JP6097359B2 - Manufacturing method of polarizing film - Google Patents

Description

  The present invention relates to a method for producing a polarizing film.

  Conventionally, polarizing films have been widely used as materials for liquid crystal display elements. As the polarizing film, a film in which a dichroic dye is adsorbed on a polyvinyl alcohol film is generally used.

  In such a method for producing a polarizing film, a step of uniaxially stretching a polyvinyl alcohol film, a step of dyeing the polyvinyl alcohol film with a dichroic dye, and treating the dyed polyvinyl alcohol film with an aqueous boric acid solution A process is included (for example, patent document 1).

  In patent document 1, when the polyvinyl alcohol film is highly stretched (4 to 6 times) in the uniaxial stretching step, it is mentioned that the polyvinyl alcohol film is easily cut. In order to solve the above-described problem, Patent Document 1 discloses an optical device for slitting both ends of a film in the flow direction of the film so as to have a predetermined width using a specific shear blade before the uniaxial stretching process. A slitting method for a polyvinyl alcohol film is disclosed.

  On the other hand, the polyvinyl alcohol film is basically dyed and treated with boric acid in an aqueous solution. However, since the polyvinyl alcohol film is water-soluble, cutting may occur. For the purpose of reducing the frequency of film cutting in an aqueous solution, Patent Document 2 discloses that the film thickness of the film is increased by performing a heat treatment at a temperature in the range of 90 to 180 ° C. after the uniaxial stretching process and before the dyeing process. The manufacturing method which processes so that it may exceed 10 micrometers and less than 20 micrometers is disclosed. According to the production method, a polarizing film that is thin and difficult to cut in an aqueous solution can be obtained.

Japanese Patent Laying-Open No. 2005-212098 (released on August 11, 2005) JP 2003-240958 A (released on August 27, 2003)

  However, in the manufacturing method of patent document 2, it is necessary to heat-process the stretched polyvinyl alcohol-type film, and it may be difficult to employ | adopt the said manufacturing method on the structure of the manufacturing apparatus to be used. Therefore, there is a demand for a production method for obtaining a polarizing film that is difficult to be cut in an aqueous solution in the dyeing step and the boric acid aqueous solution step without performing heat treatment in advance.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a method for producing a polarizing film in which a polyvinyl alcohol-based film is hardly cut in an aqueous solution without performing a heat treatment in advance. There is.

In order to solve the above-mentioned problem, the method for producing a polarizing film of the present invention stretches a long polyvinyl alcohol film in the transport direction of the film, and dyes the stretched polyvinyl alcohol film with a dichroic dye. In the production of a polarizing film, which is treated with an aqueous boric acid solution to produce a polarizing film, after stretching the polyvinyl alcohol film, before dyeing the stretched polyvinyl alcohol film, the stretched polyvinyl alcohol film It is characterized by slitting both ends.

  It is conceivable that both end portions where the thickness is uneven due to stretching serve as starting points of cutting at the time of dyeing. By slitting these both end portions, the cutting frequency of the polyvinyl alcohol film at the time of dyeing can be reduced. Moreover, in this manufacturing method, it is not necessary to heat-process a polyvinyl alcohol-type film before a slit. Since the drying furnace is larger in scale than the slitter, it can be said that this manufacturing method is easy to adopt.

  Moreover, in the manufacturing method of the polarizing film of this invention, it is preferable that the slit width of each edge part of a polyvinyl alcohol-type film is 2% or more and 100% or less with respect to the whole width of a polyvinyl alcohol-type film.

  When the slit width is in the above range, the both ends can be removed to such an extent that the cutting frequency of the polyvinyl alcohol film is reduced, and the film can be slit to such an extent that the width of the film is not significantly reduced.

Further, in the method for producing a polarizing film of the present invention, the polyvinyl alcohol film was wound into a roll prior to staining by dichroic dye, comprising the step of unwinding a rolled polyvinyl alcohol film, polyvinyl alcohol film It is preferable to slit both ends of the polyvinyl alcohol film along the conveying direction before winding the film into a roll.

  Thereby, a polyvinyl alcohol-type film can be once made into a roll shape, and can be moved, and it can dye | stain from subsequent unwinding and bridge | crosslinking by boric acid in another place. For this reason, the said manufacturing method can be implemented with more facilities.

  Moreover, in the manufacturing method of the polarizing film of this invention, the winding-up part which winds up a polyvinyl alcohol-type film by the axial rotation of a winding shaft is used, and the said winding is carried out in parallel with respect to the width direction of the said polyvinyl-alcohol-type film. The polyvinyl alcohol film is preferably wound into a roll while moving the part back and forth.

  According to the manufacturing method, the position of the polyvinyl alcohol film relative to the winding shaft changes during winding. Thereby, since both ends of the polyvinyl alcohol film are wound while moving relative to the take-up shaft, even if the polyvinyl alcohol film is rolled, it is difficult to be in an ear-high state.

Method for producing a polarizing film of the present invention, as described above, an elongated polyvinyl alcohol film was stretched in the conveying direction of the film, a polyvinyl alcohol film stretched stained with dichroic dyes, boric In the production of a polarizing film that is treated with an acid aqueous solution to produce a polarizing film, after stretching the polyvinyl alcohol film, before dyeing the stretched polyvinyl alcohol film, both ends of the stretched polyvinyl alcohol film are It is a method of slitting.

  It is conceivable that both end portions where the thickness is uneven due to stretching serve as starting points of cutting at the time of dyeing. By slitting these both end portions, the cutting frequency of the polyvinyl alcohol film at the time of dyeing can be reduced. Moreover, in this manufacturing method, there exists an effect that it is not necessary to heat-process a polyvinyl-alcohol-type film before a slit.

It is sectional drawing which shows the processing apparatus which concerns on this Embodiment. In this Embodiment, it is a graph which shows the winding time at the time of winding up a polyvinyl-alcohol-type film, and the position of a film edge part. It is a figure which shows the roll wound up by the winding method of FIG. It is sectional drawing which shows the dyeing and drying apparatus which concerns on this Embodiment. 2 is a graph showing the thickness of a polyvinyl alcohol film in Example 1 and Comparative Example 1.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3, but the present invention is not limited to this. The method for producing a polyvinyl alcohol film according to the present invention (hereinafter abbreviated as “the present production method” as appropriate) is obtained by stretching a long polyvinyl alcohol film in the film transport direction, and then stretching the stretched polyvinyl alcohol film. is based on the premise that the staining by the dichroic dye. That is, after stretching the polyvinyl alcohol film, before dyeing the stretched polyvinyl alcohol film, it is a method of slitting both ends of the polyvinyl alcohol film along the transport direction (hereinafter referred to as “polyvinyl alcohol system”). “Film” is abbreviated as “PVA film” as appropriate).

  First, this manufacturing method is demonstrated with description of the processing apparatus used with this manufacturing method. FIG. 1 is a cross-sectional view showing the processing apparatus 10. The processing apparatus 10 is an example of an apparatus that can be used in the present manufacturing method, and the present manufacturing method can be implemented by another apparatus. The processing apparatus 10 is used for stretching and slitting a PVA film, and includes an unwinding unit 1, a heat roll (stretching unit) 2, a slitter 3, a winding unit 4, and a transporting roll 5. .

  The unwinding unit 1 is provided with a roll in which the PVA film is rolled, and supplies the PVA film to the heat roll 2. The PVA film supplied from the unwinding unit 1 is continuously conveyed via the conveyance roll 5. The winding unit 4 winds up the PVA film, and the unwinding unit 1 and the winding unit 4 include a winding shaft for winding up the core of the PVA film.

  The PVA film can be obtained by saponifying a polyvinyl acetate resin. Examples of the PVA film include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, and acrylamides having an ammonium group.

  The degree of saponification of the PVA film is usually 85 mol% or more and 100 mol% or less, preferably 98 mol% or more and 100 mol% or less. The PVA film may be further modified, and for example, polyvinyl polymer modified with aldehydes, polyvinyl acetal, and the like may be used. The average degree of polymerization of the PVA film is usually 1000 or more and 10,000 or less, preferably 1500 or more and 5000 or less. Although the thickness of the PVA film before extending | stretching is not limited, For example, it can be 30 micrometers or more and 80 micrometers or less.

  The heat roll 2 has a heat source inside, and the surface thereof can be heated. A PVA film can be extended | stretched when a PVA film contacts the surface of a heat roll in a conveyance process. The film winding speed of the winding unit 4 is larger than the film unwinding speed of the unwinding unit 1, and the PVA film is uniaxially stretched in the film transport direction and wound without being loosened. The PVA film is stretched by dry stretching in the air.

  The magnification for stretching the PVA film is 4 times or more and 8 times or less, preferably 4.5 times or more and 6 times or less. If it is less than the above range, the polarizing film as the final product will not be sufficiently stretched, and the performance of the polarizing film cannot be improved. On the other hand, when it exceeds 8 times, there exists a tendency for the intensity | strength of a PVA film to fall and it becomes easy to produce a cutting | disconnection when dyeing.

  Next, both ends of the PVA film are slit by the slitter 3. In a normal method for producing a polarizing film, a slitter is used to make a dyed polarizing film have a desired product width. On the other hand, in patent document 1, although it is used for the slit of the PVA film before extending | stretching, the cutting frequency at the time of extending | stretching is reduced by making a PVA film into a predetermined width with a predetermined shear blade before extending | stretching. That is, the slit is made before the stretching of the PVA film, which can be said to be an exceptional slitting method. The invention of Patent Document 1 aims to reduce the frequency with which a film is cut during stretching.

  The inventors of the present production method investigated the cause in order to reduce the cutting frequency of the PVA film dyed after stretching, and focused on the fact that the PVA film after stretching has a thickness distribution (bias). The stretched PVA film is uniaxially stretched in the transport direction, but the entire PVA film is not stretched uniformly. Specifically, the central portion of the PVA film is stretched more, but the thickness of both end portions is thicker than the central portion. The present inventors thought that this uneven thickness might be a cause of the PVA film being easily cut during dyeing. For example, when both ends are thicker, that is, there is a bias in stretching, there are microscopically thin portions at both ends, which may be the starting point of cutting.

  Then, the present inventors came up with the point which slits the both ends of the PVA film after extending | stretching. It was expected that the cutting frequency would be reduced during dyeing by removing both end portions that were biased by stretching. The slit according to the present invention is not made to have a desired product width, but the purpose of use is also different from the method of using the slitter in Patent Document 1. The PVA film after stretching was found to be thicker at each end with a width of generally 2% or more and 10% or less with respect to the entire width of the PVA film, depending on the stretching conditions.

  Accordingly, the slit width at each end of the PVA film is preferably 2% or more and 10% or less with respect to the entire width of the PVA film. If it is less than 2%, thick portions at both ends remain, and if it exceeds 10%, the width of the PVA film is greatly reduced. Further, it is preferably 2% or more and 8% or less, and more preferably 2% or more and 5% or less. As the slitter 3, conventionally known equipment for slitting a polymer film can be used, and it is not particularly limited.

  It was revealed that when the PVA film subjected to the above treatment is dyed later, the cutting frequency of the PVA film in the aqueous solution can be greatly reduced. The degree of reduction varies depending on the film length, thickness, etc. of the PVA film, but can usually be reduced to about 30%. When the PVA film is cut by the dyeing process, it is necessary to stop the line and replace the PVA film, and the production efficiency and yield of the polarizing film are greatly reduced. In this respect, according to the present production method, the cutting frequency of the PVA film can be reduced, and it can be carried out by slitting both ends of the PVA film before dyeing before stretching, and it is not necessary to perform heat treatment in advance. Since the drying furnace is larger in scale than the slitter, it can be said that this manufacturing method is easy to adopt. The PVA film slit at both ends is once wound up by the winding unit 4. Thereby, it is possible to make a PVA film into a roll shape once, and to move it, and to perform dyeing | staining and bridge | crosslinking by boric acid from subsequent unwinding with another apparatus.

  As described above, both ends of the stretched PVA film are thicker than the center. When the slit width is relatively small, for example, when it is 2%, the thickness difference between the center and both ends of the PVA film can be reduced and cutting can be reduced by the dyeing process. The difference can remain. When such a PVA film is wound up, both ends of the PVA roll are much thicker (so-called ear height) than the center, which may cause deformation at both ends. Therefore, in order to avoid the state of the ear height, a winding method in which the core of the PVA film is installed on the winding shaft of the winding unit 4 and moved in the width direction of the PVA film may be employed (hereinafter, the winding is concerned). This method is called “oscillate”).

  The oscillate rolls the PVA film while reciprocating the winding part parallel to the width direction of the PVA film using a winding part that winds the PVA film by rotating the winding shaft. It is a method of winding in a shape. In other words, a method of winding the PVA film in a roll shape while reciprocating the winding shaft along the axial direction using a winding portion that winds the PVA film by rotating the winding shaft. It can also be said.

  In oscillating, the position of the PVA film with respect to the winding shaft changes during winding. Thereby, since both ends of the PVA film are wound up while moving relative to the winding shaft, even if the PVA film is in a roll shape, it is difficult to be in a high-pitched state. In addition, after moving the winding part in one direction parallel to the width direction of the PVA film, the movement of the winding shaft in the width direction of the PVA film may be stopped. In that case, after stopping for a fixed time, a winding part is moved to the other direction parallel to the width direction of the said PVA film.

  A specific example of the oscillate will be described with reference to FIG. FIG. 2 is a graph showing the winding height (h) when winding the PVA film and the position (L1) of one film end. The position (L1) of one film end corresponds to the amount of movement of the winding shaft positioned in parallel with the width direction of the PVA film. That is, if the winding shaft does not move in parallel with the width direction of the PVA film, the position of one film end is 0 (initial position), and the winding shaft is one of the width directions of the PVA film. The film edge also moves in that direction. In FIG. 2, when the winding shaft moves in one direction parallel to the width direction of the PVA film, the amount of movement is shown as a positive value. And when a winding axis | shaft moves to the other direction parallel to the width direction of a PVA film, the movement amount is shown with the negative value.

  In the oscillate shown in FIG. 2, during winding of the PVA film, (1) the winding shaft is moved in one direction parallel to the width direction of the PVA film (moving width L1 is increased). (2) Next, the movement of the winding shaft in a direction parallel to the width direction of the PVA film is stopped, and the end of the film is not moved in the parallel direction, and the roll thickness (direction switching film thickness L2 ). Thereafter, (3) the winding shaft is moved in another direction parallel to the width direction of the PVA film, and (4) the movement of the winding shaft in the parallel direction is stopped. The end of one film does not move in the width direction of the PVA film, the roll thickness (direction switching film thickness L2) increases, and thereafter (1) to (4) are repeated. The moving width and the direction switching film thickness L2 can be changed as appropriate, and the moving pitch is changed according to the diameter of the core of the PVA film.

  As an example, when the diameter of the core of the PVA film is 2410 mm, the movement width in the width direction of the PVA film from the initial position (movement width L1 is “0”) is set to 20 mm. In addition, the direction switching film thickness in which the PVA film is conveyed when the winding shaft is stopped is set to 0.3 mm, and the movement pitch L3 from the start of (3) to the end of (4) to (1) is set to 80 mm. doing. In this case, the distance that the take-up shaft reciprocates is 40 mm.

  In the above case, by setting the moving width L1 to 20 mm, it is possible to reduce the end portion from becoming thicker than the central portion of the film. On the other hand, when the movement width L1 is less than 20 mm, the ear height tends to occur. Moreover, by setting the direction switching film thickness L2 to 0.3 mm, the film thickness at the film end when turning back the direction of the take-up shaft is thin, and winding deviation at the film end can be reduced. On the other hand, when the direction switching film thickness L2 is less than 0.3 mm, winding deviation tends to occur at the end of the film when the moving direction of the winding shaft is turned back. The movement pitch L3 is set to 80 mm, and it is possible to reduce the edge of the film from becoming an ear height like the movement width L1. On the other hand, when the movement pitch L3 is less than 80 mm, the ear height is likely to occur.

  FIG. 3 is a view showing a roll wound up by the oscillating method shown in FIG. As shown in the figure, in the PVA roll 4a wound by the oscillating method, the end portion of the PVA film is wound so as to form irregularities. Thereby, compared with the case where the winding axis | shaft 4b is not moved, it can avoid that the edge part of a thick PVA film overlaps, and it is avoided that a PVA roll becomes an ear height, PVA. Deformation or the like hardly occurs at both ends of the roll 4a.

  Next, the steps from the step of dyeing the PVA film to the step of drying will be described with reference to FIG. FIG. 4 is a cross-sectional view showing the dyeing / drying device 20. The dyeing / drying device 20 includes an unwinding part 11, a swelling tank 12, a dyeing tank 13, a boric acid tank 14, a washing tank 15, a drying furnace 16, and an unwinding part. 11a and 11b, a drying furnace 16 and a winding unit 17 are provided.

  The unwinding unit 11 and the winding unit 17 are for unwinding and winding the film as described with reference to FIG. 1. The unwinding unit 11 is provided with a PVA film slit by the processing apparatus 10. In the part 17, the PVA film is dyed and dried, and the polarizing film bonded with the TAC (triacetyl cellulose) film is wound up.

The dyeing and drying apparatus 20 has a structure in which the PVA film sequentially passes from the swelling tank 12 to the drying furnace 16. In the swelling tank 12, the PVA film is swollen, in the dyeing tank 13, the PVA film is dyed, and the PVA film dyed in the dyeing tank 13 is subjected to boric acid treatment in the boric acid tank 14 to be polarized. Become a film. Polarizing film was washed with water aqueous boric acid solution adhered to the surface of the polarizing film at washing tank 15, it is dried in a drying oven 16. In the dyeing and drying apparatus 20, the swelling tank 12, the dyeing tank 13, the boric acid tank 14, and the water washing tank 15 are provided one by one, but in consideration of the length of the PVA film, the conveying speed of the PVA film, and the like. A tank may be provided.

  In the swelling treatment in the swelling tank 12, foreign matters such as dust and plasticizer attached to the surface of the PVA film are removed. For this reason, as the treatment liquid in the swelling tank 12, pure water; an aqueous solution of a water-soluble organic solvent, alcohols or the like is used. Among these, it is preferable to use pure water from the viewpoint that the waste liquid treatment is not complicated and the waste liquid cost is reduced.

In dyeing with dyeing tank 13 for dyeing PVA film with iodine is a dichroic dye. The dyeing process is performed under the condition that iodine is adsorbed on the PVA film, and it is required that the PVA film does not undergo extreme dissolution or devitrification. The dyeing solution stored in the dyeing tank 13 is 0.01 parts by weight or more and 0.2 parts by weight or less of iodine and 0.1 parts by weight or more and 10 parts by weight of potassium iodide with respect to 100 parts by weight of water. The aqueous solution containing the following is mentioned. The temperature of the staining liquid can be, for example, 10 ° C. or more and 50 ° C. or less, and preferably 20 ° C. or more and 40 ° C. or less. Moreover, the immersion time of a PVA film can be 10 seconds or more and 600 seconds or less, More preferably, it can be 30 seconds or more and 200 seconds or less.

In borate tank 14, by immersing the PVA film was dyed at dyeing tank 13 at an aqueous boric acid solution, a boric acid treatment Ru subjected. Thereby, a polarizing film is manufactured from a PVA film. As an aqueous boric acid solution, 2 parts by weight or more and 10 parts by weight or less, preferably 3 parts by weight or more and 5 parts by weight or less boric acid, and 10 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of water, Preferably, those containing 11 parts by weight or more and 20 parts by weight or less of potassium iodide can be used.

When boric acid in boric acid aqueous solution is less than 2 parts by weight with respect to 100 parts by weight of water, sufficient water resistance and moist heat resistance due to boric acid crosslinking cannot be obtained. Is not preferable because boric acid crystals are deposited on the film, resulting in poor appearance. Moreover, when the potassium iodide in boric acid aqueous solution is less than 10 weight part with respect to 100 weight part of water, the transmittance | permeability characteristic of a polarizing film cannot be made excellent. On the other hand, when it exceeds 30 parts by weight, the appearance reaction may be caused by the cross-linking reaction with boric acid being hindered or the crystals being deposited on the PVA film.

  In order to suitably perform the boric acid treatment, the temperature of the boric acid aqueous solution can be usually 50 ° C. or more and 70 ° C. or less, preferably 53 ° C. or more and 65 ° C. or less, and the treatment time is usually 10 seconds or more and 600 ° C. The time can be set to 2 seconds or less, preferably 20 seconds or more and 300 seconds or less, more preferably 20 seconds or more and 100 seconds or less.

  In addition to the boric acid and potassium iodide, at least one component selected from zinc iodide, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfite, potassium sulfate, sodium sulfate, etc. An aqueous boric acid solution may be used.

  In the water washing process in the water washing tank 15, the boric acid aqueous solution adhering to the surface of the polarizing film is washed with water. Examples of the water washing treatment include a method of immersing the polarizing film, a method of jetting water into the shower film, and the like. The water temperature can usually be 2 ° C. or higher and 15 ° C. or lower.

In the drying process in the drying furnace 16, water adhering to the polarizing film is removed. Usually, a polarizing film is conveyed in the drying furnace 16 maintained at 40 ° C. or more and 90 ° C. or less for 30 seconds or more and 600 seconds or less. Thereby, the post-treatment after crosslinking with boric acid is completed. If the polarizing film is wound up at this stage, a polarizing film is obtained. However, the dyeing and drying apparatus 20 has a configuration in which TAC is bonded to the polarizing film, and a polarizing plate can be obtained.

  A TAC film roll is installed in the unwinding portions 11a and 11b, and the TAC film is unwound. Although not shown, an adhesive is applied to the polarizing film conveyed from the drying furnace 16, and TAC films are bonded to both the front and back surfaces (bonding process). As the TAC film, a film having a thickness of 30 μm or more and 200 μm or less is usually used. As the adhesive used, an optically isotropic adhesive is preferably used, and examples thereof include a polyvinyl alcohol-based adhesive. The polarizing plate in which the TAC film is bonded to both sides of the PVA film is further dried at 30 ° C. or higher and 100 ° C. or lower in the drying furnace 16. Thereby, a polarizing plate is manufactured from a polarizing film and a TAC film.

  Finally, after the polarizing plate is bonded to the protective film unwound from the unwinding portions 11a and 11b, the polarizing plate is wound by the winding portion 17. Although not shown in the drawing, the polarizing plate obtained by the dyeing and drying apparatus 20 is subjected to another process, for example, a bonding process with a substrate, and is commercialized as a liquid crystal display device. In the dyeing and drying apparatus 20, the PVA film that has been wound and stretched by the processing apparatus 10 and then wound is used as a raw material. However, the winding in the processing apparatus 10 may be simplified. Absent. In this case, the winding unit 4 from the processing device 10 and the unwinding unit 11 from the dyeing and drying device 20 are removed from the line, and the lines of the processing device 10 and the dyeing and drying device 20 are continuously constructed.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Such embodiments are also included in the technical scope of the present invention.

  Moreover, this invention can include the following aspects.

Stretch the long polyvinyl alcohol film in the direction of transport of the film,
In the production of the polarizing film stretched polyvinyl alcohol film was stained by the dichroic dye to produce a polarizing film was treated with an aqueous boric acid solution,
A method for producing a polarizing film, comprising: slitting both ends of a stretched polyvinyl alcohol film after stretching the polyvinyl alcohol film and before dyeing the stretched polyvinyl alcohol film.

  The present invention will be described more specifically based on Examples and Comparative Examples and FIG. 5, but the present invention is not limited to this. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. The thickness of the PVA film was measured with a Sony Digital Micrometer M-30 measuring device.

[Example 1]
A polarizing film was produced using the processing apparatus 10 of FIG. 1 and the dyeing and drying apparatus of FIG. As the PVA film, a PVA film (VF-PS, Kuraray Co., Ltd.) having an original length of 3400 M and an original width of 2400 mm was used. First, a PVA film was installed from the unwinding unit 1 to the winding unit 4 via the transport roll 5. In addition, in order to suppress the loss of a PVA film, the lead film is connected with the winding part 4 side of the PVA film. Then, the PVA film was unwound from the unwinding part 1, and the PVA film was stretched 4.2 times using a hot roll 2 having a surface temperature of 122 ° C. Furthermore, using slitter 3, each edge part was slit 5% at a time (120 mm each (total 240 mm)) with respect to the full width of the stretched PVA film. The PVA film was wound up by a normal method without moving the winding shaft of the winding unit 4 in the width direction of the PVA film. The thickness of the PVA film was measured at a position of 500 M from the portion where the slit was started. The measurement results are shown in FIG. FIG. 5 is a graph showing the thickness of the polyvinyl alcohol film in Example 1 and Comparative Example 1.

  As shown in FIG. 5, the thickness of the PVA film in Example 1 is 17 μm or more and 19 μm or less, and it is understood that the thickness distribution of the stretched PVA film is kept small.

  Next, the lead film and the PVA film after slitting were installed from the unwinding unit 11 to the winding unit 17 of the dyeing and drying apparatus 20 via the transport roll 5. The swelling tank 12 and the washing tank 15 contain pure water for washing, and the dyeing tank 13 is an aqueous solution in which 0.06 parts by weight of iodine and 6 parts by weight of potassium iodide are mixed with 100 parts by weight of pure water. Is housed. The boric acid tank 14 contains an aqueous solution in which 8 parts by weight of boric acid is mixed with 100 parts by weight of pure water. The solution temperatures of the swelling tank 12, the dyeing tank 13, the boric acid tank 14, and the water washing tank 15 are 60 ° C., 28 ° C., 72 ° C., and 13 ° C. The immersion time of the PVA film in each bath is 10 seconds, 60 Seconds, 300 seconds, and 10 seconds. The drying temperature of the drying furnace 16 was set to 90 ° C. Under the above conditions, the PVA film was subjected to swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment to obtain a polarizing film.

  Similarly, when the dyeing process of the PVA film by the processing apparatus 10 and the dyeing and drying apparatus 20 is repeated five times, the cutting frequency of the PVA film in the dyeing process is 1/5 times, and the cutting frequency is greatly reduced. I was able to.

[Example 2]
A polarizing film was produced in the same manner as in Example 1 except that the winding of the PVA film by the winding unit 4 was performed using oscillate. The oscillating condition was that the core diameter of the PVA film was 2410 mm, the moving width L1 was 20 mm, the direction switching film thickness L2 was 0.3 mm, and the moving pitch L3 was 80 mm.

  Similarly to Example 1, when the production of the polarizing film was repeated three times, the cutting frequency of the PVA film in the dyeing treatment was 1/3 times, and the cutting frequency could be greatly reduced.

[Comparative Example 1]
A polarizing film was produced in the same manner as in Example 2 except that slitting was not performed. In the manufacturing process, the thickness of the PVA film taken up by the take-up unit 4 was measured at a position of 500 M from the portion where the slit of the PVA film was started. The measurement results are shown in FIG. As shown in FIG. 5, the thickness of the PVA film in Comparative Example 1 is 17 μm or more and 19 μm or less at the center, but both ends are 23 μm at the maximum, and the PVA film after stretching has a thickness of It can be seen that the distribution is large.

  As in Example 2, when the production of the polarizing film was repeated three times, the cutting frequency of the PVA film in the dyeing process was 2/3 times, which resulted in frequent cutting.

  From the results of Examples 1 and 2 and Comparative Example 1, it was revealed that the film cutting during the dyeing process could be suppressed by slitting both ends of the stretched PVA film and removing the thick portions after stretching. It was. From this result, it was confirmed that both ends of the film after stretching were the starting points for cutting. According to the method of this example, the cutting frequency of the PVA film can be greatly reduced, so that the production efficiency and yield of the polarizing film can be improved.

  According to the method for producing a polarizing film according to the present invention, the frequency of cutting the polyvinyl alcohol film can be reduced at the dyeing stage, and therefore, this production method can be used in the field of producing a polarizing film.

DESCRIPTION OF SYMBOLS 1 Unwinding part 2 Heat roll 3 Slitter 4 Winding part 4a PVA roll 4b Winding axis | shaft 5 Conveyance roll 10 Processing apparatus 11 Unwinding part 12 Swelling tank 13 Dyeing tank 14 Boric acid tank 15 Washing tank 16 Drying furnace 17 Winding part 20 Dyeing and drying equipment

Claims (5)

Stretch the long polyvinyl alcohol film in the direction of transport of the film,
The stretched polyvinyl alcohol film was stained by the dichroic dye, the method for producing a polarizing film to produce a polarizing film was treated with an aqueous boric acid solution,
After stretching the polyvinyl alcohol film, both ends of the stretched polyvinyl alcohol film are slit, and then the polyvinyl alcohol film is not stretched again before dyeing with the dichroic dye. A method for producing a polarizing film.   After slitting both ends of the stretched polyvinyl alcohol film, the distribution of the thickness is smaller than that of the polyvinyl alcohol film after being stretched and before slitting. The method for producing a polarizing film according to claim 1, wherein the system film is dyed.   The slit width of each edge part of a polyvinyl alcohol-type film is 2% or more and 10% or less with respect to the whole width of a polyvinyl alcohol-type film, The manufacture of the polarizing film of Claim 1 or 2 characterized by the above-mentioned. Method. The polyvinyl alcohol film was wound into a roll prior to staining by dichroic dye, comprising the step of unwinding a rolled polyvinyl alcohol film,
The polarizing film production according to any one of claims 1 to 3, wherein both ends of the polyvinyl alcohol film along the transport direction are slit before the polyvinyl alcohol film is wound into a roll. Method. The polyvinyl alcohol film is used while rewinding the winding part parallel to the width direction of the polyvinyl alcohol film using a winding part that winds the polyvinyl alcohol film by rotating the winding shaft. The method for producing a polarizing film according to claim 4, wherein the film is wound into a roll shape.