JP6666063B2 - Manufacturing method of polarizing film - Google Patents

Description

  The present invention relates to a method for producing a polarizing film that can be used as a component of a polarizing plate.

  As a polarizing film, a film obtained by adsorbing and orienting a dichroic dye such as iodine or a dichroic dye on a uniaxially stretched polyvinyl alcohol-based resin film is conventionally used. A polarizing film is usually made into a polarizing plate by laminating a protective film on one or both sides thereof with an adhesive, and is used for an image display device represented by a liquid crystal display device such as a liquid crystal television, a personal computer monitor, and a mobile phone. Used.

  Generally, a polarizing film is subjected to a treatment in which a continuous polyvinyl alcohol-based resin film that is continuously conveyed is sequentially immersed in a treatment bath such as a swelling bath, a dyeing bath, and a crosslinking bath, and is stretched during these series of treatments. It is manufactured by performing a process (for example, Patent Documents 1 and 2). Patent Documents 1 and 2 are provided in a bath in which wet stretching is performed in order to suppress breakage (stretch breakage) of the polyvinyl alcohol-based resin film when the film is wet stretched at a high magnification of 1.2 times or more. Discloses that the holding angle of the film on the guide roll where the film comes into contact first is within a predetermined range.

JP-A-2004-070104 JP 2008-250326 A

  In recent years, the thickness of the polarizing film has been increasingly required to be reduced, and when a thin film is used as the polyvinyl alcohol-based resin film as the raw material film, both ends of the film in the width direction during the polarizing film manufacturing process are required. However, there is a tendency that a curl that bends round inward or that the curl is strong and the inward curl is stuck to the inner part of the film. Such a curled or folded film may be creased, cut or broken at the time of passing through a nip roll or stretching.

  Problems such as curling and folding can occur in any process in which the film is immersed in a liquid and pulled out, but the present invention particularly aims to suppress the above problems when immersed in a crosslinking bath. That is, an object of the present invention is to provide a method for producing a polarizing film from a thin polyvinyl alcohol-based resin film, wherein a production method capable of suppressing curling or folding at both ends in the film width direction caused by immersion in a crosslinking bath. To provide.

The present invention provides a method for producing a polarizing film described below.
[1] A method of producing a polarizing film by carrying out at least a dyeing treatment and a crosslinking treatment in which two or more baths containing a crosslinking agent-containing liquid are sequentially immersed while conveying a polyvinyl alcohol-based resin film having a thickness of 65 μm or less. And
In at least one of the two or more baths, the polyvinyl alcohol-based resin film is transported along two or more guide rolls disposed in the bath, and passes last of the two or more guide rolls. The manufacturing method, wherein the final guide roll passes through the final guide roll so that the embedment angle is 100 ° or more and less than 180 °.

  [2] A stretching treatment is performed in the at least one bath having the final guide roll arranged so that the embracing angle is not less than 100 ° and less than 180 °, and the stretching ratio in the stretching treatment in each bath is 1. The production method according to [1], which is 14 times or less.

  [3] The production method according to [1] or [2], wherein the polyvinyl alcohol-based resin film subjected to the crosslinking treatment is a stretched film.

  [4] The method according to [3], wherein the polarizing film has a cumulative stretch ratio of 5.9 or less based on a polyvinyl alcohol-based resin film having a thickness of 65 μm or less.

  [5] The production method according to any one of [1] to [4], wherein the final guide roll is an expander roll.

  According to the method of the present invention, curling or folding at both ends in the film width direction due to immersion in a crosslinking bath, which has conventionally occurred in a method of manufacturing a polarizing film from a thin polyvinyl alcohol-based resin film, is effectively suppressed. Can be.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically the manufacturing method of the polarizing film which concerns on this invention, and an example of the polarizing film manufacturing apparatus used for it.

<Method for manufacturing polarizing film>
In the present invention, the polarizing film is one in which a dichroic dye (iodine or a dichroic dye) is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, polyvinyl acetate which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate with another monomer copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and the like. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  These polyvinyl alcohol-based resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may also be used.

  In the present invention, an unstretched polyvinyl alcohol-based resin film (raw film) having a thickness of 65 μm or less, preferably about 10 to 50 μm, more preferably about 10 to 35 μm is used as a starting material for producing a polarizing film. Thereby, a thin polarizing film can be obtained. When the thickness of the raw film is greater than 65 μm, the mechanical strength of the film is sufficiently high, so that the curling or folding at the edge in the film width direction caused by immersing the film in the crosslinking bath causes almost no problem.

  The width of the raw film is not particularly limited, and may be, for example, about 400 to 6000 mm. However, as the film width is larger, curling and folding are more likely to occur. Therefore, the production method of the present invention is particularly effective when the width of the raw film is large, specifically, when the film width is 1000 m or more.

  The raw film is usually prepared as a roll (wound product) of a long unstretched polyvinyl alcohol-based resin film.

  The polarizing film can be continuously manufactured as a long polarizing film by continuously transporting the above-mentioned raw film along a film transport path of a polarizing film manufacturing apparatus and performing a predetermined processing step. The predetermined treatment step is a swelling treatment step of immersing the raw film in a swelling bath, a dyeing treatment step of immersing the film after the swelling treatment step in a dyeing bath, and a crosslinking treatment step of immersing the dyed film in a crosslinking bath. Can be included. Further, between these series of processing steps (that is, before or after any one or more processing steps and / or during any one or more processing steps), a uniaxial stretching treatment is performed by a wet or dry method. Other processing steps may be added as necessary.

  Each of the above treatment steps may be a treatment in which the film is immersed in one bath, or may be a treatment in which the film is sequentially immersed in two or more baths. In the polarizing film according to the present invention, at least the crosslinking treatment step is a treatment in which the film after the dyeing treatment step is sequentially immersed in two or more crosslinking baths. This is because problems such as curling and folding are likely to occur particularly when the crosslinking treatment is performed using two or more crosslinking baths.

  Hereinafter, the method for producing a polarizing film according to the present invention will be described in more detail with reference to FIG. FIG. 1 is a cross-sectional view schematically illustrating an example of a method for manufacturing a polarizing film according to the present invention and a polarizing film manufacturing apparatus used for the method. The polarizing film manufacturing apparatus shown in FIG. 1 transports a raw (unstretched) film 10 made of a polyvinyl alcohol-based resin along a film transport path while continuously unwinding the film from a feeding roll 11. The swelling bath 13, the dyeing bath 15, the first cross-linking bath 17a, the second cross-linking bath 17b, the third cross-linking bath 17c, and the cleaning bath 19 provided on the path are sequentially passed, and finally, the drying bath 21 is passed. It is configured. The obtained polarizing film 23 can be conveyed, for example, as it is to the next polarizing plate manufacturing step (the step of bonding a protective film to one or both sides of the polarizing film 23). The arrows in FIG. 1 indicate the direction in which the film is transported.

  In the example shown in FIG. 1, three cross-linking baths are used in the cross-linking treatment step. However, the present invention is not limited to this, and it is sufficient that two or more cross-linking baths are provided as described above. Further, the present invention is not limited to the example shown in FIG. 1 and may include two or more swelling baths, dyeing baths, and washing baths. In the present specification, a bath containing a treatment liquid for treating a polyvinyl alcohol-based resin film, such as a swelling bath, a dyeing bath, a crosslinking bath, and a washing bath, is also collectively referred to as a “treatment bath”.

  The film transport path of the polarizing film manufacturing apparatus includes, in addition to the treatment bath described above, guide rolls 30 to 47 that support the transported film or can further change the film transport direction, and press and pinch the transported film. The nip rolls 50 to 57, which can apply a driving force due to the rotation to the film or can change the film conveyance direction, can be constructed at appropriate positions. For example, the guide rolls can be arranged before and after each processing bath or in the processing bath, so that the film can be introduced into and dipped into the processing bath and drawn out of the processing bath (see FIG. 1). More specifically, two or more guide rolls (three or more, not limited to the example in FIG. 1) may be provided in each processing bath, and the film may be transported along these guide rolls. The film can be immersed in the treatment bath.

  Further, in the polarizing film manufacturing apparatus shown in FIG. 1, nip rolls are disposed before and after each processing bath (nip rolls 50 to 56), and thereby, are disposed before and after any one or more processing baths. It is possible to carry out inter-roll stretching in which longitudinal directional stretching is performed with a difference in peripheral speed between nip rolls. Hereinafter, each processing step will be described.

(Swelling treatment)
The swelling treatment is performed for the purpose of removing foreign substances on the surface of the raw film 10, removing a plasticizer in the raw film 10, imparting easy dyeability, plasticizing the raw film 10, and the like. The processing conditions are determined within a range in which the object can be achieved and a range in which problems such as extreme melting and devitrification of the raw film 10 do not occur.

  Referring to FIG. 1, the swelling process is performed by conveying the raw film 10 in a swelling bath 13 (a processing liquid stored in a swelling tank) by conveying the film 10 along a film conveying path constructed by guide rolls 30 to 32 and a nip roll 50. For a predetermined time, and then withdrawn. The uniaxial stretching treatment can be performed in the swelling bath 13 by utilizing the peripheral speed difference between the nip roll 50 and the nip roll 51.

  When swelling treatment is first performed on the raw film 10, the temperature of the swelling bath 13 is, for example, about 10 to 50 ° C, preferably about 10 to 40 ° C, and more preferably about 15 to 30 ° C. The immersion time of the raw film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. When the polyvinyl alcohol-based resin film stretched in advance in a gas is swelled, the temperature of the swelling bath 13 is, for example, 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.

  The swelling bath 13 contains boric acid (JP-A-10-153709), chloride (JP-A-06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc., in addition to pure water. It is also possible to use an aqueous solution added in the range of about 0.01 to 10% by weight.

  In the swelling process, a problem that the raw film 10 swells in the width direction and wrinkles are likely to occur in the film. As one means for transporting the film while removing the wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll may be used for the guide rolls 30, 31, and / or 32, a cross guider, a bend bar, or the like. And other widening devices such as tenter clips. Another means for suppressing the generation of wrinkles is to perform a stretching treatment.

  In the swelling process, the film expands and swells also in the transport direction of the film. Therefore, when the film is not actively stretched, in order to eliminate the slack of the film in the transport direction, for example, it is disposed before and after the swelling bath 13. It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51. In order to stabilize the film transport in the swelling bath 13, the water flow in the swelling bath 13 is controlled by a submerged shower, or an EPC device (Edge Position Control device: detects the end of the film and meanders the film). It is also useful to use an apparatus for preventing the above.

  In the example shown in FIG. 1, the film drawn from the swelling bath 13 passes through the guide roll 32 and the nip roll 51 in order and is introduced into the dyeing bath 15.

(Staining treatment)
The dyeing treatment is performed for the purpose of, for example, adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within a range in which the object can be achieved and a range in which problems such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, in the dyeing process, the film after the swelling process is transported along the film transport path constructed by the guide rolls 33 to 35 and the nip roll 51 and the swelling process is performed. ) For a predetermined time and then withdrawing. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing process is preferably a film that has been subjected to at least some uniaxial stretching, or, instead of the uniaxial stretching before the dyeing, Alternatively, in addition to the uniaxial stretching treatment before the dyeing treatment, it is preferable to perform the uniaxial stretching treatment during the dyeing treatment.

  When iodine is used as the dichroic dye, the concentration in the dye bath 15 is, for example, iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100 by weight. An aqueous solution can be used. Instead of potassium iodide, another iodide such as zinc iodide may be used, or potassium iodide and another iodide may be used in combination. Further, a compound other than iodide, for example, boric acid, zinc chloride, cobalt chloride or the like may be allowed to coexist. When boric acid is added, it is distinguished from the crosslinking treatment described below in that it contains iodine. If the aqueous solution contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, the dyeing bath 15 Can be considered. The temperature of the dye bath 15 when immersing the film is usually about 10 to 45 ° C., preferably 10 to 40 ° C., more preferably 20 to 35 ° C., and the immersion time of the film is usually 30 to 600 seconds. Degree, preferably 60 to 300 seconds.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, an aqueous solution having a concentration of dichroic dye / water = about 0.001 to 0.1 / 100 by weight is used as the dyeing bath 15. be able to. The dyeing bath 15 may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one dichroic dye may be used alone, or two or more dichroic dyes may be used in combination. The temperature of the dyeing bath 15 when immersing the film is, for example, about 20 to 80 ° C., preferably 30 to 70 ° C., and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. is there.

  As described above, in the dyeing process, the film can be uniaxially stretched in the dyeing bath 15. Uniaxial stretching of the film can be performed by a method such as providing a peripheral speed difference between a nip roll 51 and a nip roll 52 disposed before and after the dyeing bath 15.

  In the dyeing process, as in the case of the swelling process, in order to transport the polyvinyl alcohol-based resin film while removing wrinkles of the film, a widening function such as an expander roll, a spiral roll, and a crown roll is applied to the guide rolls 33, 34 and / or 35. Or other widening devices such as cross guiders, bend bars, tenter clips, etc. can be used. Another means for suppressing the generation of wrinkles is to apply a stretching treatment as in the case of the swelling treatment.

  In the example shown in FIG. 1, the film drawn from the dyeing bath 15 passes through the guide roll 35 and the nip roll 52 in order and is introduced into the first crosslinking bath 17a.

(Cross-linking treatment)
The cross-linking treatment is a treatment performed for the purpose of water resistance and hue adjustment (preventing the film from becoming bluish) by cross-linking. Referring to FIG. 1, the cross-linking treatment using the first cross-linking bath 17 a is carried out along the film conveying path constructed by the guide rolls 36 to 38 and the nip roll 52 and stores the cross-linking agent-containing liquid in the first cross-linking. It can be carried out by immersing the dyed film in the bath 17a (the processing liquid contained in the crosslinking tank) for a predetermined time and then pulling out the film. The same applies to the crosslinking treatment using the second crosslinking bath 17b and the third crosslinking bath 17c.

  The crosslinking agent-containing liquid contained in the first crosslinking bath 17a, the second crosslinking bath 17b, and the third crosslinking bath 17c contains, for example, about 1 to 10 parts by weight of boric acid as a crosslinking agent with respect to 100 parts by weight of water. It can be an aqueous solution. When the dichroic dye used in the dyeing treatment is iodine, these crosslinking baths preferably contain iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by weight with respect to 100 parts by weight of water. It can be by weight. Examples of the iodide include potassium iodide, zinc iodide and the like. Further, a compound other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

  In the crosslinking treatment, the concentration of the crosslinking agent (boric acid or the like) and iodide, and the temperature of the crosslinking bath can be appropriately changed depending on the purpose. For example, when the purpose of the cross-linking treatment is water resistance by cross-linking, and the polyvinyl alcohol-based resin film is subjected to a swelling treatment, a dyeing treatment, and a crosslinking treatment in this order, the concentration of the cross-linking agent-containing liquid in the cross-linking bath is determined by weight. It can be an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100. If necessary, another crosslinking agent such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and another crosslinking agent may be used in combination. The temperature of the crosslinking bath when immersing the film is usually about 50 to 70 ° C., preferably 53 to 65 ° C., and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably Is 20 to 200 seconds. On the other hand, when the dyeing treatment and the crosslinking treatment are performed in this order on the polyvinyl alcohol-based resin film stretched in advance, the temperature of the crosslinking bath is usually about 50 to 85 ° C, preferably 55 to 80 ° C.

  In the crosslinking treatment for the purpose of adjusting the hue, for example, when iodine is used as the dichroic dye, the crosslinking agent containing boric acid / iodide / water = 1 to 5/3 to 30/100 in weight ratio Liquids can be used. The temperature of the crosslinking bath when immersing the film is usually about 10 to 45 ° C., and the immersion time for the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

  When both the crosslinking treatment for water resistance and the crosslinking treatment for hue adjustment are performed, the crosslinking treatment for hue adjustment can be performed after the crosslinking treatment for water resistance. For example, in the example of FIG. 1, the crosslinking treatment using the first crosslinking bath 17a is for water resistance, the crosslinking treatment using the second crosslinking bath 17b is for water resistance or hue adjustment, and the third crosslinking bath 17c is The used crosslinking treatment can be used for the purpose of hue adjustment. However, the crosslinking treatment for the purpose of adjusting the hue is an optional treatment and may be omitted.

  The immersion treatment of the polyvinyl alcohol-based resin film after the dyeing treatment in the crosslinking bath can be performed by transporting the film along two or more guide rolls arranged in the crosslinking bath. By subsequent film transport, the film is then drawn out of the crosslinking bath by passing through the last (most downstream) guide roll (final guide roll) arranged in the crosslinking bath. In at least one of the two or more cross-linking baths, the film is pulled out of the cross-linking bath by passing through the final guide roll so that the angle of embrace in the final guide roll is 100 ° or more and less than 180 °. In this way, by adjusting the holding angle of the final guide roll to be shallower (larger) and reducing the restraint of the film by the final guide roll, curl at both ends in the film width direction which may occur when the film is pulled out from the crosslinking bath. And folding can be suppressed or prevented.

  Here, the hugging angle in the final guide roll is the angle θ shown in FIG. 1 and is the angle formed between the film before (immediately before) passing through the final guide roll and the film after (immediately after) passing through the final guide roll. , The angle on the side where the final guide roll exists. The holding angle can take a value of 0 to 180 °, but in the present invention, this is set to 100 ° or more and less than 180 °. When the angle θ is equal to or more than 180 °, the film is no longer in a state of being hung on the final guide roll, and therefore, the hugging angle of 180 ° or more does not exist conceptually.

  From the viewpoint of more effectively suppressing or preventing curling and folding, the holding angle of the final guide roll is preferably 135 to 178 °, and more preferably 145 to 175 °.

  At least one of the two or more cross-linking baths may be a cross-linking bath having a final guide roll arranged so as to have a wrap angle of 100 ° or more and less than 180 °, but curling or folding is more effectively suppressed or From the viewpoint of prevention, when the holding angle is not adjusted, it is preferable to adjust the holding angle to the above-mentioned predetermined range in a crosslinking bath in which these problems are particularly likely to occur.

  The following crosslinking baths can be given as examples of the crosslinking bath in which inconveniences such as curling and folding are likely to occur.

  (1) A cross-linking bath in which the film tension in the cross-linking bath is smaller than that of other cross-linking baths. If the film tension is relatively small, the above-mentioned problem is likely to occur, probably because both ends of the film in the width direction are loosened.

  (2) A cross-linking bath in which the concentration of a cross-linking agent (boric acid or the like) in a cross-linking bath (liquid containing a cross-linking agent) is lower than that of other cross-linking baths. When the film is immersed in a bath having a relatively low concentration of the crosslinking agent, the concentration of the crosslinking agent in the film also decreases. Due to this, it is considered that both ends in the width direction of the film are easily loosened.

  (3) A crosslinking bath in which the temperature of the crosslinking bath is higher than other crosslinking baths. If the temperature of the cross-linking bath is relatively high, the above-mentioned problems are likely to occur, probably because both ends of the film in the width direction are loosened.

  (4) A cross-linking bath in which the stretching ratio in the cross-linking bath is smaller than that in the other cross-linking baths. In order to impart a desired cumulative stretching ratio to the obtained polarizing film and enhance its polarizing properties, uniaxial stretching treatment can be performed in a plurality of crosslinking baths among two or more crosslinking baths. If it is small (for example, if the stretching ratio in the cross-linking bath is 1.14 times or less, further 1.1 times or less, and still more preferably 1.05 times or less), it is likely that both ends in the width direction of the film become loose. The above problems are likely to occur. Referring to FIG. 1, the uniaxial stretching treatment in the cross-linking bath can be performed using the peripheral speed difference between the nip roll 54 and the nip roll 55 in the case of, for example, the third cross-linking bath 17 c (for other cross-linking baths). The same). In addition, it is also possible to perform the uniaxial stretching treatment in one of the two or more crosslinking baths, and it is also possible not to perform the uniaxial stretching treatment in the crosslinking treatment. The magnification of stretching performed in the crosslinking bath is usually 1 or more, and typically more than 1 per one crosslinking bath.

  (5) The time from the dipping of the film in the cross-linking bath (the liquid containing the cross-linking agent) to the arrival at the final guide roll (corresponding to almost the dipping time) is 5 seconds or more, or compared with other cross-linking baths. And long crosslinking bath. When the immersion time is long, the change in the concentration of the crosslinking agent and the like contained in the film tends to be large. Due to this, it is considered that both ends in the width direction of the film are easily loosened.

  When the crosslinking treatment is performed using two or more crosslinking baths, generally, the crosslinking bath of the second stage or later (including the second stage) is at least one of the above (1) to (5) than the first crosslinking bath. , And the final crosslinking bath most easily conforms to at least one of the above (1) to (5). For example, when the final cross-linking bath is used as a cross-linking bath for the purpose of adjusting the hue, the concentration of boric acid is usually lower than that of other cross-linking baths. Therefore, in the present invention, the cross-linking bath for adjusting the holding angle to the above-mentioned predetermined range preferably includes the second-stage or later cross-linking bath, and more preferably includes the final cross-linking bath. FIG. 1 shows an example in which the holding angle is adjusted to the above-mentioned predetermined range in the final third crosslinking bath 17c among the three crosslinking baths. However, the holding angle may be adjusted to the above-mentioned predetermined range for a plurality of crosslinking baths of two or more crosslinking baths or for all the crosslinking baths.

  In the cross-linking treatment, an expander roll, a spiral roll, and a crown roll are used to guide the polyvinyl alcohol-based resin film while removing the wrinkles of the film, or to more effectively suppress or prevent curling and folding. , Or other widening devices such as a cross guider, a bend bar, and a tenter clip. In order to more effectively suppress or prevent curling and folding, the above-described widening function is particularly applied to the final guide roll (the guide roll 43 in FIG. 1) arranged so that the embrace angle is 100 ° or more and less than 180 °. It is preferable to use a roll having the above, and it is particularly preferable to use an expander roll. Performing a stretching treatment during the cross-linking treatment is also effective in suppressing wrinkles, curls, and folding.

  In the example shown in FIG. 1, the film drawn from the third crosslinking bath 17c passes through the guide roll 44 and the nip roll 55 in order and is introduced into the cleaning bath 19.

(Washing treatment)
The production method of the present invention can include a washing treatment step after the crosslinking treatment step. 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. The washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in the washing bath 19 (water), spraying the film with water as a shower, or using these in combination.

  FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform a cleaning process. The temperature of the washing bath 19 in the washing treatment is usually about 2 to 40 ° C., and the immersion time of the film is usually about 2 to 120 seconds.

  In the cleaning treatment, rolls having a widening function such as an expander roll, a spiral roll, and a crown roll are used for the guide rolls 45, 46, and / or 47 in order to transport the polyvinyl alcohol-based resin film while removing wrinkles. Alternatively, other widening devices such as cross guiders, bend bars, tenter clips, etc. can be used. In the washing process, a stretching process may be performed in order to suppress the generation of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched in a wet or dry manner between the above series of processing steps (that is, before and after one or more processing steps and / or during one or more processing steps). It is processed. A specific method of the uniaxial stretching treatment is, for example, a method in which a circumferential speed difference is applied between two nip rolls (for example, two nip rolls disposed before and after a treatment bath) constituting a film transport path to perform longitudinal uniaxial stretching. Stretching, hot roll stretching, tenter stretching and the like as described in Japanese Patent No. 2731813 can be used, and inter-roll stretching is preferable. The uniaxial stretching process can be performed a plurality of times until the polarizing film 23 is obtained from the raw film 10.

  The final cumulative stretching ratio of the polarizing film 23 based on the raw film 10 (unstretched polyvinyl alcohol-based resin film having a thickness of 65 μm or less) depends on the thickness of the raw film 10, but the obtained polarization is From the viewpoint of the polarization characteristics of the film 23, it is usually at least 4.5 times, preferably at least 5.0 times. On the other hand, if the cumulative stretch ratio is too high, the film becomes excessively thin and the handleability decreases, and the film tends to tear or break during the stretching process. When the thickness is less than 35 μm, it is preferably 5.9 times or less, more preferably 5.7 times or less, and even more preferably 5.5 times or less. When the thickness of the raw film 10 is 35 μm or more and 65 μm or less, it is preferably 6.3 times or less, more preferably 6.1 times or less, and even more preferably 5.9 times or less.

  The stretching step may be performed in any of the processing steps, and in the case where the stretching processing is performed in two or more processing steps, the stretching may be performed in any of the processing steps, but from the viewpoint of enhancing the dyeability of the dichroic dye. From, the film subjected to the dyeing process is preferably a film subjected to at least some uniaxial stretching treatment, or in place of the uniaxial stretching treatment before the dyeing treatment, or in addition to the uniaxial stretching treatment before the dyeing treatment In addition, it is preferable to perform a uniaxial stretching process during the dyeing process. Thereby, the stretched film is subjected to the crosslinking treatment step.According to the present invention, the film is thinned by stretching, and the film that is easily curled or folded is crosslinked. In addition, curling and folding can be effectively suppressed or prevented. In one preferred embodiment, the stretching treatment is performed in a swelling treatment step and / or a dyeing treatment step and a crosslinking treatment step.

  As described above, the stretching treatment can contribute to suppression of wrinkles of the conveyed film, and particularly curling and folding that occur in the crosslinking treatment. When the stretching ratio in the crosslinking treatment is low, this contribution is reduced and curling or folding is likely to occur. However, according to the present invention, the stretching ratio in each crosslinking bath in the crosslinking treatment is, for example, 1.14 times or less, and further, Can be effectively suppressed or prevented from being curled or folded even when it is as low as 1.1 times or less, and even as low as 1.05 times or less.

(Drying)
After the washing treatment, a treatment for drying the polyvinyl alcohol-based resin film is preferably performed. The drying of the film is not particularly limited, but can be performed using a drying furnace 21 as in the example shown in FIG. The drying temperature is, for example, about 30 to 100 ° C., and the drying time is, for example, about 30 to 600 seconds. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 μm.

(Other processing steps)
Processing other than the processing described above can be added. Examples of treatments that can be added include immersion treatment in a boric acid-free iodide aqueous solution (complementary color treatment) and immersion treatment in a boric acid-free aqueous solution containing zinc chloride or the like (zinc treatment) performed after the crosslinking treatment. Processing).

  In addition, in order to prevent the film drawn from the swelling bath 13 and / or the dyeing bath 15 from being curled or folded, the film drawn with the processing liquid attached to both sides of the film on both sides is A process for reducing the amount of liquid adhering at both ends in the width direction may be performed. The treatment for reducing the amount of liquid attached may be applied to the crosslinking bath. For example, in at least one crosslinking bath, the treatment for reducing the amount of liquid attached and the adjustment of the embrace angle to the above-described predetermined range may be used in combination. . Here, both ends in the width direction of the film are preferably about 2 to 20% of the entire width of the film in total at both ends. The treatment for reducing the liquid adhesion amount at both ends in the width direction can be performed, for example, by the following methods a) to c).

  a) A method in which a gas is sprayed on both surfaces of a polyvinyl alcohol-based resin film drawn out of a treatment bath to remove at least liquid adhering to the surfaces at both ends in the film width direction to reduce the amount of liquid adhering. The gas spraying process can be performed using a pipe (pipe) or a hose having one or a plurality of injection holes from which gas is injected, or a gas spraying device such as an air knife.

  The type of gas used for the gas spraying process is not particularly limited, but is generally a gas inert gas such as air, nitrogen, or argon, preferably air. The injection pressure of the gas is not particularly limited as long as the attached liquid can be blown off.

  In order to suppress the curl or folding of the film drawn from the processing bath, it is sufficient to perform the gas spraying process only on the both ends in the width direction on both sides of the film, but in addition to the both ends in the width direction, other films may be used. A gas spraying process can also be performed on the surface region. For example, a gas spraying process may be performed on the entire surface of both sides of the film.

  For example, referring to FIG. 1, when performing a gas spraying process on a film drawn out of the swelling bath 13, the gas spraying device causes the film to be drawn out of the swelling bath 13 between the guide roll 32 and the nip roll 51. The guide roller 32 can be installed at a position from when it reaches the guide roll 32 or at both positions. Preferably, the gas spraying process is performed on at least the film immediately after being drawn from the liquid level of the processing bath.

  b) By contacting (pressing) rolls or bars on both sides of the polyvinyl alcohol-based resin film drawn out of the treatment bath, at least liquid adhering to the surfaces at both ends in the film width direction is dropped by the rolls or bars. A method to reduce the amount of adhesion.

  The roll to be brought into contact with the surface at both ends in the film width direction may be a pair of rolls, such as a cross guider, that sandwich the polyvinyl alcohol-based resin film drawn from the treatment bath from both sides. The liquid that has passed through the pair of rolls is peeled off in the surface area that has come into contact with the rolls. On the other hand, the bar to be brought into contact with the surface at both ends in the width direction of the film is not a rotating itself such as a roll, sandwiches the polyvinyl alcohol-based resin film drawn from the processing bath from both sides, or sequentially turns the film one by one. And a pair of rod-shaped objects that are brought into contact with. Even in the case of using such a bar, the liquid that has passed through the space between the bars is stripped of the adhered liquid in the surface area in contact with the bar.

  The surface of the roll and bar that comes into contact with the film may be made of metal such as stainless steel, or may be made of rubber, sponge, or the like. The shape of the roll and the bar may be such that the surface in contact with the film is a curved surface, but is preferably a cylindrical shape. When a cylindrical roll or bar is used, its diameter is about 5 to 100 mm, preferably 10 to 50 mm. When the diameter is in this range, the film can be smoothly transported.

  In order to suppress the curl and folding of the film drawn from the processing bath, it is sufficient to perform a process of bringing a roll or a bar into contact only with both ends in the width direction on both surfaces of the film. Alternatively, the contact treatment may be performed on other film surface regions. For example, the contact processing may be performed on both surfaces of the film. The installation angles of the roll and the bar are not particularly limited, and the longitudinal direction of the roll and the bar may be parallel to the film width direction or may be inclined with respect to the film width direction.

  For example, referring to FIG. 1, when the film drawn from the swelling bath 13 is subjected to a contact treatment with the roll or the bar, the contact treatment is performed between the guide roll 32 and the nip roll 51 and the film swells. It can be carried out between withdrawal from the bath 13 and before reaching the guide roll 32 or at both these positions. Preferably, the contact treatment with a roll or a bar is performed on at least the film immediately after being pulled out from the liquid level of the treatment bath.

  c) A method in which a polyvinyl alcohol-based resin film drawn from a treatment bath is introduced into a nip roll, and the liquid adhering to the film surface is dropped by the nip roll to reduce the amount of liquid adhering. In this method, the liquid adhering to both sides of the film is generally stripped off.

  In the case of performing the process of reducing the amount of liquid attached only to both ends in the film width direction using the method a) or b), the film drawn from the treatment bath and subjected to the process of reducing the amount of liquid attached is usually Is transported using a flat roll which is a cylindrical guide roll having a constant diameter over the entire width. That is, when the film drawn out of the processing bath and subjected to the processing for reducing the amount of liquid attached passes through the guide rolls first and then passes through the nip rolls, the one or more guide rolls must be flat rolls. Is preferred. By transporting a film that has been treated to reduce the amount of liquid attached using a flat roll that is placed horizontally with respect to the ground, liquid at the center in the width direction of the film flows into both ends during film transport. Therefore, curling and folding at both ends of the film can be more effectively suppressed.

<Polarizing plate>
A polarizing plate can be obtained by laminating a protective film on at least one side of the polarizing film manufactured as described above via an adhesive. Examples of the protective film include a film made of an acetylcellulose resin such as triacetylcellulose and diacetylcellulose; a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; An olefin-based resin film; an acrylic-based resin film; and a film made of a chain-like olefin-based resin of a polypropylene-based resin.

  In order to improve the adhesion between the polarizing film and the protective film, the surface of the polarizing film and / or the protective film to be bonded is subjected to a corona treatment, a flame treatment, a plasma treatment, an ultraviolet irradiation, a primer coating treatment, a saponification treatment, or the like. Processing may be performed. As the adhesive used for bonding the polarizing film and the protective film, an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, or an aqueous solution in which a crosslinking agent is blended therewith And water-based adhesives such as urethane-based emulsion adhesives. The UV-curable adhesive may be a mixture of an acrylic compound and a photo-radical polymerization initiator, or a mixture of an epoxy compound and a photo-cationic polymerization initiator. Further, a cationically polymerizable epoxy compound and a radically 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 initiators.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

<Example 1>
A polarizing film was manufactured using the same apparatus as the polarizing film manufacturing apparatus shown in FIG. Flat rolls were used for all the guide rolls 30 to 41.

(1) Swelling treatment step A 30 μm-thick polyvinyl alcohol film [Kuraray Co., Ltd. product name “Kuraray Poval Film VF-PE # 3000”, degree of polymerization 2400, degree of saponification 99.9 mol% or more] is continuously provided. It was transported and immersed in a swelling bath 13 containing pure water at 20 ° C. for 30 seconds. In this swelling treatment, a peripheral speed difference is applied between the nip rolls 50 and 51 so that the film width immediately after being drawn out of the swelling bath 13 is equal to or less than the film width before immersion in the swelling bath 13 (longitudinal uniaxial stretching). ) Was done. The stretching ratio based on the raw film 10 was 2.5 times.

  The film drawn from the swelling bath 13 is blown by a gas blower (air spray nozzle) installed before the guide roll 32 and a gas blower (air spray nozzle) installed between the guide roll 32 and the nip roll 51. Using a nozzle), air was jetted to both ends in the width direction on both surfaces of the film to remove the liquid adhering thereto.

(2) Dyeing Step Next, the film that passed through the nip roll 51 was immersed in a dyeing bath 15 at 30 ° C. in which iodine / potassium iodide / water (weight ratio) was 0.05 / 2/100 for 120 seconds. Also in this dyeing treatment, a peripheral speed difference is provided between the nip rolls 51 and 52 so that the film width immediately after being drawn out of the dyeing bath 15 is equal to or less than the film width before immersion in the dyeing bath 15 (longitudinal uniaxial). Stretching). The cumulative stretch ratio in the swelling process and the dyeing process based on the raw film 10 was 2.7 times (the stretch ratio in the dyeing process was 1.08 times).

(3) Cross-linking treatment step Next, in order to perform a first cross-linking treatment for water resistance, the film passed through the nip roll 52 is subjected to potassium iodide / boric acid / water (weight ratio) of 12 / 4.4. It was immersed in the first crosslinking bath 17a at 55 ° C./100 for 30 seconds. Also in this first crosslinking treatment, the nip roll 52, the first crosslinking bath 17a, and the second crosslinking bath 17a are so set that the film width immediately after being drawn from the first crosslinking bath 17a is not more than the film width before immersion in the first crosslinking bath 17a. Two rolls were stretched (longitudinal uniaxial stretching) with a difference in peripheral speed between the nip roll 53 and the nip roll 53 provided between the two crosslinking baths 17b. The cumulative stretch ratio in the swelling process, the dyeing process and the first crosslinking process based on the raw film 10 was 4.3 times (the stretching ratio in the first crosslinking process was 1.6 times).

  Next, the film after the first cross-linking treatment was immersed in a second cross-linking bath 17b having the same composition as that of the first cross-linking bath 17a at 59 ° C. for 30 seconds (second cross-linking treatment). Also in the second crosslinking treatment, the nip roll 53, the second crosslinking bath 17b, and the second crosslinking bath 17b are set so that the film width immediately after being drawn from the second crosslinking bath 17b is equal to or less than the film width before immersion in the second crosslinking bath 17b. Stretching between the rolls (longitudinal uniaxial stretching) was performed with a difference in peripheral speed between the nip roll 54 and the nip roll 54 installed between the third crosslinking bath 17c. The cumulative stretch ratio in the swelling process, the dyeing process, the first crosslinking process, and the second crosslinking process based on the raw film 10 was 5.4 times (the stretching ratio in the second crosslinking process was 1.25 times). ).

  Next, in order to perform a cross-linking treatment for the purpose of adjusting hue, it was immersed in a third cross-linking bath 17c at 40 ° C. in which potassium iodide / boric acid / water (weight ratio) was 9 / 2.9 / 100 for 15 seconds ( Third crosslinking treatment). At that time, the film was conveyed by setting the angle of holding of the film on the final guide roll 43 arranged in the third crosslinking bath 17c to 160 °. Also in the third crosslinking treatment, the peripheral speed difference between the nip roll 54 and the nip roll 55 is set so that the film width immediately after being drawn from the third crosslinking bath 17c is equal to or less than the film width before immersion in the third crosslinking bath 17c. To perform roll-to-roll stretching (longitudinal uniaxial stretching). The cumulative stretch ratio in the swelling process, the dyeing process, the first crosslinking process, the second crosslinking process, and the third crosslinking process based on the raw film 10 was 5.5 times (stretching in the third crosslinking process). Magnification is 1.02 times).

  Thereafter, the film after the third cross-linking treatment was immersed in a washing bath 19 containing pure water at 5 ° C., and then dried at 70 ° C. for 3 minutes by passing through a drying furnace 21 to produce a polarizing film 23. .

  When the above polarizing film production was continuously performed for 24 hours, no curl or fold was observed at both ends in the film width direction in any of the processing steps during the operation for 24 hours. No break or break was observed.

<Example 2>
The cumulative stretch ratio in the swelling process, the dyeing process, the first crosslinking process, the second crosslinking process, and the third crosslinking process based on the raw film 10 is 6.0 times (the stretching ratio in the third crosslinking process is 1.11 times), and the production of the polarizing film was continuously performed for 24 hours in the same manner as in Example 1. During operation for 24 hours, no curl or fold at both ends in the film width direction was observed in any of the processing steps, and no fold was found in the film, but with the cumulative stretch ratio increased to 6.0 times, During 24 hours of operation, one break of the film occurred.

<Example 3>
The production of the polarizing film was continuously performed for 24 hours in the same manner as in Example 1 except that the holding angle of the film on the final guide roll 43 arranged in the third crosslinking bath 17c was 135 °. During the operation for 24 hours, no curl or fold was found at both ends in the film width direction in any of the processing steps, and no fold or breakage of the film that could be caused by these was found.

<Example 4>
The production of the polarizing film was continuously performed for 24 hours in the same manner as in Example 1 except that the holding angle of the film on the final guide roll 43 arranged in the third crosslinking bath 17c was 110 °. Immediately every 5 hours at a location immediately after being pulled out from the third crosslinking bath 17c, a 1-mm wide fold occurred at both ends in the film width direction. However, no breakage of the film was observed during the operation for 24 hours.

<Comparative Example 1>
The production of the polarizing film was continuously performed for 24 hours in the same manner as in Example 1 except that the holding angle of the film on the final guide roll 43 arranged in the third crosslinking bath 17c was set to 80 °. At a point immediately after being drawn out from the third cross-linking bath 17c, a fold having a width of 1 mm is generated about every two hours at both ends in the film width direction. Eyes were formed and the film broke. The film broke twice during the 24-hour operation.

<Comparative Example 2>
The production of the polarizing film was continuously performed for 24 hours in the same manner as in Example 1 except that the holding angle of the film on the final guide roll 43 arranged in the third crosslinking bath 17c was 30 °. Immediately after being pulled out from the third cross-linking bath 17c, a fold of 2 mm width always occurs at both ends in the film width direction. In this state, when the film passes through the nip roll 55, a fold is formed at the end of the film. Fracture occurred. The film broke 5 times during a 24-hour run.

  Reference Signs List 10 Raw film made of polyvinyl alcohol resin, 11 Feeding roll, 13 Swelling bath, 15 Dyeing bath, 17a First crosslinking bath, 17b Second crosslinking bath, 17c Third crosslinking bath, 19 Cleaning bath, 21 Drying furnace, 23 Polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47 Guide roll, 50, 51, 52, 53, 54 , 55, 56, 57 Nip roll.

Claims (6)

A method of producing a polarizing film by carrying out at least a dyeing treatment and a crosslinking treatment of sequentially immersing in a two or more baths containing a crosslinking agent-containing liquid while conveying a polyvinyl alcohol-based resin film having a thickness of 65 μm or less, ,
In at least one of the two or more baths, the polyvinyl alcohol-based resin film is stretched at a stretch ratio of 1.14 times or less, and is stretched along two or more guide rolls arranged in the bath. A manufacturing method, wherein the wrapping angle is 100 ° or more and less than 180 ° in the last guide roll that passes last among the two or more guide rolls.   Stretching is performed in the at least one bath having the final guide rolls arranged so that the embracing angle is not less than 100 ° and less than 180 °, and the stretching ratio in the stretching in each bath is 1.14 or less. The production method according to claim 1, wherein   3. The method according to claim 1, wherein the holding angle is 135 ° or more and less than 180 °. 4. The method according to any one of claims 1 to 3 , wherein the polyvinyl alcohol-based resin film subjected to the crosslinking treatment is a stretched film. The production method according to claim 4 , wherein a cumulative stretch ratio of the polarizing film based on a polyvinyl alcohol-based resin film having the thickness of 65 µm or less is 5.9 or less. The production method according to any one of claims 1 to 5 , wherein the final guide roll is an expander roll.

Images