KR101902585B1 - Process for producing polarizing element and process for producing polarizing plate - Google Patents

Abstract

A feature of the present invention is to provide a method for producing a polarizer capable of being stably produced even when a polarizer having high optical characteristics and suppressed color unevenness is produced at a high speed.
A method for producing a polarizer comprising the steps of: at least two stages of swelling; as a guide roll in the first step, a polyvinyl alcohol film is immersed in the treatment liquid at a position after 70% Is stretched in such a manner that the temperature of the treatment liquid is 33 to 50 DEG C and the stretching magnification in the longitudinal direction is 1.2 to 2.5 times. In the second and subsequent steps, the stretching is performed in the longitudinal direction Is stretched so as to be 1.06 to 1.2 times.

Description

TECHNICAL FIELD [0001] The present invention relates to a polarizing plate manufacturing method and a polarizing plate manufacturing method,

The present invention relates to a process for producing a polarizer and a process for producing a polarizer. 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 side 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.

A liquid crystal display device is used in a personal computer, a TV, a monitor, a cellular phone, a PDA, and the like. Conventionally, as a polarizer used in a liquid crystal display device or the like, a dye-treated polyvinyl alcohol-based film is used because it has both a high transmittance and a high degree of polarization. The polarizer is produced by subjecting a polyvinyl alcohol film to various treatments such as swelling, dyeing, crosslinking and stretching in a bath, followed by washing and drying. The polarizer is usually used as a polarizer in which a transparent protective film such as triacetylcellulose is bonded to one side or both sides thereof with an adhesive.

In recent years, the performance of a liquid crystal display has progressed, and in order to obtain high visibility, it is required that there is no color unevenness in the liquid crystal panel. However, in many cases, the polarizer has color irregularities that occur due to variations in the optical characteristics over the entire area. Particularly, it is difficult to confirm this unevenness of color unless the state of the polarizing plate to which the transparent protective film is bonded to the polarizer is difficult to confirm. Therefore, the color unevenness generated in the polarizer greatly lowers the yield of the material.

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

On the other hand, if the processing speed of the entire manufacturing process in the current situation is increased in order to meet the demand for manufacturing in a short time, there is a problem that color irregularity easily occurs and the yield is greatly reduced. According to the method described in Patent Document 1, color heterogeneity can be reduced as described above. However, in order to cope with the production of a large-area polarizer, it is necessary to slow the conveying speed of the polarizer, or to increase the length of the swelling bath , The swelling treatment time needs to be considerably long, and there is a problem in that it is impossible to meet the requirement to manufacture the polarizer in a short time.

In order to solve such a problem, it has been proposed to provide two or more swelling baths in the swelling process and control the temperature of each treatment bath (Patent Documents 2 and 3). According to the method for producing a polarizer provided with such a swelling process, it is possible to produce a polarizer with a small color unevenness and a high quality in a short time. However, in the methods of Patent Documents 2 and 3, there is a problem that the polyvinyl alcohol-based film tends to be bent in the swelling bath. Further, a method of producing a polarizer having high optical properties, particularly color uniformity, by providing a water immersion step of performing a treatment at a stretching magnification of 1 to 1.05 times in addition to a swelling step has been proposed (Patent Document 4) Also in this method, there is a problem that stable production can not be performed because the polyvinyl alcohol film is bent in the water immersion process.

Japanese Patent Laid-Open No. 2004-78208 Japanese Patent Application Laid-Open No. 2006-65309 Japanese Patent Application Laid-Open No. 2006-267153 Japanese Patent Application Laid-Open No. 2008-249766

An object of the present invention is to provide a method for producing a polarizer capable of stably producing a polarizer having high optical properties and suppressing color unevenness at a high speed. It is another object of the present invention to provide a method for producing a polarizer using the obtained polarizer after the polarizer is produced by the above production method.

DISCLOSURE OF THE INVENTION The inventors of the present invention have made intensive investigations in order to solve the above problems, and as a result, they have found that the above object can be achieved by a polarizer production method or the like described below, and have completed the present invention.

That is, the present invention is a method for producing a polarizer that at least performs a swelling process, a dyeing process, and a stretching process on a polyvinyl alcohol film,

Wherein the swelling step has at least two steps of performing the swelling step by immersing the polyvinyl alcohol-based film in each processing solution through at least one guide roll disposed in the processing solution,

In the first step, a width enlarging roll having a radius of curvature of 2000 to 50,000 mm is provided at a position after 70% of the running direction of the length in which the polyvinyl alcohol film is immersed in the treatment liquid as a guide roll, Also

In the first step, stretching is carried out so that the treatment liquid temperature is 33 to 50 DEG C and the longitudinal stretching magnification is 1.2 to 2.5 times,

And the stretching step is performed so that the longitudinal stretching magnification ratio is 1.06 to 1.2 times in the second and subsequent steps.

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

In the method for producing a polarizer, it is preferable that the total draw ratio in the longitudinal direction in the swelling step is 1.3 to 2.4 times.

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

The present invention also relates to a method for producing a polarizing plate characterized in that a transparent protective film is bonded to at least one surface of the obtained polarizer after the polarizer is produced by the above-mentioned production method.

In the method for producing a polarizer of the present invention, the swelling process is performed on the polyvinyl alcohol film in at least two stages. In the first step, a widthwise enlarging roll having a predetermined radius of curvature is installed at a predetermined position in the processing liquid so that the width of the polyvinyl alcohol film is enlarged. Further, in the first step, the treatment liquid is controlled at a predetermined temperature, and the polyvinyl alcohol film is stretched while controlling the stretching ratio to a predetermined value.

In the present invention, in addition to being able to clean the surface of the polyvinyl alcohol film by the swelling process, the polyvinyl alcohol film can be swollen in a swelling bath in which the polyvinyl alcohol film is set at a high temperature, whereby unevenness (color unevenness) And polarizers having high optical characteristics (degree of polarization and simple transmittance) can be produced by swelling the polyvinyl alcohol-based film while controlling the stretching magnification in the longitudinal direction in the swelling bath to be low . Further, by providing a width expansion roll at the latter half of the swelling bath, even when the film is produced at a high speed, the film can be stably produced without causing a break in the polyvinyl alcohol film.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a conceptual diagram showing an example of a swelling process in the method for producing a polarizer of the present invention. Fig.

As the polyvinyl alcohol film to be applied to the method for producing a polarizer of the present invention, it is possible to use a film having transparency in a visible light region and dispersing and adsorbing a dichroic substance such as iodine or a dichroic dye without particular limitation. Usually, a polyvinyl alcohol film having a thickness of about 10 to 300 mu m is used. Preferably 20 to 100 mu m.

As the polyvinyl alcohol film, for example, a polyvinyl alcohol film conventionally used for a polarizer is suitably used. As a material of the polyvinyl alcohol-based film, polyvinyl alcohol or a derivative thereof may be mentioned. Examples of polyvinyl alcohol derivatives include polyvinyl formal, polyvinyl acetal and the like. In addition, olefins such as ethylene and propylene, unsaturated carboxylic acids and their alkyl esters such as acrylic acid, methacrylic acid and crotonic acid, And the like. The polymerization degree of polyvinyl alcohol is preferably about 100 to 10000, more preferably 1000 to 10000. A degree of saponification of about 80 to 100 mol% is generally used.

In addition to the above, examples of the polyvinyl alcohol film include a hydrophilic polymer film such as an ethylene / vinyl acetate copolymer partial saponification film, a dehydrated product of polyvinyl alcohol, a dehydrochlorinated product of polyvinyl chloride, etc. .

The polyvinyl alcohol-based film may contain an additive 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 or the like to be used is not particularly limited, but is preferably 20% by weight or less in the polyvinyl alcohol-based film.

In the method for producing a polarizer of the present invention, a swelling process, a dyeing process and a stretching process are performed on a polyvinyl alcohol-based film. First, the polyvinyl alcohol film is first subjected to a swelling process. The swelling process is performed in two or more steps. Each swelling step is carried out by immersing in each processing solution through a guide roll disposed in the processing solution.

In the swelling step of the first step, a widthwise enlarging roll is used as a guide roll. The width expanding roll is installed at a position after 70% of the running direction (longitudinal direction: MD direction) at a length in which the polyvinyl alcohol film is immersed in the treatment liquid. The length of the polyvinyl alcohol film according to the installation position of the width expanding roll is 0% at the point where the immersion of the polyvinyl alcohol film in the treatment liquid begins and the point at which immersion of the treatment liquid ends is 100%. The value corresponding to the installation position of the width expansion roll is calculated based on the length of the film of 100%. The mounting position of the widthwise expansion roll is based on the first point at which the polyvinyl alcohol film contacts the widthwise expansion roll. If the value corresponding to the installation position of the width expansion roll is more than 70%, the film is bent. The value according to the installation position of the width expanding roll is preferably 75% or later from the viewpoint of suppressing film bending, more preferably 80% or later, further preferably 85% or later. By providing the width expansion roll in the latter half of the swelling bath, it is possible to suppress the film from being bent when the temperature of the treatment liquid for the swelling bath is set to a higher temperature.

A roll having a width expanding roll and a local bending of a curve and having a function of expanding the width of a film to be transported. As the width expanding roll, for example, an expander roll, a crown roll, and the like can be given. In the present invention, it is preferable to use an expander roll as the width expanding roll.

As the width expanding roll, those having a radius of curvature of 2000 to 50,000 mm are used. The radius of curvature is preferably 4000 to 40000 mm. The radius of curvature is the radius of the circle when the degree of local bending of the curve of the widthwise expansion roll is approximated to a circle. If the radius of curvature of the width-widening roll is less than 2000 mm, the swelling becomes uneven, resulting in color unevenness. On the other hand, when the radius of curvature of the widthwise expansion 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 between the polyvinyl alcohol film W in the swelling process and the guide roll R and the treatment liquid X. Fig. In Fig. 1, the swelling process is performed in two stages, and the first-stage process is represented by S1 and the second-stage process is represented by S2. The swelling steps S1 and S2 have treatment liquid X (X1, X2) in each treatment tank Y (Y1, Y2). Each treatment liquid X has at least one guide roll R. At least one guide roll R may be disposed in the treatment liquid X, and a plurality of guide rolls R may be disposed in the treatment liquid X. [

S1 refers to the first swelling process, the treatment tank Y1 has the treatment liquid X1, passes through the guide rolls R11 to R14 arranged inside and outside the treatment liquid X1, and these guide rolls are wound in this order on the polyvinyl alcohol- W is transported while immersed in the treatment liquid X1. The polyvinyl alcohol film W passes through the treatment liquid X1 and is treated by the treatment liquid X1. In Fig. 1, the guide rolls R11 and R14 are located outside the treatment liquid X1, and the guide rolls R12 and R13 are disposed in the treatment liquid X1.

Further, in the swelling step in the first step, a width expanding roll is used as a guide roll. 1, a widthwise enlarging roll is used as the guide roll R13. As described above, the mounting position of the widthwise enlarging roll is set such that the point p1 at which the polyvinyl alcohol film W starts immersing in the treatment liquid X1 is 0% and the point p2 at which the immersion of the treatment liquid X1 is finished is 100% is set so that the first point of contact with the guide roll R13 (widthwise enlarged roll) becomes 70% or later, based on the length L (broken line) of the polyvinyl alcohol film W between p1 and p2. Although the guide rolls R12 and R13 are disposed in the treatment liquid X1 in Fig. 1, even when the guide rolls R12 are not disposed in the treatment liquid X1 and only the guide rolls R13 (widthwise enlarged rolls) Enlarged roll) is arranged so that the installation position satisfies 70% or later. Further, in the swelling step in the first step, it is preferable to use a flat roll as a guide roll other than the width increasing roll.

S2 is related to the second swelling process, the treatment tank Y2 has the treatment liquid X2, and through the guide rolls R21 to R24 disposed inside and outside the treatment liquid X2, the polyvinyl alcohol system The film W is transported while immersed in the treatment liquid X2. The polyvinyl alcohol film W passes through the treatment liquid X2 and is treated by the treatment liquid X2. In Fig. 1, the guide rolls R21 and R24 are located outside the treatment liquid X2, and the guide rolls R22 and R23 are disposed in the treatment liquid X1. If at least one guide roll R is arranged in the processing liquid X2 in the second swelling step, there is no particular limitation on the arrangement and the like, and a plurality of guide rolls R may be disposed in the processing liquid X2.

Also in the swelling step after the third step, the arrangement of the guide rolls is not particularly limited as in the second swelling step.

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

The temperature of the treatment liquid in the swelling process is controlled in each step. In the swelling step of the first step, the temperature of the treatment liquid is 33 to 50 캜, preferably 35 to 48 캜, more preferably 37 to 45 캜. When the temperature of the treatment liquid in the first step is less than 33 占 폚, color irregularity occurs in the obtained polarizer. On the other hand, when the temperature exceeds 50 캜, the polyvinyl alcohol-based film begins to melt. In the second and subsequent swelling steps, the temperature of the treatment liquid is preferably adjusted to about 20 to 45 캜. Further, it is preferable that the temperature is 25 to 40 占 폚. Particularly, it is preferable that the temperature of the second treatment liquid after the second treatment is set to be lower than the treatment liquid temperature of the first treatment by 3 ° C or more, because film breakage in the second and subsequent steps is suppressed. It is preferable that the temperature of the second and subsequent treatment liquids is set to be lower than 5 占 폚. The immersion time in the swelling process is usually in the range of about 10 to 300 seconds, preferably 20 to 240 seconds, in any of the steps.

In the swelling step, stretching is performed in the longitudinal direction. By conducting the stretching in the swelling step, the stretching in the stretching step after the swelling step can be controlled to be small, and the stretching failure of the film can be controlled so as not to occur. On the other hand, if the stretching magnification in the swelling step is increased, the stretching magnification in the stretching step becomes small, and in particular, the stretching step after the crosslinking step is not preferable from the viewpoint of optical properties. In the swelling step of the first step, the stretching is performed so that the stretching magnification in the machine direction is 1.2 to 2.5 times the original length of the polyvinyl alcohol film. The stretching magnification is preferably 1.3 times or more, and more preferably 1.4 times or more from the viewpoint of suppressing the film from being bent. On the other hand, the stretching magnification is preferably 2.3 times or less, more preferably 2.2 times or less, further preferably 2.1 times or less from the viewpoint of optical characteristics. Further, the draw ratio is preferably 1.2 to 2.3 times, more preferably 1.2 to 2.2 times, further preferably 1.4 to 2.1 times. If the draw ratio is less than 1.2 times, bending occurs in the film. On the other hand, if the stretching magnification is more than 2.5 times, it is not preferable from the viewpoint of the optical characteristics of the obtained polarizer.

In the second and subsequent swelling steps, the stretching is performed such that the stretching magnification in the machine direction is 1.06 to 1.2 times the original length of the polyvinyl alcohol film (film after stretching at the first stage). It is preferable that the stretching ratio is 1.06 times or more from the viewpoint of preventing the film from being bent. On the other hand, setting the stretching magnification to 1.2 or less is preferable in that the optical characteristics of the obtained polarizer are satisfied.

It is preferable that the total draw ratio in the longitudinal direction in the swelling step (the total draw ratio including the first step and the second step and thereafter) is 1.3 to 2.4 times the original length of the polyvinyl alcohol-based film. It is preferable that the total draw ratio is 1.3 times or more from the viewpoint of suppressing bending in the film. On the other hand, it is preferable that the total draw ratio is 2.4 times or less from the viewpoint of satisfying the optical characteristics of the obtained polarizer.

After the swelling step is carried out, at least a dyeing step and a stretching step are carried out.

The dyeing step is carried out by adsorbing and orienting iodine or dichromatic dye on the polyvinyl alcohol-based film. The dyeing step can be performed together with the drawing step. The dyeing is generally carried out by immersing the film in a dyeing solution. Iodine solutions are common for dyeing solutions. An iodine aqueous solution used as an iodine solution is an iodine and an aqueous solution containing an iodide ion by an iodide compound as a dissolution aid. 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, titanium iodide and the like. As the iodide compound, potassium iodide is suitable. The iodide compound used in the present invention is the same as the above in the case of using in other process.

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

The stretching process is usually carried out by performing uniaxial stretching. This stretching method can be carried out together with a dyeing step and a crosslinking step to be described later. The stretching method can be adopted both in the wet stretching method and the dry stretching method, but in the present invention, it is preferable to use the wet stretching method. As a wet stretching method, for example, a stretching step is generally performed after a dyeing step. Further, the stretching can be performed together with the crosslinking step. On the other hand, in the case of dry stretching, examples of stretching means include a roll-to-roll stretching method, a heated roll stretching method, and a compression stretching method. The unstretched film in the stretching means is usually heated. The stretching process may be performed in multiple stages.

The iodinated compound may be contained in the treatment liquid used in the wet drawing method. When the iodinated compound is contained in the treatment liquid, the concentration of the iodide compound 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 占 폚 or higher, preferably 30 to 85 占 폚, further preferably 30 to 60 占 폚. The immersion time is usually about 10 to 800 seconds, and preferably about 30 to 500 seconds.

In the stretching step, the total stretching ratio is set in the range of 3 to 17 times the total stretching ratio with respect to the original length of the polyvinyl alcohol-based film. Preferably 4 to 10 times, and more preferably 4 to 8 times. That is, the total draw ratio refers to the extension ratio of the cumulative stretch including the stretch in the process when the stretch wetting process is involved and the stretch is accompanied by another process. 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, alignment is insufficient, and it is difficult to obtain a polarizer having high optical characteristics (polarization degree). On the other hand, if the total stretching magnification is too high, stretching cutting tends to occur, and the polarizer becomes too thin, which may lower the workability in subsequent steps.

In the method for producing a polarizer according to the present invention, the swelling step is performed, the dyeing step and the stretching step are carried out at least as described above, but the crosslinking step can be further performed. The crosslinking step is usually carried out using a boron compound as a crosslinking agent. The order of the crosslinking step is not particularly limited. The crosslinking step can be carried out together with the stretching step. The crosslinking step can be carried out plural times. Examples of the boron compound include boric acid, borax and the like. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixture solution. Normally, 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 by the degree of crosslinking, the boric acid concentration is preferably used. A boric acid aqueous solution or the like may contain an iodide compound such as potassium iodide. When the iodide compound is contained in the aqueous solution of boric acid, the concentration of the iodide compound is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

The crosslinking step can be carried out by immersing the polyvinyl alcohol-based film in an aqueous boric acid 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 treatment temperature in the crosslinking step is usually 25 占 폚 or higher, preferably 30 to 85 占 폚, further preferably 30 to 60 占 폚. The treatment time is usually about 5 to 800 seconds, preferably about 8 to 500 seconds.

In the method for producing a polarizer according to the present invention, the swelling step is carried out as described above, and after the dyeing step, the stretching step and further the crosslinking step, the washing step can be carried out. Before the cleaning step, metal ion treatment may be performed in addition to the above-described steps. The metal ion treatment is carried out by immersing the polyvinyl alcohol film in an aqueous solution containing a metal salt. Various metal ions are contained in the polyvinyl alcohol-based film by metal ion treatment.

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

For metal ion treatment, a metal salt solution is used. Hereinafter, the zinc impregnation treatment will be described as a representative example in the case of using a zinc salt aqueous solution in the treatment of metal ions.

The zinc ion concentration in the zinc salt aqueous solution is in the range of 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 ion and iodine ion by potassium iodide or the like because it is easy to impregnate zinc ions. The concentration of potassium iodide 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 캜, preferably 25 to 70 캜. The immersing time is usually about 1 to 120 seconds, preferably about 3 to 90 seconds. In the zinc impregnation treatment, the zinc content in the polyvinyl alcohol film is adjusted to be in the above range by adjusting conditions such as the concentration of the zinc salt solution, the immersion temperature in the zinc salt solution of the polyvinyl alcohol film, and the immersion time . The step of zinc impregnation treatment is not particularly limited. The zinc salt may be allowed to coexist in the dyeing bath or the crosslinking bath, and may be performed simultaneously with the dyeing step and the crosslinking step.

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

The temperature of the iodide-containing aqueous solution is not particularly limited, but is preferably in the range of 15 to 40 캜, more preferably in the range of 20 to 35 캜. The contact time with the polyvinyl alcohol film is not particularly limited, but is usually in the range of 2 to 30 seconds, more preferably in the range of 3 to 20 seconds.

After each of the above processes, a drying process is finally performed to produce a polarizer. As the drying step, an appropriate method such as natural drying, air drying, heat drying and the like can be used, but heat drying is preferably used. In the case of heating and drying, the heating temperature is not particularly limited, but is preferably in the range of 25 to 80 占 폚, more preferably in the range of 30 to 70 占 폚, and still more preferably in the range of 30 to 60 占 폚. The drying time is preferably about 1 to 10 minutes.

The content of boric acid in the polyvinyl alcohol film (polarizer) after the washing step (the content of boric acid in the polarizer does not change even when the drying step is carried out) is preferably 15 to 30% by weight from the viewpoint of optical durability, % Or more, more preferably 20 wt% or more. On the other hand, if the content of the boric acid is too large, the boric acid content is preferably 30% by weight or less, more preferably 27% by weight or less, from the viewpoint of causing a dimensional change under heating in a heated environment.

The obtained polarizer may be a polarizing plate provided with a transparent protective film on at least one side thereof according to a conventional method. As a material for 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 a thermoplastic resin include cellulose resins such as triacetyl cellulose, polyester resins, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins , Cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. A thermosetting resin such as a (meth) acrylic, urethane, acrylic urethane, epoxy, or silicone resin or an ultraviolet curable resin can be used as the transparent protective film on the other side of the polarizer, .

Though the thickness of the transparent protective film can be appropriately determined, it generally ranges from 1 to 500 mu m in view of workability such as strength and handling properties and thin layer properties. Particularly preferably 1 to 300 mu m, more preferably 5 to 200 mu m. The transparent protective film is particularly suitable in the case of 5 to 150 mu m.

When a transparent protective film is provided on both sides of the polarizer, a protective film made of the same polymer material may be used for the front and back sides, or a protective film made of a different polymer material or the like 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 on which the polarizer is not adhered may be subjected to a hard coat treatment, antireflection treatment, anti-sticking treatment, or diffusion or antiglare treatment.

An adhesive is used for the adhesion treatment between the polarizer and the transparent protective film. Examples of the adhesive include an isocyanate-based adhesive, a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, a vinyl-based latex-based, and a water-based polyester. The above-mentioned adhesive is usually used as an adhesive composed of an aqueous solution, and usually contains 0.5 to 60% by weight of solids. In addition to the above, examples of the adhesive for the polarizer and the transparent protective film include an ultraviolet curable adhesive, an electron beam curable adhesive, and the like. The adhesive for the polarizing plate of the electron beam curing type exhibits an appropriate adhesion to the above various transparent protective films. In particular, it exhibits good adhesion even to an acrylic resin which is difficult to satisfy adhesiveness. The adhesive used in the present invention may 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 application of the adhesive may be carried out either to the transparent protective film or the polarizer, or to both. After the bonding, a drying step is carried out to form an adhesive layer comprising a coating and drying layer. The polarizer and the transparent protective film can be bonded by 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, a liquid crystal display device such as a reflection plate, a semitransmissive plate, a retardation plate (including a wave plate of ½ or ¼) One or two or more optical layers that have been used may be used. In particular, a reflection type polarizing plate or a transflective type polarizing plate in which a reflection plate or a transflective plate is further laminated on the polarizing plate of the present invention, an elliptically polarizing plate or circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate, Or a polarizing plate in which a brightness enhancement film is further laminated on a polarizing plate.

The optical films obtained by laminating the optical layers on the polarizing plate can be formed by sequentially laminating them separately in the process of manufacturing a liquid crystal display device or the like. However, when the optical films are laminated in advance, they are excellent in quality stability and assembly work There is an advantage that a manufacturing process of a liquid crystal display device and the like can be improved. Appropriate adhesion means such as an adhesive layer can be used for the lamination. When the polarizing plate or other optical film is adhered, such an optical axis can be set at an appropriate arrangement angle in accordance with a desired retardation property or the like.

The optical film having at least one polarizing plate or polarizing plate stacked thereon may be provided with an adhesive layer for adhering to another member such as a liquid crystal cell. The pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer is not particularly limited. For example, it is possible to appropriately select and use a polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, . Particularly, an acrylic pressure-sensitive adhesive which is excellent in optical transparency, exhibits appropriate wettability, cohesiveness and adhesive property, and has excellent weather resistance and heat resistance can be preferably used.

Laying of the adhesive layer on one side or both sides of the polarizing plate or optical film can be carried out in an appropriate manner. As an example thereof, 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 single solvent or a mixture of a suitable solvent such as toluene or ethyl acetate, A method of directly laying on a polarizing plate or an optical film by a suitable developing method such as a coating and applying method, or a method of forming an adhesive layer on a separator and attaching it to a polarizing plate or an optical film in accordance with the above- .

The adhesive layer may be provided on one side or both sides of a polarizing plate or an optical film as a superposed layer made of different composition or kind. Further, in the case of being provided on both surfaces, it is also possible to form a pressure-sensitive adhesive layer such as a composition, a kind and a thickness on the front and back of a polarizing plate or an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use and the adhesive force, and is generally 1 to 500 탆, preferably 5 to 200 탆, particularly preferably 10 to 100 탆.

The exposed surface of the adhesive layer is temporarily covered with a separator for the purpose of preventing contamination thereof until it is provided for practical use. This makes it possible to prevent contact with the adhesive layer in a conventional handling state. As the separator, suitable thin films such as a plastic film, a rubber sheet, a paper, a cloth, a nonwoven fabric, a net, a foam sheet, a metal foil and a laminate thereof may be used as the separator, Or a material obtained by coating with an appropriate releasing agent such as molybdenum disulfide or the like.

In the present invention, the respective layers such as the polarizer, the transparent protective film, the optical film, and the adhesive layer forming the polarizing plate may be coated with a coating liquid containing, for example, a salicylic ester compound or a benzophenol compound, a benzotriazole compound, Or a method in which ultraviolet light absorbing ability is imparted by a method of treating with a ultraviolet absorber such as a palladium-based compound, a rate-based compound, or a nickel complex salt compound.

The polarizing plate or optical film of the present invention can be suitably used for forming various devices such as a liquid crystal display device. The formation of the liquid crystal display device can be carried out in a conventional manner. 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 needed, and incorporating a driving circuit. However, in the present invention, Except for the use of an optical film, there is no particular limitation, and conventional methods can be used. For example, the liquid crystal cell is not particularly limited, and any type of TN, STN, pi, VA, IPS, or the like may be used.

A suitable liquid crystal display device such as a liquid crystal display in which a polarizing plate or an optical film is disposed on one side or both sides of the liquid crystal cell, or a backlight or a reflector is used in an illumination system can be formed. In this case, the polarizing plate or the optical film according to the present invention can be provided on one side or both sides of the liquid crystal cell. When polarizing plates or optical films are provided on both sides, they may be the same or different. In forming a liquid crystal display device, a suitable part such as a diffusion plate, an anti-glare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, Or more.

[Example]

Hereinafter, the present invention will be described in detail with reference to examples and comparative examples.

Example 1

As the raw material film, a polyvinyl alcohol film (average degree of polymerization: 2400, manufactured by Kuraray Co., Ltd. VF-PE-A # 6000) having a thickness of 60 탆 was used. The polyvinyl alcohol film was subjected to the following steps in the following order.

(Swelling process)

The swelling step was carried out by two swelling baths of the type shown in Fig. Pure water was used as the treatment liquid for each swelling bath. An expander roll having a radius of curvature of 20000 mm was used as the guide roll 13 arranged in the first-stage swelling bath in Fig. The expander roll was placed at a position of 80% of the length (dashed line length of p1 and p2 in Fig. 1) in which the polyvinyl alcohol film was immersed in the treatment liquid. A flat roll was used for the other guide rolls.

<First step>

The polyvinyl alcohol film was transported in a swelling bath of the first stage, uniaxially stretched at a stretching magnification factor of 1.80 while swelling in pure water adjusted to 40 DEG C for 60 seconds.

<Level 2>

Subsequently, the polyvinyl alcohol film subjected to the swelling process at the first stage was transferred to a swelling bath at the second stage and immersed in pure water adjusted to 30 DEG C for 60 seconds to swell, and a stretching ratio of 1.10 (total stretching ratio of 1.98 times ).

(Dyeing process)

An iodine staining solution having a concentration of 0.3% by weight of iodine: potassium iodide (weight ratio = 0.5: 8) was used as a treating solution for the dyeing bath. The swollen polyvinyl alcohol film was returned to the dyeing bath and dyed while being uniaxially stretched to a total draw ratio of 3 times with respect to the original length while immersed in the iodine staining solution adjusted to 30 ° C for 60 seconds.

(Crosslinking step)

As the treating solution for the crosslinking bath, an aqueous boric acid solution containing 3% by weight of boric acid and 3% by weight of potassium iodide was used. The treated polyvinyl alcohol film was transferred to a crosslinking bath and uniaxially stretched to a total draw ratio of 4 times with respect to the original length while immersed in the boric acid aqueous solution adjusted to 30 DEG C for 19 seconds.

(Drawing step)

As the treating solution for the drawing bath, an aqueous boric acid solution containing 4% by weight of boric acid and 5% by weight of potassium iodide was used. The treated polyvinyl alcohol film was conveyed in a drawing bath and uniaxially stretched to a total draw ratio of 6 times with respect to the original length while immersed in an aqueous boric acid solution adjusted to 60 DEG C for 13 seconds.

(Cleaning process)

An aqueous solution containing potassium iodide in an amount of 3% by weight was used as the treatment liquid for the cleansing bath. The treated polyvinyl alcohol film was returned to the cleansing bath and immersed in the aqueous solution adjusted to 30 DEG C for 10 seconds.

(Drying step)

Then, the treated polyvinyl alcohol-based film was dried in an oven at 60 DEG C for 4 minutes to obtain a polarizer.

(Production of polarizing plate)

A triacetylcellulose film subjected to a saponification treatment with a thickness of 80 占 퐉 on both surfaces of the polarizer obtained above was laminated via an adhesive composed of a 5% by weight aqueous solution of a completely soap-like polyvinyl alcohol, followed by adhesion with a rolling roll, And dried for a minute to prepare a polarizing plate.

Examples 2 to 14 and Comparative Examples 1 to 12

A polarizer was produced under the same conditions as in Example 1 except that the conditions in the swelling step in Example 1 were changed as shown in Table 1. Using the obtained polarizer, a polarizing plate was produced in the same manner as in Example 1. [ Further, in Comparative Example 8, since the film started to melt in the swelling step, the step following the swelling step was not performed. Comparative Example 9 is a case in which the guide roll 13 arranged in the first-stage swelling bath in Fig. 1 is not set. Comparative Example 10 is a case in which the second stage swelling bath is not provided.

<Evaluation>

The obtained polarizer and polarizer were evaluated as follows. The results are shown in Table 1.

(Color unevenness)

The state of the color unevenness of the polarizing plate was visually observed from the state of being separated from the direction of the vertical line by 50 mm and evaluated according to the following criteria.

○: Unevenness is seen.

X: No irregularities are seen.

(Twisted)

In the swelling process, the state of the film during transportation was evaluated by the following criteria.

○: Do not break.

×: It is broken.

(Mass transmittance, polarization degree)

The transmittance (Ts) and the degree of polarization (P) of the polarizing plate were measured using a spectrophotometer (V-7100, manufactured by Nippon Bunko K.K.) equipped with an integrating sphere.

The transmittance (parallel transmittance: Tp) when the two polarizers are superimposed so that the transmission axes of the two polarizers are parallel to each other and the transmittance (orthogonal transmittance: Tc) To the equations (1) and (2).

The degree of polarization P (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 100

Each transmittance is represented by a Y value corrected for visibility by a 2-degree field of view (C light source) of JIS Z8701 with 100% of total polarization obtained through a Gantry prism polarizer. The measurement wavelength was 550 nm.

A case where the polarizing plate had a simple transmittance of 43.0% and a polarization degree of 99.995% or more was evaluated as &quot;? &Quot;, and the other cases were evaluated as &quot;

R guide roll
p1 The immersion starting point of the film
p2 End point of immersion of the film
X treatment liquid
Y treatment bath

Claims (5)

A method for producing a polarizer which at least performs a swelling process, a dyeing process and a stretching process on a polyvinyl alcohol film,
Wherein the swelling step has at least two steps of immersing the polyvinyl alcohol film in each processing solution through at least one guide roll disposed in the processing solution,
In the first step, as the guide roll, there is provided a width enlarging roll having a radius of curvature of 2000 to 5000 mm at a position after 70% of the running direction in the length in which the polyvinyl alcohol film is immersed in the treatment liquid , Also,
In the first step, stretching is carried out so that the treatment liquid temperature is 33 to 50 占 폚 and the longitudinal stretching magnification is 1.2 to 2.5 times,
The second and subsequent steps are carried out after the first step,
Wherein the stretching is performed so that the treatment liquid temperature is 20 to 45 占 폚 and the longitudinal stretching magnification is 1.06 to 1.2 times in the second and subsequent steps. The method of manufacturing a polarizer according to claim 1, wherein the stretching magnification in the longitudinal direction in the first step of the swelling step is 1.2 to 2.2 times. The method of manufacturing a polarizer according to claim 1, wherein the total draw ratio in the longitudinal direction in the swelling step is 1.3 to 2.4 times. The method of manufacturing a polarizer according to claim 1, wherein the temperature of the treatment liquid in the second and subsequent steps in the swelling step is 3 ° C or more lower than the temperature of the treatment liquid in the first step. A process for producing a polarizing plate, comprising the steps of: preparing a polarizer by the production method according to any one of claims 1 to 4; and bonding a transparent protective film to at least one surface of the obtained polarizer.

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