of claim 1 or 2, in which the total light transmittance is 40-45%, and the polarization degree is more than 99.9%. For example, the polarizing plate of claim 1 or 2, wherein the total light transmittance change after 48 hours of heat and humidity resistance test at 60°C and 90%RH is 1.5% or less, and the polarization degree is 99.9% or more.

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