JP2014197050A - Production method of polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a polarizing plate which exhibits excellent productivity in a swelling process applied to a roll film comprising a polyvinyl alcohol resin and having 10 to 60 μm thickness, suppresses uneven film thickness or generation of wrinkles, and has excellent appearance.SOLUTION: When a swelling process is carried out in a plurality of swelling process tanks, a process temperature and a process time in each tank are controlled in such a manner that an expansion coefficient in a film width direction in a first swelling process tank is 90% or less of the saturated expansion coefficient at the process temperature, and that a difference in an absolute value between the expansion coefficient in the first swelling process tank and an expansion coefficient in the film width direction in a subsequent second swelling process tank is within 2 points. When the swelling process is carried out in a single swelling process tank, a process temperature and a time for passing the film in the process tank are controlled in such a manner that an expansion coefficient in the film width direction in the swelling process tank is 90% or less of the saturated expansion coefficient at the process temperature, and that a difference in an absolute value between the expansion coefficient in the swelling process tank and an expansion coefficient in the film width direction in a subsequent dye process tank is within 2 points.

Description

  The present invention relates to a method for producing a polarizing film for use in a liquid crystal display device.

  Conventionally, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film has been used. That is, an iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic dye as a dichroic dye, and the like are known. These polarizing films are usually used as polarizing plates by attaching a protective film such as triacetyl cellulose via an adhesive made of an aqueous solution of a polyvinyl alcohol-based resin on at least one side, preferably both sides thereof. Used in liquid crystal display devices such as monitors and mobile phones.

  The polarizing film is produced by subjecting the polyvinyl alcohol resin film to swelling treatment, dyeing treatment, stretching treatment, boric acid treatment (crosslinking treatment) and washing treatment, and finally drying. This stretching process is usually performed by using a pair of nip rolls and changing the rotational peripheral speed of the nip rolls.

  In recent years, the market tends to require high display quality in addition to the increase in size and thickness of liquid crystal display devices. With this trend, widening and thinning of polarizing films, for example, excellent optical characteristics over the entire area of large polarizing films There is also a need for a manufacturing method that can achieve high performance such as in-plane uniformity. In order to produce a large polarizing film, it is necessary to uniformly uniaxially stretch a wide original film. However, when using a wide original film, it is difficult to uniformly swell or uniaxially stretch compared to the conventional original film, so the light absorption axes of the obtained polarizing film are not aligned in a certain direction. In particular, optical performance such as polarization performance tends to deteriorate. In addition, the thickness of the film becomes non-uniform, and the uniformity of optical performance such as transmittance in the film surface also tends to deteriorate. An image display device to which such a polarizing film is applied has a problem that unevenness occurs in display and the image quality deteriorates. Therefore, development of a method for producing a polarizing film having the requirements for the polarizing film as described above and excellent in productivity has been performed.

  For example, in Japanese Patent No. 4229932 (Patent Document 1), a plurality of swelling treatment tanks are provided, and the bath temperature of the swelling treatment tank located on the front side of them is set to be higher than the bath temperature of the swelling treatment tank located behind. In addition, a method for producing a polarizing film is disclosed in which a high-quality polarizing film in which color unevenness is suppressed can be produced in a short time by setting a higher value. According to this manufacturing method, since the expansion amount of the resin film reaches saturation in a short time, the film is less likely to swell in the subsequent dyeing process, and color unevenness of the polarizing film due to this is suppressed. On the other hand, just by increasing the bath temperature of the swelling treatment tank located earlier as in Patent Document 1, the film rapidly swells due to the high treatment temperature, the film thickness becomes uneven, or the next swelling Depending on the temperature of the treatment bath, there is a problem that the film further swells, wrinkles are generated in the film, and the appearance deteriorates.

Japanese Patent No. 4229932 (Japanese Patent Laid-Open No. 2006-65309)

  An object of the present invention is excellent in productivity, and is excellent in appearance by suppressing unevenness of film thickness and generation of wrinkles in each treatment applied to a raw film made of polyvinyl alcohol resin, particularly in a swelling treatment. It is providing the manufacturing method of a polarizing film.

  As a result of intensive studies, the inventor applied a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment in this order to a raw film made of a polyvinyl alcohol resin in this order. The thickness of the film is 10 to 60 μm, and when the original film is passed through a plurality of swelling treatment tanks and subjected to the swelling treatment, the film in the first swelling treatment tank through which the original film passes first The first swelling treatment tank so that the expansion coefficient in the width direction is within a predetermined range, and the difference between the expansion coefficient and the expansion coefficient in the width direction of the film in the subsequent second swelling treatment tank is within the predetermined range. In addition, by adjusting the treatment temperature of the second swelling treatment tank and the time for passing through the treatment tank, even if the raw film is thin, the swelling of the film and the generation of wrinkles due to this are suppressed. In The present inventors have found that a film having a good appearance can be obtained efficiently. When a polarizing film is produced by subjecting a raw film made of polyvinyl alcohol resin to a swelling process, a dyeing process, a boric acid process, and a washing process in this order, the thickness of the original film is 10 to 60 μm. Yes, when the raw film passes through one swelling treatment tank and is subjected to swelling treatment, the expansion coefficient in the width direction of the film in the swelling treatment tank is within a predetermined range, and this expansion coefficient and subsequent dyeing By adjusting the treatment temperature of the swelling treatment tank and the dyeing treatment tank and the time for passing through the treatment tank so that the difference from the expansion coefficient in the width direction of the film in the treatment tank is within a predetermined range, the original film is thin. Even in this case, it has been found that uneven swelling of the film and generation of wrinkles due to this can be suppressed, and a film having a good appearance can be obtained efficiently. The present invention has been completed based on such findings.

  That is, according to the present invention, a method for producing a polarizing film by subjecting an original film made of polyvinyl alcohol resin to a swelling process, a dyeing process, a boric acid process, and a washing process in this order. The above-mentioned swelling treatment is made to pass through a plurality of swelling treatment tanks including at least a first swelling treatment tank and a second swelling treatment tank in order from the side on which the raw film enters. Applied, the expansion coefficient in the width direction of the film in the first swelling treatment tank is 90% or less of the saturation expansion coefficient when immersed in the treatment liquid at the same temperature, and the film width direction in the first swelling treatment tank The first swelling treatment tank and the second swelling treatment tank so that the difference when the expansion coefficient in the width direction of the film in the second swelling treatment tank is expressed as a percentage is within 2 points in absolute value. A method for producing a polarizing film is provided that adjusts the treatment temperature of the second swelling treatment tank and the time for passing through the treatment tank.

  In this method, the treatment temperature of the first swelling treatment tank is 35 to 45 ° C., and the treatment temperature of the second swelling treatment tank is 25 to 35 ° C. lower than the treatment temperature of the first swelling treatment tank. It is preferable. Moreover, in these methods, it is preferable to adjust the processing temperature of the 1st swelling processing tank and the time which passes a processing tank so that the expansion coefficient of the width direction of a polyvinyl alcohol-type resin film may be 15-25%.

  Further, according to the present invention, there is provided a method for producing a polarizing film by subjecting an original film made of polyvinyl alcohol resin to swelling treatment, dyeing treatment, boric acid treatment, and washing treatment in this order. The film has a thickness of 10 to 60 μm, and the above swelling treatment is performed by passing it through one swelling treatment tank, and the expansion coefficient in the width direction of the film in the swelling treatment tank is immersed in a treatment liquid having the same temperature. 90% or less of the saturated expansion coefficient when the film is expanded, and the difference between the expansion coefficient in the width direction of the film in the swelling treatment tank and the expansion coefficient in the width direction of the film in the dyeing treatment tank is expressed as a percentage. The polarizing film manufacturing method is characterized by adjusting the treatment temperature of the swelling treatment tank and the dyeing treatment tank and the time for passing through the treatment tank so as to be within 2 points.

  In this method, the treatment temperature of the swelling treatment tank is 35 to 45 ° C, and the treatment temperature of the dyeing treatment tank is preferably lower than the treatment temperature in the swelling treatment and 25 to 35 ° C. Moreover, in these methods, it is preferable to adjust the treatment temperature of the swelling treatment tank and the time for passing through the treatment tank so that the expansion coefficient in the width direction of the polyvinyl alcohol-based resin film is 15 to 25%.

  According to the method for producing a polarizing film of the present invention, in each treatment performed when producing a polarizing film, particularly swelling treatment, swelling unevenness of the film can be suppressed, and wrinkles and breakage of the film caused by this can be suppressed. Therefore, a polarizing film having an excellent appearance can be obtained efficiently.

  In the present invention, a polarizing film is produced by subjecting an original film made of a polyvinyl alcohol resin to swelling treatment, dyeing treatment, boric acid treatment and washing treatment in this order. And the polarizing film obtained by performing a drying process after a washing process becomes a thing by which wrinkles etc. were suppressed, and is used suitably for a polarizing plate. Hereinafter, the present invention will be described in detail.

[Production method of polarizing film]
Specifically, the polarizing film is one in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin film. The polyvinyl alcohol resin used as a raw material is usually obtained by saponifying a polyvinyl acetate resin. The degree of saponification is usually 85 mol% or more, preferably 90 mol% or more, more preferably 99 mol% or more. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, unsaturated sulfonic acids, vinyl ethers and the like. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000.

  These polyvinyl alcohol resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Usually, as a material for producing a polarizing film, an unstretched film (raw film) of a polyvinyl alcohol-based resin film having a thickness of about 10 to 60 μm, preferably about 12 to 55 μm is used. Industrially, a film having a width of 1500 to 6000 mm is practical. The thickness of the polarizing film obtained by treating the raw film in the order of swelling treatment, dyeing treatment, boric acid treatment (crosslinking treatment) and washing treatment, and finally drying is, for example, about 5 to 25 μm.

  The polarizing film is manufactured by subjecting the raw film made of polyvinyl alcohol resin as described above to solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment and washing treatment, and during the boric acid treatment and as necessary. The film is uniaxially stretched before the boric acid treatment. Uniaxial stretching may be either wet stretching or dry stretching, and is wet stretching when performed during the boric acid treatment and during the swelling treatment or dyeing treatment before the boric acid treatment, and when performed before the swelling treatment, Become. This uniaxial stretching may be performed in one step or in two or more steps, but is preferably performed in a plurality of steps. In addition, a well-known extending | stretching method is employable for the uniaxial stretching of this invention. Examples of the stretching method include inter-roll stretching in which stretching is performed with a difference in peripheral speed between two nip rolls that transport the film, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, and the like.

(Swelling treatment)
The swelling treatment is performed for the purpose of removing foreign substances on the surface of the raw film made of polyvinyl alcohol resin, removing the plasticizer in the film, imparting easy dyeability in the subsequent dyeing treatment, and plasticizing the 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 of the polyvinyl alcohol-based resin film and transparency devitrification do not occur. When the swelling treatment is first performed on the raw film, for example, the film is immersed in a treatment bath having a temperature of about 20 to 50 ° C., preferably 25 to 45 ° C. The immersion time of the film is, for example, about 30 to 300 seconds, preferably 40 to 200 seconds.

  In the swelling treatment, the polyvinyl alcohol-based resin film swells in the width direction, and wrinkles are likely to occur in the film. Therefore, a known widening device such as an expander roll (widening roll), a spiral roll, a crown roll, or a bend bar is used. It is preferable to transport the film while removing wrinkles of the film. This widening device has, for example, a first swelling treatment tank in the case where the later-described swelling treatment is performed in a plurality of treatment tanks and a swelling treatment tank in the case where the swelling treatment is performed in one treatment tank. It is effective to pass through in a high swelling treatment tank.

  In addition, for the purpose of stabilizing the transport of film in the bath, the water flow in the swelling treatment tank is controlled by an underwater shower, or an EPC device (Edge position control device) that detects the edge of the film to prevent meandering. It is also useful to use in combination.

  In the swelling treatment, the film also swells and expands in the film conveyance direction.If the film is not actively stretched, the speed of the conveyance roll such as a nip roll or a guide roll is set to eliminate the slackness of the film in the conveyance direction. It is preferable to take measures to adjust. In addition, when the raw film is subjected to swelling treatment, dyeing treatment and boric acid treatment in this order, uniaxial stretching may be performed in the swelling treatment, and in that case, the draw ratio is about 1.2 to 3 times. The ratio is preferably 1.3 to 2.5 times.

  In the swelling treatment bath, pure water, boric acid (JP-A-10-153709), chloride (JP-A-06-281816), inorganic salts, inorganic acids, alcohols and the like are about 0.01 to An aqueous solution added in the range of 10% by weight can also be used.

  As one embodiment of the present invention, a form in which the swelling treatment is performed through a plurality of steps can be mentioned. In this case, the swelling treatment is performed by passing through a plurality of swelling treatment tanks including at least a first swelling treatment tank and a second swelling treatment tank in order from the side where the raw film enters. The treatment temperature and the time for the film to pass in the first swelling treatment tank and the second swelling treatment tank are appropriately adjusted so that the expansion coefficient in the width direction of the film in each treatment tank falls within a predetermined range.

  Here, the expansion coefficient in the width direction of the film described above will be described. The expansion coefficient in the width direction of the film is the percentage of the expansion amount in the width direction of the film generated by the swelling treatment. Specifically, first, a long raw film made of polyvinyl alcohol resin is cut into a piece having a size of 50 mm in the long direction and 50 mm in the width direction, and the same processing conditions as the swelling treatment tank are applied to the film piece. Apply swelling treatment. Next, the amount of change in the width direction of the film piece before and after the swelling treatment (the length in the width direction after the swelling treatment−the length in the width direction before the swelling treatment) is the length in the width direction at the time of cutting (50 mm). It is divided and expressed as a percentage.

  Therefore, the expansion coefficient in the first swelling treatment tank in the present invention refers to the expansion coefficient when the film piece is subjected to the swelling treatment under the same treatment conditions as in the first swelling treatment tank. . This expansion coefficient is the same as that of the first swelling treatment bath and the time for the film to pass through the first swelling treatment tank in the production apparatus in an aqueous solution set at the same temperature. The film pieces are immersed for the same time in a state where no tension is applied, and the amount of change in the width direction of the film pieces generated at that time is divided by the length (50 mm) in the width direction at the time of cutting, and expressed as a percentage.

  Similarly, the expansion coefficient in the second swelling treatment tank in the present invention refers to the film piece subjected to the swelling treatment under the same treatment conditions as the first swelling treatment tank, and further in the second swelling treatment tank. The expansion coefficient when the swelling treatment is performed under the same treatment conditions as the treatment. This expansion coefficient is the same as that of the second swelling treatment bath, and the film piece subjected to the swelling treatment corresponding to the treatment in the first swelling treatment tank is in an aqueous solution set at the same temperature. The amount of change from the length in the width direction of the film piece at the time of cutting after the film piece is immersed in a state where no tension is applied to the film piece for the same time as the time for the film to pass through the second swelling treatment tank in the production apparatus ( The length in the width direction after the second swelling treatment—the length in the width direction at the time of cutting) is divided by the length in the width direction at the time of cutting (50 mm) and expressed as a percentage.

  In addition, the saturation expansion coefficient referred to in the present invention is a film fragment of 50 mm in the long direction × 50 mm in the width direction cut from the raw film separately from the one used for the calculation of the expansion coefficient in the above-described swelling treatment tank. The expansion rate when immersed in the treatment bath for 10 minutes. The saturation expansion coefficient is the amount of change in the width direction of a film piece that occurs when the film piece is immersed in a treatment bath for 10 minutes in a state where no tension is applied (the length in the width direction after immersion-the length in the width direction before immersion). ) Divided by the length (50 mm) in the width direction at the time of cutting, and expressed as a percentage.

  In the present invention, in one embodiment in which the swelling treatment is performed in a plurality of steps, the expansion coefficient in the width direction of the polyvinyl alcohol-based resin film in the first swelling treatment tank is saturated expansion when immersed in a treatment liquid at the same temperature. The time for passing through the treatment tank is adjusted so as to be 90% or less of the rate. By setting the saturation expansion coefficient to 90% or less, even when the film feed rate is increased, it is not necessary to use a huge production apparatus, and the swelling treatment can be performed efficiently. Further, the expansion coefficient in the width direction of the film in the first swelling treatment tank is preferably 70% or more. If it is less than 70%, it is difficult to uniformly swell the film surface in the swelling treatment, and color unevenness and wrinkles are likely to occur.

  In addition, when the expansion coefficient in the first swelling treatment tank is too small and the expansion coefficient in the second swelling treatment tank is large, the film rapidly swells in the second swelling treatment tank. There is a bias in the expansion coefficient between the end and the center. As a result, wrinkles may occur due to this uneven expansion coefficient when passing through the widening device inside the treatment tank. On the other hand, when the expansion coefficient in the first swelling treatment tank is too large, the film cannot be sufficiently widened by the widening device that passes through the inside of the treatment tank, and wrinkles may occur. Therefore, the difference when the expansion coefficient in the width direction of the film in the first swelling treatment tank described above and the expansion coefficient in the width direction of the film in the second swelling treatment tank are respectively expressed as percentages is within 2 points in absolute value. Thus, it is important to adjust the treatment temperature of the first swelling treatment tank and the second swelling treatment tank and the time for passing through the treatment tank.

  As described above, the first swelling treatment is performed so that the difference when the expansion coefficient in the width direction of the film in the first swelling treatment tank and the second swelling treatment tank is expressed in percentage is within 2 points in absolute value. By adjusting the treatment temperature of the tank and the second swelling treatment tank and the time for passing through the treatment tank, the shortage of treatment in the first swelling treatment tank is suppressed, and the undesired rapid in the second swelling treatment tank Swelling can be suppressed. In addition, by combining the treatment temperature of the first swelling treatment tank and the second swelling treatment tank and the time for passing through the treatment tank, it is possible to suppress the film thickness from becoming non-uniform during swelling. The generation of wrinkles is suppressed, and a polarizing film having good optical properties and appearance can be produced.

  When the swelling treatment is applied through a plurality of swelling treatment tanks, the treatment temperature of the first swelling treatment tank is higher than the treatment temperature of the second swelling treatment tank from the viewpoint of shortening the swelling treatment time. Is preferable, and it is preferable that it is 35-45 degreeC. Moreover, it is preferable that the temperature of a 2nd swelling processing tank is 25-35 degreeC. Furthermore, it is preferable to adjust the treatment temperature of the first swelling treatment tank and the time for passing through the treatment tank so that the expansion coefficient in the width direction of the film in the first swelling treatment tank is 15 to 25%.

  The time for the film to pass through the first swelling treatment tank is 10 to 60 seconds, preferably 15 to 50 seconds. The time for the film to pass through the second swelling treatment tank is also 10 to 60 seconds, preferably 15 to 50 seconds.

  As another embodiment of the present invention, a form in which the swelling treatment is performed in only one swelling treatment tank can be exemplified. In this embodiment, the raw film is taken out of the swelling treatment tank and then conveyed to the dyeing treatment tank. In this case, the treatment temperature and the time for the film to pass in the swelling treatment tank and the dyeing treatment tank are appropriately adjusted so that the expansion coefficient in the width direction of the film in each treatment tank is within a predetermined range. Specifically, as will be described in detail in the following dyeing treatment, the expansion coefficient in the width direction of the film in the swelling treatment tank is 90% or less of the saturation expansion coefficient when immersed in a treatment liquid at the same temperature, and the swelling treatment The swelling treatment tank and the dyeing treatment tank so that the difference when the expansion coefficient in the width direction of the film in the tank and the expansion coefficient in the width direction of the film in the dyeing treatment tank are each expressed in percentage are within two points in absolute value. The processing temperature and the time for passing through the processing tank are adjusted.

(Dyeing process)
The dyeing treatment is performed for the purpose of adsorbing the dichroic dye on the polyvinyl alcohol-based resin film. As the dichroic dye, iodine, a water-soluble dichroic dye, or the like can be used. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as dissolution and devitrification of the polyvinyl alcohol resin film do not occur.

  When iodine is used as the dichroic dye, the treatment bath (dye treatment bath) has, for example, a concentration of iodine / potassium iodide / water by weight ratio of about 0.003 to 0.2 / about 0.1 to 10 / 100 aqueous solution can be used. Instead of this potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added to the treatment bath, it is distinguished from boric acid treatment described later in that it contains iodine. Any dye containing about 0.03 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing treatment bath. The temperature of the treatment bath when immersing the film is about 10 to 45 ° C, preferably 25 to 35 ° C. The immersion time of the film is about 30 to 600 seconds, preferably 30 to 300 seconds.

  When a water-soluble dichroic dye is used as the dichroic dye, an aqueous solution having a concentration of dichroic dye / water = about 0.001 to 0.1 / 100 by weight can be used for the treatment bath. . This treatment bath may contain a dyeing assistant and the like, and examples thereof include inorganic salts such as sodium sulfate, surfactants and the like. The dichroic dye may be used alone or in combination of two or more dichroic dyes. The temperature of the treatment bath when dipping the film is about 20 to 80 ° C., preferably 25 to 70 ° C., and the dipping time of the film is about 30 to 600 seconds, preferably 30 to 300 seconds.

  When a polyvinyl alcohol resin film is processed in the order of swelling treatment, dyeing treatment, and boric acid treatment, the film is usually stretched by dyeing treatment. This stretching process is performed by a method of giving a difference in peripheral speed between the pair of nip rolls. The total draw ratio up to the dyeing process (the draw ratio in the dyeing process when no drawing process is performed before the dyeing process) is usually 1.6 to 4.5 times, preferably about 1.8 to 4 times. is there. When the cumulative stretching ratio until the dyeing treatment is less than 1.6 times, the film is frequently broken and tends to deteriorate the yield.

  In the dyeing process, as in the swelling process, it is preferable to convey the film while stretching the wrinkles of the film using a known widening device such as an expander roll, a spiral roll, a crown roll, or a bend bar.

  In the present invention, when the swelling treatment is performed in only one swelling treatment tank, the treatment in the swelling treatment tank and the dyeing treatment tank so that the expansion coefficient in the width direction of the film in each treatment tank is within a predetermined range. The temperature and the time for the film to pass through are appropriately adjusted.

  The expansion coefficient in the width direction of the film can be obtained in the same manner as the expansion coefficient in the width direction of the film in the first swelling treatment tank described above, and a film fragment obtained by cutting the raw film in the same manner as described above. Can be calculated from the amount of change in the width direction of the film fragments generated at this time and the length in the width direction at the time of cutting. The expansion coefficient and saturation expansion coefficient in the swelling treatment tank can also be obtained by the same method as the expansion coefficient and saturation expansion coefficient in the first swelling treatment tank described above.

  The expansion coefficient in the dyeing tank is the expansion coefficient when the film pieces subjected to the swelling process under the same processing conditions as the swelling tank are further processed under the same processing conditions as the dyeing tank. It can obtain | require similarly to the expansion coefficient in a 2 swelling processing tank. Specifically, the film piece subjected to the swelling treatment under the same treatment conditions as the swelling treatment tank is the same time as the film passes through the dyeing treatment tank in an aqueous solution set to the same composition and temperature as the dyeing treatment bath. The amount of change from the length in the width direction of the film piece at the time of cutting after being immersed in a state in which no tension is applied to the film piece (length in the width direction after dyeing process−length in the width direction at the time of cutting) , Divided by the length in the width direction at the time of cutting, and expressed as a percentage.

  In the present invention, in another embodiment in which the swelling treatment is performed only in one swelling treatment tank, the expansion coefficient in the width direction of the film in the swelling treatment tank is 90% of the saturation expansion coefficient when immersed in a treatment liquid at the same temperature. The time for passing through the treatment tank is adjusted so as to be not more than%. By setting the saturation expansion coefficient to 90% or less, even when the film feed rate is increased, it is not necessary to use a huge apparatus, and the swelling treatment can be performed efficiently. Moreover, the expansion coefficient in the width direction of the film in the swelling treatment tank is preferably 70% or more. If it is less than 70%, it is difficult to uniformly swell the film surface in the swelling treatment, and color unevenness and wrinkles are likely to occur.

  In addition, when the expansion rate in the swelling treatment tank is too small and the expansion rate in the dyeing treatment tank is large, the film swells rapidly in the dyeing treatment tank, so there is a bias in the expansion rate between the end and the center of the film. Arise. As a result, wrinkles may occur due to this uneven expansion coefficient when passing through the widening device inside the treatment tank. On the other hand, when the expansion coefficient in the swelling treatment tank is too large, the film cannot be sufficiently widened by a widening device that passes through the inside of the treatment tank, and wrinkles may occur. Therefore, swelling is performed so that the difference when the expansion coefficient in the width direction of the film in the swelling treatment tank and the expansion coefficient in the width direction of the film in the dyeing treatment tank are expressed as percentages is within two points in absolute value. It is important to adjust the treatment temperature of the treatment tank and the dyeing treatment tank and the time for passing through the treatment tank.

  In the present invention, the swelling treatment is performed so that the difference when the expansion coefficient in the width direction of the film in the swelling treatment tank and the expansion coefficient in the width direction of the film in the dyeing treatment tank are each expressed in percentage are within the above-described range. By adjusting the processing time of the tank and the dyeing tank and the time of passing through the processing tank, insufficient treatment in the swelling tank can be suppressed, and undesired rapid swelling in the dyeing tank can be suppressed. In addition, by combining the treatment temperature of the swelling treatment tank and the dyeing treatment tank with the time for passing through the treatment tank, it is possible to prevent the film thickness from becoming non-uniform at the time of swelling. Is suppressed, and a polarizing film with good optical properties and appearance can be produced.

  At this time, from the viewpoint of shortening the swelling treatment time, the temperature is preferably as high as possible within a range in which the film does not dissolve, and the treatment temperature of the swelling treatment tank is preferably 35 to 45 ° C. Moreover, it is preferable that the temperature of a dyeing | staining processing tank is 25-35 degreeC. Furthermore, it is preferable to adjust the treatment temperature of the swelling treatment tank and the time for passing through the treatment tank so that the expansion coefficient in the width direction of the film in the swelling treatment tank is 15 to 25%.

(Boric acid treatment)
The boric acid treatment is performed for the purpose of water resistance by cross-linking and hue adjustment (preventing blue and reddish film colors). In the treatment bath, an aqueous solution containing about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water is used. When the dichroic dye used in the dyeing treatment is iodine, iodide is added to water in addition to boric acid. It is preferable to contain 1-30 weight part with respect to 100 weight part. Examples of iodide include potassium iodide, sodium iodide, zinc iodide and the like. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist. In addition, boric acid treatment for water resistance may be referred to by names such as cross-linking treatment, water resistance treatment, and immobilization treatment, and boric acid treatment for hue adjustment may be complementary color treatment, toning treatment, etc. Sometimes called by name.

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

  When the raw film made of polyvinyl alcohol resin is subjected to swelling treatment, dyeing treatment, and boric acid treatment in this order, and the purpose of boric acid treatment is to make the water resistant by crosslinking, the treatment bath is The concentration may be an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100 by weight. As needed, it may replace with boric acid and may use crosslinking agents, such as a glyoxal and glutaraldehyde, and may use boric acid and a crosslinking agent together. The temperature of the treatment bath is usually about 50 to 70 ° C., preferably 55 to 65 ° C., and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds. is there. Moreover, when performing a dyeing process and a boric acid process in this order with respect to the polyvinyl alcohol-type resin film previously extended | stretched, the temperature of a boric-acid treatment bath is about 50-85 degreeC normally, Preferably it is 55-80 degreeC.

  After the boric acid treatment for water resistance, boric acid treatment for hue adjustment may be performed. For example, when the dichroic dye is iodine, the treatment bath can be an aqueous solution having a concentration of boric acid / iodide / water = 1 to 5/3 to 30/100 by weight ratio. The temperature of the treatment bath is usually about 10 to 45 ° C., and the immersion time of the film is usually about 10 to 300 seconds, preferably 10 to 100 seconds.

  These boric acid treatments may be performed a plurality of times, such as boric acid treatment for water resistance and boric acid treatment for hue adjustment. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above range. Moreover, you may perform the boric-acid process for water resistance, and the boric-acid process for hue adjustment in a some process, respectively.

(Cleaning process)
The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine attached to the polyvinyl alcohol-based resin film after the boric acid treatment. In this cleaning treatment, for example, a polarizing film subjected to boric acid treatment for water resistance and / or color tone adjustment is immersed in water, water is sprayed by a shower, or both are used in combination. Is done. The temperature of water in the washing treatment is usually about 2 to 40 ° C., and the treatment time is preferably about 5 to 120 seconds.

(Drying process)
After the washing treatment, the polarizing film can be produced by drying the polyvinyl alcohol resin film. The drying treatment is performed in a drying furnace at a temperature of about 40 to 100 ° C. for a time of about 60 to 600 seconds.

The final integrated draw ratio of the polarizing film thus produced is usually about 4.5 to 7 times, preferably about 5 to 6.5 times.
(Other processing)

  Moreover, processes other than those described above can be added for other purposes. Examples of treatments that can be added include immersion treatment in an aqueous iodide solution that does not contain boric acid (iodide treatment), immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride, etc. Zinc treatment).

[Production method of polarizing plate]
Thus, the polarizing plate which is a laminated body of a polarizing film and a protective film is formed by bonding a protective film on the at least single side | surface of the manufactured polarizing film using an adhesive agent. Examples of protective films include acetyl cellulose resin films such as triacetyl cellulose, cycloolefin resin films, cycloolefin copolymer resin films, polyester resin films such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. , Polycarbonate resin films, acrylic resin films such as polymethylmethacrylate, acyclic olefin resin films such as polypropylene and polyethylene, and the like.

  In order to improve the adhesiveness between the adhesive and the polarizing film and / or the protective film, the bonding surface of the polarizing film and / or the protective film is subjected to corona treatment, plasma treatment, flame treatment, ultraviolet treatment, primer treatment, Surface treatment such as saponification treatment, solvent treatment by solvent application and drying can also be applied.

  Instead of these protective films, a stretched film of thermoplastic resin or an optical compensation film in which a liquid crystal compound is oriented in a thermoplastic resin can be bonded to a polarizing film via an adhesive. Known stretched films of these thermoplastic resins and optical compensation films in which a liquid crystal compound is oriented in a thermoplastic resin can be used as appropriate.

  The adhesive used for laminating the polarizing film and the protective film is not particularly limited as long as it can join the polarizing film and the protective film, but an adhesive satisfying a sufficient adhesive force and transparency is selected. From these points, an ultraviolet curable adhesive is preferably used for bonding a polarizing film and a protective film. In addition, the polarizing film and the acetylcellulose-based resin film are bonded to each other in addition to the above-mentioned ultraviolet curable resin, an aqueous adhesive, for example, an aqueous solution of a polyvinyl alcohol-based resin, an aqueous solution in which a crosslinking agent is mixed, and a urethane-based resin. An emulsion adhesive or the like can be used.

  The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photo radical polymerization initiator, a mixture of an epoxy compound and a photo cationic polymerization initiator, or the like. Alternatively, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photo cationic polymerization initiator and a photo radical polymerization initiator may be used in combination as an initiator.

  When an ultraviolet curable adhesive is used, the adhesive is cured by irradiating ultraviolet rays after laminating the films. The ultraviolet light source is not particularly limited, but preferably has a light emission distribution at a wavelength of 400 nm or less, specifically, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, microwave excitation. Mercury lamps and metal halide lamps are preferably used.

The light irradiation intensity for curing the ultraviolet curable adhesive is appropriately determined depending on the composition of the adhesive and is not particularly limited, but the irradiation intensity in the wavelength region effective for activating the polymerization initiator is 0.1 to 6000 mW / It is preferable to be cm ² . By appropriately selecting the irradiation intensity from this range, the reaction time does not become too long, and the yellowing of the adhesive and the deterioration of the polarizing film due to the heat radiated from the light source and the heat generated when the adhesive is cured are suppressed Can do. The light irradiation time is also selected according to the adhesive to be cured and is not particularly limited. However, the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 10,000 mJ / cm ^2. It is preferable to set as follows.

  By appropriately selecting the integrated light amount from this range, a sufficient amount of active species derived from the polymerization initiator can be generated, the curing reaction can proceed reliably, and the irradiation time can be shortened, thus maintaining good productivity. it can. And when it is a laminated film including a polarizing film and a protective film, and the ultraviolet curable adhesive is cured by irradiation with ultraviolet rays, the polarization degree, transmittance and hue of the polarizing film, and transparency of the protective film, etc. It is preferable to perform the curing under conditions that do not reduce the various functions.

  Moreover, when using an aqueous adhesive, for example, apply the adhesive uniformly on the surface of the film or pour it between two films, overlap the two films via the coating layer, and bond them with a roll or the like. Then, a drying method can be adopted. After drying, it may be further cured at room temperature or slightly higher temperature, for example, about 20 to 45 ° C.

  The thickness of the above adhesive layer is appropriately selected from the range of about 0.001 to 5 μm depending on the type of adhesive and the combination of two films to be bonded. The thickness is preferably 0.01 μm or more, and preferably 2 μm or less.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not restrict | limited by these Examples. Moreover, the expansion coefficient of the width direction of the polyvinyl alcohol film in the following examples was measured by the following method.

<Measurement of expansion coefficient>
The expansion coefficient of the film was calculated from the amount of change in the width direction of the film before and after the immersion in the swelling treatment tank or the dyeing treatment tank to be measured. First, a film piece was prepared by cutting a long polyvinyl alcohol film (raw film) used in each of the examples and comparative examples described below into a size of 50 mm in the long direction and 50 mm in the width direction. Next, the film piece was immersed in the treatment liquid having the same composition as the treatment bath for measuring the expansion coefficient at the same temperature as the actual treatment and for the same time as the film passed through the treatment tank. . This immersion was performed in a state where no tension was applied to the film. Thereafter, the film is taken out from the processing solution, and the changed length in the width direction of the film before and after the processing with respect to the length in the width direction at the time of cutting (length after processing−length at the time of cutting 50 mm) is obtained, and the percentage is obtained. Expressed in The length of the film after the treatment was measured using a commercially available digital caliper [manufactured by Mitutoyo Corporation, “Coolant Digimatic caliper CD-15PSX”], and the dimensions of the polyvinyl alcohol film immediately after being taken out of the water tank were measured.

[Example 1]
Prepare a long polyvinyl alcohol film [trade name “Kuraray Poval Film VF-PE # 6000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more] having a thickness of 60 μm, and swelling treatment As a second swelling treatment tank containing pure water at 30 ° C. after being immersed in a first swelling treatment tank containing 37 ° C. pure water for 40 seconds while maintaining a tension state so that the film does not loosen The film was immersed for 20 seconds. At this time, in the 1st swelling processing tank, the film was conveyed through the expander roll. Next, uniaxial stretching is performed up to 2.2 times while immersing in a dyeing bath containing a 30 ° C. aqueous solution containing iodine and potassium iodide as a dyeing treatment, and the weight of potassium iodide / boric acid / water is weight. The film was immersed in a cross-linking bath containing a 55 / C aqueous solution having a ratio of 12 / 4.4 / 100 and subjected to water resistance treatment, and uniaxial stretching was performed until the cumulative draw ratio from the original fabric became 5.5 times. . Subsequently, after immersing in a complementary color treatment bath containing 40 ° C. boric acid aqueous solution, it is immersed in a washing treatment bath containing 12 ° C. pure water, and then dried at 70 ° C. for 3 minutes in a drying furnace to obtain a polarizing film. Was made. In the swelling treatment, no generation of wrinkles was observed, and no breakage of the film was observed.

(A) Saturation expansion coefficient in the first swelling treatment tank The polyvinyl alcohol film “Kuraraypoval film VF-PE # 6000” used in Example 1 was cut into a size of 50 mm in the long direction × 50 mm in the width direction. The expansion coefficient when immersed in a water tank (corresponding to the first swelling treatment tank) containing pure water at 37 ° C. for 10 minutes was defined as the saturation expansion coefficient, which was obtained. After immersion, the length of the film piece in the width direction was 62.70 mm. From the amount of change in length by immersion with respect to the length in the width direction before immersion, the saturation expansion coefficient in the first swelling treatment tank was set to 25.4%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank Separately prepare the same film fragment cut in the above (A), which is treated in the first swelling treatment tank of Example 1 Similarly, the expansion coefficient when immersed in a water tank containing pure water at 37 ° C. for 40 seconds was defined as the expansion coefficient in the first swelling treatment tank. After immersion, the length of the film piece in the width direction was 61.00 mm. From the amount of change in length in the first swelling treatment tank relative to the length in the width direction before immersion, the expansion coefficient in the width direction of the film in the first swelling treatment tank was 22.0%. Moreover, this expansion coefficient was 86.6% with respect to the saturation expansion coefficient of said (A). In Table 1 below, the expansion coefficient of the first swelling treatment tank is in the column of “Expansion coefficient 1”, and the expansion coefficient of the first swelling treatment tank relative to the saturation expansion coefficient is the column of “Expansion coefficient 1 / saturation expansion coefficient”. Respectively.

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank The same treatment as in the second swelling treatment tank is performed on the film piece subjected to the same treatment as in the first swelling treatment tank in (B) above. In order to apply, this was further immersed in a water tank containing pure water at 30 ° C. for 20 seconds. After immersion, the length of the film piece in the width direction was 60.60 mm. From the amount of change in length in the second swelling treatment tank with respect to the length in the width direction of the film piece at the time of cutting, the expansion ratio in the width direction of the film in the second swelling treatment tank was 21.2%. Moreover, the difference with the expansion coefficient of the width direction of the film in the said 1st swelling processing tank of (B) was -0.8 point. In Table 1 below, the expansion rate of the second swelling treatment tank is indicated in the column of “Expansion rate 2”, and the difference in expansion rate between the first swelling treatment tank and the second swelling treatment tank is indicated as “Expansion rate difference”. Each is shown in the column.

[Example 2]
A 50 μm-thick polyvinyl alcohol film (trade name “Kuraray Poval Film VF-PE # 5000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) was used for the raw film. A polarizing film was produced in the same manner as in Example 1 except that the swelling treatment in the first swelling treatment tank was changed to be immersed in pure water at 35 ° C. for 30 seconds. In the swelling treatment, no generation of wrinkles was observed, and no breakage of the film was observed.

(A) Saturation expansion coefficient in the first swelling treatment tank A film piece is cut from the polyvinyl alcohol film “Kuraray Poval Film VF-PE # 5000” used in Example 2, and the temperature of pure water in the water tank is set to 35 ° C. The saturated expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 1 (A) except that the change was made. After immersion, the length of the film piece in the width direction was 62.10 mm. From the amount of change in length by immersion with respect to the length in the width direction before immersion, the saturation expansion coefficient in the first swelling treatment tank was set to 24.2%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank The same film fragment as that cut in Example 2 (A) was prepared separately, and it was used in the first swelling treatment tank in Example 2. Similarly to the treatment, it was immersed in a water tank containing 35 ° C. pure water for 30 seconds to obtain the expansion coefficient in the first swelling treatment tank. After immersion, the width of the film piece in the width direction was 60.45 mm. It was 20.9% as a result of calculating | requiring the expansion coefficient of the width direction of the film in a 1st swelling processing tank like Example 1 (B). Moreover, this expansion coefficient was 86.4% with respect to the saturation expansion coefficient of said (A).

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank The same treatment as in the second swelling treatment tank is performed on the film piece subjected to the same treatment as in the first swelling treatment tank in (B) above. In order to apply, this was further immersed in a water tank containing pure water at 30 ° C. for 20 seconds. After immersion, the length of the film piece in the width direction was 60.50 mm. As a result of obtaining the expansion coefficient in the width direction of the film in the second swelling treatment tank in the same manner as in Example 1 (C), it was 21.0%. Moreover, the difference with the expansion coefficient of the width direction of the film in the said 1st swelling processing tank of (B) was +0.1 point.

Example 3
A 60 μm-thick polyvinyl alcohol film (trade name “Kuraray Poval Film VF-PE # 6000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) was used for the raw film. As the swelling treatment, the film was immersed in a swelling treatment tank containing pure water at 37 ° C. for 40 seconds while maintaining the tension state so that the film did not loosen. At this time, in the swelling processing tank, the film was conveyed via an expander roll. Next, as a dyeing treatment, uniaxial stretching is performed up to 2.2 times while immersing in a dyeing treatment tank containing a 30 ° C. aqueous solution containing iodine and potassium iodide for 60 seconds, and the weight ratio of potassium iodide / boric acid / water is The film was immersed in a crosslinking treatment tank containing a 55 ° C. aqueous solution of 12 / 4.4 / 100 and subjected to water resistance treatment, and uniaxial stretching was performed until the cumulative draw ratio from the raw material became 5.5 times. . Subsequently, after immersing in a complementary color treatment tank containing a 40 ° C. boric acid aqueous solution, it is immersed in a washing treatment tank containing 12 ° C. pure water, followed by drying at 70 ° C. for 3 minutes in a drying furnace. Manufactured. In the swelling treatment and dyeing treatment, no wrinkles were observed and no film breakage was observed.

(A) Saturation expansion rate in the swelling treatment tank The swelling treatment tank was obtained in the same manner as in Example 1 (A) except that the film piece was cut from the polyvinyl alcohol film “Kuraray Poval Film VF-PE # 6000” used in Example 3. The saturation expansion coefficient at was determined. After immersion, the length of the film piece in the width direction was 62.70 mm. From the amount of change in length by immersion with respect to the length in the width direction before immersion, the saturation expansion coefficient in the swelling treatment tank was set to 25.4%.

(B) Expansion coefficient in the width direction of the film in the swelling treatment tank Separately prepared is the same film fragment cut in the above (A), and the same as the treatment in the swelling treatment tank of Example 3 was performed at 37 ° C. It was immersed in a water tank containing water for 40 seconds, and the expansion coefficient in the swelling treatment tank was determined. After immersion, the length of the film piece in the width direction was 61.00 mm. The expansion coefficient in the width direction of the film in this swelling treatment tank was determined in the same manner as in Example 1 (B), and as a result, it was 22.0%. Moreover, this expansion coefficient was 86.6% with respect to the saturation expansion coefficient of said (A). In Table 1 below, the expansion coefficient of the swelling treatment tank is shown in the column of “Expansion coefficient 1”, and the expansion coefficient of the swelling treatment tank relative to the saturation expansion coefficient is shown in the column of “Expansion coefficient 1 / saturation expansion coefficient”.

(C) Expansion coefficient in the width direction of the film in the dyeing treatment tank The same composition as the dyeing treatment bath is applied to the film pieces subjected to the same treatment as the swelling treatment tank in (B) above, in order to perform the same treatment as in the dyeing treatment tank. And was immersed for 60 seconds in a water bath containing an aqueous solution having the same temperature (30 ° C.). After immersion, the length of the film piece in the width direction was 60.85 mm. From the amount of change in length in the dyeing tank relative to the length in the width direction of the film piece at the time of cutting, the expansion coefficient in the width direction of the film in the dyeing tank was 21.7%. Moreover, the difference with the expansion coefficient of the width direction of the film in the swelling processing tank of the said (B) was -0.3 point. In Table 1 below, the expansion rate of the dyeing treatment tank is shown in the column of “Expansion rate 2”, and the difference in expansion rate between the swelling treatment tank and the dyeing treatment vessel is shown in the column of “Expansion coefficient difference”.

[Comparative Example 1]
A polarizing film was produced in the same manner as in Example 1 except that the immersion time of the film in the first swelling treatment tank was changed to 10 seconds. Wrinkles occurred in the first swelling treatment tank and the second swelling treatment tank, and the film was frequently cut during stretching. Moreover, when the external appearance of the obtained polarizing film was confirmed, wrinkles were seen.

(A) Saturation expansion coefficient in the first swelling treatment tank The saturation expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 1 (A). The length of the film piece in the width direction after immersion was 62.70 mm, and the saturation expansion coefficient was 25.4%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank Except that the immersion time was changed to 10 seconds, the expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 1 (B). . After immersion, the width of the film piece in the width direction was 55.35 mm, and the expansion rate was 10.7%. Moreover, this expansion coefficient was 42.1% with respect to the saturation expansion coefficient of said (A).

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank Example 1 (except that the film piece used was changed to the one subjected to the same treatment as the first swelling treatment tank in (B) above. The same treatment as in C) was performed. After immersion, the length in the width direction of the film piece was 58.20 mm, and the expansion coefficient in the width direction of the film in the second swelling treatment tank was 16.4%. Moreover, the difference with the expansion coefficient of the width direction of the film in the 1st swelling processing tank of said (B) was +5.7 point.

[Comparative Example 2]
A polarizing film was produced in the same manner as in Example 2 except that the immersion time of the film in the first swelling treatment tank was changed to 10 seconds. Moreover, wrinkles were generated in the first swelling treatment tank and the second swelling treatment tank, and the film was frequently cut during stretching. When the appearance of the obtained polarizing film was confirmed, wrinkles were observed.

(A) Saturation expansion coefficient in the first swelling treatment tank The saturation expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (A). The length of the film piece in the width direction after the immersion was 62.10 mm, and the saturation expansion coefficient was 24.2%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank Except that the immersion time was changed to 10 seconds, the expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (B). . After immersion, the width of the film piece in the width direction was 56.60 mm, and the expansion rate was 13.2%. Moreover, this expansion coefficient was 54.5% with respect to the saturation expansion coefficient of said (A).

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank Example 1 (except that the film piece used was changed to the one subjected to the same treatment as the first swelling treatment tank in (B) above. The same treatment as in C) was performed. After immersion, the width in the width direction of the film piece was 59.05 mm, and the expansion coefficient in the width direction of the film in the second swelling treatment tank was 18.1%. Moreover, the difference with the expansion coefficient of the width direction of the film in the said 1st swelling processing tank of (B) was +4.9 point.

[Comparative Example 3]
A polarizing film was produced in the same manner as in Example 2 except that the immersion time of the film in the first swelling treatment tank was changed to 100 seconds. Generation | occurrence | production of the wrinkle was not seen in the 1st swelling processing tank and the 2nd swelling processing tank.

(A) Saturation expansion coefficient in the first swelling treatment tank The saturation expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (A). The length of the film piece in the width direction after the immersion was 62.10 mm, and the saturation expansion coefficient was 24.2%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank The expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (B) except that the immersion time was changed to 100 seconds. After immersion, the width of the film piece in the width direction was 61.70 mm, and the expansion rate was 23.4%. Moreover, this expansion coefficient was 96.7% with respect to the saturation expansion coefficient of said (A).

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank Example 1 (except that the film piece used was changed to the one subjected to the same treatment as the first swelling treatment tank in (B) above. The same treatment as in C) was performed. After immersion, the width in the width direction of the film piece was 61.75 mm, and the expansion coefficient in the width direction of the film in the second swelling treatment tank was 23.5%. Moreover, the difference with the expansion coefficient of the width direction of the film in the said 1st swelling processing tank of (B) was +0.1 point.

[Comparative Example 4]
A polarizing film was produced in the same manner as in Example 2 except that the treatment temperature in the first swelling treatment tank was changed to 50 ° C. Since wrinkles were generated in the first swelling treatment tank and the second swelling treatment tank, and the film was frequently cut during stretching, a polarizing film could not be produced.

(A) Saturation expansion coefficient in the first swelling treatment tank The saturation expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (A) except that the temperature of pure water was changed to 50 ° C. The length of the film piece in the width direction after the immersion was 73.10 mm, and the saturation expansion coefficient was 46.2%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank The expansion coefficient in the first swelling treatment tank was obtained in the same manner as in Example 2 (B) except that the temperature of pure water was changed to 50 ° C. It was. After immersion, the width of the film piece in the width direction was 69.30 mm, and the expansion rate was 38.6%. Moreover, this expansion coefficient was 83.5% with respect to the saturation expansion coefficient of said (A).

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank Example 1 (except that the film piece used was changed to the one subjected to the same treatment as the first swelling treatment tank in (B) above. The same treatment as in C) was performed. After immersion, the length in the width direction of the film piece was 67.00 mm, and the expansion coefficient in the width direction of the film in the second swelling treatment tank was 34.0%. Moreover, the difference with the expansion coefficient of the width direction of the film in the said 1st swelling processing tank of (B) was -4.6 points.

[Comparative Example 5]
A polarizing film was produced in the same manner as in Example 2 except that the treatment temperature in the first swelling treatment tank was changed to 20 ° C. Wrinkles occurred in the first swelling treatment tank and the second swelling treatment tank, and the film was frequently cut during stretching. When the appearance of the obtained polarizing film was confirmed, wrinkles were observed.

(A) Saturation expansion coefficient in the first swelling treatment tank The saturation expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (A) except that the temperature of pure water was changed to 20 ° C. The length of the film piece in the width direction after immersion was 59.15 mm, and the saturation expansion coefficient was 18.3%.

(B) Expansion coefficient in the width direction of the film in the first swelling treatment tank Except that the temperature of pure water was changed to 50 ° C., the expansion coefficient in the first swelling treatment tank was determined in the same manner as in Example 2 (B). Asked. After immersion, the width of the film piece in the width direction was 54.45 mm, and the expansion rate was 8.9%. Moreover, this expansion coefficient was 48.6% with respect to the saturation expansion coefficient of said (A).

(C) Expansion coefficient in the width direction of the film in the second swelling treatment tank Example 1 (except that the film piece used was changed to the one subjected to the same treatment as the first swelling treatment tank in (B) above. The same treatment as in C) was performed. After immersion, the length in the width direction of the film piece was 58.05 mm, and the expansion coefficient in the width direction of the film in the second swelling treatment tank was 16.1%. Moreover, the difference with the expansion coefficient of the width direction of the film in the said 1st swelling processing tank of (B) was +7.2 points.

  From Table 1, when Example 1 that satisfies all the provisions of the present invention and Comparative Example 1 that uses the same raw film as Example 1 but does not satisfy the provisions of the present invention are compared, As a result of the film sufficiently swollen in the swelling treatment tank, wrinkles due to the difference in expansion coefficient in the second swelling treatment tank that occurs during production do not occur, and no wrinkles are confirmed in the obtained polarizing film. Whereas the appearance was good, Comparative Example 1 was not sufficiently swollen because the treatment time was short. As a result, wrinkles and film breakage occurred during production, and wrinkles were confirmed even in the obtained polarizing film. It was. In addition, when Example 2 using a thin film film than Example 1 and Comparative Examples 2, 4 and 5 which use the same original film but do not satisfy the provisions of this application are compared, Example 2 Thus, a polarizing film having a good appearance could be produced without causing wrinkles or film breakage during production, whereas in any of the comparative examples, wrinkles or film breakage occurred during production, and the polarized light obtained It was a result that wrinkles were also seen in the film, or breakage occurred frequently and a polarizing film could not be obtained.

  Although Comparative Example 3 can produce a polarizing film with good appearance without producing film wrinkles or breakage during production, the treatment time in the first swelling treatment tank is long, and the production efficiency is higher than that in Example 2. It was low.

  Example 3, which is another embodiment of the present invention, which is an example in which the swelling treatment is performed only in one swelling treatment tank, satisfies all the provisions of the present invention, and the film is sufficiently formed in the swelling treatment tank. As a result of swelling, no wrinkles were generated due to the difference in expansion coefficient in the dyeing process that followed during production, and no wrinkles were observed in the obtained polarizing film, and the appearance was good.

Claims (6)

A method for producing a polarizing film by subjecting an original film made of polyvinyl alcohol resin to swelling treatment, dyeing treatment, boric acid treatment, and washing treatment in this order,
The thickness of the raw film is 10-60 μm,
The swelling treatment is performed by passing a plurality of swelling treatment tanks including at least a first swelling treatment tank and a second swelling treatment tank in order from the side where the raw film enters.
The expansion coefficient in the width direction of the film in the first swelling treatment tank is 90% or less of the saturation expansion coefficient when immersed in a treatment liquid at the same temperature,
The difference when the expansion coefficient in the width direction of the film in the first swelling treatment tank and the expansion coefficient in the width direction of the film in the second swelling treatment tank are each expressed as a percentage so that the absolute value is within 2 points. And adjusting the treatment temperature of the first swelling treatment tank and the second swelling treatment tank and the time for passing through the treatment tank.   The treatment temperature of the first swelling treatment tank is 35 to 45 ° C, and the treatment temperature of the second swelling treatment tank is lower than the treatment temperature of the first swelling treatment and is 25 to 35 ° C. Manufacturing method of the polarizing film.   The polarizing film of Claim 1 or 2 which adjusts the process temperature of the 1st swelling processing tank, and the time which passes a processing tank so that the expansion coefficient of the width direction of a polyvinyl alcohol-type resin film may be 15-25%. Manufacturing method. A method for producing a polarizing film by subjecting an original film made of polyvinyl alcohol resin to swelling treatment, dyeing treatment, boric acid treatment, and washing treatment in this order,
The thickness of the raw film is 10-60 μm,
The swelling treatment is performed by passing through one swelling treatment tank,
The expansion coefficient in the width direction of the film in the swelling treatment tank is 90% or less of the saturation expansion coefficient when immersed in a treatment liquid at the same temperature,
The swelling treatment tank and the difference between the expansion coefficient in the width direction of the film in the swelling treatment tank and the expansion coefficient in the width direction of the film in the dyeing treatment tank expressed as percentages are within 2 points in absolute value. The manufacturing method of the polarizing film characterized by adjusting the processing temperature of a dyeing | staining processing tank, and the time which passes a processing tank.   The method for producing a polarizing film according to claim 4, wherein the treatment temperature of the swelling treatment tank is 35 to 45 ° C, and the treatment temperature of the dyeing treatment tank is lower than the treatment temperature of the swelling treatment and is 25 to 35 ° C.   The manufacturing method of the polarizing film of Claim 4 or 5 which adjusts the processing temperature of a swelling processing tank, and the time which passes a processing tank so that the expansion coefficient of the width direction of a polyvinyl alcohol-type resin film may be 15-25%. .