TWI654225B - Method for manufacturing polarizing film - Google Patents

Abstract

The present invention provides a method for manufacturing a polarizing film, which sequentially comprises: unwinding and conveying a long polyvinyl alcohol-based resin film having a thickness of 65 μm or less from a raw material reel, thereby impregnating the polyvinyl alcohol-based resin film in A swelling treatment step drawn out after the swelling bath; and a dyeing treatment step where the film drawn from the swelling bath is dipped in a dyeing bath; wherein the polyvinyl alcohol-based resin film is dipped in the swelling bath in the width direction of the film The curling angle of at least one of the two end portions is less than 90 °.

Description

Manufacturing method of polarizing film

This invention relates to the manufacturing method of the polarizing film which can be used as a structural member of a polarizing plate.

For polarizing films, conventionally, dichroic dyes such as iodine and dichroic dyes are used to adsorb polyvinyl alcohol-based resin films oriented in one axis. Polarizing films are usually bonded to one or both sides of the protective film with an adhesive to form a polarizing plate, and are used in image display devices such as liquid crystal display devices such as liquid crystal televisions, personal computer screens, and mobile phones. .

Generally speaking, a polarizing film is processed by sequentially immersing a continuous transfer of a long polyvinyl alcohol-based resin film in a processing bath such as a swelling bath, a dyeing bath, and a cross-linking bath. It is manufactured by performing an extension treatment (for example, Japanese Patent Laid-Open No. 2001-315140 (Patent Document 1)). Patent Document 1 discloses that in order to suppress the curl at the end of the film generated when the polyvinyl alcohol-based resin film is stretched and uniformly extend, the curl angle when the polyvinyl alcohol-based resin film is immersed in water at 30 ° C for 5 minutes is 180 ° or less.

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2001-315140

The polarizing film is continuously rolled out from the raw material reel (wound roll) of the polyvinyl alcohol resin film, and is conveyed along the film body conveying path through the various processing baths as described above, and is immersed in the swelling bath to from Stretching is performed at any one or more stages between the time when the cross-linking bath is pulled out, and continuous production can be performed. However, in continuous manufacturing, the film is broken especially during the stretching process, and improvement is desired from the viewpoints of productivity and yield of the polarizing film. The problem of film breakage during the stretching treatment is particularly noticeable when the thickness of the polyvinyl alcohol-based resin film is small.

Therefore, an object of the present invention is to provide a method for producing a polarizing film capable of effectively suppressing film breakage during stretching even when a thin polyvinyl alcohol-based resin film is used.

This invention provides the manufacturing method of the polarizing film shown below.

[1] A method for manufacturing a polarizing film, which comprises sequentially rolling out a long polyvinyl alcohol-based resin film having a thickness of 65 μm or less from a raw material reel and conveying it, thereby impregnating the aforementioned polyvinyl alcohol-based resin film A swelling treatment step drawn out after the swelling bath; and a dyeing treatment step where the film drawn from the swelling bath is drawn after being immersed in a dyeing bath; wherein the film width of the polyvinyl alcohol-based resin film when being soaked in the swelling bath The curl angle of at least one of the two end portions in the degree direction is less than 90 °.

[2] The method for producing a polarizing film according to [1], wherein a time from the unwinding of the polyvinyl alcohol-based resin film from the raw material roll to immersion in the swelling bath is 750 seconds or less.

[3] The method for producing a polarizing film according to [1] or [2], wherein after the polyvinyl alcohol-based resin film is rolled out from a raw material roll until it is immersed in a swelling bath, the polymer The vinyl alcohol-based resin film is dried.

[4] The method for producing a polarizing film according to [3], wherein the drying treatment is performed so that the dryness of the curled surface of the polyvinyl alcohol-based resin film is smaller than the surface on the opposite side.

[5] The method for producing a polarizing film according to any one of [1] to [4], which is performed after the polyvinyl alcohol-based resin film is rolled out from a raw material roll until it is immersed in a swelling bath. Then, the polyvinyl alcohol-based resin film is subjected to a widening treatment.

[6] The method for producing a polarizing film according to any one of [1] to [5], wherein in the swelling treatment step, the polyvinyl alcohol-based resin film rolled out from a raw material roll is selected along The two or more rollers of the self-guide roller and the nip roller are conveyed, so that they are immersed in the swelling bath. For the two or more rollers, the maximum distance between adjacent rollers is set to L, When the maximum value of the time required for the transfer between the rollers is set to T, L is 2 m or less, or T is 30 seconds or less.

According to the method of the present invention, the traditional cause can be effectively suppressed The thin film of a polyvinyl alcohol-based resin film has a film crack at the time of the stretching process which occurs in the method of manufacturing a polarizing film.

10‧‧‧ Raw film containing polyvinyl alcohol resin

11‧‧‧ Raw Scroll

13‧‧‧Swelling bath

15‧‧‧ Dyeing bath

17‧‧‧ Cross-linking bath

19‧‧‧washing bath

21‧‧‧ drying furnace

23‧‧‧Polarizing Film

30,31,32,33,34,35,36,37,38,39,40,41,60,61‧‧‧‧Roller

50,51,52,53,54,55

FIG. 1 is a schematic cross-sectional view showing an example of a method for producing a polarizing film of the present invention and an apparatus for producing a polarizing film used in the method.

Figures 2 (a) to (c) are cross-sectional views schematically showing the curled state of the polyvinyl alcohol-based resin film and the curling angle thereof.

<Manufacturing method of polarizing film>

In the present invention, a polarizing film-based dichroic dye (iodine, dichroic dye) is adsorbed and oriented on a polyvinyl alcohol-based resin film stretched through one axis. 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. Polyvinyl acetate-based resins may be copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, and preferably about 1500 to 5,000.

These polyvinyl alcohol-based resins can also be modified, and for example, aldehyde-modified polyvinyl formaldehyde, polyvinyl acetal, and polyvinyl butyral can be used.

In the present invention, as a starting material for manufacturing a polarizing film, An unstretched polyvinyl alcohol-based resin film (raw material film) having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and still more preferably 30 μm or less is used. Thereby, a polarizing film of a thin film having an increasing market demand can be obtained. The thinner the raw material film, the more likely it is that the film is broken during the stretching process. However, according to the present invention, even when the raw material film is thin, the film can be effectively suppressed from being broken. When the thickness of the raw material film is thicker than 65 μm, film breakage during stretching due to bending (curling) does not often cause a problem. The raw material film may be a polyvinyl alcohol-based resin film which has been previously stretched in the gas phase.

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

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

The polarizing film can be continuously manufactured by rolling the long raw film from the raw material reel and continuously carrying the predetermined processing steps along the film body conveying path of the polarizing film manufacturing apparatus, thereby continuously manufacturing the long film. Polarizing film. The predetermined treatment step may include: a swelling treatment step in which the raw material film is drawn after being immersed in the swelling bath, a dyeing treatment step in which the film after the swelling treatment step is dipped in the dyeing bath, and the film after the dyeing treatment is dipped in Cross-linking treatment step drawn after the cross-linking bath. Furthermore, between the series of processing steps (that is, before and after any one or more processing steps and / or during any one or more processing steps), a wet or dry one-axis extension processing is performed. If necessary, other processing steps can be added. All of the above In the processing step, the film can be immersed in one bath, or immersed in two or more baths in sequence.

Hereinafter, the manufacturing method of the polarizing film of this invention is demonstrated in detail with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and a device for producing a polarizing film using the method. The polarizing film manufacturing apparatus shown in FIG. 1 is configured to continuously roll a raw material (unstretched) film 10 containing a polyvinyl alcohol resin from a raw material reel 11 while conveying it along a film transport path, thereby The raw material film 10 passes through a swelling bath 13, a dyeing bath 15, a cross-linking bath 17, and a washing bath 19 provided in the film body conveying path in this order, and finally is constituted by a drying furnace 21. The obtained polarizing film 23 can be transferred to the next polarizing plate manufacturing step (the step of laminating the protective film on one or both sides of the polarizing film 23) in its original state, for example. The arrows in FIG. 1 indicate the transport direction of the film.

In addition, FIG. 1 shows an example in which each of a swelling bath 13, a dyeing bath 15, a crosslinking bath 17, and a washing bath 19 is provided. If necessary, any one or more treatment tanks (such as a swelling bath) may be provided. (Bath 13, dyeing bath 15, cross-linking bath 17, and cleaning bath 19 are collectively referred to as a "treatment bath", which are installed on the membrane body conveying path and receive a treatment solution for treating a polyvinyl alcohol-based resin film) Provide 2 or more slots.

In addition to the above-mentioned processing bath, the film body conveying path of the polarizing film manufacturing device can also be provided with guide rollers 30 to 41, 60, 61, and The conveyed film is pressed / nipped, and is constructed by nip rollers 50 to 55 that impart a film or further change the conveying direction of the film by a driving force derived from its rotation. Guide rollers The nip rollers can be placed before and after each processing bath, and in the processing baths, so that the film can be introduced and immersed in the processing bath, and the film can be pulled out of the processing bath [see FIG. 1]. For example, by providing one or more guide rollers in each processing bath and conveying the film along these guide rollers, the film can be immersed in each processing bath.

The polarizing film manufacturing apparatus shown in FIG. 1 is provided with nip rollers (nip rollers 50 to 54) before and after each treatment bath, thereby allowing the nips arranged before and after the treatment bath to be used in any one or more treatment baths. A rotation speed difference is provided between the rolls, and roll-to-roll extension is performed in which the longitudinal uniaxial extension is performed. Hereinafter, each processing step will be described.

(Swelling treatment)

The swelling treatment is performed for the purpose of removing foreign matter on the surface of the raw material film 10, removing plasticizers in the raw material film 10, imparting easy dyeability, plasticizing the raw material film 10, and the like. The processing conditions are determined within a range in which the object can be achieved without causing defects such as excessive dissolution and loss of transparency of the raw material film 10.

Referring to FIG. 1, in the swelling process, the raw material film 10 can be continuously rolled out from the raw material reel 11 while being conveyed along the film body conveying path, and the raw material film 10 can be placed in a swelling bath 13 (a processing solution stored in a swelling tank) ) Pull out after immersion for a predetermined time. In the example of FIG. 1, after the raw material film 10 is rolled out and immersed in the swelling bath 13, the raw material film 10 is conveyed along a film conveyance path constructed by the guide rollers 60 and 61 and the nip roller 50. In the swelling process, the film is transported along a film transport path constructed by guide rollers 30 to 32.

In the swelling bath 13, in addition to pure water, An aqueous solution of 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, alcohol, etc., in a range of about 0.01 to 10% by weight.

The temperature of the swelling bath 13 is, for example, about 10 to 50 ° C, preferably about 10 to 40 ° C, and more preferably about 15 to 30 ° C. The immersion time of the raw material film 10 is preferably about 10 to 300 seconds, and more preferably about 20 to 200 seconds. When the raw material 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 ° C, and preferably about 30 to 60 ° C. The immersion time of the raw material film 10 is preferably about 30 to 300 seconds, and more preferably about 60 to 240 seconds.

In the present invention, the curl angle of at least one of the both ends of the film width direction when the raw material film 10 is immersed in the swelling bath 13 is less than 90 °. The raw material film 10 rolled out from the raw material reel 11 is usually in a state where at least one of the both ends in the width direction (more typically, both ends in the width direction) is warped (floating), or The state where the warpage becomes larger and both ends in the width direction are reversely warped toward the center in the width direction, curling occurs, and the curling angle when the raw material film 10 is immersed in the swelling bath 13 does not reach 90 °, which can suppress the stretching process. Rupture of the membrane. In order to more effectively suppress the cracking of the film, it is preferable that the curl angle of both of the two ends in the width direction of the film is less than 90 °. Further, for the same reason, the curl angle of at least one of the both ends in the width direction of the film is preferably 80 ° or less, and more preferably less than 75 °. It is preferable that the curl angles of both ends of the film width direction both immediately after unwinding from the raw material reel 11 and being immersed in the swelling bath 13 are less than 90 °.

FIG. 2 is a roll of a polyvinyl alcohol resin film. Sectional view of the curvature and its curl angle. Fig. 2 shows an example of curling at both ends in the film width direction. Fig. 2 (a) shows a case where the curl angle is 45 °, Fig. 2 (b) shows a case where the curl angle is 90 °, and the second Figure (c) shows the case where the curl angle is 150 °. As shown in FIG. 2, the curl angle is α °, which means that the end of the film in the curled portion is oriented in a direction of α ° with respect to the interpolated surface other than the film surface without curl. The curling angle of both ends in the width direction of the raw material film 10 continuously immersed in the swelling bath 13 can be measured by the method described in the example paragraph.

In order to make the curl angle of at least one (preferably both) of both end portions in the film width direction when the raw material film 10 is immersed in the swelling bath 13, for example, the following measures are preferred. The following means may be used alone or in combination of two or more.

[A] The environment of the unwinding step after unwinding the raw material film 10 from the raw material reel 11 to immersion in the swelling bath 13 is adjusted to appropriate conditions. The preferred environmental conditions are a temperature of 23 ± 5 ° C and a relative humidity of 20 to 70% RH. A better relative humidity is 20 to 65% RH, and a better relative humidity is 25 to 60% RH. By performing the unwinding step in such an environment, it is possible to suppress moisture absorption and curl growth of the raw material film 10.

[B] The time required for the unwinding step (the time after the raw material film 10 is unwound from the raw material reel 11 until it is immersed in the swelling bath 13) is shortened. When this time is short, it is beneficial in suppressing the growth of curl in the unwinding step, and it is also beneficial from the viewpoint of production efficiency. In general, the thinner the raw material film, the easier it is for the curl to grow in the unwinding step. The time required above is preferably 750 when the raw material film 10 of 35 μm to 65 μm is used. It is below 600 seconds, more preferably below 600 seconds, and even more preferably below 300 seconds. When using the raw material film 10 of less than 35 μm, it is preferably 650 seconds or less, more preferably 300 seconds or less, and still more preferably 150 seconds or less. On the other hand, when the above-mentioned required time is shortened to an extremely short time, the tension of the film in the unwinding step becomes difficult to control, and the transport of the film becomes unstable. Therefore, the above-mentioned required time is usually 10 seconds or more, It is preferably more than 20 seconds.

[C] In the unwinding step, the transported raw material film 10 is dried. The drying process herein refers to a drying process in which moisture in the raw material film 10 is volatilized and the moisture content of the raw material film 10 is reduced. Drying is beneficial in reducing and eliminating curls. In order to reduce or eliminate curl, it is particularly desirable to perform the drying treatment such that the curled surface of the raw material film 10 has less dryness (that is, the degree of reduction in moisture content due to drying) than the surface on the opposite side. The curled surface is a raw film surface including a curled inner surface, and referring to FIG. 2, it is a main surface on the upper side of the figure.

As a method for making the dryness of the curled surface smaller than that of the surface on the opposite side, the raw material film 10 is sandwiched between the surfaces of the surface on the opposite side of the curled surface using hot air, dry air, and infrared heaters, and the temperature is different from each other Method between a pair of rollers.

[D] In the unwinding step, the raw material film 10 to be conveyed is subjected to a widening process. The widening treatment for the purpose of expanding the width of the film is beneficial in reducing and eliminating curling when the raw material film 10 is immersed in the swelling bath 13. As the extended width processing, a roll having a function of expanding width such as an expander roll, a spiral roll, and a crown roll can be used as the guide roll, and a cross guide such as a cross guider, bend bar, tentor grip, and other extended width devices. Among them, since it is simple, it is preferable to use a roll having a function of expanding the width. For example, as the guide roller 60 and / or 61 shown in FIG. 1, a roller having a function of expanding the width can be used.

[E] In the unwinding step, a process of forcibly pressing the curled portion is performed on the conveyed raw film 10. This treatment is advantageous in the same way as the width-expanding treatment in that the curl of the raw material film 10 when immersed in the swelling bath 13 is reduced or eliminated. Specific methods include: a method of conveying a film using a device such as a conveyor belt; a method of pressing a curled portion with a roller or a rod (such as a rod that does not rotate on the body of the roller); spraying air, nitrogen, and argon on the curled portion A method in which the raw material film 10 is an inert gas.

[F] For example, in the example shown in FIG. 1, in the unwinding step, when the raw material film 10 is conveyed along a film conveyance path constructed by two or more rollers selected from a guide roller and a nip roller, it is shortened. The maximum value L of the distance between the adjacent rollers and / or the maximum value T of the time required for the transfer between the adjacent rollers is shortened. The shortening of L and / or T is advantageous in suppressing the growth of curl in the unwinding step.

The maximum value L of the distance between adjacent rollers refers to the maximum value of the distance between adjacent rollers. The distance between the adjacent rollers is calculated as the distance between the centers of the adjacent rollers. In the case of a nip roller, the center of a line connecting the centers of a pair of rollers constituting the nip roller is used instead of the center of the roller. L is usually 0.01 m or more, preferably 2 m or less, and more preferably 0.05 to 1.5 m.

Similarly, the maximum value T of the time required for conveying between adjacent rollers refers to the time required for conveying between adjacent rollers (in the example in FIG. 1, it is from the guide roller 60 to the guide roller). The largest value is the time T ₁ required for conveyance to the roller 61 and the time T ₂ required for conveyance from the guide roller 61 to the nip roller 50. The time required for conveying between adjacent rolls is determined by the time from leaving one of the adjacent rolls to contacting the other roll. T is usually 0.5 seconds or more, preferably 30 seconds or less, and more preferably 0.1 to 20 seconds.

[G] In the unwinding step, it is usually carried out by using one or more nip rollers arranged while immersing in the swelling bath, while conveying the raw material film 10 while maintaining a constant tension. In this case, the raw material roll 11 is positioned. The tension applied to the raw material film 10 disposed between the nip rollers immersed in the swelling bath 11 and the nip roller is higher than the tension applied after the nip rollers. This can suppress the growth of curl in the unwinding step. The tension applied to the raw material film 10 between the raw material reel 11 and the nip roll arranged before immersion in the swelling bath 11 is, for example, 5 to 300 N / mm, preferably 10 to 200 N / mm. The difference between the tension applied to the raw material film 10 between the raw material reel 11 and the nip roller arranged before being immersed in the swelling bath 11 and the tension applied to the nip roller is, for example, 10 N / mm or more, preferably Above 50N / mm. When the tension applied to the raw material film 10 between the raw material reel 11 and the nip roll arranged before being immersed in the swelling bath 11 is within the above-mentioned range, the effect of not only suppressing the occurrence of curling at the end of the raw material film 10, It is also preferable from the viewpoint of suppressing the occurrence of wrinkles in the raw material film 10.

In the swelling treatment, a problem that the so-called raw material film 10 swells in the width direction and causes wrinkles in the film is likely to occur. As a means for removing the wrinkles and conveying the film, a roll having a function of expanding a width such as a tenter roll, a spiral roll, a convex roll, or the like is used for the guide rolls 30, 31, and / or 32; Use other extended width devices such as cross guides, curved rods, and tenter clips. Another method for suppressing the generation of wrinkles is to perform a stretching treatment. For example, the rotation speed difference between the nip roller 50 and the nip roller 51 can be used to perform a one-axis stretching process in the swelling bath 13.

In the swelling process, since the film also swells and expands in the conveying direction of the film, in order to eliminate the slackness of the film in the conveying direction without actively stretching the film, for example, the control is arranged before and after the swelling bath 13 Means such as the speed of the nip rollers 50 and 51 are preferable. Furthermore, for the purpose of stabilizing the transport of the membrane in the swelling bath 13, the water flow in the swelling bath 13 is controlled by a shower in water, and an EPC (Edge Position Control) device is used to detect the ends of the membrane and prevent Means of meandering) are also useful.

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

(Dyeing treatment)

The dyeing treatment is performed for the purpose of adsorbing a dichroic dye and orienting the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within a range in which the purpose can be achieved without causing defects such as excessive dissolution of the film and loss of transparency. Referring to FIG. 1, the dyeing treatment can be carried out by conveying along the film body conveying path constructed by the guide rollers 33 to 35 and the nip roller 51, and passing the swelling-treated film in the dyeing bath 15 (storage The treatment liquid in the dyeing tank is immersed for a predetermined time and then pulled out. In order to improve the dyeability of the dichroic pigment, the film provided in the dyeing treatment step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or The one-axis extension process is performed during the dyeing process to replace the one-axis extension process before the dyeing process, or the one-axis extension process is performed during the dyeing process in addition to the one-axis extension process before the dyeing process.

When iodine is used as the dichroic pigment, in the dyeing bath 15, for example, an aqueous solution having a concentration in a weight ratio of iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100 can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide may be used in combination with other iodides. Furthermore, it may coexist with compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride. The addition of boric acid is different from the crosslinking treatment described later by the point of containing iodine. If the aqueous solution contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, it can be regarded as a dyeing bath 15. The temperature of the dyeing bath 15 when the film is immersed is usually about 10 to 45 ° C, preferably 10 to 40 ° C, and more preferably 20 to 35 ° C. The immersion time of the film is usually about 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 concentration of dichroic dye / water = about 0.001 to 0.1 / 100 in a weight ratio can be used in the dyeing bath 15. The dyeing bath 15 may coexist with a dyeing auxiliary agent, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant, and the like. A dichroic dye may be used individually by 1 type, and may use 2 or more types of dichroic dyes together. The temperature of the dyeing bath 15 when the film is immersed is, for example, about 20 to 80 ° C, and preferably 30 to 70 ° C. The immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

In the above-mentioned dyeing treatment step, one-axis stretching of the film can be performed in the dyeing bath 15. The membrane is stretched on one axis and can be placed in the dyeing bath 15 A method such as applying a difference in rotational speed between the front and rear nip rollers 51 and 52 is performed.

In the dyeing process, in the same manner as the swelling process, in order to remove the wrinkles of the film and convey the polyvinyl alcohol-based resin film, the guide rollers 33, 34, and / or 35 can be used with a tenter roller, a spiral roller, a convex roller, and the like. The function of the extended width roller uses other extended width devices such as cross guides, bending rods, and tenter clips. In order to suppress the generation of wrinkles, an extension treatment is performed in the same manner as the swelling treatment.

In the example shown in FIG. 1, the film system drawn from the dyeing bath 15 is introduced into the crosslinking bath 17 through the guide roller 35 and the nip roller 52 in this order.

(Cross-linking treatment)

Cross-linking treatment is a treatment performed for the purpose of resistance to water by cross-linking and equalizing color adjustment. Referring to FIG. 1, the cross-linking treatment system can be carried out by transmitting along the film body conveying path constructed by the guide rollers 36 to 38 and the nip roller 52, and transferring the dyed film to the cross-linking bath 17. (Treatment liquid stored in the cross-linking tank) is immersed for a predetermined time and then pulled out.

The crosslinking bath 17 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking bath 17 preferably contains iodide in addition to boric acid, and its content is, for example, 1 to 30 parts by weight based on 100 parts by weight of water. Examples of the iodide include potassium iodide and zinc iodide. Furthermore, it can coexist with compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like.

In the cross-linking treatment, the concentrations of boric acid and iodide and the temperature of the cross-linking bath 17 can be appropriately changed depending on the purpose. For example, for cross-linking The purpose is to perform swelling treatment, dyeing treatment, and crosslinking treatment on the polyvinyl alcohol-based resin film that is water-resistant by cross-linking. The solution containing the cross-linking agent in the cross-linking bath may be boric acid in a concentration by weight ratio / Iodide / water = 3 to 10/1 to 20/100 in water. If necessary, other cross-linking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid may be used in combination with other cross-linking agents. The temperature of the crosslinking bath when dipping the film is usually about 50 to 70 ° C, preferably 53 to 65 ° C. The dipping time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 To 200 seconds. When the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment is sequentially subjected to a dyeing treatment and a crosslinking treatment, the temperature of the crosslinking bath 17 is usually about 50 to 85 ° C, preferably 55 to 80 ° C.

In the cross-linking treatment for the purpose of adjusting hue, for example, when using iodine as a dichroic pigment, a cross-linking concentration containing boric acid / iodide / water = 1 to 5/3 to 30/100 in a weight ratio may be used. Agent solution. The temperature of the crosslinking bath when the film is impregnated is usually about 10 to 45 ° C, and the impregnation time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

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

The rotation speed difference between the nip roller 52 and the nip roller 53 may also be used to perform a uniaxial stretching process in the crosslinking bath 17.

In the cross-linking treatment, the Remove the wrinkles of the film and transfer the polyvinyl alcohol-based resin film. For the guide rollers 36, 37, and / or 38, use a roller with a function of expanding the width, such as a tenter roller, a spiral roller, and a convex roller. Use a cross guide, Bending rods, tenter clips and other extended width devices. In order to suppress the generation of wrinkles, an extension treatment is performed similarly to the swelling treatment.

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

(Washing treatment)

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 the remaining boric acid, iodine, and other agents adhered to the polyvinyl alcohol-based resin film. The washing treatment can be performed, for example, by immersing the cross-linked polyvinyl alcohol-based resin film in the washing bath 19 (water), spraying the film with water in a shower, or using them in combination. .

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

Furthermore, even in the cleaning process, for the purpose of removing the wrinkles of the film and conveying the polyvinyl alcohol-based resin film, for example, a tenter roller, a spiral roller, a convex roller can be used on the guide rollers 39, 40, and / or 41 The rolls with the function of expanding width use other expanding width devices such as cross guides, bending rods, and tenter clips. Further, in the washing treatment, an extension treatment may be performed in order to suppress the occurrence of wrinkles.

(Extended processing)

As described above, the raw material film 10 can be subjected to a one-axis stretching process using a wet method or a dry method between the above-mentioned series of processing steps (that is, before or after any one or more processing steps and / or during any one or more processing steps). A specific method of the one-axis stretching treatment may be, for example, extending between the two rollers constituting the film conveying path (for example, two nip rollers arranged before and after the processing bath) to perform longitudinal one-axis stretching between rollers. As described in Japanese Patent No. 2731813, hot roll stretching, tenter stretching, and the like, stretching between rolls is preferred. The uniaxial stretching process step may be performed a plurality of times from the raw material film 10 to the time when the polarizing film 23 is obtained. The stretching treatment as described above is advantageous in suppressing the occurrence of wrinkles in the film.

Based on the raw material film 10, the final cumulative extension ratio of the polarizing film 23 is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

The extension processing step can be performed in any processing step, and even when the extension processing is performed in two or more processing steps, the extension processing can be performed in any processing step. According to the present invention, no matter the uniaxial stretching process is performed at any stage after the swelling process step (including the swelling process step), it is possible to effectively suppress the cracking of the film during the stretching process.

(Drying)

After the washing treatment, it is preferable to perform a treatment for drying the polyvinyl alcohol-based resin film. The drying of the film is not particularly limited, and can be performed using a drying furnace 21 as in the example shown in FIG. 1. The drying temperature is, for example, about 30 to 100 ° C, and the drying time is, for example, about 30 to 600 seconds. The thickness of the polarizing film 23 obtained in the above manner is, for example, about 5 to 30 μm.

(Other processing steps)

Processing other than the above processing may be added. Examples of additional treatments include an immersion treatment (a complementary color treatment) to an aqueous iodide solution that does not contain boric acid and an immersion treatment to an aqueous solution that does not contain boric acid and contains zinc chloride, which is performed after the crosslinking treatment ( Zinc treatment).

<Polarizer>

A polarizing plate can be obtained by bonding a protective film on at least one side of the polarizing film manufactured as described above via an adhesive. Examples of the protective film include a film containing an ethyl cellulose resin such as triethyl cellulose and diethyl cellulose, and a film containing polyethylene terephthalate and polyethylene naphthalate. Films of polyester resins of diesters and polybutylene terephthalate; polycarbonate resin films; cycloolefin resin films; (meth) acrylic resin films; chain olefins containing polypropylene resins Film of resin.

In this specification, "(meth) acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

In order to improve the adhesion between the polarizing film and the protective film, surface treatments such as corona treatment, flame treatment, ultraviolet irradiation, undercoating treatment, and saponification treatment may be performed on the bonding surface of the polarizing film and / or the protective film. Examples of the adhesive used for bonding the polarizing film and the protective film include, for example, an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol resin, or an aqueous solution in which a cross-linking agent is prepared. Water-based adhesives, such as amine ester milky adhesives. The ultraviolet curable adhesive may be a mixture of a (meth) acrylic compound and a photoradical polymerization initiator, a mixture of an epoxy compound and a photocationic polymerization initiator, and the like. and, A cationic polymerizable epoxy compound and a radical polymerizable (meth) acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

[Example]

Hereinafter, the present invention will be described more specifically by illustrating examples, but the present invention is not limited to these examples. In addition, in the following examples, the curl angles of the both ends of the raw material film 10 in the width direction of the swelling bath 13 were continuously measured by the following method.

[Measurement of curl angle]

The film was visually inspected in the direction from the roller passing immediately before immersion to the swelling bath 13 to the first guide roller in the swelling bath 13, and the front end of the film end was measured every 15 ° according to the mark of the angle set at the position immediately after the immersion of the film The angle area shown (for example, when the angle area is from 0 ° to 15 °, the measurement angle is 0 °; when the angle area is from 15 ° to 30 °, the measurement angle is 15 °; the measurement angle is the minimum of the angle area Value. The same below.) In addition, an angle mark is also provided before a roll to be rolled just before being immersed in the swelling bath 13, and the curl angle is measured in the same manner.

<Example 1>

Except that two cross-linking baths 17 are used (hereinafter, the first cross-linking bath is referred to as 17a and the second cross-linking bath is referred to as 17b), the same apparatus as the polarizing film manufacturing apparatus shown in FIG. 1 is used. Manufacture of polarizing film. The guide rollers 30 to 41 are all flat rolls.

(1) Swelling treatment steps

On the one side, a polyvinyl alcohol film with a thickness of 60 μm [Kuraray Trade name "Kuraray Poval Film VF-PE # 6000", a degree of polymerization of 2400, and a degree of saponification of 99.9 mol% or more] are continuously rolled out from the raw material reel 11 and transported to keep the film tight and tight. Immerse in a swelling bath 13 containing pure water at 30 ° C for 100 seconds. The time from the unwinding of the polyvinyl alcohol film 11 to the immersion bath 13 after the unwinding of the raw material reel 11 (the time of the unwinding step) was 60 seconds, and the environment of the unwinding step was a temperature of 23 ° C and a relative humidity of 60% RH. In addition, after the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in the widthwise both ends is 30 ° or less.

(2) Dyeing process steps

Then, the film passing through the nip roller 51 was immersed in a dyeing bath 15 at 30 ° C. of iodine / potassium iodide / water (weight ratio) of 0.05 / 2/100 for 120 seconds. In this dyeing process, a rotation speed difference is provided between the nip rolls 51 and 52 to perform roll-to-roll extension (longitudinal uniaxial extension).

(3) Cross-linking processing steps

Then, in order to perform the first cross-linking treatment for the purpose of water resistance, the film having passed through the nip roller 52 was placed in a first cross-linking bath 17a at 56 ° C. of potassium iodide / boric acid / water (weight ratio) of 12 / 4.4 / 100. Dip for 30 seconds. In this first cross-linking treatment, a rotational speed difference is also provided between the nip rolls, and roll-to-roll stretching (longitudinal uniaxial stretching) is performed until the cumulative stretch ratio based on the raw material film 10 becomes 5.5 times. Then, the film after the first crosslinking treatment was immersed in a second crosslinking bath 17b at 40 ° C of potassium iodide / boric acid / water (weight ratio) of 9 / 2.9 / 100 for 15 seconds (second crosslinking treatment). .

Then, the film after the second crosslinking treatment is immersed in A washing bath 19 of pure water at 6 ° C was dried at 70 ° C for 3 minutes by passing through a drying furnace 21 to produce a polarizing film 23.

The above-mentioned manufacturing of the polarizing film was carried out continuously for 24 hours. During the 24-hour operation, no film cracking occurred in any of the processing steps. In addition, no folding of the both ends in the width direction of the film was confirmed.

<Example 2>

The production of the polarizing film was carried out continuously for 24 hours in the same manner as in Example 1 except that the environment of the unwinding step was a temperature of 23 ° C. and a relative humidity of 40% RH. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curl angle of the film in both ends in the width direction is 15 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 3>

Except that a polyvinyl alcohol film [Kuraray Poval Film VF-PE # 3000 manufactured by Kuraray Co., Ltd., a degree of polymerization of 2400, and a degree of saponification of 99.9 mol% or more] was used as a raw material film, the system is similar to the example 1 In the same manner, the production of the polarizing film is continuously performed for 24 hours. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in both ends in the width direction is 60 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 4>

The production of the polarizing film was performed continuously for 24 hours in the same manner as in Example 3, except that the time of the unwinding step was 480 seconds. Polyethylene After the enol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in the widthwise both ends is 75 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 5>

The production of the polarizing film was carried out continuously for 24 hours in the same manner as in Example 1 except that the time of the unwinding step was 600 seconds. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in both ends in the width direction is 60 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 6>

The production of the polarizing film was performed continuously for 24 hours in the same manner as in Example 1 except that the time of the unwinding step was 720 seconds. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in the widthwise both ends is 75 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 7>

The production of the polarizing film was carried out continuously for 24 hours in the same manner as in Example 3 except that the time of the unwinding step was 600 seconds. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in the widthwise both ends is 75 ° or less. In the 24-hour operation, no film rupture occurred at any processing step, and no Folding of both ends in the width direction of the film was confirmed.

<Comparative Example 1>

A polarizing film was manufactured in the same manner as in Example 3 except that the time of the unwinding step was 720 seconds. When the polyvinyl alcohol film was immersed in the swelling bath 13, the curling angle of both ends in the width direction of the film was 105 °. During the extension treatment of the cross-linking treatment, the film was cracked and a polarizing film could not be obtained.

(Example 8)

Except that after the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, a warm air at 30 ° C is blown for 30 seconds from the side opposite to the curled side of the polyvinyl alcohol film. In Comparative Example 1, the production of a polarizing film was continuously performed for 24 hours in the same manner. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in the widthwise both ends is 75 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 9>

Except that a metal rod for pressing both ends in the width direction of the film was provided in front of the nip roller 50 in the unwinding step, and the width extension treatment was performed on both ends in the width direction of the polyvinyl alcohol film. In the same manner, the production of the polarizing film was continuously performed for 24 hours. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curling angle of the film in both ends in the width direction is 60 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at the both ends in the width direction of the film was confirmed.

<Example 10>

The production of the polarizing film was carried out continuously for 24 hours in the same manner as in Example 3 except that the time of the unwinding step was 300 seconds. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curl angle of the film in the widthwise both ends is 45 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

<Example 11>

The production of the polarizing film was carried out continuously for 24 hours in the same manner as in Example 3 except that the time of the unwinding step was 150 seconds. After the polyvinyl alcohol film is unwound from the raw material reel 11 until it is immersed in the swelling bath 13, the curl angle of the film in the widthwise both ends is 45 ° or less. In the 24-hour operation, no cracking of the film occurred in any of the processing steps, and no folding at both ends in the width direction of the film was confirmed.

Claims (4)

A method for manufacturing a polarizing film, which comprises: sequentially unrolling a long polyvinyl alcohol-based resin film having a thickness of less than 35 μm from a raw material roll and conveying the same, and dipping the polyvinyl alcohol-based resin film in a swelling bath and pulling A swelling treatment step; and a dyeing treatment step in which the film drawn from the swelling bath is immersed in a dyeing bath, and wherein the polyvinyl alcohol-based resin film is rolled out from a raw material reel until it is immersed in the swelling bath. The temperature of the environment at the exit step is 23 ± 5 ° C, the relative humidity of the environment is 20 to 70% RH, the time required for the unwinding step is 650 seconds or less, and the polyvinyl alcohol resin film is immersed in a swelling bath. The curl angle of at least one of the two ends in the film width direction is less than 90 °, and after the polyvinyl alcohol-based resin film is rolled out from the raw material reel until it is dipped in the swelling bath, the polyvinyl alcohol The curly side of the resin film is dried so that the dryness of the curled surface is smaller than the surface on the opposite side. In the swelling treatment step, the polyvinyl alcohol-based resin film rolled from the raw material roll is selected from Two or more rolls of the roller and the nip roll are conveyed, so that they are immersed in the swelling bath. Regarding the two or more rolls, the maximum value of the distance between adjacent rolls is set to L, and the adjacent rolls are set to L. When the maximum value of the time required for transmission is set to T, L is 2 m or less, or T is 30 seconds or less. A method for manufacturing a polarizing film, which comprises: sequentially unrolling a long polyvinyl alcohol-based resin film having a thickness of less than 35 μm from a raw material roll and conveying the same, and dipping the polyvinyl alcohol-based resin film in a swelling bath and pulling A swelling treatment step; and a dyeing treatment step in which the film drawn from the swelling bath is immersed in a dyeing bath, and wherein the polyvinyl alcohol-based resin film is rolled out from a raw material reel until it is immersed in the swelling bath. The temperature of the environment at the exit step is 23 ± 5 ° C, the relative humidity of the environment is 20 to 70% RH, the time required for the unwinding step is 650 seconds or less, and the polyvinyl alcohol resin film is immersed in a swelling bath. The curl angle of at least one of the two end portions in the width direction of the film is less than 90 °. After the polyvinyl alcohol-based resin film is rolled out from the raw material reel and immersed in the swelling bath, the polyvinyl alcohol-based resin film is The resin film is subjected to a widening treatment. In the swelling treatment step, the polyvinyl alcohol-based resin film rolled out from the raw material reel is conveyed along two or more rollers selected from a guide roller and a nip roller, thereby making it Dip In the swelling bath, when the maximum value of the distance between adjacent rollers is L and the maximum value of the time required for conveyance between adjacent rollers is T, L It is 2 m or less, or T is 30 seconds or less. A method for manufacturing a polarizing film, which comprises: sequentially unrolling a long polyvinyl alcohol-based resin film having a thickness of 65 μm or less from a raw material reel and transporting the same, and dipping the polyvinyl alcohol-based resin film in a swelling bath and pulling A swelling treatment step; and a dyeing treatment step in which the film drawn from the swelling bath is immersed in a dyeing bath, and wherein the polyvinyl alcohol-based resin film is rolled out from a raw material reel until it is immersed in the swelling bath. The temperature of the environment at the exit step is 23 ± 5 ° C, the relative humidity of the environment is 20 to 70% RH, and the time required for the unwinding step is 750 seconds or less. The polyvinyl alcohol-based resin film is rolled from a raw material reel. Drying is performed so that the dryness of the curled surface of the polyvinyl alcohol-based resin film becomes smaller than the surface on the opposite side after being immersed in the swelling bath after being discharged, and the polyvinyl alcohol-based resin film is immersed in the swelling The curling angle of at least one of the both ends of the film in the width direction during the bath is less than 90 °. In the swelling treatment step, the polyvinyl alcohol-based resin film rolled out from the raw material reel is selected along The two or more rollers of the guide roller and the nip roller are conveyed so as to be immersed in the swelling bath. Regarding the two or more rollers, the maximum distance between the adjacent rollers is set to L, and the adjacent When the maximum value of the time required for the transfer between the rollers is set to T, L is 2 m or less, or T is 30 seconds or less. A method for manufacturing a polarizing film, which comprises: sequentially unrolling a long polyvinyl alcohol-based resin film having a thickness of 65 μm or less from a raw material reel and transporting the same, and dipping the polyvinyl alcohol-based resin film in a swelling bath and pulling A swelling treatment step; and a dyeing treatment step in which the film drawn from the swelling bath is immersed in a dyeing bath, and wherein the polyvinyl alcohol-based resin film is rolled out from a raw material reel until it is immersed in the swelling bath. The temperature of the environment at the exit step is 23 ± 5 ° C, the relative humidity of the environment is 20 to 70% RH, and the time required for the unwinding step is 750 seconds or less. The polyvinyl alcohol-based resin film is rolled from a raw material reel. The polyvinyl alcohol-based resin film is subjected to a width-expanding treatment after being discharged until it is immersed in the swelling bath. At least one of the both ends of the film width direction when the polyvinyl alcohol-based resin film is immersed in the swelling bath is curled. The angle is less than 90 °. In the swelling treatment step, the polyvinyl alcohol-based resin film rolled out from the raw material reel is conveyed along two or more rollers selected from a guide roller and a nip roller, thereby making it When it is stained in a swelling bath, regarding the two or more rollers, when the maximum value of the distance between adjacent rollers is set to L, and the maximum value of the time required for transportation between adjacent rollers is set to T, L is 2 m or less, or T is 30 seconds or less.