WO2020203640A1 - Polarizing element containing cellulose nanofibers (cnf) and polarizing plate - Google Patents

Abstract

A polarizing element which contains at least cellulose nanofibers (CNF) and a dichroic dye.

Description

Polarizing elements and polarizing plates containing cellulose nanofibers (CNF)

The present invention relates to a polarizing element or the like.

The polarizing element is generally manufactured by adsorbing and orienting iodine and / or a dichroic dye, which are dichroic dyes, on a resin film made of polyvinyl alcohol or the like. In order to improve the physical durability of the polarizing element, a polarizing plate is manufactured by laminating a protective film made of triacetyl cellulose or the like on at least one surface of the polarizing element via an adhesive layer. Polarizing plates are used in liquid crystal display devices and the like.

In recent years, cellulose nanofiber (CNF) has been attracting attention as an additive material to reinforce resin. CNF is wood containing cellulose, which is made into pulp or wood powder and further loosened into nano-sized fibers by mechanical treatment. CNF is characterized by its strength, light weight, large specific surface area, and small thermal deformation. Furthermore, it is also known as a material that has a small impact on the environment because it is derived from plants.

Patent Document 1 describes a composite of a polyvinyl alcohol (PVA) -based polymer and CNF. Patent Document 2 describes a fiber in which CNF is dispersed and blended in a PVA-based polymer. Patent Documents 3 and 4 describe an optical film made of acetylated cellulose containing CNF, and describe its use as a protective film for a polarizing plate. Patent Document 5 describes a method for dyeing CNF, and describes its use as a structural material or a reinforced plastic. However, none of the prior art documents describe a polarizing element containing a CNF.

Japanese Unexamined Patent Publication No. 2010-242063 Japanese Unexamined Patent Publication No. 2011-208293 Japanese Unexamined Patent Publication No. 2008-208231 Japanese Unexamined Patent Publication No. 2011-148914 Japanese Unexamined Patent Publication No. 2013-166818 Japanese Unexamined Patent Publication No. 1-070702

An object of the present invention is to provide a novel polarizing element having polarization performance using cellulose nanofibers.

As a result of intensive research to solve the above problems, the present inventors have found a polarizing element having the following configuration and completed the present invention.

The present invention relates to the following.
[Invention 1]
A polarizing element containing at least cellulose nanofibers (CNF) and a dichroic dye.
[Invention 2]
The polarizing element according to invention 1, wherein the dichroic dye is adsorbed on the CNF.
[Invention 3]
The polarizing element according to Invention 1 or 2, wherein CNFs adsorbed with different dichroic dyes are mixed and used.
[Invention 4]
The polarizing element according to any one of Inventions 1 to 3, wherein the CNF is oriented in a specific direction.
[Invention 5]
The polarizing element according to any one of Inventions 1 to 4, wherein CNF and a dichroic dye are contained in the binder resin.
[Invention 6]
A polarizing plate including the polarizing element according to any one of the inventions 1 to 5.
[Invention 7]
A polarizing member including the polarizing element according to any one of the inventions 1 to 5 or the polarizing plate according to the invention 6.

The present invention has succeeded in providing a new polarizing element. It was also found that by appropriately selecting the binder resin, it is possible to reduce the thickness of the polarizing plate, increase the strength, and improve the water resistance.

The polarizing element of the present invention is characterized by containing a dichroic dye and cellulose nanofibers (CNF).

In one aspect of the present invention, the polarizing element is obtained by adsorbing a dichroic dye on the CNF and orienting the dichroic dye in a certain direction, and further, the CNF on which the dichroic dye is adsorbed is used as a binder resin. It is possible to form a film by dispersing it in the film.

CNF is wood containing cellulose that is made into pulp or wood powder and then mechanically processed to loosen it into nano-sized fibers. The fiber diameter of the CNF used in the present invention is preferably about 1 nm to 100 nm, more preferably about 5 nm to 50 nm, and the length is preferably about 1 μm to 100 μm, more preferably about 1 μm to 50 μm. Examples of such CNFs include Leocrysta (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Serish (manufactured by Daicel Fine Chem), Nanocell Source (manufactured by Chuetsu Pulp & Paper), Pinfiss (manufactured by Sugino Machine Limited), and Fluorene Cellulose Fiber (manufactured by Osaka Gas Co., Ltd.) ), Modified cellulose nanofiber (manufactured by Nippon Paper Industries, Ltd.) and the like.

The dichroic dye used in the present invention is not particularly limited as long as it is suitable for the polarizing element, and known iodine and / or dichroic dye can be used. Commercially available products may be used. It is preferably a dichroic dye. For example, dichroic dyes such as azo dyes, stillben dyes, anthraquinone dyes, methine dyes, and cyanine dyes can be used.

Specifically, C.I. I. Direct Yellow 4, C.I. I. Direct Yellow 12, C.I. I. Direct Yellow 26, C.I. I. Direct Yellow 28, C.I. I. Direct Yellow 44, C.I. I. Direct Yellow 50, C.I. I. Direct Yellow 142, C.I. I. Mordant Yellow 26, C.I. I. No. 27865, C.I. I. No. 27915, C.I. I. No. 27920, C.I. I. No. 29058, C.I. I. No. 29060, C.I. I. Direct Orange 26, C.I. I. Direct Orange 39, C.I. I. Direct Orange 49, C.I. I. Direct Orange 71, C.I. I. Direct Orange 72, C.I. I. Direct Orange 107, Kayafect Orange G, C.I. I. Direct Red 2, C.I. I. Direct Red 28, C.I. I. Direct Red 31, C.I. I. Direct Red 39, C.I. I. Direct Red 79, C.I. I. Direct Red 81, C.I. I. Direct Red 83, C.I. I. Direct Red 89, C.I. I. Direct Red 117, C.I. I. Direct Red 247, C.I. I. Direct Green 80, C.I. I. Direct Green 59, C.I. I. Direct Blue 1, C.I. I. Direct Blue 15, C.I. I. Direct Blue 67, C.I. I. Direct Blue 71, C.I. I. Direct Blue 78, C.I. I. Direct Blue 83, C.I. I. Direct Blue 90, C.I. I. Direct Blue 98, C.I. I. Direct Blue 151, C.I. I. Direct Blue 168, C.I. I. Direct Blue 202, C.I. I. Direct Violet 9, C.I. I. Direct Violet 35, C.I. I. Direct Violet 48, C.I. I. Direct Violet 51, C.I. I. Direct Violet 57, C.I. I. Direct Brown 106, C.I. I. Direct Brown 223 and the like can be mentioned, and further, JP-A-1-161202, JP-A-1-172906, JP-A-1-172907, JP-A-1-183602, JP-A 1-248105, and Japanese Patent Application Laid-Open No. Examples thereof include the dichroic dyes described in Kaihei 1-265205, JP-A-9-230142, JP-A-3-12606, and the like.

Depending on the application, for example, a CNF having each of blue, red, and orange dichroic dyes adsorbed is prepared, and then these are mixed and oriented to obtain a polarizing element having a gray hue. Can be done. Alternatively, two to four dichroic dyes may be adsorbed on the CNF at the same time. Further, a plurality of dyes for the infrared region control polarizing element may be used.

The method for dyeing CNF is not particularly specified, and a general dyeing method for cellulose fibers can be applied. Compared to general cellulose fibers, CNF has a large specific surface area and is excellent in reinforcing effect, but since there are many hydroxyl groups on the surface of CNF, it is easy to form hydrogen bonds with CNF, and dye molecules. The direct dyeing method with a dye is preferable because it is bonded by intermolecular force because of its large size.

The polarizing element of the present invention can be obtained by adsorbing a dichroic dye on CNF. When it is desired to obtain the polarization performance in an arbitrary direction, the CNF adsorbed by the dichroic dye may be oriented in a desired direction. The method of orientation is not particularly limited, but the dispersion liquid containing the CNF adsorbed by the dichroic dye is oriented by sharing, or the CNF adsorbed by the dichroic dye is dispersed in the binder and then in a certain direction together with the binder. Examples thereof include a method of orienting the binder by performing a stretching treatment.

The binder resin used to orient the CNF to which the dichroic dye is adsorbed is not particularly limited as long as it is transparent, and a known resin can be used. Commercially available products may be used. It is preferably a polymer, and may be a polymer composed of a single monomer or a copolymer.

In one aspect of the present invention, the binder resin may be a hydrophilic resin. For example, polyvinyl alcohol (PVA) resin, amylose resin, starch resin, cellulose resin, polyacrylate resin, gelatin and the like can be mentioned. It may be modified with an olefin such as ethylene or propylene, or an unsaturated carboxylic acid such as crotonic acid, acrylic acid, methacrylic acid, and maleic acid. PVA is preferred.

In one aspect of the present invention, the binder resin may be a hydrophobic resin. For example, polyene resin, polyethylene glycol (PEG) resin, urethane acrylate resin and the like can be mentioned.

Since many hydroxyl groups are present on the surface of cellulose nanofibers, if they are mixed with a highly hydrophobic resin, aggregation may occur in the resin components and the reinforcing effect may be reduced. A surfactant can be contained in order to more uniformly disperse the highly hydrophilic CNF and the highly hydrophobic resin.

The content of CNF is not particularly limited and is appropriately selected depending on the desired performance of the polarizing element. In one aspect of the present invention, it is 0.1 to 95% by weight based on the binder resin. The lower limit of the content of CNF with respect to the binder resin may be 1% by weight or 5% by weight. The upper limit may be 80% by weight, 60% by weight, or 30% by weight. In one aspect of the present invention, the binder resin may not be used.

The polarizing element of the present invention may contain additives such as a cross-linking agent, a water resistant agent, a flame retardant, a leveling agent, an ultraviolet absorber, an antioxidant, and an antistatic agent.

The polarizing element of the present invention can be produced by a conventional method, and may be appropriately modified. A film-like binder resin may be used, or a CNF, a dye or the like may be contained therein (impregnated) and stretched to prepare a polarizing element. It may be adsorbed (dyed) after stretching, or may be stretched at the same time. A solution or suspension of a binder resin may be used, or a CNF, a dye, or the like may be mixed with the solution, and then the mixed solution may be formed into a film (applied to a base film, dried, stretched) to prepare a polarizing element. CNF may be mixed with a binder resin to form a film of the mixture to prepare a CNF-containing binder resin film, and then the film may be dyed and stretched. A dye may be added when the binder resin is prepared from one or more kinds of monomers. The CNF may be stained and then mixed with the binder resin. A sheet-shaped CNF may be used, dyed thereof, and then mixed with a binder resin or the like.

By mixing CNF with the binder resin before making it into a sheet, CNF is uniformly dispersed with the binder resin. A surfactant may be contained from the viewpoint of improving dispersibility. By dyeing CNF and then mixing it with a binder resin, it becomes possible to develop polarized light along the CNF fibers.

As a film manufacturing method, a casting method, an extrusion method, a calendar method, etc. can be selected.

In the casting method, for example, a hydrophilic resin as a binder resin is dissolved in water or an organic solvent to obtain a 10 to 20% solution, which is 0.5 to 2.0% water-soluble with respect to the hydrophilic resin. Add a bicolor dye to make a film-forming solution. This film-forming solution can be cast in a drum or belt shape, or applied with a roll coater, dried, and then a base film can be obtained.

In the melt extrusion method, for example, pellets obtained by impregnating a hydrophilic resin with a dichroic dye and, if necessary, plasticizer water are prepared, and then the pellets are heated, melt-kneaded, and then extruded with an extruder. It can be made into a film to obtain an original film.

The method for stretching the dyed film is not particularly limited, and wet stretching or dry stretching may be used. The draw ratio is not particularly limited, and is appropriately selected depending on the desired performance of the polarizing element.

The polarizing element of the present invention may be provided with a protective layer if necessary. Examples of the protective layer include resins, and more specifically, polyester resins, cellulose resins, acetate resins, polyether sulfone resins, fluoroalkylene resins, polycarbonate resins, polyamide resins, and polyimide resins. , Polyolefin-based resins, thermoplastic resins such as acrylic-based resins, thermosetting resins such as acrylic-based, urethane-based, acrylic urethane-based, epoxy-based, and silicone-based resins, and ultraviolet curable resins. These may be diluted with a solvent and applied to the surface of the polarizing element, or may be formed into a film and bonded to the polarizing element using an adhesive or an adhesive.

The polarizing element of the present invention thus obtained may be provided with known functional layers such as an adhesive layer, a flame-retardant layer, an antireflection layer, an antiglare layer, and a hard coat layer. A support such as a transparent glass plate may be provided.

The optical characteristics of the obtained polarizing element can be obtained by using a commercially available spectrophotometer. For example, when the polarizing element is not in the form of a sheet or a film, a microscopic region can be evaluated. It is preferable to measure using a spectrophotometer. Further, the optical characteristics of the polarizing element may be expressed numerically by the transmittance, the degree of polarization, the two-color ratio, etc. for each wavelength, and these may be expressed by a known calculation method described in JIS Z8719 or the like for visible light. It may be represented by a value corrected for visual sensitivity in the region.

The polarizing element of the present invention may be used for manufacturing various polarizing members-for example, a polarizing lens such as eyeglasses, a character or image display such as a liquid crystal display, a projector, a window glass, and an optical transmission device.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to such Examples.

Example 1
CNF aqueous dispersion (CNF is dispersed in water at a ratio of 2% by weight) (manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: Leocrysta I-2SX) 1 part by weight, as a bicolor dye, published in JP-A-3-12606. 0.2 parts by weight of the blue dye, 0.1 parts by weight of sardine, 0.1 parts by weight of sodium tripolyphosphate, and 98.6 parts by weight of pure water obtained by the method described are mixed and heated and stirred at 80 ° C. for 1 hour. After that, it was allowed to stand until it reached room temperature. Next, 0.1 ml of this mixed solution was dropped onto a glass plate, and after the glass plate was further covered, only one of the glass plates was strongly slid in one direction so that the CNF was oriented in one direction. By air-drying at room temperature for 5 minutes in this state, a adhered substance containing the dichroic dye and CNF was obtained on the surface of the glass plate.

When the obtained adhered material was confirmed using a polarizing microscope, the fiber shape of CNF was substantially oriented in the above-mentioned sliding direction, and it was colored dark blue. When the polarizer of the polarizing microscope was further rotated, it became a bright state when the orientation direction of the CNF (long axis direction) and the polarizer of the polarizing microscope were parallel, and the orientation direction of the CNF (long axis direction) and the polarizing microscope. It was confirmed that when the polarizers are orthogonal, the state becomes dark. It was confirmed that the dichroic dye was adsorbed on the CNF in the obtained fixed product, and that the fixed product was a polarizing element.

Example 2
A adhered substance was obtained on the surface of the glass plate by the same operation as in Example 1 except that Kayafect Orange G (manufactured by Nippon Kayaku Co., Ltd.) was used as the dichroic dye. When the obtained adhered substance was confirmed using a polarizing microscope, the fiber shape of CNF was substantially oriented in the above-mentioned sliding direction, and the CNF was colored orange. Further, it was confirmed that the dichroic dye was adsorbed on the CNF in the obtained fixed product by the same method as in Example 1, and that the fixed product was a polarizing element.

Claims (7)

1. Polarizing element containing at least cellulose nanofiber (CNF) and dichroic dye.
2. The polarizing element according to claim 1, wherein the dichroic dye is adsorbed on the CNF.
3. The polarizing element according to claim 1 or 2, wherein CNFs adsorbed with different dichroic dyes are mixed and used.
4. The polarizing element according to any one of claims 1 to 3, wherein the CNF is oriented in a specific direction.
5. The polarizing element according to any one of claims 1 to 4, wherein CNF and a dichroic dye are contained in the binder resin.
6. A polarizing plate including the polarizing element according to any one of claims 1 to 5.
7. A polarizing member including the polarizing element according to any one of claims 1 to 5 or the polarizing plate according to claim 6.