KR102566455B1 - Polarizers and Polarizers - Google Patents

Abstract

A light polarizer having a thin shape and very excellent heat resistance is provided. The polarizer of this invention is comprised from the polyvinyl alcohol-type resin film containing iodine, and free boric acid content is 0.4 weight% or less.

Description

Polarizers and Polarizers

The present invention relates to a polarizer and a polarizing plate.

In a liquid crystal display device, which is a representative image display device, polarizers (substantially, polarizers including polarizers) are disposed on both sides of a liquid crystal cell due to its image forming method. A polarizer is typically manufactured by dyeing a polyvinyl alcohol (PVA)-based resin film with a dichroic substance such as iodine (for example, Patent Documents 1 and 2). In recent years, the demand for thickness reduction of image display devices is increasing. Therefore, further thinning is requested|required also about a polarizer. However, as the polarizer becomes thinner, there is a problem that the heat resistance is low and the optical properties are easily changed in a high-temperature environment.

Japanese Patent Publication No. 5048120 Japanese Unexamined Patent Publication No. 2013-156391

This invention was made in order to solve the said conventional subject, and its main objective is to provide the polarizer which is thin and has very excellent heat resistance.

The polarizer of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine,

The content of free boric acid is 0.4% by weight or less.

In one embodiment, the thickness of the polarizer is 7 μm or less.

In one embodiment, the iodine content of the polarizer is 10% by weight to 25% by weight.

According to another aspect of the present invention, a polarizing plate is provided. This polarizing plate includes the polarizer and a protective film laminated on one side or both sides of the polarizer.

According to the present invention, by setting the free boric acid content contained in the polarizer to 0.4% by weight or less, a polarizer having a thin shape that has been desired for a long time but has not been realized and has extremely excellent heat resistance has been realized.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

A. Polarizer

A-1. Outline of Polarizer

The polarizer according to the embodiment of the present invention is composed of a polyvinyl alcohol (PVA)-based resin film containing iodine, and the free boric acid content is 0.4% by weight or less.

The free boric acid content of the polarizer is preferably 0.39% by weight or less, and more preferably 0.38% by weight or less. The lower limit of the free boric acid content is, for example, 0.01% by weight. Thus, it is one of the characteristics of this invention that the content of free boric acid was paid attention not to content of all the boric acids contained in a polarizer. When the free boric acid content of the polarizer is within the above range, heat resistance is excellent and a change in optical properties (eg single transmittance) in a high temperature environment can be suppressed. The free boric acid content of the polarizer can be obtained in accordance with the following procedure, typically using an inductively coupled plasma emission spectroscopy (ICP-AES) method. That is, the measurement sample obtained by freeze-pulverizing the polarizer was mixed with a mixed solution of 2-ethyl-1,3-hexanediol/chloroform (volume ratio: 10/90), and the boron content in the filtrate obtained by filtering the mixture was It is quantified using an ICP emission spectrometer. All of the obtained boron content is derived from boric acid, all boric acid in the filtrate is considered to be derived from the free boric acid of the polarizer, and the boron content is converted into the free boric acid content of the polarizer. In one embodiment, the free boric acid content of the polarizer is, as described later, by drying at a temperature lower than the conventional heating temperature (preferably, 50 ° C. or less) in the drying step in the manufacturing method of the polarizer, the above range can be adjusted within

The upper limit of the thickness of the polarizer is 7 μm in one embodiment, 3 μm in another embodiment, and 2 μm in another embodiment. The lower limit of the thickness is 0.5 μm in one embodiment, 0.6 μm in another embodiment, and 0.8 μm in still another embodiment. According to the embodiment of the present invention, a desired single transmittance as described later can be realized even with a polarizer having a thin thickness.

The iodine content of the polarizer can be appropriately set so as to achieve both sufficient polarization performance and optimal single transmittance. The iodine content is preferably 10% by weight to 25% by weight, more preferably 15% by weight to 25% by weight. According to the embodiment of the present invention, in the polarizer containing such an extremely high iodine content, conventionally difficult, extremely excellent heat resistance can be realized. More specifically, in a polarizer containing an extremely high iodine content, a change in optical properties in a high-temperature environment can be remarkably suppressed. In this specification, 'iodine content' means the amount of all iodine contained in a polarizer (PVA-type resin film). More specifically, in the polarizer, iodine exists in the form of iodine ions (I ^- ), polyiodine ions (I ₃ ^- , I ₅ ^- ), etc. means quantity. The iodine content can be calculated by, for example, a calibration curve method of fluorescence X-ray analysis. Further, polyiodine ions exist in a state in which a PVA-iodine complex is formed in the polarizer. By forming such a complex, absorption dichroism can be expressed in the wavelength range of visible light. Specifically, the complex of PVA with tri-iodide ions (PVA·I ₃ ^- ) has an absorption peak around 470 nm, and the complex of PVA with tri-iodide ions (PVA·I ₅ ^- ) has an absorption peak around 600 nm. contains the absorption peak. As a result, polyiodine ions can absorb light in a wide range of visible light depending on their form. On the other hand, iodine ion (I ^- ) has an absorption peak around 230 nm and is not substantially involved in absorption of visible light. Therefore, polyiodine ions present in a complex state with PVA may be mainly involved in the absorption performance of the polarizer.

The single transmittance (Ts) of the polarizer is preferably 30.0% to 43.0%, more preferably 35.0% to 41.0%. The degree of polarization of the polarizer is preferably 99.9% or more, more preferably 99.95% or more, still more preferably 99.98% or more. By setting the single transmittance low and the polarization degree high, the contrast can be increased and the black display can be displayed blacker, so that an image display device with excellent image quality can be realized. In addition, single transmittance is the value measured with the spectrophotometer with an integrating sphere. The single transmittance is a Y value obtained by measuring with a 2-degree field of view (C light source) of JIS Z8701 and correcting the visibility, and can be measured using, for example, a spectrophotometer with an integrating sphere (manufactured by Nippon Bunko Co., Ltd., product name: V7100).

A-2. PVA-based resin film

Examples of the PVA-based resin forming the PVA-based resin film include polyvinyl alcohol and an ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% or more and less than 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be determined according to JIS K 6726-1994. A light polarizer excellent in durability can be obtained by using PVA-type resin of such a degree of saponification. When the degree of saponification is too high, there is a possibility of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

The thickness of the PVA-based resin film is not particularly limited and may be set according to the desired thickness of the polarizer. The thickness of the PVA-based resin film is, for example, 10 μm to 200 μm.

In one embodiment, the PVA-based resin film may be a PVA-based resin layer formed on a substrate. A laminate of the base material and the PVA-based resin layer can be obtained, for example, by a method of applying a coating liquid containing the PVA-based resin to the base material or by laminating a PVA-based resin film on the base material.

B. Manufacturing method of polarizer

B-1. Outline of manufacturing method of polarizer

The method for manufacturing a light polarizer according to an embodiment of the present invention includes at least stretching and dyeing a PVA-based resin film. Typically, the manufacturing method includes a step of preparing a PVA-based resin film, a stretching step, a dyeing step, a crosslinking step, a washing step, and a drying step. Moreover, you may include a swelling process before an extending process as needed. Each step of providing a PVA-based resin film can be performed in any suitable order and timing. Therefore, each process may be performed in the above order, or may be performed in a different order from the above. You may perform one process multiple times as needed. Further, steps other than the above (for example, insolubilization step) may be performed at any appropriate timing. In the case where the PVA-based resin film is a PVA-based resin layer formed on a substrate, a laminate of the substrate and the PVA-based resin layer is provided in the above step.

Each step is described below, but as described above, each step can be performed in any appropriate order, and is not limited to the order described.

B-2. stretching process

In the stretching step, the PVA-based resin film is typically uniaxially stretched 3 to 7 times. The stretching direction may be the longitudinal direction (MD direction) of the film or the transverse direction (TD direction) of the film. The stretching method may be dry stretching, wet stretching, or a combination thereof. Moreover, when performing a crosslinking process, a swelling process, a dyeing process, etc., you may extend|stretch the PVA-type resin film. In addition, the stretching direction may correspond to the direction of the absorption axis of the resulting polarizer.

B-3. swelling process

The swelling process is usually performed before the dyeing process. A swelling process is performed by immersing a PVA system resin film in a swelling bath, for example. As the swelling bath, water such as distilled water and pure water is usually used. The swelling bath may contain any suitable other components other than water. Examples of other components include solvents such as alcohol, additives such as surfactants, iodides, and the like. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Preferably potassium iodide is used. The temperature of the swelling bath is, for example, 20°C to 45°C. In addition, immersion time is 10 second - 300 second, for example.

B-4. dyeing process

The dyeing step is a step of dyeing the PVA-based resin film with a dichroic substance. It is preferably carried out by adsorbing a dichroic substance. As the adsorption method, for example, a method of immersing a PVA-based resin film in a dye containing a dichroic substance, a method of coating the dye solution on a PVA-based resin film, a method of spraying the dye solution on a PVA-based resin film, etc. can be heard Preferably, it is the method of immersing a PVA-type resin film in a dyeing solution. This is because dichroic substances can adsorb satisfactorily.

Examples of the dichroic substance include iodine and dichroic dyes. preferably iodine. When using iodine as a dichroic substance, an iodine aqueous solution is preferably used as a dye solution. The iodine content of the iodine aqueous solution is preferably 0.04 to 5.0 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to blend iodide in an aqueous solution of iodine. As iodide, potassium iodide is preferably used. The content of iodide is preferably 0.3 to 15 parts by weight based on 100 parts by weight of water.

The liquid temperature at the time of dyeing of the dye solution can be set to any appropriate value, and is, for example, 20°C to 50°C. In the case of immersing the PVA-based resin film in the dye solution, the immersion time is, for example, 5 seconds to 5 minutes.

B-5. cross-linking process

In the crosslinking step, a boron compound is usually used as a crosslinking agent. As a boron compound, boric acid, borax, etc. are mentioned, for example. Preferred is boric acid. In the crosslinking process, the boron compound is usually used in the form of an aqueous solution.

In the case of using an aqueous solution of boric acid, the concentration of boric acid in the aqueous solution of boric acid is, for example, 1% by weight to 15% by weight, preferably 1% by weight to 10% by weight. You may further contain zinc compounds, such as iodides, such as potassium iodide, zinc sulfate, and zinc chloride, in boric acid aqueous solution.

The crosslinking step can be performed according to any suitable method. For example, a method of immersing a PVA-based resin film in an aqueous solution containing a boron compound, a method of applying an aqueous solution containing a boron compound to a PVA-based resin film, or a method of spraying an aqueous solution containing a boron compound onto a PVA-based resin film can be heard It is preferable to immerse in an aqueous solution containing a boron compound.

The temperature of the solution used for crosslinking is, for example, 25°C or higher, preferably 30°C to 85°C, and more preferably 40°C to 70°C. The immersion time is, for example, 5 seconds to 800 seconds, preferably 8 seconds to 500 seconds.

B-6. cleaning process

The washing step may typically be performed after the crosslinking step. The washing process is typically performed by immersing the PVA-based resin film in a washing liquid. A representative example of the washing liquid is pure water. You may add potassium iodide to pure water.

The temperature of the washing liquid is, for example, 5°C to 50°C. The immersion time is, for example, 1 second to 300 seconds.

B-7. drying process

The drying process can be performed according to any suitable method. As a drying method, natural drying, ventilation drying, reduced-pressure drying, heating drying etc. are mentioned, for example. Heat drying is preferably used. When heat drying is performed from the viewpoint of shortening the drying time, the heating temperature is preferably 50°C or lower, more preferably 45°C or lower, and particularly preferably 40°C or lower. Although the lower limit of the heating temperature is not particularly limited, it is the lower limit temperature that can be set in the heating and drying device. For example, 30°C. In addition, drying time is 20 second - 10 minutes, for example. In one embodiment, heat drying is performed in two or more stages. In this case, the heating temperature of at least one step is preferably a temperature within the above range. When heat-drying is performed, by setting the heating temperature within the above range, a light polarizer having very excellent heat resistance can be obtained.

C. Polarizer

The polarizer according to the embodiment of the present invention is typically used in a state in which a protective film is laminated on one side or both sides thereof (ie, as a polarizing plate). Practically, the polarizing plate includes an adhesive layer as an outermost layer. The pressure-sensitive adhesive layer typically becomes the outermost layer on the image display device side. A separator is temporarily attached to the pressure-sensitive adhesive layer so that peeling is possible, and roll formation is enabled while protecting the pressure-sensitive adhesive layer until actual use.

As the protective film, any suitable resin film is used. Examples of the material for forming the resin film include cellulosic resins such as (meth)acrylic resins, diacetyl cellulose and triacetyl cellulose, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, and polyethylene terephthalate resins. ester-based resins such as the like, polyamide-based resins, polycarbonate-based resins, copolymer resins thereof, and the like. In addition, "(meth)acrylic resin" refers to an acrylic resin and/or a methacrylic resin.

In one embodiment, a (meth)acrylic resin containing a glutarimide structure is used as the (meth)acrylic resin. (Meth)acrylic resins containing a glutarimide structure (hereinafter also referred to as glutarimide resins) are disclosed in, for example, Japanese Patent Laid-Open Nos. 2006-328329, Japanese Unexamined Patent Publication No. 2006-328334, Japanese Unexamined Patent Publication No. 2006-337491, Japanese Unexamined Patent Publication No. 2006-337492, Japanese Unexamined Patent Publication No. 2006-337493, Japanese Unexamined Patent Publication No. It describes in Unexamined-Japanese-Patent No. 2006-337569, Unexamined-Japanese-Patent No. 2007-009182, Unexamined-Japanese-Patent No. 2009-161744, and Unexamined-Japanese-Patent No. 2010-284840. Such description is incorporated herein as a reference.

When manufacturing a polarizer using the laminated body of a base material and a PVA system resin layer, you may use as a protective film as it is, without peeling a base material. Alternatively, the substrate may be peeled off and a protective film may be bonded to the polarizer.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples. In addition, the measuring method of each characteristic is as follows.

(1) Change in single transmittance Ts

A reflective polarizer (manufactured by 3M, trade name "DBEF") was bonded to the polarizer side of the laminates obtained in Examples and Comparative Examples through an adhesive layer having a thickness of 1.0 µm. Next, the thermoplastic resin base material was peeled off, and an alkali-free glass having a thickness of 1.3 mm was bonded to the peeled surface through an acrylic pressure-sensitive adhesive layer having a thickness of 20 µm, and a test sample was obtained. This test sample was heated at 80°C for 200 hours (heating test). The single transmittance of the polarizer before the test and after the heat test was measured using a spectrophotometer with an integrating sphere (manufactured by Nippon Bunko Co., Ltd., product name: V7100), respectively. From the single transmittance (Ts0) before heating and the single transmittance (Ts1) after the heating test, the single transmittance change amount (Ts) was determined using the following formula.

Ts(%) = Ts1-Ts0

(2) Iodine content

For the polarizers of the laminates obtained in Examples and Comparative Examples, fluorescence X-ray intensity (kcps) was measured using a fluorescence X-ray analyzer (manufactured by Rigaku Co., Ltd., trade name 'ZSX-PRIMUS II', measurement diameter: ψ20 mm). . On the other hand, the thickness (μm) of the polarizer was measured using a spectroscopic film thickness meter (manufactured by Otsuka Electronics Co., Ltd., trade name 'MCPD-3000'). The iodine content (% by weight) was determined using the following formula from the obtained fluorescence X-ray intensity and thickness.

(iodine concentration) = 20.5 × (fluorescence X-ray intensity)/(film thickness)

In addition, the coefficient when calculating the iodine content is different depending on the measuring equipment, but the coefficient can be obtained using an appropriate calibration curve.

(3) free boric acid content

50 mg of what cut the polarizer obtained by the Example and the comparative example into about 5 mm square with scissors was filled into the sample container with the steel ball. Thereafter, the measurement sample was freeze-pulverized using a freeze-crushing device JFC-300 (manufactured by Nippon Analytic Industry Co., Ltd.) using liquid nitrogen as a refrigerant under conditions of precooling for 7 minutes and vibration for 5 minutes. The pulverized measurement sample was left at room temperature for about 30 minutes. The obtained measurement sample was mixed with 3.5 mL of a mixed solution of 2-ethyl-1,3-hexanediol/chloroform (volume ratio: 10/90), and allowed to stand at room temperature for 24 hours. The obtained mixture was filtered using a 0.45 µm filter. After removing chloroform from the obtained filtrate on a hot plate, the residue was transferred to a Teflon (registered trademark) production decomposition vessel, acid was added, and the mixture was tightly stoppered. Microwaves were irradiated to this decomposition container, and pressure acid decomposition was carried out. After disassembly, ultrapure water was added to make a constant volume of 25 mL, and analysis was performed according to the following quantification conditions of boric acid.

<Quantification conditions of boric acid>

Device name: ICP emission spectrometer SPS-3520UV (manufactured by Hitachi High-Tech Sciences Co., Ltd.)

Measurement wavelength: B 249.848nm

All of the obtained boron contents were considered to be derived from boric acid, and were converted into boric acid contents. This boric acid content was made into free boric acid content of a polarizer.

[Example 1]

As the thermoplastic resin substrate, an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of 75° C. was used. Corona treatment was performed on one side of the substrate, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl denaturation degree 4.6%, saponification degree 99.0 mol%) were applied to the corona treated surface. As described above, an aqueous solution containing Nihon Synthetic Chemical Co., Ltd., trade name 'Gosehwamer Z200') at a ratio of 9:1 was applied and dried at 25 ° C to form a PVA-based resin layer having a thickness of 11 μm, and a laminate was produced. did

The obtained laminate was air-stretched 4.5 times in a direction orthogonal to the longitudinal direction of the laminate at 140°C using a tenter stretching machine (stretching treatment).

Next, the layered product was immersed in a dyeing bath (an aqueous solution having an iodine concentration of 1.4% by weight and a potassium iodide concentration of 9.8% by weight) at a liquid temperature of 25°C for 12 seconds and dyed (dyeing treatment).

Next, the laminate was immersed in a washing bath (pure water) at a liquid temperature of 25°C for 6 seconds (first washing treatment).

Then, it was immersed in a crosslinking bath (aqueous solution containing boron concentration of 1% by weight and potassium iodide concentration of 1% by weight) at a liquid temperature of 60°C for 16 seconds (crosslinking treatment).

Next, the laminate was immersed in a washing bath (aqueous solution having a concentration of potassium iodide of 1% by weight) at a liquid temperature of 25°C for 3 seconds (second washing treatment).

Then, the layered product was dried in an oven at 25°C for 8 seconds (first drying treatment).

Finally, the layered product was dried in an oven at 25°C for 13 seconds (second drying treatment) to obtain a layered product containing a PVA-based resin layer (polarizer) having a thickness of 1.2 μm. The iodine content of the obtained polarizer was 18.5% by weight, the free boric acid content was 0.32% by weight, and the single transmittance was 40.0%.

The obtained laminate was subjected to evaluation in (1) above. The results are shown in Table 1.

[Example 2]

In the 1st drying process and the 2nd drying process, except having dried the laminated body in 30 degreeC oven, respectively, it carried out similarly to Example 1, and obtained the laminated body containing a light polarizer. The iodine content of the obtained polarizer was 18.8% by weight, the free boric acid content was 0.32% by weight, and the single transmittance was 39.9%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 3]

In the 1st drying process and the 2nd drying process, except having dried the laminated body in 40 degreeC oven, respectively, it carried out similarly to Example 1, and obtained the laminated body containing a light polarizer. The iodine content of the obtained polarizer was 18.6% by weight, the free boric acid content was 0.39% by weight, and the single transmittance was 39.9%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 1]

In the 2nd drying process, except having dried the laminated body in a 60 degreeC oven, it carried out similarly to Example 3, and obtained the laminated body containing a polarizer. The iodine content of the obtained polarizer was 19.1% by weight, the free boric acid content was 0.45% by weight, and the single transmittance was 39.9%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]

In the 1st drying process, except having dried the layered product in a 50 degreeC oven, it carried out similarly to the comparative example 1, and obtained the layered product containing a polarizer. The iodine content of the obtained polarizer was 19.2% by weight, the free boric acid content was 0.48% by weight, and the single transmittance was 39.9%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 3]

In the 1st drying process, except having dried the laminated body in a 60 degreeC oven, it carried out similarly to the comparative example 1, and obtained the laminated body containing a light polarizer. The iodine content of the obtained polarizer was 19.3% by weight, the free boric acid content was 0.57% by weight, and the single transmittance was 40.0%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Table 1]

As is clear from Table 1, it can be seen that the light polarizers of Examples of the present invention have a very excellent heat resistance with a small change in single transmittance after heating test compared to the polarizers of Comparative Examples. Specifically, it can be said that the Ts of the polarizer of the examples is 0.75% to 0.80%, and if the Ts is a value of this level, the problem of heat resistance does not occur in actual use. The polarizers of Examples are thin, and the change in single transmittance in a high-temperature environment is remarkably suppressed. It is estimated that such an excellent effect is realized by suppressing free boric acid content of the light polarizer obtained low, and polyenization in a high-temperature environment being prevented. This is to solve a newly discovered problem by actually manufacturing a very thin (eg, thickness of 7 μm or less) polarizer, which was difficult to manufacture in the prior art, and is an unexpectedly excellent effect.

The polarizer of the present invention can be widely applied to liquid crystal panels such as liquid crystal TVs, liquid crystal displays, mobile phones, digital cameras, video cameras, portable game machines, car navigation systems, copiers, printers, fax machines, watches, and microwave ovens.

Claims (4)

It is composed of a polyvinyl alcohol-based resin film containing iodine,
The iodine content is 15% to 25% by weight,
The polarizer whose content of free boric acid is 0.4% by weight or less. According to claim 1,
A polarizer having a single transmittance of the polarizer of 30.0% to 41.0%. According to claim 1 or 2,
A polarizer in which the thickness of the polarizer is 7 μm or less. A polarizing plate comprising the polarizer according to claim 1 or 2 and a protective film laminated on one side or both sides of the polarizer.