JP5991883B2 - Method for producing polarizer and method for producing polarizing plate - Google Patents

Description

  The present invention relates to a method for producing a polarizer and a method for producing a polarizing plate. The polarizer obtained by the production method of the present invention can be used as a polarizing plate provided with a transparent protective film on at least one surface thereof. These polarizers and polarizing plates can be applied to image display devices such as liquid crystal display devices, organic EL display devices, and PDPs.

  Liquid crystal display devices are used in personal computers, TVs, monitors, mobile phones, PDAs and the like. Conventionally, as a polarizer used for a liquid crystal display device or the like, a dyed polyvinyl alcohol film has been used because it has both high transmittance and high degree of polarization. The polarizer is produced by subjecting a polyvinyl alcohol film to various treatments such as swelling, dyeing, cross-linking, and stretching in a bath, followed by washing treatment and drying. Moreover, the said polarizer is normally used as a polarizing plate with which transparent protective films, such as a triacetyl cellulose, were bonded on the single side | surface or both surfaces using the adhesive agent.

  In recent years, liquid crystal display devices have been improved in performance, and liquid crystal panels are required to have no color unevenness in order to obtain high visibility. However, the polarizer often has color unevenness caused by variations in optical characteristics over the entire area. In particular, since it is difficult to confirm this color unevenness unless it is in the state of a polarizing plate in which a transparent protective film is bonded to the polarizer, the color unevenness generated in the polarizer greatly reduces the yield of the material. Become.

  As a method for reducing the color unevenness, for example, it has been proposed to control the swelling treatment time by changing the length of a swelling bath for swelling treatment (Patent Document 1). However, with the recent increase in size of liquid crystal display devices, it has been required that large-area polarizers be manufactured in large quantities. Further, when the area of the polarizer increases, the uniformity of optical characteristics (polarization degree, single transmittance) over the entire area is required. Furthermore, polarizers are increasingly used in combination with other films such as a retardation film for correcting the viewing angle, and there is an increasing demand for manufacturing in a short time.

  On the other hand, if the processing speed of the current manufacturing process as a whole is increased in order to meet the demand for manufacturing in a short time, there is a problem that color unevenness easily occurs and the yield is greatly reduced. According to the method described in Patent Document 1, although it is possible to reduce color unevenness as described above, in order to cope with the manufacture of a large-area polarizer, the conveyance speed of the polarizer is reduced, Alternatively, by increasing the length of the swelling bath, it is necessary to lengthen the swelling treatment time considerably, and there is a problem that the demand for manufacturing a polarizer in a short time cannot be met.

  In order to solve this problem, it has been proposed to provide two or more swelling baths and control the temperature of each treatment tank in the swelling step (Patent Documents 2 and 3). According to the method for producing a polarizer provided with such a swelling step, it is possible to produce a high-quality polarizer in a short time with little color unevenness. However, the methods of Patent Documents 2 and 3 have a problem that the polyvinyl alcohol film tends to be broken in the swelling bath. In addition to the swelling step, a method for producing a polarizer having high uniformity in optical properties, particularly hue, has been proposed by providing a water immersion step for performing a treatment at a draw ratio of 1 to 1.05 times. However, this method also has a problem in that stable production cannot be achieved because the polyvinyl alcohol film breaks during the water immersion process.

JP 2004-78208 A JP 2006-65309 A JP 2006-267153 A Japanese Laid-Open Patent Publication No. 2008-249766

  An object of the present invention is to provide a method of manufacturing a polarizer that can be manufactured stably even when a polarizer having high optical characteristics and suppressed color unevenness is produced at high speed. . Moreover, this invention aims at providing the manufacturing method of the polarizing plate using the obtained polarizer, after manufacturing a polarizer with the said manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by a method for producing a polarizer shown below, and have completed the present invention.

That is, the present invention is a method for producing a polarizer, wherein a polyvinyl alcohol film is subjected to at least a swelling step, a dyeing step, and a stretching step,
The swelling step includes at least two steps of immersing the polyvinyl alcohol film in each treatment liquid through at least one guide roll disposed in the treatment liquid,
In the first step, a widening roll having a radius of curvature of 2000 to 50000 mm is installed as a guide roll at a position after 70% of the running direction in the length in which the polyvinyl alcohol film is immersed in the treatment liquid. And
In the first step, the treatment liquid temperature is 33 to 50 ° C., and stretching is performed so that the stretching ratio in the longitudinal direction is 1.2 to 2.5 times.
In the second and subsequent steps, the present invention relates to a method for producing a polarizer, wherein stretching is performed such that the stretching ratio in the longitudinal direction is 1.06 to 1.2 times.

  In the method for producing a polarizer, the draw ratio in the longitudinal direction in the first step of the swelling step is preferably 1.2 to 2.2 times.

  In the manufacturing method of the said polarizer, it is preferable that the total draw ratio of the vertical direction in the said swelling process is 1.3 to 2.4 times.

  In the method for producing a polarizer, it is preferable that the treatment liquid temperature in the second and subsequent steps is 3 ° C. lower than the first treatment liquid temperature.

  Moreover, this invention relates to the manufacturing method of the polarizing plate characterized by sticking a transparent protective film on the at least single side | surface of the obtained polarizer after manufacturing a polarizer with the said manufacturing method.

  In the method for producing a polarizer of the present invention, the swelling process is performed in at least two stages on the polyvinyl alcohol film. And in the process of the 1st step, the widening roll which has a predetermined curvature radius is installed so that it may become a predetermined position in a processing liquid, and it makes a polyvinyl alcohol-type film widen. Further, in the first step, the treatment liquid is controlled to a predetermined temperature, and the polyvinyl alcohol film is stretched while being controlled to have a predetermined stretch ratio.

  In the present invention, the swelling and anti-blocking agent on the surface of the polyvinyl alcohol film can be washed by the swelling step, and the dyeing unevenness can be obtained by swelling the polyvinyl alcohol film in a swelling bath set at a high temperature ( Non-uniformity such as color unevenness can be prevented, and high optical properties (degree of polarization, single transmittance) can be achieved by swelling the polyvinyl alcohol film while controlling the draw ratio in the longitudinal direction in the swelling bath to a low level. ) Can be manufactured. Moreover, by installing a widening roll in the latter half of the swelling bath, even when high-speed production is performed, the polyvinyl alcohol film can be stably produced without causing breakage.

It is a conceptual diagram which shows an example of the swelling process in the manufacturing method of the polarizer of this invention.

  The polyvinyl alcohol film applied to the method for producing a polarizer of the present invention is particularly limited to those having translucency in the visible light region and dispersing and adsorbing dichroic substances such as iodine and dichroic dyes. Can be used without Usually, a polyvinyl alcohol film having a thickness of about 10 to 300 μm is used. Preferably it is 20-100 micrometers.

  As a polyvinyl alcohol-type film, the polyvinyl alcohol-type film conventionally used for the polarizer is used suitably, for example. Examples of the material for the polyvinyl alcohol film include polyvinyl alcohol and derivatives thereof. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid and alkyl esters thereof, acrylamide and the like. Can be given. The degree of polymerization of polyvinyl alcohol is preferably about 100 to 10,000, and more preferably 1,000 to 10,000. A saponification degree of about 80 to 100 mol% is generally used.

  In addition to the above, polyvinyl alcohol films include hydrophilic polymer films such as partially saponified ethylene / vinyl acetate copolymers, polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. Etc.

  The polyvinyl alcohol film may contain additives such as a plasticizer and a surfactant. Examples of the plasticizer include polyols and condensates thereof, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer used is not particularly limited, but is preferably 20% by weight or less in the polyvinyl alcohol film.

  In the method for producing a polarizer of the present invention, the polyvinyl alcohol film is subjected to a swelling process, a dyeing process, and a stretching process. First, the polyvinyl alcohol film is first subjected to a swelling process. The swelling process is performed in two or more stages. Each swelling process is performed by immersing in each processing liquid via a guide roll arranged in the processing liquid.

  In the first-stage swelling process, a widening roll is used as a guide roll. The said widening roll is installed in the position after 70% of the running direction (longitudinal direction: MD direction) in the length in which the polyvinyl alcohol-type film is immersed in the process liquid. The length of the polyvinyl alcohol film according to the installation position of the widening roll is defined as 0% where the polyvinyl alcohol film starts to be immersed in the treatment liquid and 100% where the immersion of the treatment liquid ends. A value related to the installation position of the widening roll is calculated based on a length of 100% of the film. The installation position of the widening roll is based on the first location where the polyvinyl alcohol film contacts the widening roll. If the value related to the installation position of the widening roll is less than 70%, the film is broken. The value relating to the installation position of the widening roll is preferably 75% or more, more preferably 80% or more, and further preferably 85% or more, from the viewpoint of suppressing the folding of the film. By installing the widening roll in the latter half of the swelling bath, the film can be prevented from breaking when the temperature of the treatment liquid in the swelling bath is increased.

  Widening roll, refers to a roll having a local curve curve and a function of widening the conveyed film. Examples of the widening roll include an expander roll and a crown roll. In the present invention, an expander roll is preferably used as the widening roll.

  Moreover, as the said widening roll, a curvature radius is 2000-50000 mm. The curvature radius is preferably 4000 to 40000 mm. The radius of curvature is the radius of the circle when the degree of local bending of the widening roll curve is approximated to a circle. If the radius of curvature of the widening roll is less than 2000 mm, the swelling becomes non-uniform and color unevenness occurs. On the other hand, when the curvature radius of the widening roll exceeds 50000 mm, the film is bent.

  Hereinafter, the swelling process of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing the relationship among the polyvinyl alcohol film W, the guide roll R, and the treatment liquid X in the swelling step. In FIG. 1, there are two stages of the swelling process, the first stage process is represented as S1, and the second stage process is represented as S2. Swelling process S1, S2 has process liquid X (X1, X2) in each process tank Y (Y1, Y2). Each processing liquid X has at least one guide roll R. It is sufficient that at least one guide roll R is arranged in the processing liquid X, and a plurality of guide rolls R may be arranged in the processing liquid X.

  S1 is related to the first-stage swelling process, and the treatment tank Y1 has a treatment liquid X1, and the polyvinyl alcohol series in the order of these guide rolls through the guide rolls R11 to R14 arranged inside and outside the treatment liquid X1. The film W is conveyed while being immersed in the treatment liquid X1. The polyvinyl alcohol film W is treated with the treatment liquid X1 by passing through the treatment liquid X1. In FIG. 1, the guide rolls R11 and R14 are outside the processing liquid X1, and the guide rolls R12 and R13 are disposed inside the processing liquid X1.

  In the swelling process in the first stage, a widening roll is used as a guide roll. In FIG. 1, a widening roll is used as the guide roll R13. As described above, the setting position of the widening roll is set such that the p1 where the polyvinyl alcohol film W starts to be immersed in the treatment liquid X1 is 0%, and the p2 where the immersion of the treatment liquid X1 is 100%. With the length L (broken line) of the polyvinyl alcohol film W between p2 as a reference, it is installed so that the first location in contact with the guide roll R13 (widening roll) is 70% or more. In FIG. 1, the guide rolls R12 and R13 are arranged in the processing liquid X1, but the guide roll R12 is not arranged in the processing liquid X1, and only the guide roll R13 (widening roll) is arranged. The guide roll R13 (widening roll) is arranged so that the installation position satisfies 70% or more. In the swelling step in the first stage, it is preferable to use a flat roll as a guide roll other than the widening roll.

  S2 relates to the second-stage swelling process, the treatment tank Y2 has a treatment liquid X2, and a polyvinyl alcohol system in the order of these guide rolls via guide rolls R21 to R24 arranged inside and outside the treatment liquid X2. The film W is conveyed while being immersed in the treatment liquid X2. The polyvinyl alcohol film W is treated with the treatment liquid X2 by passing through the treatment liquid X2. In FIG. 1, the guide rolls R21 and R24 are outside the processing liquid X2, and the guide rolls R22 and R23 are arranged in the processing liquid X1. In the second-stage swelling process, as long as at least one guide roll R is arranged in the treatment liquid X2, there is no particular limitation on the arrangement and the like, and a plurality of guide rolls R are in the treatment liquid X2. It may be arranged.

  Further, in the swelling process after the third stage, the arrangement of the guide rolls is not particularly limited as in the second stage swelling process.

  As the treatment liquid used in the swelling step, water, distilled water, or pure water is usually used. If the main component is water, the treatment liquid may contain a small amount of an additive such as an iodide compound and a surfactant as described below, alcohol, and the like. Further, when an iodide compound is contained in the treatment liquid, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. In addition, the process liquid (a density | concentration, an additive, etc.) used at each step of a swelling process may be the same, and may differ.

  The temperature of the treatment liquid in the swelling process is controlled in each stage. In the first-stage swelling process, the temperature of the treatment liquid is 33 to 50 ° C, preferably 35 to 48 ° C, more preferably 37 to 45 ° C. When the temperature of the treatment liquid in the first step is less than 33 ° C., color unevenness occurs in the obtained polarizer. On the other hand, when it exceeds 50 degreeC, a polyvinyl alcohol-type film will melt | dissolve. In the swelling process after the second stage, it is usually preferable to adjust the temperature of the treatment liquid to about 20 to 45 ° C. Furthermore, it is preferable that it is 25-40 degreeC. In particular, it is preferable that the temperature of the treatment liquid after the second stage is set to be 3 ° C. or more lower than the temperature of the treatment liquid at the first stage from the viewpoint of suppressing film breakage in the processes after the second stage. It is preferable to set the temperature of the treatment liquid in the second and subsequent stages to be lower by 5 ° C. or more. In addition, the immersion time in the swelling step is usually in the range of about 10 to 300 seconds, preferably 20 to 240 seconds, in any stage.

  In the swelling process, stretching is performed in the longitudinal direction. By performing stretching in the swelling process, stretching in the stretching process performed after the swelling process can be controlled to be small, and the film can be controlled so as not to be stretched and broken. On the other hand, when the stretching ratio in the swelling process is increased, the stretching ratio in the stretching process is decreased. In particular, when the stretching process is performed after the crosslinking process, it is not preferable in terms of optical characteristics. In the first-stage swelling process, stretching is performed such that the stretching ratio in the longitudinal direction is 1.2 to 2.5 times the original length of the polyvinyl alcohol film. The stretching ratio is preferably 1.3 times or more, and more preferably 1.4 times or more, from the viewpoint of suppressing the folding of the film. On the other hand, the draw ratio is preferably 2.3 times or less, more preferably 2.2 times or less, and further preferably 2.1 times or less from the viewpoint of optical properties. Furthermore, the draw ratio is preferably 1.2 to 2.3 times, more preferably 1.2 to 2.2 times, and further preferably 1.4 to 2.1 times. If the draw ratio is less than 1.2, the film will be folded. On the other hand, when the draw ratio exceeds 2.5 times, it is not preferable in terms of optical properties of the obtained polarizer.

  Further, in the swelling process after the second stage, the stretching ratio in the longitudinal direction is 1.06 to 1.2 times the original length of the polyvinyl alcohol film (film after the first stage stretching). Stretching is performed. It is preferable that the draw ratio is 1.06 times or more in order to prevent the film from being broken. On the other hand, it is preferable that the draw ratio is 1.2 times or less from the viewpoint of satisfying the optical characteristics of the obtained polarizer.

  The total stretching ratio in the longitudinal direction in the swelling process (total stretching ratio including the first stage and the second and subsequent stages) is 1.3 to 2.4 times the original length of the polyvinyl alcohol film. It is preferable to stretch. It is preferable that the total draw ratio is 1.3 times or more in order to prevent the film from being folded. On the other hand, setting the total draw ratio to 2.4 times or less is preferable from the viewpoint of satisfying the optical characteristics of the obtained polarizer.

  After the swelling process is performed, at least a dyeing process and a stretching process are performed.

  The dyeing step is performed by adsorbing and orienting iodine or a dichroic dye on the polyvinyl alcohol film. The dyeing process can be performed together with the stretching process. Dyeing is generally performed by immersing the film in a dyeing solution. As the staining solution, an iodine solution is generally used. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodine ions with iodine and an iodide compound which is a dissolution aid is used. Examples of the iodide compound include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Etc. are used. As the iodide compound, potassium iodide is preferred. The iodide compound used in the present invention is the same as described above when used in other steps.

  The iodine concentration in the iodine solution is about 0.01 to 1% by weight, preferably 0.02 to 0.5% by weight. The iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 8% by weight. In iodine staining, the temperature of the iodine solution is usually about 20 to 50 ° C., preferably 25 to 40 ° C. The immersion time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  The stretching step is usually performed by performing uniaxial stretching. This stretching method can be applied together with a dyeing step and a crosslinking step described later. As the stretching method, either a wet stretching method or a dry stretching method can be employed. In the present invention, it is preferable to use a wet stretching method. As the wet stretching method, for example, it is common to perform stretching after performing a dyeing process. In addition, stretching can be performed together with the crosslinking step. On the other hand, in the case of dry stretching, examples of the stretching means include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In the stretching means, the unstretched film is usually heated. The stretching process can be performed in multiple stages.

  An iodide compound can be contained in the treatment liquid used in the wet stretching method. When the treatment solution contains an iodide compound, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. The treatment temperature in the wet stretching method is usually 25 ° C. or higher, preferably 30 to 85 ° C., more preferably 30 to 60 ° C. The immersion time is usually about 10 to 800 seconds, preferably about 30 to 500 seconds.

  In the stretching step, the total stretching ratio is set such that the total stretching ratio is in the range of 3 to 17 times the original length of the polyvinyl alcohol film. Preferably it is 4-10 times, More preferably, it is 4-8 times. That is, the said total draw ratio means the cumulative draw ratio including the extension in those processes, when an expansion wet process is included and it is accompanied by extension in other processes. The total draw ratio is appropriately determined in consideration of the draw ratio in the swelling process and the like. When the total draw ratio is low, the orientation is insufficient and it is difficult to obtain a polarizer having high optical properties (polarization degree). On the other hand, if the total draw ratio is too high, stretch breakage is likely to occur, and the polarizer becomes too thin, which may reduce the workability in the subsequent process.

  In the method for producing a polarizer of the present invention, a swelling process is performed as described above, and at least a dyeing process and a stretching process are performed. In addition, a crosslinking process can be performed. The crosslinking step is usually performed using a boron compound as a crosslinking agent. The order of the crosslinking steps is not particularly limited. The crosslinking step can be performed together with the stretching step. The crosslinking step can be performed multiple times. Examples of the boron compound include boric acid and borax. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixed solution. Usually, an aqueous boric acid solution is used. The boric acid concentration of the boric acid aqueous solution is about 2 to 15% by weight, preferably 3 to 13% by weight. In order to impart heat resistance depending on the degree of crosslinking, the boric acid concentration is preferably used. The boric acid aqueous solution or the like can contain an iodide compound such as potassium iodide. When the iodide compound is contained in the boric acid aqueous solution, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

  The crosslinking step can be performed by immersing the polyvinyl alcohol film in a boric acid aqueous solution or the like. In addition, a boron compound or the like can be applied to the polyvinyl alcohol film by a coating method, a spraying method, or the like. The processing temperature in a bridge | crosslinking process is 25 degreeC or more normally, Preferably it is 30-85 degreeC, Furthermore, it is the range of 30-60 degreeC. The treatment time is usually about 5 to 800 seconds, preferably about 8 to 500 seconds.

  In the manufacturing method of the polarizer of this invention, after performing a swelling process as mentioned above and also giving a dyeing process, an extending | stretching process, and also a bridge | crosslinking process, a washing | cleaning process can be given. Prior to the cleaning step, metal ion treatment can be performed in addition to the above steps. The metal ion treatment is performed by immersing a polyvinyl alcohol film in an aqueous solution containing a metal salt. Various metal ions are contained in the polyvinyl alcohol film by metal ion treatment.

  As metal ions, metal ions of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron are particularly preferably used in terms of color tone adjustment and durability. Among these metal ions, zinc ions are preferable from the viewpoints of color tone adjustment and heat resistance. Examples of the zinc salt include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, and zinc acetate.

  A metal salt solution is used for the metal ion treatment. Hereinafter, zinc impregnation treatment will be described as a representative example of the case of using a zinc salt aqueous solution among metal ion treatments.

  The concentration of zinc ions in the zinc salt aqueous solution is about 0.1 to 10% by weight, preferably 0.3 to 7% by weight. The zinc salt solution is preferably an aqueous solution containing potassium ions and iodine ions with potassium iodide or the like because it is easy to impregnate zinc ions. The potassium iodide concentration in the zinc salt solution is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

  In the zinc impregnation treatment, the temperature of the zinc salt solution is usually about 15 to 85 ° C, preferably 25 to 70 ° C. The immersion time is usually about 1 to 120 seconds, preferably 3 to 90 seconds. In the zinc impregnation treatment, the zinc content in the polyvinyl alcohol film is adjusted to the above range by adjusting the conditions such as the concentration of the zinc salt solution, the immersion temperature of the polyvinyl alcohol film in the zinc salt solution, and the immersion time. adjust. The stage of the zinc impregnation treatment is not particularly limited. Further, it may be carried out simultaneously with the dyeing step and the crosslinking step by allowing a zinc salt to coexist in the dyeing bath and the crosslinking bath.

  The washing step can be performed with water or an iodide-containing aqueous solution (treatment liquid). As the iodide in the iodide-containing aqueous solution, those described above can be used, and among them, for example, potassium iodide and sodium iodide are preferable. The remaining boric acid used in the crosslinking step can be washed away from the polyvinyl alcohol film by the washing step. When the aqueous solution is an aqueous potassium iodide solution, the concentration thereof is preferably in the range of 0.5 to 20% by weight, more preferably in the range of 1 to 15% by weight, and 1.5 to 7% by weight. Within the range is more preferable.

  Although the temperature of the said iodide containing aqueous solution is not specifically limited, Usually, the inside of the range of 15-40 degreeC is preferable, and the inside of the range which is 20-35 degreeC is more preferable. Further, the contact time with the polyvinyl alcohol film is not particularly limited, but is usually preferably in the range of 2 to 30 seconds, and more preferably in the range of 3 to 20 seconds.

  After performing each said process, a drying process is finally given and a polarizer is manufactured. As the drying step, an appropriate method such as natural drying, air drying, heat drying or the like can be used, but heat drying is usually preferably used. When performing heat drying, although heating temperature is not specifically limited, Usually, the inside of the range of 25-80 degreeC is preferable, The inside of the range of 30-70 degreeC is more preferable, The inside of the range of 30-60 degreeC is still more preferable. The drying time is preferably about 1 to 10 minutes.

  From the viewpoint of optical durability, the boric acid content in the polyvinyl alcohol film (polarizer) after the washing step (the boric acid content of the polarizer does not change even when the drying step is applied) is 15 to It is preferably 30% by weight, more preferably 18% by weight or more, and further preferably 20% by weight or more. On the other hand, if the boric acid content is excessively large, the dimensional change in a heating environment increases, which may induce panel warpage. Therefore, the boric acid content is preferably 30% by weight or less, and more preferably 27% by weight. % Or less is preferable.

  The obtained polarizer can be made into the polarizing plate which provided the transparent protective film in the at least single side | surface according to the conventional method. As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, Examples thereof include cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. A transparent protective film is bonded to one side of the polarizer by an adhesive layer. On the other side, as a transparent protective film, (meth) acrylic, urethane-based, acrylurethane-based, epoxy-based, silicone A thermosetting resin such as a system or an ultraviolet curable resin can be used.

  Although the thickness of a transparent protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable. The transparent protective film is particularly suitable when the thickness is 5 to 150 μm.

  In addition, when providing a transparent protective film on both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used.

  The transparent protective film may be subjected to surface modification treatment before applying the adhesive. Specific examples of the treatment include corona treatment, plasma treatment, primer treatment, and saponification treatment.

  The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a treatment for hard coat treatment, antireflection treatment, sticking prevention, or diffusion or antiglare.

  An adhesive is used for the adhesion treatment between the polarizer and the transparent protective film. Examples of the adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, and water-based polyesters. The said adhesive agent is normally used as an adhesive agent which consists of aqueous solution, and contains 0.5 to 60 weight% of solid content normally. In addition to the above, examples of the adhesive between the polarizer and the transparent protective film include an ultraviolet curable adhesive and an electron beam curable adhesive. The electron beam curable polarizing plate adhesive exhibits suitable adhesion to the various transparent protective films. In particular, it exhibits good adhesion even with respect to acrylic resins for which it was difficult to satisfy the adhesion. The adhesive used in the present invention can contain a metal compound filler.

  The polarizing plate of the present invention is produced by bonding the transparent protective film and the polarizer using the adhesive. The adhesive may be applied to either the transparent protective film or the polarizer, or to both. After the bonding, a drying process is performed to form an adhesive layer composed of a coating dry layer. Bonding of a polarizer and a transparent protective film can be performed with a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is usually about 30 to 1000 nm.

  The polarizing plate of the present invention can be used as an optical film laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including wavelength plates such as 1/2 and 1/4), and a viewing angle compensation film. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is further laminated on the polarizing plate of the present invention, an elliptical polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate. A wide viewing angle polarizing plate obtained by further laminating a viewing angle compensation film on a plate or a polarizing plate, or a polarizing plate obtained by further laminating a brightness enhancement film on the polarizing plate is preferable.

  An optical film in which the optical layer is laminated on a polarizing plate can be formed by a method of sequentially laminating separately in the manufacturing process of a liquid crystal display device or the like. There is an advantage that the manufacturing process of a liquid crystal display device or the like can be improved because of excellent stability and assembly work. For the lamination, an appropriate adhesive means such as an adhesive layer can be used. When adhering the polarizing plate and other optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.

  An adhesive layer for adhering to other members such as a liquid crystal cell may be provided on the polarizing plate described above or an optical film in which at least one polarizing plate is laminated. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance, heat resistance and the like can be preferably used.

  Attachment of the adhesive layer to one or both sides of the polarizing plate or the optical film can be performed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method in which it is directly attached on a polarizing plate or an optical film by an appropriate development method such as a casting method or a coating method, or an adhesive layer is formed on a separator according to the above, and this is applied to a polarizing plate or an optical film. The method of moving up is mentioned.

  The pressure-sensitive adhesive layer can be provided on one side or both sides of a polarizing plate or an optical film as a superimposed layer of different compositions or types. Moreover, when providing in both surfaces, it can also be set as adhesive layers with a different composition, a kind, thickness, etc. in the front and back of a polarizing plate or an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Appropriate conventional ones such as those coated with an appropriate release agent such as long-chain alkyl, fluorine-based, or molybdenum sulfide can be used.

  In the present invention, the polarizer, the transparent protective film, the optical film, and the like that form the polarizing plate described above, and each layer such as the adhesive layer include, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, and cyanoacrylates. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a compound based on nickel or a nickel complex salt compound.

  The polarizing plate or the optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate or an optical film, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except the point which uses the polarizing plate or optical film by invention, and it can apply according to the former. For example, the liquid crystal cell is not particularly limited, and an arbitrary type such as a TN type, STN type, π type, VA type, IPS type, or the like can be applied.

  An appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the polarizing plate or optical film by this invention can be installed in the one side or both sides of a liquid crystal cell. When providing a polarizing plate or an optical film on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable part such as a diffusing plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusing plate, a backlight, etc. Two or more layers can be arranged.

  The present invention will be specifically described below with reference to examples and comparative examples.

Example 1
A polyvinyl alcohol film (average polymerization degree 2400, VF-PE-A # 6000 manufactured by Kuraray Co., Ltd.) having a thickness of 60 μm was used as the raw film. The following steps were performed on the polyvinyl alcohol film in the following order.

(Swelling process)
The swelling process was performed by two swelling baths of the embodiment shown in FIG. Pure water was used as the treatment liquid for each swelling bath. As the guide roll 13 arranged in the first stage swelling bath in FIG. 1, an expander roll having a curvature radius of 20000 mm was used. The expander roll was disposed at a position of 80% of the length of the polyvinyl alcohol film immersed in the treatment liquid (the length of the broken lines p1 and p2 in FIG. 1). In addition, the other guide roll used the flat roll.

<First stage>
The polyvinyl alcohol film was conveyed to a first-stage swelling bath, immersed in pure water adjusted to 40 ° C. for 60 seconds, and uniaxially stretched at a stretching ratio of 1.80 times while swelling.

<Second stage>
Subsequently, the polyvinyl alcohol film that has been subjected to the first-stage swelling step is conveyed to a second-stage swelling bath, immersed in pure water adjusted to 30 ° C. for 60 seconds, and stretched at a draw ratio of 1. The film was uniaxially stretched to 10 (total stretching ratio: 1.98 times).

(Dyeing process)
As a treatment solution for the dyeing bath, an iodine dyeing solution having a concentration of 0.3% by weight of iodine: potassium iodide (weight ratio = 0.5: 8) was used. The swollen polyvinyl alcohol film was conveyed to a dyeing bath and dyed while being uniaxially stretched up to a total draw ratio of 3 times the original length while being immersed in the iodine dyeing solution adjusted to 30 ° C. for 60 seconds. did.

(Crosslinking process)
As a treatment solution for the crosslinking bath, a boric acid aqueous solution containing 3% by weight of boric acid and 3% by weight of potassium iodide was used. The treated polyvinyl alcohol film was conveyed to a crosslinking bath and uniaxially stretched up to a total stretch ratio of 4 times the original length while being immersed in the boric acid aqueous solution adjusted to 30 ° C. for 19 seconds.

(Stretching process)
A boric acid aqueous solution containing 4% by weight of boric acid and 5% by weight of potassium iodide was used as a treatment solution for the stretching bath. The treated polyvinyl alcohol film was conveyed to a stretching bath and uniaxially stretched up to 6 times the total stretching ratio with respect to the original length while being immersed in a boric acid aqueous solution adjusted to 60 ° C. for 13 seconds.

(Washing process)
An aqueous solution containing 3% by weight of potassium iodide was used as the treatment solution for the washing bath. The treated polyvinyl alcohol film was conveyed to a washing bath and immersed in the aqueous solution adjusted to 30 ° C. for 10 seconds.

(Drying process)
Next, the treated polyvinyl alcohol film was dried in an oven at 60 ° C. for 4 minutes to obtain a polarizer.

(Creation of polarizing plate)
A triacetyl cellulose film having a thickness of 80 μm subjected to saponification treatment was laminated on both sides of the polarizer obtained above via an adhesive composed of a 5% by weight complete saponified polyvinyl alcohol aqueous solution, After adhering, it was dried at 70 ° C. for 4 minutes to produce a polarizing plate.

Examples 2-14, Comparative Examples 1-12
In Example 1, a polarizer was produced under the same conditions as in Example 1 except that the conditions in the swelling step were changed as shown in Table 1. Moreover, the polarizing plate was produced like Example 1 using the obtained polarizer. In Comparative Example 8, since the film melted in the expansion step, the step following the expansion step was not performed. Comparative Example 9 is a case where the guide roll 13 arranged in the first-stage swelling bath in FIG. 1 is not set. Comparative Example 10 is a case where the second stage swelling bath is not provided.

<Evaluation>
The following evaluation was performed about the obtained polarizer and polarizing plate. The results are shown in Table 1.

(Color unevenness)
The state of color unevenness of the polarizing plate was visually observed from a state separated by 50 mm in the perpendicular direction, and evaluated according to the following criteria.
○: Unevenness is visible.
X: Unevenness is not visible.

(Break)
In the swelling process, the state during film transport was evaluated according to the following criteria.
○: It does not break.
X: It breaks.

(Single transmittance, degree of polarization)
The single transmittance (Ts) and polarization degree (P) of the polarizing plate were measured using a spectrophotometer with an integrating sphere (V-7100 manufactured by JASCO Corporation).
Note that the degree of polarization is such that two identical polarizers are superposed so that their transmission axes are parallel (transparency: Tp) and superposed so that their transmission axes are orthogonal to each other. In this case, the transmittance (orthogonal transmittance: Tc) is determined by applying the transmittance to the following equation.
Polarization degree P (%) = {(Tp−Tc) / (Tp + Tc)} ^1/2 × 100
Each transmittance is represented by a Y value obtained by correcting visibility with a two-degree field of view (C light source) of JIS Z8701, with 100% of the completely polarized light obtained through the Granteller prism polarizer. The measurement wavelength was 550 nm.
The case where the single transmittance of the polarizing plate was 43.0% and the polarization degree was 99.995% or more was evaluated as “◯”, and the other cases were evaluated as “X”.

R Guide roll p1 Film dipping start point p2 Film dipping end point X Treatment liquid Y Treatment bath

Claims (5)

A method for producing a polarizer, wherein the polyvinyl alcohol film is subjected to at least a swelling step, a dyeing step, and a stretching step,
The swelling step includes at least two steps of immersing the polyvinyl alcohol film in each treatment liquid through at least one guide roll disposed in the treatment liquid,
In the first step, a widening roll having a radius of curvature of 2000 to 50000 mm is installed as a guide roll at a position after 70% of the running direction in the length in which the polyvinyl alcohol film is immersed in the treatment liquid. And
In the first step, the treatment liquid temperature is 33 to 50 ° C., and stretching is performed so that the stretching ratio in the longitudinal direction is 1.2 to 2.5 times.
The second and subsequent steps are performed after the first step,
In the process after the second stage, the treatment liquid temperature is 20 to 45 ° C., and the stretching is performed so that the stretching ratio in the longitudinal direction is 1.06 to 1.2 times. .   The method for producing a polarizer according to claim 1, wherein a stretching ratio in a longitudinal direction in the first step of the swelling step is 1.2 to 2.2 times.   The method for producing a polarizer according to claim 1 or 2, wherein the total stretching ratio in the longitudinal direction in the swelling step is 1.3 to 2.4 times.   The process liquid temperature of the process after the 2nd step in the said swelling process is 3 degreeC or more lower than the process liquid temperature of the process of the 1st step, The polarizer in any one of Claims 1-3 characterized by the above-mentioned. Production method.   After manufacturing a polarizer with the manufacturing method in any one of Claims 1-4, a transparent protective film is bonded together to the at least single side | surface of the obtained polarizer, The manufacturing method of the polarizing plate characterized by the above-mentioned.

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