WO2017002719A1 - Method for producing polarizing film - Google Patents

Abstract

Provided is a method for producing a polarizing film, the method comprising: a widthwise restraining step for restraining in the widthwise direction a polyvinyl alcohol-based resin film, which had been brought into contact with a treatment solution, by bringing the film into contact with at least one free roll having a diameter of 150 mm or greater; and a drying step for drying the polyvinyl alcohol-based resin film after the widthwise restraining step.

Description

Manufacturing method of polarizing film

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

Conventionally used is a polarizing film obtained by adsorbing and orienting a dichroic dye such as iodine or a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film. A polarizing film is usually a polarizing plate obtained by laminating a protective film on one or both sides with an adhesive, and used for liquid crystal display devices such as liquid crystal televisions, monitors for personal computers and mobile phones. It is used. In recent years, with the thinning of liquid crystal display devices, a thin polarizing film is required.

In general, a polarizing film is subjected to a washing treatment after being subjected to, for example, swelling, dyeing, crosslinking, stretching, etc. in a bath on a continuous polyvinyl alcohol resin film that is continuously conveyed. It is manufactured by drying (see, for example, JP 2009-48179 A).

JP 2009-48179 A

Since the polyvinyl alcohol-based resin film subjected to the drying process is stretched, when the moisture is removed by the drying process, the film contracts in the width direction, and the thickness increases due to the contraction in the width direction. Therefore, the demand for thinning was not satisfied.

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

On the other hand, a method of suppressing the shrinkage in the width direction by performing a drying process after the moisture content of the polyvinyl alcohol resin film is lowered to some extent is also conceivable, but according to such a method, the frictional force between the polyvinyl alcohol resin film and the roll is considered. Therefore, it is necessary to mechanically fix the width direction with a tenter clip or the like only by bringing the polyvinyl alcohol resin film into contact with the roll. There was a problem that the film was easily broken.

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

This invention provides the manufacturing method of the polarizing film shown below.
[1] A width restraining step of bringing the polyvinyl alcohol-based resin film after being brought into contact with the treatment liquid into contact with at least one free roll having a diameter of 150 mm or more and restraining it in the width direction;
The manufacturing method of a polarizing film including the drying process which dries the said polyvinyl alcohol-type resin film after the said width | variety restraint process.

[2] In the width restraining 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 when the first roll comes into contact with the last roll. % Time is the manufacturing method of the polarizing film as described in [1] which is in contact with one of the rolls.

[3] The polarized light according to [1] or [2], wherein the polyvinyl alcohol-based resin film is brought into contact with the first roll in the width restraining step within 20 seconds after the contact with the treatment liquid is completed. A method for producing a film.

[4] The polarizing film according to any one of [1] to [3], wherein the polyvinyl alcohol-based resin film has a moisture content of 30% by weight or more when contacting the first roll in the width constraint step. Production method.

According to the method of the present invention, it is possible to produce a polarizing film that is thin and has a small shrinkage force by suppressing shrinkage in the width direction while suppressing breakage of the polyvinyl alcohol 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 a polarizing film manufacturing apparatus used for it. It is sectional drawing which shows typically an example of the roll structure in a width constraint part. It is sectional drawing which shows typically an example of the roll structure in a width constraint part. It is sectional drawing which shows typically an example of the roll structure in a width constraint part. It is sectional drawing which shows typically an example of the roll structure in a width constraint part.

<Production method of polarizing film>
In the present invention, the polarizing film is one in which a dichroic dye (iodine or dichroic dye) is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol 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 resin can be, for example, a copolymer of vinyl 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, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is usually about 1000 to 10,000, preferably about 1500 to 5,000.

These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used.

In the present invention, 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 even more preferably 30 μm or less is used as a starting material for manufacturing a polarizing film. Film). As a result, it is possible to obtain a thin polarizing film whose market demand is increasing. The thinner the original film, the easier it is to break the film during the stretching process. However, according to the present invention, the film can be effectively suppressed even when the original film is thin. The raw film may be a polyvinyl alcohol-based resin film that has been previously stretched in the gas phase.

The width of the original film is not particularly limited and can be, for example, about 400 to 6000 mm. However, the larger the film width, the more likely the film breaks during the stretching process.

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

After carrying out the processing process which a polarizing film conveys continuously along the film conveyance path of a polarizing film manufacturing device and contacts a processing liquid, unwinding the above-mentioned long original fabric film from an original fabric roll, By carrying out the width restraining step and then carrying out the drying step, it can be continuously produced as a long polarizing film.

Examples of the treatment step include a swelling treatment step in which the original film is dipped in a swelling bath and drawn out, a dyeing treatment step in which the film after the swelling treatment is dipped in the dyeing bath, and a film in which the dyed treatment is crosslinked It is possible to include a cross-linking treatment step that is drawn out after being immersed in the substrate. In addition, a uniaxial stretching process is performed in a wet or dry manner between these series of processing steps (that is, before and after any one or more processing steps and / or during any one or more processing steps). Other processing steps may be added as necessary. Each of the above treatment steps may be a treatment of immersing the film in one bath or a treatment of sequentially immersing in two or more baths.

In the width restraining step, the polyvinyl alcohol-based resin film after being brought into contact with the treatment liquid in the treatment 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 restraining in the width direction. The roll that contacts the polyvinyl alcohol resin film in the width restraining step may include one or a plurality of large-diameter free rolls, and in addition to this, 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 referred to in this specification means not surface contact but surface contact (the polyvinyl alcohol-based resin film is in contact with the free roll with a width in the length direction). . By the surface contact, the polyvinyl alcohol-based resin film is restrained 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 a free roll as 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 restraining step, the polyvinyl alcohol-based resin film is gently dried in a state of being restrained in the width direction, and the width is not applied to the polyvinyl alcohol-based resin film. A thin polarizing film having a small shrinkage force can be produced by suppressing the shrinkage in the direction.

The drying step is a step of drying the polyvinyl alcohol-based resin film subjected to the width constraint step to obtain a polarizing film, for example, a step of reducing the moisture 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. Drawing 1 is a sectional view showing typically an example of the manufacturing method of the polarizing film concerning the present invention, and the polarizing film manufacturing device used for it. The polarizing film manufacturing apparatus shown in FIG. 1 transports a raw fabric (unstretched) film 10 made of polyvinyl alcohol resin along a film transport path while continuously unwinding from a raw fabric roll 11. The swelling bath 13, the dyeing bath 15, the crosslinking bath 17, and the washing bath 19 provided on the conveyance path are sequentially passed, then the width restricting portion 70 is passed, and finally the drying furnace 90 is passed. Yes. The obtained polarizing film can be conveyed, for example, to the next polarizing plate production step (step of bonding a protective film on one or both sides of the polarizing film 23) as it is. The arrow in FIG. 1 has shown the conveyance direction of the film.

FIG. 1 shows an example in which one bath is provided for each of the swelling bath 13, the dyeing bath 15, the crosslinking bath 17, and the washing bath 19, but if necessary, any one or more treatment baths (swelling bath 13). The baths containing the treatment liquid for treating the polyvinyl alcohol-based resin film provided on the film conveyance path, such as the dyeing bath 15, the crosslinking bath 17, and the washing bath 19, are also collectively referred to as “treatment bath”. .) May be provided in two or more tanks.

The film transport path of the polarizing film manufacturing apparatus includes guide rolls 30 to 41 that support the film to be transported or can further change the film transport direction, in addition to the processing bath, the width restraint unit 70, and the drying furnace 90. 60, 61, 81, and nip rolls 50 to 54, 82, 83 that can press and hold the film to be conveyed and give the film a driving force by the rotation, or can further change the film conveying direction. It can construct | assemble by arrange | positioning in an appropriate position. Guide rolls and nip rolls can be arranged before and after each treatment bath, drying furnace, or in the treatment bath, whereby the film can be introduced and immersed in the treatment bath and drawn out from the treatment bath [FIG. reference〕. For example, by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls, the film can be immersed in each treatment bath.

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 the nip rolls arranged before and after any one or more treatment baths. It is possible to perform inter-roll stretching in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between them. Hereinafter, each step will be described.

(Swelling process)
The swelling treatment step is performed for the purpose of removing foreign matter on the surface of the original film 10, removing the plasticizer in the original film 10, imparting easy dyeability, and plasticizing the original film 10. The processing conditions are determined within a range in which the object can be achieved and within 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, the raw film 10 is continuously unwound from the original roll 11 and conveyed along the film conveying path, and the original film 10 is immersed in the swelling bath 13 for a predetermined time. And then withdrawing. In the example of FIG. 1, the raw film 10 is conveyed along the film conveyance path constructed by the guide rolls 60 and 61 and the nip roll 50 until the original film 10 is unwound and immersed in the swelling bath 13. Is done. In the swelling process, the film is transported along the film transport path constructed by the guide rolls 30 to 32.

As the swelling liquid of the swelling bath 13, in addition to pure water, boric acid (JP-A-10-153709), chloride (JP-A-06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohol It is also possible to use an aqueous solution to which a kind or the like is 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 original film 10 is a polyvinyl alcohol resin film previously stretched in a gas, 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, there is a problem that the raw film 10 swells in the width direction and the film is wrinkled. 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, a cross guider, a bend bar. Or using other widening devices such as tenter clips. Another means for suppressing the generation of wrinkles is to perform stretching. For example, the uniaxial stretching process 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 in the film conveyance direction. Therefore, when the film is not actively stretched, for example, it is disposed before and after the swelling bath 13 in order to eliminate the sag of the film in the conveyance 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 film conveyance in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, or an EPC device (Edge Position).
It is also useful to use a Control device: a device that detects the end of the film and prevents the film from meandering).

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 this 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 resin film after the swelling treatment. The processing conditions are determined within a range in which the object can be achieved and in a range in which defects 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 film after the swelling treatment is treated in the dye bath 15 (the treatment contained in the dyeing tank). (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 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 process before the dyeing process, it is preferable to perform the uniaxial stretching process during the dyeing process.

When iodine is used as the dichroic dye, for example, the dyeing solution of the dyeing bath 15 contains iodine / potassium iodide / water at 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 terms of containing 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 dyeing bath 15 when 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. Degree, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, for example, the concentration of the dyeing solution in the dyeing bath 15 is dichroic dye / water = about 0.001 to 0.1 / 100 by weight. An aqueous solution can be used. This 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 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 mentioned above, the film can be uniaxially stretched in the dyeing bath 15 in the dyeing process. Uniaxial stretching of the film can be performed by a method of making a peripheral speed difference between the nip roll 51 and the nip roll 52 arranged before and after the dyeing bath 15.

Also in the dyeing process, the widening function such as an expander roll, a spiral roll, or a crown roll is provided on the guide rolls 33, 34 and / or 35 in order to convey the polyvinyl alcohol resin film while removing the wrinkles of the film as in the swelling process. 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 perform a stretching process as in the swelling process.

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 this order and is introduced into the crosslinking bath 17.

(Crosslinking process)
The crosslinking treatment step is a treatment performed for the purpose of water resistance and hue adjustment (such as preventing the film from being bluish) by crosslinking. Referring to FIG. 1, the crosslinking treatment is carried along the film conveyance path constructed by the guide rolls 36 to 38 and the nip roll 52, and is subjected to the dyeing treatment in the crosslinking bath 17 (crosslinking liquid contained in the crosslinking tank). It can be carried out by immersing the film for a predetermined time and then withdrawing it.

The crosslinking liquid in the crosslinking bath 17 can 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 an iodide in addition to boric acid. The amount is, for example, 1 to 30 parts by weight with respect to 100 parts by weight of water. It can be. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

In the crosslinking treatment, the concentration of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed depending on the purpose. For example, when the purpose of the crosslinking treatment is water resistance by crosslinking, and the polyvinyl alcohol resin film is subjected to swelling treatment, dyeing treatment and crosslinking treatment in this order, the crosslinking agent-containing liquid in the crosslinking 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. As needed, it may replace with boric acid and may use other crosslinking agents, such as a glyoxal or glutaraldehyde, and may use boric acid and another crosslinking agent together. 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, more preferably. Is 20 to 200 seconds. When the polyvinyl alcohol resin film previously stretched before the swelling treatment is subjected to a dyeing treatment and a 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 adjusting the hue, for example, when iodine is used as the dichroic dye, a crosslinking agent containing boric acid / iodide / water = 1 to 5/3 to 30/100 in terms of weight ratio is contained. Liquid can be used. The temperature of the crosslinking bath when dipping the film is usually about 10 to 45 ° C., and the dipping time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment may be performed a plurality of 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 range. 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, respectively.

The uniaxial stretching process can also be performed in the crosslinking bath 17 using the peripheral speed difference between the nip roll 52 and the nip roll 53.

In the cross-linking treatment, 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 in order to convey the polyvinyl alcohol resin film while removing the wrinkles of the film as in the swelling treatment. 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 perform a stretching process as in the swelling process.

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 this order and is introduced into the film washing bath 19.

(Washing process)
The production method of the present invention can include a washing treatment step after the crosslinking treatment step. The washing treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol resin film. The washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol resin film in the film washing bath 19, spraying the film washing solution as a shower on the film, or using these together.

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

In the cleaning process, 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 for the purpose of conveying the polyvinyl alcohol resin film while removing wrinkles. Or other widening devices such as cross guiders, bend bars, tenter clips can be used. In the film cleaning process, a stretching process may be performed in order to suppress generation of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched wet or dry during the series of processing steps (that is, before and after any one or more processing steps and / or during any one or more processing steps). It is processed. A specific method of the uniaxial stretching process is, for example, between rolls that perform longitudinal uniaxial stretching with a peripheral speed difference between two nip rolls (for example, two nip rolls arranged before and after the treatment bath) constituting the film conveyance path. Stretching, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, and the like, and inter-roll stretching is preferred. The uniaxial stretching treatment step can be performed a plurality of times before the polarizing film 23 is obtained from the raw film 10. As described above, the stretching treatment is also advantageous for suppressing the generation of wrinkles on 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-described processing steps as long as it is before the width constraint step, and the stretching treatment may be performed in any processing step even when the stretching treatment is performed in two or more treatment steps. .

(Width constraint process)
After the cleaning treatment step, a width restraining 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 restrain the width direction.

In the width restraining step, the polyvinyl alcohol-based resin film need not always be in contact with the roll, but preferably 0.5 seconds or more, more preferably 2 seconds or more, from the viewpoint of effective width restraint. Preferably, there is a continuous contact time. 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 restraining step. According to the large-diameter free roll, it is easy to ensure the continuous contact time as described above. The diameter of the large-diameter free roll is preferably 200 mm or more, and 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, a load is applied to the polyvinyl alcohol-based resin film due to free roll rotation resistance, and the polyvinyl alcohol-based resin film may be easily broken. In the width constraint step, it is preferable to include two or more large-diameter free rolls.

The roll used in the width restraining step can adjust the transport direction of the polyvinyl alcohol-based resin film and can forcibly curl, and therefore preferably includes a plurality of large-diameter free rolls described above, and the number is 3 or more and 5 or less. More preferably. When multiple rolls are used, the polyvinyl alcohol-based resin film will be in contact with any roll for at least 40% of the time between contact with the first roll in the width restraint process and release from the last roll. It is preferable. When the time in contact with the roll is 40% or more, a sufficient width restraining effect can be obtained. The time in contact with the roll is more preferably 70% or more. The time in contact with the rolls can be adjusted by the number of rolls, the position of the rolls, and the holding angle to each roll. Further, from the viewpoint of effective width constraint, the continuous time during 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 that contacts the first roll in the width constraint step is the introduction point of the width constraint step, and the point released from the last roll is the derived point from the width constraint step. When there is one roll used in the width constraint step, the first roll and the last roll are the same roll. The time from the start to the end of the width constraint step is preferably 5 seconds or more. Moreover, it is preferable that the time from the start to the end of the width constraint step is less than 60 seconds. In the case of 60 seconds or more, the polyvinyl alcohol-based resin film may be dried more than necessary in the width restraining step, and the polyvinyl alcohol-based resin film may be broken in the subsequent drying step.

In the width constraint step, the polyvinyl alcohol-based resin film is gently dried in a state of being restrained in the width direction, and without applying a large load to the polyvinyl alcohol-based resin film, suppressing shrinkage in the width direction, A thin polarizing film having a small shrinkage force can be produced. In order to control the drying state in the width restraining step, it is preferable to have, for example, a hot air dryer, an infrared heater, or a means for drying them in combination. In the width constraint 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, a width restricting step is performed in the width restricting portion 70. 1 includes three free rolls 71, 72, 73 and hot air dryers 74, 75, 76 arranged to face the free rolls 71, 72, 73, respectively. It has been. Each of the hot air dryers 74, 75, and 76 sends out hot air in the upstream direction from the downstream side with members 74a, 75a, and 76a having outlets that send hot air in the downstream direction from the upstream side arranged on the line in the width direction. The delivery port is configured to include members 74b, 75b, and 76b arranged on the line in the width direction. The hot air sent from the hot air dryers 74, 75, 76 is blown onto the polyvinyl alcohol resin film in contact with the opposing free rolls 71, 72, 73, and the polyvinyl alcohol resin film is dried in the width restraining step. Is controlled. All of the three free rolls 71, 72, 73 are large-diameter free rolls. In the width restraint part 70 shown in FIG. 1, the point where the polyvinyl alcohol-based resin film contacts the free roll 71 is an introduction point of the width restraint process, and the point released from the free roll 73 is a point derived from the width restraint process. It is.

The roll configuration in the width restricting portion 70 is not limited to the form shown in FIG. FIGS. 2 to 5 schematically show other forms in the width restricting portion 70. 2 to 5, the conveyance path of the polyvinyl alcohol-based resin film 10 in the width restriction process is indicated by a solid line, the conveyance path of the polyvinyl alcohol-based resin film 10 before and after the width restriction process is indicated by a dotted line, and the conveyance direction is indicated by an arrow. It shows with. Similarly to FIG. 1, the guide roll immediately before the introduction of the width constraint process is referred to as a guide roll 54, and the guide roll immediately after being derived from the width constraint process is referred to as a guide roll 81. The transport direction of the polyvinyl alcohol-based resin film before and after the width restraint step and in the width restraint step does not necessarily coincide with the example shown in FIG. 1, but the transport 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, and 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 contacting the free roll 711 at P11 and being introduced into the width restraining step. After that, the next free roll 712 is contacted at P13 and released from the free roll 712 at P14. Then, the final free roll 713 is contacted at P15, released from the free roll 713 at P16, and derived from the width constraint step. In the example shown in FIG. 2, when the film transport speed is 10 m / min, the time required for transport between the points is 2.83 seconds for P11 to P12, 1.8 seconds for P12 to P13, and P13 to P14. Each of the free rolls 711, 712, 713 and the front and rear guide rolls are arranged so that is 2.83 seconds, P14 to P15 is 1.8 seconds, and P15 to P16 is 2.83 seconds. In this case, the time required for the width restraining step is 12.09 seconds, and 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 restraining step is in contact with one of the rolls.

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 released from the free roll 721 at P22 after contacting the free roll 721 at P21 and being introduced into the width restraining process. Thereafter, the contact is made with the next free roll 722 at P23, and the free roll 722 is released at P24. Then, the last free roll 723 is contacted at P25, released from the free roll 723 at P26, and derived from the width restraining step. In the example shown in FIG. 3, when the film conveyance speed is 10 m / min, the time required for conveyance between points is 0.9 seconds for P21 to P22, 1.59 seconds for P22 to P23, and P23 to P24. The free rolls 731, 732, 733 and the front and rear guide rolls are arranged so that is 0.38 seconds, P24 to P25 is 1.59 seconds, and P25 to P26 is 0.9 seconds. In this case, the time required for the width restraining step is 5.36 seconds, and 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 restraining step is in contact with any 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 comes into contact with the free roll 731 at P31 and is introduced into the width restraining step, and then released from the free roll 731 at P32. Thereafter, the contact is made with the next free roll 732 at P33, and the free roll 732 is released at P34. Then, the final free roll 733 is contacted at P35, released from the free roll 733 at P36, and derived from the width restraining step. In the example shown in FIG. 4, when the film conveyance speed is 10 m / min, the time required for conveyance between the points is 0.85 seconds for P31 to P32, 0.88 seconds for P32 to P33, and P33 to P34. Each of the free rolls 721, 722, 723 and the front and rear guide rolls are arranged so that is 6.36 seconds, P34 to P35 is 0.88 seconds, and P35 to P36 is 0.85 seconds. In this case, the time required for the width restraining step is 9.82 seconds, of which the time that the polyvinyl alcohol-based resin film is in contact with the roll is 8.06 seconds. Therefore, 82% of the time of the width restraining process is in contact with one of the rolls.

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 restraint process, and then released from the free roll 741 at P42 and derived from the width restraint process. In the example shown in FIG. 5, if the film conveyance speed is 10 m / min, the time required for conveyance between the points is such that the free roll 741 and the front and rear guide rolls are set such that P41 to P42 are 5.18 seconds. Has been placed. In this case, it is in contact with the roll of the polyvinyl alcohol-based resin film in all of 5.18 seconds, which is the time required for the width restraining step, that is, 100% of the time of the width restraining step.

The width constraint step is preferably performed immediately after the treatment step in which the polyvinyl alcohol-based resin film is brought into contact with the treatment liquid. In the example of FIG. 1, the process immediately before the width constraint 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 brought into contact immediately before the width restraining step may be a dyeing treatment solution in the dyeing treatment step, a crosslinking treatment solution in the crosslinking treatment step, or other treatments (complementary colors) described later. Treatment or zinc treatment). As a method of contacting the polyvinyl alcohol resin film with the treatment liquid, conventionally known methods such as immersion in a treatment bath, spraying of the treatment liquid by a shower, application of the treatment liquid, and the like are used.

The polyvinyl alcohol-based resin film is preferably introduced into the width restraining step within 20 seconds after the contact with the treatment liquid in the step immediately before the width restraining step is completed. When it exceeds 20 seconds, the time during which the polyvinyl alcohol-based resin film is gently dried in a state where the width is not restrained becomes long, and the width restraining effect may not be sufficiently exhibited. In addition, in the example shown in FIG. 1, the time when the contact with the processing liquid in the immediately preceding process is completed is the time when it is drawn out from the cleaning bath 19.

Moreover, it is preferable that the moisture content of the polyvinyl alcohol-based resin film upon introduction into the width restraining step is 30% by weight or more. When the moisture content of the polyvinyl alcohol-based resin film is less than 30% by weight, the width constraint 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 process can be regarded as the same as the moisture content at the position P <b> 1 immediately before being introduced into the width constraint portion 70.

In the width restraining 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 restraining step, a drying step is performed in which a drying treatment is performed on the polyvinyl alcohol-based resin film. The drying step is a step of further reducing the moisture content of the polyvinyl alcohol-based resin film, for example, a step of reducing the moisture content of 15% by weight or more and less than 30% by weight to a moisture content of less than 15% by weight. Examples of the drying method include a hot air dryer, an infrared heater, or a method of drying using a combination of these.

In the drying process, 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 for the drying step is, for example, 60 to 600 seconds, preferably 120 to 600 seconds. By manufacturing the thin polarizing film having a desired moisture content by having the width constraint step and the drying step as described above, it is possible to manufacture the polyvinyl alcohol resin film with high efficiency while suppressing breakage. 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 later is, for example, less than 2.70 N.

(Other processing steps for polyvinyl alcohol resin film)
Processing other than the processing described above can also be added. Examples of treatments that can be added include immersion treatment (complementary color treatment) in an aqueous iodide solution that does not contain boric acid, and immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride, etc. Zinc treatment).

<Polarizing plate>
A polarizing plate can be obtained by bonding a protective film via an adhesive on at least one surface of the polarizing film produced as described above. As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose; a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate resin film, a cyclo Examples include olefin resin films; acrylic resin films; and films made of polypropylene-based chain olefin resins.

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

Hereinafter, the present invention will be described more specifically with reference to examples. However, 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 thickness of the polarizing film was measured with a contact-type film thickness meter (trade name “DIGIMICRO MH-15M” manufactured by Nikon Corporation). In addition, 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 values.

[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 Sugano Seiki Co., Ltd.) so that the absorption axis direction (stretching direction) of the polarizing film was the major axis. The contraction force of the obtained strip-shaped evaluation sample was measured using a thermomechanical analyzer (model TMA / 6100, manufactured by SII Nano Technology Co., Ltd.). This measurement was performed in a constant dimension mode (the distance between chucks was set to 10 mm), and the specimen was left in the room at 20 ° C. for a sufficient period of time, and then the temperature setting in the sample room was changed from 20 ° C. to 80 ° C. in 1 minute. The temperature was raised, and the temperature inside the sample chamber was set to be maintained at 80 ° C. after the temperature was raised. After allowing the temperature to rise for another 4 hours, the contraction force in the long side direction of the test piece was measured in an environment at 80 ° C. In this measurement, the static load was 0 mN, and a SUS probe was used as the jig.

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

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

(2) Dyeing process Next, the film which passed the nip roll 51 was immersed for 60 seconds in the dyeing bath 15 of 28 degreeC whose iodine / potassium iodide / water (weight ratio) is 0.1 / 5/100.

(3) Crosslinking treatment step Next, in order to perform a crosslinking treatment for the purpose of water resistance, the film that has 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 68 ° C. which is 100 for 300 seconds.

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

(5) Width Restriction Step Next, the film after the cleaning process was passed through the width restriction portion 70. Table 1 shows the temperature of the hot air blown from the three hot air dryers 74 to 76 in the width restricting portion 70. Further, the moisture content of the film immediately before being introduced into the width restricting portion 70 (position P1) was measured with a moisture meter (product name: moisture meter IRMA1100, manufactured by Chino Corporation). The results are shown in Table 1. The time from taking out the film from the washing bath 19 to contacting the free roll 71 was 12 seconds. Further, in the width restricting portion 70, the time from when the film contacts the first free roll 71 until it is released from the last free roll 73 (the time of the width restricting step), and between the free roll 71 and the free roll 72 And the time which is not contacting between the free roll 72 and the free roll 73 was measured. The time of the width restraining step is 8.1 seconds, the continuous time when the film is not in contact with the free roll is 2 seconds or less, and the time when the film is in contact with the free rolls 71, 72, 73 is It was 78% with respect to the time required for the restraint process.

(6) Drying process The film after passing through the width restricting portion 70 was passed through a drying furnace 90 to produce a polarizing film. Three hot-air dryers in the drying oven 90 1-No. Table 1 shows the temperature of the hot air delivered from No. 3. Further, the moisture content of the film immediately before being introduced into the drying furnace 90 (position P3) and immediately after being introduced from the drying furnace 90 (position P4) is determined 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 temperature of the hot air sent from the three hot air dryers 74 to 76 in the width restricting portion 70 was as shown in Table 1. Similar to Example 1, the moisture content of the film immediately before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being introduced 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. As in Example 1, the film moisture immediately before being introduced into the width restraining step 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being introduced from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 4>
The temperature of the hot air sent from the three hot air dryers 74 to 76 in the width restricting section 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. As in Example 1, the film moisture immediately before being introduced into the width restraining step 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being introduced from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 5>
In the configuration within the width restricting portion 70, the free roll 72 and the hot air dryer 75 facing the free roll 72 are not provided, and the temperature of the hot air sent from the remaining two hot air dryers 74 and 76 is set as shown in Table 1. A polarizing film was produced in the same manner as Example 1 except for the above. Similar to Example 1, the moisture content of the film immediately before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being introduced from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1. In the width restricting portion 70, the time from when the film contacts the first free roll 71 until it is released from the last free roll 73 (the time of the width restricting step), and the free roll 71 and the free roll 73 The time during which there was no contact was measured. The time of the width restraint process is 6.2 seconds, the continuous time when the film is not in contact with the free roll is 2 seconds or less, and the time when the film is in contact with the free rolls 71 and 73 is the width restraint process. 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 restricting portion 70 were not used. Similar to Example 1, the moisture content of the film immediately before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being introduced 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 restricting portion 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 moisture content of the film immediately before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being introduced 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 restricting step was not performed (the width restricting 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 Raw film made of polyvinyl alcohol resin, 11 Raw roll, 13 Swelling bath, 15 Dye bath, 17 Cross-linking bath, 19 Washing bath, 21 Drying oven, 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 constraining part, 71, 72, 73 Free roll, 74, 75, 76 Hot air dryer, 90 drying oven.

Claims (4)

A width restraining step of restraining the polyvinyl alcohol-based resin film after being brought into contact with the treatment liquid in a width direction by bringing it into contact with at least one free roll having a diameter of 150 mm or more;
The manufacturing method of a polarizing film including the drying process which dries the said polyvinyl alcohol-type resin film after the said width | variety restraint process. In the width constraining step, the polyvinyl alcohol-based resin film is in contact with a plurality of rolls including the free roll, and at least 40% of the time between contact with the first roll and release from the last roll The method for producing a polarizing film according to claim 1, wherein is in contact with any of the rolls. The method for producing a polarizing film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film is brought into contact with the first roll in the width restraining step within 20 seconds after the contact with the treatment liquid is completed. The method for producing a polarizing film according to any one of claims 1 to 3, wherein the polyvinyl alcohol-based resin film has a moisture content of 30 wt% or more at the time of contact with the first roll in the width constraint step.

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