JP2010008509A - Method for producing polarizing film, polarizing plate, and optical laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polarizing film for sequentially and continuously producing a polarizing film, surely bonding the rear end part of a fed roll film with the front end part of the next roll film, and preventing breakage of in a heat seal part between the roll films. <P>SOLUTION: In this method for producing a polarizing film, while continuously feeding a polyvinyl alcohol roll film wound in a roll, the roll film is extended in the longitudinal direction in a movement course, and at the same time, the rear end part of the fed roll film and the front end part of the next roll film are bonded together, so that a polarizing film is continuously produced. The bonding is carried out by putting the rear end part of the roll film and the front end part of the next roll film together and heat-welding them mutually at 200-300°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polarizing film, a polarizing plate and an optical laminate used for a liquid crystal display device or an image display device.

Conventionally, as a method for producing a polarizing film, there is a method of forming a polarizing film by passing a roll-shaped polyvinyl alcohol-based raw film (raw roll) through a predetermined moving path while being drawn out and stretching in the moving path. It has been adopted.
In other words, a raw film made of a roll-shaped polyvinyl alcohol film is rolled out from the tip side, and the movement path of the original film is regulated by a plurality of transport rollers, while the raw film is placed in various bathtubs. Through the film, the swelling treatment, the dyeing treatment with the dichroic dye, the crosslinking treatment with the boric acid aqueous solution of the dyed original film, the stretching treatment of the crosslinked original film, the washing treatment and the drying treatment in this order, A polarizing film is produced.

  By the way, in order to continuously feed the original film into the movement path, when the remaining length of the original roll decreases, the rear end of the original roll and the leading end of the next original roll Need to be joined. As a method for that purpose, for example, a method in which an operator ties the original film and the next original film together by hand in a moving path regulated by a conveyance roller, or the original films are bonded with tape. A method is mentioned. However, it is not preferable to join the original films by such a method from the viewpoint of workability and contamination with foreign matter. Therefore, for example, as in the method described in Patent Document 1, there has been proposed a method in which the rear end portion of the preceding original film and the front end portion of the next original film are thermally welded using a heat sealer.

In Patent Document 1, a polyvinyl alcohol-based original film and the next original film are thermally welded at a temperature of 50 ° C to 90 ° C. Thereby, when joining original film, it is described that the generation | occurrence | production of the flaw in the junction part (heat seal part) of original film is suppressed, and workability | operativity becomes favorable.
JP 2007-171897 A

  However, in the method described in Patent Document 1, since the original films are thermally welded at a temperature of 50 ° C. to 90 ° C., the original films made of polyvinyl alcohol films are not reliably welded to each other and stretched. There exists a problem that the heat-sealing part of original fabric films will fracture | rupture by processing. In Patent Document 1, for each original film, the trouble of manually passing the leading end side of the original film in the movement path regulated by the conveying roller or the like is eliminated, but breakage occurs during the conveyance. If it occurs, it is necessary to insert the leading end surface of the raw film into a conveying roller for driving, so that there is a problem of work safety.

  Therefore, the problem of the present invention is that the polarizing film can be produced sequentially and continuously, and the rear end portion of the unrolled original film can be reliably bonded to the front end portion of the next original film. An object of the present invention is to provide a method for producing a polarizing film in which the heat-sealed portion between the original films does not break.

As a result of intensive studies to solve the above problems, the present inventors thermally weld the rear end of the original film and the front end of the next original film at a temperature of 200 ° C. to 300 ° C. As a result, the inventors have found a new fact that original films can be reliably bonded to each other in a short time, and have completed the present invention.
That is, in the method for producing a polarizing plate according to the present invention, the povirinyl alcohol-based raw film wound in a roll shape is continuously drawn, while the film is stretched in the longitudinal direction in the movement path and is drawn. The polarizing film is continuously manufactured by bonding the rear end portion of the obtained original film and the leading end portion of the next original film, and the bonding is performed between the rear end portion of the original film and the next It is characterized by being carried out by superimposing the leading end portion of the raw film and thermally welding at a temperature of 200 to 300 ° C. The joining is preferably performed by heat welding using a hot plate heat sealer. Moreover, it is good for the junction part by the said heat welding to be a linear form with a line width of 1-7 mm.

  Moreover, the manufacturing method of the polarizing plate concerning this invention is good to form the said joining by heat-welding at 200-300 degreeC for 1 to 25 seconds, and the joining part formed by heat welding in that case is a film. It is good that it is linear with a line width of 1 to 7 mm extending in the width direction. In particular, when the line width of the joint portion is 3 to 7 mm, the joint portion is preferably formed by heat welding at 230 to 250 ° C. for 1 to 5 seconds. When the line width of the joint portion is 1 to 3 mm, It is preferable to form the bonded portion by heat welding at 230 to 260 ° C. for 5 to 20 seconds.

  The polarizing plate according to the present invention is obtained by bonding a protective film to at least one surface of the polarizing film obtained as described above. This protective film may have a function of any of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film.

  The optical laminate according to the present invention is obtained by laminating a polarizing plate obtained as described above and at least one selected from a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. is there. Moreover, a liquid crystal display device, an image display device, etc. can be manufactured using the polarizing plate obtained as mentioned above.

  According to the method for producing a polarizing film of the present invention, for example, using a hot plate heat sealer, the rear end portion of the original film and the front end portion of the next original film are thermally welded at a temperature of 200 to 300 ° C. The raw film can be reliably bonded to each other at a heat seal portion (bonding portion) for a short time, and the bonding portion is prevented from breaking. For this reason, the efficiency of productivity and workability can be improved.

Hereinafter, the manufacturing method of the polarizing film concerning this invention is demonstrated in detail.
In the method for producing a polarizing film according to the present invention, an original film formed by winding a belt-shaped polyvinyl alcohol-based original film into a roll is unwound from the tip, and the movement path of the original film is regulated by a plurality of conveying rollers. While passing through the raw film into various baths, swelling treatment, dyeing treatment with dichroic dye, cross-linking treatment of the dyed raw film with boric acid aqueous solution, stretching treatment of the cross-linked raw film, water washing treatment and A polarizing film is manufactured by processing in order of a drying process.

  Examples of the polyvinyl alcohol-based resin that forms the polyvinyl alcohol-based raw film in the present invention are usually saponified polyvinyl acetate-based resins. As a saponification degree, it is 85 mol% or more, Preferably it is 90 mol% or more, More preferably, it is 99 mol%-100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is about 1000 to 10,000, preferably about 1500 to 5,000.

  These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used. Usually, as a starting material for producing a polarizing film, an unstretched film of a polyvinyl alcohol resin film having a thickness of 20 μm to 100 μm, preferably 30 μm to 80 μm is used. Industrially, the width of the film is practically 1500 mm to 4000 mm. The unstretched film is treated in the order of swelling treatment, dyeing treatment, crosslinking treatment, and water washing treatment, and finally dried to obtain a polyvinyl alcohol polarizing film having a thickness of, for example, about 5 to 50 μm.

  The polarizing film of the present invention is a polyvinyl alcohol uniaxially stretched film obtained by adsorbing and orienting a dichroic dye, and there are roughly two production methods as the production method. One is a method in which a polyvinyl alcohol film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, followed by drying. Secondly, an unstretched polyvinyl alcohol film is treated with an aqueous solution in the order of swelling treatment, dyeing treatment, crosslinking treatment and washing treatment, and uniaxial stretching is performed in a wet manner in the crosslinking treatment step and / or the previous step, Finally, it is a method of drying.

  In any method, the uniaxial stretching may be performed in one step or in two or more steps, but is preferably performed in a plurality of steps. As a stretching method, a known method can be adopted. For example, stretching between rolls in which stretching is performed with a difference in peripheral speed between two nip rolls for transporting a film, hot roll stretching as described in Japanese Patent No. 2731813 Method and tenter stretching method. The order of the steps is basically as described above, but there are no restrictions on the number of treatment baths or treatment conditions. Needless to say, a process not described in the above process can be freely inserted for another purpose. As an example of this step, after the crosslinking treatment, an immersion treatment with an aqueous iodide solution not containing boric acid (iodide treatment) or an immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment), etc. Can be mentioned.

The swelling step is performed for the purpose of removing foreign matter on the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The treatment conditions are determined within a range that can be achieved for these purposes and within a range that does not cause problems such as extreme dissolution and devitrification of the base film.
For example, the unstretched raw film is immersed in an aqueous solution at 10 ° C to 50 ° C, preferably 20 ° C to 40 ° C. The immersion time of the film is about 30 seconds to 300 seconds, and more preferably about 60 to 240 seconds.

  In the swelling process, problems such as swelling of the film in the width direction and wrinkling of the film are likely to occur. Therefore, the film may be spread with a known widening device such as an expander roll, spiral roll, crown roll, cross guider, bend bar, or tenter clip. It is preferable to transport the film while removing the wrinkles. In this step, since the film swells and expands in the running direction of the film, it is preferable to take measures such as controlling the speed of the conveying roller before and after the treatment tank in order to eliminate the sag of the film in the conveying direction. In addition to pure water, the swelling treatment bath used is boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water-soluble An aqueous solution to which an organic solvent, alcohol or the like is added in an amount of 0.01 wt% to 10 wt% can be used, but water is preferable for the reason described above.

  After the swelling treatment, the polyvinyl alcohol-based raw film is dyed. The normal dyeing process with a dichroic dye is performed for the purpose of adsorbing and orienting the dichroic formula on the original film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When iodine is used as the dichroic dye, for example, iodine / KI / water = 0.003 to 0.2 / 0.1 at a temperature of 10 ° C. to 45 ° C., preferably 20 ° C. to 35 ° C. and in a weight ratio. The immersion treatment is performed at a concentration of 10/100 for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, Examples thereof include tin iodide and titanium iodide. Other iodides may be used in combination with potassium iodide. Further, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. Any dye containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, a temperature of 20 ° C. to 80 ° C., preferably 30 ° C. to 70 ° C., and a weight ratio of dichroic dye / water = 0.001 to 0.001. The immersion treatment is performed at a temperature of 1/100 for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may have a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone or two or more dichroic dyes may be used at the same time.

  As described above, the film may be stretched in a dyeing tank. Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, or the like can be installed in the dyeing bath and / or at the bath entrance / exit.

  The crosslinking treatment after the stretching treatment is performed by immersing a polyvinyl alcohol film dyed with a dichroic dye in an aqueous solution containing about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain about 1 to 30 parts by weight of iodide. Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  This cross-linking treatment is performed for water resistance and hue adjustment (for example, to prevent bluish tint) by cross-linking. In the case of water resistance by crosslinking, a crosslinking agent such as glyoxal or glutaraldehyde can be used together with boric acid as necessary.

  This crosslinking treatment is performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose. The crosslinking treatment for water resistance and the crosslinking treatment for adjusting the hue are not particularly distinguished, but are carried out under the following conditions.

  When the raw film is swelled, dyed, and crosslinked, and the crosslinking treatment is intended to provide water resistance by crosslinking, boric acid is about 3 to 10 parts by weight and iodide is about 100 parts by weight of water. A crosslinking treatment bath containing 1 to 20 parts by weight is used, and is usually performed at a temperature of about 50 to 70 ° C, preferably about 55 to 65 ° C. The immersion time is usually about 30 to 600 seconds, preferably about 60 to 420 seconds, and more preferably about 90 to 300 seconds. In addition, when dye | staining and bridge | crosslinking a film extended | stretched previously, the temperature of a crosslinking treatment bath is about 50 to 85 degreeC normally, Preferably it is about 55 to 80 degreeC.

  You may perform the crosslinking process for hue adjustment after the crosslinking process for water resistance. For example, when the dichroic dye is iodine, a crosslinking bath containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. Usually, it is performed at a temperature of about 10 ° C to 45 ° C. The immersion time is usually about 3 to 300 seconds, preferably about 10 to 240 seconds. The crosslinking treatment for adjusting the hue is usually performed at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than the crosslinking treatment for water resistance.

  These cross-linking treatments may be performed in a plurality of steps, and are usually performed in 2 to 5 steps. In this case, the aqueous solution composition and concentration of each crosslinking treatment tank to be used may be the same or different within the above range. The crosslinking treatment for water resistance and the crosslinking treatment for hue adjustment may be performed in a plurality of steps, respectively. The final cumulative draw ratio is about 4.5 to 7.0 times, preferably 5.0 to 6.5 times.

  After the crosslinking treatment, it is washed with water. The water washing treatment is performed, for example, by immersing a polyvinyl alcohol film crosslinked for water resistance and / or hue adjustment in water, spraying water as a shower, or combining immersion and spraying. The temperature of the water in the washing treatment is usually about 2 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds.

  In each step after the stretching treatment, tension control may be performed so that the tension of the film becomes substantially constant. When stretching is completed in the dyeing process, the tension is controlled in the subsequent crosslinking process and washing process. When stretching is completed in the previous process of the dyeing process, tension control is performed in subsequent processes including the dyeing process and the crosslinking process.

  When the crosslinking treatment step comprises a plurality of crosslinking treatment steps, the film is stretched in the first or second crosslinking treatment step from the first to the second stage, and then washed with water from the crosslinking treatment step subsequent to the crosslinking treatment step in which the stretching treatment has been performed. Tension control is performed in each process up to the process, or the film is stretched in the crosslinking process from the first to the third stage, and each of the process from the crosslinking process to the water washing process following the crosslinking process performed the stretching process. It is preferable to perform tension control in this step, but industrially, the cross-linking treatment step following the cross-linking treatment step in which the film was stretched and stretched in the first or second cross-linking step. It is more preferable to perform tension control in each step from the water washing step to the water washing step. When the above-described iodide treatment or zinc treatment is performed after the crosslinking treatment, tension control is also performed for these steps. The tension in each step from the swelling treatment to the water washing treatment may be the same or different.

  The drying process is preferably carried out in a large number of stages by changing the tension little by little, but is naturally limited due to restrictions on equipment and is usually carried out in 2 to 3 stages. When performed in two stages, the tension in the front stage is set from the range of 600 to 1500 N / m, and the tension in the rear stage is set from the range of 300 to 1200 N / m. If the tension is too large, the film will be broken, and if it is too small, wrinkles will increase, which is not preferable.

  As the nip roll for controlling the tension in the present invention and the guide roll for controlling the film transport direction, a rubber roll, a stainless steel polishing roll and a sponge rubber roll are used.

  In this embodiment, the polarizing film wound by roll shape can be obtained by winding up the raw film which passed through each above process steps. In addition, you may make it wind up the manufactured polarizing plate by laminating | stacking a protective film on at least one surface of the polarizing film dried by the drying process, manufacturing a polarizing plate.

  A polarizing film can be produced by passing through each processing step as described above, but in this embodiment, before performing each processing step as described above on a raw film wound in a roll shape. In addition, using a hot plate heat sealer, the leading end of the next original film is joined to the rear end of the previous original film by heat welding. That is, the hot plate of a hot plate heat sealer in which the leading end portion of the next original film is overlapped with the rear end portion of the original fabric film, the overlapped portion is placed on a support base and the surface is heated to 200 to 300 ° C. The heating element) is lowered and the original film is pressurized and heat-welded. When the surface temperature of the hot plate is lower than 200 ° C., the raw fabric films cannot be completely heat-welded, causing the joint to break. On the other hand, when the surface temperature of the hot plate is higher than 300 ° C., the crystallization of the raw film proceeds and becomes brittle due to excessive heating of the bonded portion, or problems such as frequent occurrence of bubbles in the bonded portion occur.

  In accordance with the above conditions, the leading edge of the next original film can be passed through a movement path regulated by a conveyance roller or the like by following the trailing edge of the previous original film. Thus, the next raw film can also be made into a polarizing film in succession. Here, the time required for heat welding at 200 to 300 ° C. (that is, the time during which the heating element is in contact with the original film) is preferably 1 to 25 seconds.

  Further, the joining portion of the film formed by heat welding should be a strip or a line formed over almost the entire width of the original film along the width direction of the film orthogonal to the stretching direction, and particularly the linear shape. Preferably there is. The line width is usually about 1 to 7 mm, but is preferably determined in consideration of the relationship between the heat welding temperature and time in order to obtain sufficient bonding strength. Specifically, when the line width of the joint portion is 3 to 7 mm, the joint portion is formed by heat welding at 200 to 300 ° C. for 1 to 5 seconds, and the line width of the joint portion is 1 to 3 mm. At this time, the joining portion is preferably formed by heat welding at 200 to 300 ° C. for 5 to 20 seconds. In addition, the belt-like or linear joint is usually sufficient at one place, but is not limited to this, and may be carried out at two or more places. Further, the line width may be smaller than 1 mm. In that case, it is preferable to prepare a plurality of line widths.

  As described above, by joining the previous original film and the next original film with a hot plate heat sealer, the polarizing film can be manufactured successively and continuously, and the film breaks at the joint. Can be suppressed. A polarizing plate is obtained by pasting a protective film with an adhesive or the like on at least one surface of the polarizing film thus produced.

  The protective film laminated | stacked on at least one side of the polarizing film manufactured as mentioned above may be the same kind, or may be a different kind, when laminated | stacked on both surfaces. When different types of protective films are used, one of the protective films is not particularly limited, but is not limited to amorphous polyolefin resin film, polyethylene terephthalate, polyethylene naphthalate, polyester resin film such as polybutylene terephthalate, acrylic Examples thereof include resin films having low moisture permeability such as a resin film, a polycarbonate resin film, a polysulfone resin film, and an alicyclic polyimide resin film. Examples of amorphous polyolefin-based resin films include “Topas” (registered trademark) manufactured by Ticona in Germany, “Arton” (registered trademark) manufactured by JSR Corporation, and Nippon Zeon Co., Ltd. There are “ZEONOR” and “ZEONEX” (both registered trademarks) manufactured by Mitsui Chemicals, Inc. and “Apel” (registered trademarks) manufactured by Mitsui Chemicals, Inc. As the other protective film, in addition to these films, for example, a cellulose acetate resin film such as a triacetyl cellulose film or a diacetyl cellulose film is used. Examples of the triacetyl cellulose film include “Fujitack TD80”, “Fujitack TD80UF” and “Fujitack TD80UZ” manufactured by Fuji Photo Film Co., Ltd., “KC8UX2M” and “KC8UY” manufactured by Konica Corporation.

  Although the thickness of the protective film is preferably thin, if it is too thin, the strength is lowered and the processability is inferior. On the other hand, if it is too thick, the transparency is lowered or the curing time required after lamination is increased. Problems occur. Therefore, the suitable thickness of a protective film is about 5-200 micrometers, for example, Preferably it is 10-150 micrometers, More preferably, it is 20-100 micrometers.

  The polarizing film and the protective film are laminated using an adhesive such as a water solvent adhesive, an organic solvent adhesive, a hot melt adhesive, a UV curable adhesive, or a solventless adhesive. Examples of aqueous solvent-based adhesives include polyvinyl alcohol-based resin aqueous solutions and aqueous two-component urethane emulsion adhesives, and examples of organic solvent-based adhesives include two-component urethane adhesives as UV curable adhesives. Examples include epoxy resin adhesives that do not contain an aromatic ring in the molecule, such as hydrogenated epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins. Solvent-free adhesives include, for example, one-pack urethane adhesives. Respectively. When an acetylcellulose-based film whose surface to be bonded to the polarizing film is hydrophilized by saponification or the like is used as a protective film, a polyvinyl alcohol-based resin aqueous solution is suitably used as an adhesive.

  In the present invention, the protective film has a function as a retardation film, a function as a brightness enhancement film, a function as a reflection film, a function as a transflective film, a function as a diffusion film, a function as an optical compensation film, etc. It can also have an optical function. In this case, for example, by laminating an optical functional film such as a retardation film, a brightness enhancement film, a reflection film, a transflective film, a diffusion film, an optical compensation film on the surface of the protective film, it has such a function. In addition, the protective film itself can be provided with such a function. Further, the protective film itself may have a plurality of functions such as a diffusion film having the function of a brightness enhancement film.

  For example, the above-mentioned protective film is subjected to a stretching process described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, or a process described in Japanese Patent No. 3168850, so that a retardation film is obtained. The function as can be provided. Further, two or more layers having different central wavelengths of selective reflection are formed by forming micropores in the protective film by a method as described in JP-A No. 2002-169025 and JP-A No. 2003-29030. By superimposing these cholesteric liquid crystal layers, a function as a brightness enhancement film can be imparted. By forming a metal thin film on the above protective film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. By coating the protective film with a resin solution containing fine particles, a function as a diffusion film can be imparted. Moreover, the function as an optical compensation film can be provided by coating and aligning liquid crystalline compounds, such as a discotic liquid crystalline compound, on said protective film. Also, using an appropriate adhesive, brightness enhancement films such as trade name: DBEF (manufactured by 3M), trade names: viewing angle improving films such as WV film (manufactured by Fuji Photo Film Co., Ltd.), trade name : A commercially available optical functional film such as a retardation film such as Sumikalite (registered trademark) (manufactured by Sumitomo Chemical Co., Ltd.) may be directly bonded to the polarizing film.

  Further, by laminating at least one selected from the above-mentioned polarizing plate having a protective film bonded on at least one side thereof, a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective plate, an optical laminate. Can be manufactured.

  Furthermore, the polarizing film manufactured by this embodiment can be used for a liquid crystal display device etc. as a polarizing film etc. laminated | stacked on a liquid crystal cell base | substrate, In addition to a liquid crystal display device, an electroluminescent display device, plasma It can be used as a polarizing film in various image display devices such as displays and field emission displays.

  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, and used for liquid crystal display devices, image display devices, and the like. 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 viewing angle compensation, etc. In addition to adhesive layers for laminating other films, polarization conversion elements, reflectors, transflective plates, phase difference plates (including wave plates (λ plates) such as 1/2 and 1/4), viewing angle 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 prevention of sticking and diffusion or antiglare.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example.

Two sheets of polyvinyl alcohol film (Kuraray Vinylon VF-PS # 7500, polymerization degree 2400, saponification degree 99.9 mol% or more) having a thickness of 75 μm and a width of 15 mm are prepared, and the ends of these films are overlapped with each other. Then, bonding was performed on a line extending in the width direction over the entire width of the film with a hot plate heat sealer, and the tensile strength was examined. That is, the line width was set to 1.5 mm and 5 mm as shown in Tables 1, 2, and 3, respectively, and the heat welding temperature and the heat welding time were examined for each line width.
Tensile strength [N] was measured according to JISK7127, using a tensile tester (manufactured by Shimadzu Corporation: AGS-J) for each measurement condition to obtain an average value. The results are shown in Tables 1 and 2.

  As shown in Tables 1 and 2, it can be seen that in any line width, high tensile strength (bonding strength) is obtained by thermal bonding at 200 to 300 ° C. for 1 to 25 seconds. In particular, when the line width was 5 mm and heat-welded for 1 to 5 seconds, and when the line width was 1 to 3 mm and heat-welded for 5 to 20 seconds, high tensile strength (bonding strength) was obtained.

  Further, a tensile test under the conditions of a line width of 1.5 mm (temperature: 250 ° C., time: 10 seconds) between the raw films shown in Table 1 and a line width of 5 mm (temperature: 240 ° C., time: 3 seconds) shown in Table 2. The tensile strength [N] was compared with the tensile strength [N] in the tensile test using the raw film. The results are shown in Table 3. The strength of the raw film was taken as 1, and the absolute strength of each line width was shown.

  As shown in Table 3, it can be seen that the joint has the same strength as the original film.

Two sheets of polyvinyl alcohol (PVA) raw film (made by Kuraray Co., Ltd., polymerization degree 2400) having a thickness of 75 μm and a width of 350 mm are prepared, stacked on top of each other, and using a hot plate heat sealer (width 1.5 mm). And heat-sealed along the width direction at a temperature of 250 ° C. for 15 seconds.
Then, the films connected to each other were subjected to stretching treatment, and the success rate [%] of insertion of the connected films into a roll was measured by changing the stretching ratio. The results are shown in Table 4.

  From the results of Table 4, it was confirmed that the film can be inserted into the stretching roll without being broken by welding the raw materials using a hot plate heat sealer.

Claims (11)

  While continuously feeding the polyvinyl alcohol-based raw film wound in a roll shape, the film is stretched in the longitudinal direction in the movement path, and the rear end portion of the fed original film and the next original film A polarizing film manufacturing method in which a polarizing film is continuously manufactured by bonding the leading edge of the film, wherein the bonding overlaps the trailing edge of the original film and the leading edge of the next original film. A method for producing a polarizing film, which is performed by heat welding at a temperature of 200 to 300 ° C.   The method for producing a polarizing film according to claim 1, wherein the joining is performed using a hot plate heat sealer.   The method for producing a polarizing film according to claim 1 or 2, wherein the bonding is formed by heat welding at 200 to 300 ° C for 1 to 25 seconds.   The method for producing a polarizing film according to any one of claims 1 to 3, wherein the joining portion formed by the thermal welding has a linear shape with a line width of 1 to 7 mm extending in the width direction of the film.   The line width of the said junction part is 3-7 mm, and the manufacturing method of the polarizing film of Claim 4 formed by heat-welding this junction part at 200-300 degreeC for 1 to 5 seconds.   The line width of the said junction part is 1-3 mm, and the manufacturing method of the polarizing film of Claim 4 formed by heat-welding this junction part at 200-300 degreeC for 5 to 20 seconds.   The polarizing plate obtained by bonding a protective film on the at least single side | surface of the polarizing film obtained by the method of Claims 1-6.   The polarizing plate according to claim 7, wherein the protective film has a function of any one of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film.   An optical laminate comprising the polarizing plate according to claim 7 and at least one selected from a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film.   A liquid crystal display device comprising the polarizing plate according to claim 7.   An image display device comprising the polarizing plate according to claim 7.