JP2014142392A - Method of manufacturing polarization film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a polarization film, which is superior in workability and manufacturing efficiency even when using a boric acid treatment bath at a high temperature equal to or higher than 56°C for manufacturing a polarization film comprising a polyvinyl alcohol based resin.SOLUTION: When a treatment bath at a high temperature equal to or higher than 56°C is used in boric acid treatment in the method of manufacturing a polarization film by subjecting a polyvinyl alcohol based resin to dyeing treatment, boric acid treatment, and drying treatment in this order, the film is passed between entrance-side nip rolls installed in the boric acid treatment bath, and then is passed on a plurality of guide rolls installed so as to be vertically movable between the inside and the outside of the boric acid treatment bath so that the film passes on the upper side of at least one guide roll, passes on the lower side of at least another guide roll, finally passes between exit-side nip rolls, and is led out from the boric acid treatment bath. In this state, a plurality of guide rolls arranged on the outside of the boric acid treatment bath are lowered to immerse the film in the boric acid treatment bath, and boric acid treatment is performed while keeping a tension applied to the film constant in the treatment bath.

Description

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

  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 formed into polarizing plates by bonding a protective film made of polyvinyl alcohol resin on at least one side, preferably both sides, with an adhesive made of an aqueous solution of polyvinyl alcohol resin. Used in liquid crystal display devices (LCD) such as personal computer monitors and mobile phones.

  As a method for producing a polarizing film, a nip roll and a guide roll are used, and after the polyvinyl alcohol resin film is immersed in water and swollen, it is dyed with a dichroic dye, stretched, and then iodine is applied to the film. In order to fix, a method is known in which a polyvinyl alcohol resin film is treated with boric acid (crosslinking treatment), washed with water, and then dried.

  For example, in Japanese Patent No. 4323269 (Patent Document 1), when uniaxial stretching is performed on a polyvinyl alcohol-based resin film, hue unevenness is reduced by controlling the tension of the polyvinyl alcohol-based resin film in a process after the stretching process. The invention of a polarizing film is disclosed, and paragraph [0026] of the same document describes that boric acid treatment is performed using a treatment bath at 50 to 70 ° C.

  Thus, the method of performing boric acid treatment using a high-temperature treatment bath is generally performed for the purpose of promoting the crosslinking reaction in the film. For example, in Japanese Patent No. 4086197 (Patent Document 2), conveyance rolls such as a nip roll and a guide roll are installed outside the processing tank so that the polyvinyl alcohol resin film passes through the upper part of the processing tank in advance. A method is disclosed in which the film is dipped in the treatment bath by lowering the conveyance roll into the treatment bath after being conveyed. And it is described that according to this method, workability | operativity and production efficiency at the time of polarizing film manufacture can be improved. In addition, JP 2011-164553 A (Patent Document 3) discloses that a predetermined position is set when a nip roll is installed in a high-temperature boric acid treatment bath and uniaxial stretching is performed using a difference in peripheral speed between the nip rolls. Discloses a method of installing a guide roll made of sponge rubber. And according to this method, it is described that the shrinkage | contraction of the film width by a extending | stretching and the fall of an optical characteristic can be suppressed.

  On the other hand, a polarizing film and a polarizing plate to which the polarizing film is applied are required to be thinner than conventional ones. For example, a polyvinyl alcohol resin film having a thickness of 75 μm is conventionally used as a raw film for a polarizing film. However, in recent years, a polarizing film is also produced from a raw film having a thickness of 60 μm or less. When a manufacturing method such as that described in Patent Document 2 is applied to a thin original film, the wrinkles of the film and the resulting polarizing film are caused by differences in the swelling rate and stretching rate of the film due to the dipping method as compared with the conventional method. There was a tendency for color unevenness to occur. Moreover, in the manufacturing method like patent document 3, although uniform expansion | swelling and extending | stretching of a film are possible, since long-time manual work is needed, putting a hand directly in a hot bath, film immersion There is a problem that the film breaks easily because the time becomes longer and the film swells and softens than expected.

Japanese Patent No. 4323269 (Japanese Patent Laid-Open No. 2005-84505) Japanese Patent No. 4086197 (Japanese Patent Laid-Open No. 2006-126722) JP 2011-164553 A

  The present invention has been made to solve the above-described problems, and the object of the present invention is that workability and production efficiency are good even when a high-temperature boric acid treatment bath of 56 ° C. or higher is used. It is providing the manufacturing method of a polarizing film.

  As a result of intensive studies, the present inventor, in a method for producing a polarizing film from a polyvinyl alcohol-based resin film, uses a treatment bath at a high temperature of 56 ° C. or higher for boric acid treatment. By immersing the film in the treatment bath after passing through the resin film, it was found that excessive swelling and softening of the film can be prevented, and breakage of the film due to this can be suppressed, and the present invention has been completed.

  That is, according to the present invention, a method for producing a polarizing film by subjecting a polyvinyl alcohol resin film to dyeing treatment, boric acid treatment and drying treatment in this order, wherein the boric acid treatment is subjected to a dyeing treatment. The film subjected to the dyeing treatment at this time is passed through an inlet provided in the boric acid treatment bath. The boric acid treatment bath is introduced into the boric acid treatment bath through the side nip roll, contacts the at least one guide roll in the boric acid treatment bath, and passes through the outlet side nip roll also installed in the boric acid treatment bath. The manufacturing method of the polarizing film derived | led-out from is provided.

  In this method, a plurality of guide rolls including the one guide roll described above are installed so that they can be raised and lowered between and outside the boric acid treatment bath, and the film is first introduced into the boric acid treatment bath. In this case, a plurality of guide rolls installed so as to be movable up and down are arranged outside the boric acid treatment bath. Then, after the film leading edge passes through the inlet-side nip roll, it passes through at least one upper side of the plurality of guide rolls arranged outside the boric acid treatment bath, and passes through at least one other lower side. Finally, it passes through the outlet side nip roll so as to be led out from the boric acid treatment bath. In this state, the plurality of guide rolls arranged outside the boric acid treatment bath are lowered to immerse the film in the boric acid treatment bath, and the film is removed while keeping the tension on the film constant in the boric acid treatment bath. Boric acid treatment is performed so as to guide the boric acid treatment bath outlet side nip roll.

  As said polyvinyl alcohol-type resin film, the thickness of the raw film used for a dyeing | staining process can use 1-60 micrometers.

  When the dyed film is passed through the guide roll, the leading end of the film passes above the guide roll that can be moved up and down immediately after the inlet-side nip roll installed in the boric acid treatment bath. It is preferable to pass under the guide roll which can be moved up and down immediately before the exit side nip roll installed therein. In addition, the film subjected to the dyeing treatment should be immersed in the boric acid treatment bath within 20 seconds in a state where the elevating guide roll is disposed outside the boric acid treatment bath. preferable.

  This boric acid treatment bath may be an aqueous solution containing 2 to 4.5 parts by weight of boric acid with respect to 100 parts by weight of water.

  According to the present invention, when a treatment bath having a high temperature and a low concentration of boric acid is used for boric acid treatment as in the prior art, the film breakage can be suppressed, and thus productivity is improved. In particular, even when a thin polyvinyl alcohol-based resin film is employed as the raw fabric film, a polarizing film can be produced without causing the film to break. In addition, since manual operations such as passing a film through a guide roll in a high-temperature treatment bath can be minimized, workability and production efficiency are improved.

  The polarizing film produced according to the present invention has a small amount of shrinkage under high-temperature conditions such as 80 ° C. and 90 ° C., and the polarizing plate bonded to the liquid crystal cell has a small curvature due to heat.

It is a cross-sectional model drawing which shows the suitable example of arrangement | positioning of the apparatus in the manufacturing method of a polarizing film. It is the cross-sectional schematic diagram which showed one Embodiment of the boric acid process prescribed | regulated by this invention. It is the cross-sectional model diagram which showed another embodiment of the boric acid process prescribed | regulated by this invention.

  Hereinafter, the present invention will be described in detail.

[Production method of polarizing film]
The polarizing film produced according to the present invention is a polyvinyl alcohol-based resin film that has been subjected to a stretching treatment and has a dichroic dye adsorbed and oriented. The manufacturing method of the polarizing film of this invention is equipped with the process which performs a swelling process, a dyeing process, a boric-acid process, and a washing process in this order with respect to a polyvinyl alcohol-type resin film. The present invention will be described below with reference to the drawings as appropriate.

  FIG. 1 is a schematic cross-sectional view showing a preferred arrangement example of apparatuses in the method for producing a polarizing film defined in the present invention. Referring to FIG. 1, in this manufacturing apparatus, a raw film 10 made of a polyvinyl alcohol resin is unwound from a feeding roll 11, and a swelling tank 13, a dyeing tank 15, a boric acid treatment tank 17 and a washing tank 19 are provided. It is configured to pass through sequentially and finally through the drying furnace 21. FIG. 1 shows an example in which one swelling tank 13, a dyeing tank 15, a boric acid treatment tank 17, and a washing tank 19 are provided, but if necessary, a plurality of tanks are provided for one treatment. It may be provided.

(Polyvinyl alcohol resin film)
The polyvinyl alcohol resin forming the polyvinyl alcohol resin film used in the present invention 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, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually 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 butyrate and the like can also be used. Usually, as a starting material for producing a polarizing film, an unstretched polyvinyl alcohol-based resin film having a thickness of 1 to 100 μm, preferably 20 to 60 μm is used. A stretched film that has been previously stretched may be used. Industrially, the practical width of the film is 1500 to 6000 mm.

  About the manufacturing method of the polarizing film of this embodiment, a swelling process, a dyeing process, a boric acid process, a washing process, and a drying process are performed using an unstretched polyvinyl alcohol-type resin film (raw film). When using a raw film, a wet or dry stretching process is performed during any of the processes or as a separate process. This stretching process is performed by a known method. Known methods 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, and tenter stretching as described in Japanese Patent No. 2731813. Even when a pre-stretched film is used, a stretching process may be further performed.

(Swelling treatment)
The swelling treatment is performed for the purpose of removing foreign matter on the film surface, removing the plasticizer in the film, imparting easy dyeability in the subsequent dyeing treatment, and plasticizing the film. The conditions for the swelling treatment are determined within a range in which these objects can be achieved and in a range in which defects such as devitrification and extreme dissolution of the film do not occur.

  When first performing a swelling process with respect to the raw film which consists of polyvinyl alcohol-type resin, it is performed by immersing a film in the processing bath of the temperature of about 10-50 degreeC, Preferably about 20-40 degreeC, for example. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds. When the swelling treatment is performed on the polyvinyl alcohol resin film previously stretched in the air, for example, the film is immersed in a treatment bath at a temperature of about 20 to 70 ° C., preferably about 30 to 60 ° C. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

  In the swelling treatment, the polyvinyl alcohol-based resin film swells in the width direction, and problems such as wrinkling of the film are likely to occur. Therefore, widening roll (expander roll), spiral roll, crown roll, cross guider, bend bar, tenter clip, etc. It is preferable to transport the film while removing the wrinkles of the film using a known widening device. Also, for the purpose of stabilizing the film transport in the bath, the water flow in the swelling tank 13 is controlled by an underwater shower, or the EPC device (Edge Position Control device: detects the edge of the film to prevent film meandering) It is also useful to use a combination of such devices.

  In the swelling treatment, the polyvinyl alcohol-based resin film swells and expands not only in the width direction but also in the running direction of the film. Therefore, in the case where the film is not actively stretched, in order to eliminate sagging of the film in the transport direction, For example, it is preferable to take measures such as controlling the peripheral speed of the transport rolls before and after the swelling tank 13.

  Treatment baths used in the swelling treatment include pure water, boric acid (JP-A-10-153709), chlorides (JP-A-06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, An aqueous solution to which alcohols and the like are added in the range of about 0.01 to 10% by weight can also be used.

  In the swelling treatment, a uniaxial stretching treatment of the polyvinyl alcohol-based resin film can also be performed. In this case, the draw ratio is usually about 1.3 to 3 times, preferably about 1.3 to 2.5 times.

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

  When iodine is used as the dichroic dye, the concentration of the treatment bath (dye bath) is, for example, iodine / potassium iodide / water = 0.003 to 0.2 / 0.1 to 10/100 by weight ratio. An aqueous solution can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added, it is distinguished from boric acid treatment described later in that it contains iodine, and an aqueous solution containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water is regarded as a dyeing bath. Can do. The temperature of the dyeing bath when dipping the film is about 10 to 45 ° C., preferably 20 to 35 ° C., and the dipping time of the film is about 30 to 600 seconds, preferably 60 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 = 0.001 to 0.1100 by weight can be used for the treatment bath. This treatment bath may coexist with a dyeing assistant and the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Moreover, a dichroic dye may be used independently and may use 2 or more types of dichroic dye together. The temperature of the dyeing bath when dipping the film is about 20 to 80 ° C., preferably 30 to 70 ° C., and the dipping time of the film is about 30 to 600 seconds, preferably 60 to 300 seconds.

  In the dyeing process, a stretching process can be performed, and the film is stretched by a method of giving a peripheral speed difference to nip rolls installed before and after the dyeing tank. The cumulative draw ratio up to the dyeing process (or the draw ratio in the dyeing process when there is no drawing process before the dyeing process) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times. Note that if the cumulative draw ratio up to this dyeing treatment is less than 1.6 times, the frequency of film breakage increases, and the yield tends to deteriorate.

  In the dyeing process, as in the swelling process, a widening roll, a spiral roll, a crown roll, a cross guider, a bend bar, etc. are installed in the dyeing tank 15 and / or at the entrance / exit thereof to suppress wrinkles generated in the film. preferable.

(Boric acid treatment)
In the boric acid treatment, a dyeing treatment is performed on a treatment bath containing 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water for water resistance by cross-linking or hue adjustment for neutral gray of the polarizing film. It is carried out by immersing the polyvinyl alcohol resin film. In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color processing or re-dyeing processing.

  When the dichroic dye used in the dyeing treatment is iodine, the treatment bath used for the boric acid treatment preferably contains 1 to 30 parts by weight of iodide in addition to boric acid. Examples of the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

  The boric acid treatment is performed by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath depending on the purpose. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but are performed under the following conditions, respectively. For example, when the boric acid treatment is aimed at water resistance, and the raw film is subjected to swelling treatment, dyeing treatment and boric acid treatment in this order, the treatment bath has a concentration of boric acid / An aqueous solution of iodide / water = 2 to 10/1 to 20/100, more preferably an aqueous solution of boric acid / iodide / water = 2 to 4.5 / 1 to 20/100. 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 a processing bath is 20-70 degreeC normally, Preferably it is 50-65 degreeC, More preferably, it is 56-65 degreeC. The immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 to 200 seconds. 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 boric acid treatment for water resistance, boric acid treatment for hue adjustment may be performed. The conditions of the boric acid treatment for adjusting the hue are, for example, a treatment bath in which the concentration is boric acid / iodide / water = 1 to 5/1 to 30/100 by weight when the dichroic dye is iodine. Can be used. The temperature of the treatment bath is usually about 10 to 45 ° C., and the immersion time of the film is usually 3 to 300 seconds, preferably about 5 to 100 seconds.

  When a treatment bath having a high temperature and a low boric acid concentration is used for the boric acid treatment, a polarizing film having a low shrinkage can be produced. This is because, for example, when the treatment bath is at a high temperature of 50 ° C. or higher, the film tends to swell, so the stress applied to the film during stretching is relaxed, and the crosslinking reaction proceeds sufficiently depending on the temperature. This is because the dichroic dye can be firmly adsorbed to the alcohol-based resin film. Further, when the treatment bath has a low concentration of boric acid, it is possible to prevent the boric acid from being excessively present in the polarizing film. Therefore, even when the obtained polarizing film is exposed to high temperature conditions, Moreover, it is because a crosslinking reaction does not advance in a film and it can prevent that a polarizing film shrinks in a heating environment. For the above reasons, when using a high-temperature treatment bath, it is preferable to lower the concentration of boric acid from the viewpoint of suppressing the shrinkage rate of the polarizing film.

  In the present invention, when performing the boric acid treatment for water resistance described above, in the entire length between the two nip rolls of the inlet side nip roll 30 installed in the treatment bath and the outlet side nip roll 33 installed in the treatment bath, A polyvinyl alcohol-based resin film is immersed in a boric acid treatment bath. By this method, since the film swells uniformly between the two nip rolls, wrinkles of the film generated during the treatment can be suppressed, and color unevenness of the obtained polarizing film can be suppressed.

  The embodiment of the boric acid treatment for water resistance will be specifically described. The polyvinyl alcohol-based resin film subjected to the dyeing treatment passes through the nip roll 30 on the inlet side installed in the boric acid treatment bath. Then, after being introduced into the boric acid treatment bath, it comes into contact with at least one guide roll in the treatment bath and passes through the outlet side nipro 33 also installed in the boric acid treatment bath and is led out from the treatment bath. It is conveyed so that. Moreover, when the temperature of a boric-acid treatment bath is 56 degreeC or more, boric-acid treatment is given by embodiment as shown in FIG.

  FIG. 2 is a schematic cross-sectional view showing one embodiment of the boric acid treatment defined in the present invention. FIG. 2A shows a state before the film is immersed in a treatment bath and is based on a polyvinyl alcohol system. The state immediately after passing the tip of the resin film through the manufacturing apparatus is shown, and from this state, the state in which the polyvinyl alcohol-based resin film is immersed in the treatment bath is shown in FIG. Moreover, in the same figure (C), the state equivalent to the same figure (A) at the time of providing two or more guide rolls is shown, The state which immersed the polyvinyl alcohol-type resin film in the processing bath from this state (D) )Pointing out toungue.

  With reference to FIG. 2 (A), when the temperature of the boric acid treatment bath is 56 ° C. or higher, a plurality of guide rolls 35 including one guide roll in contact with the boric acid treatment bath described above are treated with boric acid. These are installed so that they can be raised and lowered between the inside and outside of the bath. These are the boric acid treatment baths when the polyvinyl alcohol resin film is first introduced into the boric acid treatment bath (when the film tip is passed through the apparatus). Is located outside. In this state, the polyvinyl alcohol-based resin film passes at least one of the plurality of guide rolls 35 disposed outside the boric acid treatment bath after the front end of the film has passed through the inlet-side nip roll 30, Further, it passes under the other at least one guide roll, and finally passes through the nip roll 33 on the outlet side so as to be led out from the boric acid treatment bath. The polyvinyl alcohol-based resin film does not need to be in particular contact with the guide roll through which it passes.

  FIG. 2A shows an example in which the polyvinyl alcohol-based resin film passes through the upper side of the guide roll 35 immediately after the inlet-side nip roll 30 and passes through the lower side of another guide roll 35. However, the method of passing the film may be reversed, and the film may pass under the guide roll 35 immediately after the entrance-side nip roll 30 and pass over the other guide roll 35. Considering the immersion time of the film immediately after the inlet side nip roll 30, it is preferable to pass the film as illustrated in FIG.

  By passing the polyvinyl alcohol-based resin film in this way, the state in which the film is immersed in a high-temperature boric acid treatment bath can be shortened, so that the film can be prevented from being lost or broken.

  In the immersion of the polyvinyl alcohol resin film in the boric acid treatment bath, the plurality of guide rolls 35 arranged outside the boric acid treatment bath are lowered from the state of FIG. 2A to the boric acid treatment bath, This is performed in the form shown in FIG. At this time, the rotational peripheral speeds of the entrance-side nip roll 30 and the exit-side nip roll 33 are adjusted so that the tension applied to the film is constant. Further, by adjusting the position of the guide roll 35, it is possible to adjust the optical properties such as the hue and polarization performance of the obtained polarizing film, and the film width.

  2C and 2D show an example in which three or more guide rolls 35 are installed in FIGS. 2A and 2B, and the number of guide rolls 35 is different. However, the method of passing the film through the manufacturing apparatus, the dipping method, and the like may be performed in the same manner as the method shown in FIGS.

  Further, FIG. 3 shows a case where the temperature of the boric acid treatment bath is 56 ° C. or higher, which is an embodiment different from the embodiment shown in FIG. 2, and a fixed roll 40 is installed in the treatment bath. The embodiment is shown in a schematic cross-sectional view. FIG. 3 (A) shows a state immediately before the film is immersed in the treatment bath and immediately after the tip of the polyvinyl alcohol-based resin film is passed through the manufacturing apparatus. The state which immersed the polyvinyl alcohol-type resin film in the processing bath is shown. 3 (A) and 3 (B) correspond to an example in which the fixed roll 40 is installed in the treatment bath in the embodiment shown in FIGS. 2 (C) and 2 (D). The passing method and the dipping method may be performed in the same manner as the method of FIG. 2 described above.

  Referring to FIG. 3A, the polyvinyl alcohol-based resin film can be moved up and down installed outside the boric acid treatment bath after passing through the inlet-side nip roll 30 installed in the treatment bath as in FIG. A plurality of guide rolls 35 are passed through, but the upper side or the lower side is alternately passed as shown in the figure. Thereafter, the leading edge of the film passes through the outlet side nip roll 33 and is led out from the boric acid treatment bath. At this time, the guide roll through which the film and the film pass below may be either in contact with or not in contact.

  FIG. 3A shows an example in which the polyvinyl alcohol-based resin film passes through the upper side of the guide roll 35 immediately after the inlet-side nip roll 30 and passes through the lower side of another subsequent guide roll 35. The method of passing the film may be reversed, and the film may be passed through the lower side of the guide roll 35 immediately after the inlet-side nip roll 30 and the upper side of the subsequent another guide roll 35. Considering the immersion time of the film immediately after the inlet side nip roll 30, it is preferable to pass the film as illustrated in FIG.

  In the immersion of the polyvinyl alcohol resin film in the boric acid treatment bath, the plurality of guide rolls 35 arranged outside the boric acid treatment bath are lowered from the state of FIG. 3A described above into the boric acid treatment bath, This is performed in the form shown in FIG. At this time, in the treatment bath, the film and the guide roll may be in contact with each other or not in contact with each other. Similarly to FIG. 2, the boric acid treatment time and the guide roll distance can be adjusted by adjusting the guide roll position at this time.

  In the present invention, when the leading end of the polyvinyl alcohol-based resin film is passed through the manufacturing apparatus as shown in FIGS. 2 (A) and 2 (C) and FIG. 3 (A), the elevating guide roll 35 is placed outside the boric acid treatment bath. When the polyvinyl alcohol resin film is immersed in the boric acid treatment bath, the time is preferably adjusted to be within 20 seconds, and more preferably within 16 seconds. The time during which the polyvinyl alcohol-based resin film is immersed in the boric acid treatment bath is preferably a short time in a state where the elevating guide roll 35 is disposed outside the boric acid treatment bath. If the time of immersion in the boric acid treatment bath exceeds 20 seconds, the polyvinyl alcohol-based resin film may be dissolved, resulting in inconveniences such as breakage due to the tension due to conveyance.

  In the present invention, the boric acid treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the aqueous solution composition of each boric acid treatment bath used and the treatment temperature thereof may be the same or different as long as they are within the above range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment described above may be performed in a plurality of steps, respectively, and it is often performed to perform the boric acid treatment for water resistance twice. This is one of the embodiments. When performing the boric acid treatment for water resistance twice, it is preferable to change the temperature of each treatment bath, and the temperature of one boric acid treatment bath is preferably set to 56 ° C. or higher. At this time, it is more preferable that the temperature of the first boric acid treatment bath is less than 56 ° C., and the temperature of the second boric acid treatment bath is 56 ° C. or more.

  In the present invention, when the processing temperature is 56 ° C. or higher, as described above with reference to FIGS. 2 and 3, after passing the polyvinyl alcohol-based resin film through the manufacturing apparatus using the guide roll 35 that can be raised and lowered, The elevating guide roll 35 is lowered to the boric acid treatment bath and the film is immersed in the treatment bath.

  Although the embodiment of the boric acid treatment of the present invention has been described above, this boric acid treatment method exhibits an excellent effect when the thickness of the raw film subjected to the dyeing treatment is 60 μm or less. . When the thickness of the raw film exceeds 60 μm, the sufficient thickness tends not to cause problems such as melting and breaking of the film even with boric acid treatment at 55 ° C. or higher. Therefore, the present invention makes it possible to produce a sufficiently thin polarizing film from a thin original film.

  Even during the boric acid treatment, the polyvinyl alcohol resin film can be stretched.

(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. The cleaning treatment is performed, for example, by immersing a polyvinyl alcohol-based resin film treated with boric acid for water resistance and / or color adjustment in water, or spraying water as a shower on the film, or using these in combination. . The temperature of water in the washing treatment is usually about 10 to 40 ° C., and the immersion time is about 2 to 120 seconds.

(Drying process)
After the draining treatment, the polarizing film can be produced by drying the polyvinyl alcohol-based resin film. The film can be dried in the drying furnace 21 at a temperature of about 40 to 100 ° C. for about 60 to 600 seconds, for example.

  The boric acid content of the polarizing film after undergoing the drying treatment is 2 to 4.5% by weight, preferably 2.5 to 4% by weight. When the boric acid content is less than 2% by weight, crosslinking in the polyvinyl alcohol-based resin film becomes insufficient, and thus the film strength tends to decrease. In addition, when the boric acid content exceeds 4.5%, by containing boric acid that does not contribute to the polymer cross-linking of the film at a high concentration, the cross-linking reaction of the polymer progresses over time, Accordingly, the polyvinyl alcohol-based resin film tends to shrink.

  The final cumulative magnification of the polarizing film produced as described above is usually 4.5 to 7 times, preferably 5 to 6.5 times. Moreover, the thickness is 5-50 micrometers, for example. A polarizing film is used as a component of a polarizing plate described below.

[Production method of polarizing plate]
The above-mentioned polarizing film is made into a polarizing plate by pasting a protective film on at least one surface thereof with an adhesive.

  As a material constituting the protective film, for example, cycloolefin resin, cellulose acetate resin, polyethylene terephthalate, polyester resin such as polyethylene naphthalate and polybutylene terephthalate, polycarbonate resin, acrylic resin, polypropylene resin, etc. The film material conventionally used widely in this field | area can be mentioned. When a protective film is bonded on both surfaces of a polarizing film, each protective film may be the same and may be a different kind of film.

  The cycloolefin resin is, for example, a thermoplastic resin (also referred to as a thermoplastic cycloolefin resin) having a monomer unit made of a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene monomer. The cycloolefin-based resin may be a hydrogenated product of the above-described cycloolefin ring-opening polymer or a ring-opening copolymer using two or more cycloolefins. It may be an addition polymer with an aromatic compound having such a polymerizable double bond. Those having a polar group introduced are also effective.

  When a protective film is formed using a copolymer of a cycloolefin and a chain olefin and / or an aromatic compound having a vinyl group, examples of the chain olefin include ethylene and propylene. Examples of the aromatic compound include styrene, α-methylstyrene, and nuclear alkyl-substituted styrene. In such a copolymer, the monomer unit composed of cycloolefin may be 50 mol% or less, but is preferably about 15 to 50 mol%. In particular, when a protective film is formed using a terpolymer of a cycloolefin, a chain olefin, and an aromatic compound having a vinyl group, the monomer unit composed of cycloolefin has a relatively small amount as described above. It can be. In such a terpolymer, the monomer unit composed of a chain olefin is usually 5 to 80 mol%, and the monomer unit composed of an aromatic compound having a vinyl group is usually 5 to 80 mol%.

  Cycloolefin-based resins are commercially available as appropriate, such as “TOPAS” (manufactured by Topas Advanced Polymers GmbH), “Arton” (manufactured by JSR Corporation), “ZEONOR” and “ZEONEX” “ZEONEX” ”(manufactured by Nippon Zeon Co., Ltd.),“ Apel ”(manufactured by Mitsui Chemicals, Inc.),“ Oxis (OXIS) ”(manufactured by Okura Kogyo Co., Ltd.), etc. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. In addition, for example, “Essina” and “SCA40” (manufactured by Sekisui Chemical Co., Ltd.), “Zeonor Film” (manufactured by Nippon Zeon Co., Ltd.), etc. Commercial products may be used.

  The cycloolefin resin film may be uniaxially stretched or biaxially stretched. By stretching, an arbitrary retardation value can be given to the cycloolefin-based resin film. Stretching is usually performed continuously while unwinding a film roll, and in a heating furnace, the roll traveling direction (film longitudinal direction), the direction perpendicular to the traveling direction (film width direction), or both Stretched. As the temperature of the heating furnace, a range from the vicinity of the glass transition temperature of the cycloolefin resin to the glass transition temperature + 100 ° C. is usually employed. The draw ratio is usually 1.1 to 6 times, preferably 1.1 to 3.5 times.

  When the cycloolefin-based resin film is in a roll-wound state, the films tend to adhere to each other and easily cause blocking. Therefore, the cycloolefin-based resin film is usually rolled after the protective film is bonded. In addition, since the cycloolefin resin film generally has poor surface activity, the surface to be bonded to the polarizing film is subjected to surface treatment such as plasma treatment, corona treatment, saponification treatment, ultraviolet irradiation treatment, and flame (flame) treatment. Is preferred. Among these, plasma treatment that can be carried out relatively easily, particularly atmospheric pressure plasma treatment, and corona treatment are preferable.

  The cellulose acetate-based resin is a cellulose partial or completely esterified product, and examples thereof include a film composed of cellulose acetate ester, propionate ester, butyrate ester, mixed ester thereof, and the like. More specifically, a triacetyl cellulose film, a diacetyl cellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film, and the like can be given. As such a cellulose ester-based resin film, an appropriate commercially available product, for example, “Fujitac TD80”, “Fujitac TD80UF”, “Fujitac TD80UZ” and “Fujitac TD60UL” [Fuji Film Co., Ltd. “KC8UX2M”, “KC8UY”, “KC4UYW”, and “KC6UAW” (manufactured by Konica Minolta Advanced Layer Co., Ltd.) and the like can be suitably used.

  Moreover, the cellulose acetate type-resin film which provided the phase difference characteristic as a protective film is also used suitably. As commercial products of the cellulose acetate-based resin film provided with such retardation characteristics, “WV BZ 438” (manufactured by Fuji Film Co., Ltd.), “KC4FR-1”, “KC4CR-1” and “ KC4AR-1 ″ [manufactured by Konica Minolta Advanced Layer Co., Ltd.], and the like. Cellulose acetate is also called acetyl cellulose or cellulose acetate.

  The thickness of the protective film used in the method for producing a polarizing plate is preferably thin, but if it is too thin, the strength is lowered and the processability is poor. On the other hand, when it is too thick, problems such as a decrease in transparency and a longer curing time after lamination occur. Therefore, an appropriate thickness of the protective film is, for example, 5 to 200 μm, preferably 10 to 150 μm, and more preferably 10 to 100 μm.

  In order to improve the adhesiveness between the adhesive and the polarizing film and / or protective film, the polarizing film and / or protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet treatment, primer coating treatment, saponification treatment, etc. A surface treatment may be applied.

  In addition, the protective film may be subjected to surface treatments such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment and antifouling treatment, either singly or in combination of two or more. The protective film may contain an ultraviolet absorber such as a benzophenone compound and a benzotriazole compound, and a plasticizer such as a phenyl phosphate compound and a phthalate compound.

  In addition, 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. Can have a function. In this case, for example, by laminating an optical functional film such as a retardation film, a brightness enhancement film, a reflective film, a transflective film, a diffusion film, and an optical compensation film on the surface of the protective film, such a function is achieved. In addition, the protective film itself can be provided with such a function. In addition, a protective film may have a plurality of functions such as a diffusion film having a function of a brightness enhancement film.

  The function as a retardation film is, for example, subjected to the stretching process described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or the process described in Japanese Patent No. 3168850, to the protective film described above. It can be given by doing.

  The retardation characteristics of the retardation film can be appropriately selected, for example, such that the front retardation value is in the range of 5 to 100 nm and the thickness direction retardation value is in the range of 40 to 300 nm. In addition, by forming micropores in the above protective film by a method as described in JP 2002-169025 A or JP 2003-29030 A, or two or more layers having different selective reflection center wavelengths. By superimposing the cholesteric liquid crystal layer, a function as a brightness enhancement film can be imparted.

  The function as a reflective film or a transflective film is formed by forming a metal thin film on the protective film by vapor deposition or sputtering, and the function as a diffusion film is obtained by coating the protective film with a resin solution containing fine particles, respectively. Can be granted. The function as an optical compensation film can be imparted by coating and aligning a protective film with a liquid crystal compound such as a discotic liquid crystal compound. The protective film may contain a compound that develops a retardation, and various optical functional films may be directly bonded to the polarizing film using an appropriate adhesive. Examples of commercially available optical functional films include brightness enhancement films such as “DBEF” (manufactured by Sumitomo 3M Co., Ltd. in Japan) and “WV film” [Fuji Film ( ”, Etc.”, “Arton Film” (manufactured by JSR Corporation), “ZEONOR FILM” (manufactured by ZEON CORPORATION), “Essina” (manufactured by Sekisui Chemical Co., Ltd.), “ Examples thereof include retardation films such as “VA-TAC film” (manufactured by Konica Minolta Advanced Layer Co., Ltd.) and “Sumikalite” (manufactured by Sumitomo Chemical Co., Ltd.).

(Adhesive layer)
Examples of the adhesive constituting the adhesive layer include a water-based adhesive and an active energy ray-curable adhesive. The active energy ray-curable adhesive is preferably used because it is not necessary to dry the adhesive and it is easy to prevent deterioration of the polarizing film due to drying.

  Examples of the active energy ray-curable adhesive include an adhesive made of an epoxy resin composition containing an epoxy compound that is cured by irradiation with active energy rays from the viewpoint of weather resistance, refractive index, cationic polymerization, and the like. . Examples of such an epoxy compound include a glycidyl ether of a polyol having an alicyclic ring, an aliphatic epoxy compound, and an alicyclic epoxy compound. An epoxy compound suitably used for such an active energy ray-curable adhesive is described in detail in, for example, Japanese Patent No. 4306270 (= Japanese Patent Laid-Open No. 2004-245925), but the outline is also described here. I will do it.

  The glycidyl ether of a polyol having an alicyclic ring is obtained by glycidyl etherifying a nuclear hydrogenated polyhydroxy compound obtained by selectively hydrogenating an aromatic polyol under pressure in the presence of a catalyst. Can be. Examples of the aromatic polyol include bisphenol type compounds such as bisphenol A, bispheel F, and bisphenol S; novolac type resins such as phenol novolac resin, cresol novolac resin, and hydroxybenzaldehyde phenol novolac resin; tetrahydroxydiphenylmethane, Examples thereof include tetrahydroxybenzophenone and polyfunctional compounds such as polyvinylphenol. Glycidyl ether can be obtained by reacting an alicyclic polyol obtained by hydrogenating the aromatic ring of these aromatic polyols with epichlorohydrin. Among the glycidyl ethers of polyols having such alicyclic rings, it is preferable to use hydrogenated bisphenol A diglycidyl ether.

  The aliphatic epoxy compound can be a polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof. More specifically, 1,4-butanediol diglycidyl ether; 1,6-hexanediol diglycidyl ether; glycerin triglycidyl ether; trimethylolpropane triglycidyl ether; polyethylene glycol diglycidyl ether; propylene Diglycidyl ether of glycol; Polyether polyol obtained by adding one or more alkylene oxides (ethylene oxide or propylene oxide) to an aliphatic polyhydric alcohol such as ethylene glycol, propylene glycol or glycerin Examples thereof include glycidyl ether.

  The alicyclic epoxy compound means an epoxy compound having one or more epoxy groups bonded to the alicyclic ring in the molecule. The “epoxy group bonded to the alicyclic ring” means a bridged oxygen atom —O— in the structure represented by the following formula (I). In the following formula (I), m is an integer of 2 to 5.

A compound in which a group in the form of removing one or more hydrogen atoms in (CH ₂ ) _m in the above formula (I) is bonded to another chemical structure can be an alicyclic epoxy compound. One or more hydrogen atoms in (CH ₂ ) _m may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among alicyclic epoxy compounds, an epoxy compound having an oxabicyclohexane ring [m = 3 in the above formula (I)] or an oxabicycloheptane ring [m = 4 in the above formula (I)] It is preferably used because it exhibits excellent adhesion between the polarizing film and the protective film. Although the alicyclic epoxy compound used preferably below is specifically illustrated, it is not limited to these compounds.

(A) Epoxycyclohexylmethyl epoxycyclohexanecarboxylates: represented by the following formula (II), wherein R ¹ and R ² are each independently a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms. Represents.

(B) Epoxycyclohexanecarboxylates of alkanediol: represented by the following formula (III), wherein R ³ and R ⁴ are each independently a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms. N represents an integer of 2-20.

(C) Epoxycyclohexylmethyl esters of dicarboxylic acid: represented by the following formula (IV), wherein R ⁵ and R ⁶ are each independently a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms. P represents an integer of 2-20.

(D) Epoxycyclohexyl methyl ethers of polyethylene glycol: represented by the following formula (V), wherein R ⁷ and R ⁸ are each independently a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms. Q represents an integer of 2 to 10.

(E) Epoxycyclohexyl methyl ethers of alkanediol: represented by the following formula (VI), wherein R ⁹ and R ¹⁰ are each independently a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms. And r represents an integer of 2 to 20.

(F) diepoxy trispiro compound: represented by the following formula (VII), wherein R ¹¹ and R ¹² each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(G) Diepoxy monospiro compound: represented by the following formula (VIII), wherein R ¹³ and R ¹⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(H) Vinylcyclohexene diepoxide: represented by the following formula (IX), wherein R ¹⁵ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(I) Epoxycyclopentyl ethers: represented by the following formula (X), wherein R ¹⁶ and R ¹⁷ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(J) Diepoxytricyclodecane: represented by the following formula (XI), wherein R ¹⁸ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

Among the alicyclic epoxy compounds exemplified above, for example, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate [compound of R ¹ = R ² = H in formula (II)], 3,4- Epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate [compound of formula (II) where R ¹ = 4-CH ₃ , R ² = 4-CH ₃ ], ethylene bis (3,4 -Epoxycyclohexanecarboxylate) [compound of formula (III), R ³ = R ⁴ = H, n = 2], bis (3,4-epoxycyclohexylmethyl) adipate [in formula (IV), R ⁵ = R ⁶ = H, p = 4 compound], bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate [in formula (IV), R ⁵ = 4 -CH ₃ , R ⁶ = 4-CH ₃ , p = 4 compound], ethylene glycol bis (3,4-epoxycyclohexyl methyl ether) [in the formula (VI), R ⁹ = R ¹⁰ = H, r = 2 Is a compound that is commercially available or an analogue thereof, and is more preferably used because it is relatively easy to obtain.

  In the active energy ray-curable adhesive, the epoxy compound may be used alone or in combination of two or more. The epoxy equivalent of the epoxy compound used in this composition is generally 30 to 3000 g / equivalent, preferably 50 to 1500 g / equivalent. When the epoxy equivalent is less than 30 g / equivalent, there is a possibility that the flexibility of the protective film after curing is lowered or the adhesive strength is lowered. On the other hand, when it exceeds 3000 g / equivalent, compatibility with other components may be lowered.

  The active energy ray-curable adhesive may contain an oxetane compound in addition to the above epoxy compound. By adding an oxetane compound, the viscosity of the adhesive described above can be lowered and the curing rate can be increased.

  The oxetane compound is a compound having at least one oxetane ring (four-membered ether) in the molecule, such as 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3 -Oxetanyl) methoxymethyl] benzene, 3-ethyl-3- (phenoxymethyl) oxetane, di [(3-ethyl-3-oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane And phenol novolac oxetane. The amount of the oxetane compound is usually 50% by weight or less, preferably 10 to 40% by weight, based on the whole active energy ray-curable compound. Oxetane compounds can be easily obtained as commercial products. For example, all of them are trade names sold by Toagosei Co., Ltd., “Aron Oxetane OXT-101”, “Aron Oxetane OXT-121”. , “Aron oxetane OXT-211”, “Aron oxetane OXT-221”, “Aron oxetane OXT-212”, and the like.

  In this adhesive, from the viewpoint of reactivity, cationic polymerization is preferably used as a curing reaction of the epoxy compound, and a cationic polymerization initiator is preferably added to the composition. The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and starts an epoxy group polymerization reaction. Hereinafter, a cationic polymerization initiator that generates a cationic species or a Lewis acid upon irradiation with active energy rays and initiates a polymerization reaction of an epoxy group is referred to as a “photo cationic polymerization initiator”.

  The method of curing the adhesive by irradiation with active energy rays using a cationic photopolymerization initiator enables curing at room temperature, reducing the need to consider the heat resistance of the polarizing film or distortion due to expansion, and the polarizing film. It is advantageous in that the protective film can be adhered well. In addition, since the cationic photopolymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an adhesive.

  The photocationic polymerization initiator may be of any type, but specific examples include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; iron-arene There are complexes.

  Examples of the aromatic diazonium salt include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, and benzenediazonium hexafluoroborate. Examples of the aromatic iodonium salt include diphenyliodonium tetrakis (pentafluorophenyl) borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, and di (4-nonylphenyl) iodonium hexafluorophosphate.

  Examples of the aromatic diazonium salt include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, and benzenediazonium hexafluoroborate.

  Examples of the aromatic iodonium salt include diphenyliodonium tetrakis (pentafluorophenyl) borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di (4-nonylphenyl) iodonium hexafluorophosphate, and the like.

  Examples of the aromatic sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, 4,4′-bis (diphenylsulfonio) diphenylsulfide bishexa. Fluorophosphate, 4,4'-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluoroantimonate, 4,4'-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bis Hexafluorophosphate, 7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone Hexafluoroantimonate, 7- [di (p-tolui) ) Sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate, 4-phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide hexafluorophosphate, 4- (p-tert-butylphenylcarbonyl) -4'-diphenyl Sulfonio-diphenyl sulfide hexafluoroantimonate, 4- (p-tert-butylphenylcarbonyl) -4'-di (p-toluyl) sulfonio-diphenyl sulfide, tetrakis (pentafluorophenyl) borate, and the like.

  Examples of the iron-arene complex include xylene-cyclopentadienyl iron (II) hexafluoroantimonate, cumene-cyclopentadienyl iron (II) hexafluorophosphate, xylene-cyclopentadienyl iron (II). And tris (trifluoromethylsulfonyl) methanide.

  Commercially available products of these photocationic polymerization initiators can be easily obtained. For example, “Kayarad PCI-220” and “Kayarad PCI-620” [Nippon Kayaku Co., Ltd. "UVI-6990" (manufactured by Dow Chemical Co.), "Adekaoptomer SP-150" and "Adekaoptomer SP-170" (manufactured by ADEKA Corporation), "CI-5102", " "CIT-1370", "CIT-1682", "CIP-1866S", "CIP-2048S" and "CIP-2064S" (manufactured by Nippon Soda Co., Ltd.), "DPI-101", "DPI-102" , “DPI-103”, “DPI-105”, “MPI-103”, “MPI-105”, “BBI-101”, “BBI-102”, “BBI-10” 3 ”,“ BBI-105 ”,“ TPS-101 ”,“ TPS-102 ”,“ TPS-103 ”,“ TPS-105 ”,“ MDS-103 ”,“ MDS-105 ”,“ DTS-102 ” And “DTS-103” (manufactured by Midori Chemical Co., Ltd.), “PI-2074” (manufactured by Rhodia), and the like.

  These photocationic polymerization initiators may be used alone or in combination of two or more. Among these, in particular, the aromatic sulfonium salt has an ultraviolet absorption property even in a wavelength region of 300 nm or more, so it has excellent curability, gives good mechanical strength, and is good between the polarizing film and the protective film. Since it can give the hardened | cured material which has adhesiveness, it is used preferably.

  The compounding amount of the cationic photopolymerization initiator is usually 0.5 to 20 parts by weight, preferably 1 to 6 parts by weight, based on 100 parts by weight of the total of the cationic polymerizable compounds including the epoxy compound and the oxetane compound. is there. If the amount of the cationic photopolymerization initiator is small, the curing becomes insufficient, and the mechanical strength and the adhesion between the polarizing film and the protective film tend to be lowered. On the other hand, if the amount of the cationic photopolymerization initiator is too large, the amount of ionic substances in the cured product will increase, resulting in an increase in the hygroscopicity of the cured product, which may reduce the durability of the resulting adhesive layer. is there.

  Active energy ray curable adhesives include ion trapping agents, antioxidants, chain transfer agents, tackifiers, thermoplastic resins, fillers, flow regulators, leveling agents, plasticizers and antifoaming agents, etc. Additives can be blended. Examples of the ion trapping agent include antimony-based, powdered bismuth-based, magnesium-based, aluminum-based, calcium-based, titanium-based and mixed inorganic compounds, and antioxidants include hindered phenol-based antioxidants. Agents and the like.

  Active energy ray-curable adhesives can be used as solventless adhesives that are substantially free of solvent components, but each coating method has an optimum viscosity range, A solvent may be included. As the solvent, it is preferable to use a solvent that dissolves the epoxy compound constituting the adhesive well without degrading the optical performance of the polarizing film. For example, hydrocarbons typified by toluene, typified by ethyl acetate, etc. And organic solvents such as esters. The viscosity of the active energy ray-curable adhesive used in the present invention is, for example, in the range of about 5 to 1000 mPa · s, preferably 10 to 200 mPa · s, and more preferably 20 to 100 mPa · s. . There is no particular limitation on the coating method of the active energy ray-curable adhesive, and for example, a protective film or a polarizing film can be applied by various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater. What is necessary is just to apply to a bonding surface.

Thus, the above-mentioned protective film is bonded onto the adhesive layer formed on the polarizing film. When bonding a protective film on both surfaces of a polarizing film, two protective films may be bonded one step at a time, and both surfaces may be bonded in one step. The laminated body of the polarizing film and the protective film is irradiated with active energy rays to cure the adhesive. The light source used for irradiation with active energy rays is not particularly limited, but has a light emission distribution at a wavelength of 400 nm or less, for example, 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 A mercury lamp, a metal halide lamp, etc. can be used. The light irradiation intensity is determined for each target composition and is not particularly limited. However, the irradiation intensity in the wavelength region effective for activation of the initiator is preferably 10 to 5000 mW / cm ^2. . When the light irradiation intensity is less than 10 mW / cm ² , the reaction time becomes too long, and when it exceeds 5000 mW / cm ² , yellowing of the adhesive layer is caused by heat radiated from the lamp and heat generated during polymerization of the composition. And the polarizer may be deteriorated.

The irradiation time of the active energy ray is controlled for each composition to be cured and is not particularly limited, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 5000 mJ / cm ^2. It is preferable to set to. When the above integrated light quantity is less than 10 mJ / cm ² , the active species derived from the initiator is not sufficiently generated, and the resulting protective film may be insufficiently cured, while the integrated light quantity is 5000 mJ. If it exceeds / cm ² , the irradiation time becomes very long, which is disadvantageous for improving productivity. The thickness of the adhesive layer after curing is usually 0.1 to 10 μm, more preferably 0.2 to 4 μm.

  Examples of the water-based adhesive include a polyvinyl alcohol-based resin aqueous solution and a water-based two-component urethane emulsion adhesive. Polyvinyl alcohol resins used as adhesives include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as other single quantities copolymerizable with vinyl acetate. And vinyl alcohol copolymers obtained by saponifying the copolymer with the polymer, and modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups. A polyhydric aldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, a zinc compound, or the like may be added as an additive to the water-based adhesive. When such an aqueous adhesive is used, the resulting adhesive layer is usually much thinner than 1 μm.

  The adhesive is usually applied at a temperature of 15 to 40 ° C after its preparation, and the bonding temperature is usually in the range of 15 to 30 ° C. When using a water-system adhesive, after bonding a film, in order to remove the water contained in a water-system adhesive, it is made to dry. The drying temperature is preferably 30 ° C. or higher and lower than 110 ° C. If the drying temperature is less than 30 ° C., the adhesive surface tends to be peeled off. If the drying temperature is 110 ° C. or more, the optical performance of a polarizing film or the like may be deteriorated by heat. The drying time can be 1 to 1000 seconds.

  After drying, it may be further cured at room temperature or a slightly higher temperature, for example, at a temperature of about 20 to 45 ° C. for about 12 to 600 hours. The temperature at the time of curing is generally set lower than the temperature adopted at the time of drying.

  The polarizing plate produced as described above includes a polarizing film and a protective film bonded to at least one surface of the polarizing film. For example, the polarizing plate is bonded to a liquid crystal cell via a pressure-sensitive adhesive layer to display a liquid crystal display. It can be used as a component of the device. In this case, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is usually based on an acrylic resin, styrene resin, silicone resin, or the like, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. It consists of a composition. Furthermore, a pressure-sensitive adhesive layer exhibiting light scattering properties can be formed by mixing fine particles in the pressure-sensitive adhesive.

  The pressure-sensitive adhesive layer is preferably thinly applied within a range that does not impair properties such as processability and durability. For example, the thickness is preferably 1 to 40 μm, and more preferably 3 to 25 μm. In particular, when the thickness of the pressure-sensitive adhesive layer is 3 to 25 μm, it has good processability and is suitable for suppressing the dimensional change of the polarizing film. On the other hand, if the pressure-sensitive adhesive layer is less than 1 μm, the adhesiveness is lowered, and if it exceeds 40 μm, problems such as the pressure-sensitive adhesive protruding easily occur.

  The method of forming this pressure-sensitive adhesive layer on a transparent film or a polarizing film is not particularly limited, and a solution containing each component including the above-mentioned base polymer is formed on the surface of the transparent film or the surface of the polarizing film. After applying and drying to form a pressure-sensitive adhesive layer, it may be bonded to a separator or other type of film, or after forming a pressure-sensitive adhesive layer on the separator, it is applied to the surface of a transparent film or the surface of a polarizing film. You may laminate.

[Polarizer]
The polarizing plate produced as described above preferably has a single hue b value of 2.5 to 4.5. A single hue b value is in such a numerical range, and the liquid crystal display device is configured using a polarizing plate appropriately colored, thereby facilitating the adjustment of the hue of the liquid crystal display screen. When the single hue b value is less than 2.5, since the coloring of the polarizing plate is not sufficient, it may be difficult to adjust the hue when a liquid crystal display device is configured using this. The polarizing plate of the present invention preferably has a hue b value of −1.5 to 0.1 when the two polarizing plates are arranged orthogonally. When the orthogonal hue b value is within such a numerical range, color unevenness in the display image can be suppressed.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
A 75 μm thick polyvinyl alcohol film (trade name “Kuraray Vinylon VF-PE # 7500” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) containing 30 ° C. pure water swelled The film was immersed in the bath for 100 seconds while keeping the tension state so that the film did not loosen, and the film was sufficiently swollen. Next, the film was immersed for 90 seconds in a dyeing tank at 30 ° C. in which the weight ratio of iodine / potassium iodide / water was 0.02 / 1.5 / 100, and the cumulative draw ratio from the original film was 2.2 times. Uniaxial stretching was performed until Subsequently, the immersion time is 30 seconds in the first boric acid treatment bath for water resistance in which potassium iodide / boric acid / water is set to 55 / C at a weight ratio of 12 / 4.4 / 100. After passing through the film as described above, the film was passed through an aqueous solution of the same composition in a second boric acid treatment bath for water resistance set at 59 ° C. so that the immersion time was 30 seconds.

  When the film is passed through the second boric acid treatment bath described above, the front end of the polyvinyl alcohol film passes through the nip roll on the inlet side installed in the treatment bath as shown in FIG. Passing through the upper side of a mechanically elevating guide roll arranged outside the treatment bath and then passing under the mechanically elevating guide roll arranged outside another bath, Finally, it passed through a nip roll on the outlet side installed in the treatment bath so as to be led out from the boric acid treatment bath. At this time, the time during which the polyvinyl alcohol film was immersed in the boric acid treatment bath was 17 seconds.

  After the film spreads uniformly, the film is immersed in the solution while simultaneously lowering the elevating guide roll while applying a constant tension to the film, and then the cumulative draw ratio from the original film is 5.5. Uniaxial stretching was performed until doubling. Subsequently, after being immersed in a boric acid-containing aqueous solution for adjusting the hue at 40 ° C., it was immersed in a washing tank containing pure water at 12 ° C. and dried at 70 ° C. for 3 minutes to produce a polarizing film. As a result, the film was not broken and the film could be produced efficiently.

[Example 2]
Immediately after the inlet-side nip roll, it passes under the mechanically elevating and lowering guide roll arranged outside the processing bath, and then the mechanically elevating and lowering guide roll arranged outside the other bath A polarizing film was produced in the same manner as in Example 1, except that the nip roll on the outlet side installed in the treatment bath was finally passed. As a result, the film was not broken and the film could be produced efficiently.

Example 3
Using a polyvinyl alcohol film (trade name “Kuraray Vinylon VF-PE # 5000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) having a thickness of 50 μm, in the same manner as in Example 1. A polarizing film was produced. As a result, the film was not broken and the film could be produced efficiently.

Example 4
Using a polyvinyl alcohol film having a thickness of 30 μm (trade name “Kuraray Vinylon VF-PE # 3000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) in the same manner as in Example 1. A polarizing plate roll was produced.

[Comparative Example 1]
A polarizing film in the same manner as in Example 1 except that no elevating guide roll is installed and a film is passed between the inlet side nip roll and the outlet side nip roll installed in the second boric acid treatment bath. Was made. As a result, the time for manual work was long in the high-temperature treatment bath, and the workability was low. In addition, after passing the leading edge of the film through a manufacturing apparatus, the film frequently breaks when it was stretched, and the film had to be used excessively, resulting in longer manufacturing time and lower production efficiency.

[Comparative Example 2]
A polarizing film in the same manner as in Example 3 except that no elevating guide roll is installed and a film is passed between the inlet nip roll and the outlet nip roll installed in the second boric acid treatment bath. Was made. As a result, the time for manual work was long in the high-temperature treatment bath, and the workability was low. In addition, after passing the leading edge of the film through a production apparatus, the film always ruptured when stretched, and a polarizing film could not be produced.

[Comparative Example 3]
Comparative Example 1 except that the second boric acid treatment bath was set to 55 ° C., the film was passed through the apparatus, the guide roll was lowered to immerse the film, and the treatment bath was heated to 59 ° C. Similarly, a polarizing film was produced. As a result, it took 100 minutes for the bath temperature to stabilize at 59 ° C., and the production efficiency was low.

  Example 1 and 2 which manufactured the polarizing film with the manufacturing method of this invention, and the comparison which produced the polarizing film by the method which does not correspond to the manufacturing method of this invention using the same polyvinyl alcohol film (raw film) as Example 1 From the comparison of Example 1, it can be seen that the boric acid treatment method defined in the present invention can prevent breakage of the film and is excellent in productivity when a high-temperature treatment bath is used for boric acid treatment. Further, from the comparison of Examples 3 and 4 using a raw film having a thinner film thickness than Example 1 and Comparative Example 2 using the same film as Example 3, the present invention is a polarizing film having a small thickness. It is found to be particularly effective when manufacturing

  Furthermore, using the same polyvinyl alcohol film, after passing the film through a guide roll installed outside, the guide roll was lowered and the film was immersed in a high-temperature treatment bath. From the comparison of Comparative Example 1 in which the film was passed through the apparatus in the treatment bath and Comparative Example 3 in which the temperature of the treatment bath was increased after passing the film in the treatment bath, the film was passed through the film in the high temperature treatment bath. It can be seen that when the temperature of the treatment bath is increased after passing through the film and passing through the film, it takes time and the production efficiency is low. From the above, it can be seen that the present invention is excellent in production efficiency.

10: Raw film of polyvinyl alcohol resin,
11 ... Feed roll,
13 ... swelling tank,
15 …… Dyeing tank,
17 …… Boric acid treatment tank,
19 …… Cleaning tank,
21 …… Drying furnace,
23 …… Polarizing film,
30: nip roll on the inlet side of the boric acid treatment bath,
33 …… Nip roll on the outlet side of the boric acid treatment bath,
35 …… A guide roll that can be raised and lowered,
40: Fixed roll.

Claims (5)

A method for producing a polarizing film by subjecting a polyvinyl alcohol-based resin film to dyeing treatment, boric acid treatment, and drying treatment in this order,
The boric acid treatment is performed by passing the film subjected to the dyeing treatment through a boric acid treatment bath composed of an aqueous solution containing boric acid and having a temperature of 56 ° C. or higher.
The film subjected to the dyeing treatment is introduced into the boric acid treatment bath through an inlet-side nip roll installed in the boric acid treatment bath, and at least one guide roll in the boric acid treatment bath. Coming out of the boric acid treatment bath through an exit side nip roll, also in contact with the boric acid treatment bath,
A plurality of guide rolls including the one guide roll are installed so as to be movable up and down between inside and outside the boric acid treatment bath,
When the film is first introduced into the boric acid treatment bath, a plurality of guide rolls installed so as to be movable up and down are arranged outside the boric acid treatment bath,
The front end of the film passes through the inlet-side nip roll, and then passes through at least one upper side of a plurality of guide rolls arranged outside the boric acid treatment bath, and passes through at least one other lower side. And finally pass through the outlet nip roll to be led out of the boric acid treatment bath,
In this state, a plurality of guide rolls arranged outside the boric acid treatment bath are lowered to immerse the film in the boric acid treatment bath, while maintaining a constant tension on the film in the boric acid treatment bath. The method for producing a polarizing film, wherein the film is guided to a nip roll on the boric acid treatment bath outlet side.   2. The method for producing a polarizing film according to claim 1, wherein the polyvinyl alcohol-based resin film has a thickness of a raw film subjected to the dyeing treatment of 1 to 60 μm.   The tip of the film subjected to the dyeing treatment is passed through the upper side of the guide roll which can be moved up and down immediately after the inlet side nip roll installed in the boric acid treatment bath, and is installed in the boric acid treatment bath. The manufacturing method of the polarizing film of Claim 1 or 2 which passes the lower side of the guide roll which can be moved up and down immediately before an exit side nip roll.   The film that has been subjected to the dyeing treatment is set so that the time of immersion in the boric acid treatment bath is within 20 seconds in the state where the elevating guide roll is disposed outside the boric acid treatment bath. The manufacturing method of the polarizing film in any one of Claims 1-3.   The said boric-acid treatment bath is a manufacturing method of the polarizing film in any one of Claims 1-4 containing 2-4.5 weight part of boric acids with respect to 100 weight part of water.

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