KR102595687B1 - Manufacturing method of polarizing film - Google Patents

Abstract

A width restraint step of restraining the polyvinyl alcohol-based resin film after contacting the treatment liquid in the width direction by contacting it with at least one pre-roll with a diameter of 150 mm or more, and after the width restraint step, the polyvinyl alcohol-based resin film A method of producing a polarizing film comprising a drying process.

Description

Manufacturing method of polarizing film

The present invention relates to a method of manufacturing a polarizing film that can be used as a structural member of a polarizing plate.

As a polarizing film, a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented has been conventionally used. Polarizing films are usually made into polarizing plates by bonding a protective film to one or both sides using an adhesive, and are used in image display devices such as liquid crystal displays such as liquid crystal televisions, monitors for personal computers, and mobile phones. Recently, as liquid crystal display devices have become thinner, thinner polarizing films have been required.

In general, polarizing films are made by subjecting a continuously conveyed long polyvinyl alcohol-based resin film to various treatments, such as swelling, dyeing, crosslinking, and stretching, in a bath, followed by washing treatment, and then drying the film. It is manufactured by (for example, see Japanese Patent Laid-Open No. 2009-48179).

Patent Document 1: Japanese Patent Publication No. 2009-48179

Since the polyvinyl alcohol-based resin film subjected to the drying process has been subjected to stretching treatment, the film shrinks in the width direction when moisture is removed through the drying process, and the thickness tends to increase due to the shrinkage in the width direction. , it was not possible to satisfy Park Hyeong-hwa’s demands.

Patent Document 1 describes providing a thin polarizing film by suppressing shrinkage in the width direction during the drying process by drying the polyvinyl alcohol-based resin film by contacting it with a plurality of heat rolls. . However, when a polyvinyl alcohol-based resin film with 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-based resin film is prone to fracture.

On the other hand, a method of suppressing shrinkage in the width direction by performing a drying process after the moisture content of the polyvinyl alcohol-based resin film has become low to a certain level is also conceivable. However, according to this method, the friction between the polyvinyl alcohol-based resin film and the roll decreases. Therefore, the width direction cannot be sufficiently restrained simply by bringing the polyvinyl alcohol-based resin film into contact with the roll, and it is necessary to mechanically fix the width direction with a tenter clip or the like. As expected, the polyvinyl alcohol-based resin film There was a problem that it was easy to break.

The purpose of the present invention is to provide a method for producing a polarizing film that can produce a thin polarizing film with small shrinkage force by suppressing shrinkage in the width direction while suppressing breakage of the polyvinyl alcohol-based resin film.

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

[1] A width restraint step of restraining the polyvinyl alcohol-based resin film after contacting the treatment liquid in the width direction by contacting it with at least one pre-roll with a diameter of 150 mm or more;

A method of producing a polarizing film comprising a drying process of drying the polyvinyl alcohol-based resin film after the width constraint process.

[2] In the width restraint step, the polyvinyl alcohol-based resin film is brought into contact with a plurality of rolls including the pre-roll, and is provided at least for a period between contacting the first roll and being released from the last roll. The method for producing a polarizing film according to [1], wherein 40% of the time is in contact with any one roll.

[3] The polyvinyl alcohol-based resin film is the polarized light according to [1] or [2], which is brought into contact with the first roll in the width restraint process within 20 seconds after the contact with the treatment liquid is terminated. Method of manufacturing the film.

[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 of 30% by weight or more at the time of first contact with the roll in the width restraint step.

According to the method of the present invention, fracture of the polyvinyl alcohol-based resin film is suppressed while shrinkage in the width direction is suppressed, and a thin polarizing film with small shrinkage force can be manufactured.

1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing method according to the present invention and a polarizing film manufacturing apparatus used therein.
Fig. 2 is a cross-sectional view schematically showing an example of the roll configuration within the width restraint section.
Fig. 3 is a cross-sectional view schematically showing an example of the roll configuration within the width restraint section.
Fig. 4 is a cross-sectional view schematically showing an example of the roll configuration within the width restraint section.
Fig. 5 is a cross-sectional view schematically showing an example of the roll configuration within the width restraint section.

<Method for producing polarizing film>

In the present invention, the polarizing film is a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye (iodine or dichroic dye) is adsorbed and oriented. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying polyvinyl acetate-based resin. The saponification degree is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as a copolymer of vinyl acetate and other monomers copolymerizable with it. Other monomers that can be copolymerized include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

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

In the present invention, as a starting material for producing a polarizing film, unstretched polyvinyl having a thickness of 65 ㎛ or less (for example, 60 ㎛ or less), preferably 50 ㎛ or less, more preferably 35 ㎛ or less, even more preferably 30 ㎛ or less. An alcohol-based resin film (raw film) is used. As a result, it is possible to obtain a thin polarizing film for which market demand is increasing. The thinner the raw film, the easier it is to cause film breakage during stretching, but according to the present invention, even when the raw film is thin, film breakage can be effectively suppressed. The raw film may be a polyvinyl alcohol-based resin film previously subjected to stretching treatment in the gas phase.

The width of the raw film is not particularly limited, and may be, for example, about 400 to 6000 mm, but the larger the film width, the more likely it is that the film will break during stretching.

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

The polarizing film is subjected to a treatment process in which the above-mentioned long raw film is continuously conveyed along the film conveyance path of the polarizing film manufacturing apparatus and brought into contact with the treatment liquid while unwinding from the raw roll, and then subjected to a width restraint process. By performing a drying process later, it can be continuously manufactured as a long polarizing film.

The above treatment processes include, for example, a swelling treatment process in which the raw film is immersed in a swelling bath and then taken out, a dyeing treatment process in which the film after the swelling treatment is taken out after being immersed in a dyeing bath, and a dyeing treatment process in which the film after the dyeing treatment is taken out after being immersed in a crosslinking bath. A crosslinking treatment process may be included. Additionally, between these series of treatment processes (i.e., before and after and/or during one or more treatment processes), uniaxial stretching treatment is performed in a wet or dry manner. Other treatment steps may be added as needed. Each of the above treatment steps may be a treatment in which the film is immersed in one bath, or may be a process in which the film is sequentially immersed in two or more baths.

In the width constraint step, the polyvinyl alcohol-based resin film after being brought into contact with the treatment liquid in the above treatment step is brought into contact with at least one pre-roll with a diameter of 150 mm or more (hereinafter also referred to as a “large-diameter pre-roll”) in the width direction. It is a process that binds. The roll that contacts the polyvinyl alcohol-based resin film in the width restraint step may include one or more large-diameter pre-rolls, as well as a pre-roll and a drive roll with a diameter of less than 150 mm. The contact of the polyvinyl alcohol-based resin film to the roll as used herein refers not to point contact but to surface contact (the polyvinyl alcohol-based resin film is in contact with the pre-roll with a width in the longitudinal direction). By surface contact, the polyvinyl alcohol-based resin film is restrained in the width direction.

Here, a free roll refers to a roll to which no drive means such as a motor is attached. By using a pre-roll as a means to restrain the width direction of the polyvinyl alcohol-based resin film brought into contact with the treatment liquid as described above, fracture of the polyvinyl alcohol-based resin film can be suppressed. In the present invention, by applying this width restraint process, the polyvinyl alcohol-based resin film is dried gently while restrained in the width direction, and shrinkage in the width direction is suppressed without applying a large load to the polyvinyl alcohol-based resin film. , a polarizing film that is thin and has low shrinkage force can be manufactured.

The drying process is a process of obtaining a polarizing film by drying the polyvinyl alcohol-based resin film to which the width restraint process has been performed, and is a process of reducing the moisture content to, for example, less than 15% by weight.

Hereinafter, the method for manufacturing a polarizing film according to the present invention will be described in more detail with reference to FIG. 1. 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing method according to the present invention and a polarizing film manufacturing apparatus used therein. The polarizing film manufacturing apparatus shown in FIG. 1 transports the raw (unstretched) film 10 made of polyvinyl alcohol-based resin along the film conveyance path while continuously unwinding from the raw roll 11, thereby forming the film conveyance path. The swelling bath 13, the dyeing bath 15, the cross-linking bath 17, and the washing bath 19 installed on the top are sequentially passed through, then passed through the width restraint part 70, and finally into the drying furnace ( 90) is configured to pass. The obtained polarizing film can, for example, be conveyed as is to the next polarizing plate manufacturing process (a process of bonding a protective film to one or both sides of the polarizing film 23). The arrow in FIG. 1 indicates the transport direction of the film.

In addition, Figure 1 shows an example in which one set each of the swelling bath 13, the dyeing bath 15, the cross-linking bath 17, and the washing bath 19 are installed, but more than one treatment bath (swelling bath ( 13), a general term for baths containing a treatment liquid for treating a polyvinyl alcohol-based resin film installed on the film transport path, such as a dyeing bath (15), a cross-linking bath (17), and a washing bath (19). Therefore, it is also called a “treatment bath.”) You may install two or more baths.

The film transport path of the polarizing film manufacturing apparatus includes, in addition to the treatment bath, width restraint section 70, and drying furnace 90, guide rolls 30 to 41 that support the transported film or can also change the film transport direction. 60, 61, 81), or nip rolls 50 to 54, 82, 83 that can apply driving force to the film by pressing and clamping the conveyed film by rotating it or change the film conveyance direction. It can be built by placing it in an appropriate location. Guide rolls and nip rolls can be placed before and after each treatment bath or drying furnace or within the treatment bath, thereby allowing the film to be introduced into, immersed in, and extracted from the treatment bath (see Fig. 1). For example, the film can be immersed in each treatment bath by installing one or more guide rolls in each treatment bath and transporting the film along these guide rolls.

The polarizing film manufacturing apparatus shown in FIG. 1 has nip rolls disposed in front and behind each treatment bath (nip rolls 50 to 54), and thereby, among one or more processing baths, nip rolls disposed in front and behind the treatment baths. It is possible to perform inter-roll stretching by performing vertical uniaxial stretching with a peripheral speed difference between the rolls. Below, each process is explained.

(Swelling treatment process)

The swelling treatment process is performed for the purposes of removing foreign matter from the surface of the raw film 10, removing the plasticizer in the raw film 10, providing easy dyeing properties, and plasticizing the raw film 10. Processing conditions are determined within a range that can achieve the purpose and do not cause problems such as extreme dissolution or loss of transparency of the raw film 10.

Referring to FIG. 1, the swelling treatment process involves transporting the raw film 10 along a film transport path while continuously unwinding the raw film 10 from the raw roll 11, and immersing the raw film 10 in the swelling bath 13 for a predetermined period of time. This can be done by doing and then withdrawing. In the example of FIG. 1, between unwinding the raw film 10 and immersing it in the swelling bath 13, the raw film 10 is pulled by the guide rolls 60, 61 and the nip roll 50. It is conveyed along the established film conveyance path. In the swelling process, the film is conveyed along a film conveyance path constructed by the guide rolls 30 to 32.

The swelling liquid of the swelling bath 13 includes, in addition to pure water, boric acid (Japanese Patent Application Laid-open No. 10-153709), chloride (Japanese Patent Application Laid-Open No. 06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, and alcohol. It is also possible to use an aqueous solution containing about 0.01 to 10% by weight of addition.

The temperature of the swelling bath 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, and more preferably about 15 to 30°C. The immersion time of the raw film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. In addition, when the raw film 10 is a polyvinyl alcohol-based resin film previously stretched in a base, the temperature of the swelling bath 13 is, for example, about 20 to 70°C, and 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, the raw film 10 is likely to swell in the width direction and cause wrinkles to form in the film. As a means for conveying the film while removing this wrinkle, a roll having a widening function such as an expander roll, spiral roll, or crown roll is used on the guide rolls 30, 31, and/or 32, or Other widening devices such as cloth guiders, bend bars, and tenter clips may be used. Another means to suppress the occurrence of wrinkles is to perform stretching treatment. For example, uniaxial stretching treatment can be performed in the swelling bath 13 using the difference in peripheral speed between the nip roll 50 and the nip roll 51.

In the swelling treatment, the film swells and expands in the transport direction of the film, so when the film is not actively stretched, for example, nips placed in front and behind the swelling bath 13 are used to eliminate sagging of the film in the transport direction. It is desirable to devise means such as controlling the speed of the rolls 50 and 51. In addition, for the purpose of stabilizing the transport of the film 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 Control device: detects the edge of the film to control the meandering of the film). It is also useful to use a device that prevents

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

(Dyeing treatment process)

The dyeing treatment step is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol-based resin film after the swelling treatment. Processing conditions are determined within a range that can achieve the purpose and do not cause problems such as extreme dissolution or loss of transparency of the film. Referring to Figure 1, in the dyeing treatment process, the film is transported along a film transport path constructed by the guide rolls 33 to 35 and the nip roll 51, and the film after the swelling treatment is placed in the dyeing bath 15 (accommodated in the dyeing bath). It can be carried out by immersing the treatment in a treatment solution for a predetermined period of time and then withdrawing it. In order to increase the dyeability of the dichroic dye, the film provided in the dyeing treatment process is preferably a film that has undergone at least a certain degree of uniaxial stretching treatment, or is subjected to uniaxial stretching treatment instead of or before dyeing treatment. In addition, it is preferable to perform uniaxial stretching treatment during dyeing treatment.

When using iodine as a dichroic dye, for example, an aqueous solution having a concentration of iodine/potassium iodide/water = about 0.003 to 0.3/about 0.1 to 10/100 in weight ratio can be used as the dyeing solution of the dyeing bath 15. Instead of potassium iodide, other iodides such as zinc iodide may be used, and potassium iodide and other iodides may be used together. Additionally, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may be coexisted. The case of adding boric acid is different from the cross-linking treatment described later in that it contains iodine, and if the aqueous solution contains about 0.003 parts by weight or more of iodine based on 100 parts by weight of water, it can be considered a dyeing bath (15). . The temperature of the dye bath 15 when immersing the film is usually about 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C, and the immersion time of the film is usually 30 to 600 seconds. degree, preferably 60 to 300 seconds.

When using a water-soluble dichroic dye as a dichroic dye, for example, an aqueous solution having a concentration of dichroic dye/water = about 0.001 to 0.1/100 in weight ratio can be used as the dyeing solution of the dyeing bath 15. This dyeing bath 15 may contain a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. One type of dichroic dye may be used individually, and two or more types of dichroic dyes may be used together. The temperature of the dye bath 15 when immersing the film is, for example, about 20 to 80 ° C., preferably 30 to 70 ° C., and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. am.

In the dyeing treatment process as described above, the film can be uniaxially stretched in the dyeing bath 15. Uniaxial stretching of the film can be performed by a method such as adding a peripheral speed difference between the nip rolls 51 and nip rolls 52 disposed in front and behind the dye bath 15.

In the dyeing treatment, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles in the film as in the swelling treatment, the guide rolls 33, 34 and/or 35 are provided with a widening function such as an expander roll, a spiral roll, or a crown roll. You can use a roll with a , or use other widening devices such as a cloth guider, bend bar, or tenter clip. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment, similar to swelling treatment.

In the example shown in FIG. 1, the film taken out from the dyeing bath 15 passes sequentially through the guide roll 35 and the nip roll 52 and is introduced into the crosslinking bath 17.

(Cross-linking treatment process)

The crosslinking treatment process is a treatment performed for purposes such as water resistance by crosslinking and color adjustment (preventing the film from turning blue, etc.). Referring to FIG. 1, the crosslinking treatment involves transporting the film along a film transport path constructed by the guide rolls 36 to 38 and the nip roll 52, and dyeing the film in the crosslinking bath 17 (crosslinking liquid contained in the crosslinking bath). This can be carried out by immersing the subsequent film for a predetermined period of time and then pulling it out.

The crosslinking liquid 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 liquid preferably contains iodide in addition to boric acid, and the amount can be, for example, 1 to 30 parts by weight based on 100 parts by weight of water. Examples of iodide include potassium iodide, zinc iodide, and the like. Additionally, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may be coexisted.

In the crosslinking treatment, the concentrations 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, dyeing treatment, and crosslinking treatment are performed on the polyvinyl alcohol-based resin film in this order, the concentration of the crosslinking agent-containing liquid in the crosslinking bath is expressed by weight ratio. It may be an aqueous solution of boric acid/iodide/water = 3 to 10/1 to 20/100. If necessary, other cross-linking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, and boric acid and other cross-linking agents may be used together. The temperature of the crosslinking bath when immersing the film is usually about 50 to 70 ℃, preferably 53 to 65 ℃, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably. is 20 to 200 seconds. In addition, when dyeing treatment and cross-linking treatment are performed in this order on a polyvinyl alcohol-based resin film previously stretched before swelling treatment, the temperature of the cross-linking bath 17 is usually about 50 to 85 ° C., preferably 55 to 80 ° C. It is ℃.

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

The crosslinking treatment may be performed multiple times, and is usually performed 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 crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color adjustment may each be performed in a plurality of processes.

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

In the crosslinking treatment, as in the swelling treatment, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles in the film, the guide rolls 36, 37, and/or 38 are provided with expansion rolls such as expander rolls, spiral rolls, and crown rolls. You can use functional rolls or other widening devices such as cloth guiders, bend bars, or tenter clips. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment, similar to swelling treatment.

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

(Cleaning treatment process)

The manufacturing method of the present invention may 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 attached to the polyvinyl alcohol-based resin film. The cleaning treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in the film cleaning bath 19, spraying a film cleaning liquid on the film as a shower, or using a combination of these.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform a cleaning treatment. 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.

Also, in the cleaning treatment, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, the guide rolls 39, 40 and/or 41 are provided with rolls having a widening function such as an expander roll, a spiral roll, or a crown roll. You can use , or you can use other widening devices such as cloth guiders, bend bars, and tenter clips. Additionally, in the film cleaning treatment, stretching treatment may be performed to suppress the occurrence of wrinkles.

(Stretching treatment process)

As described above, the raw film 10 is uniaxially stretched in a wet or dry manner between the series of processing steps (that is, before and after and/or during one or more processing steps). A specific method of uniaxial stretching treatment is, for example, inter-roll stretching, in which longitudinal uniaxial stretching is performed by adding a peripheral speed difference between two nip rolls (e.g., two nip rolls disposed in front and behind the treatment bath) that constitute the film transport path, Japan. It may be hot roll stretching, tenter stretching, etc. as described in Patent No. 2731813, and is preferably inter-roll stretching. The uniaxial stretching treatment process can be performed several times until the polarizing film 23 is obtained from the raw film 10. As described above, stretching treatment is also advantageous for suppressing wrinkles in the film.

The final cumulative stretching ratio of the polarizing film 23 based on the raw film 10 is usually about 4.5 to 7 times, and 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 restraint step, and even when the stretching treatment is performed in two or more processing steps, the stretching treatment may be performed in any of the processing steps.

(width constraint process)

After the cleaning treatment process, a width restraint process is performed in which the polyvinyl alcohol-based resin film is brought into contact with at least one large-diameter pre-roll with a diameter of 150 mm or more to restrain the width direction.

In the width restraint process, the polyvinyl alcohol-based resin film does not always have to be in contact with the roll, but from the viewpoint of achieving effective width restraint, the polyvinyl alcohol-based resin film is preferably in continuous contact for 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 with a diameter of 150 mm or more as a roll used in the width restraint process. Using a large-diameter pre-roll, it is easy to secure the continuous contact time described above. The diameter of the large diameter pre-roll is preferably 200 mm or more, and 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 pre-roll rotation resistance, and there is a risk that the polyvinyl alcohol-based resin film may be easily broken. In the width restraint process, it is preferable to include two or more large diameter pre-rolls.

The rolls used in the width restraint process can adjust the transport direction of the polyvinyl alcohol-based resin film and can also force curl, so it is preferable that there are multiple rolls including the large diameter pre-rolls described above, and three or more five rolls. It is more preferable that it is below. When multiple rolls are used, the polyvinyl alcohol-based resin film is on one 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 desirable to be in contact. When the time in contact with the roll is 40% or more, a sufficient width restraint 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 of each roll. Additionally, from the viewpoint of performing effective width restraint, it is preferable that the continuous time during which the polyvinyl alcohol-based resin film is not in contact with the roll is 2 seconds or less.

In addition, in this specification, the point of contact with the first roll in the width restraint process is taken as the introduction point of the width restraint process, and the point released from the last roll is taken as the derivation point from the width restraint process. When there is only one roll used in the width restraint process, the first roll and the last roll are the same roll. It is preferable that the time from the start to the end of the width restraint process is 5 seconds or more. Additionally, it is preferable that the time from start to end of the width restraint process is less than 60 seconds. In the case of 60 seconds or more, the drying of the polyvinyl alcohol-based resin film in the width restraint step may proceed more than necessary, and the polyvinyl alcohol-based resin film may break in the subsequent drying step.

In the width restraint process, the polyvinyl alcohol-based resin film is dried gently while restrained in the width direction, and shrinkage in the width direction is suppressed without applying a large load to the polyvinyl alcohol-based resin film, resulting in a thin polarized light with a small shrinkage force. Films can be manufactured. In order to control the drying state in the width restraint process, it is desirable to have, for example, a means for drying using a hot air dryer, an infrared heater, or a combination thereof. In the width restraint process, the highest temperature that the polyvinyl alcohol-based resin film reaches is, for example, 30 to 100°C, preferably 50 to 80°C.

In Figure 1, a width constraint process is performed within the width constraint portion 70. In the width restraint portion 70 shown in FIG. 1, three pre-rolls 71, 72, and 73 and hot air dryers 74, 75 arranged to face each of the pre-rolls 71, 72, and 73, respectively. 76) is installed. Each hot air dryer (74, 75, 76) has members (74a, 75a, 76a) arranged on a line in the width direction with an outlet for sending out hot air from the upstream side to the downstream direction, and sends hot air from the downstream side to the upstream direction. The configuration is such that the discharge port for sending out air is provided with members 74b, 75b, and 76b arranged on a line in the width direction. Hot air sent from the hot air dryers (74, 75, 76) is sprayed on the polyvinyl alcohol-based resin film in contact with the opposing pre-rolls (71, 72, 73) to form a polyvinyl alcohol-based resin film in the width restraint process. The drying state is controlled. All three pre-rolls (71, 72, and 73) are large-diameter pre-rolls. Within the width restraint portion 70 shown in FIG. 1, the point where the polyvinyl alcohol-based resin film contacts the free roll 71 is the introduction point of the width restraint process, and the point released from the free roll 73 is the point from the width restraint process. This is the derivation point.

The roll configuration within the width restraint portion 70 is not limited to the form shown in FIG. 1. 2 to 5 schematically show other configurations within the width restraint portion 70. 2 to 5, the transport path of the polyvinyl alcohol-based resin film 10 in the width restraint process is shown by a solid line, and the transport path of the polyvinyl alcohol-based resin film 10 before and after the width restraint process is shown by a dotted line. and the conveyance direction is indicated by an arrow. Moreover, similarly to FIG. 1, the guide roll immediately before introduction of the width restraint process is set as the guide roll 54, and the guide roll immediately after being introduced in the width restraint process is set as the guide roll 81. The conveyance direction of the polyvinyl alcohol-based resin film before and after the width restraint process and in the width restraint process does not necessarily correspond to the example shown in FIG. 1, but the conveyance direction can be adjusted appropriately by using a guide roll or the like.

In the example shown in FIG. 2, three pre-rolls 711, 712, and 713 with a diameter of 300 mm are arranged. The polyvinyl alcohol-based resin film contacts the pre-roll 711 at P11 and is introduced into the width restraint process, and then is released from the pre-roll 711 at P12. After that, it contacts the next pre-roll 712 at P13 and is released from the pre-roll 712 at P14. Then, it contacts the final pre-roll 713 at P15, is released from the pre-roll 713 at P16, and is derived from the width restraint process. In the example shown in Figure 2, if the transport speed of the film is 10 m/min, the time required for transport between each point is 2.83 seconds for P11 to P12, 1.8 seconds for P12 to P13, and 2.83 seconds for P13 to P14. , each pre-roll 711, 712, 713 and the front and rear guide rolls are arranged so that P14 to P15 is 1.8 seconds and P15 to P16 is 2.83 seconds. In this case, the time taken for the width restraint process is 12.09 seconds, of which the time the polyvinyl alcohol-based resin film is in contact with the roll is 8.49 seconds. Therefore, 70% of the time during the width constraint process is in contact with one roll.

In the example shown in FIG. 3, three pre-rolls 721, 722, and 723 with a diameter of 150 mm are arranged. The polyvinyl alcohol-based resin film contacts the pre-roll 721 at P21 and is introduced into the width restraint process, and then is released from the pre-roll 721 at P22. After that, it contacts the next pre-roll 722 at P23 and is released from the pre-roll 722 at P24. Then, it comes into contact with the last pre-roll 723 at P25, is released from the pre-roll 723 at P26, and is derived from the width restraint process. In the example shown in Figure 3, if the transport speed of the film is 10 m/min, the time required for transport between each point is 0.9 seconds for P21 to P22, 1.59 seconds for P22 to P23, and 0.38 seconds for P23 to P24. , the pre-rolls 731, 732, and 733 and the front and rear guide rolls are arranged so that P24 to P25 is 1.59 seconds and P25 to P26 is 0.9 seconds. In this case, the time required for the width restraint process 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 during the width constraint process, one roll is in contact.

In the example shown in FIG. 4, two pre-rolls 731 and 733 with a diameter of 120 mm and a pre-roll 732 with a diameter of 450 mm are arranged. The polyvinyl alcohol-based resin film contacts the pre-roll 731 at P31 and is introduced into the width restraint process, and then is released from the pre-roll 731 at P32. After that, it contacts the next pre-roll 732 at P33 and is released from the pre-roll 732 at P34. Then, it contacts the last pre-roll 733 at P35, is released from the pre-roll 733 at P36, and is derived from the width restraint process. In the example shown in Figure 4, if the transport speed of the film is 10 m/min, the time required for transport between each point is 0.85 seconds for P31 to P32, 0.88 seconds for P32 to P33, and 6.36 seconds for P33 to P34. , the pre-rolls 721, 722, and 723 and the front and rear guide rolls are arranged so that P34 to P35 is 0.88 seconds, and P35 to P36 is 0.85 seconds. In this case, the time taken for the width restraint process is 9.82 seconds, of which the time the polyvinyl alcohol-based resin film is in contact with the roll is 8.06 seconds. Therefore, 82% of the time during the width constraint process, one roll is in contact.

In the example shown in FIG. 5, a pre-roll 741 with a diameter of 550 mm is arranged. The polyvinyl alcohol-based resin film is introduced into the width restraint process by contacting the free roll 741 at P41, and then is released from the free roll 741 at P42 and is derived from the width restraint process. In the example shown in FIG. 5, if the transport speed of the film is 10 m/min, the pre-roll 741 and the front and rear guide rolls are arranged so that the time required for transport between each point is 5.18 seconds for P41 to P42. there is. In this case, it is in contact with the roll of the polyvinyl alcohol-based resin film for all of 5.18 seconds, which is the time required for the width restraint process, that is, 100% of the time for the width restraint process.

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

The polyvinyl alcohol-based resin film is preferably introduced into the width restraint process within 20 seconds after contact with the treatment liquid in the process immediately before the width restraint process is terminated. If it exceeds 20 seconds, the time for the polyvinyl alcohol-based resin film to dry gently without the width being restrained becomes long, and there is a risk that the width restraint effect may not be sufficiently expressed. Here, in the case of the example shown in FIG. 1, the point in time when contact with the treatment liquid in the immediately preceding process ends is the point in time when it is withdrawn from the cleaning bath 19.

Additionally, the moisture content of the polyvinyl alcohol-based resin film when introduced into the width restraint process is preferably 30% by weight or more. If the moisture content of the polyvinyl alcohol-based resin film is less than 30% by weight, there is a risk that the width restraint effect may not be sufficiently expressed. In addition, in the device shown in FIG. 1, the moisture content at the time of introduction into the width restraint process can be considered to be the same as the moisture content at the position P1 immediately before introduction into the width restraint portion 70.

In the width restraint process, the highest temperature that the polyvinyl alcohol-based resin film reaches is, for example, 30 to 100°C, preferably 50 to 80°C.

(drying process)

After the width restraint process, a drying process is performed in which the polyvinyl alcohol-based resin film is subjected to a drying treatment. The drying process is a process of further reducing the moisture content of the polyvinyl alcohol-based resin film, for example, from a 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 treatment include drying using a hot air dryer, an infrared heater, or a combination thereof.

In the drying process, the highest temperature that the polyvinyl alcohol-based resin film reaches is, for example, 30 to 100°C, preferably 50 to 90°C. The drying process time is, for example, 60 to 600 seconds, preferably 120 to 600 seconds. By having the width restraint process and drying process as described above, when manufacturing a thin polarizing film having a desired moisture content, it can be manufactured with high efficiency while suppressing breakage of the polyvinyl alcohol-based resin film. 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 treatment processes for polyvinyl alcohol-based resin films)

Processing other than the above may be added. Examples of treatments that can be added include immersion treatment in an aqueous iodide solution not containing boric acid (complementary color treatment), which is performed after the crosslinking treatment step, and immersion treatment in an aqueous solution containing zinc chloride, etc. but not boric acid ( zinc treatment).

<Polarizer>

A polarizing plate can be obtained by bonding a protective film to at least one side of the polarizing film manufactured as described above via an adhesive. Examples of the protective film include films made of acetylcellulose-based resins such as triacetylcellulose and diacetylcellulose; Films made of polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; Polycarbonate-based resin film, cycloolefin-based resin film; Acrylic resin film; A film made of chain olefin resin of polypropylene resin can be mentioned.

In order to improve the adhesion of the polarizing film and the protective film, surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer application treatment, and saponification treatment is performed on the bonding surface of the polarizing film and/or the protective film. It's also good. Adhesives used to bond the polarizing film and the protective film include, for example, active energy ray-curable adhesives such as ultraviolet curable adhesives, aqueous solutions of polyvinyl alcohol-based resins or aqueous solutions mixed with cross-linking agents, and water-based adhesives such as urethane-based emulsion adhesives. I can hear it. The ultraviolet curing adhesive may be a mixture of an acrylic compound and a radical photopolymerization initiator, or a mixture of an epoxy compound and a cationic photopolymerization initiator. Additionally, a cationically polymerizable epoxy compound and a radically polymerizable acrylic compound can be used together, and a photocationic polymerization initiator and a radical photopolymerization initiator can also be used together as an initiator.

Example

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

[Measurement of film thickness]

The film thickness of the polarizing film was measured using a contact-type film thickness gauge (trade name "DIGIMICRO MH-15M" manufactured by Nikon Corporation). In addition, the film thickness of the polarizing film was measured at 15 points in different width directions, and the average value was calculated. Table 1 shows the average values.

[Measurement of contraction force]

An evaluation sample with a width of 2 mm and a length of 50 mm was cut 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 shrinkage force of the obtained single-type evaluation sample was measured using a thermomechanical analysis device (model TMA/6100, manufactured by SI Nano Technology Co., Ltd.). This measurement is carried out in dimensional constant mode (distance between chucks is 10 mm), and after leaving the test piece in a room at 20°C for a sufficient period of time, the room temperature setting of the sample is raised from 20°C to 80°C in 1 minute. , After the temperature increase, the room temperature of the sample was set to be maintained at 80°C. After the temperature was raised and left for an additional 4 hours, the shrinkage force in the long side direction of the test piece was measured in an environment of 80°C. In this measurement, the static load was set to 0 mN, and a SUS probe was used for the jig.

<Example 1>

A polarizing film was manufactured using an apparatus similar to the polarizing film manufacturing apparatus shown in FIG. 1. As the free rolls 71, 72, and 73 disposed within the width restraint portion 70, those with a diameter of 300 mm were used. Additionally, within the drying furnace 90, No. 1~No. Drying was performed using three hot air dryers in 3.

(1) Swelling treatment process

A polyvinyl alcohol film with a thickness of 30 ㎛ [Kurare Co., Ltd. brand name "Kurare Foam VF-PE #3000", degree of polymerization 2400, degree of saponification 99.9 mol% or more] is conveyed continuously and is compressed by about 4 times in a dry process. It continued. The obtained stretched polyvinyl alcohol film was 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 tension so as not to loosen the film.

(2) Dyeing treatment process

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

(3) Cross-linking treatment process

Next, in order to carry out cross-linking treatment for the purpose of water resistance, the film that has passed through the nip roll 52 is placed in a first cross-linking bath at 68°C with a potassium iodide/boric acid/water (weight ratio) of 10.5/7.5/100 ( 17) was immersed for 300 seconds.

(4) Cleaning treatment process

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

(5) Width constraint process

Next, the film after the cleaning treatment was passed through the width restraint section 70. The temperature of the hot air blown from the three hot air dryers 74 to 76 in the width restraint portion 70 was as shown in Table 1. Additionally, the moisture content of the film immediately before being introduced into the width restraint portion 70 (position P1) was measured using a moisture content meter (product name: moisture meter IRMA1100, manufactured by Chino Corporation). The results are shown in Table 1. The time from removing the film from the washing bath 19 to contacting the pre-roll 71 was 12 seconds. In addition, in the width restraint portion 70, the time from when the film contacts the first pre-roll 71 to being released from the last pre-roll 73 (time of the width restraint process), ) and the pre-roll 72 and between the pre-roll 72 and the pre-roll 73 were measured. The time of the width restraint 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 the film is in contact with the pre-rolls (71, 72, 73) is the time taken for the width restraint process. It was 78%.

(6) Drying process

The film after passing through the width restraint section 70 was passed through the drying furnace 90 to produce a polarizing film. Three hot air dryers No. 1 in the drying furnace 90. 1~No. The temperature of the hot air discharged from 3 was as shown in Table 1. In addition, the moisture content of the film immediately before being introduced into the drying furnace 90 (position P3) and immediately after being taken out of the drying furnace 90 (position P4) was measured using a moisture content meter (product name: moisture meter IRMA110, manufactured by Chino Corporation). It was measured by . 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 blown from the three hot air dryers 74 to 76 in the width restraint portion 70 was as shown in Table 1. Similar to Example 1, the film immediately before being introduced into the width restraint portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being taken out from the drying furnace 90 (position P4) The moisture content was measured. The results are shown in Table 1.

<Example 3>

Three hot air dryers No. 1 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 blown from 3 was as shown in Table 1. Similar to Example 1, the film immediately before being introduced into the width restraint process 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being taken out of the drying furnace 90 (position P4) The moisture content 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 restraint portion (70) and the number of three hot air dryers 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 blown from 3 was as shown in Table 1. Similar to Example 1, the film immediately before being introduced into the width restraint process 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being taken out of the drying furnace 90 (position P4) The moisture content was measured. The results are shown in Table 1.

<Example 5>

In the configuration within the width restraint portion 70, the pre-roll 72 and the hot air dryer 75 opposing it are not installed, and the temperatures of the hot air sent from the remaining two hot air dryers 74 and 76 are shown in Table 1. A polarizing film was produced in the same manner as in Example 1 except that it was carried out as shown. Similar to Example 1, the film immediately before being introduced into the width restraint portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being taken out from the drying furnace 90 (position P4) The moisture content was measured. The results are shown in Table 1. In addition, within the width restraint portion 70, the time from when the film contacts the first pre-roll 71 to release from the last pre-roll 73 (time of the width restraint process), ) and the non-contact time between the pre-roll (73) 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 pre-roll is 2 seconds or less, and the time the film is in contact with the pre-rolls 71 and 73 is relative to the time taken for the width restraint process. It was 44%.

<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 restraint portion 70 were not used. Similar to Example 1, the film immediately before being introduced into the width restraint portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being taken out from the drying furnace 90 (position P4) The moisture content was measured. The results are shown in Table 1.

<Example 7>

The three hot air dryers 74 to 76 in the width restraint portion 70 were not used, and the three hot air dryers No. 74 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 blown from 3 was as shown in Table 1. Similar to Example 1, the film immediately before being introduced into the width restraint portion 70 (position P1), immediately before being introduced into the drying furnace 90 (position P3), and immediately after being taken out from the drying furnace 90 (position P4) The moisture content 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 restraint process was not performed (it was not passed through the width restraint portion 70). Similarly to Example 1, the moisture content of the film immediately before being introduced into the main drying furnace 90 (position P3) and immediately after being taken out of the main drying furnace 90 (position P4) was measured. The results are shown in Table 1.

10: raw film made of polyvinyl alcohol-based resin, 11: raw roll, 13: swelling bath, 15: dyeing bath, 17: crosslinking bath, 19: washing bath, 21; Drying furnace, 23: Polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 60, 61, 81: Guide roll, 50, 51, 52, 53, 54 , 82, 83: nip roll, 70: width restraint, 71, 72, 73: pre-roll, 74, 75, 76: hot air dryer, 90: drying furnace.

Claims (4)

A width restraining step of restraining the polyvinyl alcohol-based resin film after contacting the treatment liquid in the width direction by contacting at least one pre-roll with a diameter of 150 mm or more;
After the width restraint process, it includes a drying process of drying the polyvinyl alcohol-based resin film,
The drying process is a method of producing a polarizing film, which is a process of reducing the moisture content of the polyvinyl alcohol-based resin film from 18% by weight to less than 30% by weight to less than 15% by weight. The method according to claim 1, wherein in the width restraint step, the polyvinyl alcohol-based resin film is brought into contact with a plurality of rolls including the pre-roll, between contacting the first roll and being released from the last roll. A method of producing a polarizing film wherein at least 40% of the time is in contact with any one roll. The production of 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 restraint step within 20 seconds after contact with the treatment liquid is terminated. method. The method for producing a polarizing film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film has a moisture content of 30% by weight or more at the time of first contact with the roll in the width restraint step.

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