KR20180025902A - Method for producing polarizing film - Google Patents

Abstract

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 the polyvinyl alcohol based resin film into contact with at least one pre roll having a diameter of 150 mm or more and a width restricting step, And drying the polarizing film.

Description

Method for producing polarizing film

The present invention relates to a method for producing a polarizing film usable as a constituent member of a polarizing plate.

In the polarizing film, a uniaxially stretched polyvinyl alcohol resin film is conventionally used in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented. The polarizing film is usually used for an image display apparatus such as a liquid crystal television, a personal computer monitor, and a mobile phone, which are typically liquid crystal display devices, by bonding a protective film to one or both sides thereof with an adhesive. In recent years, a thin polarizing film has been demanded in accordance with the thinness of a liquid crystal display device.

In general, a polarizing film is produced by subjecting a continuous long polyvinyl alcohol-based resin film to various treatments such as swelling, dyeing, crosslinking, and drawing in a bath, then performing a washing treatment, (See, for example, Japanese Patent Application Laid-Open No. 2009-48179).

Patent Document 1: JP-A-2009-48179

Since the polyvinyl alcohol based resin film provided in the drying step is subjected to the stretching treatment, when the moisture is removed by the drying step, the film shrinks in the width direction and tends to become thick due to shrinkage in the width direction , It was not possible to satisfy the requirement of thinning.

Patent Document 1 discloses that a polyvinyl alcohol based resin film is dried in contact with a plurality of hot rolls in the drying step to suppress shrinkage in the width direction in the drying step to provide a thin polarizing film . However, when the polyvinyl alcohol based resin film having a high water content is brought into contact with the hot roll and restrained in the width direction, there is a problem that the polyvinyl alcohol based resin film tends to break.

On the other hand, a method of suppressing the shrinkage in the transverse direction by carrying out the drying step after the water content of the polyvinyl alcohol-based resin film becomes low to some extent may be considered. However, according to this method, the frictional force between the polyvinyl alcohol- Therefore, it is not possible to sufficiently restrict the widthwise direction only by bringing the polyvinyl alcohol-based resin film into contact with the roll, and it is necessary to mechanically fix the width direction by means of a tenter clip or the like, and also a polyvinyl alcohol- There was a problem that it tends to break easily.

An object of the present invention is to provide a polarizing film production method capable of suppressing shrinkage in a width direction while suppressing breakage of a polyvinyl alcohol-based resin film, and to produce a polarizing film having a small thickness and a small shrinking force.

The present invention provides a method for producing a polarizing film described below.

[1] a width restricting step of restricting the polyvinyl alcohol-based resin film, which has been brought into contact with the treatment liquid, in at least one of the at least one pre-roll having a diameter of 150 mm or more,

And a drying step of drying the polyvinyl alcohol based resin film after the width restraining step.

[2] In the width-restraining step, the polyvinyl alcohol-based resin film is brought into contact with a plurality of rolls including the pre-roll, and at least a portion between the first roll and the first roll, And the time of 40% is in contact with any one of the rolls.

[3] The polyvinyl alcohol based resin film according to [1] or [2], wherein the polyvinyl alcohol based resin film is in contact with the first roll in the width restraining step within 20 seconds after the completion of the contact with the treatment liquid ≪ / RTI >

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

According to the method of the present invention, it is possible to suppress shrinkage in the width direction while suppressing breakage of the polyvinyl alcohol-based resin film, and to produce a polarizing film that is thin and has small shrinkage force.

1 is a cross-sectional view schematically showing an example of a polarizing film producing method and a polarizing film producing apparatus used therefor according to the present invention.
2 is a cross-sectional view schematically showing an example of the roll configuration in the width restraining portion.
3 is a cross-sectional view schematically showing an example of the roll configuration in the width restricting portion.
4 is a cross-sectional view schematically showing an example of the roll configuration in the width restraining portion.
5 is a cross-sectional view schematically showing an example of the roll configuration in the width restraining portion.

≪ Polarizing Film Production Method >

In the polarizing film of the present invention, a dichroic dye (iodine or a 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, and more preferably about 99 mol% or more. The polyvinyl acetate resin may be, for example, a polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and other monomers copolymerizable therewith, and the like. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The polymerization degree of the polyvinyl alcohol-based resin is usually about 1000 to 10000, and preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified, and examples thereof include polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like.

In the present invention, as a starting material for polarizing film production, an unoriented polyvinyl (meth) acrylate having a thickness of 65 占 퐉 or less (for example, 60 占 퐉 or less), preferably 50 占 퐉 or less, more preferably 35 占 퐉 or less, Alcohol-based resin film (original film) is used. As a result, a polarizing film of a thin film which is increasingly in demand in the market can be obtained. Thinning of the original film tends to cause film breakage during stretching treatment. However, according to the present invention, even if the original film is thin, breakage of the film can be effectively suppressed. The original film may be a polyvinyl alcohol-based resin film that has been subjected to stretching treatment in advance in a gas phase.

The width of the original film is not particularly limited, and may be, for example, about 400 to 6000 mm. The larger the film width, the easier the film breakage tends to occur in the stretching treatment.

In the present invention, the original film is prepared as a roll (disk roll) of a long unoriented polyvinyl alcohol based resin film.

The polarizing film is subjected to a processing step in which the long original film is loosened from the disk roll and is continuously conveyed along the film conveying path of the polarizing film producing apparatus so as to be brought into contact with the processing liquid, It is possible to continuously produce it as a long polarizing film by carrying out a drying process later.

Examples of the treatment step include a swelling treatment step in which the original film is dipped in a swelling bath and then drawn out, a dyeing treatment step in which the swelled film is dipped in a dyeing bath and then drawn out, a film after dying treatment is dipped in a crosslinking bath And a crosslinking treatment step of withdrawing the crosslinking agent. In addition, uniaxial stretching treatment is carried out either wet or dry between these series of treatment steps (that is, before and / or after any one or more treatment steps). Other treatment steps may be added as necessary. The respective treatment steps may be a treatment for immersing the film in one bath or a treatment for sequentially immersing the film in two or more baths.

In the width restraining step, the polyvinyl alcohol-based resin film which has been brought into contact with the treatment liquid in the above-mentioned treatment step is brought into contact with at least one pre-roll having a diameter of 150 mm or more (hereinafter also referred to as a & . The roll for contacting the polyvinyl alcohol based resin film in the width restraining step may include one or a plurality of large-diameter pre-rolls, and further, a pre-roll and a drive roll having a diameter of less than 150 mm. The contact of the polyvinyl alcohol-based resin film in this specification with a roll is not a point contact but a surface contact (a polyvinyl alcohol based resin film has a width in the longitudinal direction and is in contact with the pre-roll). By the surface contact, the polyvinyl alcohol-based resin film is restrained in the width direction.

Here, the pre-roll refers to a roll to which no driving means such as a motor is attached. As described above, by using a pre-roll as means for restraining the width direction of the polyvinyl alcohol-based resin film brought into contact with the treatment liquid, breakage of the polyvinyl alcohol-based 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 the state of being restrained in the width direction, thereby suppressing shrinkage in the width direction without applying a large load to the polyvinyl alcohol- , And a thin polarizing film having a small contracting force can be produced.

The drying step is a step of drying the polyvinyl alcohol-based resin film subjected to the width restraining step to obtain a polarizing film, which is a step of reducing the moisture content to, for example, less than 15% by weight.

Hereinafter, a method for producing a polarizing film according to the present invention will be described in detail with reference to FIG. 1 is a cross-sectional view schematically showing an example of a polarizing film producing method and a polarizing film producing apparatus used therefor according to the present invention. The polarizing film producing apparatus shown in Fig. 1 is a system in which a disc (unstretched) film 10 made of a polyvinyl alcohol resin is successively unwound from a disc roll 11 and conveyed along a film conveying path, The dyeing bath 15, the crosslinking bath 17 and the cleansing bath 19, and then passed through the width restricting portion 70. Finally, 90 in the direction indicated by the arrow. The obtained polarizing film can be transported, for example, as it is in the following polarizing plate producing step (a step of bonding a protective film to one or both surfaces of the polarizing film 23). The arrows in Fig. 1 indicate the transport direction of the film.

1 shows an example in which one swirl bath 13, a staining bath 15, a crosslinking bath 17 and a cleansing bath 19 are provided in each case. However, if necessary, any one treatment bath A bath containing a treatment liquid for treating a polyvinyl alcohol based resin film provided on a film transport path, such as a dyeing bath 15, a crosslinking bath 17, and a cleansing bath 19, (Hereinafter also referred to as a " treatment bath ").

The film transport path of the polarizing film producing apparatus includes guide rolls 30 to 41, which can support the film to be transported or change the film transport direction, in addition to the processing bath, the width restricting portion 70 and the drying furnace 90, 60, 61, 81), nip rolls 50 to 54, 82, 83 capable of applying a driving force to the film by pressing and holding the film to be transported or changing the film transport direction It can be constructed by arranging it at an appropriate position. The guide rolls and nip rolls can be disposed in front of and behind the respective treatment baths, drying furnaces, and treatment baths, whereby the introduction and immersion of the film in the treatment bath and the withdrawal from the treatment bath can be performed (see FIG. For example, by providing at least one guide roll in each treatment bath and transporting the film in accordance with these guide rolls, the film can be immersed in each treatment bath.

In the polarizing film producing apparatus shown in Fig. 1, nip rolls (nip rolls 50 to 54) are arranged before and after each treatment bath, whereby in the at least one treatment bath, It is possible to carry out roll-to-roll stretching in which longitudinally uniaxial stretching is carried out by attaching a main speed difference (circumferential speed difference) therebetween. Hereinafter, each step will be described.

(Swelling treatment step)

The swelling process is carried out for the purpose of removing foreign substances on the surface of the original film 10, removing plasticizers in the original film 10, imparting easy dyeability, plasticizing the original film 10, and the like. The processing conditions are determined within a range in which the object can be achieved and within a range that does not cause problems such as extreme melting of the original film 10 and loss of transparency.

1, the swelling process is a process in which the original film 10 is conveyed along the film conveying path while continuously releasing from the original roll 11, and the original film 10 is immersed in the swelling bath 13 for a predetermined time And then withdrawing it. In the example of Fig. 1, the original film 10 is held between the guide rolls 60 and 61 and the nip roll 50 between the release of the original film 10 and the immersion in the swelling bath 13 And is transported along the constructed film transport path. In the swelling process, the film is transported along the film transport path established by the guide rolls 30 to 32.

As the swelling liquid of the swelling bath 13, boric acid (Japanese Unexamined Patent Application Publication No. 10-153709), chloride (Japanese Unexamined Patent Application Publication No. 06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohol Or the like in an amount of about 0.01 to 10% by weight.

The temperature of the swelling bath 13 is, for example, about 10 to 50 占 폚, preferably about 10 to 40 占 폚, and more preferably about 15 to 30 占 폚. The immersion time of the original 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 based resin film previously stretched in a gas, the temperature of the swelling bath 13 is, for example, about 20 to 70 캜, preferably about 30 to 60 캜. The immersion time of the original film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling process, there is a problem that the original film 10 is swollen in the width direction and the film is wrinkled. As a means for transporting the film while removing the wrinkles, a roll having a wider width function such as an expander roll, a spiral roll and a crown roll may be used for the guide rolls 30, 31 and / or 32, Using other widening devices such as cross gauders, bend bars, tenter clips or the like. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment. For example, the uniaxial stretching process can be performed in the swelling bath 13 using the difference in speed between the nip roll 50 and the nip roll 51. [

In the swelling treatment, since the film swells and expands even in the transport direction of the film, when the film is not actively stretched, in order to eliminate sagging of the film in the transport direction, for example, It is preferable to take measures such as controlling the speed of the rolls 50 and 51 or the like. Further, for the purpose of stabilizing the film transportation in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower or an EPC apparatus (Edge Position Control apparatus: detecting the end of the film, Or the like) may be used in combination.

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

(Dyeing process)

The dyeing treatment step is carried out for the purpose of adsorbing and orienting the dichroic dye to the swollen polyvinyl alcohol resin film. The treatment conditions are determined within a range that can attain the object and within a range that does not cause problems such as extreme melting of the film or loss of transparency. Referring to Fig. 1, the dyeing process is carried out along the film transport path established by the guide rolls 33 to 35 and the nip roll 51, and the film after the swelling process is transferred to the dyeing bath 15 Treating solution) for a predetermined time, and then withdrawing it. In order to enhance the dyeability of the dichroic dye, the film provided in the dyeing process is preferably a film subjected to uniaxial stretching at least to some degree, or may be subjected to a uniaxial stretching process before the dyeing process, , It is preferable to perform uniaxial stretching treatment at the time of dyeing treatment.

When iodine is used as the dichroic dye, an aqueous solution having a concentration of iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100 at a concentration, for example, can be used for the dyeing solution of the dyeing bath 15. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, compounds other than iodide such as boric acid, zinc chloride, cobalt chloride, and the like may coexist. The addition of boric acid is distinguished from a crosslinking treatment to be described later in that it contains iodine and can be regarded as a dyeing bath 15 if the aqueous solution contains about 0.003 part by weight or more of iodine per 100 parts by weight of water . The temperature of the dyeing bath 15 at the time of immersing the film is usually about 10 to 45 캜, preferably 10 to 40 캜, more preferably 20 to 35 캜, and the immersion time of the film is usually 30 to 600 seconds , Preferably 60 to 300 seconds.

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

In the dyeing treatment step as described above, uniaxial stretching of the film can be performed in the dyeing bath 15. The uniaxial stretching of the film can be performed by attaching a speed difference between the nip rolls 51 and the nip rolls 52 arranged before and after the dyeing bath 15, for example.

In the dyeing process, the guide rolls 33, 34 and / or 35 are provided with widening functions such as an expander roll, a spiral roll, and a crown roll in order to transport the polyvinyl alcohol resin film while removing the wrinkles of the film, Or using other widening devices such as cloth guiders, bend bars, tenter clips, or the like. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment in the same manner as in the swelling treatment.

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

(Cross-linking treatment step)

The crosslinking treatment is a treatment for the purpose of, for example, water resistance by crosslinking and color adjustment (to prevent the film from becoming blue). 1, the cross-linking treatment is carried out along the film conveyance path constructed by the guide rolls 36 to 38 and the nip roll 52, and the cross-linking treatment is performed on the cross-linking bath 17 (cross-linking solution contained in the cross- By immersing the film for a predetermined period of time, and then withdrawing the film.

The crosslinking solution of the crosslinking bath 17 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking solution preferably contains iodide in addition to boric acid, and the amount thereof may be, for example, 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide and zinc iodide. Further, compounds other than iodide such as 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 swelling treatment, the dyeing treatment and the crosslinking treatment are carried out in this order on the polyvinyl alcohol resin film, the crosslinking agent- And an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100. If necessary, other crosslinking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and another crosslinking agent may be used in combination. The temperature of the crosslinking bath at the time of immersing the film is generally about 50 to 70 DEG C, preferably 53 to 65 DEG C, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, Is 20 to 200 seconds. When the dyeing treatment and the crosslinking treatment are performed in this order on the polyvinyl alcohol based resin film that has been stretched before the swelling treatment, the temperature of the crosslinking bath 17 is usually about 50 to 85 캜, preferably 55 to 80 캜 / RTI >

In the crosslinking treatment for color adjustment, for example, when iodine is used as the dichroic dye, a solution containing a crosslinking agent having a concentration of boric acid / iodide / water = 1 to 5/3 to 30/100 can be used . The temperature of the crosslinking bath at the time of immersing the film is usually about 10 to 45 DEG C, and the immersing time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

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

It is also possible to perform the uniaxial stretching process in the crosslinking bath 17 using the difference in speed between the nip roll 52 and the nip roll 53. [

In the cross-linking treatment, as in the case of the swelling treatment, wrinkles such as an expander roll, a spiral roll, and a crown roll are applied to the guide rolls 36, 37 and / or 38 in order to transport the polyvinyl alcohol- Or using other widening devices such as cloth guiders, bend bars, tenter clips or the like. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment in the same manner as in the swelling treatment.

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

(Cleaning Treatment Process)

The production method of the present invention may include a washing treatment step after the crosslinking treatment step. The cleaning treatment is carried out for the purpose of removing excess boric acid or iodine adhered to the polyvinyl alcohol-based resin film. The cleaning treatment can be carried out, for example, by immersing a crosslinked polyvinyl alcohol resin film in a film cleansing bath 19, spraying the film with a film washing liquid as a shower, or by using them in combination.

Fig. 1 shows an example of a case where the polyvinyl alcohol-based resin film is immersed in a cleansing bath 19 to perform a cleaning treatment. The temperature of the film cleansing bath 19 in the film cleaning process is usually about 2 to 40 占 폚, 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, and a crown roll may be provided on the guide rolls 39, 40 and / or 41 for the purpose of transporting the polyvinyl alcohol- Or by using other widening devices such as cloth guiders, bend bars, tenter clips or the like. Further, in the film washing treatment, a stretching treatment may be performed to suppress the occurrence of wrinkles.

(Stretching process step)

As described above, the original film 10 is uniaxially stretched in a wet or dry manner during the series of processing steps (that is, before and / or after any one of the processing steps). A specific method of the uniaxial stretching treatment is, for example, a roll-to-roll stretching method in which longitudinal uniaxial stretching is performed by attaching a main speed difference between two nip rolls (for example, two nip rolls disposed before and after the treatment bath) Hot roll stretching, tenter stretching, and the like as described in Japanese Patent No. 2731813, and preferably roll-to-roll stretching. The uniaxial stretching process can be carried out several times between the original film 10 and the polarizing film 23. As described above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles in the film.

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

The stretching treatment step may be carried out in any of the above-mentioned treatment steps if it is before the width restraining step, and in the case of performing the stretching treatment in two or more treatment steps, the stretching treatment may be performed in any treatment step.

(Width restricting process)

After the cleaning treatment step, the polyvinyl alcohol based resin film is subjected to a width restraining step of restraining the width direction by bringing the polyvinyl alcohol based resin film into contact with at least one large-diameter pre-roll having a diameter of 150 mm or more.

In the width-constraining step, the polyvinyl alcohol-based resin film is not always required to be in contact with the roll, but from the viewpoint of effective width restraint, it is preferably 0.5 seconds or more, more preferably 2 seconds or more, It is desirable to have time. The present invention includes at least one large-diameter pre-roll having a diameter of 150 mm or more as the roll used in the width restraining step. With the large-diameter pre-roll, it is easy to ensure the continuous contact time as described above. The diameter of the large-diameter pre-roll is preferably 200 mm or more, more preferably 300 mm or more. The diameter of the large diameter pre-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 the pre-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 pre-rolls.

The roll used in the width restraining step can be adjusted in the conveying direction of the polyvinyl alcohol based resin film and can be curled, and therefore, it is preferable that the rolls include a plurality of the above-mentioned large diameter pre rolls, Or less. When a plurality of rolls are used, the polyvinyl alcohol-based resin film has a time period of at least 40% between the time of contacting the first roll in the width restraining step and releasing it from the last roll, It is preferable to contact them. When the time of 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 of contact with the roll can be adjusted by the number of rolls, the position of the rolls, and the holding angle with each roll. From the standpoint of effective width restraint, 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 of contact with the first roll in the width restraining step is taken as the introduction point of the width restraining step, and the point released from the last roll is taken as the derivation point from the width restraining step. If there is only one roll used in the width constraining process, the first roll and the last roll become the same roll. It is preferable that the time from the start to the end of the width restraining step is 5 seconds or more. It is preferable that the time from the start to the end of the width restraining step is less than 60 seconds. If it is more than 60 seconds, drying of the polyvinyl alcohol-based resin film in the width-constraining step proceeds more than necessary, and the polyvinyl alcohol-based resin film may be broken in the drying step in the subsequent stage.

In the width-restraining step, the polyvinyl alcohol-based resin film is gently dried in a state in which it is restrained in the width direction, thereby suppressing shrinkage in the width direction without applying a large load to the polyvinyl alcohol- A film can be produced. For controlling the drying state in the width restraining step, for example, it is preferable to have a hot-air drier, an infrared heater, or a means for drying them in combination. In the width constraining step, the maximum temperature reached by the polyvinyl alcohol based resin film is, for example, 30 to 100 占 폚, preferably 50 to 80 占 폚.

In Fig. 1, the width restricting step is performed in the width restricting portion 70. Fig. In the width restricting portion 70 shown in Fig. 1, three pre-rolls 71, 72, and 73 and hot air dryers 74, 75, 76 are provided. Each of the hot air dryers 74, 75, and 76 has members 74a, 75a, and 76a having a delivery port for delivering hot air in the downstream direction from the upstream side to a downstream side in the width direction, And members 74b, 75b, and 76b in which the outlets for sending out are disposed on the lines in the width direction. The hot wind sent out from the hot air dryers 74, 75, and 76 is sprayed on the polyvinyl alcohol resin film in contact with the opposing pre rolls 71, 72, and 73 to form the polyvinyl alcohol based resin film Is controlled. The three pre-rolls 71, 72, and 73 are all large-diameter pre-rolls. In the width restricting portion 70 shown in Fig. 1, the point where the polyvinyl alcohol based resin film contacts the pre-roll 71 is the introduction point of the width restraining step, and the point released from the pre- .

The roll configuration in the width restricting portion 70 is not limited to the configuration shown in Fig. Figs. 2 to 5 schematically show other shapes in the width restricting portion 70. Fig. 2 to 5, the conveying path of the polyvinyl alcohol based resin film 10 in the width restraining step is indicated by a solid line and the conveying path of the polyvinyl alcohol based resin film 10 before and after the width restraining step is indicated by a dotted line And the conveying direction is indicated by an arrow. 1, the guide roll just before introduction of the width restraining step is used as the guide roll 54, and the guide roll immediately after the width restraining step is used as the guide roll 81. [ The conveying direction of the polyvinyl alcohol based resin film before and after the width restraining step and the width restraining step is not necessarily coincident with 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 pre-rolls 711, 712 and 713 having a diameter of 300 mm are arranged. The polyvinyl alcohol based resin film comes into contact with the pre-roll 711 at P11 and is introduced into the width-restraining step, and then released from the pre-roll 711 at P12. It then contacts the next pre-roll 712 at P13 and is released from the pre-roll 712 at P14. Then, at P15, the last free roll 713 is contacted and released from the pre-roll 713 at P16, and it is derived from the width restraining step. In the example shown in Fig. 2, when the transporting speed of the film is 10 m / min, the time required for transporting between the points is 2.83 seconds, P12 to P13 are 1.8 seconds, P13 to P14 are 2.83 seconds 715, and 713 and front and rear guide rolls are arranged so that P14 to P15 are 1.8 seconds and P15 to P16 are 2.83 seconds. In this case, the time taken 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, the time of 70% of the width restraining step is in contact with any one of the rolls.

In the example shown in Fig. 3, three pre-rolls 721, 722 and 723 having a diameter of 150 mm are arranged. The polyvinyl alcohol based resin film comes into contact with the pre-roll 721 at P21 and is introduced into the width-restraining step, and is released from the pre-roll 721 at P22. It then contacts the next pre-roll 722 at P23 and is released from the pre-roll 722 at P24. Then, in P25, the last free roll 723 is contacted and released from the pre-roll 723 in P26, and is derived from the width restraining process. In the example shown in Fig. 3, when the transporting speed of the film is 10 m / min, the time required for conveying between the respective points is 0.9 seconds in P21 to P22, 1.59 seconds in P22 to P23, 0.38 seconds in P23 to P24 725, and 733 and the front and rear guide rolls are arranged so that P24 to P25 are 1.59 seconds and P25 to P26 are 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 width constraining process is in contact with any one of the rolls.

In the example shown in Fig. 4, two pre-rolls 731 and 733 having a diameter of 120 mm and a pre-roll 732 having a diameter of 450 mm are arranged. The polyvinyl alcohol based resin film comes into contact with the pre-roll 731 at P31 and is introduced into the width restraining step, and then released from the pre-roll 731 at P32. It then contacts the next pre-roll 732 at P33 and is released from the pre-roll 732 at P34. Then, in P35, the last free roll 733 is contacted and released from the pre-roll 733 at P36, and is derived from the width restraining step. In the example shown in Fig. 4, when the transporting speed of the film is 10 m / min, the time required for transportation between the respective points is 0.85 sec for P31 to P32, 0.88 sec for P32 to P33, 6.36 sec 728, 723 and the front and rear guide rolls are arranged such that P34 to P35 are 0.88 second and P35 to P36 are 0.85 second. In this case, the time taken for the width restraining step is 9.82 seconds, and the time for which the polyvinyl alcohol based resin film is in contact with the roll is 8.06 seconds. Thus, 82% of the width constraining process is in contact with any one of the rolls.

In the example shown in Fig. 5, a pre-roll 741 having a diameter of 550 mm is disposed. The polyvinyl alcohol based resin film is brought into contact with the pre-roll 741 at P41 and introduced into the width restraining step, and then released from the pre-roll 741 at P42, and is derived from the width restraining step. In the example shown in Fig. 5, the pre-roll 741 and the front and rear guide rolls are arranged such that the time taken for conveying between the respective points becomes 5.18 seconds when the conveying speed of the film is 10 m / min have. In this case, the roll is in contact with the roll of the polyvinyl alcohol-based resin film at the time of 5.18 seconds, which is the time required for the width restraining step, that is, 100% of the width restraining step.

The width restraining step is preferably performed immediately after the treatment step of treating the polyvinyl alcohol based resin film in contact with the treatment liquid. In the example of Fig. 1, the process just before the width restraining process is a cleaning process, and the process liquid is a cleaning process liquid. The treatment liquid to which the polyvinyl alcohol based resin film is brought into contact immediately before the width restraining step may be a dyeing treatment liquid in the dyeing treatment step or a crosslinking treatment liquid in the crosslinking treatment step, and may be any other treatment (complementary coloring treatment or zinc treatment) May be used. Methods for contacting the polyvinyl alcohol-based resin film with the treatment liquid include conventionally known methods such as immersion in a treatment bath, spraying with a treatment liquid, spraying of the treatment liquid, and the like.

It is preferable that the polyvinyl alcohol based resin film is introduced into the width restraining step within 20 seconds after the completion of the contact with the treatment liquid in the step immediately before the width restraining step. If it exceeds 20 seconds, the time for gently drying the polyvinyl alcohol-based resin film in a state in which the polyvinyl alcohol-based resin film is not constrained in width is prolonged, and there is a fear that the effect of the width restricting effect is not sufficiently exhibited. Here, the point of time when the contact with the treatment liquid in the immediately preceding process is terminated is the point of time when it is drawn out from the cleansing bath 19 in the case shown in Fig.

The moisture content of the polyvinyl alcohol-based resin film when it is introduced into the width constraining step is preferably 30% by weight or more. When the moisture content of the polyvinyl alcohol-based resin film is less than 30% by weight, there is a fear that the effect of the width restraint is not sufficiently exhibited. In the apparatus shown in Fig. 1, the water content at the time of introduction into the width restraining step can be regarded as the same as the moisture content at the position P1 immediately before introduction into the width restraining part 70. [

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

(Drying step)

After the width restraining step, the polyvinyl alcohol-based resin film is subjected to a drying step of drying treatment. The drying step is a step of further lowering the moisture content of the polyvinyl alcohol-based resin film, and is a step of lowering the water content from 15% by weight or more to less than 30% by weight and from 15% by weight to less than 15% by weight. As a drying method, for example, a hot air dryer, an infrared heater, or a method of drying them by using them in combination is exemplified.

In the drying process, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30 to 100 占 폚, preferably 50 to 90 占 폚. The time of the drying process is, for example, 60 to 600 seconds, preferably 120 to 600 seconds. In the production of a thin polarizing film having a desired moisture content by having the above-described width constraining step and drying step as described above, the polyvinyl alcohol based resin film can be produced with high efficiency while suppressing the breakage of the polyvinyl alcohol based resin film. The thickness of the polarizing film 23 obtained in the above-described manner is, for example, about 5 to 30 mu m, and the shrinking force measured by a method described later is, for example, less than 2.70 N.

(Other Treatment Processes for Polyvinyl Alcohol-based Resin Film)

Processing other than the above-described processing may be added. Examples of the treatment which can be added include an immersion treatment (complementary treatment) in an aqueous iodide solution containing no boric acid, which is performed after the crosslinking treatment step, an immersion treatment in an aqueous solution containing zinc chloride or the like Zinc treatment).

<Polarizer>

A polarizing plate can be obtained by bonding a protective film to at least one side of a polarizing film produced as described above through an adhesive. As the protective film, for example, a film comprising an acetylcellulose-based resin such as triacetylcellulose or diacetylcellulose; A film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; Polycarbonate resin film, cycloolefin resin film; Acrylic resin film; And a film made of a chain olefin resin of a polypropylene type resin.

A surface treatment such as a corona treatment, a flame treatment, a plasma treatment, an ultraviolet irradiation, a primer coating treatment, or a saponification treatment is performed on the bonding surfaces of the polarizing film and / or the protective film to improve the adhesion between the polarizing film and the protective film It is also good. Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray curable adhesive such as an ultraviolet ray curable adhesive or an aqueous solution of a polyvinyl alcohol resin or an aqueous solution containing a crosslinking agent and an aqueous adhesive such as a urethane emulsion adhesive . 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 cationic photopolymerization initiator, and the like. In addition, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photocationic polymerization initiator and a photo radical polymerization initiator may be used together as an initiator.

Example

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 the shrinkage force were measured by the following method.

[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 thereof was calculated. Table 1 shows the average value.

[Measurement of retraction 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 Seisakusho Co., Ltd.) so that the absorption axis direction (stretching direction) of the polarizing film was the long axis. The shrinking force of the resulting evaluation sample of the monolith type was measured using a thermomechanical analyzer (Type TMA / 6100, manufactured by SAI Nanotechnology Co., Ltd.). This measurement was carried out in a constant size mode (with a chuck distance of 10 mm) and the sample was allowed to stand in a room at 20 ° C for a sufficient time and then the room temperature setting of the sample was raised from 20 ° C to 80 ° C for 1 minute , And the temperature of the sample was kept at 80 캜 after the temperature was raised. After standing for 4 hours, the shrinkage force of the test piece in the longitudinal direction was measured under the environment of 80 캜. In this measurement, a static load was set to 0 mN, and a probe made of SUS was used for the jig.

&Lt; Example 1 >

A polarizing film was produced by using the same apparatus as the polarizing film producing apparatus shown in Fig. As the pre-rolls 71, 72, and 73 disposed in the width restricting portion 70, those having a diameter of 300 mm were used. Further, in the drying furnace 90, 1 to No. 3 &lt; / RTI &gt;

(1) swelling treatment process

The film was dry-dug four times while continuously feeding a polyvinyl alcohol film having a thickness of 30 占 퐉 (trade name: Kurarupo Foot Film VF-PE # 3000, manufactured by Kuraray Co., Ltd., degree of polymerization: 2400, degree of saponification: 99.9 mol% . The stretched polyvinyl alcohol film thus obtained was conveyed while being loosened continuously from the disk roll 11 and immersed in a swirling bath 13 containing pure water at 40 DEG C for 60 seconds while maintaining the tension so that the film was not loosened.

(2) Dyeing process

Subsequently, the film passed through the nip roll 51 was immersed in a dye bath 15 at 28 DEG C for 60 seconds in which the ratio of iodine / potassium iodide / water (weight ratio) was 0.1 / 5/100.

(3) Crosslinking treatment process

Next, in order to carry out the crosslinking treatment for the purpose of waterproofing, the film passed through the nip rolls 52 was passed through a first cross-linking bath (68 ° C.) having a potassium iodide / boric acid / water (weight ratio) of 10.5 / 17) for 300 seconds.

(4) Cleaning process

The film after the second crosslinking treatment was immersed in a cleansing bath 19 containing pure water at 5 占 폚.

(5) Width Restraint Process

Subsequently, the film after the cleaning treatment was passed through the width restricting portion 70. The temperature of the hot air blown from the three hot air dryers 74 to 76 in the width restricting portion 70 was set as shown in Table 1. The moisture percentage of the film immediately before introduction into the width restricting portion 70 (position P1) was measured by a moisture content meter (product name: moisture meter IRMA1100, manufactured by Chino Corporation). The results are shown in Table 1. The time taken for the film to come into contact with the pre-roll 71 after taking out the film from the cleansing bath 19 was 12 seconds. In the width restricting portion 70, the time from the contact of the film with the first pre-roll 71 to the release from the last pre-roll 73 (the time of the width restraining step) ) And the pre-roll 72 and between the pre-roll 72 and the pre-roll 73 were measured. The duration of the width constraining process is 8.1 seconds, the continuous time when the film is not in contact with the pre-roll is 2 seconds or less, and the time during which the film is in contact with the pre-rolls 71, 72, To 78%.

(6) Drying process

After passing the width restricting portion 70, the film was passed through the drying furnace 90 to produce a polarizing film. Three hot-air dryer No. 3 in the drying furnace 90; 1 to No. The temperature of the hot air sent out from the heat exchanger 3 was set as shown in Table 1. The water content of the film immediately before being introduced into the drying furnace 90 (position P3) and immediately after being discharged from the drying furnace 90 (position P4) was measured with a moisture content meter (product name: moisture meter IRMA110, manufactured by Chisso Corporation) . The results are shown in Table 1.

&Lt; Example 2 >

A polarizing film was produced in the same manner as in Example 1 except that the temperature of the hot air sent out from the three hot air dryers 74 to 76 in the width restricting portion 70 was changed as shown in Table 1. [ (Position P3) just before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), immediately after being drawn out from the drying furnace 90 (position P4) Was measured. The results are shown in Table 1.

&Lt; Example 3 >

In the drying process, the three hot-air driers No. 1 to No. A polarizing film was produced in the same manner as in Example 1, except that the temperature of the hot air sent out from the polarizing plate was changed as shown in Table 1. (Position P4) just before being introduced into the drying furnace 90 (position P3), immediately after being introduced into the drying furnace 90 (position P4), just before being introduced into the width restraining step 70 Was measured. The results are shown in Table 1.

<Example 4>

The temperature of the hot air sent out from the three hot air dryers 74 to 76 in the width restricting portion 70 and the temperature of the hot air supplied from the three hot air dryer 74 in the drying furnace 90 in the drying step. 1 to No. A polarizing film was produced in the same manner as in Example 1, except that the temperature of the hot air sent out from the polarizing plate was changed as shown in Table 1. (Position P4) just before being introduced into the drying furnace 90 (position P3), immediately after being introduced into the drying furnace 90 (position P4), just before being introduced into the width restraining step 70 Was measured. The results are shown in Table 1.

&Lt; Example 5 >

The temperature of the hot air sent out from the remaining two hot air dryers 74 and 76 is set in Table 1 without installing the pre roll 72 and the hot air dryer 75 opposed thereto in the structure of the width restricting portion 70, A polarizing film was produced in the same manner as in Example 1, (Position P3) just before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), immediately after being drawn out from the drying furnace 90 (position P4) Was measured. The results are shown in Table 1. The time from the time when the film comes into contact with the first pre-roll 71 to the time when the film is released from the last pre-roll 73 (the time of the width restraining step) ) And the pre-roll 73 were measured. The duration of the width restraining process is 6.2 seconds, the continuous time when the film is not in contact with the pre-roll is 2 seconds or less, and the time during which the film is in contact with the pre-rolls 71, 44%.

&Lt; 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. (Position P3) just before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), immediately after being drawn out from the drying furnace 90 (position P4) Was measured. The results are shown in Table 1.

&Lt; Example 7 >

Three hot-air dryers 74 to 76 in the width restricting portion 70 are not used, and three hot-air dryers 74 to 76 in the drying furnace 90 in the drying step are used. 1 to No. A polarizing film was produced in the same manner as in Example 1, except that the temperature of the hot air sent out from the polarizing plate was changed as shown in Table 1. (Position P3) just before being introduced into the width restricting portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), immediately after being drawn out from the drying furnace 90 (position P4) Was measured. The results are shown in Table 1.

&Lt; Comparative Example 1 &

A polarizing film was produced in the same manner as in Example 1 except that the film was not subjected to the width restraining step (the film was not passed through the width restricting portion 70). The moisture content of the film immediately after being introduced from the present drying furnace 90 (position P4) immediately before introduction into the present drying furnace 90 (position P3) was measured. The results are shown in Table 1.

10: original film made of a polyvinyl alcohol-based resin, 11: disk roll, 13: swelling bath, 15: dyeing bath, 17: crosslinking bath, 19: A drying furnace 23, a 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 restricting portion, 71, 72, 73: pre-roll, 74, 75, 76: hot air dryer, 90:

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 the polyvinyl alcohol based resin film into contact with at least one pre roll having a diameter of 150 mm or more,
And a drying step of drying the polyvinyl alcohol based resin film after the width restraining step. The method according to claim 1, wherein in the width restraining step, the polyvinyl alcohol-based resin film is in contact with a plurality of rolls including the pre-roll and between the first roll and the last roll Wherein at least 40% of the time is in contact with any one of the rolls. The method for producing a polarizing film according to claim 1 or 2, wherein the polyvinyl alcohol based resin film is a film obtained by forming a polarizing film in contact with the first roll in the width restraining step within 20 seconds after completion of the contact with the treatment liquid Way. The method of producing a polarizing film according to any one of claims 1 to 3, wherein the polyvinyl alcohol based resin film has a moisture content at the time of contact with the first roll in the width restraining step of 30 wt% or more.

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