TWI565975B - Polarizer and manufacturing method thereof - Google Patents

Description

Polarizer and manufacturing method thereof Technical field

The present invention relates to a polarizing member and a method of manufacturing the same. Further, the present invention relates to a polarizing plate using the polarizing member. The polarizer or the polarizing plate can be used as the polarizing plate or the polarizing plate alone or in the optical film of the polarizing plate or the polarizing plate, and can form an image display device such as a liquid crystal display device or a flat panel display such as an organic EL display device.

Background technique

Conventionally, a polarizing member used in a liquid crystal display device or the like has been widely used as an absorbing dichroic polarizer in which a polyvinyl alcohol-based film is dyed with iodine or a dichroic dye and uniaxially stretched. Further, the polarizing member is bonded to a transparent protective film such as saponified triacetyl cellulose on both sides or one side of the polarizing member, and is used as a reinforced polarizing plate.

In particular, in recent years, from the viewpoint of low power consumption of the liquid crystal display device, it is desired to increase the white luminance of the liquid crystal display device, and it is desired to develop a polarizer having a high light transmittance. However, when only the light transmittance of the monomer is increased, the degree of polarization decreases, which in turn causes a problem of reduced display contrast. On the other hand, when the degree of polarization is increased, there is a problem that the transmittance of the monomer is lowered, which in turn causes a decrease in white luminance. Thus, the transmittance and the degree of polarization of the polarizer are exchanged. Therefore, it is required to develop a polarizing member having both high light transmittance and high polarization.

For example, Patent Document 1 discloses a polarizing plate having a light transmittance of 41.1 to 44.3 and a degree of polarization of 99% or more.

However, the polarizing plate described above is still unsatisfactory in terms of light transmittance and polarization.

Prior technical literature Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-92847

Summary of invention

It is an object of the present invention to provide a polarizing member which has both high light transmittance and high degree of polarization, that is, white brightness and display contrast, and a method of manufacturing the same.

In order to solve the above problems, the present inventors have intensively reviewed and found that the above object can be attained by the method for producing a polarizing member described below, and the present invention has been completed.

That is, the present invention relates to a method for producing a polarizing member which is characterized in that at least a swelling step, a dyeing step, a crosslinking step and an extending step are carried out on a polyvinyl alcohol-based film, which is characterized in that it is in the swelling step. The crystallinity of the polyvinyl alcohol-based film is controlled to 25 to 32% by extending the polyvinyl alcohol-based film by 1.4 to 2.4 times.

The crystal portion (platelet layer) of PVA is arbitrarily present on the raw material film formed of polyvinyl alcohol (hereinafter referred to as "PVA") before stretching. When such a raw material film is stretched, the crystal portion collapses and is elongated. That is, it is considered that the crystallinity of the raw material film is reduced as it extends.

After the swelling step, the iodine is adsorbed on the PVA by the dyeing step, and the shape It is dichromatic in the form of an iodine-PVA complex. Iodine can only be adsorbed on the amorphous portion of PVA and cannot be adsorbed on the crystal portion. When the crystallinity of the PVA film is too high when the polyvinyl alcohol-based film (hereinafter referred to as "PVA film") is dyed with iodine, the adsorption site of iodine is insufficient, and the iodine-PVA complex is less likely to form. On the other hand, if the crystallinity of the PVA film is too low, the stress applied during stretching is lowered, and the alignment of the PVA is not high, and the iodine-PVA complex is not easily formed.

The present inventors have paid attention to the crystallinity of the PVA film, and found that the PVA film is extended by 1.4 to 2.4 times by the swelling step of the step before the dyeing step, and the crystallinity of the PVA film is controlled to 25 to 32%, and then, By performing the dyeing step, a polarizing member having both high light transmittance and high degree of polarization can be obtained.

The polarizing member obtained by the above manufacturing method has a boron content of 4 to 5.5% by weight, a monomer transmittance of 43.0% or more, and a degree of polarization of 99.99% or more, and has high light transmittance and high polarization. Polarizer. When the boron content is less than 4% by weight, the optical characteristics tend to be lowered. When the boron content exceeds 5.5% by weight, there is a tendency that elongation fracture tends to occur in the stretching step.

Moreover, the present invention relates to a polarizing plate in which a transparent protective film is laminated on at least one surface of the polarizing member.

Further, the present invention relates to an optical film comprising at least one of the aforementioned polarizers or the polarizing plates.

Further, the present invention relates to an image display device comprising the aforementioned optical film.

The polarizing member of the present invention has both high light transmittance and high polarization, and by using the polarizing member, the liquid crystal display device can be simultaneously improved. White brightness and improved display contrast.

Form for implementing the invention

The PVA film (raw material film) of the raw material of the polarizer usually has a crystallinity of 35 to 50%. When the degree of crystallinity is too high, the elongation is lowered and the adsorption site of iodine or the like is insufficient, so that the polarization characteristics are lowered. On the other hand, if the degree of crystallinity is too low, no tension is applied to the film during stretching, and PVA is less likely to be aligned, so that the polarization characteristics are lowered. For example, when a PVA film having a crystallinity of 30% is used, and the PVA film is not stretched in the swelling step, the crystallinity of the PVA film after the swelling step is in the range of 25 to 32%, but the polarizing characteristics of the present invention are not obtained. That is, the initial crystallinity of the PVA film is lowered by the elongation in the swelling step, and the crystallinity is controlled to 25 to 32% by stretching, whereby the polarizing characteristics of the present invention are obtained.

In the PVA film, an additive such as a plasticizer or a surfactant may be added. The plasticizer may, for example, be a polyhydric alcohol, a condensate thereof or the like, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer or the like to be used is not particularly limited, but it is suitably 20% by weight or less in the polyvinyl alcohol-based film.

The polarizing member of the present invention is produced by performing at least a swelling step, a dyeing step, a crosslinking step, and an extending step on the PVA film.

The swelling step is carried out prior to the dyeing step. By the swelling step, the dirt or the anti-caking agent on the surface of the PVA film can be washed, and the PVA film is swollen to prevent the unevenness of the dyeing unevenness.

In the swelling step, the treatment liquid is usually water, distilled water, pure water. When the main component is water, the treatment liquid may be added with a small amount of an additive such as an iodinated compound or a surfactant, or ethanol. When the treatment liquid contains an iodinated compound, the concentration of the iodinated compound is about 0.1 to 10% by weight, and preferably 0.2 to 5% by weight.

The treatment temperature in the swelling step is usually adjusted to about 20 to 45 ° C, and 25 to 40 ° C is better. Further, uneven swelling and a part thereof may become uneven in dyeing in the dyeing step, so that uneven swelling does not occur. The immersion time is usually about 10 to 300 seconds, and preferably 20 to 240 seconds.

In the method for producing a polarizing member of the present invention, it is necessary to control the crystallinity of the PVA film to 25 to 32% in the swelling step by extending the PVA film by 1.4 to 2.4 times with respect to the original length. The stretching ratio should be 1.4 to 2.2 times. Thereby, the crystallinity of the PVA film can be controlled to 27 to 32%. Moreover, the stretching ratio is particularly preferably 1.6 to 2.0 times. Thereby, the crystallinity of the PVA film can be controlled to 28 to 31%.

The dyeing step is carried out on a swelled PVA film by adsorption, alignment of iodine or a dichroic dye. In the method for producing a polarizing member of the present invention, in order to dye in a state in which the adsorption portion of iodine or the like is large and the alignment of the amorphous portion of PVA is high, the dyeing step is such that the crystallinity of the PVA film is 25 The mode of ~32% is carried out.

Dyeing is usually carried out by immersing the above film in a dyeing solution. The staining solution is typically an iodine solution. The iodine aqueous solution used as the iodine solution is iodine or an aqueous solution containing iodide ions as a dissolution aid such as potassium iodide. In addition, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, iodide can be used. An auxiliary agent such as an iodide such as titanium. The iodine concentration is about 0.01 to 0.5% by weight, and preferably 0.02 to 0.4% by weight, and the potassium iodide concentration is about 0.01 to 10% by weight, and preferably 0.02 to 8% by weight. When iodine is dyed, the temperature of the iodine solution is usually about 20 to 50 ° C, and preferably 25 to 40 ° C. The immersion time is usually about 10 to 300 seconds, and preferably 20 to 240 seconds.

In the crosslinking step, a boron compound is usually used as a crosslinking agent. The crosslinking step can also be carried out together with the extension step. The crosslinking step can be carried out most times. Examples of the boron compound include boric acid, borax, and the like. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixed solution. Usually, an aqueous boric acid solution is used. In order to make the boron content in the polarizing member 4 to 4.5% by weight, the boric acid concentration of the boric acid aqueous solution should be about 2 to 10% by weight, and more preferably 3 to 8% by weight. The boric acid aqueous solution may contain an iodinated compound such as potassium iodide. When the iodinated compound is contained in the aqueous boric acid solution, the concentration of the iodinated compound is about 0.1 to 10% by weight, and more preferably 0.2 to 5% by weight.

The crosslinking step is carried out by dipping the dyed PVA film into an aqueous boric acid solution. Further, it can be carried out by a boron compound such as coating or spraying on the PVA film. The treatment temperature in the crosslinking step is usually 25 ° C or higher, and preferably 30 to 85 ° C, and more preferably 30 to 60 ° C. The processing time is usually 10 to 800 seconds, and 30 to 500 seconds is better.

The extension step typically performs a uniaxial extension. The stretching method is not particularly limited, and any of the wet stretching method and the dry stretching method may be employed. Examples of the extension means of the dry stretching method include a method of stretching between rolls, a method of stretching a heating roll, a method of compressing and stretching, and the like. The extension can be done in multiple stages. The stretching ratio of the stretched film can be appropriately set according to the purpose, but the total stretch ratio is 2~7 times, and preferably 3~6.8 times, and 3.5~6.5 times better.

Then, a washing step is performed on the PVA film. The precipitate generated on the surface of the stretched film can be removed by the washing step.

The washing step can be carried out by washing with water such as water, distilled water, pure water or the like. The washing step is usually carried out by immersing the PVA film in a water washing bath. Further, the washing step can be carried out by immersing in an aqueous solution containing an iodide such as potassium iodide. For example, the potassium iodide concentration of the aqueous solution is preferably about 0.5 to 10% by weight, and more preferably 1 to 8% by weight. The washing bath temperature in the washing step is usually 5 to 50 ° C, and preferably 10 to 45 ° C, and 15 to 40 ° C is more preferable. The immersion time is usually from 1 to 300 seconds, and more preferably from 10 to 240 seconds. Further, the washing of the aqueous solution may be carried out in combination with washing with water, and may be carried out before or after washing with water.

Then, a drying step may be performed on the PVA film.

The polarizing member produced by the above method has a boron content of 4 to 5.5% by weight, a monomer light transmittance of 43.0% or more, and a degree of polarization of 99.99% or more.

The polarizing member obtained can be formed into a polarizing plate having a transparent protective film on at least one side thereof according to a general method. The transparent protective film can be provided as a coating layer of a polymer, or as a laminate of a film or the like. As the transparent polymer or film material forming the transparent protective film, a suitable transparent material can be used, but it is preferable to use transparency, mechanical strength, thermal stability, and moisture barrier property. The material for forming the transparent protective film may, for example, be a polyester polymer such as polyethylene terephthalate or polyethylene naphthalate, or a cellulose system such as diethyl cellulose or triacetyl cellulose. A styrene polymer such as a polymer, a polystyrene or an acrylonitrile-styrene copolymer (AS resin), a polycarbonate polymer or the like. Further, the polymer forming the transparent protective film may also be For example, polyethylene, polypropylene, polyolefin having a ring- or norbornene structure, a polyolefin-based polymer such as an ethylene-propylene copolymer, a vinyl chloride-based polymer, nylon, and an aromatic polyamine. Amine polymer, quinone polymer, fluorene polymer, polyether fluorene polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride A polymer, a butyral polymer, an aryl ester polymer, a polyoxymethylene polymer, an epoxy polymer, or a mixture of the above polymers. The transparent protective film can be formed into a cured layer of a thermosetting type or an ultraviolet curable resin such as an acrylic type, an urethane type, an urethane type, an epoxy type or a polyoxymethylene type.

Further, for example, a polymer film described in JP-A-2001-343529 (WO01/37007), for example, contains (A) a thermoplastic resin having a substituted and/or unsubstituted quinone imine group in a side chain. And (B) a resin composition of a thermoplastic resin having a substituted and/or unsubstituted benzene and a nitrile group in a side chain. Specific examples thereof include a film containing a cross-copolymer of isobutylene and N-methylbutyleneimine and a resin composition of an acrylonitrile-styrene copolymer. As the film, a film formed of a mixed extrusion of a resin composition or the like can be used. Since these films have a small phase difference and a small photoelastic coefficient, the unevenness due to the strain of the polarizing plate can be eliminated, and the moisture permeability is small, so that the humidifying durability is excellent.

The thickness of the transparent protective film can be appropriately determined, but it is generally about 1 to 500 μm in view of workability such as strength and handleability, and thinness. Particularly preferred is 1 to 300 μm, and 5 to 200 μm is more preferable.

Also, the transparent protective film should be as color-free as possible. Therefore, it is best to use Rth=(nx-nz). d (where the slow axis of the nx film plane The refractive index to the refractive index, the refractive index in the thickness direction of the nz film, and the thickness of the d-type film) are transparent protective films having a phase difference in the thickness direction of the film of -90 nm to +75 nm. By using the thickness direction retardation value (Rth) of -90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate due to the protective film can be substantially eliminated. The thickness direction retardation (Rth) is preferably -80 nm to +60 nm, and -70 nm to +45 nm is particularly preferable.

The protective film is preferably a triacetyl cellulose film, a norbornene film, a cycloolefin film, or an acrylic resin film from the viewpoints of polarizing characteristics and durability. Triethylene fluorene cellulose films are particularly desirable. Further, when a transparent protective film is provided on both sides of the polarizer, a protective film made of the same polymer material may be used on the front and back surfaces, and a protective film made of a different polymer material or the like may be used.

On the surface of the transparent protective film that is not attached to the polarizer, a hard coat layer, a reflection preventing treatment, and a treatment for preventing adhesion, diffusion, or anti-glare may be performed.

The anti-reflection treatment layer, the anti-adhesion layer, the diffusion layer or the anti-glare layer may be provided separately from the transparent protective film as an optical layer, in addition to being disposed on the transparent protective film itself.

The subsequent treatment of the polarizer and the transparent protective film uses an adhesive. Examples of the subsequent agent include an isocyanate-based adhesive, a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, an ethylene-based latex, and an aqueous polyester. As the above-mentioned adhesive, an adhesive composed of an aqueous solution is usually used.

The polarizing plate of the present invention is manufactured by bonding the transparent protective film and the polarizing member using the above-mentioned adhesive, and the coating of the adhesive can be transparent. The protective film or the polarizing member may be carried on either of them or both. After bonding, a drying step is performed to form an adhesive layer composed of a dried coating layer. The bonding of the polarizing member and the transparent protective film can be performed by a roll laminator. The thickness of the layer is not particularly limited, but is usually about 0.1 to 5 μm.

The polarizing plate of the present invention can be used as an optical film laminated with other optical layers in actual use. The optical layer is not particularly limited, but, for example, one or two or more reflective sheets, a semi-transmissive sheet, a phase difference plate (including a wavelength plate of 1/2 or 1/4 or the like), a viewing angle compensation film, or the like can be used. A certain optical layer such as a liquid crystal display device is formed. It is particularly preferable to further laminate a reflective polarizing plate or a semi-transmissive polarizing plate of a reflecting plate or a semi-transmissive reflecting plate on the polarizing plate of the present invention, and further laminate an elliptically polarizing plate or a circular polarizing plate of the phase difference plate on the polarizing plate. Further, a wide viewing angle polarizing plate of a viewing angle compensation film is further laminated on the polarizing plate, or a polarizing plate of a brightness improving film is further laminated on the polarizing plate.

The polarizing plate or optical film of the present invention can be suitably used for various devices for forming a liquid crystal display device or the like. The formation of the liquid crystal display device can be performed in accordance with a conventional person. That is, the liquid crystal display device is generally formed by appropriately assembling a liquid crystal cell, a polarizing plate or an optical film, and a constituent component such as an illumination system as needed, and assembling the driving circuit, but in the present invention, in addition to using the polarizing plate of the present invention The optical film is not particularly limited, and may be any conventional one. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can also be used.

Example

Hereinafter, the implementation of the constitution and effect of the present invention will be specifically shown. The example is explained. In addition, in each example, a part and % are a weight basis unless it mentions especially.

(Measurement of crystallinity of PVA)

A PVA film (manufactured by KURARAY Co., Ltd., trade name: VF-PS #7500) having a width of 20 mm, a length of 30 mm, and a thickness of 75 μm was placed in an extension machine, and the PVA film was stretched in water at 25 ° C while being at a small angle. The crystallinity was measured by X-ray scattering method (wavelength line of Spring-8, implementation of BL40B2, X-ray wavelength λ = 1 Å). The crystallinity of each stretching ratio is shown in Table 1.

(Measurement of boron content in polarizer)

The fabricated polarizer was dried at 120 ° C, and the weight of the polarizer was measured. Next, mannitol and bromoquinol blue were added as a titration indicator to the solution obtained by completely dissolving the polarizer in pure water, and an aqueous solution of NaOH (0.1 mol/L) was dropped. When the color of the solution changed from orange to blue, the aqueous solution of NaOH was stopped and the amount of dripping was measured. The boron content in the polarizer was calculated by the following formula.

Boron content (% by weight) = 0.1 × {Drop amount of NaOH aqueous solution (ml) / 1000} × 10.81 × {1/weight of polarizing member (g)} × 100

Example 1 (production of polarizer)

A PVA film (manufactured by KURARAY Co., Ltd., trade name: VF-PS #7500) having a thickness of 75 μm was immersed in a warm water (swelling bath) at 25° C. to swell, and extended in the flow direction with respect to the original length so that the stretching ratio was 1.4 times. . Then, the PVA film was immersed in an aqueous iodine solution (dye bath) containing 30% of iodine concentration of 0.04% and potassium iodide concentration of 0.4% for 60 seconds, and dyed while being opposite to the original length. The extension in the flow direction is such that the stretching ratio is 3.3 times. Next, the PVA film was immersed in an aqueous solution containing 30% by weight of boric acid and 3 % by weight of potassium iodide for 30 seconds. Then, the PVA film was immersed in an aqueous solution (extension bath) containing 60% by weight of boric acid and 5% by weight of potassium iodide for 40 seconds, and was stretched in the flow direction with respect to the original length so that the stretching ratio was 6 times. Then, the PVA film was immersed in an aqueous solution containing 30% by weight of potassium iodide at 30 ° C for 10 seconds, and washed, and then dried at 50 ° C for 4 minutes to obtain a polarizing member.

Examples 2 to 4, Comparative Examples 1 to 2

A polarizer was produced in the same manner as in Example 1 except that the stretching ratio was changed as shown in Table 1 in the swelling step of Example 1.

(Evaluation)

The polarizing elements obtained in the examples and the comparative examples were evaluated for the following optical characteristics. The results are shown in Table 1.

<Optical characteristics>

The spectroscopic transmittance of the polarizer of light having a wavelength of 380 to 780 nm was measured using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, trade name: V7100). The transmittance for each linearly polarized light was measured as 100% by full polarization obtained by Glan-Taylor. From the measured spectral transmittance, the Y value of the 2° field of view of the C light source is calculated according to the CIE1931 Yxy color system. The equivalent values are used as the monomer transmittance (Ts (Y)), the parallel transmittance (Tp (Y)), and the vertical transmittance (Tc (Y)).

The degree of polarization (P) is calculated by {(parallel transmittance - vertical transmittance) / (parallel transmittance + vertical transmittance) ^1/2 × 100 (%).

Table 1

Industrial availability

The polarizer and the polarizing plate of the present invention can be used for producing a video display device such as a liquid crystal display device or a flat panel display such as an organic EL display device.

Claims (5)

A method for producing a polarizing member, comprising at least a swelling step, a dyeing step, a crosslinking step, and an extending step on a polyvinyl alcohol-based film, wherein the polyvinyl alcohol-based film is characterized in that the polyvinyl alcohol-based film is formed by the polyvinyl alcohol The film is extended by 1.4 to 2.0 times (but, except for 2.0 times), and the crystallinity of the polyvinyl alcohol film is controlled to be 28 to 32%. A polarizing member is obtained by the production method of the first aspect of the patent application, and has a boron content of 4 to 5.5% by weight, a monomer light transmittance of 43.0% or more, and a degree of polarization of 99.99% or more. A polarizing plate is formed by laminating a transparent protective film on at least one side of a polarizing member according to claim 2 of the patent application. An optical film comprising at least one polarizing member as claimed in claim 2 or a polarizing plate according to claim 3 of the patent application. An image display device comprising the optical film of item 4 of the patent application.