KR20170013167A - Method for producing polarizing film - Google Patents

Abstract

Provided is a production method for a polarizing film, comprising an elongation process in which a polyvinyl alcohol-based resin film is immersed in a treatment bath, conveyed, and subjected to a uniaxial elongation process using the difference in peripheral speed between an upstream nip roll and a downstream nip roll, wherein the elongation process has a low width reduction elongation process in which the width reduction rate (R) is 0.55 (%/sec) or less. The width reduction rate (R) is calculated by formula (1) in which the width at the time of passing the upstream nip roll is W1 (mm), the width (mm) at the time of passing the downstream nip roll is W2 (mm), and the time required for conveying from the upstream nip roll to the downstream nip roll is T (seconds).

Description

METHOD FOR PRODUCING POLARIZING FILM [0002]

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

The polarizing film is conventionally used in which a uniaxially stretched polyvinyl alcohol based resin film is adsorbed and aligned with a dichroic dye such as iodine or a dichroic dye. The polarizing film is usually used as a polarizing plate by bonding a protective film to one side or both sides thereof with an adhesive, and is used in 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.

In general, the polarizing film is formed by sequentially performing a process of continuously immersing a continuous long-length polyvinyl alcohol-based resin film in a treatment bath such as a swelling bath, a dyeing bath, and a crosslinking bath, (For example, Japanese Unexamined Patent Publication (Kokai) No. 2001-315140).

The polarizing film is transported along a film transport path passing through various treatment baths as described above while being continuously unwound from the original roll (wound product) of the polyvinyl alcohol-based resin film, and is immersed in a swelling bath And then taken out from the crosslinking bath, the stretching process can be continuously performed. However, there is a case where the film is broken during the continuous production, particularly during the stretching treatment, and improvement has been required from the viewpoints of the productivity and the yield of the polarizing film.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a polarizing film production method capable of suppressing film breakage during stretching treatment.

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

[1] A method for producing a polyvinyl alcohol-based resin film, which comprises a stretching step of carrying a polyvinyl alcohol-based resin film while immersing it in a treatment bath to perform uniaxial stretching using a difference in peripheral velocity (peripheral speed difference) between an upstream-

The drawing step has a low width reduction rate drawing step in which the width reduction ratio (R) is 0.55 (% / second) or less,

The width reduction ratio (R) is set such that the width of the polyvinyl alcohol-based resin film at the time of passing the upstream nip roll is W1 (mm), the width at the time of passing through the downstream nip roll is W2 (mm) (1), where T (seconds) is a time required for conveyance to the downstream nip roll.

[2] The process for producing a polarizing film according to [1], wherein the low-width-reduction stretching step has a step of stretching a polyvinyl alcohol-based resin film at the time of passing through the downstream-side nip roll at a cumulative stretching magnification of 4.5 times or more.

[3] The process for producing a polarizing film according to [1] or [2], wherein the low-width-reduction stretching step comprises a step of carrying out uniaxial stretching while being immersed in a crosslinking bath.

[4] The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,

The method for producing a polarizing film according to [3], wherein the low-width reduction rate stretching step includes a step of carrying out uniaxial stretching while being immersed in a crosslinking bath disposed after the second conveying direction.

[5] The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,

The stretching step has a first stretching step at the first crosslinking step in the carrying direction accompanied by immersion in a crosslinking bath,

 The method for producing a polarizing film according to any one of [1] to [4], wherein the cumulative stretching magnification of the polyvinyl alcohol-based resin film at the time of passing through the upstream-side nip roll is 2.5 or more in the first crosslinking stretching step.

[6] The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,

The stretching step has a second crosslinking stretching step in the second transporting direction accompanied by immersion in a crosslinking bath,

The method for producing a polarizing film according to any one of [1] to [5], wherein the cumulative stretch ratio of the polyvinyl alcohol resin film at the time of passing through the upstream-side nip roll is 4.0 or more in the second crosslinking stretching step.

[7] The production method of a polarizing film according to any one of [1] to [6], wherein the thickness of the polyvinyl alcohol based resin film is 65 μm or less in terms of unstretched.

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 the present invention.

≪ 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, an unstretched polyvinyl alcohol-based resin having a thickness of preferably 65 占 퐉 or less (for example, 60 占 퐉 or less), more preferably 50 占 퐉 or less, and even more preferably 35 占 퐉 or less, 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. Thinning of the original film tends to cause film breakage during stretching treatment. However, according to the present invention, even when the original film is thin (for example, 60 탆 or less), breakage of the film can be effectively suppressed. It is also preferable to use a disc having a thickness of 10 탆 or more. The width of the original film is not particularly limited, and may be, for example, about 400 to 6000 mm. Generally, the larger the film width, the more likely the film breakage occurs during the stretching treatment. However, according to the present invention, it is possible to effectively suppress the breakage of the film even if the original film width is large.

In the present invention, the original film can be 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 unrolling the long original film from the disk roll while continuously carrying the film along the film transport path of the polarizing film producing apparatus and performing a predetermined treatment process. The predetermined processing includes a swelling treatment step in which the original film is dipped in a swelling bath and then taken out, a dyeing treatment step in which the film after the swelling treatment step is dipped in a dyeing bath, and the film after dyeing is dipped in a crosslinking bath and taken out And a crosslinking treatment process.

In the present invention, the film is collectively referred to as a treatment bath (a bath containing a treatment liquid for treating a polyvinyl alcohol-based resin film provided on a film transport path such as a swelling bath, a dye bath, a crosslinking bath, In a process of any of the above-described processing steps of immersing in a treating bath (also referred to as a " treating bath ") in which the uniaxial stretching is carried out in parallel with the upstream side nip roll and the downstream side nip roll Respectively.

In the present invention, the process from the upstream nip roll to the downstream nip roll is referred to as "upstream nip roll" and "downstream nip roll", where one nip roll and the next nip roll along the transport path different from the main nip roll are referred to as "upstream nip roll" Process. The production method of the present invention has at least one such stretching step. In addition to the above-described stretching step involving immersing the film in the treatment bath, the film may be subjected to a stretching step in vapor phase before and after immersing the film in the treatment bath.

Each of the treatment baths provided on the conveyance path may have one kind of treatment bath of the same kind or a plurality of treatment baths of the same kind. In addition, even when the polyvinyl alcohol-based resin film is accompanied by immersion in a plurality of treatment baths until reaching the next downstream nip roll from the upstream nip roll, the upstream nip roll to the next downstream nip roll And a stretching process. On the other hand, until the next upstream nip roll reaches the next downstream nip roll, it is accompanied by immersion in a treatment bath (for example, a crosslinking bath), until the next downstream nip roll reaches the next downstream nip roll Even if they are accompanied by immersion in a bath (for example, a crosslinking bath), they are each subjected to a separate stretching process. The nip roll on the downstream side of the drawing step of the front end may also serve as the upstream side nip roll of the drawing step of the next step. In the present invention, other treatment steps may be added as necessary.

In the present invention, the stretching step accompanied by immersion of the film in a treatment bath has a low width reduction ratio drawing step in which the width reduction ratio (R) is 0.55 (% / sec) or less. The present inventors have found that it is effective to adjust the width reduction ratio (R) in order to suppress the breakage of the film, and to have a low width reduction ratio drawing process in which the width reduction ratio (R) is 0.55% will be. From the viewpoint of suppressing breakage, it is particularly effective to perform the low-width reduction rate stretching process for a film having a cumulative stretch ratio of 2.4 or more, and it is more effective to perform the low-width reduction rate stretching process for a film having a cumulative stretch ratio of 4.0 or more . The width reduction ratio R in the low width reduction rate drawing process is preferably 0.50% / second or less, and more preferably 0.45% / second or less. The width reduction ratio R is usually 0.01 (% / sec) or more. Here, the width reduction ratio (R) is a value obtained by dividing the width of the polyvinyl alcohol-based resin film at the time of passing through the upstream-side nip roll by W1 (mm) in the drawing step involving immersion in the treatment bath, (1) when the width of the alcoholic resin film is W2 (mm), and the time required for transport from the upstream side nip roll to the downstream side nip roll is T (seconds).

Hereinafter, a method of manufacturing a polarizing film according to the present invention will be described in detail with reference to FIG. 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 the present invention. The polarizing film producing apparatus shown in Fig. 1 is a system in which a disc (unstretched) film 10 made of a polyvinyl alcohol-based resin is conveyed along a film conveying path while being successively unwound from a disc roll 11, The dyeing bath 15, the first crosslinking bath 16, the second crosslinking bath 17 and the cleansing bath 18 are successively passed through the drying bath 21 and finally the drying bath 21 To pass through. The obtained polarizing film 23 can be transported, for example, in the next polarizing plate producing step (a step of bonding a protective film to one surface or both surfaces of the polarizing film 23). The arrows in Fig. 1 indicate the transport direction of the film.

The film transport path of the polarizing film producing apparatus includes, in addition to the above treatment bath, guide rolls 30 to 44, 60 and 61 capable of supporting the transported film or changing the film transport direction further, And the nip rolls 50 to 56 which can change the film transport direction can be disposed at appropriate positions. The guide rolls and the nip rolls can be arranged before and 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. 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.

1, the nip rolls (nip rolls 50 to 55) are arranged before and after each processing bath, and accordingly, in any one or more of the processing baths, the nip rolls Roll stretching (stretching step) in which longitudinal uniaxial stretching is carried out with a difference in speed between the nip roll and the downstream nip roll. Hereinafter, each processing step will be described.

(Swelling treatment)

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, facilitating dyeing, and plasticizing the original film 10. The processing conditions are determined within a range that can achieve the above object 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 carried out in such a manner that the original film 10 is continuously unwound from the original roll 11, conveyed along the film conveying path, and the original film 10 is conveyed to the swelling bath 13 Processing solution) for a predetermined period of time, and subsequently removing the solution. 1, the original film 10 is sandwiched between the guide rolls 60 and 61 and the film built by the nip roll 50 until the original film 10 is loosened and then immersed in the swelling bath 13 And is conveyed along the conveying path. In the swelling process, the film is transported along the film transport path established by the guide rolls 30 to 32.

In addition to pure water, boric acid (Japanese Patent Laid-open No. Hei 10-153709), chloride (Japanese Patent Laid-open No. 06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, In an amount 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 widening 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 bars, tenter clips, and the like.

In the swelling treatment, the stretching step of performing the uniaxial stretching treatment using the peripheral speed difference between the nip roll (upstream nip roll) 50 and the nip roll (downstream nip roll) 51 may be performed in parallel. By performing the stretching process in parallel, the occurrence of wrinkles can be suppressed.

In the swelling treatment, since the film swells and expands even in the transport direction of the film, when the film is not actively stretched, it is preferably arranged before and after the swelling bath 13 in order to eliminate the looseness of the film in the transport direction It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51 and the like. Further, for the purpose of stabilizing 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 taken out from the swelling bath 13 passes through the guide roll 32 and the nip roll 51 in order, and is introduced into the dyeing bath 15.

(Dyeing treatment)

The dyeing treatment is carried out for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol-based resin film after the swelling treatment. The treatment conditions are determined within a range in which the above objects can be achieved and within a range in which problems such as extreme melting of the film or disintegration 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 ) For a predetermined period of time, and subsequently, removing it. In order to enhance the dyeability of the dichroic dye, the film to be provided in the dyeing treatment step is preferably a film subjected to at least some degree of uniaxial stretching treatment, In addition to the axial stretching treatment, it is preferable to perform a stretching step in which the uniaxial stretching treatment is carried out in parallel during the dyeing treatment. The stretching process performed in parallel with the dyeing process can be performed by placing a major speed difference between the nip roll (upstream nip roll) 51 and the nip roll (downstream nip roll) 52 disposed before and after the dyeing bath 15.

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 at a concentration of, for example, a weight ratio can be used for 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 per 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, for example, an aqueous solution having a dichroic dye / water concentration of about 0.001 to 0.1 / 100 in a concentration by weight ratio can be used for the dyeing bath 15. The dyeing bath 15 may contain a dyeing aid or the like, for example, an inorganic salt such as sodium sulfate or a surfactant. 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, preferably 60 to 300 Seconds.

In the dyeing process, the polyvinyl alcohol based resin film is transported while removing the wrinkles of the film as in the swelling process. Therefore, the woven fabric 33 is wound on the guide rolls 33, 34 and / or 35 with widening functions such as expander rolls, spiral rolls, Or other widening devices such as cross guiders, bend bars, tenter clips or the like. Further, in order to suppress the occurrence of wrinkles, a drawing step performed simultaneously with the dyeing treatment is also effective.

In the example shown in Fig. 1, the film taken out from the dyeing bath 15 is introduced into the first crosslinking bath 16 through the guide roll 35 and the nip roll 52 in order.

(First crosslinking treatment)

The first crosslinking treatment is a treatment performed for the purpose of, for example, water resistance by crosslinking and color adjustment (preventing the film from becoming bluish). 1, the first crosslinking treatment is carried out along the film conveyance path established by the guide rolls 36 to 38 and the nip roll 52, and the first crosslinking bath 16 (treatment liquid accommodated in the crosslinking tank) By immersing the film after the dyeing treatment for a predetermined period of time and subsequently removing the film.

The first crosslinking bath 16 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 first crosslinking bath 16 preferably contains iodide in addition to boric acid, and the amount thereof is, 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 first crosslinking treatment, the concentration of boric acid and iodide and the temperature of the first crosslinking bath 16 can be appropriately changed depending on the purpose. For example, in the case where the purpose of the first crosslinking treatment is water resistance by crosslinking, and the swelling treatment, the dyeing treatment and the first crosslinking treatment are performed in this order on the polyvinyl alcohol resin film, the crosslinking agent- May be an aqueous solution having a concentration of boric acid / iodide / water = 3 to 10/1 to 20/100 in a weight ratio. If necessary, other crosslinking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and another crosslinking agent may be used in combination. The temperature of the first crosslinking bath at the time of immersing the film is usually about 50 to 70 캜, preferably 53 to 65 캜, and the immersing time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds , And more preferably 20 to 200 seconds. When the dyeing treatment and the first cross-linking treatment are performed in this order on the polyvinyl alcohol-based resin film previously stretched before the swelling treatment, the temperature of the cross-linking bath 17 is usually about 50 to 85 캜, preferably 55 Lt; / RTI >

In the first crosslinking treatment for 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 = 1/5/3 to 30/100 is used . The temperature of the first crosslinking bath at the time of immersing the film is usually about 10 to 45 占 폚, and the immersing time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

In the first crosslinking treatment, the stretching step of uniaxial stretching treatment using the main speed difference between the nip roll (upstream nip roll) 52 and the nip roll (downstream nip roll) 53 may be performed in parallel. This stretching process is also effective for suppressing the occurrence of wrinkles.

In the first crosslinking treatment, the polyvinyl alcohol-based resin film is transported while removing the wrinkles of the film as in the swelling treatment, so that the guide rolls 36, 37 and / It is possible to use a roll having a widening function, or to use another widening device such as a cross guider, a bend bar, and a tenter clip.

1, the film taken out from the first crosslinking bath 16 is introduced into the second crosslinking bath 17 through the guide roll 38 and the nip roll 53 in order.

(Second crosslinking treatment)

1, the second cross-linking treatment is carried out along the film conveyance path constructed by the guide rolls 39 to 41 and the nip roll 53, and the second cross-linking bath 17 (treatment liquid accommodated in the cross-linking tank) By immersing the film after the first crosslinking treatment for a predetermined period of time and subsequently removing the film.

As for the second crosslinking treatment, the above description in the first crosslinking treatment is applied. Therefore, in the second crosslinking treatment, the uniaxial stretching process may be performed in parallel using the main speed difference between the nip roll (upstream nip roll) 53 and the nip roll (downstream nip roll) 54.

In the production apparatus of the present invention, the case where two crosslinking baths 16 and 17 are provided has been described. However, the number of crosslinking baths is not limited as long as there are one or more crosslinking baths. The crosslinking treatment is usually carried out 2 to 5 times. The composition and temperature of the crosslinking bath at the third and subsequent transferring directions in the case of having three or more crosslinking baths may be the same or different if they are within the above-described range with respect to the first crosslinking bath. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for color adjustment may be performed in a plurality of steps, respectively.

(Cleaning treatment)

The production method of the present invention may include a washing treatment step after the crosslinking treatment step. The cleaning treatment is carried out for the purpose of removing excess boric acid or iodine adhered to the polyvinyl alcohol-based resin film. The cleaning treatment can be carried out, for example, by immersing a crosslinked polyvinyl alcohol-based resin film in a cleansing bath (water) 18, spraying water to the film as a shower, or using them in combination.

Fig. 1 shows an example in which the polyvinyl alcohol-based resin film is immersed in a cleansing bath 18 to perform a cleaning treatment. The temperature of the cleansing bath 18 in the cleansing treatment is usually about 2 to 40 占 폚, and the immersion time of the film is usually about 2 to 120 seconds.

Also in the cleaning process, the rolls having the widening function such as the expander roll, the spiral roll, and the crown roll may be provided on the guide rolls 42, 43 and / or 44 for the purpose of transporting the polyvinyl alcohol- Or using other widening devices such as cross guiders, bend bars, tenter clips or the like.

In the cleaning process, the stretching process in which the uniaxial stretching process is performed using the peripheral speed difference between the nip roll (upstream nip roll) 54 and the nip roll (downstream nip roll) 55 may be performed in parallel. The stretching process is also effective for suppressing the generation of wrinkles.

(Drawing process)

The production method of the present invention has a stretching step in which the film is uniaxially stretched in parallel with the above series of treatment steps. A specific method of the uniaxial stretching treatment is a roll-to-roll stretching in which uniaxial stretching is performed using the main speed difference between the upstream side nip roll and the downstream side nip roll as described above. Further, in addition to the stretching step by the inter-roll stretching, a stretching treatment by thermal roll stretching or tenter stretching as described in Japanese Patent No. 2731813 may be combined. The stretching treatment can be carried out a plurality of times until the polarizing film 23 is obtained from the original film 10. As described above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles in the film.

The final cumulative stretching magnification of the polarizing film 23 based on the original film 10 is not limited, but is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

As a result of intensive studies, the inventors of the present invention have found that the film tends to be broken in the stretching process in which the film has a cumulative stretching magnification of 4.5 times or more and in the stretching process in which the crosslinked film is stretched. The width reduction ratio R is 0.55 (% / second) or less, preferably 0.50 (% / second) or less, and more preferably 0.45% or less in the stretching process by roll- / Sec < / RTI > or less), it was found that breakage can be suppressed. The inventors of the present invention have further found that, in the low-width reduction rate stretching process, the stretching process in which the cumulative stretching magnification of the polyvinyl alcohol-based resin film at the time of passing through the nip roll on the downstream side is 4.5 times or more , And a step of carrying out uniaxial stretching by being carried while immersed in a crosslinking bath [b], preferably at least one of the following: The two steps may be carried out together, or the two steps may be the same drawing step.

About [a]

In the case of having a plurality of drawing processes with a cumulative drawing magnification of 4.5 times or more at the time of passing through the downstream side nip roll, at least one of these drawing processes is a low width reduction rate drawing process. Further, there is an effect of suppressing the breakage of the film even if there is at least one low-width reduction rate stretching process in which the cumulative stretching ratio at the time of passing through the downstream-side nip roll is 4.5 times or more and the width decreasing rate (R) is 0.55 It is preferable that all of the drawing step in which the cumulative drawing magnification at the time of passing the nip roll is 4.5 times or more is the low width reduction rate drawing step. As a result, the effect of suppressing film breakage can be further improved.

The draw ratio in the drawing step in which the cumulative draw ratio at the time of passing through the downstream side nip roll is 4.5 or more is preferably 1.25 or less, more preferably 1.21 or less. By setting this stretching magnification ratio, breakage of the film can be further suppressed.

About [b]

When a plurality of stretching steps involving immersion in a crosslinking bath of a polyvinyl alcohol-based resin film is provided, at least one of such stretching steps is a low width decreasing rate stretching step. Further, in the case of having a plurality of crosslinking baths, it is preferable that the stretching step involving immersion in the second or subsequent crosslinking bath (after the second crosslinking bath) is a low width reduction rate stretching step. In the second and subsequent crosslinking baths, the crosslinking of the film is progressing even after the first crosslinking bath, and accordingly, the stretching process involving immersion in the crosslinking bath for the second time and thereafter is a low- It is possible to further improve the suppression effect of fracture.

About [a] and [b]

For the first stretching process in the carrying direction accompanied by immersion in a crosslinking bath (referred to as " stretching process during first crosslinking "), the cumulative stretch ratio of the polyvinyl alcohol resin film at the time of passing through the upstream- And more preferably 2.7 times or more. When the total draw ratio is higher than this range, the draw ratio in the cross-linking bath must be increased, and if the draw ratio in the cross-linking bath is high, the film is liable to be broken. Further, with respect to the second stage stretching step (also referred to as " second stretching step during crosslinking ") accompanied by immersion in a crosslinking bath, the cumulative stretch ratio of the polyvinyl alcohol resin film at the time of passing through the upstream- Fold, and more preferably at least 4.2 times. As the crosslinking progresses, the film tends to be broken at the time of stretching. Therefore, if the cumulative stretching magnification is 4.0 times or more at the time of introduction into the stretching step during the second crosslinking, the breaking of the film is suppressed even if the total stretching magnification is high .

The width reduction ratio R in the drawing step can be determined by, for example, a stretch ratio from the upstream nip roll to the downstream nip roll in the stretching step, the temperature of the treatment bath, the composition of the treatment bath (for example, Concentration), or the cumulative stretching magnification and temperature before the stretching step.

(Dry treatment)

It is preferable to carry out a treatment for drying the polyvinyl alcohol based resin film after the washing treatment. 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 processing steps)

Processing other than the above-described processing may be added. Examples of the treatment that can be added include an immersion treatment (complementary treatment) in an iodide aqueous solution containing no boric acid, which is performed after the crosslinking treatment, an immersion treatment in an aqueous solution containing zinc chloride or the like without containing boric acid Processing).

<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 made of an acetylcellulose-based resin such as triacetylcellulose or diacetylcellulose; Films 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.

In order to improve the adhesion between the polarizing film and the protective film, surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment and saponification treatment may be performed on the bonding surfaces of the polarizing film and / 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, 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 is described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples, polarizing films were produced using the same apparatus as the apparatus for producing polarizing films shown in Fig. All of the guide rolls 30 to 44 use flat rolls.

&Lt; Example 1 >

(1) swelling treatment

An unstretched polyvinyl alcohol film having a thickness of 30 탆 and a width of 450 mm (trade name: Kurarupo Foot Film VF-PE # 3000, manufactured by Kuraray Co., Ltd., degree of polymerization: 2400, degree of saponification: 99.9 mol% , And the film was immersed in a swelling bath 13 containing pure water at 30 DEG C for 100 seconds while keeping the film in a relaxed state so as not to loosen the film.

(2) Dyeing treatment

Next, the film passed through the nip roll 51 was immersed in a dyeing bath 15 at 30 캜 for 120 seconds with iodine / potassium iodide / water (weight ratio) of 0.05 / 2/100. Concurrently with this dyeing treatment, longitudinal uniaxial stretching between rolls (called "stretching step during dyeing") was carried out with a peripheral speed difference between the nip rolls 51, 52.

(3) First crosslinking treatment

Next, in order to carry out the first crosslinking treatment for the purpose of water resistance, the film passed through the nip roll 52 is subjected to a first crosslinking treatment at 56 占 폚 with a potassium iodide / boric acid / water (weight ratio) of 12 / And immersed in the bath 16. Also in this case, longitudinal uniaxial stretching between the rolls (stretching step in the first crosslinking step) was carried out in parallel with the first crosslinking treatment with a main speed difference between the nip rolls 52 and 53. The cumulative draw ratio (which can be regarded as the same as the draw ratio at the completion of the dyeing and drawing process) and the film width W1 at the start of the first crosslinking step, that is, at the time of passing through the upstream nip roll 52, Table 1 shows the cumulative stretching magnification and the film width W2 at the end of the drawing process, that is, at the time of passing through the downstream nip roll 53. Fig. Table 1 shows the time (T) required for the first crosslinking step.

(4) Second crosslinking treatment

Subsequently, the film after the first crosslinking treatment was immersed in a second crosslinking bath 17 at 40 캜 in which potassium iodide / boric acid / water (weight ratio) was 12 / 4.4 / 100. Also in this case, in parallel with the second crosslinking treatment, vertical uniaxial stretching (second crosslinking stretching step) between the rolls was carried out with a relative speed difference between the nip rolls 53, 54. The cumulative stretching magnification and the film width W1 at the start of the second crosslinking step, that is, at the time of passing through the upstream nip roll 53, and the cumulative stretching at the end of the second crosslinking drawing step, Table 1 shows the magnification and film width (W2). Table 1 shows the time (T) required for the second crosslinking step.

(5) Cleaning process, drying process

Thereafter, the film after completion of the second crosslinking treatment and the third stretching step was dipped in a cleansing bath 18 containing pure water at 6 DEG C, and then dried at 70 DEG C for 3 minutes by passing through a drying oven 21 , And a polarizing film 23 were produced.

(6) Calculation of width reduction rate

The width W1 (mm) of the film at the time of passing through the upstream-side nip roll 52, the width W2 (mm) of the film at the time of passing through the downstream-side nip roll 53, The width reduction ratio R calculated by the above equation (1) was calculated from the time T (seconds) necessary for conveyance to the downstream side nip roll 53. [ Table 1 shows the calculation results of the width reduction rate (R) (% / sec).

Similarly, the width W1 (mm) of the film at the time of passing through the upstream-side nip roll 53, the width W2 (mm) of the film at the time of passing through the downstream-side nip roll 54, The width reduction ratio R calculated from the above formula (1) was calculated from the time T (seconds) necessary for conveyance from the upstream side nip roll 53 to the downstream side nip roll 54. Table 1 shows the calculation results of the width reduction rate (R) (% / sec).

(7) Rupture evaluation

The polarizing film was continuously produced, and the continuous running time in which the film was broken or the continuous running time in which the film was not broken was confirmed. When the film was broken, the breakage frequency of the film per hour was calculated from the continuous execution time until the breakage of the film occurred. As for Example 1, the polarizing film was continuously produced for 24 hours. As a result, no breakage of the film occurred in any of the processing steps during 24 hours of operation. The results are shown in Table 1.

&Lt; Examples 2 to 5 &

With respect to Examples 2 to 5, manufacturing conditions different from those of Example 1 were shown in Table 1, and other production conditions were the same as in Example 1 to prepare a polarizing film. The polarizing film thus obtained was subjected to calculation of the width reduction rate and break evaluation of the stretching step in the first crosslinking step and the stretching step in the second crosslinking step. The results are shown in Table 1.

As shown in Table 1, in Examples 2 and 3, the polarizing film was continuously produced for 24 hours. As a result, no breakage of the film occurred in any of the processing steps during 24 hours of operation. In Example 4, the polarizing film was continuously produced for 72 hours. As a result, no breakage of the film occurred in any of the processing steps during 72 hours of operation. In Example 5, the film was broken when the polarizing film was continuously produced for 60 hours.

&Lt; Comparative Examples 1 to 3 &

For Comparative Examples 1 to 3, the manufacturing conditions different from those of Example 1 were shown in Table 1, and the polarizing films were produced in the same manner as in Example 1 except for the production conditions. The polarizing film thus obtained was subjected to the calculation of the width reduction rate in the first crosslinking time stretching step and the stretching step in the second crosslinking step and the breakage evaluation. The results are shown in Table 1.

As shown in Table 1, in Comparative Example 1, the film was broken when the polarizing film was continuously produced for 3.5 hours. In Comparative Example 2, the film was broken at the time when the polarizing film was continuously produced for 2.5 hours. In Comparative Example 3, the film was broken when the polarizing film was continuously produced for 4 hours.

16: a first crosslinking bath; 17: a second crosslinking bath; 18: a wash liquor; 21: a drying bath; , 23: polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, , 54, 55, 56: Nip roll.

Claims (7)

And a stretching step of carrying the uniaxial stretching using a main speed difference between the upstream side nip roll and the downstream side nip roll by transporting the polyvinyl alcohol based resin film while immersing the film in a treatment bath,
The drawing step has a low width reduction rate drawing step in which the width reduction ratio (R) is 0.55 (% / second) or less,
The width reduction ratio (R) is set such that the width of the polyvinyl alcohol-based resin film at the time of passing the upstream nip roll is W1 (mm), the width at the time of passing through the downstream nip roll is W2 (mm) (1), wherein T (seconds) is a time required for transporting the film to the downstream nip roll.

The method of producing a polarizing film according to claim 1, wherein the low-width reduction rate stretching step has a step of stretching the polyvinyl alcohol-based resin film at a cumulative stretching magnification of 4.5 times or more at the time of passing through the downstream-side nip roll. The method of producing a polarizing film according to any one of claims 1 to 5, wherein the low-width-reduction stretching step is carried out while being immersed in a crosslinking bath to perform uniaxial stretching. The polyvinyl alcohol-based resin film according to claim 3, wherein the polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
Wherein the low-width reduction rate stretching step has a step of carrying out uniaxial stretching while being immersed in a crosslinking bath disposed at the second and subsequent positions in the transport direction. The polyvinyl alcohol-based resin film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The stretching step has a first stretching step at the first crosslinking step in the carrying direction accompanied by immersion in a crosslinking bath,
Wherein the cumulative stretch ratio of the polyvinyl alcohol-based resin film at the time of passing through the upstream-side nip roll in the first crosslinking stretching step is at least 2.5 times. The polyvinyl alcohol-based resin film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The stretching step has a second crosslinking stretching step in the second transporting direction accompanied by immersion in a crosslinking bath,
Wherein the cumulative stretch ratio of the polyvinyl alcohol-based resin film at the time of passing through the upstream-side nip roll in the second crosslinking stretching step is at least 4.0 times. The method for producing a polarizing film according to claim 1 or 2, wherein the thickness of the polyvinyl alcohol-based resin film is not more than 65 占 퐉.

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