JP6756465B2 - Method of manufacturing polarizing film - Google Patents

Description

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

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

Generally, a polarizing film is obtained by subjecting a long polyvinyl alcohol-based resin film that is continuously conveyed to various treatments such as swelling, dyeing, cross-linking, and stretching in a bath, and then performing a cleaning treatment. It is produced by drying (see, for example, Japanese Patent Application Laid-Open No. 2009-48179).

Japanese Unexamined Patent Publication No. 2009-48179

Since the polyvinyl alcohol-based resin film used in the drying step is stretched, the film shrinks in the width direction when water is removed by the drying step, and the thickness increases due to the shrinkage in the width direction. It tended to be, and could not satisfy the demand for thinning.

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

On the other hand, a method of suppressing shrinkage in the width direction by performing a drying step after the water content of the polyvinyl alcohol-based resin film becomes low to some extent is conceivable. However, according to such a method, the frictional force between the polyvinyl alcohol-based resin film and the roll However, it is not possible to sufficiently restrain the width direction by just bringing the polyvinyl alcohol resin film into contact with the roll, and it is necessary to mechanically fix the width direction with a tenter clip or the like. There was a problem that the film was easily broken.

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

The present invention provides a method for producing a polarizing film shown below.
[1] A width restraint step in which the polyvinyl alcohol-based resin film after being brought into contact with the treatment liquid is brought into contact with at least one free roll having a diameter of 150 mm or more and restrained in the width direction.
A method for producing a polarizing film, which comprises a drying step of drying the polyvinyl alcohol-based resin film after the width restraint step.

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

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

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

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

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

<Manufacturing method of 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 the polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The polyvinyl acetate-based resin can be, for example, a polyvinyl acetate which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids and the like. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000.

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

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

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

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

The polarizing film is prepared after carrying out a treatment step in which the above-mentioned long raw film is unwound from the raw roll and continuously conveyed along the film conveying path of the polarizing film manufacturing apparatus to be brought into contact with the processing liquid. By carrying out the width constraint step and then the drying step, it is possible to continuously produce a long polarizing film.

The treatment steps include, for example, a swelling treatment step of immersing the raw film in a swelling bath and then pulling it out, a dyeing treatment step of immersing the swelling treatment film in a dyeing bath and then pulling it out, and a cross-linking bath of the dyed film. It can include a cross-linking process of pulling out after immersion in. In addition, uniaxial stretching treatment is performed wet or dry between these series of treatment steps (that is, before and after any one or more treatment steps and / or during any one or more treatment steps). If necessary, other processing steps may be added. Each of the above treatment steps may be a treatment of immersing the film in one bath, or a treatment of sequentially immersing the film in two or more baths.

In the width restraint step, the polyvinyl alcohol-based resin film after being brought into contact with the treatment liquid in the treatment step is brought into contact with at least one free roll having a diameter of 150 mm or more (hereinafter, also referred to as “large diameter free roll”). This is a process of restraining in the width direction. The roll that brings the polyvinyl alcohol resin film into contact in the width restraint step may include one or a plurality of large-diameter free rolls, and in addition, a free roll having a diameter of less than 150 mm and a driving roll. The contact of the polyvinyl alcohol-based resin film with the roll as used herein means surface contact (the polyvinyl alcohol-based resin film is in contact with the free roll with a width in the length direction) rather than point contact. .. The surface contact constrains the polyvinyl alcohol-based resin film in the width direction.

Here, the free roll is a roll to which a driving means such as a motor is not attached. By using a free roll as a means for restraining the width direction of the polyvinyl alcohol-based resin film in contact with the treatment liquid as described above, breakage of the polyvinyl alcohol-based resin film can be suppressed. In the present invention, by providing such a width restraint step, the polyvinyl alcohol-based resin film is gently dried in a state of being restrained in the width direction, and the width is not applied to the polyvinyl alcohol-based resin film. It is possible to produce a thin polarizing film having a small shrinkage force by suppressing the shrinkage in the direction.

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

Hereinafter, the method for producing a polarizing film according to the present invention will be described in more detail with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an example of a 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 a raw fabric (unstretched) film 10 made of a polyvinyl alcohol-based resin along a film transport path while continuously unwinding the raw fabric (unstretched) film 10 from the raw fabric roll 11. The swelling bath 13, the dyeing bath 15, the cross-linking bath 17, and the washing bath 19 provided on the transport path are sequentially passed, then the width restraint portion 70 is passed, and finally the drying furnace 90 is passed. There is. The obtained polarizing film can be directly conveyed to, for example, the next polarizing plate manufacturing step (step of laminating a protective film on one or both sides of the polarizing film 23). The arrows in FIG. 1 indicate the film transport direction.

Note that FIG. 1 shows an example in which one swelling bath 13, one dyeing bath 15, one cross-linking bath 17, and one washing bath 19 are provided, but if necessary, one or more treatment baths (swelling bath 13) are provided. , A bath containing a treatment liquid for treating a polyvinyl alcohol-based resin film provided on a film transport path, such as a dyeing bath 15, a cross-linking bath 17, and a washing bath 19, is also collectively referred to as a “treatment bath”. .) May be provided in two or more tanks.

In addition to the processing bath, the width restraint portion 70, and the drying furnace 90, the film transport path of the polarizing film manufacturing apparatus includes guide rolls 30 to 41 that can support the film to be transported or further change the film transfer direction. 60, 61, 81 and nip rolls 50 to 54, 82, 83 capable of pressing and holding the film to be conveyed and applying a driving force due to the rotation to the film, or further changing the film conveying direction. It can be constructed by arranging it at an appropriate position. The guide roll and the nip roll can be arranged before and after each treatment bath and drying furnace or in the treatment bath, whereby the film can be introduced and immersed in the treatment bath and pulled out from the treatment bath [Fig. 1]. reference〕. For example, the film can be immersed in each treatment bath by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls.

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

(Swelling process)
The swelling treatment step is performed for the purpose of removing foreign matter on the surface of the raw film 10, removing the plasticizer in the raw film 10, imparting easy dyeability, and plasticizing the raw film 10. The treatment conditions are determined within a range in which the object can be achieved and within a range in which problems such as extreme dissolution and devitrification of the raw film 10 do not occur.

With reference to FIG. 1, in the swelling treatment step, the raw film 10 is continuously unwound from the raw film roll 11 and conveyed along the film transport path, and the raw film 10 is immersed in the swelling bath 13 for a predetermined time. It can then be done by pulling it out. In the example of FIG. 1, the raw film 10 is conveyed along the film conveying path constructed by the guide rolls 60 and 61 and the nip roll 50 from the time when the raw film 10 is unwound until it is immersed in the swelling bath 13. Will be done. In the swelling treatment, the film is transported along the film transport path constructed by the guide rolls 30 to 32.

In addition to pure water, the swelling liquid of the swelling bath 13 includes boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, and alcohols. It is also possible to use an aqueous solution to which the like is added in the range of about 0.01 to 10% by weight.

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

In the swelling treatment, a problem that the raw film 10 swells in the width direction and the film is wrinkled tends to occur. As one means for transporting the film while removing the wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used for the guide rolls 30, 31 and / or 32, or a cross guider or a bend bar. , Other widening devices such as tenter clips may be used. Another means for suppressing the occurrence of wrinkles is to apply a stretching treatment. For example, the uniaxial stretching treatment can be performed in the swelling bath 13 by utilizing 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. Therefore, when the film is not actively stretched, it is arranged before and after the swelling bath 13 in order to eliminate the slack of the film in the transport direction. It is preferable to take measures such as controlling the speeds of the nip rolls 50 and 51. Further, for the purpose of stabilizing the film transfer in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, and an EPC device (Edge Position Control device: the edge of the film is detected to meander the film. It is also useful to use a device to prevent the above.

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

(Dyeing process)
The dyeing treatment step is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The treatment conditions are determined within a range in which the object can be achieved and within a range in which problems such as extreme dissolution and devitrification of the film do not occur. With reference to FIG. 1, in the dyeing treatment step, the film is conveyed along the film transfer path constructed by the guide rolls 33 to 35 and the nip roll 51, and the film after the swelling treatment is transferred to the dyeing bath 15 (process housed in the dyeing tank). It can be carried out by immersing in a liquid) for a predetermined time and then withdrawing. In order to enhance the dyeability of the dichroic dye, the film to be subjected to the dyeing treatment step is preferably a film subjected to at least some degree of uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment. Alternatively, in addition to the uniaxial stretching treatment before the dyeing treatment, it is preferable to perform the uniaxial stretching treatment during the dyeing treatment.

When iodine is used as the bicolor dye, the dyeing solution in the dyeing bath 15 has a concentration of, for example, iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 / 10 / by weight. An aqueous solution of 100 can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added, it is distinguished from the 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 with respect to 100 parts by weight of water, the dyeing bath 15 Can be regarded as. The temperature of the dyeing 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 immersing time of the film is usually 30 to 600 seconds. The degree, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, the dyeing solution in the dyeing bath 15 has, for example, a concentration of the dichroic dye / water = about 0.001 to 0.1 / 100 by weight. An aqueous solution can be used. The dyeing bath 15 may coexist with a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one kind of dichroic dye may be used alone, or two or more kinds of dichroic dyes may be used in combination. The temperature of the dyeing bath 15 when immersing the film is, for example, about 20 to 80 ° C., preferably 30 to 70 ° C., and the immersing time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. is there.

As described above, in the dyeing process, the film can be uniaxially stretched in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method such as providing a peripheral speed difference between the nip roll 51 and the nip roll 52 arranged before and after the dyeing bath 15.

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

In the example shown in FIG. 1, the film drawn from the dyeing bath 15 passes through the guide roll 35 and the nip roll 52 in this order and is introduced into the cross-linking bath 17.

(Crosslinking process)
The cross-linking treatment step is a treatment performed for the purpose of making the film water resistant by cross-linking and adjusting the hue (preventing the film from becoming bluish, etc.). With reference to FIG. 1, the cross-linking treatment is carried out along the film transport path constructed by the guide rolls 36 to 38 and the nip roll 52, and the cross-linking bath 17 (cross-linking liquid contained in the cross-linking tank) is dyed. This can be done by immersing the film for a predetermined time and then pulling it out.

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

In the cross-linking treatment, the concentrations of boric acid and iodide and the temperature of the cross-linking bath 17 can be appropriately changed depending on the purpose. For example, when the purpose of the cross-linking treatment is to make the polyvinyl alcohol-based resin film water-resistant by cross-linking, and the polyvinyl alcohol-based resin film is subjected to the swelling treatment, the dyeing treatment, and the cross-linking treatment in this order, the concentration of the cross-linking agent-containing liquid in the cross-linking bath is a weight ratio. It can be an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100. If necessary, other cross-linking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and other cross-linking agents may be used in combination. The temperature of the cross-linking bath when immersing the film is usually about 50 to 70 ° C., preferably 53 to 65 ° C., 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. When the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment is subjected to the dyeing treatment and the cross-linking treatment in this order, the temperature of the cross-linking bath 17 is usually about 50 to 85 ° C., preferably 55 to 80 ° C. ..

In the cross-linking treatment for the purpose of adjusting the hue, for example, when iodine is used as the dichromatistic dye, the concentration is boric acid / iodide / water = 1 to 5/3 to 30/100 in terms of weight ratio. Liquids can be used. The temperature of the cross-linking bath when the film is immersed 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 cross-linking treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinked bath used may be the same or different as long as it is within the above range. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for hue adjustment may each be performed in a plurality of steps.

Uniaxial stretching treatment can also be performed in the cross-linked bath 17 by utilizing the difference in peripheral speed between the nip roll 52 and the nip roll 53.

In the cross-linking treatment as well, in order to convey the polyvinyl alcohol-based resin film while removing the wrinkles of the film as in the swelling treatment, the guide rolls 36, 37 and / or 38 have a widening function such as an expander roll, a spiral roll, and a crown roll. It is possible to use a roll having a cross guider, a bend bar, and other widening devices such as a tenter clip. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment as in the swelling treatment.

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

(Washing process)
The production method of the present invention can include a cleaning treatment step after the crosslinking treatment step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering 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 the film cleaning solution as a shower on the film, or using these in combination.

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

Also in the cleaning treatment, for the purpose of transporting the polyvinyl alcohol-based resin film while removing wrinkles, rolls having a widening function such as an expander roll, a spiral roll, and a crown roll are used for the guide rolls 39, 40 and / or 41. Alternatively, other widening devices such as cross guiders, bend bars and tenter clips can be used. Further, in the film cleaning treatment, a stretching treatment may be performed in order to suppress the occurrence of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched in a wet or dry manner during the series of treatment steps (that is, before and after any one or more treatment steps and / or during any one or more treatment steps). It is processed. A specific method of uniaxial stretching treatment is, for example, between rolls that perform longitudinal uniaxial stretching with a difference in peripheral speed between two nip rolls constituting a film transport path (for example, two nip rolls arranged before and after the treatment bath). Stretching, thermal roll stretching, tenter stretching, etc. as described in Japanese Patent No. 2731813 can be performed, and inter-roll stretching is preferable. The uniaxial stretching treatment step can be carried out a plurality of times until the polarizing film 23 is obtained from the raw film 10. As described above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles in the film.

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

The stretching treatment step may be performed in any of the above-mentioned treatment steps as long as it is before the width constraint step, and even when the stretching treatment is performed in two or more treatment steps, the stretching treatment may be performed in any of the treatment steps. ..

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

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

Since the transport direction of the polyvinyl alcohol-based resin film can be adjusted and curl can be forced, the number of rolls used in the width restraint step is preferably a plurality including the above-mentioned large-diameter free rolls, and is preferably 3 or more and 5 or less. Is even more preferable. When multiple rolls are used, the polyvinyl alcohol-based resin film contacts one of the rolls for at least 40% of the time between contacting the first roll in the width constraint step and releasing from the last roll. It is preferable to do so. When the time of contact with the roll is 40% or more, a sufficient width restraining effect can be obtained. The time of contact with the roll is more preferably 70% or more. The time of contact with the rolls can be adjusted by the number of rolls, the arrangement position of the rolls, and the holding angle to each roll. Further, from the viewpoint of effectively constraining the width, the continuous time during which the polyvinyl alcohol-based resin film is not in contact with the roll is preferably 2 seconds or less.

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

In the width restraint step, the polyvinyl alcohol-based resin film is gently dried in a state of being 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. It is possible to manufacture a thin polarizing film having a small shrinkage force. In order to control the drying state in the width constraint step, it is preferable to have, for example, a hot air dryer, an infrared heater, or a means for drying in combination thereof. In the width restraint step, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30 to 100 ° C., preferably 50 to 80 ° C.

In FIG. 1, the width restraint step is performed in the width restraint portion 70. In the width restraint portion 70 shown in FIG. 1, three free rolls 71, 72, 73 and hot air dryers 74, 75, 76 arranged so as to face each of the free rolls 71, 72, 73 are provided. Has been done. Each of the hot air dryers 74, 75, 76 sends out hot air from the upstream side to the upstream direction with the members 74a, 75a, 76a whose outlets for sending hot air from the upstream side to the downstream direction are arranged on the line in the width direction. It is configured to include members 74b, 75b, 76b whose outlets are arranged on a line in the width direction. The hot air sent from the hot air dryers 74, 75, 76 is blown onto the polyvinyl alcohol-based resin film in contact with the opposite free rolls 71, 72, 73, and the drying state of the polyvinyl alcohol-based resin film in the width restraint step. Is controlled. All three free rolls 71, 72, and 73 are large diameter free rolls. In the width restraint portion 70 shown in FIG. 1, the point where the polyvinyl alcohol-based resin film comes into contact with the free roll 71 is the introduction point of the width restraint step, and the point released from the free roll 73 is the derivation point from the width restraint step. Is.

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

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

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

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

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

The width constraint step is preferably performed immediately after the treatment step in which the polyvinyl alcohol-based resin film is brought into contact with the treatment liquid for treatment. In the example of FIG. 1, the step immediately before the width constraint step is the cleaning step, and the treatment liquid is the cleaning treatment liquid. The treatment liquid to which the polyvinyl alcohol-based resin film is brought into contact immediately before the width constraint step may be a dyeing treatment liquid in the dyeing treatment step, a cross-linking treatment liquid in the cross-linking treatment step, or other treatments (complementary colors) described later. It may be a treatment liquid (treatment or zinc treatment). 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 of the treatment liquid with a shower or the like, application of the treatment liquid, or the like are used.

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

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

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

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

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

(Other processing steps for polyvinyl alcohol-based resin film)
It is also possible to add a process other than the above process. Examples of treatments that can be added are immersion treatment in an iodide aqueous solution containing no boric acid (complementary color treatment) and immersion treatment in an aqueous solution containing zinc chloride or the like without boric acid, which are performed after the cross-linking treatment step. Zinc treatment) is included.

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

In order to improve the adhesiveness between the polarizing film and the protective film, the surface to which the polarizing film and / or the protective film is bonded is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. Treatment may be applied. The adhesive used for bonding the polarizing film and the protective film is an active energy ray-curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, or an aqueous solution containing a cross-linking agent. , Water-based adhesives such as urethane-based emulsion adhesives can be mentioned. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, a mixture of an epoxy compound and a photocationic polymerization initiator, or the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

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

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

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

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

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

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

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

(4) Washing Treatment Step The film after the second cross-linking treatment was immersed in a washing bath 19 containing pure water at 5 ° C.

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

(6) Drying Step The film after passing through the width restraint portion 70 was passed through a drying furnace 90 to prepare a polarizing film. Three hot air dryers No. 3 in the drying oven 90. 1-No. The temperature of the hot air sent from No. 3 was set 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 derived from the drying furnace 90 (position P4) is measured by a moisture content meter (product name: moisture meter IRMA110, Chino Co., Ltd.). Made 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 temperatures of the hot air sent from the three hot air dryers 74 to 76 in the width restraint portion 70 were as shown in Table 1. Similar to the first embodiment, the moisture content of 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 derived from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

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

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

<Example 5>
In the configuration inside the width restraint portion 70, the free roll 72 and the hot air dryer 75 facing the free roll 72 were not provided, and the temperatures of the hot air sent from the remaining two hot air dryers 74 and 76 were set as shown in Table 1. A polarizing film was produced in the same manner as in Example 1 except for the above. Similar to the first embodiment, the moisture content of 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 derived from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1. In the width restraint portion 70, the time from the contact of the film with the first free roll 71 to the release from the last free roll 73 (time of the width restraint step) and the time of the free roll 71 and the free roll 73. The time of non-contact between them was measured. The time of the width restraint step is 6.2 seconds, the continuous time when the film is not in contact with the freeroll is 2 seconds or less, and the time when the film is in contact with the freerolls 71 and 73 is the width restraint step. It was 44% of the time required for.

<Example 6>
A polarizing film was produced in the same manner as in Example 1 except that the three hot air dryers 74 to 76 in the width restraint portion 70 were not used. Similar to the first embodiment, the moisture content of 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 derived from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

<Example 7>
The three hot air dryers 74 to 76 in the width restraint portion 70 were not used, and the three hot air dryers No. 3 in the drying furnace 90 in the drying step. 1-No. A polarizing film was produced in the same manner as in Example 1 except that the temperature of the hot air sent from No. 3 was as shown in Table 1. Similar to the first embodiment, the moisture content of 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 derived from the drying furnace 90 (position P4). The rate was measured. The results are shown in Table 1.

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

10 Raw fabric film made of polyvinyl alcohol resin, 11 Raw fabric roll, 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, 81 guide rolls, 50, 51, 52, 53, 54, 82, 83 nip rolls, 70 width restraints, 71, 72, 73 free rolls, 74,75,76 Hot air dryer, 90 dryer.

Claims (5)

A width restraint step of contacting the polyvinyl alcohol-based resin film after contact with the treatment liquid with at least one free roll having a diameter of 150 mm or more and restraining the film in the width direction.
After the width constraint step, seen including a drying step of drying the polyvinyl alcohol resin film,
The drying step is a step of reducing the polyvinyl alcohol-based resin film from a water content of 18% by weight or more and less than 30% by weight to a water content of less than 15% by weight, which is a method for producing a polarizing film. The drying step does not include a step of applying tension in the width direction of the polyvinyl alcohol-based resin film to restrain the width direction and drying the film.
The step of drying while restraining the width direction is
A step of drying the polyvinyl alcohol-based resin film while maintaining the width direction with a tenter.
The step of bringing the polyvinyl alcohol-based resin film into contact with the heat belt and drying it, or
This is a step of bringing the polyvinyl alcohol-based resin film into contact with a hot roll and drying it.
The method for producing a polarizing film according to claim 1 . In the width restraint step, the polyvinyl alcohol-based resin film is contacted with a plurality of rolls including the free roll, and the time from contacting the first roll to being released from the last roll is at least 40%. The method for producing a polarizing film according to claim 1 or 2 , wherein is in contact with any of the rolls. The polarized light according to any one of claims 1 to 3 , wherein the polyvinyl alcohol-based resin film is brought into contact with the first roll in the width restraint step within 20 seconds after the contact with the treatment liquid is completed. How to make a film. The method for producing a polarizing film according to any one of claims 1 to 4 , wherein the polyvinyl alcohol-based resin film has a water content of 30% by weight or more at the time of contact with the first roll in the width constraint step.

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