JP2006267153A - Manufacturing method of polarizing film, polarizing film, polarizing plate, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a polarizing film having a uniform optical characteristic. <P>SOLUTION: In the manufacturing method of polarizing film, the polarizing film is manufactured by subjecting a polyvinyl alcohol based film to at least a swelling process, a dyeing process, a fixing process, and a stretching process. Further, the swelling process includes procedures of successively immersing the polyvinyl alcohol based film into bath solutions in a plurality of swelling tanks and is set so as to satisfy the following relation; (bath temperature of the (N+1)th swelling tank) - (bath temperature of the Nth swelling tank) > 7°C, wherein N is a natural number. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a polarizing film useful as a material for a polarizing plate suitably used for a flat panel display such as a liquid crystal display device (hereinafter, appropriately referred to as LCD) and an electroluminescence display device (hereinafter, appropriately referred to as ELD), The present invention relates to a polarizing film manufactured using this manufacturing method, a polarizing plate including the polarizing film, and an image display device (LCD or the like).

  Currently, polarizing plates for flat panel displays, particularly polarizing plates used in LCDs, are generally made from polyvinyl alcohol (PVA) film, and dichroic such as iodine in order to obtain sufficient optical properties as LCDs. A PVA film containing a substance is first stretched to produce a polarizing film, and a protective film is bonded to the polarizing film. As the protective film, a saponified triacetyl cellulose (TAC) film is preferably used. For example, the protective film is bonded to a polarizing film using a PVA adhesive.

  If it demonstrates concretely about the manufacturing method of a polarizing film, it will carry out the swelling process which conveys the PVA-type film (raw material) which is a hydrophilic polymer film with a guide roll, and immerses it in the bath liquid in a swelling treatment tank. Fixing the film to swell, then immersing it in a solution containing the dichroic substance in the dyeing tank and applying it to the dyeing process, and then stretching it while immersing it in the solution containing the boron compound in the fixing tank In general, a polarizing film is produced by performing a treatment (including a stretching treatment).

  Here, with the recent high definition and high functionality of LCDs, there has been a further demand for improvement in screen uniformity and quality. In addition, with the diversification of use environments, high heat resistance, moist heat resistance, water resistance, and the like have been required. Furthermore, from the viewpoint of portability, a reduction in thickness and weight is also required. Due to these demands for LCDs, there are also demands for high performance and high functionality such as uniformity of optical properties, high heat resistance, moisture and heat resistance, water resistance, thinning, etc. for polarizing plates for LCDs. Has been made.

  In view of the demand for the polarizing plate as described above, a PVA-based film with improved thickness uniformity has been proposed, but even if such a film is used, the optical characteristics of the produced polarizing film May be non-uniform (for example, phase difference unevenness or unevenness in the content of the dichroic substance).

  The present invention has been made to solve the problems of the prior art, and includes a method for producing a polarizing film having uniform optical characteristics, a polarizing film produced using the production method, and the polarizing film. It is an object to provide a polarizing plate and an image display device.

  In order to solve the above-mentioned problems, the inventors of the present invention diligently studied the manufacturing process of the polarizing film, and as a result, swelling unevenness generated in the initial stage of the swelling treatment for the polyvinyl alcohol film remains in the subsequent process. Was first found. Then, a plurality of swelling treatment tanks are prepared, and the bath liquid in the swelling treatment tank is set to a higher temperature as the latter stage is reached (the difference in bath temperature between adjacent swelling treatment tanks is set to be larger than 7 ° C.). It has been found that if the swelling is set to be saturated, the progress of swelling in the initial stage is alleviated to suppress swelling unevenness, and as a result, a polarizing film having uniform optical properties can be produced. In order to effectively alleviate the progress of swelling in the initial stage, it is preferable to set the bath temperature of the first swelling treatment tank to a low temperature of 0 to 25 ° C. If the temperature is set higher than 55 ° C., the film becomes soft. If tension is applied to improve the transportability, the film may be stretched more than necessary, which may adversely affect the optical properties. I found it. The present invention has been completed based on the knowledge found by the inventors of the present invention.

  That is, the present invention is a method for producing a polarizing film by performing at least a swelling treatment step, a dyeing treatment step, an immobilization treatment step and a stretching treatment step on a polyvinyl alcohol film, wherein the swelling treatment step comprises: Including a procedure of sequentially immersing the polyvinyl alcohol film in a bath solution in a plurality of swelling treatment tanks, wherein the bath temperature of the (N + 1) th swelling treatment tank−the bath temperature of the Nth swelling treatment tank> 7 ° C. (where N Is a natural number), the bath temperature of the first swelling treatment tank is set to 0 to 25 ° C., and the bath temperature of the last swelling treatment tank is set to 7 to 55 ° C. A manufacturing method is provided.

  Moreover, this invention comprises the polarizing film manufactured using the said manufacturing method, the polarizing plate characterized by the transparent protective layer being formed in the at least one surface of the said polarizing film, and the said polarizing plate. It is also provided as an image display device characterized by the above.

  According to the method for producing a polarizing film of the present invention, it is possible to produce a polarizing film having a uniform optical property by suppressing the progress of swelling in the initial stage and suppressing swelling unevenness.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram schematically showing a production line for carrying out a method for producing a polarizing film according to an embodiment of the present invention. As shown in FIG. 1, the production line according to this embodiment includes a plurality of swelling treatment tanks 10, a dyeing treatment tank 20, an immobilization treatment tank 30, and a drying furnace 40. When manufacturing a polarizing film with the manufacturing line which concerns on this embodiment, a polyvinyl alcohol (PVA) type film is first conveyed sequentially to the several swelling processing tank 10 first.

  As the PVA film according to the present embodiment, a film obtained by forming a stock solution obtained by dissolving a polyvinyl alcohol resin in water or an organic solvent by an arbitrary method such as a casting method, a casting method, an extrusion method, or the like. It can be used as appropriate. The degree of polymerization of the polyvinyl alcohol resin used is preferably in the range of 100 to 5000, more preferably in the range of 1400 to 4000, from the viewpoint of the solubility of the resin in the solvent.

  The PVA film is sequentially immersed in a bath solution (for example, pure water subjected to reverse osmosis membrane treatment) in the plurality of swelling treatment tanks 10 and subjected to a swelling treatment step. Here, the bath temperature of the (N + 1) th swelling treatment tank 10−the bath temperature of the Nth swelling treatment tank 10> 7 ° C. (where N is a natural number). By setting in this way, the progress of swelling in the initial stage is mitigated, swelling unevenness is suppressed, and thus a polarizing film having uniform optical characteristics can be produced, and the swelling can be saturated in a short time. It is also possible to increase the manufacturing efficiency of the polarizing film. Moreover, in this embodiment, as a preferable aspect, the bath temperature of the first swelling treatment tank 10 is set to 0 to 25 ° C. (more preferably 0 to 20 ° C.), and the last swelling treatment tank (for example, two If the swelling treatment tank is provided, the bath temperature of the second swelling treatment tank) 10 is set to 7 to 55 ° C. (more preferably 30 to 40 ° C.). According to such a preferred embodiment, the progress of swelling in the initial stage is effectively mitigated, while there is an advantage that the PVA film is stretched more than necessary and the optical properties are not hindered.

  Next, the film subjected to the swelling treatment in the plurality of swelling treatment tanks 10 is conveyed to the dyeing treatment tank 20 and subjected to the dyeing treatment process. As a bath solution in the dyeing treatment tank 20, a solution in which a dichroic substance (iodine in this embodiment) is dissolved in a solvent can be used, and the film is dyed by immersing the film in the solution for 1 to 20 minutes. (Iodine adsorption) is applied. The iodine concentration in the solution is usually 0.1 to 1.0 part by mass per 100 parts by mass of water as a solvent. In order to increase the dyeing efficiency, the solution contains potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, It is possible to add 0.02 to 20 parts by mass, preferably 2 to 10 parts by mass of an auxiliary agent made of iodide such as tin iodide or titanium iodide. As the solvent, water is generally used, but a small amount of an organic solvent compatible with water may be added. In addition, the dyeing | staining process demonstrated above can also be performed simultaneously with a swelling process by making the bath liquid of the swelling processing tank 10 mentioned above into the aqueous solution containing dichroic substances, such as an iodine and an organic dye.

  Next, the film subjected to the dyeing process in the dyeing tank 20 is conveyed to the immobilization tank 30 and is immersed in the bath solution in the immobilization tank 30 and stretched, thereby effecting the dyeing on the film. An immobilization treatment (crosslinking treatment) step is performed for sustaining. As the bath liquid in the immobilization treatment tank 30, a solution in which a boron compound is dissolved can be used. As a composition of such a boron compound-containing solution, usually 1 to 10 parts by mass of a PVA cross-linking agent such as boric acid, borax, glyoxal, and glutaraldehyde per 100 parts by mass of water as a solvent is contained. The This is because, when the concentration of the crosslinking agent is less than 1 part by mass, sufficient optical properties cannot be obtained, whereas when it exceeds 10 parts by mass, the stretching force generated in the film during stretching increases and the film shrinks. It is because it becomes the cause. In order to obtain uniform characteristics in the film plane, the solution contains potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide. Auxiliary agents made of iodide such as calcium iodide, tin iodide and titanium iodide can be added in an amount of 0.05 to 15% by mass, preferably 0.5 to 8% by mass. Moreover, the temperature of a solution is normally set to the range of 20-70 degreeC, Preferably it is 40-60 degreeC. The immersion time is not particularly limited, but is usually 1 second to 15 minutes, preferably 5 seconds to 10 minutes. As the solvent, a small amount of an organic solvent compatible with water may be added in addition to water.

  The film that has been subjected to the immobilization treatment in the immobilization treatment tank 30 further has an aqueous iodide solution (sulfuric acid such as potassium iodide having a water temperature of 10 to 60 ° C, preferably 30 to 40 ° C, and a concentration of 0.1 to 10% by mass. It is washed with water (not shown in FIG. 1) by being immersed in an auxiliary agent such as zinc or zinc chloride for 1 second to 1 minute, and conveyed to the drying furnace 40. In the drying furnace 40, the drying process is preferably performed at 10 ° C. to 150 ° C., more preferably 20 ° C. to 80 ° C., and the film is carried out as a polarizing film. The thickness of the polarizing film is not particularly limited, but is preferably about 5 to 80 μm.

  The PVA film is subjected to a stretching treatment, but the total stretching ratio obtained by accumulating the stretching ratio in each step is preferably set in a range of 3 to 7 times, and particularly in a range of 5 to 6.5 times. It is preferable to set. This is because when the total draw ratio is less than 3 times, it is difficult to obtain a polarizing film having a high degree of polarization, and when it exceeds 7 times, the film tends to break. In addition, the stretching method, the number of stretching, and the like are not particularly limited, and the stretching process may be performed in each step of the dyeing process and the fixing process described above, or may be performed only in any one of the processes. Is possible. It is also possible to provide a separate stretching tank and perform the stretching process in the stretching tank. Furthermore, you may perform a extending | stretching process in multiple times by the same process.

  The polarizing film manufactured as described above is formed into a polarizing plate by forming a transparent protective layer on both sides or one side. Such a transparent protective layer can be formed as a polymer-coated layer or a film laminate layer. As the transparent polymer or film material for forming the transparent protective layer, an appropriate transparent material can be used, but in addition to optical transparency and mechanical strength, those excellent in thermal stability and moisture barrier properties are preferable. Used.

  Examples of the material for forming the transparent protective layer include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as cellulose diacetate and triacetyl cellulose (TAC), acrylic polymers such as polymethyl methacrylate, Examples thereof include styrene polymers such as polystyrene and acrylonitrile / styrene copolymer (AS resin), and polycarbonate polymers.

  In addition, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or these A polymer mixture or the like can also be exemplified as a material for forming the transparent protective layer.

  Further, the transparent protective layer can be formed as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylurethane, epoxy, or silicone.

  In addition, when forming a transparent protective layer on both surfaces of a polarizing film, each transparent protective layer may be formed from the same material, and can also be formed from a different material. The thickness of the transparent protective layer is not particularly limited, but is generally 500 μm or less, preferably 1 to 300 μm, more preferably 5 to 200 μm. Further, the surface of the transparent protective layer that does not come into contact with the polarizing film is subjected to, for example, saponification treatment with alkali, plasma treatment, glow discharge treatment, corona discharge treatment, high frequency treatment, electron beam treatment, etc. Hard coat layer for anti-sticking, anti-reflection layer for anti-reflection of external light on the surface of polarizing film, anti-sticking layer for anti-adhesion with adjacent layer, diffuses transmitted light of polarizing film It is also possible to provide a diffusion layer for expanding the viewing angle, an antiglare layer provided with a fine concavo-convex structure for the purpose of preventing reflection of external light on the surface of the polarizing film, and the like.

  As the transparent protective layer, a cellulose polymer such as triacetyl cellulose is preferably used from the viewpoints of polarization characteristics and durability, and it is particularly preferable to attach a triacetyl cellulose film to the polarizing film. For bonding the polarizing film and the transparent protective layer (transparent protective film), a polyvinyl alcohol (PVA) resin and a crosslinking agent can be used as an adhesive.

  As said PVA-type resin, unsubstituted PVA resin and PVA resin which has a highly reactive functional group are used suitably. In particular, a PVA resin having a highly reactive functional group (for example, a polyvinyl alcohol resin modified with an acetoacetyl group) is preferably used in that the durability of the polarizing plate is improved.

  Examples of the crosslinking agent include (1) alkylene diamines having 2 amino groups and alkylene groups such as ethylene diamine, triethylene diamine, and hexamethylene diamine (particularly hexamethylene diamine is preferable), (2) tolylene diisocyanate, Hydrogenated tolylene diisocyanate, trimethylolpropane-tolylene diisocyanate adduct, triphenylmethane triisocyanate, methylene bis (4-phenylmethane triisocyanate, isophorone diisocyanate, and isocyanates such as ketoxime block or phenol block, 3) Ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin di or triglycidyl ether, 1,6-hexanedi Diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diglycidyl amine and other epoxies, (4) monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, (5) glyoxal, malondialdehyde , Succindialdehyde, glutardialdehyde, maleidialdehyde, phthaldialdehyde and other dialdehydes (especially glyoxal is preferred), (6) alkylated methylol urea, alkylated methylol melamine, acetoguanamine, benzoguanamine and formaldehyde Amino-formaldehyde resins such as condensates (especially alkylated methylol melamine is preferred), (7) sodium, potassium, magnesium, calcium It can be mentioned beam, aluminum, iron, divalent metal or trivalent metal salts and oxides such as nickel.

  The polarizing plate according to the present embodiment can be preferably used as a component of various image display devices such as an ELD and a PDP including an LCD. For example, the LCD can have an appropriate structure according to the prior art such as a transmissive type, a reflective type, or a transmissive / reflective type in which the polarizing plate is disposed on one side or both sides of a liquid crystal cell. The liquid crystal cell forming the LCD is arbitrary, and for example, a liquid crystal cell of an appropriate type such as an active matrix driving type typified by a thin film transistor type may be used. Moreover, when arrange | positioning the polarizing plate which concerns on this embodiment on both sides of a liquid crystal cell, the same structure may be sufficient and a different structure may be sufficient. Furthermore, when forming the LCD, for example, appropriate components such as a prism array sheet, a lens array sheet, a diffusion plate, and a backlight can be arranged in one or more layers at appropriate positions.

  Hereinafter, the features of the present invention will be further clarified by showing examples and comparative examples.

<Example>
A polyvinyl alcohol film having a thickness of 75 μm was first swelled by immersing it in an aqueous bath solution (pure water) having a bath temperature of 20 ° C. in the first swelling treatment tank for 50 seconds, and then in the second swelling treatment tank. It was immersed in an aqueous bath solution (pure water) having a bath temperature of 40 ° C. for 10 seconds to swell. In the first and second swelling treatment tanks, not only the swelling treatment but also the uniaxial stretching treatment is performed, and the stretching ratio is 2.7 times in total in the two tanks (2 times in the first swelling treatment tank, And 1.35 times in the second swelling treatment tank). Next, the film subjected to the swelling treatment was immersed in an aqueous iodine solution having a bath temperature of 30 ° C. in the dyeing treatment tank for 30 seconds to perform the dyeing treatment. Subsequently, the dyed film was immersed for 10 seconds in an aqueous solution containing 3% by weight boric acid and 3% by weight potassium iodide at a bath temperature of 40 ° C. in an immobilization treatment tank. Treatment). Furthermore, the film after the fixing treatment is immersed in an aqueous solution containing 4% by weight boric acid and 5% by weight potassium iodide at a bath temperature of 55 ° C. in a stretching tank until the cumulative stretching ratio becomes 6 times. Stretched uniaxially. And the film after the said extending | stretching was conveyed to the drying furnace, the drying process for 2 minutes was given at 50 degreeC, and the polarizing film was produced.

<Comparative Example 1>
A polarizing film was produced under the same conditions as in the Examples except that only one swelling treatment tank (also subjected to stretching treatment) was used, the bath temperature was 30 ° C., and the time for immersion in the bath solution was 50 seconds.

<Comparative example 2>
A polarizing film was produced under the same conditions as in the example except that the bath temperature in the first swelling treatment tank was 20 ° C. and the bath temperature in the second swelling treatment tank was 60 ° C.

<Evaluation results>
Measure the degree of polarization of the polarizing films prepared in Examples and Comparative Examples 1 and 2 at a pitch of 2 mm in the width direction of the film (the degree of polarization was measured using a spectro photometer DOT-3C manufactured by Murakami Color Research Laboratory). The average value and variation were evaluated. Note that the variation in the measured values was calculated by the standard deviation of the measured values / the average value of the measured values. The evaluation results are shown in Table 1.

  As shown in Table 1, the polarizing films of the examples not only show the same degree of polarization as the polarizing films of Comparative Examples 1 and 2, but also the variation is compared to the polarizing films of Comparative Examples 1 and 2. Very small and uniform optical properties could be obtained.

FIG. 1 is a block diagram schematically showing a production line for carrying out a method for producing a polarizing film according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Plural swelling processing tank 20 ... Dyeing processing tank 30 ... Immobilization processing tank 40 ... Drying furnace

Claims (4)

A method for producing a polarizing film by subjecting at least a swelling treatment step, a dyeing treatment step, an immobilization treatment step and a stretching treatment step to a polyvinyl alcohol film,
The swelling treatment step includes a procedure of sequentially immersing the polyvinyl alcohol film in a bath solution in a plurality of swelling treatment tanks,
The bath temperature of the (N + 1) th swelling treatment tank−the bath temperature of the Nth swelling treatment tank> 7 ° C. (where N is a natural number),
The manufacturing method of the polarizing film characterized by setting the bath temperature of the 1st swelling processing tank to 0-25 degreeC, and setting the bath temperature of the last swelling processing tank to 7-55 degreeC.   The polarizing film manufactured using the manufacturing method of Claim 1.   A polarizing plate, wherein a transparent protective layer is formed on at least one surface of the polarizing film according to claim 2.   An image display device comprising the polarizing plate according to claim 3.

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