JP2020129152A - Production method for polarizing film - Google Patents

Abstract

To provide a production method for a polarizing film by which a thin polarizing film having a low shrinking force can be produced while suppressing breakage of a polyvinyl alcohol resin film and suppressing shrinkage in a width direction.SOLUTION: The production method of a polarizing film includes: a width restriction step of bringing a polyvinyl alcohol resin film after brought into contact with a processing liquid, into contact with at least one free roll having a diameter of 150 mm or more to restrict the film in a width direction; and a drying step of, after the width restriction step, drying the polyvinyl alcohol resin film.SELECTED DRAWING: Figure 1

Description

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

As the polarizing film, a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented is conventionally used. A polarizing film is usually used as a polarizing plate by laminating a protective film on one or both sides with an adhesive, and is used in image display devices typified by liquid crystal display devices such as liquid crystal televisions, personal computer monitors and mobile phones. It is used. In recent years, as the liquid crystal display device has become thinner, a thinner polarizing film has been required.

In general, a polarizing film is a continuous polyvinyl alcohol-based resin film that is continuously conveyed, in a bath, for example, after each treatment such as swelling, dyeing, crosslinking, stretching, and the like, after performing a cleaning treatment. It is manufactured by drying (see, for example, JP 2009-48179 A).

JP, 2009-48179, A

Since the polyvinyl alcohol-based resin film provided in the drying step is stretched, the film shrinks in the width direction when moisture is removed by the drying step, and the thickness increases due to the shrinkage in the width direction. However, the demand for thinning has not been satisfied.

Patent Document 1 provides a thin polarizing film by suppressing shrinkage in the width direction in the drying step by bringing a polyvinyl alcohol-based resin film into contact with a plurality of hot rolls and drying in the drying step. Is listed. However, when a polyvinyl alcohol-based resin film having a high water content is brought into contact with a hot roll and constrained in the width direction, there is a problem that the polyvinyl alcohol-based resin film is easily broken.

On the other hand, a method of suppressing shrinkage in the width direction by performing a drying step after the moisture content of the polyvinyl alcohol-based resin film becomes low to some extent is conceivable. According to such a method, the frictional force between the polyvinyl alcohol-based resin film and the roll is reduced. Therefore, the width direction cannot be sufficiently restrained only by bringing the polyvinyl alcohol resin film into contact with the roll, and it is necessary to mechanically fix the width direction with a tenter clip or the like. There is a problem that the film is easily broken.

An object of the present invention is to provide a method for producing a polarizing film capable of producing a thin polarizing film having a small shrinking force by suppressing shrinkage in the width direction while suppressing breakage of the polyvinyl alcohol-based resin film. To do.

The present invention provides the following method for producing a polarizing film.
[1] A width constraining step of constraining the polyvinyl alcohol-based resin film after contacting the treatment liquid with at least one free roll having a diameter of 150 mm or more to constrain it in the width direction,
And a drying step of drying the polyvinyl alcohol-based resin film after the width restraining step.

[2] In the width constraining step, the polyvinyl alcohol-based resin film is brought into contact with a plurality of rolls including the free roll, and at least 40 from a time when the first roll is contacted to a time when it is released from the last roll. %, the method for producing a polarizing film according to [1], which is in contact with either roll.

[3] The polarized light according to [1] or [2], wherein the polyvinyl alcohol-based resin film is contacted with the first roll in the width constraining step within 20 seconds after the contact with the treatment liquid is completed. Film manufacturing method.

[4] In the polarizing film according to any one of [1] to [3], the polyvinyl alcohol-based resin film has a water content of 30% by weight or more at the time of contact with the first roll in the width constraining step. Production method.

According to the method of the present invention, it is possible to manufacture a thin polarizing film having a small shrinkage force by suppressing shrinkage in the width direction while suppressing breakage of the polyvinyl alcohol-based resin film.

It is sectional drawing which shows typically an example of the manufacturing method of the polarizing film which concerns on this invention, and the polarizing film manufacturing apparatus used for it. It is sectional drawing which shows typically an example of the roll structure in a width restraint part. It is sectional drawing which shows typically an example of the roll structure in a width restraint part. It is sectional drawing which shows typically an example of the roll structure in a width restraint part. It is sectional drawing which shows typically an example of the roll structure in a width restraint part.

<Method of manufacturing polarizing film>
In the present invention, the polarizing film is a uniaxially stretched polyvinyl alcohol resin film in which a dichroic dye (iodine or dichroic dye) is adsorbed and oriented. The polyvinyl alcohol resin that constitutes the polyvinyl alcohol resin film is usually obtained by saponifying a polyvinyl acetate 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 and 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 1000 to 10000, preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified, and for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like may be used.

In the present invention, as a starting material for producing a polarizing film, an unstretched polyvinyl alcohol-based resin film (raw fabric) having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and further preferably 30 μm or less Film) is used. As a result, it is possible to obtain a thin polarizing film whose market demand is increasing. The thinner the raw film is, the more likely the film is broken during the stretching treatment. However, according to the present invention, the film break can be effectively suppressed even when the raw film is thin. The raw film may be a polyvinyl alcohol-based resin film that has been stretched in the gas phase in advance.

The width of the raw film is not particularly limited and may be, for example, about 400 to 6000 mm, but the larger the film width, the more easily the film breaks during the stretching treatment.

In the present invention, the raw film is prepared as a roll (raw roll) of a long unstretched polyvinyl alcohol resin film.

Polarizing film, while unwinding the long raw fabric film from the raw fabric roll, after carrying out the treatment step of being continuously transported along the film transport path of the polarizing film manufacturing apparatus to contact the treatment liquid, By performing the width constraining step and then performing the drying step, it is possible to continuously manufacture a long polarizing film.

Examples of the treatment step include, for example, a swelling treatment step in which the raw film is immersed in a swelling bath and then drawn out, a dyeing treatment step in which the film after the swelling treatment is immersed in a dyeing bath and then drawn out, and a film after the dyeing treatment is crosslinked. A cross-linking treatment step may be included in which the cross-linking treatment is performed after the dipping. In addition, a uniaxial stretching treatment is performed by a wet or dry method between these series of treatment steps (that is, before and/or after any one or more treatment steps and/or during any one or more treatment steps). Other processing steps may be added as needed. Each of the above-mentioned treatment steps may be a treatment of dipping the film in one bath, or a treatment of successively dipping in two or more baths.

In the width constraining step, the polyvinyl alcohol-based resin film after being brought into contact with the processing liquid in the processing step is brought into contact with at least one free roll having a diameter of 150 mm or more (hereinafter, also referred to as “large diameter free roll”). This is a step of constraining in the width direction. The roll with which the polyvinyl alcohol resin film is brought into contact in the width constraining step may include one or more large-diameter free rolls, and in addition, a free roll having a diameter of less than 150 mm and a drive roll. The contact of the polyvinyl alcohol-based resin film with the roll as referred to in the present specification means not a point contact but a surface contact (the polyvinyl alcohol-based resin film is in contact with the free roll with a width in the length direction). .. Due to the surface contact, the polyvinyl alcohol resin film is constrained in the width direction.

Here, the free roll is a roll to which a driving means such as a motor is not attached. By using the free roll as a means for restraining the width direction of the polyvinyl alcohol resin film brought into contact with the treatment liquid as described above, breakage of the polyvinyl alcohol resin film can be suppressed. In the present invention, by providing such a width constraining step, the polyvinyl alcohol-based resin film will be gently dried in the state of being constrained in the width direction, without applying a large load to the polyvinyl alcohol-based resin film, the width By suppressing the shrinkage in the direction, a thin polarizing film having a small shrinkage force can be manufactured.

The drying step is a step of obtaining a polarizing film by drying the polyvinyl alcohol-based resin film that has been subjected to the width constraining step, for example, a step of reducing the water content to less than 15% by weight.

Hereinafter, the manufacturing method of the 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 showing an example of a method for manufacturing a polarizing film according to the present invention and an apparatus for manufacturing a polarizing film used for the method. The polarizing film manufacturing apparatus shown in FIG. 1 is a film produced by feeding a raw (unstretched) film 10 made of a polyvinyl alcohol-based resin along a film feeding path while continuously unwinding it from a raw roll 11. The swelling bath 13, the dyeing bath 15, the cross-linking bath 17, and the washing bath 19 provided on the transport path are sequentially passed, then the width restraint 70 is passed, and finally the drying oven 90 is passed. There is. The obtained polarizing film can be conveyed as it is, for example, to the next polarizing plate manufacturing step (a step of laminating a protective film on one side or both sides of the polarizing film 23). The arrow in FIG. 1 indicates the transport direction of the film.

Although FIG. 1 shows an example in which one swelling bath 13, one dyeing bath 15, one crosslinking bath 17 and one washing bath 19 are provided, any one or more treatment baths (swelling bath 13 , A dye bath 15, a cross-linking bath 17, and a washing bath 19, which collectively contain a treatment liquid for treating a polyvinyl alcohol-based resin film provided on a film transport path, are also collectively referred to as a “treatment bath”. .) may be provided in two or more tanks.

In addition to the processing bath, the width restraint unit 70, and the drying oven 90, the film transport path of the polarizing film manufacturing apparatus supports the transported film, or guide rolls 30 to 41 capable of changing the film transport direction. 60, 61, 81, and nip rolls 50 to 54, 82, 83 capable of pressing and sandwiching a conveyed film and giving a driving force to the film by its rotation or further changing the film conveying direction. It can be constructed by arranging it at an appropriate position. The guide rolls and nip rolls can be arranged before and after each treatment bath, a drying oven, or in the treatment bath, so that the film can be introduced into the treatment bath, dipped in the treatment bath, and withdrawn from the treatment bath [Fig. 1]. reference〕. For example, the film can be immersed in each treatment bath by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls.

In the polarizing film manufacturing apparatus shown in FIG. 1, nip rolls are arranged before and after each treatment bath (nip rolls 50 to 54), whereby nip rolls arranged before and after the treatment bath in any one or more treatment baths. It is possible to perform roll-to-roll stretching in which longitudinal uniaxial stretching is performed with a peripheral speed difference. Each step will be described below.

(Swelling process)
The swelling treatment step is performed for the purpose of removing foreign matters on the surface of the raw film 10, removing the 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 dissolution and devitrification of the raw film 10 do not occur.

Referring to FIG. 1, in the swelling treatment step, while unwinding the raw fabric film 10 from a raw fabric roll 11, the raw fabric film 10 is transported along a film transport path, and the raw fabric film 10 is immersed in a swelling bath 13 for a predetermined time. And then withdrawing. In the example of FIG. 1, from the unwinding of the raw fabric film 10 to the dipping in the swelling bath 13, the raw fabric film 10 is transported along the film transport path constructed by the guide rolls 60 and 61 and the nip roll 50. To be done. In the swelling process, the film is conveyed along the film conveyance path constructed by the guide rolls 30 to 32.

As the swelling liquid for the swelling bath 13, in addition to pure water, boric acid (JP-A-10-153709), chloride (JP-A06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohol It is also possible to use an aqueous solution in which the compounds are added in the range of about 0.01 to 10% by weight.

The temperature of the swelling bath 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, 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 raw film 10 is a polyvinyl alcohol-based resin film stretched in gas in advance, 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 raw film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling treatment, a problem that the raw film 10 swells in the width direction and wrinkles are formed in the film easily occurs. As one means for conveying the film while removing the wrinkles, a roll having a widening function such as an expander roll, a spiral roll or a crown roll is used for the guide rolls 30, 31 and/or 32, or a cross guider or a bend bar. , Other widening devices such as tenter clips may be used. Another means for suppressing the generation of wrinkles is to carry out a stretching treatment. For example, 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.

In the swelling treatment, the film swells and expands also in the transport direction of the film. Therefore, when the film is not stretched positively, the film is placed before and after the swelling bath 13 in order to eliminate the slack of the film in the transport direction. It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51. Further, for the purpose of stabilizing the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 can be controlled by an underwater shower, or an EPC device (Edge Position).
Control device: A device that detects the edge of the film and prevents the film from meandering) is also useful.

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.

(Dyeing process)
The dyeing treatment step is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within the range where the object can be achieved, and within the range where problems such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, in the dyeing treatment step, the film after the swelling treatment is conveyed along the film conveyance path constructed by the guide rolls 33 to 35 and the nip roll 51, and the dyeing bath 15 (the treatment stored in the dyeing tank is performed. It can be carried out by soaking in a liquid for a predetermined time and then withdrawing. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing treatment step is preferably a film that has been subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, 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 dyeing solution in the dyeing bath 15 has, for example, a concentration of iodine/potassium iodide/water in a weight ratio of about 0.003 to 0.3/about 0.1 to 10/. An aqueous solution of 100 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. In addition, 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 the crosslinking treatment described later in that it contains iodine, and 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 regarded as The temperature of the dyeing bath 15 at the time of dipping the film is usually about 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C, and the dipping time of the film is usually 30 to 600 seconds. It is about 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic pigment, the dyeing solution in the dyeing bath 15 has, for example, a concentration of dichroic dye/water of about 0.001 to 0.1/100 by weight. An aqueous solution can be used. The dyeing bath 15 may coexist with a dyeing aid 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 dipping the film is, for example, about 20 to 80° C., preferably 30 to 70° C., and the dipping 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 treatment step, the film can be uniaxially stretched in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method of providing a peripheral speed difference between the nip rolls 51 and 52 arranged before and after the dyeing bath 15.

In the dyeing process as well, as in the swelling process, in order to convey the polyvinyl alcohol-based resin film while removing the wrinkles of the film, the guide rolls 33, 34 and/or 35 have a widening function such as an expander roll, a spiral roll or a crown roll. Can be used, or other widening devices such as cross guiders, bend bars, tenter clips can be used. Another means for suppressing the generation of wrinkles is to carry out a stretching treatment as in 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 crosslinking bath 17.

(Crosslinking process)
The crosslinking treatment step is a treatment performed for the purpose of making the film resistant to water and adjusting the hue (for example, preventing the film from becoming bluish). With reference to FIG. 1, the crosslinking treatment is carried along a film conveying path constructed by the guide rolls 36 to 38 and the nip roll 52, and after the dyeing treatment in the crosslinking bath 17 (the crosslinking liquid stored in the crosslinking tank). It can be carried out by soaking the film for a predetermined time and then withdrawing it.

The cross-linking liquid of the cross-linking bath 17 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking liquid preferably contains 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. Can be Examples of iodides 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.

In the cross-linking treatment, the concentrations of boric acid and iodide, and the temperature of the cross-linking bath 17 can be appropriately changed depending on the purpose. For example, the purpose of the cross-linking treatment is water resistance by cross-linking, and when the polyvinyl alcohol-based resin film is subjected to swelling treatment, dyeing treatment and cross-linking treatment in this order, the cross-linking agent-containing liquid in the cross-linking bath has a concentration by weight ratio. It can be an aqueous solution of boric acid/iodide/water=3 to 10/1 to 20/100. If necessary, other cross-linking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, and boric acid and other cross-linking agents may be used in combination. The temperature of the crosslinking bath when dipping the film is usually about 50 to 70° C., preferably 53 to 65° C., and the dipping time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably Is 20 to 200 seconds. When the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment is subjected to the dyeing treatment and the crosslinking treatment in this order, the temperature of the crosslinking bath 17 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 concentration of the crosslinking agent is boric acid/iodide/water=1 to 5/3 to 30/100. A liquid can be used. The temperature of the crosslinking bath when dipping the film is usually 10 to 45°C.
The dipping time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment may be carried out multiple times, usually 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different as long as they are within the above ranges. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment may be performed in a plurality of steps.

The uniaxial stretching treatment may be performed in the crosslinking bath 17 by utilizing the peripheral speed difference between the nip roll 52 and the nip roll 53.

Also in the cross-linking treatment, as in the swelling treatment, in order to convey the polyvinyl alcohol-based resin film while removing the wrinkles of the film, a widening function such as an expander roll, a spiral roll or a crown roll is provided on the guide rolls 36, 37 and/or 38. Can be used, or other widening devices such as cross guiders, bend bars, tenter clips can be used. Another means for suppressing the generation of wrinkles is to carry out a stretching treatment as in the swelling treatment.

In the example shown in FIG. 1, the film drawn from the crosslinking bath 17 passes through the guide roll 38 and the nip roll 53 in order and is introduced into the film washing bath 19.

(Cleaning process)
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 resin film. The cleaning treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in the film cleaning bath 19, spraying a film cleaning liquid on the film as a shower, or by 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 film washing bath 19 in the film washing treatment is usually about 2 to 40° C., and the dipping time of the film is usually about 2 to 120 seconds.

Even in the cleaning treatment, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used for the guide rolls 39, 40 and/or 41. Alternatively, other widening devices such as cross guiders, bend bars, tenter clips can be used. In addition, in the film washing process, a stretching process may be performed to suppress the generation of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched by a wet or dry method during the series of treatment steps (that is, before and/or after any one or more treatment steps and/or during any one or more treatment steps). It is processed. A specific method of the uniaxial stretching treatment is, for example, between rolls that perform longitudinal uniaxial stretching by providing a peripheral speed difference between two nip rolls (for example, two nip rolls arranged before and after the treatment bath) that form a film transport path. Stretching, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, and the like can be used, and interroll stretching is preferable. The uniaxial stretching treatment step can be performed a plurality of times before obtaining the polarizing film 23 from the original film 10. As described above, the stretching treatment is also advantageous in suppressing the generation of wrinkles in the film.

The final cumulative draw ratio of the polarizing film 23 based on the original film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

The stretching treatment step may be performed in any of the above treatment steps as long as it is before the width constraining step, and in the case where the stretching treatment is performed in two or more treatment steps, the stretching treatment may be performed in any treatment step. ..

(Width restraint process)
After the cleaning step, a width constraining step is performed in which the polyvinyl alcohol-based resin film is brought into contact with at least one large-diameter free roll having a diameter of 150 mm or more to constrain the width direction.

In the width constraining step, the polyvinyl alcohol-based resin film does not need to be constantly in contact with the roll, but from the viewpoint of effective width constraining, it is preferably 0.5 seconds or longer, more preferably 2 seconds or longer. It is preferred that there is a continuous contact time of. The present invention includes at least one large-diameter free roll having a diameter of 150 mm or more as a roll used in the width constraining step. According to the large diameter free roll, it becomes easy to secure the continuous contact time as described above. The diameter of the large diameter free roll is preferably 200 mm or more, more preferably 300 mm or more. The diameter of the large-diameter free roll is preferably less than 450 mm. When the diameter is 450 mm or more, the polyvinyl alcohol-based resin film may be loaded due to the free roll rotation resistance, and the polyvinyl alcohol-based resin film may be easily broken. In the width constraining step, it is preferable to include two or more large-diameter free rolls.

The number of rolls used in the width constraining step is preferably 3 or more and 5 or less, including the large-diameter free roll described above, because the direction in which the polyvinyl alcohol-based resin film is conveyed can be adjusted and curling can be performed. Is more preferable. When multiple rolls are used, the polyvinyl alcohol-based resin film is in contact with either roll for at least 40% of the time between the first roll being contacted with the width restraining step and the release from the last roll. Preferably. When the time of contact with the roll is 40% or more, a sufficient width restraining effect can be obtained. The contact time with the roll is more preferably 70% or more. The time of contact with the rolls can be adjusted by the number of rolls, the position of the rolls, and the angle of wrapping the rolls. Further, from the viewpoint of effectively restraining the width, the continuous time in which the polyvinyl alcohol-based resin film is not in contact with the roll is preferably 2 seconds or less.

In this specification, the point of contact with the first roll in the width constraining step is the introduction point of the width constraining step, and the point released from the last roll is the derivation point of the width constraining step. When only one roll is used in the width constraining step, the first roll and the last roll are the same roll. The time from the start to the end of the width constraining step is preferably 5 seconds or more. Further, the time from the start to the end of the width constraining step is preferably less than 60 seconds. When it is 60 seconds or more, the polyvinyl alcohol-based resin film may be dried more than necessary in the width constraining step, and the polyvinyl alcohol-based resin film may be broken in the subsequent drying step.

In the width constraining step, the polyvinyl alcohol-based resin film will be gently dried in a state of being constrained in the width direction, without applying a large load to the polyvinyl alcohol-based resin film, and suppressing the shrinkage in the width direction, It is possible to manufacture a thin polarizing film having a small shrinkage force. In order to control the dried state in the width constraining step, it is preferable to have, for example, a hot air dryer, an infrared heater, or a means for drying them together. In the width constraining step, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30 to 100°C, preferably 50 to 80°C.

In FIG. 1, the width constraining step is performed in the width constraining portion 70. In the width restraint portion 70 shown in FIG. 1, three free rolls 71, 72, 73 and hot air dryers 74, 75, 76 arranged so as to face the respective free rolls 71, 72, 73 are provided. Has been. Each of the hot air dryers 74, 75, and 76 sends hot air from the downstream side to the upstream direction and members 74a, 75a, and 76a in which outlets for sending hot air from the upstream side to the downstream direction are arranged on the line in the width direction. The delivery port is configured to include members 74b, 75b, 76b arranged on the line in the width direction. Dry state of the polyvinyl alcohol-based resin film in the width constraining step by blowing hot air sent from the hot-air dryers 74, 75, 76 onto the polyvinyl alcohol-based resin film in contact with the opposing free rolls 71, 72, 73 Is controlled. The three free rolls 71, 72, 73 are all large diameter free rolls. In the width constraining portion 70 shown in FIG. 1, the point where the polyvinyl alcohol-based resin film contacts the free roll 71 is the introduction point of the width constraining step, and the point released from the free roll 73 is the derivation point from the width constraining step. Is.

The roll configuration in the width constraining portion 70 is not limited to the form shown in FIG. 2 to 5 schematically show other forms in the width constraining portion 70. 2 to 5, the transport path of the polyvinyl alcohol-based resin film 10 in the width constraining step is indicated by a solid line, the transport path of the polyvinyl alcohol-based resin film 10 before and after the width constraining step is indicated by a dotted line, and the transport direction is indicated by an arrow. Indicate. Further, as in FIG. 1, the guide roll immediately before the introduction of the width constraining step is the guide roll 54, and the guide roll immediately after being derived from the width constraining step is the guide roll 81. The conveying direction of the polyvinyl alcohol-based resin film before and after the width constraining step and in the width constraining step does not necessarily match the example shown in FIG. 1, but the conveying direction can be appropriately adjusted by using a guide roll or the like.

In the example shown in FIG. 2, three free rolls 711, 712, 713 having a diameter of 300 mm are arranged. The polyvinyl alcohol-based resin film is released from the free roll 711 at P12 after being brought into contact with the free roll 711 at P11 and introduced into the width constraining step. Then, it contacts the next free roll 712 at P13, and is released from the free roll 712 at P14. Then, it comes into contact with the last free roll 713 at P15, is released from the free roll 713 at P16, and is derived from the width restraining process. In the example shown in FIG. 2, when the transport speed of the film is 10 m/min, the time required for transport between the respective points is P83 to P12 is 2.83 seconds, P12 to P13 is 1.8 seconds, and P13 to P14. Is set to 2.83 seconds, P14 to P15 is set to 1.8 seconds, and P15 to P16 is set to 2.83 seconds, the free rolls 711, 712, 713 and the front and rear guide rolls are arranged. In this case, the time required for the width constraining step is 12.09 seconds, of which the time during which the polyvinyl alcohol-based resin film is in contact with the roll is 8.49 seconds. Therefore, 70% of the time of the width restraint process is in contact with either roll.

In the example shown in FIG. 3, three free rolls 721, 722, 723 having a diameter of 150 mm are arranged. The polyvinyl alcohol-based resin film is brought into contact with the free roll 721 at P21 and introduced into the width constraining step, and then released from the free roll 721 at P22. Then, it contacts the next free roll 722 at P23, and is released from the free roll 722 at P24. Then, it comes into contact with the last free roll 723 at P25, is released from the free roll 723 at P26, and is derived from the width restraining step. In the example shown in FIG. 3, assuming that the film transport speed is 10 m/min, the time required for transport between the points is 0.9 seconds for P21 to P22, 1.59 seconds for P22 to P23, and P23 to P24. Is 0.38 seconds, P24 to P25 is 1.59 seconds, and P25 to P26 is 0.9 seconds, the free rolls 731, 732, 733 and the front and rear guide rolls are arranged. In this case, the time required for the width constraining step is 5.36 seconds, of which the time during which the polyvinyl alcohol-based resin film is in contact with the roll is 2.18 seconds. Therefore, 41% of the time of the width constraining step is in contact with either roll.

In the example shown in FIG. 4, two free rolls 731 and 733 having a diameter of 120 mm and a free roll 732 having a diameter of 450 mm are arranged. The polyvinyl alcohol-based resin film is released from the free roll 731 at P32 after being brought into contact with the free roll 731 at P31 and introduced into the width constraining step. Then, it contacts the next free roll 732 at P33, and is released from the free roll 732 at P34. Then, it comes into contact with the last free roll 733 at P35, is released from the free roll 733 at P36, and is derived from the width restraining step. In the example shown in FIG. 4, when the transport speed of the film is 10 m/min, the time required for transport between the points is P5 to P32: 0.85 seconds, P32 to P33: 0.88 seconds, P33 to P34. Is set to 6.36 seconds, P34 to P35 is set to 0.88 seconds, and P35 to P36 is set to 0.85 seconds. The free rolls 721, 722, 723 and the front and rear guide rolls are arranged. In this case, the time required for the width constraining step is 9.82 seconds, of which the time during which the polyvinyl alcohol-based resin film is in contact with the roll is 8.06 seconds. Therefore, 82% of the time of the width restraint process is in contact with either roll.

In the example shown in FIG. 5, a free roll 741 having a diameter of 550 mm is arranged. The polyvinyl alcohol-based resin film is brought into contact with the free roll 741 at P41 and introduced into the width constraining step, then released from the free roll 741 at P42, and led out from the width constraining step. In the example shown in FIG. 5, assuming that the film transport speed is 10 m/min, the free roll 741 and the front and rear guide rolls are set so that the time required for transport between the points is P41 to P42 of 5.18 seconds. It is arranged. In this case, the roll is kept in contact with the polyvinyl alcohol-based resin film roll during the entire width constraining step of 5.18 seconds, that is, 100% of the width constraining step.

The width constraining step is preferably performed immediately after the treatment step in which the polyvinyl alcohol resin film is treated by contacting it with a treatment liquid. In the example of FIG. 1, the process immediately before the width constraining process is a cleaning process, and the processing liquid is a cleaning processing liquid. The treatment liquid with which the polyvinyl alcohol-based resin film is contacted immediately before the width constraining process may be a dyeing treatment liquid in the dyeing treatment process or a cross-linking treatment liquid in the cross-linking treatment process, or other treatments described later (complementary color). Treatment or zinc treatment). As a method of contacting the polyvinyl alcohol-based resin film with the treatment liquid, a conventionally known method such as immersion in a treatment bath, spraying of the treatment liquid with a shower, coating of the treatment liquid, or the like is used.

The polyvinyl alcohol-based resin film is preferably introduced into the width constraining step within 20 seconds after the contact with the treatment liquid in the step immediately before the width constraining step is completed. If it exceeds 20 seconds, the polyvinyl alcohol-based resin film may be gently dried in a state where the width is not constrained, and the width constraining effect may not be sufficiently exhibited. In the case of the example shown in FIG. 1, the point of time when the contact with the treatment liquid in the immediately preceding step ends is the point of time when the washing bath 19 is pulled out.

Further, the water content of the polyvinyl alcohol-based resin film at the time of introduction into the width constraining step is preferably 30% by weight or more. When the water content of the polyvinyl alcohol-based resin film is less than 30% by weight, the width restraining effect may not be sufficiently exhibited. In the apparatus shown in FIG. 1, the moisture content at the time of introduction into the width constraint step can be regarded as the same as the moisture content at the position P1 immediately before being introduced into the width constraint portion 70.

In the width constraining step, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30 to 100°C, preferably 50 to 80°C.

(Drying process)
After the width constraining step, a drying step of performing a drying process on the polyvinyl alcohol-based resin film is performed. The drying step is a step of further reducing the water content of the polyvinyl alcohol-based resin film, for example, a step of reducing the water content of 15% by weight or more and less than 30% by weight to a water content of less than 15% by weight. Examples of the drying method include a hot air dryer, an infrared heater, and a method of drying them in combination.

In the drying step, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30 to 100°C, preferably 50 to 90°C. The time of the drying step is, for example, 60 to 600 seconds, preferably 120 to 600 seconds. By having the width constraining step and the drying step as described above, in manufacturing a thin polarizing film having a desired moisture content, while suppressing breakage of the polyvinyl alcohol-based resin film, it is possible to manufacture with high efficiency. it can. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 μm, and the shrinkage force measured by the method described below is, for example, less than 2.70 N.

(Other treatment steps for polyvinyl alcohol resin film)
It is also possible to add processing other than the processing described above. Examples of treatments that may be added include a dipping treatment in a boric acid-free iodide aqueous solution (complementary color treatment), a dipping treatment in a boric acid-free aqueous solution containing zinc chloride, etc., which is performed after the crosslinking treatment step Zinc treatment).

<Polarizing plate>
A polarizing plate can be obtained by bonding a protective film to at least one surface of the polarizing film manufactured as described above via an adhesive. Examples of the protective film include a film made of acetyl cellulose resin such as triacetyl cellulose and diacetyl cellulose; a film made of polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate resin film, cyclo An olefin resin film; an acrylic resin film; a film made of a chain olefin resin of polypropylene resin.

In order to improve the adhesiveness between the polarizing film and the protective film, the bonding surface of the polarizing film and/or the protective film is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. You may give a process. As the adhesive used for laminating the polarizing film and the protective film, an active energy ray curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of polyvinyl alcohol-based resin, or an aqueous solution in which a crosslinking agent is blended , A water-based adhesive such as a urethane emulsion adhesive. The ultraviolet curable adhesive can be a mixture of an acrylic compound and a photo radical polymerization initiator, a mixture of an epoxy compound and a photo cationic polymerization initiator, and the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples, the film thickness and shrinkage force were measured by the following methods.

[Measurement of film thickness]
The film thickness of the polarizing film was measured with a contact-type film thickness meter (trade name "DIGIMICRO MH-15M" manufactured by Nikon Corporation). The film thickness of the polarizing film was measured at 15 points at different positions in the width direction, and the average value was calculated. Table 1 shows the average value.

[Measurement of contraction force]
An evaluation sample having a width of 2 mm and a length of 50 mm was cut out with a super cutter (manufactured by Ogino Seiki Co., Ltd.) such that the absorption axis direction (stretching direction) of the polarizing film was the major axis. The shrinkage force of the obtained strip-shaped evaluation sample was measured using a thermomechanical analyzer (manufactured by SII Nanotechnology Inc., model TMA/6100). This measurement was performed in the constant dimension mode (the distance between chucks was 10 mm), the test piece was left in a room at 20°C for a sufficient time, and then the temperature inside the sample room was set from 20°C to 80°C in 1 minute. The temperature was raised, and after the temperature was raised, the temperature inside the sample chamber was set to be maintained at 80°C. After the temperature was raised, the mixture was allowed to stand for another 4 hours, and then the shrinkage force in the long side direction of the test piece was measured in an environment of 80°C. In this measurement, the static load was set to 0 mN, and a SUS probe was used for the jig.

<Example 1>
A polarizing film was manufactured using an apparatus similar to the polarizing film manufacturing apparatus shown in FIG. As the free rolls 71, 72, 73 arranged in the width constraining portion 70, those having a diameter of 300 mm were used. Further, in the drying furnace 90, No. 1-No. Drying was performed using three hot air dryers No. 3 and No. 3.

(1) Swelling treatment step A polyvinyl alcohol film having a thickness of 30 μm (trade name “Kuraray Poval Film VF-PE#3000” manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree 99.9 mol% or more) is continuously added. While being transported, it was uniaxially stretched about 4 times by a dry method. The stretched polyvinyl alcohol film thus obtained is continuously unrolled from the original roll 11 and conveyed, and immersed in a swelling bath 13 containing pure water at 40° C. for 60 seconds while maintaining a tension so that the film does not sag. did.

(2) Dyeing process step Next, the film that has passed through the nip roll 51 was immersed in a dyeing bath 15 at 28° C. in which iodine/potassium iodide/water (weight ratio) was 0.1/5/100 for 60 seconds.

(3) Cross-linking treatment step Next, in order to perform a cross-linking treatment for the purpose of waterproofing, the film passed through the nip roll 52 has a potassium iodide/boric acid/water (weight ratio) of 10.5/7.5/. It was immersed in the first crosslinking bath 17 at 100° C. and 68° C. for 300 seconds.

(4) Cleaning Treatment Step The film after the second crosslinking treatment was immersed in a cleaning bath 19 containing pure water at 5°C.

(5) Width restraint step Next, the film after the cleaning treatment was passed through the width restraint section 70. The temperatures of the hot air blown from the three hot air dryers 74 to 76 in the width restraint unit 70 are as shown in Table 1. Further, the water content of the film immediately before being introduced into the width restraint portion 70 (position P1) was measured by a water content meter (product name: water content meter IRMA1100, manufactured by Chino Co., Ltd.). The results are shown in Table 1. It took 12 seconds from the time when the film was taken out of the cleaning bath 19 to the time when it came into contact with the free roll 71. Further, in the width constraining portion 70, the time from the first contact of the film with the first free roll 71 until the film is released from the last free roll 73 (width constraining step time), and the time between the free roll 71 and the free roll 72. And the time during which there is no contact between the free roll 72 and the free roll 73 was measured. The time of the width constraining step is 8.1 seconds, the continuous time in which the film is not in contact with the free roll is 2 seconds or less, and the time in which the film is in contact with the free rolls 71, 72, 73 is It was 78% of the time required for the restraint step.

(6) Drying process The film after passing through the width constraining portion 70 was passed through a drying oven 90 to produce a polarizing film. The three hot air dryers No. 1-No. The temperature of the hot air delivered from No. 3 was as shown in Table 1. Further, the moisture content of the film immediately before being introduced into the drying oven 90 (position P3) and immediately after being led out of the drying oven 90 (position P4) is measured by a moisture content meter (product name: moisture meter IRMA110, Chino Co., Ltd.). Manufactured). The results are shown in Table 1.

<Example 2>
A polarizing film was produced in the same manner as in Example 1 except that the temperatures of the hot air sent from the three hot air dryers 74 to 76 in the width constraining section 70 were set as shown in Table 1. Similar to Example 1, the water content of the film immediately before being introduced into the width constraining portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being drawn out from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 3>
Three hot air dryers No. 3 in the drying furnace 90 in the drying process. 1-No. A polarizing film was produced in the same manner as in Example 1 except that the temperature of the hot air sent from No. 3 was as shown in Table 1. Similar to Example 1, the water content of the film immediately before being introduced into the width constraining step 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being discharged from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 4>
The temperatures of the hot air sent from the three hot air dryers 74 to 76 in the width restraint unit 70, and the three hot air dryers No. 3 in the drying furnace 90 in the drying process. 1-No. A polarizing film was produced in the same manner as in Example 1 except that the temperature of the hot air sent from No. 3 was as shown in Table 1. Similar to Example 1, the water content of the film immediately before being introduced into the width constraining step 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being discharged from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 5>
In the configuration inside the width restraint portion 70, the free roll 72 and the hot air dryer 75 facing the free roll 72 are not provided, and the temperatures of the hot air sent from the remaining two hot air dryers 74 and 76 are as shown in Table 1. A polarizing film was produced in the same manner as in Example 1 except for the above. Similar to Example 1, the water content of the film immediately before being introduced into the width constraining portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being drawn out from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1. In the width constraining section 70, the time from the first contact of the film with the first free roll 71 until the film is released from the last free roll 73 (the time of the width constraining step), and the free roll 71 and the free roll 73. The time of no contact was measured. The time of the width constraining step is 6.2 seconds, the continuous time in which the film is not in contact with the free roll is 2 seconds or less, and the time in which the film is in contact with the free rolls 71 and 73 is the width constraining step. It was 44% of the time required for.

<Example 6>
A polarizing film was produced in the same manner as in Example 1 except that the three hot air dryers 74 to 76 in the width constraining portion 70 were not used. Similar to Example 1, the water content of the film immediately before being introduced into the width constraining portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being drawn out from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 7>
The three hot air dryers 74 to 76 in the width restriction unit 70 were not used, and the three hot air dryers No. 3 in the drying furnace 90 in the drying process were used. 1-No. A polarizing film was produced in the same manner as in Example 1 except that the temperature of the hot air sent from No. 3 was as shown in Table 1. Similar to Example 1, the water content of the film immediately before being introduced into the width constraining portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being drawn out from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Comparative Example 1>
A polarizing film was produced in the same manner as in Example 1 except that the width constraining step was not performed (the width constraining portion 70 was not passed). In the same manner as in Example 1, the moisture content of the film was measured immediately before being introduced into the main drying furnace 90 (position P3) and immediately after being introduced from the main drying furnace 90 (position P4). The results are shown in Table 1.

10 original film made of polyvinyl alcohol resin, 11 original roll, 13 swelling bath, 15 dyeing bath, 17 crosslinking bath, 19 washing bath, 21 drying furnace, 23 polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 60, 61, 81 Guide roll, 50, 51, 52, 53, 54, 82, 83 Nip roll, 70 Width restraint, 71, 72, 73 Free roll, 74,75,76 Hot air dryer, 90 Drying furnace.

Claims (4)

A width constraining step of constraining the polyvinyl alcohol-based resin film after contacting the treatment liquid with at least one free roll having a diameter of 150 mm or more to constrain it in the width direction,
And a drying step of drying the polyvinyl alcohol-based resin film after the width restraining step. In the width constraining step, the polyvinyl alcohol-based resin film is contacted with a plurality of rolls including the free roll, and at least 40% of the time from the contact with the first roll to the release from the last roll. The method for producing a polarizing film according to claim 1, wherein the is in contact with any of the rolls. The method for producing a polarizing film according to claim 1, wherein the polyvinyl alcohol-based resin film is brought into contact with the first roll in the width constraining step within 20 seconds after the contact with the treatment liquid is completed. The method for producing a polarizing film according to claim 1, wherein the polyvinyl alcohol-based resin film has a water content of 30% by weight or more when it comes into contact with the first roll in the width constraining step.

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