JP2013097113A - Method for producing polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for smoothly and inexpensively producing thin-type polarizing films having excellent polarizing performance and hue.SOLUTION: The method for producing polarizing films includes a step of uniaxially extending a primary film primarily consisting of polyvinyl alcohol polymer in water bath containing crosslinking agent, and satisfies the following expressions (1) and (2). (1): 1≤A≤60 and (2): -0.0725×A+63.0≤B≤-0.0725×A+67.3 [In the expressions (1) and (2), A represents the thickness (unit: μm) of the primary film and B represents a temperature (unit: °C) for performing the uniaxial extension].

Description

  The present invention relates to a method for producing a polarizing film used in a liquid crystal display device or the like. More specifically, the present invention relates to a method for producing a polarizing film using a polyvinyl alcohol polymer film as a raw film, which can smoothly produce a thin polarizing film excellent in polarizing performance at low cost. .

  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 having a light switching function. The application field of this LCD is also used in small computers such as calculators and watches in the early stages of development, and in recent years, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, personal phones, and indoors and outdoors. Extensive spread to measuring instruments. Among these, particularly in a liquid crystal monitor, a liquid crystal television, and the like, a high-brightness backlight is often used. Therefore, a polarizing plate applied to these has excellent polarization performance and hue and is high-quality. It has been requested.

  The polarizing plate is generally uniaxially stretched in the longitudinal direction of a polyvinyl alcohol polymer film (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”) and dyed with iodine or a dichroic dye, Alternatively, a tripolar cellulose acetate (TAC) is applied to a polarizing film obtained by dyeing and uniaxially stretching in the longitudinal direction and then fixing with a boron compound (in some cases, dyeing and fixing may be performed simultaneously). A protective film such as a film or an acetic acid / cellulose butyrate (CAB) film is laminated.

  In such a situation, the polarizing film is required to be manufactured at a low cost in addition to the high quality as described above. In addition, due to the thinning of the LCD, the applied polarizing film is also required to be thin. Therefore, in order to meet such a demand, a polarizing film thinner than before has been required.

  In order to produce a thin polarizing film, it is conceivable to use a thin PVA polymer film corresponding to this as a raw film, but it is conventionally known that such a thin PVA polymer film is used. When a polarizing film is produced by the method, since the PVA polymer is a hydrophilic polymer, the thin PVA polymer film is water in the step of bringing the PVA polymer film into contact with water, such as a uniaxial stretching step. This makes it difficult to produce a polarizing film. Also, for example, in order to obtain a thin polarizing film having optical properties comparable to the polarizing performance and hue of a thick polarizing film uniaxially stretched in water or an aqueous solution, a dichroic substance is obtained by stretching at a higher magnification. Although it is conceivable that the film is sufficiently oriented, when a thin PVA polymer film is uniaxially stretched by a conventionally known method, it is easy to cause stretching breakage, and it is difficult to smoothly stretch at a high magnification. It was easy to connect.

  By the way, as a method for producing a thin polarizing film, a thin PVA polymer layer formed on a resin base material having a certain thickness is uniaxially stretched in a state of being integrated with the resin base material. A method of forming a film on a material is known (see, for example, Patent Documents 1 to 3). However, since the polarizing film obtained by such a method is integrated with the resin base material, its use is limited. Moreover, it is difficult to uniaxially stretch at a high magnification by such a method, and the polarizing performance There is still a problem that it is difficult to obtain a high-quality polarizing film excellent in hue and hue.

Japanese Patent No. 4691205 JP 2000-338329 A International Publication No. 2010/100917

  The objective of this invention is providing the manufacturing method of the polarizing film which can manufacture the polarizing film excellent in the polarization performance and the hue thinly smoothly at low cost.

  As a result of intensive studies to achieve the above object, the inventors of the present invention produce a polarizing film by uniaxially stretching a single-layer raw film mainly composed of a PVA polymer in a water bath containing a crosslinking agent. In this case, by controlling the temperature at which uniaxial stretching is performed within a specific range according to the thickness of the raw film, it is possible to smoothly produce a high-quality polarizing film excellent in polarization performance and hue despite being thin. The present invention was completed through further studies based on the findings.

That is, the present invention
[1] A method for producing a polarizing film comprising a step of uniaxially stretching a raw film mainly composed of a PVA polymer in a water bath containing a crosslinking agent, which satisfies the following formulas (1) and (2): Production method,
1 ≦ A ≦ 60 (1)
−0.0725 × A + 62.0 ≦ B ≦ −0.0725 × A + 67.3 (2)
[In the above formulas (1) and (2), A represents the thickness (unit: μm) of the original film, and B represents the temperature (unit: ° C.) at which the uniaxial stretching is performed. ]
[2] The production method of the above [1], wherein the raw film is a single layer film,
[3] The production method of the above [1] or [2], wherein the PVA polymer contains 1 to 4 mol% of ethylene units,
[4] The method according to any one of [1] to [3], wherein A is 45 or less,
About.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the polarizing film which can manufacture the polarizing film excellent in the polarization performance and the hue thinly smoothly at low cost is provided.

  The raw film used in the present invention contains a PVA polymer as a main component. By using a raw film containing a PVA polymer as a main component, it is possible to stretch at a high magnification and to produce a polarizing film excellent in polarizing performance smoothly and at low cost. From the viewpoint of the polarizing performance of the obtained polarizing film, the content of the PVA polymer in the raw film is preferably 75% by mass or more, more preferably 80% by mass or more, and 85% by mass or more. More preferably.

  The PVA polymer contained in the raw fabric film can be produced by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester, and as a specific example, saponifying a homopolymer of polyvinyl ester. PVA (unmodified PVA) produced by a modified PVA graft copolymerized with a small amount of comonomer (preferably less than 5 mol% relative to vinyl alcohol units) on the main chain of PVA; Small amount of comonomer (preferably relative to vinyl ester) Less than 15 mol%, more preferably less than 5 mol%) modified PVA produced by saponifying copolymerized modified polyvinyl ester; some of the hydroxyl groups of unmodified or modified PVA are formalin, butyraldehyde, benzaldehyde, etc. So-called polyvinyl acetals crosslinked with aldehydes , And the like fat.

  Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like. Among these, vinyl acetate is preferable from the viewpoint of availability.

  Examples of the comonomer include α-olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, Acrylic acid esters such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid or salts thereof; methyl methacrylate, Ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Methacrylic esters Acrylamide derivatives such as acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid or its salt, acrylamide propyl dimethylamine or its salt, N-methylol acrylamide or its derivative Methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid or salts thereof, methacrylamide propyl dimethylamine or salts thereof, N-methylol methacrylamide or derivatives thereof; N-vinylamides such as vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl Vinyl ethers such as 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; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, Vinyl halides such as vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt or ester thereof; itaconic acid or a salt or ester thereof; vinylsilyl such as vinyltrimethoxysilane Compound; isopropenyl acetate and the like can be mentioned, and one or more of these can be used. Among these, α-olefins are preferable, and ethylene is particularly preferable.

  When the PVA polymer contains an ethylene unit, the polarizing performance and durability performance of the obtained polarizing film can be improved, and color spots can be reduced. The content of ethylene units in the PVA polymer is preferably 1 to 4 mol%, more preferably 1.5 to 3 mol%, based on the number of moles of all structural units constituting the PVA polymer. More preferably, it is 2-3 mol%. When the content of the ethylene unit is 1 mol% or more, the polarizing film and the durability performance improving effect and color spot reducing effect of the obtained polarizing film are further exhibited. On the other hand, when the content of the ethylene unit is 4 mol% or less, the high affinity of the PVA polymer with water can be maintained, the uniformity of the obtained polarizing film surface can be improved, and Color spots on the film can be eliminated more effectively.

The saponification degree of the PVA polymer is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more, from the viewpoint of the polarization performance and durability of the polarizing film and the polarizing plate produced therefrom. 99.3 mol% or more is most preferable.
The degree of saponification of the PVA polymer 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 the PVA polymer. The ratio (mol%) occupied by the number of moles of vinyl alcohol units is shown. The degree of saponification of the PVA polymer can be measured by the method described in JIS K6726-1994.

The degree of polymerization of the PVA polymer is preferably 1000 or more, more preferably 1500 or more, and further preferably 2000 or more, from the viewpoint of the polarizing film and the polarizing performance and durability of the polarizing plate. The upper limit of the degree of polymerization of the PVA polymer is preferably 8000, and more preferably 6000.
The degree of polymerization of the PVA polymer can be measured according to the description of JIS K6726-1994. That is, after re-saponifying and purifying the PVA polymer, it can be determined from the intrinsic viscosity measured in water at 30 ° C.

  The raw film preferably contains a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. One or more of these may be used. Can be used. Among these, diglycerin, ethylene glycol, or glycerin is preferably used from the viewpoint of improving the stretchability of the raw film.

  As content of the polyhydric alcohol in a raw fabric film, 1-30 mass parts is preferable with respect to 100 mass parts of PVA-type polymers, 3-25 mass parts is more preferable, and 5-20 mass parts is further more preferable. When content of a polyhydric alcohol is 1 mass part or more, it can suppress that the dyeability and stretchability at the time of polarizing film manufacture fall. On the other hand, when the content of the polyhydric alcohol is 30 parts by mass or less, it can be suppressed that the raw film becomes too flexible and the handleability is lowered.

The raw film preferably contains a surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable.
Suitable examples of the anionic surfactant include carboxylic acid types such as potassium laurate, sulfate ester types such as octyl sulfate, and sulfonic acid types such as dodecylbenzene sulfonate.
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. The allyl phenyl ether type is preferred.
These surfactants may be used alone or in combination of two or more.

  As content of surfactant, 0.01-1 mass part is preferable with respect to 100 mass parts of PVA polymer, 0.02-0.5 mass part is more preferable, 0.05-0.3 mass Part is more preferred. A raw film having a surfactant content of 0.01 parts by mass or more is excellent in film forming properties during film formation and releasability from a substrate such as a drum used for film formation. A quality polarizing film can be obtained. On the other hand, when the content of the surfactant is 1 part by mass or less, it is possible to suppress the surfactant from being eluted on the surface of the raw film and causing the blocking to lower the handleability.

  The raw film is composed of components other than the above-described PVA polymer, plasticizer and surfactant, for example, dichroic dyes, stabilizers (antioxidants, ultraviolet absorbers, heat stabilizers, etc.), phase A solubilizer, an antiblocking agent, a flame retardant, an antistatic agent, a lubricant, a dispersant, a fluidizing agent, an antibacterial agent, an antifreezing agent, a pH adjusting agent, a concealing agent, an anticoloring agent, an oil agent and the like may be included. These other components may be used individually by 1 type, or may use 2 or more types together.

  As a method for forming a raw film, in addition to a method for forming a film by a melt extrusion film forming method using a raw film forming solution obtained by melting a water-containing PVA polymer, for example, a PVA polymer is a liquid. Casting film-forming method using a film-forming stock solution dissolved in a medium, wet film-forming method (a method of discharging into a poor solvent), gel film-forming method (after the film-forming stock solution is once cooled and gelled, liquid A method of extracting and removing the medium to obtain a raw film), and a method using a combination thereof. Among these, the melt extrusion film forming method and the casting film forming method are preferable from the viewpoint of obtaining a good polarizing film.

  Examples of the liquid medium include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, water, and the like. 1 type or 2 types or more of these can be used. Among these, dimethyl sulfoxide, water, or a mixture of glycerin and water is preferably used.

  Although the density | concentration of the PVA-type polymer in the said film forming undiluted | stock solution also changes with the polymerization degree etc. of a PVA-type polymer, 20-70 mass% is suitable, 25-60 mass% is more suitable, 30- 55 mass% is further more suitable, and 35-50 mass% is the most suitable. When the concentration of the PVA-based polymer is 70% by mass or less, the viscosity of the film-forming stock solution becomes too high, and it is possible to suppress the filtration and defoaming of the film-forming stock solution from being difficult. It becomes easy to obtain a little raw film. Moreover, when the density | concentration of a PVA-type polymer is 20 mass% or more, the viscosity of a film forming undiluted solution will not become low too much, and it will become easy to obtain the original fabric film which has the target thickness. In addition, the film-forming stock solution may contain one or more of the above-described plasticizers, surfactants, and other components as necessary.

The above A (unit: μm) representing the thickness of the raw film used in the present invention must satisfy the following formula (1). If A is less than 1 (μm), the strength of the raw film is too low to perform uniform uniaxial stretching, and color spots tend to occur on the polarizing film. On the other hand, when A exceeds 60 (μm), it becomes difficult to obtain a thin polarizing film, and when the original film is uniaxially stretched, the film thickness tends to fluctuate due to neck-in at the end. The color spots on the polarizing film are easily emphasized. In addition, stretchability also decreases. The A preferably satisfies the following formula (1 ′), and more preferably satisfies the following formula (1 ″).
1 ≦ A ≦ 60 (1)
10 ≦ A ≦ 50 (1 ′)
20 ≦ A ≦ 40 (1 ″)

  The raw film may be either a single layer film or a multilayer film, but is preferably a single layer film from the viewpoint of reduction in production cost. In the case where the raw film is a multilayer film, the multilayer film needs to have a PVA polymer as a main component as a whole, and the content ratio of the PVA polymer with respect to the entire multilayer film is 75. The content is preferably at least mass%, more preferably at least 80 mass%, and even more preferably at least 85 mass%.

  The method for producing the polarizing film from the original film is not particularly limited as long as it is a method that satisfies the provisions of the present invention including the step of uniaxially stretching the original film in a water bath containing a crosslinking agent. A polarizing film can be produced by subjecting the film to preliminary swelling, dyeing, uniaxial stretching, hue adjustment, drying treatment, and the like.

  The preliminary swelling can be performed by immersing the raw film in water. The temperature of water when immersed in water is preferably within a range of 20 to 40 ° C, more preferably within a range of 25 to 35 ° C, and within a range of 30 to 35 ° C. Further preferred. Moreover, as time to immerse in water, it is preferable to exist in the range of 0.1 to 5 minutes, for example, and it is more preferable to be in the range of 0.5 to 3 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.

  Dyeing can be carried out at any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching, but the PVA polymer tends to increase the degree of crystallinity due to uniaxial stretching, and the dyeability may decrease. Therefore, it is preferable to dye in an arbitrary step prior to uniaxial stretching or a uniaxial stretching step. As dyes used for dyeing, iodine-potassium iodide; 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 Examples include dichroic dyes such as yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107, and the like, and these can be used alone or in combination of two or more. The dyeing of the original film is usually performed by immersing the original film in a solution containing the above dye, but it may be performed by a method such as mixing a dye into a film-forming stock solution used for producing the original film. .

  The production method of the present invention includes a step of uniaxially stretching the raw film in a water bath containing a crosslinking agent, and it is necessary to satisfy formula (2) described later. A uniaxially stretched raw film in a water bath containing a cross-linking agent provides a polarizing film with strong dye adsorption. Examples of the crosslinking agent include boron compounds such as borates such as boric acid and borax; polyvalent aldehyde compounds such as glyoxal and glutaraldehyde, and one of these is used alone. Or two or more of them may be used in combination. Among these crosslinking agents, a boron compound is preferable and boric acid is more preferable from the viewpoints of optical properties and availability of the obtained polarizing film. The concentration of the cross-linking agent in the water bath containing the cross-linking agent is preferably 1 to 15% by mass and 2 to 7% by mass because the optical properties of the obtained polarizing film can be improved and shrinkage can be effectively prevented. More preferred is 3 to 6% by mass. In the water bath containing the cross-linking agent, the cross-linking agent may be completely dissolved in water or may be partly or completely dispersed without being dissolved, but all the cross-linking agents are dissolved in water. It is preferable because a polarizing film having uniform performance can be easily obtained.

The water bath containing a crosslinking agent preferably further contains an auxiliary agent in addition to the crosslinking agent. When the water bath containing the crosslinking agent further contains an auxiliary agent, it is possible to obtain a polarizing film having more uniform optical characteristics in the plane. Examples of the auxiliary agent include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples thereof include iodides such as titanium, and one of these may be used alone, or two or more may be used in combination. The concentration of the auxiliary agent in the water bath containing the crosslinking agent is preferably in the range of 0.05 to 15% by mass, more preferably in the range of 0.5 to 8% by mass, and 2 to 5% by mass. More preferably, it is in the range of%.
Further, as described above, the uniaxial stretching can be performed simultaneously with the dyeing. In this case, it is preferable that the water bath containing the crosslinking agent further contains a dye.

  Uniaxial stretching when producing a polarizing film from a raw fabric film may be performed in one step or in multiple stages, and when performed in multiple stages, at least one stage contains a crosslinking agent. What is necessary is just to satisfy | fill Formula (2) mentioned later while being performed in a water bath.

  The stretching ratio of uniaxial stretching (when the uniaxial stretching is performed in multiple stages, the total stretching ratio, that is, the ratio based on the original length) is the original film before uniaxial stretching from the viewpoint of the polarizing film and the polarizing performance of the polarizing plate. Is preferably 5 times or more, more preferably 6 times or more. Although there is no upper limit in the strict sense about the draw ratio, it is preferable that the draw ratio is 8 times or less because uniform stretching is easy. When the draw ratio is excessively high, the film tends to break. On the other hand, if the draw ratio is too low, the polarization degree of the polarizing plate may be insufficient.

Further, in the production method of the present invention, the above A (unit: μm) representing the thickness of the raw film and B (unit: ° C.) representing the temperature at which uniaxial stretching needs to satisfy the following formula (2). is there. When B is lower than the lower limit value represented by the formula (2), the polarizing performance of the polarizing film that can decrease the limit stretching ratio is lowered. Moreover, when B exceeds the upper limit shown by Formula (2), stretch | stretch cut | run_off occurs and it becomes difficult to manufacture a polarizing film smoothly. The B preferably satisfies the following formula (2 ′), and more preferably satisfies the following formula (2 ″).
−0.0725 × A + 63.0 ≦ B ≦ −0.0725 × A + 67.3 (2)
−0.0725 × A + 63.1 ≦ B ≦ −0.0725 × A + 66.3 (2 ′)
−0.0725 × A + 63.3 ≦ B ≦ −0.0725 × A + 66.0 (2 ″)

  The hue adjustment is preferably performed after dyeing and uniaxial stretching, and can be performed by immersing the original film after dyeing and uniaxial stretching in a hue adjusting bath. Examples of the hue adjustment bath include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. A water bath containing an iodide such as titanium may be mentioned. The concentration of iodide in the water bath is preferably in the range of 0.05 to 15% by mass because the hue when the finally obtained polarizing film is orthogonally arranged can be improved. More preferably, it is in the range of ˜8% by mass, and further preferably in the range of 2-5% by mass. Moreover, the said hue adjustment bath may further contain boron compounds, such as a boric acid and a borate, as needed.

  The temperature of the hue adjusting bath is usually about 20 to 70 ° C, preferably 25 to 65 ° C, more preferably 30 to 60 ° C. Moreover, the immersion time at the time of immersing in a hue adjustment bath is although it does not specifically limit, Since the hue at the time of orthogonally arrange | positioning the polarizing film finally obtained can be improved, 1 to 60 second is preferable, and 2-30 The second is more preferable, and 3 to 20 seconds is more preferable. Setting the immersion time in the hue adjusting bath and the concentration of iodide and the like in the above ranges is preferable from the viewpoint of adjusting the hue when the polarizing plates are arranged orthogonally.

  By the drying treatment, water absorbed in steps such as pre-swelling, dyeing, uniaxial stretching and hue adjustment can be removed. The drying temperature is usually in the range of 20 to 150 ° C, but preferably in the range of 40 to 100 ° C. If the drying temperature is too low, the drying time becomes longer and the production efficiency may decrease. On the other hand, when the drying temperature is too high, the obtained polarizing film is deteriorated, and the polarizing performance and the hue may be insufficient. The heat drying time is usually about 1 to 5 minutes.

  According to the production method of the present invention, a thin polarizing film can be produced. As thickness of the said polarizing film, 3-30 micrometers is preferable and 5-20 micrometers is more preferable.

  The polarizing film obtained by the production method of the present invention can be preferably used in the form of a polarizing plate in which a protective film that is optically transparent and has mechanical strength is bonded to 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 the polarizing film and the protective film include polyvinyl alcohol-based adhesives and urethane-based adhesives, among which polyvinyl alcohol-based adhesives are suitable.

  The polarizing plate obtained as described above can be used as a component of an LCD after being coated with an acrylic-based pressure-sensitive adhesive and then bonded to a glass substrate. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, and the like may be bonded simultaneously.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the following Examples and Comparative Examples, the polarizing performance and hue of the polarizing film were measured or evaluated by the following methods.

(1) Polarizing performance of polarizing film:
From a central part in the width direction of the polarizing film obtained in the following examples or comparative examples, a square sample of about 4 cm × 4 cm is taken in parallel to the orientation direction of the polarizing film, and a spectrophotometer with an integrating sphere (JASCO) Using the “V7100” manufactured by Co., Ltd., the single transmittance Ts ′ and the degree of polarization P of this sample were obtained, and the surface transmittance was removed from the single transmittance Ts ′ to calculate the single transmittance Ts corrected for visibility. did.
Further, the dichroic ratio Rd of the polarizing film was calculated by the following formula. In the following formula, Ts represents the single transmittance (%) corrected for the visibility, and P represents the degree of polarization (%).
Rd = log (Ts / 100−Ts / 100 × P / 100) / log (Ts / 100 + Ts / 100 × P / 100)

(2) Color of polarizing film:
In the measurement of the polarization performance in (1) above, the b value based on the Hunter Lab color system was obtained and used as an index for hue evaluation. The closer the b value is to 0, the higher the neutrality of the polarizing film and the better the hue.

[Example 1]
A 20 μm-thick PVA film (PVA content of 88% by mass) containing 6 parts by mass of glycerin with respect to 100 parts by mass of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was pre-swelled. The polarizing film was manufactured by dyeing, uniaxial stretching and drying. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.3 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution of 30 ° C. for 1 minute, and the original length is the same as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.4 times. Subsequently, the PVA film was uniaxially stretched in a 4% by weight boric acid aqueous solution at 61.8 ° C. so as to be 6.3 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 8 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 43.9%, the degree of polarization (P) is 99.99%, the dichroic ratio (Rd) obtained by calculation is 75.6, and the polarization performance. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Example 2]
A PVA film having a thickness of 20 μm containing 6 parts by mass of glycerin (modified PVA content of 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.3 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution of 30 ° C. for 1 minute, and the original length is the same as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.4 times. Subsequently, the PVA film was uniaxially stretched in a 4 mass% boric acid aqueous solution at 64.2 ° C. so as to be 6.2 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 8 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 43.8%, the degree of polarization (P) is 99.99%, the dichroic ratio (Rd) obtained by calculation is 74.3, and the polarization performance. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Example 3]
A PVA film having a thickness of 30 μm containing 6 parts by mass of glycerin (modified PVA content of 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.3 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution of 30 ° C. for 1 minute, and the original length is the same as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.4 times. Subsequently, the PVA film was uniaxially stretched in a 4% by mass boric acid aqueous solution at 62.0 ° C. so as to be 6.2 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 12 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 43.6%, the degree of polarization (P) is 99.99%, and the dichroic ratio (Rd) obtained by calculation is 75.0. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Example 4]
A PVA film having a thickness of 30 μm containing 6 parts by mass of glycerin (modified PVA content of 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.5 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution of 30 ° C. for 1 minute, and the original length is the same as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.6 times. Subsequently, the PVA film was uniaxially stretched in a 4% by mass boric acid aqueous solution at 63.0 ° C. so as to be 6.2 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 12 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 44.1%, the degree of polarization (P) is 99.98%, the dichroic ratio (Rd) obtained by calculation is 73.2, and the polarization performance. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Example 5]
A PVA film having a thickness of 40 μm containing 6 parts by mass of glycerin (modified PVA content: 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.5 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Subsequently, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in a 30 ° C. aqueous solution at 4% by mass for 1 minute. The film was dyed while being uniaxially stretched to 2.6 times. Subsequently, the PVA film was uniaxially stretched in a 4 mass% boric acid aqueous solution at 60.5 ° C. so as to be 6.5 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 17 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 43.9%, the degree of polarization (P) is 99.99%, the dichroic ratio (Rd) obtained by calculation is 77.1, and the polarization performance. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Example 6]
A PVA film having a thickness of 40 μm containing 6 parts by mass of glycerin (modified PVA content: 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 2.2 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Subsequently, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in a 30 ° C. aqueous solution at 4% by mass for 1 minute. The film was dyed while being uniaxially stretched to be 3.3 times. Subsequently, the PVA film was uniaxially stretched in a 4% by weight boric acid aqueous solution at 63.0 ° C. so as to be 6.5 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 16 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 43.7%, the degree of polarization (P) is 99.99%, and the dichroic ratio (Rd) obtained by calculation is 76.1. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Example 7]
A PVA film having a thickness of 50 μm and containing 12 parts by mass of glycerin with respect to 100 parts by mass of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was used as a raw film, and this was pre-swelled. The polarizing film was manufactured by dyeing, uniaxial stretching and drying. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.6 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution at 30 ° C. for 3 minutes, and the original length is in the same direction as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.7 times. Subsequently, the PVA film was uniaxially stretched in a 4 mass% boric acid aqueous solution at 60.7 ° C. so as to be 6.5 times the original length in the same direction as the uniaxial stretching. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 20 μm.
The obtained polarizing film had a good hue. The single transmittance (Ts) corrected for visibility is 43.7%, the degree of polarization (P) is 99.99%, the dichroic ratio (Rd) obtained by calculation is 76.7, and the polarization performance. Was very good. Furthermore, the drawing film was not cut during the production of the polarizing film, and the polarizing film could be produced smoothly.

[Comparative Example 1]
A PVA film having a thickness of 20 μm containing 6 parts by mass of glycerin (modified PVA content of 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.3 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution of 30 ° C. for 1 minute, and the original length is the same as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.4 times. Subsequently, the PVA film was uniaxially stretched in the same direction as the uniaxial stretching in a 4 mass% boric acid aqueous solution at 58.5 ° C. However, since the stretching break occurred at the preliminary test stage, Uniaxial stretching was performed up to 5.6 times the original length, which is the stretching ratio. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 9 μm.
The obtained polarizing film had a single transmittance (Ts) corrected for visibility of 44.0% and a polarization degree (P) of 99.92%, and the dichroic ratio (Rd) determined by calculation was 62.%. 1 and the polarization performance was insufficient. Moreover, compared with the polarizing film of Examples 1-7, the hue was inferior.

[Comparative Example 2]
A PVA film having a thickness of 30 μm containing 6 parts by mass of glycerin (modified PVA content of 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.5 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution of 30 ° C. for 1 minute, and the original length is the same as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.6 times. Subsequently, the PVA film was uniaxially stretched in the same direction as the uniaxial stretching in a 4% by weight boric acid aqueous solution at 59.0 ° C., but the stretching break occurred at the preliminary test stage. Uniaxial stretching was performed up to 6.2 times the original length, which is the stretch ratio. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 12 μm.
The obtained polarizing film had a single transmittance (Ts) corrected for visibility of 44.0% and a degree of polarization (P) of 99.94%, and the dichroic ratio (Rd) determined by calculation was 64.%. 2 and the polarization performance was insufficient. Moreover, compared with the polarizing film of Examples 1-7, the hue was inferior.

[Comparative Example 3]
A PVA film having a thickness of 40 μm containing 6 parts by mass of glycerin (modified PVA content: 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.8 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Subsequently, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in a 30 ° C. aqueous solution of 4% by mass for 1 minute, and the original length is in the same direction as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.9 times. Subsequently, the PVA film was uniaxially stretched in the same direction as the uniaxial stretching in a 4% by weight boric acid aqueous solution at 59.0 ° C., but the stretching break occurred at the preliminary test stage. Uniaxial stretching was performed up to 6.2 times the original length, which is the stretch ratio. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 18 μm.
The obtained polarizing film had a single transmittance (Ts) corrected for visibility of 43.7% and a polarization degree (P) of 99.97%, and the dichroic ratio (Rd) determined by calculation was 66. 7 and the polarization performance was insufficient. Moreover, compared with the polarizing film of Examples 1-7, the hue was inferior.

[Comparative Example 4]
A 40 μm-thick PVA film (PVA content 82 mass%) containing 12 parts by mass of glycerin with respect to 100 parts by mass of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was pre-swelled. The polarizing film was manufactured by dyeing, uniaxial stretching and drying. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.8 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Subsequently, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in a 30 ° C. aqueous solution at 4% by mass for 1 minute. The film was dyed while being uniaxially stretched to 2.9 times. Subsequently, the PVA film was uniaxially stretched in the same direction as the uniaxial stretch in a 4 mass% boric acid aqueous solution at 65.0 ° C., but the original film was unable to withstand the high temperature and fusing occurred, so that a polarizing film was obtained. I couldn't.

[Comparative Example 5]
A PVA film having a thickness of 40 μm containing 6 parts by mass of glycerin (modified PVA content: 88% by mass) with respect to 100 parts by mass of modified PVA having a saponification degree of 99.3 mol%, a polymerization degree of 2400, and an ethylene unit content of 2 mol%. Using it as a raw film, this was pre-swelled, dyed, uniaxially stretched and dried to produce a polarizing film. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.8 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Subsequently, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in a 30 ° C. aqueous solution at 4% by mass for 1 minute. The film was dyed while being uniaxially stretched to 2.9 times. Subsequently, the PVA film was uniaxially stretched in water at 63.0 ° C. in the same direction as the uniaxial stretch. Was uniaxially stretched up to 5.0 times. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 25 μm.
The obtained polarizing film had a single transmittance (Ts) corrected for visibility of 43.7% and a polarization degree (P) of 99.41%, and the dichroic ratio (Rd) obtained by calculation was 43.3%. 3 and the polarization performance was insufficient. Moreover, compared with the polarizing film of Examples 1-7, the hue was inferior.

[Comparative Example 6]
A 75 μm thick PVA film (PVA content 82 mass%) containing 12 parts by mass of glycerin with respect to 100 parts by mass of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was pre-swelled. The polarizing film was manufactured by dyeing, uniaxial stretching and drying. That is, the PVA film was uniaxially stretched so that the length of the PVA film was 1.8 times the original length while being pre-swelled by being immersed in 30 ° C. water for 30 seconds. Then, the iodine / potassium iodide concentration ratio (mass ratio) is 1/100 and the total concentration of both is immersed in an aqueous solution at 30 ° C. for 3 minutes, and the original length is in the same direction as the uniaxial stretching. The film was dyed while being uniaxially stretched to 2.9 times. Subsequently, the PVA film was uniaxially stretched in a 40.0% by weight boric acid aqueous solution at 60.0 ° C. in the same direction as the uniaxial stretching. Uniaxial stretching was performed up to 6.3 times the original length, which is the stretching ratio. Thereafter, the PVA film was taken out and dried with hot air at 60 ° C. to obtain a polarizing film having a thickness of 30 μm.
The obtained polarizing film had a single transmittance of 44.3% corrected for visibility, a polarization degree (P) of 99.30%, and a dichroic ratio (Rd) determined by calculation of 46.4. The polarization performance was at an insufficient level. Moreover, compared with the polarizing film of Examples 1-7, the hue was inferior.

  The above results are shown in Table 1 below.

  According to the present invention, a thin polarizing film excellent in polarization performance and hue can be produced smoothly and at low cost. Taking advantage of the thinness of the polarizing film, liquid crystal displays such as calculators, watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring instruments used indoors and outdoors. It can be effectively used as a raw material for a polarizing plate which is a component of the apparatus, and is particularly useful as a raw material for a polarizing plate for a liquid crystal monitor or a liquid crystal television.

Claims (4)

A method for producing a polarizing film comprising a step of uniaxially stretching a raw film comprising a polyvinyl alcohol polymer as a main component in a water bath containing a crosslinking agent, wherein the production method satisfies the following formulas (1) and (2): .
1 ≦ A ≦ 60 (1)
−0.0725 × A + 63.0 ≦ B ≦ −0.0725 × A + 67.3 (2)
[In the above formulas (1) and (2), A represents the thickness (unit: μm) of the original film, and B represents the temperature (unit: ° C.) at which the uniaxial stretching is performed. ]   The manufacturing method of Claim 1 whose said raw film is a single layer film.   The manufacturing method of Claim 1 or 2 with which the said polyvinyl alcohol-type polymer contains 1-4 mol% of ethylene units.   The manufacturing method of any one of Claims 1-3 whose said A is 45 or less.