JP2007328252A - Polarizing film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polarizing films which are excellent in hue and with which the leakage of blue light is almost suppressed when a pair of the polarizing films are allowed to cross orthogonally so as to be set into a cross Nicol state and the leakage of yellow light is almost suppressed when a pair of the polarizing films are arranged parallelly so as to be set into a parallel Nicol state. <P>SOLUTION: The polarizing film includes cracks. The sizes of the cracks are 5-25 μm, and the number of cracks per 100 μm<SP>2</SP>areas of the polarizing film is 2-15. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarizing film and a method for producing the same. More specifically, the present invention relates to a polarizing film having improved hue and a method for producing the same.

  A polarizing plate having a light transmission and shielding function is an important component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The application fields of this liquid crystal display device are also from small devices such as calculators and wristwatches in the early stages of development, in recent years to notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, indoors and outdoors. It has spread to a wide range of measuring instruments and the like, and especially for liquid crystal televisions and the like, the screen is becoming larger. With the expansion of the use of liquid crystal display devices, there is an increasing demand for higher display quality, that is, improved color reproducibility. In addition to the optical characteristics such as high polarization, high polarization, and high transmittance, improvement in hue is strongly demanded.

  Conventionally used polarizing plates are generally a method of uniaxially stretching a polyvinyl alcohol film and then dyeing with iodine or a dichroic dye, a method of dyeing and uniaxially stretching and then fixing with a boron compound, In any of the methods, a polarizing film manufactured by a method of performing a fixing process simultaneously with dyeing or the like has a configuration in which a protective film such as a cellulose triacetate film or an acetic acid / butyric acid cellulose film is bonded to one side or both sides.

In particular, a polarizing film dyed with iodine has a high light transmittance and degree of polarization, a high dichroic ratio, and high contrast. Therefore, in producing a polarizing plate for a liquid crystal display device, a polarizing film dyed with iodine is generally used. However, in a polarizing film dyed with iodine, it is said that a complex of PVA and iodine exists in two types of ionic forms, I ₃ ⁻ and I ₅ ⁻ , and the hue of the polarizing film is in a completely neutral gray state. It is difficult. For this reason, the phenomenon of light leakage of a specific wavelength is likely to occur, in particular, the phenomenon of light leakage of blue light is likely to occur, and the hue is poor.

  For improving the hue in the polarizing film using iodine, the method of adding zinc chloride in the polarizing film manufacturing process (Patent Documents 1 and 2) is well known, but the study is limited to the reduction of red, Sufficient investigation has not been made on the target light leakage of blue light in the present invention.

  Moreover, although the method (patent documents 3-8) which improves a hue by devising the manufacturing conditions of a polarizing film is reported, all methods balance the production amount of two types of ion forms of an iodine complex. In particular, the hue of the polarizing film has not yet reached a completely neutral gray state.

JP 54-16575 A Japanese Patent Laid-Open No. 61-175602 JP-A-8-304624 JP 2001-91736 A JP 2002-22950 A JP 2002-174728 A JP 2002-214436 A JP 2002-258043 A

  The object of the present invention is excellent in hue, there is little light leakage of blue light when two polarizing films are orthogonally crossed to make a crossed Nicol state, and two polarizing films are stacked in parallel to form a parallel Nicol state It is in providing the polarizing film which has the outstanding performance that there is little yellow coloring when making it, and its manufacturing method.

As a result of intensive studies, the present inventors have found that a polarizing film containing cracks has less leakage of blue light when two sheets are orthogonally crossed to form a crossed Nicol state, and two sheets are stacked in parallel to form a parallel Nicol state. As a result, the present invention was completed by finding out that it has excellent properties such as little yellow coloring.
That is, the present invention provides a polarizing film containing cracks.

  The polarizing film of the present invention makes use of the property of being excellent in hue, and is a calculator, wristwatch, notebook computer, liquid crystal monitor, liquid crystal color projector, liquid crystal television, in-vehicle navigation system, mobile phone, measuring device used indoors and outdoors. It can be effectively used for the production of a polarizing plate which is a component of a liquid crystal display device such as, and is useful as a raw material for a polarizing plate for a liquid crystal monitor or liquid crystal television that requires particularly high color reproducibility.

The present invention is described in detail below.
First, the crack referred to in the present invention is a minute gap existing in the polarizing film and does not penetrate in the thickness direction of the polarizing film. This crack is caused by stretching a polyvinyl alcohol film in which particulate matter of a water-soluble inorganic salt is dispersed (hereinafter, “polyvinyl alcohol film” may be abbreviated as “PVA film”) or water-soluble inorganic salt. It can be formed in a polarizing film by immersing a PVA film in which salt particulates are dispersed in water, eluting the water-soluble inorganic salt and then stretching.

  In the present invention, the size of the crack is preferably 5 to 25 μm, more preferably 8 to 20 μm, and particularly preferably 10 to 16 μm. Since the effect of improving the hue is less likely to be exhibited as the crack is smaller, it is not preferable that the crack is smaller than 5 μm. Moreover, since the fall of the transmittance | permeability of a polarizing film becomes so large that a crack is large and the quality as a polarizing film falls, it is not preferable that it is larger than 25 micrometers. In order to control the size of the crack, there are a method of changing the amount of the water-soluble inorganic salt added, a method of changing the stretch ratio of the PVA film when manufacturing the polarizing film, and the like.

  The number of cracks present in the polarizing film of the present invention is preferably 2-15, more preferably 3-10, more preferably 4-8 per 100 square μm area of the polarizing film. Particularly preferred. The smaller the number of cracks, the more difficult the hue improving effect is exhibited. Moreover, since the fall of the transmittance | permeability of a polarizing film becomes so large that the number of cracks is large and the quality as a polarizing film falls, it is not preferable that the number of cracks is more than 15. The number of cracks can be controlled by adjusting the type and / or addition amount of the water-soluble inorganic salt, and the apparent number of cracks by changing the draw ratio of the PVA film when manufacturing a polarizing film. Therefore, it is preferable to implement these methods in combination as appropriate.

  Polyvinyl alcohol used in the present invention (hereinafter, polyvinyl alcohol may be abbreviated as “PVA”) is vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate. It is obtained by saponifying a polyvinyl ester obtained by polymerization using one or two vinyl esters such as vinyl stearate and vinyl benzoate. In particular, PVA obtained by using vinyl acetate as a vinyl ester is preferably used from the viewpoints of ease of production, availability, cost, and the like.

A typical example of PVA that can be used in the present invention is a saponified product of a vinyl ester homopolymer (PVA homopolymer). However, the PVA used in the PVA film of the present invention is not limited to a saponified product of a vinyl ester homopolymer. If the effects of the present invention are not impaired, a modified PVA polymer or vinyl ester is used as the PVA polymer. Further, a saponified product of a copolymer of a small amount of other copolymerizable monomers, a polyvinyl acetal polymer obtained by crosslinking a part of hydroxyl groups of a PVA polymer, and the like can also be used.
Among them, examples of the modified PVA polymer include graft copolymerization of unsaturated carboxylic acid or a derivative thereof, unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, and the like at a ratio of less than 5 mol%. Examples thereof include a modified PVA polymer produced by saponifying a modified polyvinyl ester, and an unmodified or modified PVA polymer.

  Examples of other copolymerizable monomers that can be used for the production of a saponified product of a copolymer of vinyl ester and a small amount of other copolymerizable monomers include, for example, ethylene, propylene, 1-butene, isobutene, Other C2-C30 α-olefins; (meth) acrylic acid and salts thereof; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (meth) acrylic acid i-propyl, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, ( (Meth) acrylic acid esters such as (meth) acrylic acid octadecyl; (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid and its salt, (meth) acrylamidopropyldimethylamine and its salt, N-methylol (meth) acrylamide and its derivatives, etc. (Meth) acrylamide derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i- Vinyl ethers such as butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and salts thereof or esters thereof; itaconic acid and salts thereof or esters thereof A vinylsilyl compound such as vinyltrimethoxysilane; isopropenyl acetate; an unsaturated sulfonic acid; The PVA polymer used in the present invention can have a structural unit derived from one or more of the other polymerizable monomers described above.

When PVA is a saponified product of a copolymer of vinyl ester and another copolymerizable monomer, the proportion of structural units derived from the other copolymerizable monomer constitutes the PVA polymer. It is preferably 15 mol% or less, preferably 10 mol% or less, more preferably 5 mol% or less based on the total structural units.
In particular, when the other copolymerizable monomer is a monomer that promotes water solubility of the PVA polymer, such as (meth) acrylic acid or sulfonic acid, the polarizing film is changed from the PVA film. In order to prevent the film from being dissolved or melted during the treatment in an aqueous solution during production, the polymerization rate of the water-soluble monomer is preferably 5 mol% or less, particularly 3 mol% or less.

  In this invention, it is preferable that the polymerization degree of PVA is 2000 or more from the point of the polarization performance of a polarizing film. If the degree of polymerization of PVA is less than 2000, the polarizing performance of the polarizing film obtained from the PVA film will not be good, and the degree of light leakage will be greatly increased. Therefore, it should be applied to liquid crystal display devices such as liquid crystal televisions. It becomes difficult. The higher the degree of polymerization of PVA, the better the polarizing performance of the resulting polarizing film. Therefore, increasing the degree of polymerization has a certain effect on reducing the degree of light leakage. If the polymerization degree of PVA is too high, the production cost of PVA is likely to increase, poor process passability during film formation, and the like. Therefore, the polymerization degree of PVA is preferably 2000 to 10000, preferably 2000 to 8000. More preferably, it is more preferably 2200 to 5000. In addition, the polymerization degree of PVA as used in this specification means the polymerization degree measured by the method according to description of JISK6726.

Furthermore, in the present invention, the degree of saponification of PVA is preferably 99.0 mol% or more, more preferably 99.9 mol% or more, and particularly preferably 99.95% or more. In order to facilitate the formation of water-soluble inorganic salt particles, the higher the degree of saponification, the better. When the degree of saponification of PVA is lower than 99.0 mol%, it tends to be difficult to form water-soluble inorganic salt particles.
In the present specification, the degree of saponification of PVA is the total number of moles of units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification among the structural units constituting the polymer. The ratio (mol%) of the unit actually saponified to the vinyl alcohol unit. The degree of saponification can be measured according to the method described in JIS K6726.

In the present invention, the water-soluble inorganic salt does not bleed out on the surface of the PVA film, but needs to be incorporated into the PVA film and aggregate to form particulate matter. Nitrate, nitrite, carbonate, borate, sulfate, phosphate, monohydrogen phosphate, dihydrogen phosphate, oxide and the like. The water-soluble inorganic salt can be used alone or in combination of two or more.
When a polarizing film is produced using a PVA film in which particulate matter of a water-soluble inorganic salt is dispersed, if the water-soluble inorganic salt remains in the polarizing film, it may cause deterioration of durability and the like. In the production process of the polarizing film, it is preferable to quickly elute from the PVA film. From this point, magnesium nitrate is particularly preferable as the water-soluble inorganic salt.

  The content of the water-soluble inorganic salt in the PVA film is preferably 3 to 30% by weight, and more preferably 5 to 20% by weight. If the content of the water-soluble inorganic salt is less than 3% by weight, the effect of improving the hue of a polarizing film produced using a PVA film tends to be difficult to be exhibited, which is not preferable. Moreover, when there is more content of water-soluble inorganic salt than 30 weight%, since there exists a tendency for the fall of the transmittance | permeability of a polarizing film to become large, it is unpreferable.

  In the present invention, the average particle size of the water-soluble inorganic salt particles dispersed in the PVA film is preferably 1 to 5 μm, particularly preferably 2 to 3 μm. If the average particle size is smaller than 1 μm, the effect of improving the hue of a polarizing film produced using a PVA film tends to be difficult to be exhibited, which is not preferable. On the other hand, if the average particle size is larger than 5 μm, the decrease in the transmittance of the polarizing film tends to increase, such being undesirable. The average particle diameter of the particulate matter of the water-soluble inorganic salt is determined by selecting the type of the water-soluble inorganic salt, or the viscosity and concentration of the raw film forming solution when producing the PVA film, and further, the PVA film after film formation It can be controlled by adjusting the drying temperature. These methods can be implemented in combination as appropriate.

  The number of water-soluble inorganic salt particulates dispersed in the PVA film is preferably 2 to 15 and more preferably 5 to 10 per 100 square μm area of the PVA film. When the number of the particulate matter is less than 2, it is not preferable because the effect of improving the hue of the polarizing film produced using the PVA film tends to be hardly exhibited. On the other hand, when the number of the particulate matter is more than 15, it is not preferable because there is a tendency that the transmittance decreases when the polarizing film is formed. The number of water-soluble inorganic salt particles can be determined by selecting the type of water-soluble inorganic salt, or the viscosity and concentration of the raw film forming solution when producing a PVA film, and the drying temperature of the PVA film after film formation. It can be controlled by adjusting. These methods can be implemented in combination as appropriate.

  In the present invention, it is desirable that the PVA film contains a plasticizer together with the above-described PVA and water-soluble inorganic salt. By containing a plasticizer, the PVA film can be stretched when a polarizing film is produced from the PVA film. Improvements can be made. As the plasticizer, polyhydric alcohol is preferably used, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. 1 type (s) or 2 or more types can be contained. Among these, glycerin is preferably used because the stretchability of the PVA film becomes better.

  The addition amount of the plasticizer is preferably 3 to 20 parts by mass, more preferably 5 to 15 parts by mass, and particularly preferably 7 to 12 parts by mass with respect to 100 parts by mass of PVA. If the added amount of the plasticizer is small, the stretchability of the PVA film becomes poor and it becomes difficult to produce the polarizing film smoothly. On the other hand, if the added amount of the plasticizer is too large, the plasticizer bleeds out on the surface of the PVA film. As a result, the handleability of the PVA film is lowered.

  Moreover, the PVA film may contain an antioxidant, an antifreezing agent, a pH adjuster, a concealing agent, a coloring inhibitor, an oil agent, and the like as necessary.

  The thickness of the PVA film is not particularly limited, but is generally 20 to 120 μm, more preferably 30 to 100 μm, and particularly preferably about 40 to 80 μm. When the PVA film is too thin, stretching breakage is likely to occur during the uniaxial stretching process for producing the polarizing film, and it becomes difficult to obtain a polarizing film having excellent polarizing performance. Moreover, when a PVA film is too thick, it will become easy to generate | occur | produce a stretching spot at the time of the uniaxial stretching process for manufacturing a polarizing film.

  The width | variety in particular of a PVA film is not restrict | limited, It can determine according to the use etc. of the polarizing film manufactured from a PVA film. In recent years, the enlargement of screens of liquid crystal televisions and monitors has progressed. From this point of view, if the width of the PVA film is 3 m or more, it is suitable for these applications. On the other hand, if the width of the PVA film is too large, it is difficult to uniformly carry out uniaxial stretching itself when a polarizing plate is produced with a device that has been put to practical use, so the width of the PVA film is 6 m or less. Is preferred.

  In the present invention, the production method of the PVA film is not particularly limited. In the case where the PVA film forming stock solution is uniformly mixed with PVA and a water-soluble inorganic salt, and further contains a plasticizer and other additives. Any of the known methods can be used as long as these components are uniformly mixed and the thickness and width after film formation are as uniform as possible and can be suitably used for the production of a polarizing film. You may manufacture by the method of.

  Examples of the solvent used for the preparation of the film-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and triethylene glycol. Examples thereof include methylolpropane, ethylenediamine, and diethylenetriamine, and one or more of these can be used. Among these, water is preferably used from the viewpoint of load on the environment and recoverability.

  The volatile fraction of the film-forming stock solution containing PVA (content ratio of volatile components such as a solvent removed by volatilization or evaporation during film formation) varies depending on the film-forming method, film-forming conditions, etc. It is preferably 50 to 95% by mass, more preferably 55 to 90% by mass, and particularly preferably 60 to 85% by mass. If the volatile fraction of the film-forming stock solution is too low, the viscosity of the film-forming stock solution will be too high, making filtration and defoaming difficult when preparing the stock solution, and making it difficult to produce a PVA film free from foreign matter and defects. is there. On the other hand, if the volatile fraction of the film-forming stock solution is too high, the concentration of the film-forming stock solution will be too low, and there will be no problem if a film is produced on a trial basis in the laboratory, but it is difficult to produce an industrial PVA film Become.

  In addition, it is preferable to add a surfactant in the stock solution for producing a PVA film, and the addition of the surfactant improves the film-forming property and suppresses the occurrence of film thickness spots. In addition, the film can be easily peeled off from the metal roll or belt used for film formation. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable from the viewpoint of releasability from a metal roll or belt, and a nonionic surfactant is particularly preferable. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzene sulfonate are suitable. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkylphenyl ether types such as polyoxyethylene octylphenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene laurylamino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.

  When a surfactant is added to the film-forming stock solution, the addition amount is 0.01 to 0.5 parts by weight, more preferably 0.02 to 0.03 parts by weight, particularly 0.05 to 100 parts by weight of PVA. -0.1 mass part is preferable. When the addition amount of the surfactant is less than 0.01 parts by mass, the effect of improving the film forming property and the peelability due to the addition of the surfactant is less likely to appear, whereas when it exceeds 0.5 parts by mass, The surfactant may bleed out on the surface of the PVA film, causing blocking, and handling properties may be reduced.

  As a film forming method for forming a PVA film using the above-mentioned film forming stock solution, a dry casting film forming method or an extrusion film forming method is preferable. In addition, a wet film forming method or a gel film forming method can also be employed, and in that case, it is necessary to pay attention to the elution of the water-soluble inorganic salt. Moreover, the method by these combination, etc. are employable. Among these film forming methods, the extrusion film forming method is preferably employed because a PVA film having a uniform thickness and width and good physical properties can be obtained. The PVA film is dried or heat-treated as necessary.

In film formation, a T-type slit die, a hopper plate, an I-die, a lip coater die, or the like is used. The belt is uniformly discharged (cast) on the peripheral surface, and volatile components are evaporated and dried from one surface of the film discharged (cast) on the first roll, followed by discharge (flow). The other surface of the rolled film is passed over the peripheral surface of the rotating second heating roll (drying roll) and dried, and the periphery of one or a plurality of rotating heating rolls arranged downstream thereof A method of further drying on the surface or passing through a hot air drying apparatus and then winding it on a winding apparatus is preferably employed industrially. Roll drying and hot air drying can also be combined as appropriate.
In order to adjust the PVA film to an appropriate state, it is desirable to add a heat treatment device, a humidity control device, and a speed adjustment mechanism such as a motor and a transmission for driving each roll.
In general, the drying process in the production process of the PVA film is performed at a drying temperature of 50 to 150 ° C., particularly 60 to 120 ° C., and has excellent stretchability and dyeability when producing a polarizing film. It is preferable from the point that the polarizing performance and durability of the obtained polarizing film are improved.

The polarizing film manufacturing method at the time of manufacturing a polarizing film from a PVA film is not particularly limited, and any method conventionally employed when manufacturing a polarizing film using a PVA film as a raw film may be adopted. Good.
In order to produce a polarizing film from a PVA film, for example, moisture adjustment of the PVA film, dyeing, uniaxial stretching, fixing treatment, drying treatment, and heat treatment as necessary may be performed, such as dyeing, uniaxial stretching, fixing treatment, etc. The order of operations is not particularly limited. Further, uniaxial stretching may be performed in two or more stages, or may be performed simultaneously with dyeing or fixing treatment.

  Dyeing is preferably performed using iodine, and the dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Usually, dyeing is generally performed by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide, and an aqueous solution containing iodine and potassium iodide is also used in the present invention. A dyeing method is preferably employed. It is preferable that the concentration of iodine in the aqueous dyeing solution is 0.01 to 0.5% by mass and the concentration of potassium iodide is 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C, particularly 25 to 40 ° C.

Uniaxial stretching may be performed by either a wet stretching method performed in a solvent such as water or a dry heat stretching method performed in air. In the case of the wet stretching method, uniaxial stretching in water, uniaxial stretching in a dyeing solution not containing boric acid, uniaxial stretching in a dyeing solution containing boric acid, uniaxial stretching in a boric acid aqueous solution, It can be performed by multi-stage stretching over the process.
The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is wet-stretched, and preferably 50 to 180 ° C. when dry-heat stretching is performed.
In addition, the stretching ratio of uniaxial stretching (total stretching ratio in the case of uniaxial stretching in multiple stages) is preferably 4 times or more, particularly 5 times or more from the viewpoint of the polarizing performance of the obtained polarizing film. The upper limit of the stretching ratio is not particularly limited, but is preferably 8 times or less from the viewpoint of uniform stretching.

  In the production of the polarizing film, in order to strengthen the adsorption of iodine to the PVA film, a fixing treatment is often performed. In the present invention, it is preferable to perform the fixing treatment in producing the polarizing film. As the treatment bath used for the fixing treatment, an aqueous solution to which one or more of boron compounds such as boric acid and borax are added is usually used. Moreover, you may add an iodine compound and a metal compound in the processing bath for fixing processes as needed. The concentration of the boron compound in the treatment bath for fixing treatment is generally about 2 to 15% by mass, particularly about 3 to 10% by mass. The temperature of the treatment bath during the fixing treatment is preferably 15 to 60 ° C, particularly preferably 25 to 40 ° C.

  The above-described uniaxial stretching, dyeing treatment, fixing treatment and the like are performed, and then the obtained polarizing film is dried. It is preferable to perform the drying process of the obtained polarizing film at 30-150 degreeC, especially 50-150 degreeC. When the moisture content of the polarizing film is about 10% or less after drying, applying tension to the polarizing film and performing heat treatment at about 80 to 120 ° C. for about 1 to 5 minutes will result in dimensional stability, durability, etc. Can be obtained.

  The polarizing film obtained as described above is usually used as a polarizing plate by bonding a protective film having optical transparency and mechanical strength on both sides or one side. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive for bonding include PVA adhesives and urethane adhesives. Among them, PVA adhesives are preferable.

  The polarizing plate obtained as described above is used as a component of a liquid crystal display device after being coated with an acrylic-based pressure-sensitive adhesive and then bonded to a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

  The present invention will be specifically described below with reference to examples and the like, but the present invention is not limited to the following examples. In the following examples, polarization performance and hue were evaluated by the following methods.

(1) Polarization degree of polarizing film:
(I) Transmittance Two square samples of 4 cm × 4 cm were taken in parallel with the orientation direction of the polarizing film from the central part in the width direction of the polarizing film obtained in the following examples or comparative examples. Using a spectrophotometer U-4100 (attached to integrating sphere) manufactured by Seisakusho, in accordance with JIS Z 8722 (measuring method of object color), the visibility of the visible light region of the C light source and the 2-degree visual field is corrected. About the polarizing film sample of 1 sheet, the transmittance | permeability of the light at the time of inclining 45 degree | times with respect to the extending | stretching axis direction and the light transmittance at the time of inclining -45 degree | times were measured, and those average values (Y1) were calculated | required. .
For the other polarizing film sample, the light transmittance when tilted by 45 degrees and the light transmittance when tilted by -45 degrees were measured in the same manner as described above, and the average value (Y2) was calculated. Asked.
Y1 and Y2 obtained above were averaged to obtain the transmittance (Y) (%) of the polarizing film.

(Ii) Polarization degree:
The light transmittance (Y で) when the two polarizing films collected in (i) above are stacked so that their orientation directions are parallel, and the light when they are stacked so that their orientation directions are orthogonal to each other. The transmittance (Y⊥) was measured by the same method as the transmittance measuring method, and the degree of polarization was determined from the following equation.
Polarization degree (V /%) = {(Y‖−Y⊥) / (Y‖ + Y⊥)} ^1/2 × 100

(2) Color of polarizing film:
In order to evaluate the presence or absence of blue light leakage of the polarizing film, b value was calculated and evaluated by Hunter Lab color system. The two polarizing film samples collected in (i) of (1) above were overlapped so that the b value (b‖) when the stretching axis directions were parallel and the stretching axis directions were orthogonal to each other. In this case, the b value (b⊥) was measured by the same method as the transmittance measuring method, and the b value was obtained from the following equation.

b value = | b‖−b⊥ |

Example 1
(1) 100 parts by mass of PVA having an average degree of polymerization of 2400 and a degree of saponification of 99.95 mol%, 20 parts by mass of magnesium nitrate anhydride and a 10% PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer are dried on a metal roll at 60 ° C. Thus, a PVA film having a thickness of 75 μm was obtained. Furthermore, the obtained film was fixed to a frame and heat-treated at 140 ° C. for 3 minutes. The hot water cutting temperature of the PVA film after the heat treatment was 68.2 ° C., and the degree of swelling was 200%.
When the obtained PVA film was observed with a phase-contrast microscope, particulate matter having an average particle diameter of 3 μm was produced in the PVA film, and there were 10 particulate matter on average per 100 square μm of film area. It was confirmed that Particulate matter having an average particle diameter of 3 μm was generated in the PVA film, and it was confirmed that 10 particulates were present on average per 100 square μm of film area. The average particle size is a value obtained by randomly selecting five particles in the film and measuring each particle size, and averaging the values. The number of particles is determined from the PVA film. This is a value obtained by counting the number of three randomly selected particulate matters by microscopic observation and averaging them.
(2) After immersing the PVA film obtained in (1) above in pure water at 30 ° C. for 3 minutes, 0.04% by mass of iodine, 4% by mass of potassium iodide and 4% by mass of boric acid Was immersed in an aqueous solution (dye bath) (temperature 30 ° C.) for 30 seconds to adsorb iodine. Next, after uniaxially stretching 5.4 times in an aqueous boric acid solution (boric acid concentration 4 wt%, 50 ° C.), an aqueous solution further containing 6 mass% potassium iodide and 4 mass% boric acid ( (35 ° C.) for 4 minutes. Then, it dried at 50 degreeC for 4 minute (s), and obtained the polarizing film.
When the obtained polarizing film was observed with a phase-contrast microscope, an elongated crack having a major axis in the stretching direction was generated, and its size (long axis length) was about 10 μm. It was confirmed that there were 8 on average per 100 square μm area. The length of the major axis is a value obtained by randomly selecting five cracks in the polarizing film and measuring each major axis and averaging them. The number of cracks is random from the polarizing film. This is a value obtained by counting the number of cracks at the three locations selected in (1) by microscopic observation and averaging them.
The transmittance of this polarizing film is 44.1%, the degree of polarization is 98.4%, the b value is 2.9, and compared with the polarizing film obtained when magnesium nitrate is not added (Comparative Example 1). The b value was small and the hue was excellent.

Example 2
(1) 100 parts by weight of PVA having an average polymerization degree of 2400 and a saponification degree of 99.95 mol%, 5 parts by weight of magnesium nitrate anhydride and 12 parts by weight of glycerol as a plasticizer are dried on a metal roll at 60 ° C. Thus, a PVA film having a thickness of 75 μm was obtained. Furthermore, the obtained film was fixed to a frame and heat-treated at 130 ° C. for 3 minutes. The hot water cutting temperature of the PVA film after the heat treatment was 68.2 ° C., and the degree of swelling was 202%.
The obtained PVA film was observed with a phase contrast microscope in the same manner as in Example 1. As a result, particulate matter having an average particle diameter of 2 μm was produced in the PVA film, and the particulate matter was per 100 square μm of film area. It was confirmed that there were five on average.
(2) Using the PVA film obtained in (1) above, the time for immersing the PVA film in the dyeing bath was changed to 75 seconds, and the ratio of uniaxial stretching in the boric acid aqueous solution was changed to 5.5 times. A polarizing film was obtained in the same manner as in Example 1 except that.
When the obtained PVA film was observed with a phase-contrast microscope in the same manner as in Example 1, a long and narrow crack with the stretching direction as the major axis was generated, and the size (length of the major axis) was about 11 μm. Moreover, it was confirmed that four cracks exist on average per 100 square micrometers of film area.
The transmittance of this polarizing film is 43.6%, the degree of polarization is 99.7%, the hue is 4.0, and compared with the polarizing film obtained when magnesium nitrate is not added (Comparative Example 1), The b value was small and the hue was excellent.

Example 3
(1) PVA 100% by weight of PVA having an average polymerization degree of 2400 and a saponification degree of 99.95 mol% and PVA 10% aqueous solution of magnesium nitrate anhydride 20 parts by weight on a metal roll at 60 ° C. A film was obtained. Furthermore, the obtained film was fixed to a frame and heat-treated at 140 ° C. for 3 minutes. The hot water cutting temperature of the PVA film after heat treatment was 68.9 ° C., and the degree of swelling was 200%.
When the obtained PVA film was observed with a phase-contrast microscope in the same manner as in Example 1, particulate matter having an average particle diameter of 3 μm was produced in the PVA film, and the particulate matter was per 100 square μm of film area. It was confirmed that there were 10 on average.
(2) Using the PVA film obtained in (1) above, changing the time for immersing the PVA film in the dyeing bath to 60 seconds and changing the uniaxial stretching ratio in the boric acid aqueous solution to 5.15 times. A polarizing film was obtained in the same manner as in Example 1 except that.
When the obtained PVA film was observed with a phase-contrast microscope in the same manner as in Example 1, a long and narrow crack with the stretching direction as the major axis was generated, and the size (length of the major axis) was about 15 μm. Moreover, it was confirmed that seven cracks exist on average per 100 square micrometers of film area.
The transmittance of this polarizing film is 43.6%, the degree of polarization is 99.65%, the hue is 3.8, compared with the polarizing film obtained when magnesium nitrate is not added (Comparative Example 1), The b value was small and the hue was excellent.

Example 4
(1) 100 parts by weight of PVA having an average degree of polymerization of 2,400 and a degree of saponification of 99.95 mol%, 20 parts by weight of magnesium nitrate anhydride and 12 parts by weight of glycerol as a plasticizer are dried on a metal roll at 60 ° C. Thus, a PVA film having a thickness of 75 μm was obtained. Furthermore, the obtained film was fixed to a frame and heat-treated at 140 ° C. for 3 minutes. The hot water cutting temperature of the PVA film after heat treatment was 68.2 ° C., and the degree of swelling was 200%.
When the obtained PVA film was observed with a phase-contrast microscope in the same manner as in Example 1, particulate matter having an average particle diameter of 3 μm was produced in the PVA film, and the particulate matter was per 100 square μm of film area. It was confirmed that there were 10 on average.
(2) Example 1 except that the PVA film obtained in (1) above was used, the time for immersing the PVA film in the dyeing bath was changed to 45 seconds, and the temperature of the boric acid aqueous solution was changed to 55 ° C. In the same manner, a polarizing film was obtained.
When the obtained PVA film was observed with a phase-contrast microscope in the same manner as in Example 1, a long and narrow crack with the stretching direction as the major axis was generated, and the size (length of the major axis) was about 16 μm. In addition, it was confirmed that four cracks exist on average per 100 square μm of film area.
The transmittance of this polarizing film is 44.3%, the degree of polarization is 98.73%, the hue is 2.3, and compared with the polarizing film (Comparative Example 1) obtained when magnesium nitrate is not added, The b value was small and the hue was excellent.

Comparative Example 1
(1) PVA having an average polymerization degree of 2400 and a saponification degree of 99.95 mol%, 100 parts by weight of PVA, and 12 parts by weight of glycerol as a plasticizer, 10% PVA aqueous solution dried on a metal roll at 60 ° C. A film was obtained. Furthermore, the obtained film was fixed to a frame and heat-treated at 130 ° C. for 3 minutes. The hot water cutting temperature of the PVA film after the heat treatment was 68.9 ° C., and the degree of swelling was 198%.
When the obtained PVA film was observed with a phase contrast microscope, no particulate matter was generated in the film.
(2) Using the PVA film obtained in (1) above, the time for immersing the PVA film in the dyeing bath was changed to 3 minutes, and the ratio of uniaxial stretching in the boric acid aqueous solution was changed to 5.3 times. A polarizing film was obtained in the same manner as in Example 1 except that.
When the obtained polarizing film was observed with a phase contrast microscope, no cracks were generated.
The transmittance of this polarizing film is 43.4%, the degree of polarization is 99.94%, the hue is 4.5, and compared with the polarizing film obtained when magnesium nitrate is added (Examples 1 to 4). The b value was large and the hue was inferior.

According to the present invention, it is possible to provide a polarizing film excellent in hue, which is difficult to achieve with the prior art. That is, according to the present invention, a polarizing film in which two polarizing films are orthogonally crossed in a crossed Nicol state with little light leakage of blue light and in a parallel Nicol state in which two polarizing films are paralleled is little colored yellow light. Can be provided.
The polarizing film of the present invention has improved hue, and can be effectively used for the production of a polarizing plate which is a member for parts of liquid crystal display devices and liquid crystal televisions that require particularly high color reproducibility.

Claims (7)

  A polarizing film containing cracks.   The polarizing film according to claim 1, wherein the crack has a size of 5 to 25 μm.   The polarizing film according to claim 1, wherein 2 to 15 cracks are present per 100 square μm area of the polarizing film.   The method for producing a polarizing film according to any one of claims 1 to 3, wherein a polyvinyl alcohol film in which particulate matter of a water-soluble inorganic salt is dispersed is stretched.   The method for producing a polarizing film according to claim 4, wherein the polyvinyl alcohol film in which the particulate matter of the water-soluble inorganic salt is dispersed is stretched after being immersed in water.   The method for producing a polarizing film according to claim 4 or 5, wherein the water-soluble inorganic salt is magnesium nitrate. The method for producing a polarizing film according to any one of claims 4 to 6, wherein the content of the water-soluble inorganic salt in the polyvinyl alcohol film is 5 to 20% by weight.