JP6402096B2 - Polyvinyl alcohol film - Google Patents

Description

  The present invention relates to a polyvinyl alcohol film capable of easily producing a polarizing film excellent in hue, a method for producing the same, a method for producing a polarizing film using the same, and a polarizing film excellent in hue.

A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film. As a polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter referred to as “polyvinyl alcohol”). iodine based dye "to the sometimes abbreviated as" PVA ") in a matrix formed by uniaxially stretched (oriented film was oriented by uniaxial stretching) (I ₃ ^- and I ₅ ^-, etc.) two-color, such as The thing which adsorb | sucks the characteristic pigment has become the mainstream. Such a polarizing film can be obtained by uniaxially stretching a PVA film preliminarily containing a dichroic dye, adsorbing a dichroic dye simultaneously with uniaxial stretching of the PVA film, or dichroic after uniaxially stretching the PVA film. It is manufactured by adsorbing a dye or the like (see Patent Document 1).

  LCDs are used in a wide range of devices such as small devices such as calculators and wrist watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. .

JP-A-5-245858

  By the way, in recent years, there is a demand for lowering the brightness of the backlight to reduce power consumption, but when a conventional polarizing film is used, it is necessary to correct the hue by arranging another optical film, etc. There has been a problem that the LCD screen becomes dark due to the low transmittance of the optical film. On the other hand, when an optical film having a high transmittance is used, there is a problem that the hue cannot be sufficiently corrected.

  Accordingly, the present invention provides a polarizing film that can produce an LCD that is excellent in hue and excellent in hue without using an optical film having low transmittance, and that can produce a bright LCD, and the polarizing film It aims at providing the PVA film which can manufacture easily.

  As a result of intensive studies to achieve the above object, the inventors of the present invention are excellent in hue when using a PVA film in which the stress after stretching in water shows a specific aging behavior, It is possible to easily produce a polarizing film capable of producing a bright LCD without using a low-transmittance optical film and having a bright screen; the degree of saponification and the degree of swelling are in a specific range. When the PVA film is heat-treated under specific conditions, the above PVA film is easily produced; and b value when arranged in a parallel Nicol state with respect to linearly polarized light and b when arranged in a crossed Nicol state A polarizing film that satisfies a specific relationship with the value produces an LCD that is excellent in hue and excellent in hue without using an optical film with low transmittance. It can, moreover found that it is possible to produce a bright LCD of the screen, and completed the present invention by further extensive studies based on the findings.

[1] A PVA film having a minimum slope of −0.84 to −0.783 N / mm ² · sec and a degree of swelling of 180 to 220%, wherein the PVA film is included in the PVA film. A PVA film having a saponification degree of 98 to 99.5 mol% and a raw film for producing a polarizing film;
A sample of 3 cm in the width direction cut out from the PVA film was set in an autograph so as to be stretched in the length direction with a distance between chucks of 1.5 cm, immersed in water at 30 ° C. for 1 minute, and then 240% / Stretched in the length direction at a speed of minutes, the distance between chucks was fixed when the stress reached 11.1 N / mm ² , and the subsequent stress change over time was plotted with time on the horizontal axis and stress on the vertical axis. The minimum value of the slope at each point on the graph.
[2] The method for producing a PVA film according to the above [1], comprising a step of heat-treating a PVA film having a saponification degree of 98 to 99.5 mol% and a swelling degree of 250% or more at 135 to 148 ° C. ;
[3] The production method according to [ 2 ] above, wherein the heat treatment is performed for 0.5 minutes or more;
[4] A method for producing a polarizing film, comprising a step of stretching the PVA film of the above [ 1 ];
[5] a b value when disposed in parallel Nicol state with respect to linearly polarized light and X, the b value when disposed in a cross Nicol state upon the Y, in a polarizing film satisfies the following formula (I) A polarizing film produced using the PVA film of [1] above ;
Y ≧ 1.9X-8.3 (I)
[6] The polarizing film according to [ 5 ], which satisfies the following formula (II):
5 ≧ Y ≧ −5 (II)

  According to the present invention, a polarizing film capable of producing an LCD excellent in hue and excellent in hue without using an optical film having low transmittance, and capable of producing an LCD having a bright screen, and a method for producing the same, And the PVA film which can manufacture the said polarizing film easily, and its manufacturing method are provided.

Hereinafter, the present invention will be described in detail.
(PVA film)
The minimum value of the following inclination of the PVA film of the present invention is -0.84 to -0.783 N / mm ² · sec.
A sample of 3 cm in the width direction cut out from the PVA film was set in an autograph so as to be stretched in the length direction with a distance between chucks of 1.5 cm, immersed in water at 30 ° C. for 1 minute, and then 240% / Stretched in the length direction at a speed of minutes, and when the stress became 11.1 N / mm ² , the distance between chucks was fixed, and the time-dependent change in stress thereafter was expressed in time (unit: seconds) on the horizontal axis. The minimum value of the slope (tangential slope) at each point on the graph when the stress (unit: N / mm ² ) is plotted on the vertical axis.
The stress is obtained by dividing the tension (unit: N) at each time point by the cross-sectional area (3 cm × PVA film thickness) (unit: mm ² ) of the original sample.

When the minimum value of the inclination is out of the above range, the hue of the obtained polarizing film is lowered. Although the present invention is not limited at all, the reason why the minimum value of the inclination and the hue of the obtained polarizing film are related can be considered as follows. That is, the minimum value of the inclination is related to the microscopic behavior of PVA molecules in the stretching process when actually manufacturing a polarizing film using the PVA film, and this microscopic behavior is related to iodine. This is considered to affect the state of the dichroic dye such as a system dye.
From the viewpoint of the hue of the polarizing film obtained, the minimum value of the inclination is preferably at least -0.825N / mm ² · sec, more preferably at -0.815N / mm ² · sec or more, - still more preferably 0.8N / mm ² · sec or more, and is preferably from -0.786N / mm ² · sec, more preferably at most -0.79N / mm ² · sec More preferably, it is −0.793 N / mm ² · sec or less.

  As PVA contained in the PVA film of the present invention, vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate, etc. Those obtained by saponifying a polyvinyl ester obtained by polymerizing one or more of these vinyl esters can be used. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of ease of production of PVA, availability, cost, and the like.

  The polyvinyl ester is preferably obtained by using only one or two or more types of vinyl ester as a monomer. It may be a copolymer of two or more kinds of vinyl esters and other monomers copolymerizable therewith.

  Examples of other monomers copolymerizable with the vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide, N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl (Meth) acrylamide derivatives such as amide, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamidepropyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; halogenated vinyl such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; vinegar Allyl compounds such as allyl acid and allyl chloride; maleic acid or its salt, ester or acid anhydride; itaconic acid or its salt, ester or acid anhydride; vinylsilyl compound such as vinyltrimethoxysilane; unsaturated sulfonic acid be able to. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer.

The proportion of structural units derived from the other monomers described above in the polyvinyl ester is preferably 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester, and is preferably 10 mol%. Hereinafter, it may be 5 mol% or less.
In particular, when the other monomer described above is a monomer that may promote the water solubility of the obtained PVA, such as (meth) acrylic acid or unsaturated sulfonic acid, In order to prevent PVA from being dissolved in the production process, the proportion of structural units derived from these monomers in the polyvinyl ester is 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester. It is preferable that it is 3 mol% or less.

  PVA may be modified with one or two or more types of graft copolymerizable monomers as long as the effects of the present invention are not impaired. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in PVA (structural units in the graft modified portion) is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA. .

  PVA may have some of its hydroxyl groups crosslinked or uncrosslinked. Moreover, said PVA may react with aldehyde compounds, such as acetaldehyde and a butyraldehyde, etc. to form an acetal structure, and the said PVA does not react with these compounds and does not form an acetal structure. May be.

  The average degree of polymerization of PVA is preferably in the range of 1,000 to 9,500, the average degree of polymerization is more preferably 1,500 or more, further preferably 2,000 or more, Moreover, it is more preferable that it is 9,200 or less, and it is further more preferable that it is 6,000 or less. When the average degree of polymerization is 1,000 or more, the polarizing performance of the polarizing film is improved. On the other hand, when the average degree of polymerization is 9,500 or less, the productivity of PVA is improved. In addition, the average degree of polymerization of PVA can be measured according to description of JIS K6726-1994.

  The saponification degree of PVA is preferably in the range of 98 to 99.5 mol%, the saponification degree is more preferably 98.3 mol% or more, and further preferably 98.6 mol% or more. Preferably, it is 98.7 mol% or more, more preferably 99.3 mol% or less, further preferably 99.1 mol% or less, and less than 99 mol%. Is particularly preferred. If the degree of saponification of PVA is within the above range, the reason is not necessarily clear, but the LCD itself is excellent in hue and excellent in hue without using an optical film with low transmittance, It has been found that a polarizing film capable of producing a bright LCD can be produced more easily. In this specification, the degree of saponification of PVA refers to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units of PVA. The proportion (mol%) occupied by the number of moles of vinyl alcohol units. The degree of saponification can be measured according to the description of JIS K6726-1994.

  It is preferable that a PVA film contains a plasticizer from a viewpoint of the extending | stretching improvement at the time of extending | stretching it. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylol propane. One or more of the agents can be included. Among these, glycerin is preferable from the viewpoint of the effect of improving stretchability.

It is preferable that content of the plasticizer in a PVA film exists in the range of 1-20 mass parts with respect to 100 mass parts of PVA contained in it. When the content is 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the PVA film from becoming too flexible and handling properties from being lowered. The content of the plasticizer in the PVA film is more preferably 2 parts by mass or more with respect to 100 parts by mass of PVA, further preferably 4 parts by mass or more, particularly preferably 5 parts by mass or more, The amount is more preferably 15 parts by mass or less, and further preferably 12 parts by mass or less.
Although depending on the manufacturing conditions of the polarizing film, the plasticizer contained in the PVA film is eluted when the polarizing film is manufactured. Therefore, the total amount does not always remain in the polarizing film.

  The PVA film may further contain components such as an antioxidant, an antifreezing agent, a pH adjusting agent, a masking agent, an anti-coloring agent, an oil agent, and a surfactant as necessary.

  The content of PVA in the PVA film is preferably in the range of 50 to 99% by mass from the viewpoint of ease of preparation of the desired polarizing film, and the content is preferably 75% by mass or more. More preferably, it is more preferably 80% by mass or more, particularly preferably 85% by mass or more, more preferably 98% by mass or less, further preferably 96% by mass or less, 95 It is particularly preferable that the content is not more than mass%.

  There is no restriction | limiting in particular in the thickness of the PVA film of this invention, According to the thickness of the target polarizing film, etc., it can set suitably. As a specific thickness, for example, it can be in the range of 2 to 100 μm, further in the range of 5 to 65 μm, and can also be in the range of 8 to 50 μm.

  The shape of the PVA film is not particularly limited, but is preferably a long PVA film because it can be used continuously when producing a polarizing film. The length (length in the length direction) of the long PVA film is not particularly limited, and can be appropriately set according to the application of the polarizing film to be produced, for example, in the range of 1 to 20,000 m. It can be.

  The width of the PVA film is not particularly limited and can be appropriately set according to the use of the polarizing film to be produced. For example, the width can be 0.1 m or more. From the point of progress of conversion, it is suitable for these uses when the width of the PVA film is 0.5 m or more, more preferably 1.0 m or more. On the other hand, if the width of the PVA film is too wide, it tends to be difficult to uniformly stretch the polarizing film when the polarizing film is produced by a device that has been put to practical use. Therefore, the width of the PVA film is 7 m or less. Is preferred.

  The degree of swelling of the PVA film of the present invention is preferably in the range of 180 to 220% from the viewpoint of productivity and performance of the polarizing film, and the degree of swelling is more preferably 185% or more, and 190 % Or more, more preferably 195% or more, more preferably 215% or less, further preferably 210% or less, and particularly preferably 205% or less. . The degree of swelling of the PVA film can be measured by the method described later in the examples. The degree of swelling of the PVA film can be adjusted to a smaller value by, for example, increasing the heat treatment conditions.

(Method for producing PVA film)
Although there is no restriction | limiting in particular in the method for manufacturing the PVA film of this invention, According to the manufacturing method of the PVA film of this invention described below, since the PVA film of this invention can be manufactured easily, it is preferable. That is, the method for producing a PVA film of the present invention includes a PVA film having a saponification degree of 98 to 99.5 mol% and a swelling degree of 250% or more, which is within a range of 135 to 148 ° C. Including a step of heat treatment at a temperature.

  The PVA used can be the same as that described above in the description of the PVA film of the present invention, and therefore, redundant description is omitted here. Also, the plasticizer and other components that can be included as optional components in the PVA film used, and the shape such as thickness, etc. shall be the same as those described above in the description of the PVA film of the present invention. Therefore, redundant description is omitted here.

  There is no restriction | limiting in particular in the manufacturing method of the PVA film provided to heat processing, It can manufacture by a conventionally well-known method. Specifically, for example, film formation can be performed using a film-forming stock solution in which PVA is dissolved in a liquid medium, or a film-forming stock solution in which PVA and a liquid medium are included and PVA is melted.

  Examples of the liquid medium used for preparing the membrane forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Trimethylolpropane, ethylenediamine, diethylenetriamine and the like can be mentioned, and one or more of these can be used. Among them, water is preferably used from the viewpoint of environmental load and recoverability.

  The volatile fraction of the film-forming stock solution (content ratio of a volatile component such as a liquid medium removed by volatilization or evaporation during film formation) varies depending on the film-forming method, film-forming conditions, etc., but generally 50 It is preferable that it is -95 mass%, Furthermore, it is 55-90 mass%, Especially 60-85 mass%. If the volatile fraction of the film-forming stock solution is too low, the viscosity of the film-forming stock solution becomes too high, making filtration and defoaming difficult when preparing the film-forming stock solution, making it difficult to produce a PVA film with few foreign matters and defects. Tend. On the other hand, when the volatile fraction of the film-forming stock solution is too high, the concentration of the film-forming stock solution becomes too low, and industrial PVA film tends to be difficult to form.

  As a film forming method for forming a PVA film to be subjected to heat treatment, for example, a wet film forming method, a gel film forming method, a casting film forming method, an extrusion film forming method, or the like can be employed. A method based on a combination of these can also be employed. Among the above film forming methods, the casting film forming method or 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.

  As a specific film forming method, a T-type slit die, hopper plate, I-die, lip coater die, etc. are used to uniformly discharge the film forming stock solution onto the peripheral surface of a heated roll (or belt) that rotates. Then, volatile components are evaporated from one surface of the film discharged onto the roll (or belt) and dried to form a PVA film, or one or more after being dried in this way And a method of forming a PVA film by further drying on the peripheral surface of a heated heated roll or by passing it through a hot air drying apparatus. The PVA film after film formation may be subjected to a heat treatment to be described later by unwinding it as necessary after being once wound by a winding device. However, the PVA film continuously formed as described above may be used. Alternatively, the film may be wound after the heat treatment described below is continuously performed.

  As surface temperature of the roll used for film forming, it can be set as 50-100 degreeC, for example. Moreover, as drying temperature at the time of discharging a film forming undiluted solution on a belt, it can be 50-100 degreeC, for example.

  The degree of swelling of the PVA film subjected to the heat treatment is preferably 300% or more, more preferably 400% or more, since the PVA film of the present invention can be more easily produced. , Preferably not more than 1,000%. The volatile fraction of the PVA film subjected to the heat treatment can be, for example, 10% by mass or less, and further 8% by mass or less.

  The temperature in the heat treatment is preferably 137 ° C. or higher, more preferably 139 ° C. or higher, further preferably higher than 140 ° C., because the PVA film of the present invention can be produced more easily. It is preferable that it is 145 degrees C or less.

  Although it does not restrict | limit in particular in heat processing time, since it can manufacture the PVA film of this invention more easily, it is preferable that it is 0.5 minute or more, it is more preferable that it is 0.8 minute or more, and 30 It is preferably not more than 15 minutes, and more preferably not more than 15 minutes.

(Production method of polarizing film)
The application of the PVA film of the present invention is not particularly limited, but according to the PVA film of the present invention, an LCD having excellent hue itself and excellent hue without using an optical film having low transmittance is manufactured. In addition, since it is possible to easily produce a polarizing film capable of producing an LCD with a bright screen, it is preferably used as a raw film for producing a polarizing film.

  There is no restriction | limiting in particular in the method of manufacturing a polarizing film using the PVA film of this invention, It can manufacture by the method including the process of extending | stretching the PVA film of this invention. Specifically, for example, first, a PVA film, By subjecting to a swelling step, then subjecting to a dyeing step, further subjecting to a crosslinking step if necessary, then subjecting to a stretching step, subjecting to a fixing treatment step and / or washing step as necessary, and to a drying step Can be manufactured.

  The swelling step can be performed by immersing the PVA film in water. The temperature of the water when immersed in water is preferably in the range of 20 to 40 ° C., more preferably 22 ° C. or higher, even more preferably 25 ° C. or higher. The temperature is more preferably 38 ° C. or lower, and further preferably 35 ° C. or lower. By making the said temperature into the range of 20-40 degreeC, a PVA film can be swollen efficiently. Moreover, as time to immerse in water, it is preferable to exist in the range for 0.1 to 5 minutes, and it is more preferable to be in the range for 0.5 to 3 minutes. A PVA film can be efficiently swollen by setting it within the range of 0.1 to 5 minutes. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

The dyeing | staining process in a dyeing process can be performed by immersing a PVA film in the aqueous solution containing a dichroic dye. As the dichroic dye, iodine based dye (I ₃ ^- and I ₅ ^-, etc.), and the like dichroic organic dyes. The iodine dye can be obtained, for example, by bringing iodine (I ₂ ) into contact with potassium iodide. Examples of the dichroic organic dye include direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107 and the like. Among these dichroic dyes, iodine-based dyes are preferable from the viewpoints of handleability, availability, and polarization performance. Incidentally, the dichroic dye may either be two or more even alone, for example, I ₃ ^- may be a balanced mixture as ^- and I _5.

The concentration of the dichroic dye in the aqueous solution containing the dichroic dye can be appropriately set according to the type of the dichroic dye used, for example, within a range of 0.001 to 1% by mass. However, when an iodine-potassium iodide aqueous solution is used as the aqueous solution containing the dichroic dye, the iodine-based dye can be efficiently adsorbed on the PVA film, so that the concentration of iodine (I ₂ ) used is As a concentration of 0.01 to 2% by mass, more preferably 0.02 to 0.5% by mass, and the concentration of potassium iodide (KI) used as The ratio of the mass of potassium iodide used relative to the mass of iodine used is preferably in the range of 10 to 200 times by mass, and preferably in the range of 15 to 150 times by mass. Ri preferred. The aqueous solution containing the dichroic dye may contain a boron compound such as boric acid such as boric acid or borax. The temperature of the aqueous solution containing the dichroic dye is preferably in the range of 5 to 50 ° C., and preferably in the range of 15 to 40 ° C., because the dichroic dye can be efficiently adsorbed to the PVA film. It is more preferable. In addition, a dyeing | staining process can be abbreviate | omitted when using the PVA film which previously contained the dichroic dye.

  By performing the crosslinking step on the PVA film, it is possible to more effectively prevent PVA from eluting into water when wet-stretching at a relatively high temperature. From this viewpoint, the crosslinking step is preferably performed after the dyeing step and before the stretching step. The crosslinking step can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent as a crosslinking bath. As the crosslinking agent, one or more of boron compounds such as boric acid and borate such as borax can be used. The concentration of the crosslinking agent in the crosslinking bath is preferably in the range of 1 to 15% by mass, more preferably 2% by mass or more, more preferably 7% by mass or less, and 6% by mass or less. More preferably. Sufficient stretchability can be maintained when the concentration of the crosslinking agent is in the range of 1 to 15% by mass. The crosslinking bath may contain an auxiliary agent such as potassium iodide. The temperature of the crosslinking bath is preferably in the range of 20 to 50 ° C, particularly in the range of 25 to 40 ° C. It can bridge | crosslink efficiently by making the said temperature into the range of 20-50 degreeC.

  There is no restriction | limiting in particular in the extending | stretching method at the time of extending | stretching a PVA film, You may carry out by any of a wet extending | stretching method and a dry-type extending | stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing one or more boron compounds such as boric acid such as boric acid and borax, or in the above-described dyeing bath or a fixing treatment bath described later. It can also be done inside. In the case of the dry stretching method, stretching may be performed at room temperature, stretching may be performed while applying heat, or stretching may be performed after water absorption. Among these, the wet stretching method is preferable from the viewpoint of the uniformity of the thickness in the width direction of the obtained polarizing film, and it is more preferable to stretch in a boric acid aqueous solution. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0 mass%, more preferably 1.0 mass% or more, and 1.5 mass%. More preferably, it is more preferably 5.0% by mass or less, and further preferably 4.0% by mass or less. When the concentration of boric acid is in the range of 0.5 to 6.0% by mass, a polarizing film having excellent thickness uniformity in the width direction can be obtained. The aqueous solution containing the above boron compound may contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass. When the concentration of potassium iodide is in the range of 0.01 to 10% by mass, a polarizing film with better polarization performance can be obtained.

  The temperature at which the PVA film is stretched is preferably in the range of 5 to 90 ° C., more preferably 10 ° C. or higher, and more preferably 80 ° C. or lower. More preferably, it is not higher than ° C. When the temperature is in the range of 5 to 90 ° C., a polarizing film having excellent thickness uniformity in the width direction can be obtained.

  The stretching ratio at the time of stretching the PVA film is preferably 4 times or more, more preferably 5 times or more, and further preferably 6 times or more. By setting the draw ratio of the PVA film within the above range, a polarizing film that is more excellent in polarizing performance can be obtained. The upper limit of the draw ratio of the PVA film is not particularly limited, but is preferably 8 times or less. Stretching of the PVA film may be performed at one time or divided into a plurality of times, but when performed in a plurality of times, the total stretching ratio obtained by multiplying the stretching ratio of each stretching is within the above range. I just need it. In addition, the draw ratio in this specification is based on the length of the PVA film before extending | stretching, and the state which is not extending | stretched corresponds to 1 time of draw ratio.

  The stretching of the PVA film is preferably uniaxial stretching from the viewpoint of the performance of the obtained polarizing film. There is no particular limitation on the direction of uniaxial stretching in stretching a PVA film, and uniaxial stretching or lateral uniaxial stretching in the length direction can be adopted. However, since a polarizing film having superior polarization performance can be obtained, the length direction Uniaxial stretching is preferred. Uniaxial stretching in the length direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, lateral uniaxial stretching can be performed using a tenter type stretching machine.

  The fixing treatment step is mainly performed in order to strengthen the adsorption of the iodine-based pigment on the PVA film. The fixing treatment step can be performed by immersing the PVA film before stretching, during stretching or after stretching in a fixing treatment bath. As the fixing treatment bath, an aqueous solution containing one or more of boron compounds such as boric acid such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed treatment bath as needed. The concentration of the boron compound in the aqueous solution containing the boron compound used as the fixing treatment bath is generally within the range of 0.1 to 15% by mass, and particularly preferably within the range of 1 to 10% by mass. By making the said density | concentration in the range of 0.1-15 mass%, adsorption | suction of an iodine type pigment | dye can be strengthened more. The temperature of the fixing treatment bath is preferably in the range of 10 to 60 ° C, particularly in the range of 15 to 40 ° C. By making the said temperature into the range of 10-60 degreeC, adsorption | suction of an iodine type pigment | dye can be strengthened more.

  The washing process is often performed to remove unnecessary chemicals and foreign matters on the film surface and to adjust the optical performance of the finally obtained polarizing film. The cleaning step can be performed by immersing the PVA film in a cleaning bath or by spraying a cleaning liquid on the PVA film. Water can be used as the washing bath or the washing liquid, and potassium iodide may be contained therein.

  The drying conditions in the drying step are not particularly limited, but it is preferable to perform the drying at a temperature within the range of 30 to 150 ° C, particularly within the range of 50 to 130 ° C. A polarizing film excellent in dimensional stability is easily obtained by drying at a temperature in the range of 30 to 150 ° C.

(Polarizing film)
According to the manufacturing method of said polarizing film, when b value at the time of arrange | positioning in a parallel Nicol state with respect to linearly polarized light is set to X, and b value at the time of arrange | positioning to a cross Nicol state is set to Y, the following formula | equation A polarizing film satisfying (I) is obtained, and the polarizing film itself has an excellent hue, and an LCD having an excellent hue can be produced without using an optical film having a low transmittance. A bright LCD can be produced.
Y ≧ 1.9X-8.3 (I)
The above X and Y preferably satisfy the following formula (I ′), and more preferably satisfy the following formula (I ″).
Y ≧ 1.9X-8 (I ′)
Y ≧ 1.9X-7.5 (I ″)
In addition, said X and Y can be calculated | required using a spectrophotometer (for example, "V7100" etc. by JASCO Corporation), and can be specifically calculated | required by the method mentioned later in an Example.

The above Y depends on the use form of the polarizing film, but preferably satisfies the following formula (II), more preferably satisfies the following formula (II ′), and the following formula (II ″): It is more preferable to satisfy.
5 ≧ Y ≧ −5 (II)
3.5 ≧ Y ≧ −3.5 (II ′)
3 ≧ Y ≧ −3 (II ″)

(Usage form)
The polarizing film is usually used as a polarizing plate by attaching a protective film on both sides or one side. Examples of the protective film include those that are optically transparent and have mechanical strength. Specifically, for example, cellulose triacetate (TAC) film, acetic acid / cellulose butyrate (CAB) film, acrylic film, and polyester film. A film or the like can be used. In addition, examples of the adhesive for bonding include a PVA adhesive and a urethane adhesive, and a PVA adhesive is preferable.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In addition, the time-dependent change behavior of stress after the PVA film was stretched in water (minimum value of inclination), the degree of swelling of the PVA film, and the parallel Nicol state and the crossed Nicol state employed in the following Examples and Comparative Examples Each measuring method of b value (X and Y) of a polarizing film when arrange | positioning to is shown below.

[Aging behavior of stress after stretching PVA film in water (minimum slope)]
A rectangular sample measuring 3 cm in the width direction and 5.5 cm in the length direction was cut out from the central part in the width direction of the PVA film after heat treatment obtained in the following examples or comparative examples, and this was long with a distance between chucks of 1.5 cm. It is set on an autograph ("AG-I" manufactured by Shimadzu Corporation) so as to be stretched in the vertical direction, immersed in water (pure water) at 30 ° C for 1 minute, and then at a rate of 240% / min in the water. After stretching in the length direction, when the stress reached 11.1 N / mm ² , the distance between chucks was fixed, and the subsequent change in stress over time was measured. The obtained data is plotted in a graph with time (unit: second) on the horizontal axis and stress (unit: N / mm ² ) on the vertical axis, and the slope of each point on the graph (tangential slope) The minimum value was obtained.

[Swelling degree of PVA film]
A rectangular sample of 10 cm in the width direction and 20 cm in the length direction was cut out from the PVA film to be measured, and this sample was further cut into strips having a width of 2 to 3 mm and a length of 20 cm. Thereafter, all these strip-like samples were immersed in 1,000 g of distilled water at 30 ° C. as they were. After stripping for 30 minutes, a strip-shaped sample is taken out and centrifuged using a centrifuge (KOKUSAN XEM-KL-5886) for 5 minutes at 3,000 rpm. Mass after dehydration “N” (total of all strip-shaped samples) ) Was measured. Subsequently, the strip-shaped sample was dried with a dryer at 105 ° C. for 16 hours, and then the mass “M” (total of all the strip-shaped samples) was measured, and the degree of swelling was calculated by the following formula (III). . In addition, the same measurement was performed 3 times and the average value was employ | adopted.
Swelling degree (%) = 100 × N / M (III)

[B value (X and Y) of polarizing film when arranged in parallel Nicol state and crossed Nicol state]
From the central part in the width direction of the polarizing film obtained in the following examples or comparative examples, a rectangular sample of 4 cm in the length direction of the polarizing film was collected, and a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation " V7100 "), this sample was placed in a parallel Nicol state with respect to the polarizing plate of the spectrophotometer, the b value was obtained, and this value was taken as X. Next, the above sample was placed in a crossed Nicols state with respect to the polarizing plate of the spectrophotometer, and a b value was obtained. The b value was measured in accordance with JIS Z 8722 (measuring method of object color), and correction of visibility in the visible light region with a C light source and a 2 ° field of view was performed.

[Example 1]
100 parts by mass of PVA (saponified product of vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 98.9 mol%), 10 parts by mass of glycerin as a plasticizer, sodium polyoxyethylene lauryl ether sulfate as a surfactant 0 A film-forming stock solution consisting of 1 part by mass and water and having a volatile content of 85% by mass is cast on a metal drum at 80 ° C. and dried until the volatile content (water content) becomes 5% by mass. A long PVA film having a thickness of 1.5 m and a width of 30 cm (PVA film before heat treatment) was used. The degree of swelling of this PVA film was 480%.

This PVA film was heat-treated at a temperature of 142 ° C. for 10 minutes. The minimum value of the inclination of the obtained PVA film (PVA film after heat treatment) was −0.796 N / mm ² · second, the degree of swelling was 200%, and the thickness was 30 μm.

A polarizing film was produced by performing a swelling process, a dyeing process, a crosslinking process, a stretching process, a fixing process process, and a drying process on the PVA film (PVA film after heat treatment).
That is, after the above PVA film is immersed in water at a temperature of 30 ° C. for 1 minute, it is uniaxially stretched (MD) in the length direction (MD) twice as long as the original length, and then used. As long as it is immersed in a dyeing bath at a temperature of 30 ° C. mixed with water at a concentration of 0.02% by mass of iodine and 0.6% by mass of potassium iodide up to 3 times the original length While being uniaxially stretched in the length direction (MD) (second-stage stretching) and then immersed in a crosslinking bath at a temperature of 32 ° C. containing boric acid at a concentration of 2.5 mass% for 2 minutes, the original length Is uniaxially stretched in the length direction (MD) up to 3.6 times (third-stage stretching), and further contains boron at a temperature of 57 ° C. containing 2.8% by mass of boric acid and 5% by mass of potassium iodide. Uniaxial stretching (MD) in the length direction (MD) up to 6.2 times the original length while immersed in acid / potassium iodide aqueous solution ( (Stage stretching), and then the film was washed by immersing in a potassium iodide aqueous solution at a temperature of 22 ° C. containing 1.5% by mass of boric acid and 5% by mass of potassium iodide for 5 seconds, Subsequently, a polarizing film having a thickness of 12 μm was produced by drying for 240 seconds with a dryer at 60 ° C. X and Y were calculated | required by the above-described method using the obtained polarizing film.
The above results are shown in Table 1.

[Example 2]
A PVA film and a polarizing film were produced in the same manner as in Example 1 except that the temperature in the heat treatment was changed from 142 ° C. to 138 ° C., and the same evaluation as in Example 1 was performed.
The above results are shown in Table 1.

[Comparative Example 1]
A PVA film and a polarizing film were produced in the same manner as in Example 1 except that PVA having a saponification degree of 99.9 mol% was used, and the same evaluation as in Example 1 was performed.
The above results are shown in Table 1.

[Comparative Example 2]
A PVA film and a polarizing film were produced in the same manner as in Comparative Example 1 except that the temperature in the heat treatment was changed from 142 ° C. to 125 ° C., and the same evaluation as in Example 1 was performed.
The above results are shown in Table 1.

[Comparative Example 3]
A PVA film and a polarizing film were produced in the same manner as in Example 1 except that the temperature in the heat treatment was changed from 142 ° C. to 133 ° C., and the same evaluation as in Example 1 was performed.
The above results are shown in Table 1.

Claims (6)

A polyvinyl alcohol film having a minimum slope value of −0.84 to −0.783 N / mm ² · sec and a degree of swelling of 180 to 220%, and the polyvinyl alcohol film contained in the polyvinyl alcohol film. A polyvinyl alcohol film having a saponification degree of 98 to 99.5 mol% and being a raw film for producing a polarizing film.
A sample of 3 cm in the width direction cut out from the polyvinyl alcohol film was set in an autograph so as to be stretched in the length direction at a distance of 1.5 cm between chucks, immersed in water at 30 ° C. for 1 minute, and then 240% in the water. When the stress reaches 11.1 N / mm ² , the distance between chucks is fixed, the subsequent stress change with time is plotted on the horizontal axis, and the stress is plotted on the vertical axis. The minimum slope value at each point on the graph. The production of the polyvinyl alcohol film according to claim 1, comprising a step of heat-treating a polyvinyl alcohol film having a saponification degree of 98 to 99.5 mol% and a swelling degree of 250% or more at 135 to 148 ° C. Method. The manufacturing method of Claim 2 which heat-processes for 0.5 minute or more. The manufacturing method of a polarizing film including the process of extending | stretching the polyvinyl alcohol film of Claim 1 . When the b value when arranged in the parallel Nicol state with respect to the linearly polarized light is X, and the b value when arranged in the crossed Nicol state is Y, the polarizing film satisfies the following formula (I) , A polarizing film produced using the PVA film according to claim 1 .
Y ≧ 1.9X-8.3 (I) The polarizing film of Claim 5 which satisfy | fills the following formula | equation (II).
5 ≧ Y ≧ −5 (II)