JP7068377B2 - Polarizing film and polarizing plate containing it - Google Patents

Description

The present invention relates to a polarizing film and a polarizing plate including the polarizing film.

The polarizing plate is widely used in an image display device such as a liquid crystal display device. Generally, the polarizing plate has a structure in which a protective film is attached to one or both sides of a polarizing film formed by adsorbing and orienting a dichroic dye such as iodine on a polyvinyl alcohol-based resin film. In recent years, with the development of image display devices for mobile devices, flat-screen televisions, and the like, there is an increasing demand for thinner polarizing plates and thus polarizing films.

Japanese Unexamined Patent Publication No. 2015-57669 (Patent Document 1) discloses a thin polarizing plate composed of a polyvinyl alcohol-based resin film having a thickness of 10 μm or less.

Japanese Unexamined Patent Publication No. 2015-57669

The polarizing film may crack with use, and improvement is required. This problem becomes more remarkable as the thickness of the polarizing film becomes smaller.

An object of the present invention is to provide a thin polarizing film having excellent crack resistance and a polarizing plate containing the same.

The present invention provides the following polarizing films and polarizing plates.
[1] A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film.
A polarizing film having a thickness of 15 μm or less and a polyvinyl alcohol-based resin having a birefringence of 0.040 or more.

[2] The birefringence is 0.050 or less.
The polarizing film according to [1].

[3] The content of the element boron is 3.0% by weight or more and 6.0% by weight or less.
The polarizing film according to [1] or [2].

[4] The polarizing film according to any one of the above [1] to [3] and the polarizing film.
A protective film laminated on at least one surface of the polarizing film and
A polarizing plate including.

According to the present invention, it is possible to provide a thin polarizing film having excellent crack resistance and a polarizing plate containing the same.

It is a schematic sectional drawing which shows an example of the layer structure of the polarizing plate which concerns on this invention. It is a schematic sectional drawing which shows another example of the layer structure of the polarizing plate which concerns on this invention.

(1) Polarizing film The polarizing film according to the present invention has a polyvinyl alcohol-based resin film (hereinafter, also referred to as a PVA-based resin film) in which a bicolor dye is adsorbed and oriented, has a thickness of 15 μm or less, and has a thickness of 15 μm or less. The polyvinyl alcohol-based resin (hereinafter, also referred to as PVA-based resin) constituting the polarizing film has a double refractive index of 0.040 or more. The double refractive index of the PVA-based resin is an index showing the orientation of the PVA-based resin, and is a value obtained by dividing the phase difference value R _pva of the PVA-based resin by the thickness of the polarizing film. The method for measuring R _pva of the PVA-based resin and the method for calculating the birefringence index follow the description in the section of the following Examples.

The polarizing film according to the present invention in which the birefringence of the PVA-based resin is 0.040 or more is excellent in crack resistance and may be excellent in optical characteristics such as polarization characteristics. From the viewpoint of crack resistance and optical properties of the polarizing film, the birefringence of the PVA-based resin is preferably 0.041 or more, more preferably 0.042 or more, and more preferably 0.043 or more. Is even more preferable, and 0.045 or more is even more preferable. The birefringence of the PVA-based resin is usually 0.050 or less.

The birefringence of the PVA-based resin is measured as a measurement sample when the polarizing film exists as a single substance (when it exists alone). On the other hand, when a protective film or the like is bonded to the polarizing film as a polarizing plate, the protective film and the adhesive layer are removed from the polarizing plate, and the polarizing film contained in the polarizing plate is isolated. Is used as a measurement sample.

The thickness of the polarizing film is 15 μm or less, preferably 10 μm or less, and more preferably 8 μm or less, from the viewpoint of reducing the thickness of the polarizing plate. The thickness of the polarizing film is usually 2 μm or more. The smaller the thickness, the easier it is for the crack resistance to decrease. However, according to the present invention, it is possible to provide a polarizing film having good crack resistance and excellent durability even if the thickness is 15 μm or less.

The boron content of the polarizing film is preferably 3.0% by weight or more and 6.0% by weight or less. The fact that the boron content in the polarizing film is in the above range is advantageous in terms of improving the crack resistance of the polarizing film, and may also be advantageous in terms of the optical characteristics of the polarizing film. In order to exhibit excellent crack resistance or even better optical properties, the boron content in the polarizing film should be 3.5% by weight or more and 5.5% by weight or less within the above range. Is preferable, and it is more preferably 4.0% by weight or more and 5.0% by weight or less. Boron in the polarizing film is considered to exist in a free state as boric acid (H ₃ BO ₃ ), or boric acid exists in a state of forming a crosslinked structure with a unit of a PVA-based resin. The boron content is the amount of the boron atom (B) itself, including those existing in the compound state as described above.

The boron content in the polarizing film is determined by, for example, dissolving the polarizing film in pure water, adding mannitol, and titrating the obtained solution with an aqueous sodium hydroxide solution to quantify the amount of boron. , Can be calculated as a weight percentage of the amount of boron with respect to the weight of the polarizing film. Further, the amount of boron in the polarizing film can be quantified by the high frequency inductively coupled plasma (ICP) emission spectroscopy, and can be calculated as the weight percentage of boron with respect to the weight of the polarizing film.

The visible sensitivity correction single transmittance Ty of the polarizing film can be a value usually obtained in an image display device such as a liquid crystal display device to which the polarizing film or a polarizing plate containing the polarizing film is applied, and specifically, 40 to 40. It is preferably in the range of 47%. Ty is more preferably in the range of 41-45%, in which case the balance between Ty and Py is better. If Ty is too high, Py is lowered and the display quality of the image display device is lowered. When Ty is excessively low, the brightness of the image display device is lowered and the display quality is lowered, or it becomes necessary to increase the input power in order to sufficiently increase the brightness.

The luminous efficiency correction degree of polarization Py of the polarizing film is preferably 99.9% or more, and more preferably 99.95% or more.

The Ty and Py of the polarizing film are measured by themselves as a measurement sample when they exist as a single substance (when they exist alone). On the other hand, when a protective film or the like is bonded to the polarizing film as a polarizing plate, the protective film and the adhesive layer are removed from the polarizing plate, and the polarizing film contained in the polarizing plate is isolated. Is used as a measurement sample.

The polarizing film according to the present invention is a PVA-based resin film in which a dichroic dye is adsorbed and oriented, and preferably a uniaxially stretched PVA-based resin film in which a dichroic dye is adsorbed and oriented. .. As the dichroic dye, iodine or a dichroic organic dye can be used.

As the PVA-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. In addition, "(meth) acrylic" represents at least one selected from the group consisting of acrylic and methacrylic. The same applies to other terms with "(meta)".

The degree of saponification of the PVA-based resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, and more preferably in the range of 94.0 to 94.0 to 100.0 mol%. It is in the range of 100.0 mol%. When the saponification degree is less than 80.0 mol%, the water resistance of the obtained polarizing film tends to decrease. When a PVA-based resin having a saponification degree of more than 99.5 mol% is used, the dyeing rate becomes slow, the productivity is lowered, and a polarizing film having sufficient polarizing performance may not be obtained.

The degree of saponification is the ratio of the acetic acid group (acetoxy group: -OCOCH ₃ ) contained in the polyvinyl acetate resin, which is the raw material of the PVA resin, changed to a hydroxyl group by the saponification step in terms of unit ratio (mol%). The following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetic acid groups)
Defined in. The degree of saponification can be determined in accordance with JIS K 6726 (1994). The higher the degree of saponification, the higher the proportion of hydroxyl groups, and therefore the lower the proportion of acetic acid groups that inhibit crystallization.

The average degree of polymerization of the PVA-based resin is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the PVA-based resin can also be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain a polarizing film having preferable polarizing performance, and if it exceeds 10,000, the solubility in a solvent deteriorates, and it may be difficult to form a PVA-based resin film.

The polarizing film of the present invention is a step of producing a PVA-based resin film by a known method such as, for example, a melt extrusion method or a solvent casting method; a step of uniaxially stretching the PVA-based resin film; A step of adsorbing a bicolor dye by dyeing with a sex dye; a step of treating a PVA-based resin film on which the bicolor dye is adsorbed with a boric acid aqueous solution (crosslinking treatment step); and a treatment with a boric acid aqueous solution. It can be manufactured by a method including a step of washing with water later.

The uniaxial stretching of the PVA-based resin film can be performed before, simultaneously with, or after dyeing the dichroic dye. If the uniaxial stretching is performed after staining, the uniaxial stretching may be performed before the boric acid treatment or during the boric acid treatment. Further, uniaxial stretching may be performed at these a plurality of steps.

In uniaxial stretching, rolls having different peripheral speeds may be uniaxially stretched, or thermal rolls may be used to uniaxially stretch the rolls. Further, the uniaxial stretching may be a dry stretching in which the film is stretched in the atmosphere, or a wet stretching in which the PVA-based resin film is swollen with water or a solvent. The draw ratio is usually about 3 to 8 times.

As a method of dyeing the PVA-based resin film with a dichroic dye, for example, a method of immersing the dichroic dye-based resin film in an aqueous solution (dyeing bath) containing the dichroic dye is adopted. The PVA-based resin film is preferably immersed in water before the dyeing treatment.

When iodine is used as the dichroic dye, the PVA-based resin film is usually immersed in a dyeing bath containing iodine and potassium iodide, and the PVA-based resin is dyed with iodine. The iodine content in this dyeing bath can be about 0.003 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide can be about 0.15 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing bath can be about 10 to 45 ° C.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing a PVA-based resin film in a dyeing bath containing a water-soluble dichroic organic dye and dyeing is usually adopted. The content of the dichroic organic dye in the dyeing bath is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-3 to 1 part by weight per 100 parts by weight of water. This dyeing bath may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dyeing bath is usually about 20 to 80 ° C.

In the step of treating the PVA-based resin film on which the dichroic dye is adsorbed with the boric acid aqueous solution, the PVA-based resin film on which the dichroic dye is adsorbed is usually immersed in the boric acid aqueous solution (bridge bath). As the boric acid source contained in the boric acid aqueous solution, a boron compound such as boric acid or borax is used. Further, a cross-linking agent such as glyoxal or glutaraldehyde may be used together with the boron compound. Water can be used as the solvent of the boric acid aqueous solution, but an organic solvent compatible with water may be further contained. In order to adjust the birefringence of the PVA-based resin of the polarizing film to 0.040 or more, the concentration of boric acid in the boric acid aqueous solution should be 3 to 8% by weight, and the immersion time in the cross-linking bath should be adjusted as appropriate. It is more preferable that the concentration of boric acid is 4 to 7% by weight and the immersion time in the cross-linking bath is appropriately adjusted.

The boric acid aqueous solution can further contain iodide. By adding iodide, the in-plane polarization performance of the polarizing film can be made more uniform. Specific examples of iodide are the same as above. The concentration of iodide in the boric acid aqueous solution is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight.

The cross-linking treatment with an aqueous boric acid solution is usually carried out at a temperature of 40 to 80 ° C, preferably 50 to 70 ° C. If the temperature is too low, the progress of the crosslinking reaction tends to be insufficient, while if the temperature is too high, the film tends to be cut in the crosslinking bath, and the processing stability tends to be significantly lowered. The time for the crosslinking treatment is usually 10 to 600 seconds, preferably 60 to 420 seconds, and more preferably 90 to 300 seconds.

The cross-linking treatment can also be performed at the same time as the dyeing treatment by blending the boron compound in the dyeing bath. Further, the treatment of immersing in the cross-linking bath may be performed twice or more by using two or more kinds of cross-linking baths having different compositions.

The PVA-based resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing the boric acid-treated PVA-based resin film in water. The temperature of water in the washing treatment is usually about 2 to 40 ° C. The immersion time is usually about 1 to 120 seconds.

After washing with water, it is dried to obtain a polarizing film. The drying process can be performed using a hot air dryer or a far infrared heater.

The polarizing film of the present invention may be produced by using a PVA-based resin layer and a base film for supporting the polarizing film. This method is described in, for example, Japanese Patent Application Laid-Open No. 2012-103466. In this case, the polarizing film is, for example, the following step:
A resin layer forming step of applying a coating liquid containing a PVA-based resin to at least one surface of a base film and then drying to form a PVA-based resin layer to obtain a laminated film.
Stretching step of uniaxially stretching a laminated film to obtain a stretched film,
It can be produced by a method including a dyeing step of obtaining a polarizing laminated film by dyeing a PVA-based resin layer of a stretched film with a dichroic dye to form a polarizing film. After the dyeing step, a protective film is attached to the outer surface of the polarizing film, and then the base film is peeled off to obtain a polarizing plate containing the polarizing film and the protective film. The method using the base film as described above is advantageous in obtaining a thin-film polarizing film and a polarizing plate.

(2) Polarizing Plate FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate according to the present invention. Like the polarizing plate 1 shown in FIG. 1, the polarizing plate according to the present invention is a polarizing film 5 according to the present invention and a first protective film laminated on one surface of the polarizing film 5 via a first adhesive layer 15. It can be a polarizing plate with a double-sided protective film including 10 and a second protective film 20 laminated on the other surface via a second adhesive layer 25. The polarizing plate 1 may further have another optical layer, an adhesive layer, or the like laminated on the first protective film 10 and / or the second protective film 20.

Further, the polarizing plate according to the present invention is, like the polarizing plate 2 shown in FIG. 2, a first laminated film 5 according to the present invention and one surface thereof via a first adhesive layer 15. A polarizing plate with a single-sided protective film including the protective film 10 may be used. The polarizing plate 2 may further have another optical layer (or optical film), an adhesive layer, or the like laminated on the first protective film 10 and / or the polarizing film 5.

Since the polarizing plate according to the present invention includes the polarizing film 5 having excellent crack resistance according to the present invention, it is excellent in durability and may be excellent in optical characteristics such as polarization characteristics. ..

As another optical layer (or optical film), a reflective polarizing film that transmits a certain kind of polarized light and reflects polarized light having the opposite property; a film with an antiglare function having an uneven shape on the surface; a surface. Examples include a film with an antireflection function; a reflective film having a reflective function on the surface; a semi-transmissive reflective film having both a reflective function and a transmissive function; a viewing angle compensating film and the like.

The first and second protective films 10 and 20, respectively, are translucent (preferably optically transparent) thermoplastic resins such as chain polyolefin resins (polypropylene resins and the like) and cyclic polyolefin resins (preferably optically transparent). Polyethylene-based resins such as norbornene-based resins); cellulose ester-based resins such as triacetyl cellulose and diacetyl cellulose; polyester-based resins; polycarbonate-based resins; (meth) acrylic-based resins; polystyrene-based resins; or mixtures thereof. It can be a film made of a copolymer or the like. The first protective film 10 and the second protective film 20 may be the same type of protective film as each other, or may be different types of protective films.

The first and / or the second protective films 10 and 20 may be protective films having optical functions such as a retardation film and a luminance improving film. For example, a retardation film to which an arbitrary retardation value is imparted by stretching a film made of the thermoplastic resin (uniaxial stretching or biaxial stretching, etc.) or forming a liquid crystal layer or the like on the film. Can be.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resin and polypropylene resin, and copolymers composed of two or more kinds of chain olefins.

Cyclic polyolefin resin is a general term for resins that are polymerized with cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin resin include a ring-opened (co) polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymer of a cyclic olefin and a chain olefin such as ethylene or propylene (typically). Is a random copolymer), a graft polymer obtained by modifying these with an unsaturated carboxylic acid or a derivative thereof, and a hydride thereof. Among them, a norbornene-based resin using a norbornene-based monomer such as a norbornene or a polycyclic norbornene-based monomer is preferably used as the cyclic olefin.

Cellulose ester-based resins are esters of cellulose and fatty acids. Specific examples of the cellulose ester resin include triacetyl cellulose (TAC) and diacetyl cellulose. Further, these copolymers or those in which a part of the hydroxyl group is modified with another substituent can also be used. Of these, TAC is particularly preferable.

The polyester-based resin is a resin other than the above-mentioned cellulose ester-based resin having an ester bond, and is generally composed of a polyvalent carboxylic acid or a derivative thereof and a polycondensate of a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethylterephthalate, and dimethyl naphthalenedicarboxylate. As the polyhydric alcohol, diol can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol and the like.

Specific examples of the polyester-based resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexanedimethylterephthalate, and polycyclohexanedimethylnaphthalate.

The polycarbonate-based resin is composed of a polymer in which a monomer unit is bonded via a carbonate group. The polycarbonate-based resin may be a resin called modified polycarbonate having a modified polymer skeleton, a copolymerized polycarbonate, or the like.

The (meth) acrylic resin is a resin containing a compound having a (meth) acryloyl group as a main constituent monomer. Specific examples of the (meth) acrylic resin include poly (meth) acrylic acid esters such as polymethyl methacrylate; methyl methacrylate- (meth) acrylic acid copolymers; methyl methacrylate- (meth) acrylic acids. Ester copolymer; Methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymer; (meth) methyl acrylate-styrene copolymer (MS resin, etc.); Methyl methacrylate and alicyclic hydrocarbon group It contains a copolymer with a compound having (for example, a methyl methacrylate-cyclohexyl methacrylate copolymer, a methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.). A polymer containing a poly (meth) acrylic acid C _1-6 alkyl ester as a main component, such as methyl poly (meth) acrylate, is preferably used, and more preferably, a polymer containing methyl methacrylate as a main component (50 to 100) is used. A methyl methacrylate-based resin having a weight of% by weight, preferably 70 to 100% by weight) is used.

On the surface of the first and / or second protective films 10 and 20 opposite to the polarizing film 5, a surface treatment layer such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer (Coating layer) can also be formed.

The thicknesses of the first and second protective films 10 and 20 are preferably 90 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less, from the viewpoint of reducing the thickness of the polarizing plates 1 and 2. The thickness is usually 5 μm or more from the viewpoint of strength and handleability.

(3) As the adhesive forming the first and second adhesive layers 15 and 25, a water-based adhesive or an active energy ray-curable adhesive can be used. The adhesive forming the first adhesive layer 15 and the adhesive forming the second adhesive layer 25 may be of the same type or different types.

Examples of the water-based adhesive include an adhesive made of a polyvinyl alcohol-based resin aqueous solution, a water-based two-component urethane-based emulsion adhesive, and the like. Of these, a water-based adhesive composed of an aqueous solution of polyvinyl alcohol-based resin is preferably used.

The polyvinyl alcohol-based resin used for the water-based adhesive includes vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, and vinyl acetate and other simple polymers capable of copolymerizing with it. A polyvinyl alcohol-based polymer obtained by saponifying a copolymer with a weight, a modified polyvinyl alcohol-based polymer in which the hydroxyl groups thereof are partially modified, or the like can be used. The water-based adhesive may contain additives such as polyhydric aldehydes, water-soluble epoxy compounds, melamine-based compounds, zirconia compounds, and zinc compounds.

When a water-based adhesive is used, it is preferable to carry out a drying step in which the polarizing film 5 and the protective film are bonded together and then dried in order to remove water contained in the water-based adhesive. After the drying step, a curing step of curing at a temperature of, for example, about 20 to 45 ° C. may be provided.

The active energy ray-curable adhesive means an adhesive that cures by irradiating with an active energy ray such as ultraviolet rays, and includes, for example, a polymerizable compound and a photopolymerization initiator, and a photoreactive resin. Those containing a binder resin and a photoreactive cross-linking agent, and the like can be mentioned. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy-based monomers, photocurable (meth) acrylic-based monomers, and photocurable urethane-based monomers, and oligomers derived from photopolymerizable monomers. can. Examples of the photopolymerization initiator include substances that generate active species such as neutral radicals, anionic radicals, and cationic radicals when irradiated with active energy rays such as ultraviolet rays. As the active energy ray-curable adhesive containing a polymerizable compound and a photopolymerization initiator, those containing a photocurable epoxy monomer and a photocationic polymerization initiator can be preferably used.

When an active energy ray-curable adhesive is used, the polarizing film 5 and the protective film are bonded together, and if necessary, a drying step is performed, and then the active energy ray-curable adhesive is irradiated. Perform a curing step to cure the energy. The light source of the active energy ray is not particularly limited, but ultraviolet rays having a emission distribution having a wavelength of 400 nm or less are preferable, and specifically, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, and a micro. A wave-excited mercury lamp, a metal halide lamp, or the like can be used.

By laminating the first protective film 10 to one side of the polarizing film 5 via the first adhesive layer 15 according to a conventional method, the polarizing plate 2 with the single-sided protective film shown in FIG. 2 can be obtained. If the second protective film 20 is attached to the other surface of the polarizing film 5 via the second adhesive layer 25, the polarizing plate 1 with the double-sided protective film shown in FIG. 1 can be obtained. When obtaining the polarizing plate 1 with the double-sided protective film, the first and second protective films 10 and 20 may be bonded at the same time or sequentially.

The polarizing plate is applied to another member (for example, a liquid crystal display device) on the first protective film 10 or the second protective film 20 in the polarizing plate 1 shown in FIG. 1 and on the polarizing film 5 in the polarizing plate 2 shown in FIG. A pressure-sensitive adhesive layer for bonding to the liquid crystal cell) may be laminated. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually based on a (meth) acrylic resin, a styrene-based resin, a silicone-based resin, or the like, and a cross-linking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. It consists of a pressure-sensitive adhesive composition. Further, it can be used as a pressure-sensitive adhesive layer containing fine particles and exhibiting light scattering properties. The thickness of the pressure-sensitive adhesive layer can be 1 to 40 μm, but it is preferably formed thin as long as the characteristics of processability and durability are not impaired, and specifically, it is preferably 3 to 25 μm.

The method for forming the pressure-sensitive adhesive layer is not particularly limited, and a pressure-sensitive adhesive composition (adhesive solution) containing each component including the above-mentioned base polymer is applied to the protective film surface or the polarizing film surface. The pressure-sensitive adhesive layer may be formed by drying to form a pressure-sensitive adhesive layer, or the pressure-sensitive adhesive layer may be transferred to a protective film surface or a polarizing film surface after forming the pressure-sensitive adhesive layer on a separator (release film). When the pressure-sensitive adhesive layer is formed on the protective film surface or the polarizing film surface, the protective film surface or the polarizing film surface, or one or both sides of the pressure-sensitive adhesive layer may be subjected to surface treatment, for example, corona treatment, if necessary. good.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples. In the following example, the thickness of the polarizing film was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

<Example 1>
[Preparation of polarizing film]
An unstretched polyvinyl alcohol film [“VF-PE # 3000” manufactured by Kuraray Co., Ltd.] having an average degree of polymerization of about 2400 and a degree of polymerization of 99.9 mol% and a thickness of 30 μm is immersed in pure water at 20 ° C. The dyeing treatment was carried out by immersing the film in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 1/2/100 at 30 ° C. for 75 seconds. Then, it is immersed in an aqueous solution having a potassium iodide / boric acid / water weight ratio of 12/4/100 at 56.5 ° C. for 55 seconds, followed by a potassium iodide / boric acid / water weight ratio of 9/3. It was treated with boric acid by immersing it in a / 100 aqueous solution at 40 ° C. for 10 seconds. Subsequently, the film was washed with pure water at 5 ° C. and then dried at 60 ° C. to prepare a polarizing film having a thickness of about 13 μm in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. The uniaxial stretching was mainly carried out in the steps of iodine staining and boric acid treatment. The draw ratio based on the unstretched polyvinyl alcohol film was 5.4 times.

[Preparation of polarizing plate]
Between the obtained polarizing film and the first protective film [TAC film "KC2UAW" manufactured by Konica Minolta Opto Co., Ltd., thickness: 25 μm], and between the polarizing film and the second protective film [Cyclic polyolefin manufactured by JSR Co., Ltd.] A water-based adhesive is injected between the film and the product name "FEKB015D3" (thickness: 15 μm), which is a based resin film, and bonded to each other, and the first protective film / water-based adhesive / polarizing film / water-based adhesive / second protection is applied. A laminated film made of a film was obtained. The obtained laminated film was passed through a hot air dryer and heat-treated at 60 ° C. for 120 seconds to dry the water-based adhesive to obtain a polarizing plate. The above water-based adhesive has a concentration of 3 weight obtained by dissolving polyvinyl alcohol powder [trade name "Gosefimer" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization 1100] in hot water at 95 ° C. An aqueous solution prepared by mixing a cross-linking agent [sodium glyoxylate manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] with 10 parts by weight of polyvinyl alcohol powder at a ratio of 2.5 parts by weight with 10 parts by weight of polyvinyl alcohol powder was used.

<Example 2>
Immerse in an aqueous solution with a potassium iodide / boric acid / water weight ratio of 12/6/100 at 56.5 ° C. for 55 seconds, followed by a potassium iodide / boric acid / water weight ratio of 9/6/100. A polarizing film and a polarizing plate were prepared in the same manner as in Example 1 except that the boric acid treatment was carried out by immersing the mixture in the aqueous solution of No. 1 at 40 ° C. for 10 seconds.

<Example 3>
Immerse in an aqueous solution with a potassium iodide / boric acid / water weight ratio of 12/5/100 at 56.5 ° C. for 55 seconds, followed by a potassium iodide / boric acid / water weight ratio of 9/5/100. The polarizing film and the polarizing film were prepared in the same manner as in Example 1 except that the boric acid treatment was performed by immersing the solution in the aqueous solution of No. 1 at 40 ° C. for 10 seconds to set the stretching ratio based on the unstretched polyvinyl alcohol film to 5.3 times. A polarizing plate was prepared.

<Example 4>
An unstretched polyvinyl alcohol film [“VF-PE # 2000” manufactured by Kuraray Co., Ltd.] having an average degree of polymerization of about 2400 and a degree of saponification of 99.9 mol% and a thickness of 20 μm was uniaxially stretched about 4 times by a dry method. After immersing in pure water at 40 ° C while maintaining a tense state, the dyeing treatment is performed by immersing in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.1 / 5/100 at 28 ° C for 60 seconds. Then, the mixture was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 10.5 / 7.5 / 100 at 64 ° C. for 300 seconds, subsequently washed with pure water at 5 ° C., and then at 40 ° C. A drying treatment was carried out to prepare a polarizing film having a thickness of about 7 μm in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film, and a polarizing plate was prepared by the same method as in Example 1.

<Comparative Example 1>
Immerse in an aqueous solution with a potassium iodide / boric acid / water weight ratio of 12 / 1.5 / 100 at 56.5 ° C. for 55 seconds, followed by a potassium iodide / boric acid / water weight ratio of 9/1. A polarizing film and a polarizing plate were prepared in the same manner as in Example 1 except that the boric acid treatment was carried out by immersing the mixture in a 5/100 aqueous solution at 40 ° C. for 10 seconds.

<Comparative Example 2>
Immerse in an aqueous solution with a potassium iodide / boric acid / water weight ratio of 12/1/100 at 56.5 ° C. for 55 seconds, followed by a potassium iodide / boric acid / water weight ratio of 9/1/100. A polarizing film and a polarizing plate were prepared in the same manner as in Example 1 except that the boric acid treatment was carried out by immersing the mixture in the aqueous solution of No. 1 at 40 ° C. for 10 seconds.

[Measurement of optical characteristics of polarizing film]
(1) Measurement of the double refractive index of polyvinyl alcohol-based resin For the obtained polarizing film, the phase difference measurement of iodine phase difference value _{Ri and polyvinyl alcohol phase difference value R pva at} a wavelength of 1000 nm (unit: nm). The measurement was performed using an apparatus [“KOBRA-WR0 / IR” manufactured by Oji Measuring Instruments Co., Ltd.). Specifically, it is as follows.

_{Ri and R pva are} obtained by measuring the phase difference value in the wavelength region where there is no absorption band of iodine. Specifically, the phase difference measuring device is used to measure the phase difference value at a plurality of wavelengths λ having a wavelength of 850 nm or more. Plot the measured phase difference value R (λ) at each wavelength λ, and plot this with the following Selmeyer equation:
R (λ) = A + B / (λ ^{2-600 2 )}
Is fitted by the method of least squares. Here, A and B are fitting parameters and are coefficients determined by the least squares method.

At this time, the phase difference value R (λ) can be separated into a phase difference value R _pva of polyvinyl alcohol (PVA) having no wavelength dependence and a phase difference value R _i of iodine having a strong wavelength dependence. R _pva and R _i are the following formulas, respectively:
R _pva = A
R _i = B / (λ ^{2-600 2 )}
It is represented by. Based on these equations, the value of R _pva at the wavelength λ = 1000 nm was calculated.

The film thickness of the portion where R _pva was measured was measured with a contact type film thickness meter [“DIGIMICRO MH-15M” manufactured by Nikon Corporation].

Using the obtained R _pva and film thickness values, the following formula:
Birefringence = R _pva (nm) / film thickness (nm)
The birefringence index derived from the polyvinyl alcohol (PVA) -based resin was calculated from. The results are shown in Table 1.

(2) Measurement of Luminosity Factor Correction Single Transmittance Ty and Luminosity Factor Correction Polarity Py A test piece having a size of about 30 mm in length × about 30 mm in width was cut out from the obtained polarizing film to prepare a measurement sample. The unit transmittance and the degree of polarization of the obtained measurement sample were measured. The results are shown in Table 1. Elemental transmittance and degree of polarization are based on the following definitions and measurement methods.

The simple substance transmittance and the degree of polarization are as follows:
Elemental transmittance (λ) = 0.5 × (Tp (λ) + Tc (λ))
Degree of polarization (λ) = 100 × (Tp (λ) -Tc (λ)) / (Tp (λ) + Tc (λ))
Defined in.

Tp (λ) is the transmittance (%) of the polarizing film measured in relation to the incident linear polarization at the wavelength λ nm and parallel Nicol, and Tc (λ) is the relationship between the incident linear polarization at the wavelength λ nm and cross Nicol. It is the transmittance (%) of the polarizing film measured in. However, the single transmittance (λ) and the degree of polarization (λ) obtained for each wavelength are subjected to the visual sensitivity correction, and the visual sensitivity correction single transmittance (Ty) and the visual sensitivity correction polarization degree (Py) are obtained, respectively. ), And the single transmittance and the degree of polarization in the present specification refer to the visual sensitivity correction single transmittance (Ty) and the visual sensitivity correction polarization degree (Py), respectively. Ty and Py were measured using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation] equipped with a C light source.

[Measurement of boron content of polarizing film]
About 0.2 g of the polarizing film was added to 170 ml of pure water and completely dissolved at 95 ° C., and then 30 g of an aqueous mannitol solution (12.5% by weight) was added to prepare a sample solution for measurement. An aqueous sodium hydroxide solution (1 mol / l) was dropped until the sample solution for measurement reached the neutralization point, and the boron content (% by weight) in the polyvinyl alcohol film was calculated from the dropping amount from the following formula.
Boron content = 1.08 x sodium hydroxide aqueous solution dropping amount (ml) / weight of polarizing film (g)
The results are shown in Table 1.

[Evaluation of crack resistance of polarizing plate]
The obtained polarizing plate was cut out at 6 cm in the absorption axis direction of the polarizing plate and 8 cm in the transmission axis direction of the polarizing film to prepare a sample for evaluation. The evaluation sample was placed in an oven set at 80 ° C. (dry) for 1 hour, then the sample was taken out and allowed to stand for 15 minutes in an environment of 23 ° C. and 55% RH. Then, the sample was immersed in tap water at room temperature for 30 minutes, and then the number of cracks generated at the end of the sample was visually observed. The results are shown in Table 1.

1, 2, polarizing plate, 5 polarizing film, 10 first protective film, 15 first adhesive layer, 20 second protective film, 25 second adhesive layer.

Claims (2)

A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film.
The thickness is 15 μm or less, the birefringence of the polyvinyl alcohol-based resin is 0.042 or more and 0.045 or less.
Luminosity factor correction polarization degree Py is 99.9% or more,
Luminosity factor correction single transmittance Ty is 42.9% or more and 43.7 % or less.
A polarizing film having a boron content of 3.8 % by weight or more and 4.7% by weight or less. The polarizing film according to claim 1 and
A protective film laminated on at least one surface of the polarizing film and
A polarizing plate including.

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