JP5982096B2 - Manufacturing method of polarizing film - Google Patents

Description

  The present invention relates to a method for producing a polarizing film in which a strip-like polyvinyl alcohol-based resin film is moved and stretched in the longitudinal direction in the moving path to produce a polarizing film.

Conventionally, an optical film including a polarizing film or the like is used in an image display device such as a liquid crystal display device.
As a method for producing this type of polarizing film, a polyvinyl alcohol-based resin film (raw film) is fed out from a raw roll obtained by winding a belt-shaped polyvinyl alcohol-based resin (PVA) film as a roll into a roll. The film is stretched through an apparatus provided with a plurality of rollers for guiding the original film and various chemical baths while regulating the movement path of the original film, for example, the original film The film is moved in the longitudinal direction and continuously immersed in a swelling bath or dyeing bath, and then the original film is nipped with the roller at two locations in the front and rear, and the stretching is performed by applying tension between them. Have been.

By the way, in this type of polarizing film manufacturing method, it is very complicated and wastes time to wrap a new original film around a roller or the like every time the original film roll is replaced. As a result, the two original films, in which the leading edge of the original film fed from the next original film roll is joined and connected to the end of the preceding original film, are successively converted into a polarizing film. It is made to be processed.
As this type of joining means, conventionally, an adhesive joining means such as an adhesive tape or an adhesive, a suture joining means such as a rivet or a thread, or a heating and melting joining means such as a heat sealer has been employed.

However, each of the methods described above has the following problems.
・ Problems in adhesive bonding with adhesive tapes and adhesives In the process of immersing the raw film in a swelling bath or dyeing bath, the components of the adhesive dissolve into the chemical solution, contaminating the chemical solution, In addition to being a cause of foreign matter adhesion, the bonding strength is reduced by the adhesive being dissolved in the chemical or swollen by the components of the chemical, and the connecting portion is broken before reaching the desired draw ratio in the drawing process. There is a risk of causing it.
・ Problems in stitching with rivets and threads, etc. In this method, holes for passing rivets and threads are made in the original fabric film, so when the tension is applied to the connecting part, There is a risk of causing breakage.
In order to prevent this, if the number of holes is reduced to ensure a wide gap between the holes, when tension is applied, wrinkles are likely to occur and there is a risk of causing uneven drawing.
・ Problems in heat-melt bonding with heat sealers, etc. As bonding means that can solve the problems in adhesive bonding and suture bonding as described above, there are means for bonding with heat sealers as shown in Patent Documents 1 and 2 below. Are known.
In this method, there is a low risk of contaminating the drug solution as compared with adhesive bonding, and there is no need to provide a hole as in suture bonding.
However, in the heat sealer, the welded region and the periphery thereof tend to be denatured by the heat received during welding and become hardened compared to the normal part.
Therefore, if tension is applied across this welded region during stretching, stress is likely to be concentrated at the boundary between the cured portion and the normal portion, and the region before the whole reaches the desired stretch ratio. May be extremely stretched.
Therefore, if stretching is performed at a high stretching ratio, there is a possibility that the raw film is broken at the connecting portion.

JP 2007-171897 A JP 2010-8509 A

In order to impart a high polarizing function to the polarizing film, it is generally required to add a stretch of 5.25 times or more. However, the conventional connecting method as described above for a raw film made of a polyvinyl alcohol resin is used. When connecting with, the connecting part cannot withstand a stretching load of 5.25 times or more and may break, so the stretching ratio while the connecting part passes should be changed to less than 5.25 times. Measures are taken to avoid breakage.
However, when the above-mentioned avoidance measures are selected, the stretch ratio before and after the connecting portion is not the desired ratio (5.25 times or more), so it cannot be used as a product, resulting in material loss. Will be generated.

In this way, it is difficult to continuously convey the raw film made of the connected polyvinyl alcohol-based resin, while stretching the raw film at a stretch ratio of 5.25 times or more, Moreover, the connection method which enables this extending | stretching and conveyance was not proposed until now.
That is, the conventional polarizing film manufacturing method has a problem that it is difficult to efficiently manufacture a polarizing film having a high polarizing function.

  An object of this invention is to provide the manufacturing method of the polarizing film which can manufacture efficiently the polarizing film which has a high polarization function in view of the said problem.

The manufacturing method of the polarizing film according to the present invention for solving the above problems includes a first step of feeding a belt-like polyvinyl alcohol-based resin film from the distal end side to the moving path and stretching in the longitudinal direction in the moving path; ,
A second step of joining and connecting the rear end side of the preceding first polyvinyl alcohol-based resin film and the front end side of the next second polyvinyl alcohol-based resin film;
A polarizing film manufacturing method for continuously manufacturing a polarizing film,
In the second step, the rear end side and the front end side are joined in an overlapped state, and the extension amount of the joint portion at the time of stretching at a stretch ratio of 4.2 times in the moving path is a non-joined portion. It connects so that it may become 30% or more with respect to the elongation amount of.

  Here, in the present invention, the amount of elongation of the joined portion and the non-joined portion means the amount of elongation per unit length when unstretched. Thus, the end of the preceding first band-like polyvinyl alcohol-based resin film of the two or more band-shaped polyvinyl alcohol-based films to be stretched, and the second band-shaped polyvinyl alcohol-based resin film connected thereto When the joint portion with the tip portion is stretched at a stretch ratio of 4.2 times, the elongation amount of the joint portion can be brought close to the elongation amount of the non-joint portion. Therefore, when the stretching is applied, the concentration of stress at the boundary portion between the bonded portion and the non-bonded portion can be reduced as compared with the case where heat sealing is performed. Therefore, for example, even when stretched at a stretch ratio of 5.25 times or more, it is possible to avoid the occurrence of breakage at the joint, and even when the joint passes, continuously without changing the stretching conditions. Stretch can be added. Therefore, the working efficiency, productivity, yield, and material loss can be reduced.

  Moreover, it is preferable to implement the manufacturing method of the polarizing film which concerns on this invention by connecting the said 2nd process by joining the said terminal part and the said front-end | tip part by laser welding.

Thereby, since the said terminal part and the said front-end | tip part are joined by laser welding, a chemical | medical solution will be contaminated compared with the case where it adheres by use of an adhesive agent etc., or joint strength will be reduced by this chemical | medical solution. The fear can be suppressed.
In addition, when the end portion and the tip portion are heated in the thickness direction as in heat sealing or the like, the joined portion which is a welded portion is difficult to be cooled, and the crystallinity of the joined portion is hardly lowered. In addition, since the periphery of the joint is continuously heated at a temperature lower than the melting point of the polyvinyl alcohol-based resin film, the region where the crystallinity is high and hardens around the joint is relatively large. On the other hand, in laser welding, since it is possible to locally heat and weld only the region in the vicinity of the interface between the end portion and the tip portion, the welded portion is rapidly cooled to The crystallinity of the joint can be lowered, and the region that is heated and cured at a temperature lower than the melting point around the joint can be made relatively small. This makes it possible to suppress the breakage of the film even when the film is stretched at a higher draw ratio when the stretch is applied than when the joint is formed by laser welding than when the joint is formed by heat sealing or the like. It becomes. Thereby, the junction part by laser welding can be extended without a fracture | rupture rather than the junction part by heat sealing etc. FIG.
In this way, it is possible to achieve a connection such that the elongation amount of the joint portion is 30% or more with respect to the elongation amount of the non-joint portion. Connections that do not occur are possible. Therefore, for example, even when the joint portion passes, the stretching can be continuously applied without changing the stretching conditions. As a result, it is possible to more reliably improve the working efficiency, improve the productivity, improve the yield, and reduce the material loss.
In addition, there is no conventional example about connecting the polyvinyl alcohol-type resin film used for a polarizing film by a laser in this way, This is achieved for the first time by this invention.

  Moreover, it is preferable that the manufacturing method of the polarizing film which concerns on this invention distributes a light absorber to the interface part of the said terminal part and the said front-end | tip part, and implements the said laser welding.

  Thereby, since the light absorptivity of the laser beam in the interface part of a front-end | tip part and a terminal part increases, both can be welded more efficiently.

  Moreover, it is preferable that the manufacturing method of the polarizing film which concerns on this invention implements the said laser welding with an infrared laser with a wavelength of 800 nm or more and 11000 nm or less.

  Thereby, since the said terminal part and front-end | tip part can be fuse | melted more efficiently, the 1st and 2nd polyvinyl alcohol-type resin film can be joined and connected more efficiently.

  Moreover, as for the manufacturing method of the polarizing film which concerns on this invention, the draw ratio of each non-joining part and joining part of said 1st polyvinyl alcohol-type resin film and said 2nd polyvinyl alcohol-type resin film is 5 respectively. It is preferably 25 times or more.

  Thereby, it becomes possible to improve the quality as a polarizing film.

  As described above, according to the present invention, it is possible to efficiently manufacture a polarizing film having a high polarization function.

The schematic perspective view which showed the apparatus used for the manufacturing method of the polarizing film of one Embodiment The schematic perspective view which showed a mode that a raw film was connected and supplied to the manufacturing apparatus of a polarizing film The schematic front view which showed the mechanism of the principal part of the connection apparatus for connecting a raw film The graph which shows the ratio of the amount of elongation in Example 1 and Comparative Example 1

Embodiments of the present invention will be described below.
First, the preferable extending | stretching apparatus for enforcing the manufacturing method of the polarizing film of this embodiment is demonstrated, referring drawings.
The stretching apparatus according to the present embodiment is configured such that the original film 1 is formed from an original roll in which a belt-like polyvinyl alcohol-based resin film (hereinafter also referred to as “original film” or simply “film”) is wound in a roll shape. The raw film supply unit 3 to be fed out, a plurality of immersion baths 4 for immersing the fed raw film 1 in a predetermined chemical solution, and the original film 1 to pass through the immersion bath 4 A plurality of rollers 9 for restricting the movement path of the anti-film 1, a stretching means for stretching the original film 1 in the movement path, and a roll immersed in the plurality of immersion baths 4 and stretched as a polarizing film And a polarizing film winder 10 that winds up into a shape.

1 and 2 are schematic perspective views showing one embodiment of a preferred stretching apparatus.
As shown in FIG. 1, as a plurality of immersion baths 4, a swelling bath 4 a storing a swelling solution for swelling a polyvinyl alcohol-based resin film in order from the upstream side in the film flow direction, and a staining solution for dyeing the swollen film Stored dye bath 4b, cross-linking bath 4c storing a cross-linking agent solution for cross-linking the molecular chains of the resin constituting the film, stretching bath 4d for stretching the film in the bath, and the stretching bath The stretching apparatus is provided with five types of immersion baths 4 called cleaning baths 4e in which a cleaning solution for cleaning the film passed through 4d is stored.

Further, the stretching device of this aspect includes a drying device 11 for drying the cleaning liquid adhering to the film on the downstream side of the cleaning bath 4e and the upstream side of the winding unit 10 in the film movement path, specifically, a drying oven. Is provided.
Furthermore, in the stretching apparatus of this embodiment, a film 12 for lamination such as a surface protective film (for example, a triacetyl cellulose film or a cycloolefin polymer film) wound in a roll shape is dried by the drying apparatus 11. A laminating device is provided for laminating the laminating film 12 on both sides of the dried film.

  As the stretching means, so-called roll stretching means 9a is employed. That is, in the movement path, a plurality of pairs of nip rollers 9a configured to sandwich the film between them and send them out downstream in the flow direction are arranged, and the peripheral speed of the downstream set in the flow direction is the upstream side. A configuration with a higher speed is employed.

Further, the stretching apparatus is configured to continuously stretch two or more original film, and the end of the first original film among the two or more original films, A device for connecting the original film is provided. That is, as shown in FIG. 2, before the end portion 1 a of the preceding first raw film 1 is passed through the regulated movement path, the stretching apparatus is specifically placed in the immersion bath 4. Before passing, the end part 1a of the first original film 1 and the front end part 1b of a new original film (second original film) that passes through the movement path next to the original film 1 A connecting device (not shown in FIG. 2) for connecting and connecting by laser welding is provided.
In FIG. 2, a portion (welded portion) joined by laser irradiation is indicated by a black coating portion 30.

Next, a preferred coupling device will be described with reference to FIG.
FIG. 3 is a schematic configuration diagram showing a connecting device that joins and connects raw films by laser welding.
FIG. 3 shows a front view of the connecting device in which the raw film to be connected is viewed from the side surface in the TD direction (width direction).
As shown in FIG. 3, the coupling device includes a stage 40 having a flat upper surface portion, a pressurizing member 50 disposed above the stage 40 and movably disposed in the vertical direction, and the pressurizing unit. A laser source (not shown) disposed above the member 50, and a terminal portion 1a of the preceding first original film 1 and a new second original film 1 connected thereto. The top end portion 1b is superposed vertically on the stage 40, and the laser light R is irradiated from the laser light source while pressurizing the superposed portion with the pressurizing member 50. The interface portion with the tip portion 1b can be heated and melted to be welded, and the pressurizing member 50 is made of a transparent member having excellent laser light R transparency.

  In addition, the coupling device is configured to perform the surface contact at the interface portion so that the light absorption of the laser light R at the interface portion between the end portion 1a and the tip portion 1b is increased and welding can be performed more efficiently. It is also possible to provide a coating device for previously applying a light absorbent to the surface (or both surfaces) of either the end portion 1a or the tip portion 1b.

The light absorber used here is not particularly limited as long as it absorbs the laser beam R and generates heat, and carbon black, pigments, dyes, and the like can be used.
For example, a phthalocyanine absorbent, a naphthalocyanine absorbent, a polymethine absorbent, a diphenylmethane absorbent, a triphenylmethane absorbent, a quinone absorbent, an azo absorbent, a diimmonium salt, or the like can be used.
Moreover, when using the laser light source which emits the laser beam R which has a wavelength of 800 nm-1200 nm, a commercial light absorber can be used as a trade name "Clearweld" from the US Gentex company, for example.

  These absorbents can be diluted with an organic solvent or the like and applied by the coating apparatus. Examples of the coating apparatus include a dispenser, an inkjet printer, a screen printer, a two-fluid type, a one-fluid type, or an ultrasonic wave. A general coating apparatus such as a spray, a stamper, or a coater can be employed.

  In addition, the type of laser light source used in the coupling device is not particularly limited, but the laser light to be used may be one or both of the originals at the interface of the old and new original film at the part where the old and new original films are overlapped. It is preferably absorbed by a light absorbent disposed on the surface of the anti-film and plays a role of generating heat, and preferably has a wavelength with high absorption sensitivity of the light absorbent used.

Specifically, the types of laser light include semiconductor lasers having wavelengths in the visible or infrared range, fiber lasers, femtosecond lasers, picosecond lasers, solid lasers such as YAG lasers, and gas lasers such as CO ₂ lasers. Is mentioned.
Among these, a semiconductor laser and a fiber laser that can easily obtain a laser beam that is inexpensive and uniform in the plane are preferable.
For the purpose of accelerating melting while avoiding decomposition of the raw film, a continuous wave CW laser is preferable to a pulsed laser in which high energy is instantaneously input.
The output (power) of the laser beam, the beam size and shape, the number of irradiations, the scanning speed, etc. are the optical properties such as the target film and the light absorptivity of the light absorber and the polymer constituting the film Although it may be optimized as appropriate for differences in thermal characteristics such as melting point and glass transition point (Tg), a polyvinyl alcohol resin is efficiently fluidized in a portion irradiated with a laser to obtain a strong bond. for it, the power density of the irradiated laser light, in the range of 200W / cm ² ~10,000W / cm ² is preferably in the range of 300W / cm ² ~5,000W / cm ² but more preferably, it is particularly preferably in the range of ^{1,000W / cm 2 ~3,000W / cm 2} .

  Further, such laser irradiation conditions are not particularly limited as long as the ratio of elongation described later can be set to 30% or more. Further, in order to lower the crystallinity of the joint, laser joining can be performed while cooling the surface of the joint.

The laser light source used in the coupling device is preferably one that can irradiate laser light with a spot diameter (irradiation width) of a predetermined size at the interface between the old and new original film.
The irradiation spot diameter (irradiation width) is preferably 1/10 or more and 3 times or less of the overlap width of the old and new original film at a power satisfying the irradiation laser power density.
If it is less than 1/10 of the overlapping width, the unjoined portion of the overlapping portion is large, and it may flutter when transported after joining, possibly hindering good transportability.
In addition, irradiation with a laser having a width of 3 times or more does not affect the bonding and stretching characteristics, but is not preferable from the viewpoint of energy utilization efficiency.
Preferably, it is 1/5 or more and 2 times or less of the overlap width.
The overlapping width of the old and new original film is preferably 0.1 mm or more and less than 50 mm, and more preferably 0.5 mm or more and less than 30 mm.
This is because when the overlap width is less than 0.1 mm, it is difficult to overlap and dispose a wide original film with high repeatability. When the overlap width is 50 mm or more, the unbonded area becomes large and is transported after bonding. This is because the film may flutter.
In addition, in the overlapped part of the old and new original film, good transportability of the film is ensured that a sufficient area of the leading edge of each original film is joined so that the two leading parts do not flutter during conveyance. Is preferable in realizing the above. In view of such a viewpoint, the width of the unbonded portion in the overlapping portion of the old and new original film is preferably 5 mm or less, more preferably 2 mm or less, and 0 mm (the entire surface of the overlapping portion is bonded). More preferably).

As the integrated irradiation dose of the laser beam is preferably in a range of ^{5J / cm 2 ~400J / cm 2} , more preferably in the range of ^{10J / cm 2 ~300J / cm 2} , 30J / Particularly preferably, it is within the range of cm ^{2 to} 150 J / cm ² .
Therefore, it is preferable to employ a laser light source that can satisfy these conditions in the coupling device.

As the pressurizing member 50 that pressurizes the old and new original films (the end part 1a of the old original film and the front end part 1b of the new original film), which are superposed in such laser light irradiation, on the stage, the laser light used A glass member exhibiting high transparency can be used.
As the vulcanizing pressure strength that during the irradiation of the laser beam is preferably in a range of 0.5~100kgf / cm ^2, and more preferably in the range of 10~70kgf / cm ^2.
Therefore, as the pressurizing member 50 preferably employed in the coupling device, the shape of the glass member is not particularly limited as long as it is a member that can pressurize with such strength. Can be used.
The thickness of the glass member is not particularly limited, but if it is too thin, good pressure cannot be applied due to strain, and if it is too thick, the laser beam utilization efficiency decreases, so the thickness in the direction of laser beam transmission is 3 mm or more and less than 30 mm. It is preferably 5 mm or more and less than 20 mm.

Examples of the material of the pressing member 50 include quartz glass, non-alkali glass, Tempax, Pyrex (registered trademark), Vycor, D263, OA10, AF45, and Zerodur.
In order to increase the utilization efficiency of the laser beam R, the glass member used as the pressure member 50 preferably has high transparency with respect to the laser beam wavelength used, and has a light transmittance of 50% or more. Preferably, it has a light transmittance of 70% or more.

In the case where the pressing member 50 is configured using a glass member as described above, a polyvinyl alcohol-based resin is used so that a wider area can be more uniformly pressed and good bonding can be performed over the entire area. A cushion layer having a cushioning property superior to that of the glass member can be formed on a portion in contact with the film.
That is, it is possible to employ a pressure member 50 including a rubber sheet having a good light transmittance, a transparent resin sheet having a cushioning property, and the like. For example, the back side is formed of a glass member, and a polyvinyl alcohol resin film and It is possible to employ a pressure member 50 having a transparent rubber sheet on the front side in contact therewith.

For the formation of the cushion layer, for example, a rubber material such as silicon rubber or urethane rubber or a resin material such as polyethylene can be used.
The thickness of the cushion layer is preferably 50 μm or more and less than 5 mm, more preferably 1 mm or more and less than 3 mm.
When the thickness is less than 50 μm, the cushioning property is poor, and in the case of 5 mm or more, the absorption or scattering of the laser beam is caused by the cushion layer, and the energy of the laser beam reaching the contact interface between the end portion 1a and the tip portion 1b May be reduced.
The cushion layer preferably has a light transmittance of 30% or more with respect to the laser light wavelength to be used, and more preferably 50% or more.
In addition, a cushion layer similar to the cushion layer can be disposed on the upper surface of the stage 40. When arranged on the stage, the optical properties of the material for forming the cushion layer, that is, the light transmission property is not particularly limited. In addition to the above-described silicon rubber, for example, polycarbonate, polyethylene terephthalate, norbornene, etc. Resins, cycloolefin polymers, polymethyl methacrylate, polyimide, triacetyl cellulose, and the like can also be used.

  In the manufacturing method of the polarizing film of the present embodiment, the connecting device is configured so that laser welding can be performed along the overlapped portions of the overlapped old and new original film to form a line-shaped welded portion. For example, a line is formed by using a mechanism for scanning a spot beam condensed to a desired beam size by a condensing lens along the overlapping portion, or using an optical member such as a cylindrical lens or a diffractive optical element. A mechanism to shape and irradiate the overlapping part of the original film with a shaped laser beam, and a mechanism to melt and heat and bond together by arranging multiple laser light sources along the overlapping part and simultaneously irradiating without scanning Etc. are preferably provided.

  Although not described in detail here, various mechanisms used in a general laser welding apparatus and its peripheral devices can be adopted as the above-described connecting apparatus.

  Next, a method for producing a polarizing film using a stretching device equipped with such a connecting device will be described.

In the method for producing a polarizing film of the present embodiment, a first step of feeding a strip-like polyvinyl alcohol-based resin film into the movement path from the tip side and stretching in the longitudinal direction in the movement path, and a preceding first A second step of joining and connecting the rear end side of the polyvinyl alcohol-based resin film and the front end side of the next second polyvinyl alcohol-based resin film, and continuously producing a polarizing film.
Further, in the second step, the rear end side and the front end side are joined in an overlapped state, and the amount of extension of the welded portion that is a joint portion at the time of stretching at a stretch ratio of 4.2 times in the moving path. Are connected so as to be 30% or more with respect to the amount of elongation of the welded portion which is a non-joined portion.

Specifically, in the method for producing a polarizing film of the present embodiment, as the first step, a swelling step in which the original film is immersed in the swelling bath 4a to swell, and the swollen film into the dyeing bath 4b. A dyeing process for immersing and dyeing, a crosslinking process for immersing the dyed film in the crosslinking bath 4c to crosslink the molecular chains of the resin constituting the film, and the film after the crosslinking process in the stretching bath 4d A stretching process for stretching is performed.
That is, in the manufacturing method of the polarizing film of this embodiment, extending | stretching is implemented in each bath of the swelling bath 4a to the extending | stretching bath 4d so that it may finally become a target draw ratio.
Moreover, in the manufacturing method of the polarizing film of this embodiment, the washing | cleaning process which wash | cleans the film after the said extending | stretching process, the drying process which dries this wash | cleaned film with the drying apparatus 11, The surface protection film in this dried film A laminating step for laminating is performed.

And the manufacturing method of the polarizing film of this embodiment sets one original fabric roll in the said original fabric film supply part 3, sends out an original fabric film continuously from this original fabric film supply part 3, It is made by performing a winding process in which the product (polarizing film) that has been subjected to the above-described process in the moving path and finally finished the laminating process is wound in a roll shape in the polarizing film winding unit 10. Before the first roll of the first roll ends, the roll of the roll is fed out from the second roll of the new roll, and the leading edge of the new roll of roll is prepared. A connecting step of joining and connecting the end portion 1b to the end portion 1a of the preceding first raw roll is separately performed as the second step.
In this way, the original film is continuously supplied from the new original roll to the stretching device, and the first step is performed to continuously produce the polarizing film. Moreover, a polarizing film can be manufactured sequentially one after another by repeatedly performing the first step and the second step.

  In addition, as a raw film (band-shaped polyvinyl alcohol-type resin film) used for such a process, the following can be employ | adopted.

As a raw film used in the method for producing a polarizing film of the present embodiment, a film made of a polyvinyl alcohol polymer resin material used as a raw material of the polarizing film can be used. Specifically, for example, a polyvinyl alcohol film A partially saponified polyvinyl alcohol film or a dehydrated film of polyvinyl alcohol can be used.
Usually, these original fabric films are used in the state of an original fabric roll wound in a roll shape as described above.
The polymerization degree of the polymer that is a material for forming the polyvinyl alcohol-based resin film is generally 500 to 10,000, preferably in the range of 1,000 to 6,000, and in the range of 1,400 to 4,000. More preferably.
Furthermore, in the case of a partially saponified polyvinyl alcohol film, the degree of saponification is preferably 75 mol% or more, more preferably 98 mol% or more, for example, from the viewpoint of solubility in water, and 98.3 to 99. More preferably, it is in the range of 8 mol%.

As the polyvinyl alcohol-based resin film, a film formed by an arbitrary method such as a casting method in which a stock solution dissolved in water or an organic solvent is cast, a casting method, an extrusion method, or the like can be appropriately used.
The retardation value of the raw film is preferably 5 nm to 100 nm.
Moreover, in order to obtain a polarizing film with uniform in-plane, it is preferable that the retardation variation in the polyvinyl alcohol-based resin film is as small as possible, and the in-plane retardation variation of the polyvinyl alcohol-based resin film as the raw film is the measurement wavelength. It is preferably 10 nm or less at 1000 nm, and more preferably 5 nm or less.

In addition, as a water absorption state when joining by laser welding, it is preferable that it is 2 mass%-15 mass%, and the water absorption of 4 mass%-10 mass% is still more preferable.
If the raw film before being connected has a water absorption of 15% by mass or more, foaming due to water evaporation tends to occur in the heat-melted part during laser welding, which may cause poor bonding.
On the other hand, when the water absorption is less than 2% by mass, the resin fluidity in the portion where the raw film is heated with a laser becomes poor, which may cause a reduction in bonding efficiency.
For this reason, it is preferable that the water absorption rate of the raw film used for bonding is in the above range.
In addition, about this water absorption, it calculates | requires by comparing the mass before and behind drying, for example, a polyvinyl alcohol-type resin film is heated at 83 degreeC * 1 hour, and the heating loss is the polyvinyl alcohol-type resin film before a heating. It can be determined by dividing by mass.

  Next, each process for adding a stretch to the above-mentioned original film with the above-mentioned stretching device and processing it into a polarizing film will be described.

(Swelling process)
In this step, for example, the original film fed from the original film supply unit 3 is guided by the roller 9 to the swelling bath 4a filled with water while keeping the moving speed constant, and the original film is submerged in water. Immerse the film.
As a result, the raw film is washed with water, and the surface of the raw film can be cleaned of stains and anti-blocking agents, and the original film can be swollen with water to prevent unevenness such as dyeing unevenness. it can.

In addition to water, glycerin, potassium iodide or the like may be appropriately added to the swelling liquid in the swelling bath 4a. When these are added, the concentration is 5% by mass if glycerin is added. Hereinafter, it is preferable to set it as 10 mass% or less in potassium iodide.
The temperature of the swelling liquid is preferably in the range of 20 to 45 ° C, more preferably 25 to 40 ° C.
The immersion time during which the original film is immersed in the swelling liquid is preferably 2 to 180 seconds, more preferably 10 to 150 seconds, and particularly preferably 30 to 120 seconds.
Further, the polyvinyl alcohol-based resin film may be stretched in the length direction in this swelling bath, and the stretching ratio at that time is preferably about 1.1 to 3.5 times including stretching due to swelling.

(Dyeing process)
The film that has undergone the swelling process is immersed in the dyeing solution stored in the dyeing bath 4b by the roller 9 as in the swelling process, and the dyeing process is performed.
For example, the method of adsorbing the dichroic substance to the film is performed by immersing the polyvinyl alcohol-based resin film that has undergone the swelling process in a dyeing solution containing a dichroic substance such as iodine. be able to.
A conventionally known substance can be used as the dichroic substance, and examples thereof include iodine and organic dyes.

Organic dyes include, for example, Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Sky Blue, Direct First Orange S, First Black, etc. can be used.
These dichroic substances may be used alone or in combination of two or more.

When using the said organic dye, it is preferable to combine 2 or more types from the point which aims at neutralization of the visible region, for example.
Specific examples include a combination of Congo Red and Splat Blue G, Splat Orange GL and Direct Sky Blue, or a combination of Direct Sky Blue and First Black.
As the dyeing solution for the dyeing bath, a solution in which the dichroic substance is dissolved in a solvent can be used.
As the solvent, water can be generally used, but an organic solvent compatible with water may be further added.
As a density | concentration of the dichroic substance in this dyeing | staining liquid, it is preferable to set it as the range of 0.010-10 mass%, It is more preferable to set it as the range of 0.020-7 mass%, 0.025-5 mass % Is particularly preferable.

Further, when iodine is used as the dichroic substance, it is preferable to further add an iodide because the dyeing efficiency can be further improved.
Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples include titanium.
The addition ratio of these iodides is preferably 0.010 to 10% by mass, and more preferably 0.10 to 5% by mass in the dyeing bath.
Among these, it is preferable to add potassium iodide, and the ratio (mass ratio) of iodine and potassium iodide is preferably in the range of 1: 5 to 1: 100, and is preferably 1: 6 to 1:80. The range is more preferable, and the range of 1: 7 to 1:70 is particularly preferable.

Although the immersion time of the film in the said dyeing bath is not specifically limited, It is preferable to set it as the range for 0.5 to 20 minutes, and the range for 1 to 10 minutes is still more preferable. Moreover, it is preferable to make the temperature of a dyeing bath into the range of 5-42 degreeC, and it is more preferable to set it as the range of 10-35 degreeC.
Further, the film may be stretched in the length direction in this dyeing bath, and the total stretch ratio accumulated at this time is preferably about 1.1 to 4.0 times.
In addition, as a dyeing | staining process, you may employ | adopt the method of apply | coating or spraying the aqueous solution containing a dichroic substance on the said polymer film other than the method of immersing in the above dyeing | staining baths, for example.
Moreover, in this invention, you may employ | adopt the film formed into a film from the polymer raw material with which the dichroic substance was mixed beforehand as a raw film used without performing a dyeing | staining process.

(Crosslinking process)
Next, the film is introduced into the crosslinking bath 4c for storing the crosslinking agent solution, and the film is immersed in the crosslinking agent solution to carry out the crosslinking step.
A conventionally known substance can be used as the crosslinking agent.
For example, boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde can be used.
These may be used alone or in combination of two or more.
When two or more types are used in combination, for example, a combination of boric acid and borax is preferable, and the addition ratio (molar ratio) is preferably in the range of 4: 6 to 9: 1. : It is more preferable to set it as the range of 4.5-7: 3, and it is most preferable to set it as 6: 4.
As the crosslinking agent solution for the crosslinking bath, a solution obtained by dissolving the crosslinking agent in a solvent can be used.
For example, water can be used as the solvent, but an organic solvent compatible with water may be used in combination. Although the density | concentration of the crosslinking agent in the said crosslinking agent liquid is not specifically limited, It is preferable to set it as the range of 1-10 mass%, and it is more preferable to set it as 2-6 mass%.

An iodide may be added to the cross-linking agent solution in the cross-linking bath in order to impart in-plane uniform characteristics to the polarizing film.
Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples thereof include titanium, and the content of iodide in the case of adding these is preferably 0.05 to 15% by mass, and more preferably 0.5 to 8% by mass.
As a combination of the crosslinking agent and iodide, a combination of boric acid and potassium iodide is preferable, and a ratio (mass ratio) of boric acid and potassium iodide is in a range of 1: 0.1 to 1: 3.5. Preferably, it is more preferable to set it in the range of 1: 0.5 to 1: 2.5.

The temperature of the crosslinking agent solution in the crosslinking bath is preferably preferably in the range of 20 to 70 ° C., and the immersion time of the polyvinyl alcohol-based resin film is usually in the range of 1 second to 15 minutes. The time is preferably 5 seconds to 10 minutes.
In the crosslinking step, the film may be stretched in the length direction in a crosslinking bath, and the total stretch ratio accumulated at this time is preferably about 1.1 to 5.0 times.
In addition, as a dyeing process, it may replace with the processing method immersed in a crosslinking agent liquid, and may implement by a method of apply | coating or spraying a crosslinking agent containing solution as a bridge | crosslinking process.

(Stretching process)
The stretching step is a step of stretching the dyed and cross-linked polyvinyl alcohol resin film in the length direction thereof, for example, so that the total stretch ratio accumulated as described later becomes about 5.25 to 8 times. In the wet stretching method, stretching is performed by applying tension in the length direction in a state where the film is immersed in a solution stored in a stretching bath. In addition, the elongation amount of the joining part and non-joining part of the 1st polyvinyl alcohol film and 2nd polyvinyl alcohol by extending | stretching is mentioned later.
The solution stored in the stretching bath is not particularly limited. For example, a solution to which various metal salts, iodine, boron or zinc compounds are added can be used.
As a solvent of this solution, water, ethanol, or various organic solvents can be appropriately used.
Especially, it is preferable to use the solution which added about 2-18 mass% of boric acid and / or potassium iodide, respectively.
When boric acid and potassium iodide are used simultaneously, the content ratio (mass ratio) is about 1: 0.1 to 1: 4, more preferably about 1: 0.5 to 1: 3. It is preferable to use in.
The temperature of the solution in the stretching bath is preferably in the range of 40 to 67 ° C, and more preferably 50 to 62 ° C, for example.

(Washing process)
The washing step is a step of washing away unnecessary residues such as boric acid adhering to the previous treatment by passing the film through a washing bath in which a washing liquid such as water is stored.
Iodide is preferably added to the water, for example, sodium iodide or potassium iodide is preferably added.
When potassium iodide is added to the water of the washing bath, the concentration is usually 0.1 to 10% by mass, preferably 3 to 8% by mass.
Furthermore, the temperature of the cleaning liquid is preferably 10 to 60 ° C, and more preferably 15 to 40 ° C.
In addition, the number of cleaning treatments, i.e., the number of repetitions of lifting from the cleaning liquid after being immersed in the cleaning liquid is not particularly limited, and a plurality of cleaning baths may store water having different types and concentrations of additives. In addition, the cleaning step may be performed by passing a film through them.
In addition, when pulling up the film from the immersion bath in each step, in order to prevent the occurrence of liquid dripping, a conventionally known liquid breaker roll such as a pinch roll is used, or the liquid is scraped off by an air knife. Depending on the method, excess water may be removed.

(Drying process)
The film that has been washed in the washing step can be introduced into the dryer 11 and dried by an appropriate method such as natural drying, wind drying, or heat drying, and the drying step can be performed.
Among these, if the drying step by heat drying is carried out, it is preferable that the heat drying conditions are a heating temperature of about 20 to 80 ° C. and a drying time of about 1 to 10 minutes.
Furthermore, it is preferable that the drying temperature be as low as possible for the purpose of preventing deterioration of the film regardless of the method.
More preferably, it is 60 degrees C or less, and it is especially preferable to set it as 45 degrees C or less.

(Lamination process) and (Winding process)
In this embodiment, the polarizing film wound by roll shape can be obtained by implementing the winding process which winds up the film which passed through the above processes with a winding roller.
In this embodiment, the winding step may be performed after performing a laminating step of appropriately laminating a surface protective film or the like on one or both sides of the polarizing film dried in the drying step. .
The final total draw ratio of the polarizing film thus produced is preferably any one of the draw ratios in the range of 5.25 to 8.0 times with respect to the original film. It is more preferable that the drawing ratio is any one of 5 to 7.0 times.
The draw ratio as described above is preferable because if the final total draw ratio is less than 5.25 times, it is difficult to obtain a polarizing film having high polarization characteristics, and if it exceeds 8.0 times, the film is broken. This is because there is a risk of causing it.

  The final total draw ratio of the polarizing film is preferably any one of the draw ratios in the range of 5.25 to 8.0 times in the non-bonded portion (that is, the original fabric film). It is more preferable that the drawing ratio is any one of the range of 0.5 to 7.0 times.

(Linking process)
As described above, in the present embodiment, before all of one raw roll is supplied to the stretching apparatus, the polyvinyl alcohol-based resin film (raw film) is further fed out from the next raw roll, A connecting step (the second step) is performed in which the leading end portion 1b of the new original film is joined and connected in a state where it is overlapped with the end portion 1a of the original roll where each step is performed by a stretching apparatus. To do. Further, in the connecting step, the tip portion 1b and the end portion 1a are joined in an overlapped state, and the amount of elongation of the joined portion at the time of stretching at a stretch ratio of 4.2 times in the first step (movement path) is And it connects so that it may become 30% or more with respect to the elongation amount of a non-joining part.
Thus, the high draw ratio required in order to provide a high polarization function by joining the front-end | tip part of the following 1st original film, and the front-end | tip part of the next original film, for example, 5. In the step of stretching the second original film without changing the stretching conditions even when the joining portion passes, the second raw film is stretched (first step). The polarizing film can be produced efficiently.
That is, the first raw film and the second original film can be continuously passed through the drawing apparatus without changing the drawing conditions, thereby improving work efficiency, improving productivity, improving yield and reducing material loss. Reduction effect is obtained.

In addition, it is not necessary to perform this connection process after finishing the process (the 1st process) of extending the 1st original film completely, for example, in the latter stage side of the 1st process, It can be performed in parallel with the first step.
For example, a first raw roll is supplied to the swelling bath 4a through the accumulator using a stretching apparatus having an accumulator between the connecting device and the swelling bath 4a, and the first raw roll is wound. When the end portion is approached, the raw film accumulated in the accumulator is supplied to the swelling bath 4a side while the end portion is stopped, and the first raw film is stretched (the first It is possible to carry out a connecting step by laser welding of the front end portion of the new raw roll and the end portion while carrying out the step.

  Moreover, after implementing the connection process which connects two strip-shaped polyvinyl alcohol-type resin films previously, extending | stretching of the one polyvinyl alcohol-type resin film of the connected strip-shaped polyvinyl alcohol-type resin films (the said 1st process) ) May be started.

In the connecting step, the end portion of the first polyvinyl alcohol-based resin film and the tip portion of the second strip-like polyvinyl alcohol-based resin film are overlapped, and the end portion and the tip portion thus overlapped are overlapped. Can be carried out by laser welding the interface portion. Specifically, a light absorber is applied to one or both of the leading end 1a of the preceding film and the leading end 1b of the new film, and the width of the overlapping portion is 0.1 mm. The old and new original film is superposed on the stage 40 so as to be less than 20.0 mm above and below, and the superposed part is pressurized with the pressure member 50 and irradiated with laser light. Then, it can be carried out by forming the welded portion 30 by compatibilizing the resins at the film interface.
By welding with laser light in this way, it is possible to lower the crystallinity of the joint and reduce the area where the crystallinity increases around the joint as compared to the case where welding is performed with a heat sealer. It is possible to form a joint where stress concentration hardly occurs around the joint during stretching.

This will be described in detail. For example, a raw film in which a region where the crystallinity is increased (cured region) is formed around the joint by being joined by a heat sealer is supplied to the stretching device, Even if it passes through the swelling bath 4a, the dyeing bath 4b, and the crosslinking bath 4c having a temperature of about 30 ° C., it hardly swells in the cured region, and also in the stretching bath 4d of about 60 ° C. in the cured region. Since the film is hardly swollen and stretched, a region having a large strain is formed before and after the cured region. This is because, when heated by a heat sealer, the periphery of the bonded portion joined by the heat sealer is continuously heated at a temperature lower than the melting point of the raw film, thereby making the crystallinity higher than that of the non-bonded portion (bulk). This is because it hardens and does not easily swell, so it is difficult to soften, and thus it is difficult to stretch during stretching.
And when the hardening area | region around this junction part receives extending | stretching with the extending | stretching bath 4d, it will produce a fracture | rupture, and when this fracture | rupture generate | occur | produces, it becomes impossible to extend a junction part any more.

  On the other hand, in the present embodiment, only the vicinity of the interface is heated selectively and locally in the overlapping portion of the old and new original film by irradiation with laser light, and the molten region is rapidly cooled. This makes it possible to promote the amorphization of the joint by such rapid cooling and to lower the crystallinity of the joint. In addition, since the region heated at a temperature lower than the melting point of the raw film in the periphery of the joint portion can be made smaller than that in the case of welding with a heat sealer, the increase in crystallinity in the periphery is suppressed. Can do. As described above, by promoting the amorphization of the joint and suppressing the crystallization around the joint, the joint and its periphery are easily softened by swelling and easily stretched during stretching. Further, as the laser beam irradiation spot is made smaller, more local heating is possible, so that the region where the crystallinity is increased around the joint can be made smaller.

Thus, in this embodiment, since the vicinity of the interface between the end portion and the tip portion is locally heated in the joint portion, the crystallinity is lowered in the joint portion, and the crystallization is high in the vicinity of the joint portion. Can be made smaller. Thereby, since it can make it easy to extend a joint part, suppressing hardening in the periphery of a joined part, concentration of stress in a boundary part of a joined part and a non-joined part can be eased.
For example, when the swelling bath 4a, the dyeing bath 4b, and the crosslinking bath 4c are set to a temperature of about 30 ° C., the softening effect due to swelling cannot be expected so much, but the stretching bath is set to 50 to 62 ° C. The swelling of the part and its periphery proceeds, and these can be stretched. That is, the joint can be stretched without breaking around the joint.
That is, the stretchability of the region not affected by heat (non-joined portion) and the region affected by heat (joined portion) in welding can be approximated and is high while suppressing problems such as fracture. Stretching at a magnification can be performed.

  In the present embodiment, by performing laser welding in the connecting step, the joint portion is easily stretched during stretching as described above. Then, by appropriately setting the laser irradiation conditions described above, the connection is such that the stretch amount of the joint portion when stretched at a stretch ratio of 4.2 times is 30% or more with respect to the stretch amount of the non-joint portion. It becomes possible. In addition, after the laser light irradiation, the bonding portion is cooled to make the bonding portion more amorphous, and the ratio of the elongation amount of the bonding portion to the elongation amount of the non-bonding portion is easily increased. Can do. For example, by cooling the pressure member 50 with the pressure member 50 in contact with the joint, the joint after laser irradiation can be cooled. Further, for example, by spraying water on the joint, it is possible to promote swelling of the joint after laser irradiation and to make the joint easy to stretch. Hereinafter, the elongation amount of the joint portion relative to the elongation amount of the non-joint portion when stretched at a stretch ratio of 4.2 times may be simply referred to as “elongation amount ratio”.

  Thus, by setting the ratio of the elongation amount to 30% or more, the stretchability between the non-joined part and the joined part can be approximated, and the stretching at a high magnification is performed while suppressing problems such as breakage. obtain. Further, in the stretching step, it is preferable to connect so that the elongation ratio is 50% or more, and it is more preferable to connect so as to be 60% or more.

  On the other hand, in view of the fact that the stretchability of the joined portion and the non-joined portion can be more approximated as the stretch amount of the joined portion approaches the stretch amount of the non-joined portion, the ratio of the stretch amount is preferably as large as possible. However, if the amorphization of the joint portion is promoted too much, there is a possibility that breakage may occur on the contrary because of excessive elongation during stretching. Therefore, in consideration of such a viewpoint, it is preferable to connect so that the elongation ratio is 150% or less.

  Further, as described above, the stretching bath 4d is preferably set to 50 to 62 ° C., and thereby, the swelling of the heat-denatured area can be further advanced and the heat-denatured area itself can be stretched. It is possible to facilitate the stretching of the joint portion so as to be at least%.

The amount of elongation of the non-joined portion is defined as the length (Q) at which the unstretched region having a certain length P in the width direction and the perpendicular direction becomes the length Q by stretching. -P).
Further, when the unstretched region having a fixed length R in the width direction and the vertical direction at the joint becomes the length S by stretching, the elongation amount of the joint portion described above is the length (S -R).
Then, by dividing the stretched lengths at the non-joined part and the joint part by the unstretched unit lengths P and R, respectively, the elongation amount per unit of the non-joined part and the joint part when unstretched is (Q− P) / P, (S-R) / R, and by dividing the elongation amount of the joint obtained by the conversion by the elongation amount of the non-joint portion and multiplying by 100, the ratio of the elongation amount (% ) Is calculated.
In such a case, the elongation amounts of the non-joined part and the joined part are respectively the difference (Q / P-1) and (S / R-1) of the draw ratio after stretching with respect to the stretch ratio when unstretched. Using the difference in draw ratio, the elongation ratio can also be calculated by the elongation ratio = (S / R-1) / (Q / P-1).
In addition, when calculating the ratio of the elongation amount, when using the difference in the draw ratio, the ratio of the elongation amount can be calculated without performing such conversion.
Further, when measuring the elongation amount of the non-joined portion, the above-mentioned constant length P can be set as appropriate, and when measuring the amount of elongation of the joint portion, the above-mentioned constant length S is joined. It can be the length of the entire part.

  Further, the length of the non-joined part and the joined part when not stretched and after stretching can be measured with a length measuring microscope. As such a measuring microscope, for example, MM-40 manufactured by Nikon Corporation can be used.

In the case of welding with a heat sealer, the hardened region is unlikely to swell, so the progress of softening due to swelling is slow, and even when stretched under the same temperature conditions, breakage is likely to occur.
Thus, in the manufacturing method of the polarizing film of this embodiment, the junction part with a low possibility of fracture | rupture by extending | stretching can be formed.

In addition, although the thickness of the polarizing film manufactured by the manufacturing method of this embodiment is not specifically limited, It is preferable that a non-joining part is 5-40 micrometers.
If the thickness of the non-bonded portion is 5 μm or more, the mechanical strength does not decrease, and if it is 40 μm or less, the optical characteristics do not decrease, and thinning can be realized even when applied to an image display device.

The polarizing film manufactured by this embodiment can be used for a liquid crystal display device etc. as a polarizing film laminated | stacked on a liquid crystal cell substrate, and besides a liquid crystal display device, an electroluminescent display device, a plasma display, and an electric field It can be used as a polarizing film in various image display devices such as an emission display.
In practical use, various optical layers can be laminated on both sides or one side to form an optical film, or various surface treatments can be applied to an image display device such as a liquid crystal display device.
The optical layer is not particularly limited as long as it satisfies the required optical characteristics. For example, a transparent protective layer for the purpose of protecting a polarizing film, an alignment liquid crystal layer for the purpose of visual compensation, etc. In addition to adhesive layers for laminating other films, polarization conversion elements, reflectors, transflective plates, retardation plates (including wave plates (λ plates) such as 1/2 and 1/4), visual compensation Films used for forming image display devices such as films and brightness enhancement films can be used.
Examples of the surface treatment include hard coat treatment, antireflection treatment, surface treatment for the purpose of preventing sticking, diffusion or anti-glare.
Although the manufacturing method of the polarizing film of this embodiment is as above, this invention is not limited to this embodiment, and can change a design suitably in the range which this invention intends.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

(Evaluation example 1)
Raw film: Polyvinyl alcohol resin (PVA) film (manufactured by Kuraray Co., Ltd.,
(Thickness 75μm, width 30mm, water absorption 6%)
-Overlap width: 1.5 mm width-Heat fusion bonding means: Laser-Laser: Semiconductor laser (wavelength 940 nm, power 70 W, spot diameter 2 mmφ,
Power density 2,228 W / cm ² , scanning speed 50 mm / sec, integrated dose
89J / cm ² , top hat beam)
-Light absorber: Trade name "Clearweld LD120C" (manufactured by Gentex, USA)
Solvent acetone), 2.0mm wide on the upper surface of the raw film placed on the lower side
10 nL / mm ² coating / pressurizing member: quartz glass plate (10 mm thick)
-Pressurizing condition: Pressed against the original film overlap part with a load of 60 kgf / cm ² -Length measurement: Length measuring microscope (Nikon Corporation, MM-40)

Example 1
Under the above basic conditions, two raw films are connected, and the length before and after the joint is cut out by about 50 mm. In the stretching apparatus as shown in FIG. 1, the stretching ratio is 2.6 times in the swelling bath and in the dyeing bath. The film was stretched to 3.4 times, 3.6 times for the crosslinking bath, and 6.0 times for the stretching bath, and then passed through a washing bath to batch-produce polarizing films.

  And the length of the junction part after extending | stretching by each draw ratio was measured, and the elongation length of a junction part was computed by subtracting the length (1.5 mm) at the time of non-extension | stretching from the length after extending | stretching. . Moreover, the length after extending | stretching a raw film (equivalent to a non-joining part) on the conditions similar to Example 1 is measured, and the length at the time of undrawing (48.5 mm) is subtracted from the length after extending | stretching. Thus, the elongation length of the non-joined part was calculated. Next, by dividing the stretch length of the joint and non-joint portions by the unstretched lengths of 1.5 mm and 48.5 mm, respectively, they are converted into the stretch amount per unit length when unstretched. The elongation ratio (%) was calculated by dividing the elongation amount of the bonded portion by the elongation amount of the non-joined portion and multiplying by 100.

(Comparative Example 1)
The overlap width of the old and new original film is set to 30 mm, and heat sealing is performed at 66 ° C. for 2 seconds using a nichrome wire with a width of 3 mm. A polarizing film was batch-produced in the same manner as in Example 1 except that the two line-shaped welds were formed.
As a result, in the process of manufacturing the polarizing film, breakage occurred at the accumulated total draw ratio of 4.8, and the film could not be drawn to the desired draw ratio of 6.0 times.
Further, in the same manner as in Example 1, after measuring the length of the stretched joint and the original film (corresponding to the non-bonded portion) at each stretch ratio, the stretched length of the joint after stretching was not stretched. By subtracting the length (3.0 mm), the elongation length of the joined portion is calculated, and for the non-joined portion, the unstretched length (47 mm) is subtracted from the length after stretching. The elongation length of was calculated. Then, by dividing the elongation length of the joint portion and the non-joint portion by the unstretched length of 3.0 mm and 47 mm, respectively, it is converted into the amount of elongation per unit length when unstretched, and the joint portion after conversion The elongation ratio (%) was calculated by dividing the amount of elongation by the amount of elongation of the non-joined portion and multiplying by 100.

In Table 1, the measurement result of the length after each extending | stretching in a non-joining part and a joining part in Example 1, and the calculation result of the ratio of a draw ratio, elongation length, and elongation amount are shown. Table 2 shows the measurement results of the stretch length after each stretching in the non-joined part and the joined part and the calculation result of the ratio of the stretch ratio, the stretch length and the stretch amount in Comparative Example 1. Moreover, in Example 1 and Comparative Example 1, the relationship between the draw ratio in a extending process and the ratio of the said elongation amount is shown in FIG. In Table 1, Table 2, and FIG. 4, the draw ratio indicates the accumulated total draw ratio.

As can be seen from Table 1 and FIG. 4, in Example 1 (the legend “●” in FIG. 4), the elongation ratio increases as the draw ratio in the drawing process increases. When stretching at a magnification of 4.2, the elongation ratio was 43.4%. When this sample was further stretched, it was 75.5% at a stretch ratio of 4.8 times, and 86.8% at a stretch ratio of 6.0 times, and no break was observed even when stretched at a stretch ratio of 6.0 times. Moreover, even after extending | stretching by the draw ratio 6.0 time, the joining state of the junction part was favorable.
On the other hand, as can be seen from Table 2 and FIG. 4, in Comparative Example 1 (the legend “◯” in FIG. 4), even when the draw ratio in the drawing process is increased, there is little increase in the ratio of the above-mentioned elongation amount. At the time of stretching at a magnification of 4.2, the elongation ratio was 8.3%. When this sample was further stretched, breakage was observed before the draw ratio reached 4.8 times.

  As described above, the elongation ratio when stretched at a stretch ratio of 4.2 times is set to 30% or more. For example, even if the stretch ratio is stretched at a stretch ratio of 5.25 times or more, breakage at the joint is generated. It turns out that it can be avoided.

(Example 2)
Except for changing the width of the original film to 3,900 mm, the old and new original films were connected under the above basic conditions, and the polarizing film was manufactured by roll-to-roll under the polarizing film manufacturing conditions described in Table 1 above. As a result, as in Example 1, the ratio of the elongation when stretched at a stretch ratio of 4.2 was 43.4%. Even if the joined sample was further stretched to a cumulative total stretch ratio of 6.0 times, it was not broken and could be continuously passed.

(Example 3)
Two original films were connected under the above basic conditions except that the overlap amount (joint width) of the old and new original films was 1 mm and the laser power was 85 W. Further, in the same manner as in Example 1, the front and back of the connected raw film were cut out by about 50 mm, and the polarizing film was batch-produced by stretching so that the stretching ratio was finally 6.0 times. . Then, in the same manner as in Example 1, the elongation length of the joined portion and the non-joined portion after stretching at a draw ratio of 4.2 times was measured, and the ratio of the elongation amount was calculated. The results are shown in Table 3 together with the results of Example 1 and Comparative Example 1.

Example 4
The two original films were connected in the same manner as in Example 1 except that the overlap amount (joint width) of the old and new original films was 2 mm and the laser power was 80 W, and then the polarizing films were batch-produced. . Then, in the same manner as in Example 1, the elongation lengths of the joined portion and the non-joined portion after stretching at each draw ratio were measured, and the ratio of the elongation amount was calculated. The results are shown in Table 3.

(Comparative Example 2)
Except that the heating conditions were 250 ° C. and 5 seconds, in the same manner as in Comparative Example 1, two raw films were connected, and then a polarizing film was batch-produced.
As a result, in the process of manufacturing the polarizing film, breakage occurred at the accumulated total draw ratio of 5.0, and the film could not be drawn to the desired draw ratio of 6.0 times.
Moreover, it carried out similarly to the comparative example 1, measured the elongation length of the junction part after extending | stretching by each draw ratio, and the non-joining part, and computed the ratio of elongation amount. The results are shown in Table 3.

  As described above, in Examples 1, 3, and 4 shown in Table 3, the film was not broken even when stretched to a stretch ratio of 6.0. On the other hand, in Comparative Examples 1 and 2, breakage was observed at draw ratios of 4.8 and 5.0, respectively, and the film could not be drawn to a draw ratio of 6.0.

  From the above, it can be seen that according to the present invention, a polarizing film having a high polarizing function can be produced more efficiently than in the conventional method.

1: Raw film (band-shaped polyvinyl alcohol-based resin film), 1a: terminal portion, 1b: tip portion, 4d: stretching bath, 9: roller

Claims (3)

A first step of feeding a belt-like polyvinyl alcohol-based resin film from the tip side into the moving path and extending in the immersion bath in the longitudinal direction in the moving path;
A second step of joining and connecting the rear end side of the preceding first polyvinyl alcohol-based resin film and the front end side of the next second polyvinyl alcohol-based resin film;
A polarizing film manufacturing method for continuously manufacturing a polarizing film,
In the second step, the rear end side and the front end side are joined in an overlapped state, and the extension amount of the joint portion at the time of stretching at a stretch ratio of 4.2 times in the moving path is a non-joined portion. The rear end side and the front end side are joined by joining by laser welding so that the elongation amount is 30% or more,
Each of the first polyvinyl alcohol-based resin film and the second polyvinyl alcohol-based resin film has a non-joining part and a joining part having a stretching ratio of 5.25 times or more, respectively, and the non-joining part. The method for producing a polarizing film is characterized in that the stretch ratio is larger than the stretch ratio of the joint.   The method for producing a polarizing film according to claim 1, wherein the laser welding is performed by arranging a light absorber at an interface between the rear end side and the front end side.   The method for producing a polarizing film according to claim 1, wherein the laser welding is performed with an infrared laser having a wavelength of 800 nm to 1200 nm.

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