JP2017027013A - Production method of polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a polarizing film by which breakage of a film in a stretching process can be suppressed.SOLUTION: The production method of a polarizing film includes a stretching step of subjecting a polyvinyl alcohol resin film to uniaxial stretching by conveying the film while immersing the film in a treatment bath using a peripheral speed difference between upstream nip rolls and downstream nip rolls. The stretching step includes a stretching step with a low width reduction rate, where a width reduction rate R is 0.55 (%/sec) or less. The width reduction rate R is calculated by formula (1) below, where W1 (mm) represents a width of the polyvinyl alcohol resin film when the film passes through the upstream nip rolls, W2 (mm) represents a width of the film when the film passes through the downstream nip rolls, and T (sec) represents a time necessary to convey the film from the upstream nip rolls to the downstream nip rolls.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a polarizing film that can be used as a constituent member of a polarizing plate.

  Conventionally used is a polarizing film obtained by adsorbing and orienting a dichroic dye such as iodine or a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film. A polarizing film is usually a polarizing plate obtained by laminating a protective film on one or both sides with an adhesive, and used for liquid crystal display devices such as liquid crystal televisions, monitors for personal computers and mobile phones. It is used.

  In general, a polarizing film is subjected to a treatment in which a long polyvinyl alcohol resin film continuously conveyed is sequentially immersed in a treatment bath such as a swelling bath, a dyeing bath, and a crosslinking bath, and stretched between these series of treatments. It is manufactured by processing (for example, Patent Document 1).

JP 2001-315140 A

  The polarizing film is continuously unwound from the roll (rolled product) of the polyvinyl alcohol-based resin film while being transported along the film transport path passing through the various treatment baths as described above, and is also used as a swelling bath. A continuous production can be carried out by applying a stretching treatment at any one or more stages from the immersion to the withdrawal from the crosslinking bath. However, the film may break during continuous production, particularly during the stretching process, and improvements have been demanded from the viewpoint of productivity and the yield of the polarizing film.

  Then, this invention aims at provision of the manufacturing method of the polarizing film which can suppress the film fracture | rupture at the time of an extending | stretching process.

This invention provides the manufacturing method of the polarizing film shown below.
[1] It has a stretching process in which a polyvinyl alcohol-based resin film is transported while being immersed in a treatment bath and is uniaxially stretched using a difference in peripheral speed between the upstream nip roll and the downstream nip roll,
The stretching step includes a low width reduction rate stretching step in which the width reduction rate R is 0.55 (% / second) or less,
The width reduction rate R is defined as W1 (mm) when the polyvinyl alcohol resin film passes through the upstream nip roll, W2 (mm) when the downstream nip roll passes, and from the upstream nip roll. The manufacturing method of a polarizing film calculated by following formula (1) when the time required for conveyance to the said downstream nip roll is set to T (second).

  [2] The polarizing film according to [1], wherein the low width reduction rate stretching step includes a step of stretching the polyvinyl alcohol-based resin film at a cumulative stretch ratio of 4.5 times or more when passing through the downstream nip roll. Production method.

  [3] The method for producing a polarizing film according to [1] or [2], wherein the low width reduction rate stretching step includes 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 said low width reduction rate extending process is a manufacturing method of the polarizing film as described in [3] which has the process of conveying and carrying out uniaxial stretching, being immersed in the bridge | crosslinking bath arrange | positioned after the conveyance direction 2nd.

[5] The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The stretching step includes a first stretching step at the time of first crosslinking in the conveying direction involving immersion in a crosslinking bath,
The polarizing film production according to any one of [1] to [4], wherein, in the first crosslinking-time stretching step, a cumulative stretch ratio of the polyvinyl alcohol-based resin film when passing through the upstream nip roll is 2.5 times or more. Method.

[6] The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The stretching step includes a second stretching step at the time of second crosslinking in the transport direction involving immersion in a crosslinking bath,
Production of the polarizing film according to any one of [1] to [5], wherein in the second crosslinking stretching step, the cumulative stretching ratio of the polyvinyl alcohol-based resin film when passing through the upstream nip roll is 4.0 times or more. Method.

  [7] The method for producing a polarizing film according to any one of [1] to [6], wherein the polyvinyl alcohol-based resin film has an unstretched thickness of 65 μm or less.

  According to the method of the present invention, film breakage during stretching can be effectively suppressed.

It is sectional drawing which shows typically an example of the manufacturing method of the polarizing film which concerns on this invention, and a polarizing film manufacturing apparatus used for it.

<Production method of polarizing film>
In the present invention, the polarizing film is one in which a dichroic dye (iodine or 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, more preferably about 99 mol% or more. The polyvinyl acetate resin can be, for example, a copolymer of vinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer copolymerizable therewith. 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, preferably about 1500 to 5000.

  These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used.

  In the present invention, an unstretched polyvinyl alcohol-based resin film (raw film) having a thickness of preferably 65 μm or less (for example, 60 μm or less), more preferably 50 μm or less, and even more preferably 35 μm or less is used as a starting material for producing a polarizing film. Use. As a result, it is possible to obtain a thin polarizing film whose market demand is increasing. The thinner the original film, the easier it is to cause film breakage during the stretching process. However, according to the present invention, even when the original film is thin (for example, 60 μm or less), the film breakage can be effectively suppressed. In addition, it is preferable to use a raw film having a thickness of 10 μm or more. The width of the raw film is not particularly limited and can be, for example, about 400 to 6000 mm. Usually, the larger the film width, the more likely the film breaks during the stretching treatment. However, according to the present invention, the film breakage can be effectively suppressed even when the original film width is large.

  In the present invention, the raw film can be prepared as a roll (raw roll) of a long unstretched polyvinyl alcohol-based resin film.

  The polarizing film is a long film by carrying out a predetermined processing step by continuously conveying the long original film from the original film roll along the film conveying path of the polarizing film manufacturing apparatus. It can be continuously produced as a polarizing film. The predetermined treatment steps include a swelling treatment step in which the original film is dipped in a swelling bath, a drawing treatment step in which the film after the swelling treatment step is dipped in the dyeing bath, and a drawing treatment step in which the film after the dyeing treatment is drawn is a crosslinking bath. It is possible to include a cross-linking treatment step that is drawn out after being immersed in the substrate.

  In the present invention, the film is treated with a treatment bath (such as a swelling bath, a dyeing bath, a crosslinking bath and a washing bath) containing a treatment liquid for treating a polyvinyl alcohol resin film provided on the film transport path. In one or more of the above-described processing steps that are transported while being immersed in a “processing bath” in general terms, the difference in peripheral speed between the upstream nip roll and the downstream nip roll is utilized. It has the extending process which performs uniaxial stretching in parallel.

  In the present invention, one nip roll and the next nip roll along the transport path having a different peripheral speed are referred to as an “upstream nip roll” and a “downstream nip roll”, respectively, and the process from the upstream nip roll to the downstream nip roll is performed. One stretching process is used. The production method of the present invention has one or more such stretching steps. In addition, you may have the extending | stretching process performed in a gaseous phase before and after immersing a film in a processing bath other than said stretching process with the immersion to the processing bath of a film.

  Each of the treatment baths as described above provided on the transfer path may have one or a plurality of treatment baths of the same kind. Even when the polyvinyl alcohol-based resin film is immersed in a plurality of treatment baths from the upstream nip roll to the next downstream nip roll, the interval between the upstream nip roll and the next downstream nip roll is not affected. One stretching process is used. On the other hand, the processing bath (for example, a crosslinking bath) is immersed from the upstream nip roll to the next downstream nip roll, and the processing bath of the same type as the previous stage is required from the next upstream nip roll to the next downstream nip roll. Even when it is accompanied by immersion in (for example, a crosslinking bath), these are set as separate stretching steps. The downstream nip roll in the preceding drawing process may also serve as the upstream nip roll in the next drawing process. In the present invention, other processing steps may be added as necessary.

  In this invention, it has the low width reduction rate extending | stretching process whose width reduction rate R is 0.55 (% / second) or less as said extending process with the immersion to the processing bath of a film. In order to suppress breakage of the film, it is effective for the inventors to adjust the width reduction rate R, and the width reduction rate R is 0.55 (% / second) or less. It has been found that having a process is effective. The width reduction rate R in the low width reduction rate stretching step is preferably 0.50 (% / second) or less, more preferably 0.45 (% / second) or less. The width reduction rate R is usually 0.01 (% / second) or more. Here, the width reduction rate R is the width of the polyvinyl alcohol-based resin film when passing through the upstream nip roll in the stretching step involving immersion in the treatment bath, W1 (mm), and the polyvinyl alcohol-based resin when passing through the downstream nip roll. When the width of the film is W2 (mm) and the time required for transport from the upstream nip roll to the downstream nip roll is T (seconds), the value is calculated by the following formula (1).

  Hereinafter, it demonstrates in detail about the manufacturing method of the polarizing film which concerns on this invention, referring FIG. Drawing 1 is a sectional view showing typically an example of the manufacturing method of the polarizing film concerning the present invention, and the polarizing film manufacturing device used for it. The polarizing film manufacturing apparatus shown in FIG. 1 transports a raw fabric (unstretched) film 10 made of polyvinyl alcohol resin along a film transport path while continuously unwinding from a raw fabric roll 11. The swelling bath 13, the dyeing bath 15, the first crosslinking bath 16, the second crosslinking bath 17, and the cleaning bath 18 provided on the conveyance path are sequentially passed, and finally the drying furnace 21 is passed. The obtained polarizing film 23 can be conveyed, for example, to the next polarizing plate production step (step of bonding a protective film on one or both sides of the polarizing film 23) as it is. The arrow in FIG. 1 has shown the conveyance direction of the film.

  The film transport path of the polarizing film manufacturing apparatus supports guide films 30 to 44, 60, 61 that can support the film to be transported or further change the film transport direction in addition to the processing bath, and the film to be transported. Can be constructed by placing the nip rolls 50 to 56 at appropriate positions so that the film can be pressed and sandwiched, and a driving force can be applied to the film by rotating the film. Guide rolls and nip rolls can be arranged before and after each treatment bath or in the treatment bath, whereby the film can be introduced and immersed in the treatment bath and drawn out from the treatment bath (see FIG. 1). For example, by providing one or more guide rolls 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 manufacturing apparatus shown in FIG. 1, nip rolls are arranged before and after each treatment bath (nip rolls 50 to 55), and thereby, nip rolls arranged before and after any one or more treatment baths. It is possible to perform inter-roll stretching (stretching step) in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between the gaps (between the upstream nip roll and the downstream nip roll). Hereinafter, each processing step will be described.

(Swelling treatment)
The swelling treatment is performed for the purpose of removing foreign matter on the surface of the original film 10, removing the plasticizer in the original film 10, imparting easy dyeability, 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 in which problems such as extreme dissolution and devitrification of the raw film 10 do not occur.

  Referring to FIG. 1, in the swelling treatment, the original film 10 is continuously unwound from the original roll 11 and conveyed along the film conveyance path, and the original film 10 is accommodated in the swelling bath 13 (swelled in a swelling tank). In the treated liquid) for a predetermined time and then withdrawing. In the example of FIG. 1, the raw film 10 is conveyed along the film conveyance path constructed by the guide rolls 60 and 61 and the nip roll 50 until the original film 10 is unwound and immersed in the swelling bath 13. Is done. In the swelling process, the film is conveyed along the film conveyance path constructed by the guide rolls 30 to 32.

  In addition to pure water, the swelling bath 13 contains boric acid (JP-A-10-153709), chloride (JP-A-06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohols, and the like. It is also possible to use an aqueous solution 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 ° C., preferably about 10 to 40 ° C., and more preferably about 15 to 30 ° C. The immersion time of the raw film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. Moreover, when the raw fabric film 10 is a polyvinyl alcohol-based resin film previously stretched in gas, the temperature of the swelling bath 13 is, for example, about 20 to 70 ° C, preferably about 30 to 60 ° C. The immersion time of the raw film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

  In the swelling treatment, the problem that the original film 10 swells in the width direction and the film is wrinkled easily occurs. As one means for conveying the film while removing the wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used for the guide rolls 30, 31 and / or 32, a cross guider, a bend bar. Or using other widening devices such as tenter clips.

  In the swelling process, a stretching process for performing a uniaxial stretching process using a difference in peripheral speed 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 generation of wrinkles can be suppressed.

In the swelling treatment, the film swells and expands in the film conveyance direction. Therefore, when the film is not actively stretched, for example, it is disposed before and after the swelling bath 13 in order to eliminate the sag of the film in the conveyance direction. It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51. Further, for the purpose of stabilizing the film conveyance in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, or an EPC device (Edge Position).
It is also useful to use a Control device: a device that detects the end of the film and prevents the film from meandering).

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

(Dyeing process)
The dyeing treatment is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within a range in which the object can be achieved and in a range in which defects such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, the dyeing process is carried along a film conveyance path constructed by guide rolls 33 to 35 and nip roll 51, and the film after the swelling treatment is dyed in bath 15 (treatment liquid contained in a dyeing tank). ) For a predetermined time and then withdrawing. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing treatment step is preferably a film subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, Alternatively, in addition to the uniaxial stretching process before the dyeing process, it is preferable to perform a stretching process in which the uniaxial stretching process is performed in parallel with the dyeing process. The stretching process performed in parallel with the dyeing process can be performed by making a peripheral speed difference between the nip roll (upstream nip roll) 51 and the nip roll (downstream nip roll) 52 arranged before and after the dyeing bath 15.

  When iodine is used as the dichroic dye, the concentration in the dyeing bath 15 is, for example, iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100 by weight. An aqueous solution can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added, it is distinguished from the crosslinking treatment described later in terms of containing iodine. If the aqueous solution contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, the dyeing bath 15 Can be considered. The temperature of the dyeing bath 15 when dipping the film is usually about 10 to 45 ° C., preferably 10 to 40 ° C., more preferably 20 to 35 ° C., and the dipping time of the film is usually 30 to 600 seconds. Degree, preferably 60 to 300 seconds.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, an aqueous solution having a concentration of dichroic dye / water = about 0.001 to 0.1 / 100 by weight is used for the dyeing bath 15. be able to. This dyeing bath 15 may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one dichroic dye may be used alone, or two or more dichroic dyes may be used in combination. The temperature of the dyeing bath 15 when dipping the film is, for example, about 20 to 80 ° C., preferably 30 to 70 ° C., and the dipping time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. is there.

  Also in the dyeing process, the widening function such as an expander roll, a spiral roll, or a crown roll is provided on the guide rolls 33, 34 and / or 35 in order to convey the polyvinyl alcohol resin film while removing the wrinkles of the film as in the swelling process. Can be used, or other widening devices such as cross guiders, bend bars, tenter clips can be used. In addition, in order to suppress generation | occurrence | production of a wrinkle, the extending | stretching process performed in parallel at the time of a dyeing process is also effective.

  In the example shown in FIG. 1, the film drawn from the dyeing bath 15 passes through the guide roll 35 and the nip roll 52 in this order and is introduced into the first crosslinking bath 16.

(First cross-linking treatment)
The first crosslinking treatment is a treatment performed for the purpose of water resistance and hue adjustment (for example, preventing the film from being bluish) by crosslinking. Referring to FIG. 1, the first crosslinking treatment is conveyed along a film conveyance path constructed by the guide rolls 36 to 38 and the nip roll 52, and is fed to the first crosslinking bath 16 (treatment liquid accommodated in the crosslinking tank). It can be carried out by immersing the film after the dyeing treatment for a predetermined time and then pulling it out.

  The first crosslinking bath 16 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid with respect to 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 100 parts by weight of water. It can be 30 parts by weight. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

  In the first cross-linking treatment, the concentration of boric acid and iodide and the temperature of the first cross-linking bath 16 can be appropriately changed depending on the purpose. For example, when the purpose of the first cross-linking treatment is water resistance by cross-linking and the polyvinyl alcohol resin film is subjected to swelling treatment, dyeing treatment and first cross-linking treatment in this order, the cross-linking agent-containing liquid of the first cross-linking bath is The aqueous solution may have a concentration of boric acid / iodide / water = 3 to 10/1 to 20/100 by weight. As needed, it may replace with boric acid and may use other crosslinking agents, such as a glyoxal or glutaraldehyde, and may use boric acid and another crosslinking agent together. The temperature of the first crosslinking bath when dipping the film is usually about 50 to 70 ° C., preferably 53 to 65 ° C., and the dipping time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, More preferably, it is 20 to 200 seconds. Moreover, when performing a dyeing | staining process and a 1st crosslinking process in this order with respect to the polyvinyl alcohol-type resin film previously extended | stretched before the swelling process, the temperature of the crosslinking bath 17 is about 50-85 degreeC normally, Preferably it is 55-80 degreeC. It is.

  In the first cross-linking treatment for adjusting the hue, for example, when iodine is used as the dichroic dye, the cross-linking is performed at a weight ratio of boric acid / iodide / water = 1 to 5/3 to 30/100. An agent-containing liquid can be used. The temperature of the first crosslinking bath when dipping the film is usually about 10 to 45 ° C., and the dipping time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

  In the first cross-linking treatment, a stretching process for performing a uniaxial stretching treatment using a peripheral speed difference between the nip roll (upstream nip roll) 52 and the nip roll (downstream nip roll) 53 can be performed in parallel. Such a stretching process is also effective for suppressing the generation of wrinkles.

  In the first crosslinking treatment, an expander roll, a spiral roll, a crown roll, etc. are used as guide rolls 36, 37 and / or 38 in order to convey the polyvinyl alcohol resin film while removing the wrinkles of the film as in the swelling treatment. A roll having a widening function can be used, or another widening device such as a cross guider, a bend bar, or a tenter clip can be used.

  In the example shown in FIG. 1, the film drawn from the first crosslinking bath 16 passes through the guide roll 38 and the nip roll 53 in order and is introduced into the second crosslinking bath 17.

(Second cross-linking treatment)
With reference to FIG. 1, the second crosslinking treatment is conveyed along the film conveyance path constructed by the guide rolls 39 to 41 and the nip roll 53, and is supplied to the second crosslinking bath 17 (treatment liquid accommodated in the crosslinking tank). It can be carried out by immersing the film after the first crosslinking treatment for a predetermined time and then pulling it out.

  About the 2nd bridge | crosslinking process, the said description in 1st bridge | crosslinking process is applied. Therefore, in the second cross-linking treatment, a uniaxial stretching process using a peripheral speed difference between the nip roll (upstream nip roll) 53 and the nip roll (downstream nip roll) 54 can be performed in parallel.

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

(Cleaning process)
The production method of the present invention can include a washing treatment step after the crosslinking treatment step. The washing treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol resin film. The washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in a washing bath (water) 18, spraying water as a shower on the film, or using these in combination.

  FIG. 1 shows an example in which a cleaning process is performed by immersing a polyvinyl alcohol-based resin film in a cleaning bath 18. The temperature of the washing bath 18 in the washing treatment is usually about 2 to 40 ° C., and the immersion time of the film is usually about 2 to 120 seconds.

  In the cleaning process, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as the guide rolls 42, 43 and / or 44 for the purpose of transporting the polyvinyl alcohol resin film while removing wrinkles. Or other widening devices such as cross guiders, bend bars, tenter clips can be used.

  In the cleaning process, a stretching process for performing a uniaxial stretching process using a difference in peripheral speed 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.

(Extension process)
The production method of the present invention includes a stretching step of uniaxially stretching the film in parallel with the series of processing steps. As described above, the specific method of the uniaxial stretching process is inter-roll stretching in which uniaxial stretching is performed by utilizing the peripheral speed difference between the upstream nip roll and the downstream nip roll. Moreover, in addition to the extending | stretching process by extending | stretching between rolls, you may carry out combining the extending | stretching process by hot roll extending | stretching, a tenter extending | stretching, etc. which are described in patent 271813. The stretching process can be carried out a plurality of times before the polarizing film 23 is obtained from the raw film 10. As described above, the stretching treatment is also advantageous for suppressing the generation of wrinkles on the film.

  The final cumulative draw ratio of the polarizing film 23 based on the original fabric 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 present inventors have found that the film is likely to break in a stretching process in which the cumulative stretching ratio of the film is 4.5 times or more and a stretching process in which the film having undergone crosslinking has been stretched. And about the extending | stretching process by roll extending | stretching which is easy to produce the film fracture | rupture, the width reduction rate R is 0.55 (% / sec) or less, Preferably it is 0.50 (% / sec) or less, More preferably, 0.45 ( % / Sec) was found to be able to suppress breakage by the low width reduction rate stretching step. In addition to these findings, in the production method of the present invention, as the low width reduction rate stretching step, [a] the cumulative stretching ratio when passing through the downstream nip roll of the polyvinyl alcohol-based resin film is 4.5 times or more. It is preferable to have at least one of a step of stretching and [b] a step of carrying out uniaxial stretching while being immersed in a crosslinking bath, thereby further improving the effect of suppressing breakage of the film. . In addition, you may have both two processes, or two processes may be the same extending | stretching process.

About [a] When there are a plurality of stretching steps having a cumulative stretching ratio of 4.5 times or more when passing through the downstream nip roll, at least one of such stretching steps is a low width reduction rate stretching step. Even if there is only one low width reduction rate stretching step in which the cumulative stretching ratio when passing through the downstream nip roll is 4.5 times or more and the width reduction rate R is 0.55 (% / second) or less. Although there exists an effect which suppresses the fracture | rupture of a film, it is preferable that all the extending processes in which the cumulative draw ratio at the time of downstream nip roll passage become 4.5 times or more are low width reduction rate extending processes. Thereby, the suppression effect of the fracture | rupture of a film can further be improved.

  The draw ratio in the drawing step in which the cumulative draw ratio when passing through the downstream nip roll is 4.5 times or more is preferably 1.25 times or less, and more preferably 1.21 times or less. By setting it as such a draw ratio, the fracture | rupture of a film can further be suppressed.

About [b] When there are a plurality of stretching steps involving immersion of the polyvinyl alcohol-based resin film in a crosslinking bath, at least one of such stretching steps is a low width reduction rate stretching step. Moreover, when it has a some crosslinking bath, it is preferable that the extending | stretching process accompanied by the immersion to the 2nd or subsequent crosslinking bath (after 2nd crosslinking bath) is a low width reduction rate extending | stretching process. In the second and subsequent cross-linking baths, the film is more cross-linked than the first cross-linking bath, and therefore the stretching step involving immersion in the second and subsequent cross-linking baths is a low width reduction rate stretching step. Thereby, the suppression effect of the fracture | rupture of a film can further be improved.

Regarding [a] and [b] For the first stretching step in the conveying direction involving immersion in the crosslinking bath (also referred to as “first stretching step during crosslinking”), the cumulative stretching of the polyvinyl alcohol-based resin film when passing through the upstream nip roll The magnification is preferably 2.5 times or more, and more preferably 2.7 times or more. Below this range, if the total draw ratio is high, it is necessary to increase the draw ratio in the crosslinking bath, and if the draw ratio in the crosslinking bath is high, the film tends to break. In addition, in the second stretching step in the conveying direction accompanied by immersion in the crosslinking bath (also referred to as “second stretching step during crosslinking”), the cumulative stretch ratio of the polyvinyl alcohol-based resin film when passing through the upstream nip roll is 4. It is preferably 0 times or more, more preferably 4.2 times or more. As the crosslinking progresses, the film is likely to break during stretching. Therefore, when the total stretching ratio is higher than 4.0 times when introduced into the second stretching process, the total stretching ratio is higher. However, the breakage of the film can be suppressed.

  The width reduction rate R in the stretching step is, for example, the stretching 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, boric acid concentration in the crosslinking bath), or the stretching. It can be adjusted by the cumulative stretching ratio, temperature, etc. before the process.

(Drying process)
It is preferable to perform the process which dries a polyvinyl-alcohol-type resin film after a washing process. The drying of the film is not particularly limited, but can be performed using a drying furnace 21 as in the example shown in FIG. The drying temperature is, for example, about 30 to 100 ° C., and the drying time is, for example, about 30 to 600 seconds. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 μm.

(Other processing steps)
Processing other than the processing described above can also be added. Examples of treatments that can be added include immersion treatment (complementary color treatment) in an aqueous iodide solution that does not contain boric acid, and immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride, etc. (zinc) Processing).

<Polarizing plate>
A polarizing plate can be obtained by bonding a protective film via an adhesive on at least one surface of the polarizing film produced as described above. As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose; a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate resin film, a cyclo Examples include olefin resin films; acrylic resin films; and films made of polypropylene-based chain olefin resins.

  Surfaces such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. on the polarizing film and / or protective film bonding surface in order to improve the adhesion between the polarizing film and the protective film Processing may be performed. As an adhesive used for laminating a polarizing film and a protective film, an active energy ray curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of a polyvinyl alcohol resin, or an aqueous solution in which a crosslinking agent is blended. And water-based adhesives such as urethane emulsion adhesives. 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 photo cationic polymerization initiator, or the like. Alternatively, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photo cationic polymerization initiator and a photo radical polymerization initiator may be used in combination as an initiator.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the following examples, a polarizing film was manufactured using an apparatus similar to the polarizing film manufacturing apparatus shown in FIG. All the guide rolls 30 to 44 were flat rolls.

<Example 1>
(1) Swelling treatment Unstretched polyvinyl alcohol film having a thickness of 30 μm and a width of 450 mm (trade name “Kuraray Poval Film VF-PE # 3000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) The film was transported while being continuously unwound from the raw roll 11, and immersed in a swelling bath 13 containing pure water at 30 ° C. for 100 seconds while maintaining a tension state so that the film does not loosen.

(2) Dyeing treatment Next, the film that passed through the nip roll 51 was immersed in a dyeing bath 15 at 30 ° C. in which iodine / potassium iodide / water (weight ratio) was 0.05 / 2/100 for 120 seconds. In parallel with this dyeing treatment, longitudinal uniaxial stretching between rolls (referred to as “dyeing process during dyeing”) was performed with a difference in peripheral speed between the nip rolls 51 and 52.

(3) First cross-linking treatment Next, in order to perform the first cross-linking treatment for the purpose of water resistance, the film that has passed through the nip roll 52 has a potassium iodide / boric acid / water (weight ratio) of 12 / 4.4. It was immersed in the 1st crosslinking bath 16 of 56 degreeC which is / 100. Here, in parallel with the first cross-linking treatment, a circumferential speed difference was made between the nip rolls 52 and 53 to perform longitudinal uniaxial stretching between the rolls (first cross-linking stretching step). Cumulative draw ratio at the start of the first cross-linking stretching step, that is, when passing through the upstream nip roll 52 (can be regarded as the same as the draw ratio at the end of the dyeing and stretching step), the film width (W1), and the first cross-stretching stretching step Table 1 shows the cumulative draw ratio and the film width (W2) at the end, that is, when passing through the downstream nip roll 53. Table 1 shows the time (T) required for the first cross-linking stretching step.

(4) Second cross-linking treatment Subsequently, the film after the first cross-linking treatment is immersed in a second cross-linking bath 17 at 40 ° C. in which potassium iodide / boric acid / water (weight ratio) is 12 / 4.4 / 100. did. Here, in parallel with the second cross-linking treatment, a circumferential speed difference was provided between the nip rolls 53 and 54 to perform longitudinal uniaxial stretching between the rolls (second cross-linking stretching step). Cumulative draw ratio and film width (W1) at the start of the second cross-linking stretching process, that is, when passing through the upstream nip roll 53, and cumulative stretching ratio and film width at the end of the second cross-linking stretching process, that is, when passing through the downstream nip roll 54 (W2) is shown in Table 1. Table 1 shows the time (T) required for the second crosslinking stretching step.

(5) Washing step, drying step Thereafter, the film after finishing the second crosslinking treatment and the third stretching step is immersed in a washing bath 18 containing 6 ° C. pure water, and then passed through a drying furnace 21. The polarizing film 23 was produced by drying at 70 ° C. for 3 minutes.

(6) Calculation of width reduction rate In the first cross-linking stretching step, the width of the film when passing through the upstream nip roll 52 is W1 (mm), the width of the film when passing through the downstream nip roll 53, W2 (mm), upstream From the time T (seconds) required for conveyance from the side nip roll 52 to the downstream nip roll 53, the width reduction rate R calculated by the above formula (1) was calculated. Table 1 shows the calculation result of the width reduction rate R (% / second).

  Similarly, in the second cross-linking stretching step, the width of the film when passing through the upstream nip roll 53 is W1 (mm), the width of the film when passing through the downstream nip roll 54 (mm), and the downstream side from the upstream nip roll 53 From the time T (seconds) required for conveyance to the nip roll 54, the width reduction rate R calculated by the above equation (1) was calculated. Table 1 shows the calculation result of the width reduction rate R (% / second).

(7) Evaluation of Breaking Polarized film production was carried out continuously, and the continuous execution time at which film breakage occurred or the continuous execution time that continued without film breakage was confirmed. When the film breaks, the frequency of film breaks per hour is calculated from the continuous execution time until the film breaks. About Example 1, when polarizing film manufacture was implemented continuously for 24 hours, the fracture | rupture of the film did not occur in any process process during operation for 24 hours. The results are shown in Table 1.

<Examples 2 to 5>
About Examples 2-5, it showed in Table 1 about the manufacturing conditions different from Example 1, and produced the polarizing film similarly to Example 1 in other manufacturing conditions. About the obtained polarizing film, calculation of the width reduction rate of the extending | stretching process at the time of 1st bridge | crosslinking and the extending | stretching process at the time of 2nd bridge | crosslinking and fracture | rupture evaluation were performed. The results are shown in Table 1.

  As shown in Table 1, for Examples 2 and 3, polarizing film production was carried out continuously for 24 hours. During the operation for 24 hours, no film breakage occurred in any of the treatment steps. About Example 4, when the polarizing film manufacture was implemented continuously for 72 hours, the fracture | rupture of the film did not occur in any process process during operation for 72 hours. About Example 5, when the polarizing film manufacture was implemented continuously for 60 hours, the film broke.

<Comparative Examples 1-3>
About Comparative Examples 1-3, it showed in Table 1 about the manufacturing conditions different from Example 1, and produced the polarizing film similarly to Example 1 in other manufacturing conditions. About the obtained polarizing film, calculation of the width reduction rate of the extending | stretching process at the time of 1st bridge | crosslinking and the extending | stretching process at the time of 2nd bridge | crosslinking and fracture | rupture evaluation were performed. 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 when the polarizing film was continuously produced for 2.5 hours. In Comparative Example 3, the film broke when the polarizing film was continuously produced for 4 hours.

  10 Raw film made of polyvinyl alcohol resin, 11 Raw roll, 13 Swelling bath, 15 Dye bath, 16 First cross-linking bath, 17 Second cross-linking bath, 18 Washing bath, 21 Drying furnace, 23 Polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 60, 61 Guide roll, 50, 51, 52, 53, 54, 55, 56 Nip roll.

Claims (7)

It has a stretching process in which a polyvinyl alcohol-based resin film is transported while being immersed in a treatment bath and is uniaxially stretched using a peripheral speed difference between the upstream nip roll and the downstream nip roll,
The stretching step includes a low width reduction rate stretching step in which the width reduction rate R is 0.55 (% / second) or less,
The width reduction rate R is defined as W1 (mm) when the polyvinyl alcohol resin film passes through the upstream nip roll, W2 (mm) when the downstream nip roll passes, and from the upstream nip roll. The manufacturing method of a polarizing film calculated by following formula (1) when the time required for conveyance to the said downstream nip roll is set to T (second).
  The said low width reduction rate extending process is a manufacturing method of the polarizing film of Claim 1 which has the process of extending | stretching the cumulative draw ratio of the polyvinyl alcohol-type resin film at the time of downstream nip roll passage 4.5 times or more.   The said low width reduction rate extending process is a manufacturing method of the polarizing film of Claim 1 or 2 which has the process of conveying and carrying out a uniaxial stretching, being immersed in a crosslinking bath. The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The said low width reduction rate extending process is a manufacturing method of the polarizing film of Claim 3 which has the process of conveying and carrying out uniaxial stretching, being immersed in the crosslinking bath arrange | positioned after the conveyance direction 2nd. The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The stretching step includes a first stretching step at the time of first crosslinking in the conveying direction involving immersion in a crosslinking bath,
The production of the polarizing film according to any one of claims 1 to 4, wherein in the first stretching step at the time of crosslinking, the cumulative stretching ratio of the polyvinyl alcohol-based resin film when passing through the upstream nip roll is 2.5 times or more. Method. The polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking baths,
The stretching step includes a second stretching step at the time of second crosslinking in the transport direction involving immersion in a crosslinking bath,
The production of the polarizing film according to any one of claims 1 to 5, wherein in the second stretching step at the time of crosslinking, the cumulative stretching ratio of the polyvinyl alcohol-based resin film when passing through the upstream nip roll is 4.0 times or more. Method.   The manufacturing method of the polarizing film of any one of Claims 1-6 whose thickness of the said polyvinyl alcohol-type resin film is 65 micrometers or less by unstretched.