KR20170073700A - Polarizing film production method - Google Patents

Abstract

The present invention relates to a method of producing a polarizing film for producing a polarizing film (23) from a polyvinyl alcohol based resin film (10), characterized in that the polyvinyl alcohol based resin film is contained in a treatment tank (13, 15, 17, 19) A transfer step of transferring the polyvinyl alcohol resin film immersed in the treatment liquid along a roll; and a transfer step of transferring the polyvinyl alcohol resin film immersed in the treatment liquid onto the rolls 32, 35, 38, 41, 51, 52, 53, 54 And a roll cleaning step of cleaning the surface of the polarizing film with a roll cleaning liquid.

Description

TECHNICAL FIELD [0001] The present invention relates to a polarizing film,

The present invention relates to a method for producing a polarizing film usable as a constituent member of a polarizing plate.

In the polarizing film, a uniaxially stretched polyvinyl alcohol resin film is conventionally used in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented. The polarizing film is usually used for an image display apparatus represented by a liquid crystal display device such as a liquid crystal television, a personal computer monitor, and a cellular phone by bonding a protective film to one side or both sides thereof with an adhesive to form a polarizing plate.

In general, a polarizing film is a film obtained by sequentially dipping a continuous long polyvinyl alcohol-based resin film in a treating bath such as a swelling bath, a dyeing bath, or a crosslinking bath, (For example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2015-11151

The polarizing film is a film obtained by continuously feeding a film from a raw (original) roll (wound product) of a polyvinyl alcohol-based resin film and transporting the polyvinyl alcohol-based resin layer in a transport path between the various treatment baths as described above By arranging the rolls, the polyvinyl alcohol-based resin layer is drawn after being immersed in one treatment bath and transported so as to be immersed in the next treatment bath to be continuously produced.

However, when a polarizing film produced by continuous manufacturing is observed, defects such as adhesion of dirt on the surface of the polarizing film may occur. As a result of studying the cause of such defects, it has been found that the treatment liquid in the treatment bath brought in by the polyvinyl alcohol-based resin film adheres to the surface of the roll placed in the transfer path between the treatment baths, And the surface of the roll was contaminated. The surface of the polyvinyl alcohol-based resin film was transported by the contaminated roll, so that the surface of the polyvinyl alcohol-based resin film was sometimes transferred with dirt. Particularly, since the treatment liquid in the dyeing bath or the crosslinking bath is adjusted by dissolving the salt, contamination of the surface of the roll caused by the treatment liquid in the treatment bath brought in by the polyvinyl alcohol based resin film can be prevented And it was easy to occur on the surface of rolls arranged to pull out the polyvinyl alcohol-based resin film. Further, since the polyvinyl alcohol-based resin film is hydrophilic and immediately after being drawn out from the treatment bath, the polyvinyl alcohol-based resin film is in a swollen state by the treatment liquid, deformation due to transfer of dirt on the roll surface and dirt on the roll surface is likely to occur. In addition, the surface of the roll was easily contaminated by the eluted components from the polyvinyl alcohol-based resin film.

Therefore, the present invention provides a method for producing a polarizing film in which contamination of the surface of a roll carrying a polyvinyl alcohol-based resin film disposed in a conveying path between various treatment baths is suppressed, and generation of surface defects such as dirt adhesion is suppressed .

The present invention provides a method for producing a polarizing film described below.

[1] A method for producing a polarizing film from a polyvinyl alcohol-based resin film,

An immersion step of immersing the polyvinyl alcohol-based resin film in a treatment liquid contained in a treatment tank,

A conveying step of conveying the polyvinyl alcohol resin film immersed in the treatment liquid along a roll;

And a roll cleaning step of cleaning the surface of the roll with a roll cleaning liquid.

[2] The process for producing a polarizing film according to the above [1], wherein in the roll cleaning step, the treatment liquid is used as the roll cleaning liquid.

[3] The production method of a polarizing film according to [2], wherein the roll cleaning liquid is recovered in the treatment tank after the roll cleaning step.

[4] The dipping step may be a dyeing treatment step in which the polyvinyl alcohol resin film is dyed with a dichroic dye, or a crosslinking treatment step in which the polyvinyl alcohol resin film is dipped in a crosslinking solution and crosslinked, The method for producing a polarizing film according to any one of [1] to [3].

[5] The polarizing film according to any one of [1] to [4], wherein the roll cleaning step includes a step of drawing the roll cleaning liquid onto the surface of the roll or a step of dipping the surface of the roll in the roll cleaning liquid ≪ / RTI >

According to the method of the present invention, it is possible to suppress the contamination of the surface of the rolls disposed in the transport path between the treatment baths during the continuous production of the polarizing film, and to produce a polarizing film in which surface defects such as dirt adhesion are suppressed have.

1 is a cross-sectional view schematically showing an example of a polarizing film producing method and a polarizing film producing apparatus used therefor according to a first embodiment of the present invention.
2 is a perspective view showing an example of the relationship between the nip roll and the shower shown in Fig.
3 is a cross-sectional view schematically showing an example of a polarizing film producing method and a polarizing film producing apparatus used therefor according to a second embodiment of the present invention.
4 is a graph showing the results of measurement of the boric acid content of the first crosslinking bath in Example 2 and Comparative Example 2. Fig.
5 is a graph showing the results of measurement of the boric acid content of the second crosslinking bath in Example 2 and Comparative Example 2. Fig.

≪ Polarizing Film Production Method >

In the polarizing film of the present invention, a dichroic dye (iodine or a dichroic dye) is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The polyvinyl acetate resin may be, for example, a polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and other monomers copolymerizable therewith, and the like. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, and preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified, and examples thereof include polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like.

In the present invention, as a starting material for producing a polarizing film, an unstretched poly (meth) acrylate having a thickness of 65 占 퐉 or less (for example, 60 占 퐉 or less), preferably 50 占 퐉 or less, more preferably 35 占 퐉 or less, Vinyl alcohol resin film (original film) is used. As a result, a polarizing film of a thin film which is increasingly in demand in the market can be obtained. The original film may be a polyvinyl alcohol-based resin film subjected to stretching treatment in advance in the gas phase.

The width of the original film is not particularly limited and may be, for example, about 400 to 6000 mm. However, as the film width is larger, the film tends to be easily broken during the stretching treatment.

In the present invention, the original film is prepared as a roll (disk roll) of a long unoriented polyvinyl alcohol based resin film.

The polarizing film can be continuously produced as a long polarizing film by continuously carrying the above-mentioned long original film along the film conveying path of the polarizing film producing apparatus while performing the predetermined treatment process while being unwound from the original roll. The predetermined processing step includes an immersion step of immersing the original film in a processing solution (hereinafter also referred to as a " processing bath ") accommodated in the processing vessel, and a transporting step of transporting the original film drawn out from the processing bath along the roll. The immersion process and the transfer process are repeatedly performed on different treatment baths to produce a polarizing film.

In the present invention, in addition to the immersion process and the transport process for producing the polarizing film from the polyvinyl alcohol-based resin film, a roll cleaning process for cleaning the roll for transporting the original film drawn from the treatment bath is provided. It is preferable that such a roll cleaning step is performed simultaneously with the continuous production of the polarizing film. By having the roll cleaning step, the present invention can prevent contamination of the surface of a roll that carries the original film, and prevent defects such as dirt adhering to the surface of the polarizing film due to such contamination.

 As the roll cleaning liquid, in addition to pure water, the same treatment liquid as that contained in the immediately preceding treatment tank can be used, but a treatment liquid is preferably used. Even when the polyvinyl alcohol based resin film to be conveyed is in direct contact with the roll cleaning liquid or when the conveyed polyvinyl alcohol based resin film is in contact with the roll cleaning liquid adhered to the roll surface, It is possible to prevent defects from being caused in the polyvinyl alcohol-based resin film. When the treatment liquid is used as the roll cleaning liquid, it is preferable that the treatment liquid is recovered in the immediately preceding treatment tank after the roll cleaning process. When the treatment liquid is not used as the roll cleaning liquid, the concentration of the treatment liquid on the polyvinyl alcohol-based resin film changes when the roll cleaning liquid comes in contact with the polyvinyl alcohol-based resin film, and defects such as stains may occur. Therefore, when the treatment liquid is not used as the roll cleaning liquid, it is preferable to supply the roll cleaning liquid to the roll surface so that the roll cleaning liquid does not directly contact the polyvinyl alcohol resin film. It is also preferable that the roll cleaning liquid adhered to the surface of the roll is recovered so as not to come into contact with the polyvinyl alcohol-based resin film with a scraper or the like.

Specifically, the immersion step includes a swelling treatment step in which the original film is immersed in a swelling solution (hereinafter also referred to as " swelling bath ") contained in the swelling bath, and a film drawn out from the swelling bath in the subsequent conveying step (Hereinafter also referred to as a " crosslinking bath ") accommodated in a crosslinking tank is immersed in a dyeing solution which is dipped in a dyeing solution A film washing step of immersing the film drawn out from the crosslinking bath by a crosslinking treatment step in which it is immersed in a film washing tank (hereinafter also referred to as " film cleansing bath ") accommodated in a film washing tank, and the like. The uniaxial stretching treatment is carried out either wet or dry in a series of the immersion process and the transfer process (that is, before and / or after any one or more of the immersion processes). If necessary, other processing steps may be added. Each of the above-described immersion processes may be a process of immersing the film in one bath or a process of sequentially immersing the film in two or more baths.

Hereinafter, a method of manufacturing a polarizing film according to the present invention will be described in more detail with reference to Figs. 1 to 3. Fig.

[First Embodiment]

1 is a cross-sectional view schematically showing an example of a polarizing film producing method and a polarizing film producing apparatus used therefor according to a first embodiment of the present invention. The polarizing film producing apparatus shown in Fig. 1 is configured such that an original (non-stretchable) film 10 made of a polyvinyl alcohol-based resin is conveyed along a film conveying path while being continuously unwound from the original roll 11, The dyeing bath 15, the crosslinking bath 17 and the cleansing bath 19 which are provided on the surface of the substrate W in order and then finally passed through a drying oven 21 . The obtained polarizing film 23 can be conveyed as it is, for example, in the following polarizing plate producing step (a step of bonding a protective film to one side or both sides of the polarizing film 23). The arrows in Fig. 1 indicate the transport direction of the film.

On the other hand, FIG. 1 shows an example in which a swirl bath 13, a dye bath 15, a crosslink bath 17 and a cleansing bath 19 are provided one by one, Two or more treatment baths may be provided. The term " treatment liquid " is a generic term including a swelling tank, a dyeing tank, a crosslinking tank and a washing tank, and the term " treatment liquid " is a generic term including a swollen liquid, Bath "is a general term including a swelling bath, a dyeing bath, a crosslinking bath, and a cleansing bath.

The film transport path of the polarizing film producing apparatus includes, in addition to the above treatment bath, guide rolls 30 to 41, 60 and 61 capable of supporting the transported film or changing the film transport direction, The nip rolls 50 to 55 can be constructed by sandwiching the nip rolls 50 to 55 so that the driving force by the rotation can be given to the film or the film transport direction can be changed. The guide rolls and nip rolls can be disposed before or after each treatment bath and the treatment bath, whereby the introduction and immersion of the film in the treatment bath and the withdrawal from the treatment bath can be performed (see Fig. 1). For example, by providing at least one guide roll in each treatment bath and transporting the film along these guide rolls, the film can be immersed in each treatment bath.

In the polarizing film producing apparatus shown in Fig. 1, nip rolls are arranged before and after each treatment bath (nip rolls 50 to 54), whereby in the at least one treatment bath, It is possible to carry out roll-to-roll stretching in which longitudinally uniaxial stretching is carried out with a main speed difference between the rolls.

The polarizing film producing apparatus shown in Fig. 1 is provided with guide rollers 32, 35, 38 and 41 arranged behind each treatment bath 13, 15, 17 and 19, (71 to 78) are provided. During the continuous production of the polarizing film, the roll cleaning liquid is led to the surfaces of the guide rolls 32, 35, 38 and 41 and the nip rolls 51 to 54 by the shower 71 to 78, 38, and 41 and nip rolls 51 to 54 are cleaned (roll cleaning process). Each step will be described below.

(Swelling treatment step)

The swelling process is performed for the purpose of removing foreign substances on the surface of the original film 10, removing the plasticizer in the original film 10, imparting easiness of dyeing, and plasticizing the original film 10. The processing conditions are determined within a range in which the object can be achieved and within a range that does not cause problems such as extreme melting or devitrification of the original film 10.

1, the swelling process is a process in which the original film 10 is conveyed along the film conveying path while continuously winding the original film 10 from the original roll 11, and the original film 10 is conveyed to the swelling bath 13 for a predetermined time Immersing it in water, and withdrawing it continuously. 1, the original film 10 is sandwiched between the guide rolls 60 and 61 and the nip roll 50 during the time from the unwinding of the original film 10 to the immersion in the swelling bath 13 And is transported along the film transport path established by the transport mechanism. In the swelling process, the film is transported along the film transport path established by the guide rolls 30 to 32.

Examples of the swelling liquid of the swelling bath 13 include pure water, boric acid (Japanese Unexamined Patent Publication No. 10-153709), chloride (Japanese Unexamined Patent Publication No. 06-281816), inorganic acid, inorganic salt, It is also possible to use an aqueous solution in which alcohols and the like are added in the range of about 0.01 to 10% by weight.

The temperature of the swelling bath 13 is, for example, about 10 to 50 占 폚, preferably about 10 to 40 占 폚, and more preferably about 15 to 30 占 폚. The immersion time of the original film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. When the original film 10 is a polyvinyl alcohol based resin film previously stretched in a gas, the temperature of the swelling bath 13 is, for example, about 20 to 70 캜, preferably about 30 to 60 캜. The immersion time of the original film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling process, there is a problem that the original film 10 swells in the width direction and wrinkles occur in the film. As a means for transporting the film while removing the wrinkles, a roll having a wider width function such as an expander roll, a spiral roll, and a crown roll may be used for the guide rolls 30, 31 and / or 32, Or using other widening devices such as cross guiders, bend bars, tenter clips, and the like. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment. For example, the uniaxial stretching process can be performed in the swelling bath 13 using the difference in speed between the nip roll 50 and the nip roll 51.

In the swelling process, since the film swells and expands even in the transport direction of the film, in order not to elongate the film in the transport direction when the film is not actively stretched, for example, It is preferable to take measures such as controlling the speed of the rolls 50 and 51 or the like. Further, in order to stabilize the film transportation in the swelling bath 13, the water flow in the swelling bath 13 may be controlled by an underwater shower, an EPC apparatus (Edge Position Control apparatus: detecting the end of the film, Or the like) may be used in combination.

In the example shown in Fig. 1, the film drawn out from the swelling bath 13 is introduced into the dyeing bath 15 through the guide roll 32 and the nip roll 51 in order.

(Dyeing process)

The dyeing treatment step is carried out for the purpose of adsorbing and orienting the dichroic dye to the swollen polyvinyl alcohol resin film. The processing conditions are determined within a range in which the object can be achieved and within a range in which the problems such as extreme melting or disintegration of the film do not occur. 1, the dyeing process is carried out along the film transport path established by the guide rolls 33 to 35 and the nip roll 51, and the film after the swelling process is transported to the dyeing bath 15 Processing solution) for a predetermined period of time, and then withdrawing it. In order to enhance the dyeability of the dichroic dye, the film provided in the dyeing process is preferably a film subjected to uniaxial stretching at least to some degree, or may be subjected to a uniaxial stretching process before the dyeing process, , It is preferable to perform uniaxial stretching treatment at the time of dyeing treatment.

When iodine is used as the dichroic dye, an aqueous solution having an iodine / potassium iodide / water concentration of about 0.003 to 0.3 / about 0.1 to 10/100 in terms of the concentration by weight can be used for the dyeing bath of the dyeing bath 15. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, compounds other than iodide such as boric acid, zinc chloride, cobalt chloride, etc. may be coexistent. When boric acid is added, it is distinguished from a crosslinking treatment to be described later in that it contains iodine. If the aqueous solution contains about 0.003 part by weight or more of iodine with respect to 100 parts by weight of water, it is regarded as a dyeing bath 15 . The temperature of the dyeing bath 15 at the time of immersing the film is usually about 10 to 45 占 폚, preferably 10 to 40 占 폚, more preferably 20 to 35 占 폚, 600 seconds, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, an aqueous solution having a dichroic dye / water concentration of about 0.001 to 0.1 / 100 in terms of the concentration by weight, for example, can be used for the dyeing solution of the dyeing bath 15. In the dyeing bath 15, a dyeing auxiliary or the like may be coexisted, and for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. The dichroic dye may be used alone, or two or more dichroic dyes may be used in combination. The temperature of the dyeing bath 15 at the time of immersing the film is, for example, about 20 to 80 캜, preferably 30 to 70 캜, and the immersion time of the film is usually about 30 to 600 seconds, Seconds.

In the dyeing treatment step as described above, uniaxial stretching of the film can be performed in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method such as placing a major speed difference between the nip roll 51 and the nip roll 52 disposed before and after the dyeing bath 15.

In the dyeing process, as in the swelling process, the guide rolls 33, 34 and / or 35 are provided with widening functions such as an expander roll, a spiral roll, and a crown roll in order to transport the polyvinyl alcohol- Or other widening devices such as cross guiders, bend bars, tenter clips or the like. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment in the same manner as in the swelling treatment.

In the example shown in Fig. 1, the film drawn out from the dyeing bath 15 is introduced into the crosslinking bath 17 through the guide roll 35 and the nip roll 52 in this order.

(Cross-linking treatment step)

The crosslinking treatment is a treatment for the purpose of, for example, water resistance by crosslinking and color adjustment (preventing the film from becoming blue). 1, the cross-linking treatment is carried out along the film conveyance path constructed by the guide rolls 36 to 38 and the nip roll 52, and the cross-linking treatment is performed on the cross-linking bath 17 (cross-linking solution contained in the cross- By immersing the film for a predetermined period of time, and subsequently withdrawing the film.

The crosslinking solution of the crosslinking bath 17 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking solution preferably contains iodide in addition to boric acid, and the amount thereof may be, for example, 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide and zinc iodide. Further, compounds other than iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may be coexistent.

In the crosslinking treatment, the concentration of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed depending on the purpose. For example, when the purpose of the crosslinking treatment is water resistance by crosslinking, and the swelling treatment, the dyeing treatment and the crosslinking treatment are carried out in this order on the polyvinyl alcohol resin film, the crosslinking agent- And an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100. If necessary, other crosslinking agents such as glyoxal or glutaraldehyde may be used in place of boric acid, or boric acid and another crosslinking agent may be used in combination. The temperature of the crosslinking bath at the time of immersing the film is usually about 50 to 70 DEG C, preferably 53 to 65 DEG C, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, And preferably 20 to 200 seconds. When the dyeing treatment and the crosslinking treatment are carried out in this order on the polyvinyl alcohol-based resin film that has been stretched before the swelling treatment, the temperature of the crosslinking bath 17 is usually about 50 to 85 ° C, preferably about 55 to 85 ° C, 80 ° C.

In the crosslinking treatment for the purpose of color adjustment, for example, when iodine is used as the dichroic dye, a solution containing a crosslinking agent having a concentration of boric acid / iodide / water = 1 to 5/3 to 30/100 can be used . The temperature of the crosslinking bath at the time of immersing the film is usually about 10 to 45 占 폚, and the immersion time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment may be performed a plurality of times, usually 2 to 5 times. In this case, the composition and temperature of each crosslinking bath to be used may be the same or different depending on the above-mentioned range. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color adjustment may each be performed in a plurality of steps.

It is also possible to perform uniaxial stretching processing in the crosslinking bath 17 by using the peripheral speed difference between the nip roll 52 and the nip roll 53. [

In the cross-linking treatment, the guide rolls 36, 37 and / or 38 are provided with widening functions such as an expander roll, a spiral roll, and a crown roll in order to transport the polyvinyl alcohol-based resin film while removing the wrinkles of the film, Or other widening devices such as cross guiders, bend bars, tenter clips or the like. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment in the same manner as in the swelling treatment.

In the example shown in Fig. 1, the film drawn out from the crosslinking bath 17 is introduced into the film cleaning bath 19 through the guide roll 38 and the nip roll 53 in order.

(Film washing process step)

The production method of the present invention may include a film washing treatment process after the crosslinking treatment process. The film cleaning treatment is performed for the purpose of removing excess boric acid or iodine adhered to the polyvinyl alcohol-based resin film. The film washing treatment can be carried out, for example, by immersing a crosslinked polyvinyl alcohol resin film in a film cleansing bath 19, spraying a film washing liquid on the film, or using them in combination.

Fig. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a film cleansing bath 19 to perform a cleaning treatment. The temperature of the film cleansing bath 19 in the film cleaning process is usually about 2 to 40 DEG C, and the immersion time of the film is usually about 2 to 120 seconds.

On the other hand, also in the film cleaning process, the guide rolls 39, 40 and / or 41 are provided with widening functions such as expander rolls, spiral rolls, and crown rolls for the purpose of transporting the polyvinyl alcohol- Rolls, or other widening devices such as cross guiders, bend bars, tenter clips or the like. Further, in the film washing treatment, a stretching treatment may be performed to suppress the occurrence of wrinkles.

(Stretching process step)

As described above, the original film 10 is uniaxially stretched in a wet or dry manner during the series of processing steps (that is, before and / or after any one or more processing steps). A specific method of the uniaxial stretching treatment is, for example, a roll-to-roll stretching method in which longitudinal uniaxial stretching is performed with a main speed difference between two nip rolls constituting a film transport path (for example, two nip rolls disposed before and after the treatment bath) Heat roll stretching, tenter stretching, and the like as described in Japanese Patent No. 2731813, and is preferably inter-roll stretching. The uniaxial stretching process can be carried out a plurality of times from the original film 10 to the polarizing film 23. As described above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles of the film.

The final cumulative stretch magnification of the polarizing film 23 based on the original film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

The stretching treatment step may be carried out in any treatment step, and in the case of performing the stretching treatment in two or more treatment steps, the stretching treatment may be performed in any treatment step. According to the present invention, even when the uniaxial stretching process is performed at any stage after the swelling process (including the swelling process), the film breakage during the stretching process can be effectively suppressed.

(Drying Treatment Step)

After the washing treatment step, the polyvinyl alcohol based resin film is desirably dried. The drying of the film is not particularly limited, but can be carried out using the drying furnace 21 as in the example shown in Fig. The drying temperature is, for example, about 30 to 100 DEG C, and the drying time is about 30 to 600 seconds. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 占 퐉.

(Other Treatment Processes for Polyvinyl Alcohol-based Resin Film)

Processing other than the above-described processing may be added. Examples of treatments that can be added include an immersion treatment (complementary color treatment) in an iodide aqueous solution containing no boric acid, which is carried out after the crosslinking treatment step, an immersion treatment in an aqueous solution containing no zinc chloride Immersion treatment (zinc treatment).

(Roll cleaning step)

The roll cleaning step is a cleaning step of cleaning each roll disposed in the conveying path between the two treatment baths with the roll cleaning liquid during the above-described continuous production of producing the polarizing film from the polyvinyl alcohol based resin film. The method of cleaning the rolls is not particularly limited. However, it is also possible to use a method in which the surfaces of the rolls (the guide rolls 32, 35, 38, 41 and the nip rolls 51, 52, 53, 54) A method in which the roll cleaning liquid is led to the surface of each roll by the shower 71 to 78 arranged so as to clean the surface of each roll can be suitably employed.

The cleaning of each roll with the roll cleaning liquid is preferably carried out during the continuous production of the polarizing film, and is preferably carried out at all times during the continuous production. Even if the polyvinyl alcohol-based resin film 10 carried in the treatment bath comes in with the treatment liquid in the treatment bath and adheres to the surface of each roll by such a roll cleaning process, it is immediately washed by the roll cleaning liquid, It is possible to prevent the surface of the roll from being contaminated by precipitation. The arrangement position of the rollers 71 to 78 relative to the rolls, the amount of the roll cleaning liquid to be drawn out, and the angle of extraction can be appropriately adjusted, and the roll cleaning liquid is supplied to the rolls on the upper and lower sides of the rolls, But it is preferable that the roll cleaning liquid is not directly poured onto the polyvinyl alcohol resin film to be conveyed. The amount of the roll cleaning liquid to be discharged is set to an amount necessary for suppressing at least the contamination of the roll surface.

1, for all the rolls (guide rolls 32, 35, 38, 41 and nip rolls 51, 52, 53, 54) disposed after each treatment tank, However, it may be arranged only on the surface of the roll which is susceptible to contamination, and it is arranged so as to be opposed to the surface of at least one roll. Examples of rolls that are susceptible to contamination include a guide roll 35 and a nip roll 52 immediately behind the dyeing bath 15 and a guide roll 38 and a nip roll 53 immediately behind the crosslinking bath 17 . Since the dye concentration in the dyeing bath 15 and the crosslinking solution in the crosslinking bath 17 often have a higher salt concentration than other treatment baths, Is likely to be precipitated.

2 is a perspective view showing an example of the relationship between the rolls on the upper side of the nip rolls 51, 52, 53, 54 and the shower 72, 74, 76, 78 in Fig. The showers 72, 74, 76 and 78 have a configuration in which a plurality of nozzles are arranged at equal intervals from one end in the width direction of the rolls 51, 52, 53 and 54 toward the other end, , 76, and 78, the roll cleaning liquid is brought into contact with the entire widthwise direction of the roll surface. Therefore, when the roll cleaning liquid continues to be drawn from the shower 72, 74, 76, 78, the rolls 51, 52, 53, 54 ) Can be brought into contact with the entire surface of the roll cleaning liquid, thereby preventing contamination of the roll surface.

As the roll cleaning liquid used in the shower 71, 72 for cleaning the guide roll 32 and the nip roll 51 disposed behind the swelling bath 13, a swelling liquid is suitable. It is preferable that the polarizing film producing apparatus includes means for recovering the roll cleaning liquid led to the guide roll 32 and the nip roll 51 into the swelling tank.

As the roll cleaning liquid used for the shower 73 (74) for cleaning the guide roll 35 and the nip roll 52 disposed behind the dyeing bath 15, a dyeing solution is suitable. The polarizing film producing apparatus preferably includes means for recovering the roll cleaning liquid led to the guide roll 35 and the nip roll 52 in the dyeing bath.

As the roll cleaning liquid used for the shower rolls 75 and 76 for cleaning the guide rolls 38 and the nip rolls 53 disposed behind the crosslinking bath 17, a crosslinking liquid is suitable. The polarizing film producing apparatus preferably includes means for recovering the roll cleaning liquid led to the guide roll 38 and the nip roll 53 into the crosslinking tank.

As the roll cleaning liquid used for the shower 77, 78 for cleaning the guide roll 41 and the nip roll 54 disposed behind the film cleansing bath 19, a film cleaning liquid is suitable. It is preferable that the polarizing film producing apparatus includes means for recovering the roll cleaning liquid led to the guide roll 71 and the nip roll 54 into the film washing tank.

As described above, as the roll cleaning liquid, a treatment liquid used in a treatment tank immediately before a roll to be cleaned is suitable. In addition, it is preferable that the roll cleaning liquid supplied to the roll cleaning includes means for recovering the roll cleaning liquid in the processing tank used as the processing liquid. Further, from the viewpoint of prevention of foreign matter contamination, the roll cleaning liquid provided for the roll cleaning may be subjected to a filtration treatment and recovered in the treatment tank.

As a result of producing a polarizing film by the polarizing film producing apparatus shown in Fig. 1, defects such as adhesion of dirt were not observed on its surface.

1 shows a shower as a member for drawing a roll cleaning liquid on the surface of the roll, but it is not limited to a shower if the roll cleaning liquid can be led to the surface of the roll. The shower is a member for ejecting the cleaning liquid in a linear shape, and in addition to the shower, there is a member for ejecting the cleaning liquid in liquid or mist form, a member for dropping or flowing down the roll cleaning liquid by gravity, And the like. Further, the roll cleaning itself may have a structure in which the roll cleaning liquid exudes from the inside thereof, whereby the roll cleaning process may be performed by leading the roll cleaning liquid from the inside to the roll surface. As a member for applying the roll cleaning liquid to the surface of the roll, there is exemplified a brush having a structure in which the roll cleaning liquid exudes, and the surface of the roll to be cleaned is cleaned with a roll cleaning liquid. On the other hand, the roll cleaning step may include a step of immersing the surface of the roll to be cleaned in the roll cleaning liquid, instead of the step of drawing the roll cleaning liquid onto the surface of the roll to be cleaned. Specifically, a method may be used in which a liquid pool of a roll cleaning liquid is provided in a rotation path of a roll to be cleaned, and the entire surface of the roll is cleaned through the liquid pool every one revolution. Also in this method, as the roll cleaning liquid, it is preferable that the roll cleaning liquid after the roll cleaning is recovered in the immediately preceding treatment tank by using the treatment liquid used in the immediately preceding treatment tank.

[Second Embodiment]

3 is a cross-sectional view schematically showing an example of a polarizing film producing method and a polarizing film producing apparatus used therefor according to a second embodiment of the present invention. The polarizing film producing apparatus shown in Fig. 3 is a device in which a disc (unstretched) film 10 made of a polyvinyl alcohol-based resin is conveyed along a film conveying path while being continuously unwound from the disc roll 11, The dyeing bath 15, the first crosslinking bath 17a, the second crosslinking bath 17b and the cleansing bath 19 are successively passed through the drying bath 21, As shown in FIG. The obtained polarizing film 23 can be conveyed as it is, for example, in the following polarizing plate producing step (a step of bonding a protective film to one side or both sides of the polarizing film 23). Arrows in Fig. 3 indicate the transport direction of the film.

The polarizing film producing apparatus shown in Fig. 3 includes guide rolls 130 to 148, 60 and 61 which can support the film to be conveyed or change the film conveying direction in addition to the treatment bath, By placing the nip rolls 50, 51, 52, 53a, 53b, 54, 55 capable of imparting driving force to the film by pivoting, or changing the film transport direction, can do. The guide roll or nip roll can be placed before or after each treatment bath and in the treatment bath, whereby the introduction and immersion of the film in the treatment bath and the withdrawal from the treatment bath can be performed (see Fig. 3).

In the polarizing film producing apparatus shown in Fig. 3, nip rolls are arranged before and after each treatment bath (nip rolls 50, 51, 52, 53a, 53b, 54, 55). This makes it possible to perform roll-to-roll stretching in which longitudinal uniaxial stretching is carried out with a major difference in speed between nip rolls arranged before and after one or more treatment baths.

In the polarizing film producing apparatus shown in Fig. 3, in order to face the nip rolls 51, 52, 53a, 53b, 54 disposed behind the respective treatment baths 13, 15, 17a, 17b, , 172a, 172b, 173a, 173b, 174a, 174b, 175a, and 175b. During the continuous production of the polarizing film, roll cleaning liquid is applied to the surfaces of the nip rolls 51, 52, 53a, 53b, 54 by the shower (171a, 171b, 172a, 172b, 173a, 173b, 174a, 174b, 175a, And the surfaces of the nip rolls 51, 52, 53a, 53b and 54 are cleaned (roll cleaning step). The polarizing film producing apparatus shown in Fig. 3 is provided with recovery plates 81, 82, 83, 84, and 85 corresponding to the respective treatment tanks, whereby the nip rolls 51, 52, 53a, 53b The roll cleaning liquid used for cleaning the surfaces of the nip rolls 51, 52, 53a, 53b, and 54 is recovered in the treatment tank immediately before the nip rolls 51, 52, 53a, 53b, Each step will be described below.

Details of the swelling treatment step, the dyeing treatment step, the crosslinking treatment step, the film washing treatment step, the stretching treatment step, the drying treatment step and other treatment steps for the polyvinyl alcohol based resin film are the same as those described in the first embodiment same. In the second embodiment, the first crosslinking bath 17a and the second crosslinking bath 17b are used in the crosslinking process. The first crosslinking bath 17a is used for the crosslinking treatment for the purpose of water resistance as described in the crosslinking treatment step of the first embodiment and the second crosslinking bath 17b is used for the crosslinking treatment of the first embodiment And can be used for the crosslinking treatment for the purpose of color adjustment as described in the process. The crosslinking solution of the first crosslinking bath 17a may be an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100 in weight ratio, and the content of boric acid may be 2 to 10 wt%. In the first crosslinking bath 17a, since the polyvinyl alcohol based resin film is easy to absorb boric acid, in order to maintain the boric acid concentration in the first crosslinking bath 17a, when the polarizing film is continuously produced, Boric acid may be added to the first crosslinking bath 17a every time a predetermined amount of the polyvinyl alcohol-based resin film is conveyed.

(Roll cleaning step)

During the above-described continuous production in which a polarizing film is produced from a polyvinyl alcohol-based resin film, the roll cleaning process is performed by rotating each of the nip rolls 51, 52, 53a, 53b, and 54 disposed on the conveying path between the two treatment baths And a cleaning step of cleaning the substrate with a cleaning liquid. By the shower (171a, 171b, 172a, 172b, 173a, 173b, 174a, 174b, 175a, 175b) arranged to face the surface of each nip roll (51, 52, 53a, 53b, 54) The roll cleaning liquid is led out to the surface, and the surface of each nip roll is cleaned.

The cleaning of each roll with the roll cleaning liquid is preferably carried out during the continuous production of the polarizing film, and is preferably carried out at all times during the continuous production. Even if the polyvinyl alcohol-based resin film 10 carried in the treatment bath comes in with the treatment liquid in the treatment bath and adheres to the surface of each roll by such a roll cleaning process, it is immediately washed by the roll cleaning liquid, It is possible to prevent the surface of the roll from being contaminated by precipitation. The arrangement position of the rollers, the amount of the roll washing liquid, and the angle of extraction can be appropriately adjusted, and the roll cleaning liquid is supplied to rolls The upstream side and the downstream side in the transport direction, or any combination thereof. However, it is preferable that the roll cleaning liquid is not directly poured onto the transported polyvinyl alcohol-based resin film. The amount of the roll cleaning liquid to be discharged is set to an amount necessary for suppressing at least the contamination of the roll surface.

3, all the nip rolls 51, 52, 53a, 53b, and 54 disposed after each treatment tank are provided with shower (171a, 171b, 172a, 172b, 173a, 173b, 174a, 174b, 175a, and 175b are provided. However, they may be disposed only on the surface of the roll that is susceptible to contamination, and may be disposed to face the surface of at least one roll. The nip rolls 53 after the first crosslinking bath 17a and the nip rolls 53b behind the second crosslinking bath 17b are used as rolls which are susceptible to contamination. . Since the dye solution in the dyeing bath 15 and the crosslinking solution in the crosslinking baths 17a and 17b often have a higher salt concentration than other treatment baths, The salt is likely to precipitate. The shower for cleaning the roll is not limited to the arrangement in the nip roll only, and may be arranged in the guide roll as in the first embodiment.

As the roll cleaning liquid used in the shower 171a or 171b for cleaning the nip roll 51 disposed behind the swelling bath 13, a swelling liquid is suitable. The roll cleaning liquid derived from the nozzles 171a and 171b to the nip roll 51 is recovered in the swelling bath 13 through the recovery plate 81. [ Therefore, even when the swollen liquid in the swelling bath 13 is taken out and adhered to the nip roll 51 by the polyvinyl alcohol based resin film to be conveyed, the sweep bath 13 And by using the swelling liquid as the roll cleaning liquid, the composition of the swelling liquid in the swelling bath 13 can be kept constant. The swollen liquid used in the shower (171a, 171b) may be supplied from the swelling bath (13). By constituting in this way, the swelling liquid is circulated, so that the composition and liquid amount of the swelling liquid in the swelling bath 13 can be kept constant.

As the roll cleaning liquids used in the washers 172a and 172b for cleaning the nip rolls 52 disposed behind the dyeing bath 15, a dyeing solution is suitable. The roll cleaning liquid led to the nip rolls 52 from the washers 172a and 172b is recovered in the dyeing bath 15 through the recovery plate 82. [ Therefore, even if the dyeing solution in the dyeing bath 15 is taken out and adhered to the nip roll 52 by the polyvinyl alcohol based resin film being transported, the dyeing bath 15 , And the composition of the dyeing solution in the dyeing bath 15 can be kept constant by using a dyeing solution as the roll cleaning liquid. The dyeing solution used in the shower (172a, 172b) may be supplied from the dyeing bath (15). By constituting in this way, the dyeing liquid is circulated, so that the composition and liquid amount of the dyeing solution in the dyeing bath 15 can be kept constant.

As the roll cleaning liquid used in the shower 173a or 173b for cleaning the nip roll 53a disposed behind the first crosslinking bath 17a, a crosslinking liquid having the same composition as the crosslinking liquid in the first crosslinking bath 17a is suitable Do. The roll cleaning liquid led to the nip rolls 53a from the nozzles 173a and 173b is recovered in the first crosslinking bath 17a through the recovery plate 83. [ Therefore, even when the crosslinked liquid in the first crosslinking bath 17a is taken out and adhered to the nip roll 53a by the polyvinyl alcohol based resin film to be conveyed, It is easy to keep the composition of the crosslinking liquid in the first crosslinking bath 17a constant by using the crosslinking liquid as the roll washing liquid recovered in the crosslinking bath 17a. The crosslinking liquid used in the shower 173a, 173b may be supplied from the first crosslinking bath 17a. With this configuration, since the cross-linking liquid is circulated, it becomes easy to keep the composition and liquid amount of the cross-linking liquid in the first cross-linking bath 17a constant.

As the roll cleaning liquid used in the shower 174a or 174b for cleaning the nip roll 53b disposed behind the second crosslinking bath 17b, a crosslinking liquid having the same composition as the crosslinking liquid in the second crosslinking bath 17b is suitable Do. The roll cleaning liquid led to the nip rolls 53b from the nozzles 174a and 174b is recovered in the second crosslinking bath 17b through the recovery plate 84. [ Therefore, even when the crosslinked liquid in the second crosslinking bath 17b is carried out and adhered to the nip roll 53b by the polyvinyl alcohol based resin film to be conveyed, And the composition of the crosslinking liquid in the second crosslinking bath 17b can be kept constant by using the crosslinking liquid as the roll washing liquid recovered in the crosslinking bath 17b. The crosslinking liquid used in the shower 174a, 174b may be supplied from the second crosslinking bath 17b. By such a constitution, since the crosslinking liquid circulates, the composition and the liquid amount of the crosslinking liquid in the second crosslinking bath 17b can be kept constant.

As the roll cleaning liquids used in the washers 175a and 175b for cleaning the nip rolls 54 disposed behind the film cleansing bath 19, film cleaning liquids are suitable. The roll cleaning liquid led to the nip roll 54 from the washers 175a and 175b is recovered to the film cleaning bath 19 through the recovery plate 85. [ Therefore, even when the film cleaning liquid in the film cleansing bath 19 is taken out and adhered to the nip roll 54 by the polyvinyl alcohol based resin film being conveyed, The composition of the film washing liquid in the film cleansing bath 19 can be kept constant by using the film washing liquid as the roll washing liquid. The film cleaning liquid used in the shower (175a, 175b) may be supplied from the film cleaning bath (19). With this configuration, the film cleaning liquid is circulated, so that the composition and liquid amount of the film cleaning liquid in the film cleaning bath 19 can be kept constant.

As described above, even when the processing liquid in the processing tank is taken out and adhered to the roll by the polyvinyl alcohol-based resin film being conveyed, it is recovered in the processing tank by the cleaning step of the roll, , And even when a polarizing film is continuously produced, a polarizing film having uniform properties can be produced.

On the other hand, from the viewpoint of prevention of foreign matter contamination, the roll cleaning liquid provided for the roll cleaning may be subjected to filtration treatment and then recovered in the treatment tank.

As a result of producing a polarizing film by the polarizing film producing apparatus shown in Fig. 3, no defects such as adhesion of dirt were observed on its surface. Also, even if the polarizing film was continuously produced, the polarizing film having uniform characteristics could be continuously produced without greatly changing the composition of each processing bath.

<Polarizer>

A polarizing plate can be obtained by bonding a protective film to at least one side of a polarizing film produced as described above through an adhesive. As the protective film, for example, a film comprising an acetylcellulose-based resin such as triacetylcellulose or diacetylcellulose; A film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; Polycarbonate resin film, cycloolefin resin film; Acrylic resin film; And a film made of a chain olefin resin of a polypropylene type resin.

The surface of the polarizing film and / or the protective film may be subjected to surface treatment such as a corona treatment, a flame treatment, a plasma treatment, an ultraviolet ray irradiation, a primer coating treatment or a saponification treatment in order to improve the adhesion between the polarizing film and the protective film good. Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray curable adhesive such as an ultraviolet ray curable adhesive or an aqueous solution of a polyvinyl alcohol resin or an aqueous solution containing a crosslinking agent and an aqueous adhesive such as a urethane emulsion adhesive . The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photo radical polymerization initiator, a mixture of an epoxy compound and a cationic photopolymerization initiator, and the like. In addition, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photocationic polymerization initiator and a photo radical polymerization initiator may be used together as an initiator.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

&Lt; Example 1 >

The two crosslinking baths 17 (hereinafter, the first crosslinking bath is referred to as a first crosslinking bath 17a and the second crosslinking bath is referred to as a second crosslinking bath 17b) A polarizing film was produced using the same apparatus as the polarizing film producing apparatus shown in Fig. The guide rolls 30 to 41 were all made of flat rolls.

(Kurarupo pig film VF-PE # 3000, trade name, manufactured by Kuraray Co., Ltd., average degree of polymerization of 2400, degree of saponification of 99.9 mol% or more) was withdrawn from the roll at a thickness of 30 占 퐉 on a long polyvinyl alcohol , And immersed in a swelling bath 13 made of pure water at 20 캜 for a residence time of 31 seconds (swelling treatment step). Thereafter, the film drawn out from the swelling bath 13 was immersed in a dyeing bath 15 at 30 DEG C containing iodine with a potassium iodide / water ratio of 2/100 (weight ratio) for a residence time of 122 seconds (dyeing treatment step) . Subsequently, the film drawn from the dyeing bath 15 was immersed in a first crosslinking bath 17a at 56 deg. C at a boric acid / potassium iodide / water ratio of 4.1 / 12/100 (weight ratio) for a retention time of 70 seconds, (Crosslinking treatment step) in a second crosslinking bath 17b at 40 占 폚 at a ratio of boric acid / potassium iodide / water of 2.9 / 9/100 (weight ratio). In the dyeing treatment step and the crosslinking treatment step, vertical uniaxial stretching was carried out by roll-to-roll stretching in a bath. The total draw ratio based on the original film was set to 5.36 times. Next, the film drawn out from the second crosslinking bath 17b was immersed in a cleansing bath 19 made of pure water at 5 deg. C for a retention time of 3 seconds (cleaning treatment step). Thereafter, the film was dried for 190 seconds in a drying furnace (21) at 60 占 폚 to obtain a polarizing film having a thickness of 13.1 占 퐉.

During the continuous production of the polarizing film, the guide roll 32 for withdrawing the polyvinyl alcohol film from the swelling bath 13 is washed with pure water using a shower 71, and a polyvinyl alcohol film is removed from the dyeing bath 15 The guide roll 35 for drawing is washed with a dyeing solution having the same composition as that of the dyeing bath 15 using a shower 73 and a guide roll for drawing the polyvinyl alcohol film from the second crosslinking bath 17b 38 and the nip roll 53 are washed with a crosslinking solution having the same composition as that of the second crosslinking bath 17b by using the shower 75 or 76 and a guide for withdrawing the polyvinyl alcohol film from the cleansing bath 19 The rolls 41 and the nip rolls 54 were cleaned with pure water using a shower 77, 78.

No precipitation of salts or the like occurred on the surface of each roll even if the polarizing film was continuously manufactured for 7 hours by cleaning the guide roll and nip roll drawn out from each treatment bath. In addition, defects as a cause of contamination on the roll surface did not occur in the polarizing film.

&Lt; Example 2 >

A polarizing film was produced using the same apparatus as the polarizing film producing apparatus shown in Fig. All of the guide rolls 130 to 148 were flat rolls. 3, no shower for cleaning the guide rolls 132, 136, 140, 144, 148 is shown. In this embodiment, however, the cleanliness of these guide rolls, the cleaning of the nip roll .

(Trade name: Kurarupo Pfal Film VF-PE # 3000, manufactured by Kuraray Co., Ltd.), an average degree of polymerization of 2400, a degree of saponification of 99.9 mol% or more, a thickness of 30 m and a width of 450 mm Was continuously conveyed at 16 m / hour while being unwound from the roll, and immersed in a swelling bath 13 made of pure water at 20 캜 for a residence time of 31 seconds (swelling treatment step). Thereafter, the film drawn out from the swelling bath 13 was immersed in a dyeing bath 15 at 30 DEG C containing iodine with a potassium iodide / water ratio of 2/100 (weight ratio) for a residence time of 122 seconds (dyeing treatment step) . Subsequently, the film drawn out from the dyeing bath 15 was passed through a first crosslinking bath 17a (having a weight ratio of 4.1 / 12/100) of potassium borate / potassium iodide / water and a liquid amount of the first crosslinking solution of 280 L ) And then immersed in a second crosslinking bath 17b at 40 DEG C having a boric acid / potassium iodide / water ratio of 2.9 / 9/100 (weight ratio) and a liquid amount of the second crosslinking liquid of 75 L And immersed in a residence time of 13 seconds (crosslinking treatment step). In the dyeing treatment step and the crosslinking treatment step, vertical uniaxial stretching was carried out by roll-to-roll stretching in a bath. The total draw ratio based on the original film was set to 5.36 times. Next, the film drawn out from the second crosslinking bath 17b was immersed in a cleansing bath 19 made of pure water at 5 deg. C for a retention time of 3 seconds (cleaning treatment step). Thereafter, the film was dried for 190 seconds in a drying furnace (21) at 60 占 폚 to obtain a polarizing film having a thickness of 13.1 占 퐉. On the other hand, 10 g of boric acid was added to the first crosslinking bath 17a every one hour after the polarizing film was started to be transported, and the amount of boric acid to be reduced was compensated for because it was absorbed by the film.

During the continuous production of the polarizing film, the nip roll 51 behind the swelling bath 13 is washed with pure water using the shower 171a and 171b and the nip roll 52 behind the dye bath 15 is showered 172a The nip rolls 53a behind the first crosslinking bath 17a are washed with a dyeing solution having the same composition as that of the dyeing bath 15 using a shower 173a or 173b, The nip roll 53b behind the second crosslinking bath 17b was washed with a crosslinking solution having the same composition as that of the second crosslinking bath 17b using the shower plates 174a and 174b And the nip roll 54 behind the cleansing bath 19 was rinsed with pure water using a shower 175a, 175b. The guide rolls 132, 136, 140, 144, and 148 disposed immediately before the nip rolls 51, 52, 53a, 53b, and 54 were also cleaned in the same manner as the nip rolls.

Precipitation of salts or the like occurs on the surface of each roll even if the polarizing film is manufactured while the nip rolls 51, 52, 53a, 53b, and 54 disposed behind each treatment bath are cleaned to produce a polarizing film continuously for 7 hours Did not do it. In addition, defects as a cause of contamination on the roll surface did not occur in the polarizing film.

&Lt; Comparative Example 1 &

A polarizing film of Comparative Example 1 was produced in the same manner as in Example 1 except that the guide roll drawn out from each treatment bath and the nip roll were not cleaned.

In the case where the guide roll and the nip roll drawn out from each treatment bath were not cleaned, after the polarizing film was continuously produced for one hour, contamination on each roll was confirmed. In particular, much contamination was observed on the guide roll 38 and the nip roll 53 for pulling out the polyvinyl alcohol film from the second crosslinking bath 17b. Further, defects such as deformation and adhered foreign matter were observed in the polarizing film produced after continuously producing the polarizing film for one hour, and the contamination of each roll was transferred.

&Lt; Comparative Example 2 &

A polarizing film of Comparative Example 2 was produced in the same manner as in Example 2 except that the nip rolls 51, 52, 53a, 53b and 54 disposed after each treatment bath were not cleaned. In Comparative Example 2, after the polarizing film was continuously produced for one hour, contamination on the nip rolls 51, 52, 53a, 53b and 54 was confirmed. In particular, much contamination was observed in the nip roll 53b behind the second crosslinking bath 17b. Further, defects such as deformation and adhered foreign matter were observed in the polarizing film produced after continuously producing the polarizing film for one hour, and the contamination of each roll was transferred.

<Measurement of Composition of Boric Acid Concentration in Crosslinking Bath>

After the production of the polarizing film and the boric acid content of the first crosslinking bath 17a and the second crosslinking bath 17b before the production of the polarizing film were started in the manufacturing process of Example 2 and Comparative Example 2, The contents of boric acid in the first crosslinking bath 17a and the second crosslinking bath 17b were measured every one hour. On the other hand, the content of boric acid in the first crosslinking bath 17a after the start of the production of the polarizing film was measured immediately after the addition of 10 g of boric acid. As the boric acid content, 170 ml of pure water and 30 g of mannitol aqueous solution (12.5% by weight) were added to about 5 g of the first crosslinking bath 17a or the second crosslinking bath 17b to prepare a sample solution for measurement, (1 mol / l) is added dropwise until the solution reaches the neutralization point, and the boron content of the first crosslinking bath (17a) or the second crosslinking bath (17b) from the dropwise amount is adjusted by the following formula:

Boron content (parts by weight) = (6.18 x drop of sodium hydroxide aqueous solution (ml) / (weight of cross-linking solution (g) -6.18 x drop of sodium hydroxide aqueous solution (ml)))

Lt; / RTI &gt; Table 1 shows the results of measurement of the boric acid content of the first crosslinking bath 17a. Table 2 shows the results of measurement of the boric acid content of the second crosslinking bath 17b.

4 and 5 are graphs showing the results shown in Tables 1 and 2, respectively. It can be seen from Tables 1 and 2 that the difference between the maximum value and the minimum value of the boric acid content in the first crosslinking bath 17a and the second crosslinking bath 17b is 0.06 part by weight and 0.05 part by weight, On the other hand, in the case of Comparative Example 2, the difference between the maximum value and the minimum value of the boric acid content in the first crosslinking bath 17a and the second crosslinking bath 17b was 0.08 part by weight and 0.13 part by weight, respectively, . According to the second embodiment, the variation of the composition of the first crosslinking bath 17a and the second crosslinking bath 17b can be further suppressed, so that a polarizing film having uniform characteristics can be produced.

10: original film made of polyvinyl alcohol-based resin
11: disk roll 13: swelling bath
15: dye bath 17: bridging bath
19: Three lusts 21: Dried by
23: polarizing film
30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 60,
50, 51, 52, 53, 54, 55: nip roll
174a, 174b, 175a, 175b: a shower, a shower, a shower, a shower,

Claims (5)

A method for producing a polarizing film from a polyvinyl alcohol-based resin film,
An immersion step of immersing the polyvinyl alcohol-based resin film in a treatment liquid contained in a treatment tank,
A conveying step of conveying the polyvinyl alcohol resin film immersed in the treatment liquid along a roll;
And a roll cleaning step of cleaning the surface of the roll with a roll cleaning liquid. The method of manufacturing a polarizing film according to claim 1, wherein in the roll cleaning step, the treatment liquid is used as the roll cleaning liquid. The method of manufacturing a polarizing film according to claim 2, wherein the roll cleaning liquid is recovered in the treatment tank after the roll cleaning step. The method according to any one of claims 1 to 3, wherein the immersing step is a step of dyeing the polyvinyl alcohol resin film by dipping the polyvinyl alcohol resin film in a staining solution and dyeing the film with a dichroic dye, Wherein the cross-linking treatment is a cross-linking step of immersing in a cross-linking solution to cross-link. The method according to any one of claims 1 to 4, wherein the roll cleaning step includes a step of drawing the roll cleaning liquid onto the surface of the roll or a step of dipping the surface of the roll in the roll cleaning liquid A method for producing a polarizing film.

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