CN106575008B

CN106575008B - Method for producing polarizing film

Info

Publication number: CN106575008B
Application number: CN201580040056.2A
Authority: CN
Inventors: 纲谷圭二; 吉田直纪
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2014-08-04
Filing date: 2015-07-27
Publication date: 2019-12-24
Anticipated expiration: 2035-07-27
Also published as: JPWO2016021432A1; CN106575008A; KR101990222B1; JP2018063443A; TW201613990A; KR20170040241A; TWI654225B; WO2016021432A1; JP2017211657A; JP6294491B2

Abstract

The invention provides a method for manufacturing a polarizing film, which sequentially comprises the following steps: a swelling treatment step of conveying a long polyvinyl alcohol resin film having a thickness of 65 μm or less while winding the polyvinyl alcohol resin film from a raw material roll, thereby immersing the polyvinyl alcohol resin film in a swelling bath and then taking out the polyvinyl alcohol resin film; and a dyeing treatment step of immersing the film drawn out from the swelling bath in a dyeing bath and then drawing out the film, wherein a curl angle of at least one of both ends in a film width direction when the polyvinyl alcohol resin film is immersed in the swelling bath is less than 90 °.

Description

Method for producing polarizing film

Technical Field

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

Background

Conventionally, a polarizing film obtained by adsorbing a dichroic dye such as iodine or a dichroic dye to a uniaxially stretched polyvinyl alcohol resin film and orienting the resin film has been used. A polarizing plate is generally formed by laminating a protective film on one or both surfaces of a polarizing film using an adhesive, and the polarizing film is used for an image display device represented by a liquid crystal display device such as a liquid crystal television, a display for a personal computer, and a mobile phone.

Generally, a polarizing film is manufactured by: a treatment is performed in which a long polyvinyl alcohol resin film continuously conveyed is immersed in a treatment bath such as a swelling bath, a dyeing bath, and a crosslinking bath in this order, and an elongation treatment is performed during the series of treatments [ for example, japanese patent application laid-open No. 2001-. Patent document 1 discloses the following: in order to uniformly stretch a polyvinyl alcohol resin film while suppressing curling of the film ends that occurs during stretching, the polyvinyl alcohol resin film is immersed in water at 30 ℃ for 5 minutes at a curl angle of 180 DEG or less.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open No. 2001-315140

Disclosure of Invention

Problems to be solved by the invention

The polarizing film can be continuously manufactured by: the stretching treatment is performed at any one or more stages of the time from the immersion in the swelling bath to the drawing out from the crosslinking bath while continuously taking out the film from the raw material roll (wound material) of the polyvinyl alcohol-based resin film and conveying the film along the film conveying path through the various treatment baths as described above. However, the film may be broken during continuous production, particularly during stretching, and improvement is required from the viewpoint of productivity and polarizing film yield. The problem of film breakage during stretching treatment is particularly significant when the thickness of the polyvinyl alcohol resin film is small.

Accordingly, an object of the present invention is to provide a method for producing a polarizing film, which can effectively suppress film breakage during stretching treatment even when a thin polyvinyl alcohol resin film is used.

Means for solving the problems

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

The method for manufacturing the polarizing film sequentially comprises the following steps:

[1] a swelling treatment step of conveying a long polyvinyl alcohol resin film having a thickness of 65 μm or less while winding the polyvinyl alcohol resin film from a raw material roll, thereby immersing the polyvinyl alcohol resin film in a swelling bath and then drawing out the polyvinyl alcohol resin film; and

a dyeing treatment step of immersing the film drawn out from the swelling bath in a dyeing bath and then drawing out the film,

at least one of both ends of the polyvinyl alcohol resin film in the film width direction has a curl angle of less than 90 DEG when immersed in a swelling bath.

[2] The production method according to [1], wherein the time from winding the polyvinyl alcohol resin film out of the log to immersing the polyvinyl alcohol resin film in a swelling bath is 750 seconds or less.

[3] The production method according to [1] or [2], wherein the polyvinyl alcohol resin film is dried during a period from when the polyvinyl alcohol resin film is wound out from the web to when the polyvinyl alcohol resin film is immersed in a swelling bath.

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

[5] The production method according to any one of [1] to [4], wherein the polyvinyl alcohol resin film is subjected to a widening treatment during a period from when the polyvinyl alcohol resin film is wound out from a log to when the polyvinyl alcohol resin film is immersed in a swelling bath.

[6] In the production method according to any one of [1] to [5], in the swelling treatment step, the polyvinyl alcohol resin film wound from a raw material roll is conveyed along two or more rolls selected from a guide roll and a grip roll to immerse the polyvinyl alcohol resin film in a swelling bath,

the two or more rollers are configured such that L is 2m or less or T is 30 seconds or less when a maximum value of a distance between adjacent rollers is L and a maximum value of a time required for conveyance between adjacent rollers is T.

Effects of the invention

According to the method of the present invention, film breakage during stretching, which has conventionally occurred in a method for producing a polarizing film from a thin polyvinyl alcohol-based resin film, can be effectively suppressed.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing method and a polarizing film manufacturing apparatus used in the polarizing film manufacturing method of the present invention.

Fig. 2 is a sectional view schematically showing the state of curling of the polyvinyl alcohol resin film and the curling angle thereof.

Detailed Description

< method for producing polarizing film >

In the present invention, the polarizing film is a polarizing film obtained by adsorbing and orienting a dichroic dye (iodine or dichroic dye) to a uniaxially stretched polyvinyl alcohol resin film. The polyvinyl alcohol resin constituting the polyvinyl alcohol resin film is generally obtained by saponifying a polyvinyl acetate resin. The saponification degree thereof is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The polyvinyl acetate resin may be, for example, a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of the other copolymerizable monomer include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The polymerization degree of the polyvinyl alcohol resin is usually about 1000 to 10000, preferably about 1500 to 5000.

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

In the present invention, as a starting material for producing a polarizing film, an unstretched polyvinyl alcohol resin film (blank 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. Thus, a polarizing film which is a film having an increasing market demand can be obtained. The thinner the blank film, the more likely film breakage occurs during the stretching process, and according to the present invention, film breakage can be effectively suppressed even when the blank film is thin. When the thickness of the blank film is larger than 65 μm, film breakage during stretching treatment due to folding (curling) is not a problem in many cases. The base film may be a polyvinyl alcohol resin film which has been subjected to stretching treatment in a gas phase in advance.

The width of the blank film is not particularly limited, and may be, for example, about 400 to 6000mm, but there is a tendency that: the larger the film width, the more likely film breakage occurs during the stretching process.

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

The polarizing film can be continuously produced as a long polarizing film by continuously conveying the long blank film along a film conveying path of a polarizing film production apparatus and performing a predetermined treatment process while the blank film is wound up from the blank roll. The predetermined treatment step may include a swelling treatment step of immersing the blank film in a swelling bath and then drawing out the blank film; a dyeing treatment step of immersing the film after the swelling treatment step in a dyeing bath and then taking out the film; and a crosslinking treatment step of immersing the dyed film in a crosslinking bath and then taking out the film. In addition, the uniaxial stretching treatment is performed in a wet or dry manner during the series of treatment steps (i.e., before or after any one or more treatment steps and/or during any one or more treatment steps). Other treatment steps may be added as necessary. The above-described respective treatment steps may be a treatment in which the film is immersed in one bath, or may be a treatment in which the film is immersed in two or more baths in sequence.

Hereinafter, the method for producing the polarizing film of the present invention will be described in more detail with reference to fig. 1. Fig. 1 is a cross-sectional view schematically showing an example of the polarizing film manufacturing method and the polarizing film manufacturing apparatus used in the polarizing film manufacturing method of the present invention. The polarizing film manufacturing apparatus shown in fig. 1 is configured to: the raw film 10 made of a polyvinyl alcohol resin (not stretched) is continuously wound out from a raw roll 11 while being conveyed along a film conveying path, whereby the raw film 10 is passed through a swelling bath 13, a dyeing bath 15, a crosslinking bath 17, and a cleaning bath 19 provided in the film conveying path in this order, and finally the raw film 10 is passed through a drying furnace 21. The obtained polarizing film 23 can be directly transferred to the next polarizing plate production step (step of attaching a protective film to one side or both sides of the polarizing film 23), for example. The arrows in fig. 1 indicate the transport direction of the film.

Fig. 1 shows an example in which the swelling bath 13, the dyeing bath 15, the crosslinking bath 17, and the cleaning bath 19 are each provided with one tank, but two or more tanks may be provided as needed for any one or more treatment baths (baths such as the swelling bath 13, the dyeing bath 15, the crosslinking bath 17, and the cleaning bath 19 that are provided in the film transport path and that contain a treatment liquid for treating a polyvinyl alcohol resin film may be collectively referred to as "treatment baths").

The film transport path of the polarizing film manufacturing apparatus may be constructed by arranging guide rollers 30 to 41, 60, 61 and nip rollers 50 to 55 at appropriate positions in addition to the treatment bath, the guide rollers 30 to 41, 60, 61 may support the transported film or may change the film transport direction, and the nip rollers 50 to 55 may press and nip the transported film to apply a driving force generated by the rotation of the film to the film or may change the film transport direction. The guide rolls and the nip rolls can be disposed before and after the treatment baths and in the treatment baths, whereby the film can be introduced into the treatment baths, immersed in the treatment baths, and drawn out of the treatment baths (see fig. 1). For example, the film can be immersed in each treatment bath by providing one or more guide rollers in each treatment bath and conveying the film along the guide rollers.

In the polarizing film manufacturing apparatus shown in fig. 1, since the nip rollers (nip rollers 50 to 54) are arranged before and after each treatment bath, the inter-roller stretching in which the circumferential speed difference is provided between the nip rollers arranged before and after the treatment bath and the longitudinal uniaxial stretching is performed in any one or more treatment baths can be performed. The respective treatment steps are explained below.

(swelling treatment)

The swelling treatment is performed for the purpose of removing foreign matter on the surface of the blank film 10, removing a plasticizer in the blank film 10, imparting dyeability, plasticizing the blank film 10, and the like. The treatment conditions are determined within a range that can achieve the object and that does not cause problems such as excessive dissolution and devitrification of the green material film 10.

Referring to fig. 1, the swelling treatment can be performed by conveying the blank film 10 along the film conveying path while continuously winding the blank film 10 from the blank roll 11, immersing the blank film 10 in the swelling bath 13 (the treatment liquid stored in the swelling tank) for a predetermined time, and then drawing out the blank film 10. In the example of fig. 1, the blank film 10 is conveyed along the film conveying path constituted by the guide rollers 60 and 61 and the nip roller 50 during a period from when the blank film 10 is wound up to when the blank film 10 is immersed in the swelling bath 13. In the swelling treatment, the film is conveyed along the film conveying path constructed by the guide rollers 30 to 32.

The swelling bath 13 may be an aqueous solution prepared by adding boric acid (JP-A-10-153709), chloride (JP-A-06-281816), an inorganic acid, an inorganic salt, a water-soluble organic solvent, an alcohol, or the like to the amount of about 0.01 to 10% by weight, in addition to pure water.

The temperature of the swelling bath 13 is, for example, about 10 to 50 ℃, preferably about 10 to 40 ℃, and more preferably about 15 to 30 ℃. The dipping time of the blank film 10 is preferably about 10 to 300 seconds, and more preferably about 20 to 200 seconds. In the case where the base film 10 is a polyvinyl alcohol resin film stretched in a gas in advance, the temperature of the swelling bath 13 is, for example, about 20 to 70 ℃, preferably about 30 to 60 ℃. The dipping time of the blank 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 widthwise opposite ends of the film when the blank film 10 is immersed in the swelling bath 13 is less than 90 °. In the blank film 10 wound out from the blank roll 11, curling such as a state in which at least one of the widthwise both ends (more typically, both widthwise both ends) of the blank film 10 is warped (raised), or a state in which the warp is further increased and the widthwise both ends are turned over in the direction of the widthwise central portion is generally generated, but by making the curl angle when the blank film 10 is immersed in the swelling bath 13 smaller than 90 °, film breakage during stretching treatment can be suppressed. In order to more effectively suppress film breakage, it is preferable that the curl angle of both ends in the film width direction is less than 90 °. For the same reason, the curl angle of at least one of the widthwise opposite ends of the film is preferably 80 ° or less, and more preferably less than 75 °. More preferably, the curl angle of both ends in the film width direction is less than 90 ° during the period from immediately after the blank roll 11 is wound up to the time when the film is immersed in the swelling bath 13.

Fig. 2 is a film cross-sectional view schematically showing the state of curling of a polyvinyl alcohol resin film and the curling angle thereof. Fig. 2 shows an example in which curling has occurred at both ends in the film width direction, and fig. 2 (a) shows a case in which the curl angle is 45 °, fig. 2 (b) shows a case in which the curl angle is 90 °, and fig. 2 (c) shows a case in which the curl angle is 150 °. As shown in fig. 2, the curl angle α ° means that the end of the curled film portion is oriented in a direction α ° with respect to the pushed-out surface of the uncurled film surface. The curl angle of both widthwise end portions of the base film 10 continuously immersed in the swelling bath 13 can be measured by the method described in the section of examples.

In order to make the curl angle of at least one (preferably both) of the widthwise opposite end portions of the film smaller than 90 ° when the blank film 10 is immersed in the swelling bath 13, for example, the following method is preferably employed. In the following methods, only one method may be adopted, or two or more methods may be combined.

The environment in the unwinding step is adjusted to an appropriate condition, and the unwinding step is a step from unwinding the blank film 10 from the blank roll 11 to immersing the blank film 10 in the swelling bath 13. The preferable environmental conditions are that the temperature is 23 +/-5 ℃ and the relative humidity is 20-70% RH. The relative humidity is more preferably 20 to 65% RH, and the relative humidity is more preferably 25 to 60% RH. By performing the unwinding process under such an environment, moisture absorption of the blank film 10 can be suppressed, and further, the growth of the curl can be suppressed.

The time required for the above-mentioned unwinding step (the time from unwinding the blank film 10 from the blank roll 11 to immersing the blank film 10 in the swelling bath 13) is kept short. Shortening this time is advantageous in suppressing the growth of curl in the unwinding step, and is also advantageous from the viewpoint of production efficiency. Generally, as the thickness of the blank film is smaller, the curl tends to grow in the winding-out step. When the blank film 10 having a thickness of 35 to 65 μm is used, the required time is preferably 750 seconds or less, more preferably 600 seconds or less, and still more preferably 300 seconds or less. When the blank film 10 having a thickness of less than 35 μm is used, the required time is preferably 650 seconds or less, more preferably 300 seconds or less, and still more preferably 150 seconds or less. On the other hand, if the required time is too short, it is difficult to control the tension of the film in the unwinding step and the film conveyance becomes unstable, and therefore the required time is usually 10 seconds or more, preferably 20 seconds or more.

In the unwinding step, the blank film 10 is dried. The drying treatment here means a treatment of volatilizing moisture in the green film 10 to reduce the water content of the green film 10. The drying process is advantageous in reducing or eliminating curl. In order to reduce or eliminate the curl, it is particularly preferable to perform the drying treatment so that the dryness of the curled surface of the blank film 10 (i.e., the degree of decrease in the water content due to drying) is smaller than that of the surface on the opposite side. The curled surface refers to the blank film surface including the inner surface of the curl, and refers to the upper main surface in the drawing with reference to fig. 2.

As a method of making the dryness of the curled surface smaller than that of the opposite side, there is a method of applying hot air, dry air, an infrared heater from the opposite side surface side, or sandwiching the blank film 10 between a pair of rollers having different temperatures.

In the unwinding step, the spreading process is performed on the fed blank film 10. The widening treatment for the purpose of increasing the film width is advantageous in reducing or eliminating the curl when the blank film 10 is immersed in the swelling bath 13. Examples of the widening process include a widening roll such as a spreader roll, a helical roll, or a crowned roll, and other widening devices such as a cloth guide, a curved bar, or a tenter. Among them, a process using a roll having a widening function is preferable for simplicity. For example, as the guide roller 60 and/or the guide roller 61 shown in fig. 1, a roller having a widening function may be used.

In the unwinding step, the curl portion of the fed blank film 10 is forcibly pressed into the film. This treatment is also advantageous in reducing or eliminating curling of the blank film 10 when immersed in the swelling bath 13, as in the widening treatment. Specific examples of the method include a method of conveying the film by an apparatus such as a conveyor, a method of pressing a roller or bar (rod) (a rod-like object which is not a member rotating by itself such as a roller) against the curled portion, and a method of spraying an inert gas such as air, nitrogen, or argon onto the curled portion of the raw film 10.

For example, in the case where the blank film 10 is conveyed along the film conveying path constituted by two or more rollers selected from the guide roller and the pinch roller in the unwinding step as in the example shown in fig. 1, the maximum value L of the distance between the adjacent rollers is shortened, and/or the maximum value T of the time required for conveying between the adjacent rollers is shortened. Shortening 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 is the maximum value among the distances between adjacent rollers. The distance between adjacent rollers is determined as the distance between the centers of the adjacent rollers. In the case of the nip roller, the center of a line connecting the centers of a pair of rollers constituting the nip roller is used instead of the roller center. L is usually 0.01m or more, preferably 2m or less, and more preferably 0.05 to 1.5 m.

Similarly, the maximum value T of the time required for conveyance between the adjacent rollers means the time required for conveyance between the adjacent rollers (in the example of fig. 1, the time T required for conveyance from the guide roller 60 to the guide roller 61₁And the time T required for the conveyance from the guide roller 61 to the grip roller 50₂) The largest value of (1). The time required for conveyance between adjacent rollers is determined as the time from when one of the adjacent rollers is separated to when the other roller comes into contact with the roller. T is usually 0.5 seconds or more, preferably 30 seconds or less, and more preferably 0.1 to 20 seconds.

In the unwinding step, the blank film 10 is generally conveyed by one or more nip rollers disposed at a position before the dipping in the swelling bath while keeping the tension of the blank film constant, and in this case, the tension applied to the blank film 10 between the blank roller 11 and the nip roller disposed at a position immediately before the dipping in the swelling bath is set to be higher than the tension applied after the nip roller. This can suppress the growth of curl in the unwinding step. The tension applied to the web film 10 between the web roll 11 and the nip roll disposed at a position immediately before the immersion into the swelling bath is, for example, 5 to 300N/mm, preferably 10 to 200N/mm. The difference between the tension applied to the web film 10 between the web roll 11 and the nip roll disposed immediately before the immersion into the swelling bath and the tension applied after the nip roll is, for example, 10N/m or more, preferably 50N/m or more. The tension on the web film 10 between the web roll 11 and the nip roller disposed at the position immediately before immersion into the swelling bath and the setting of the above-described difference in tension in the above-described range are preferable from the viewpoint of: not only has the effect of suppressing the generation of curl at the end portions of the blank film 10, but also suppresses wrinkling of the blank film 10.

In the swelling treatment, it is easy to produce a problem that the green film 10 swells in the width direction to cause wrinkles to enter the film. As one method for conveying the film while removing the wrinkles, the following method can be mentioned: the guide rolls 30, 31 and/or 32 may be rolls having a widening function such as spreader rolls, helical rolls and crowned rolls, or other widening devices such as cloth guides, bent bars and tenter clips. Another method for suppressing wrinkling is to perform an extension process. For example, the uniaxial stretching treatment may be performed in the swelling bath 13 by utilizing the difference in the peripheral speed between the nip roller 50 and the nip roller 51.

In the swelling treatment, since the film is swollen and expanded along the film transport direction, in the case where the film is not actively stretched, it is preferable to adopt a method of controlling the speed of the nip rollers 50 and 51 disposed before and after the swelling bath 13, for example, in order to eliminate the slack in the film transport direction. In addition, for the purpose of stabilizing the transport of the film in the swelling bath 13, it is also useful to Control the water flow in the swelling bath 13 by spraying with water, or to use an EPC device (Edge Position Control device: a device for detecting the end of the film and preventing the meandering of the film) in combination, or the like.

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

(dyeing treatment)

The dyeing treatment is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol resin film after the swelling treatment. The treatment conditions are determined within a range that can achieve the object and within a range that does not cause defects such as excessive dissolution and devitrification of the film. Referring to fig. 1, the dyeing process may be performed by transporting the film along a film transport path constituted by guide rollers 33 to 35 and a nip roller 51, immersing the swollen film in a dyeing bath 15 (a treatment liquid contained in a dyeing bath) for a predetermined time, and then drawing out the film. In order to improve the dyeing property of the dichroic dye, the film to be subjected to the dyeing step is preferably a film after being subjected to at least a certain degree of uniaxial stretching treatment, or is preferably subjected to uniaxial stretching treatment at the time of dyeing treatment instead of the uniaxial stretching treatment before dyeing treatment, or is preferably subjected to uniaxial stretching treatment at the time of dyeing treatment in addition to the uniaxial stretching treatment before dyeing treatment.

When iodine is used as the dichroic dye, the dyeing bath 15 may be an aqueous solution having a concentration of, for example, iodine/potassium iodide/water of about 0.003 to 0.3/about 0.1 to 10/100 in terms of weight ratio. Instead of potassium iodide, other iodide such as zinc iodide may be used, or potassium iodide and other iodide may be used together. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, and the like may be coexistent. In the case of adding boric acid, unlike the crosslinking treatment described later in terms of including iodine, if the aqueous solution contains about 0.003 parts by weight or more of iodine per 100 parts by weight of water, it can be regarded as the dyeing bath 15. The temperature of the dyeing bath 15 for dipping the film is usually about 10 to 45 ℃, preferably 10 to 40 ℃, more preferably 20 to 35 ℃, and the dipping 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, the dyeing bath 15 may be an aqueous solution having a concentration of the dichroic dye/water of about 0.001 to 0.1/100 by weight, for example. The dyeing bath 15 may contain a dyeing assistant and the like, for example, an inorganic salt such as sodium sulfate, a surfactant and the like. The dichroic dye may be used alone or in combination of two or more kinds. The temperature of the dyeing bath 15 for dipping the film is, for example, about 20 to 80 ℃, preferably about 30 to 70 ℃, and the dipping time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

In the dyeing step, as described above, the uniaxial stretching of the film can be performed in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method such as providing a circumferential speed difference between the nip roll 51 and the nip roll 52 disposed before and after the dyeing bath 15.

In the dyeing process, in order to remove wrinkles of the film and convey the polyvinyl alcohol resin film at the same time as in the swelling process, the guide rolls 33 and 34 and/or the guide roll 35 may be a roll having a widening function such as a spreader roll, a helical roll or a crowned roll, or another widening device such as a cloth guide, a looper or a tenter. Another method for suppressing wrinkling is to perform an elongation treatment, as in the swelling treatment.

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

(crosslinking treatment)

The crosslinking treatment is a treatment for the purpose of imparting hydration resistance, color tone adjustment (prevention of film bluing, etc.) and the like by crosslinking. Referring to fig. 1, the crosslinking treatment can be performed by conveying the film along a film conveying path constituted by the guide rollers 36 to 38 and the nip roller 52, immersing the dyed film in the crosslinking bath 17 (the treatment liquid stored in the crosslinking tank) for a predetermined time, and then drawing out the film.

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

In the crosslinking treatment, the concentrations of boric acid and iodide, and the temperature of the crosslinking bath 17 may be appropriately changed depending on the purpose. For example, when the polyvinyl alcohol resin film is subjected to swelling treatment, dyeing treatment, and crosslinking treatment in this order in order to make use of resistance to water by crosslinking treatment, the crosslinking agent-containing solution of the crosslinking bath may be an aqueous solution of: the concentration of the aqueous solution is 3-10/1-20/100 in terms of weight ratio. If necessary, other crosslinking agents such as glyoxal and glutaraldehyde may be used in place of the boric acid, or boric acid and other crosslinking agents may be used together. The temperature of the crosslinking bath in the film dipping is usually about 50 to 70 ℃, preferably 53 to 65 ℃, and the film dipping time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 to 200 seconds. When the polyvinyl alcohol resin film stretched in advance before the swelling treatment is subjected to the dyeing treatment and the crosslinking treatment in this order, the temperature of the crosslinking bath 17 is usually about 50 to 85 ℃, and preferably 55 to 80 ℃.

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

The crosslinking treatment may be carried out a plurality of times, and is usually carried out 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different as long as they are within the above ranges. The crosslinking treatment for imparting hydration resistance by crosslinking and the crosslinking treatment for adjusting the color tone may be performed in a plurality of steps.

The uniaxial stretching treatment may be performed in the crosslinking bath 17 by using the difference in the peripheral speed between the nip roll 52 and the nip roll 53.

In the crosslinking treatment, in order to carry out the film wrinkling and the polyvinyl alcohol resin film transfer in the same manner as in the swelling treatment, the guide rolls 36 and 37 and/or the guide roll 38 may be a roll having a widening function such as a spreader roll, a helical roll or a crowning roll, or another widening device such as a cloth guide, a bending bar or a tenter nip. Another method for suppressing wrinkling is to perform an elongation treatment, as in the swelling treatment.

In the example shown in FIG. 1, the film drawn out from the crosslinking bath 17 is guided to the cleaning bath 19 through the guide roller 38 and the nip roller 53 in this order.

(cleaning treatment)

The production method of the present invention may include a cleaning treatment step after the crosslinking treatment step. The cleaning treatment is performed for the purpose of removing an excess of a chemical agent such as boric acid or iodine attached to the polyvinyl alcohol resin film. The cleaning treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol resin film in a cleaning bath 19 (water) or spraying water mist on the film, or by using the above methods in combination.

Fig. 1 shows an example of a case where a polyvinyl alcohol resin film is immersed in a cleaning bath 19 and subjected to a cleaning treatment. The temperature of the cleaning bath 19 in the cleaning treatment is usually about 2 to 40 ℃, and the immersion time of the film is usually about 2 to 120 seconds.

In the cleaning process, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, the guide rollers 39 and 40 and/or the guide roller 41 may be rollers having a widening function such as spreader rollers, helical rollers, and crowned rollers, or other widening devices such as cloth guides, loopers, and tenter clips. In addition, the stretching treatment may be performed to suppress the wrinkles in the cleaning treatment.

(elongation treatment)

As described above, the blank film 10 is subjected to the uniaxial stretching treatment in a wet or dry manner during the series of treatment steps (i.e., before or after any one or more treatment steps and/or during any one or more treatment steps). Specific examples of the uniaxial stretching treatment include inter-roll stretching in which a circumferential speed difference is provided between two nip rolls constituting a film transport path (for example, two nip rolls disposed before and after a treatment bath) to perform uniaxial stretching in the longitudinal direction, hot roll stretching as described in japanese patent No. 2731813, tenter stretching, and the like, and the inter-roll stretching is preferable. The uniaxial stretching step may be performed a plurality of times until the polarizing film 23 is obtained from the blank film 10. As described above, the stretching treatment is also advantageous in suppressing wrinkling of the film.

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

The stretching step may be performed in any treatment step, and even when the stretching treatment is performed in two or more treatment steps, the stretching treatment may be performed in any treatment step. According to the present invention, even when uniaxial stretching treatment is performed at an arbitrary stage after the swelling treatment step (including the swelling treatment step), film cracking during stretching treatment can be effectively suppressed.

(drying treatment)

It is preferable to perform a treatment of drying the polyvinyl alcohol resin film after the washing treatment. The drying of the film is not particularly limited, and may 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 ℃, 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 treatment Process)

Processing other than the above-described processing may be added. Examples of the treatment that can be added include an immersion treatment (complementary color treatment) in which the crosslinking treatment is followed by immersion in an aqueous iodide solution that does not contain boric acid, and an immersion treatment (zinc treatment) in which the crosslinking treatment is followed by immersion in an aqueous solution that does not contain boric acid and contains zinc chloride or the like.

< polarizing plate >

The polarizing plate can be obtained by bonding a protective film to at least one surface of the polarizing film produced as described above via an adhesive. Examples of the protective film include films 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-based resin film; a cycloolefin resin film; a (meth) acrylic resin film; a film made of a chain olefin resin such as a polypropylene resin.

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

In order to improve the adhesiveness between the polarizing film and the protective film, the surface of the polarizing film and/or the protective film to be bonded may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, undercoating treatment, or saponification treatment. Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol resin, an aqueous solution prepared by blending a crosslinking agent with the aqueous solution, and an aqueous adhesive such as a urethane emulsion adhesive. The ultraviolet-curable adhesive may be a mixture of a (meth) acrylic compound and a photo radical polymerization initiator, a mixture of an epoxy compound and a photo cation polymerization initiator, or the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable (meth) acrylic compound may be used together, and a photo cationic polymerization initiator and a photo radical polymerization initiator may be used together as the initiator.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. In the following examples, the curl angle at both ends in the width direction of the blank film 10 continuously immersed in the swelling bath 13 was measured by the following method.

[ measurement of curl Angle ]

The film was visually observed from the roll passing immediately before the film was immersed in the swelling bath 13 in the direction of the first guide roll in the swelling bath 13, and the angle region indicated by the leading end of the film end was measured every 15 ° according to the mark of the angle provided at the position immediately before the film was immersed (for example, the measurement angle was the minimum value of the angle region as in the case where the measurement angle was 0 ° or more and less than 15 ° in the angle region, and was 15 ° or more and less than 30 ° in the angle region). An angle mark was also provided immediately before the roll passed immediately after the film was unwound and before the film was immersed in the swelling bath 13, and the curl angle was measured in the same manner.

< example 1>

Polarizing films were produced using the same polarizing film production apparatus as shown in fig. 1 except that two crosslinking baths 17 were used (hereinafter, the first crosslinking bath is referred to as 17a, and the second crosslinking bath is referred to as 17 b). The guide rollers 30 to 41 all use flat rollers.

(1) Swelling treatment Process

The polyvinyl alcohol film (trade name "CREI PVA film VF-PE # 6000" manufactured by CREI, manufactured by Koka corporation) having a thickness of 60 μm, a polymerization degree of 2400 and a saponification degree of 99.9 mol% or more was continuously wound out from a stock roll 11 while being transported, and the film was immersed in a swelling bath 13 containing pure water at 30 ℃ for 100 seconds while being kept in a stretched state so as not to loosen the film. The time from when the polyvinyl alcohol film was taken out from the web roll 11 to when the polyvinyl alcohol film was immersed in the swelling bath 13 (the time of the take-out step) was 60 seconds, and the environment of the take-out step was 23 ℃ and 60% RH relative to the relative humidity. Further, the curling angle at both ends in the film width direction is 30 ° or less during the period from when the polyvinyl alcohol film is wound out from the web roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13.

(2) Dyeing process

Subsequently, the film passed through the nip roller 51 was immersed in a 30 ℃ dyeing bath 15 containing iodine/potassium iodide/water (weight ratio) of 0.05/2/100 for 120 seconds. In this dyeing process, a difference in circumferential speed is provided between the nip rollers 51 and 52, and inter-roller stretching (uniaxial longitudinal stretching) is performed.

(3) Crosslinking treatment step

Next, in order to perform the first crosslinking treatment for the purpose of water resistance, the film having passed through the nip roll 52 was immersed for 30 seconds in the first crosslinking bath 17a at 56 ℃ at a potassium iodide/boric acid/water (weight ratio) of 12/4.4/100. In the first crosslinking treatment, inter-roll stretching (uniaxial longitudinal stretching) was also performed by providing a difference in circumferential speed between the nip rolls until the cumulative draw ratio based on the blank film 10 became 5.5 times. Next, the film after the first crosslinking treatment was immersed for 15 seconds in a second crosslinking bath 17b at 40 ℃ in which potassium iodide/boric acid/water (weight ratio) was 9/2.9/100 (second crosslinking treatment).

Then, the second crosslinked film was immersed in a cleaning bath 19 containing pure water at 6 ℃ and then passed through a drying oven 21 to be dried at 70 ℃ for 3 minutes, thereby producing a polarizing film 23.

After the polarizing film was continuously produced for 24 hours, no film breakage occurred in any of the treatment steps during the 24-hour operation. In addition, folding-in of both ends in the film width direction was not confirmed.

< example 2>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 1 except that the environment in the unwinding step was changed to 23 ℃ and 40% RH. The curling angle at both ends in the film width direction is 15 ° or less during the period from the time when the polyvinyl alcohol film is wound from the web roll 11 to the time when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

< example 3>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 1 except that a 30 μm thick polyvinyl alcohol film (trade name "CREI PVA film VF-PE # 3000" manufactured by CREI, Ltd.), and the polymerization degree of 2400 and the saponification degree of 99.9 mol% or more were used as the base film. The curling angle at both ends in the film width direction is 60 ° or less during the period from when the polyvinyl alcohol film is wound out from the web roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour working period, no film breakage occurred in any of the treatment steps, and no folding-in was observed at both ends in the film width direction.

< example 4>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 3 except that the winding-out step was carried out for 480 seconds. The curling angle of both ends in the film width direction is 75 ° or less during the period from when the polyvinyl alcohol film is wound out from the raw material roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

< example 5>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 1 except that the winding-out step was carried out for 600 seconds. The curling angle of both ends in the film width direction is 60 ° or less during the period from when the polyvinyl alcohol film is wound out from the raw material roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

< example 6>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 1 except that the winding-out step was carried out for 720 seconds. The curling angle of both ends in the film width direction is 75 ° or less during the period from when the polyvinyl alcohol film is wound out from the raw material roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

< example 7>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 3 except that the winding-out step was carried out for 600 seconds. The curling angle of both ends in the film width direction is 75 ° or less during the period from when the polyvinyl alcohol film is wound out from the raw material roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

< comparative example 1>

Polarizing film production was performed in the same manner as in example 3, except that the winding-out step was performed for 720 seconds. The curling angle of both ends in the film width direction when the polyvinyl alcohol film was immersed in the swelling bath 13 was 105 °. The film was broken during the stretching treatment in the crosslinking treatment, and a polarizing film could not be obtained.

< example 8>

Polarizing film production was carried out continuously for 24 hours in the same manner as in comparative example 1, except that a warm air of 30 ℃ was blown from the side of the polyvinyl alcohol film opposite to the winding surface for 30 seconds from the time when the polyvinyl alcohol film was wound out from the web roll 11 to the time when the polyvinyl alcohol film was immersed in the swelling bath 13. The curling angle at both ends in the film width direction is 75 ° or less during the period from when the polyvinyl alcohol film is wound out from the web roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and no folding-in was observed at both ends in the film width direction.

< example 9>

Polarizing film production was carried out continuously for 24 hours in the same manner as in comparative example 1, except that metal rods for pressing both widthwise ends of the film were provided immediately before the nip roll 50 in the unwinding step, and the widening treatment was carried out on both widthwise ends of the polyvinyl alcohol film. The curling angle at both ends in the film width direction is 60 ° or less during the period from when the polyvinyl alcohol film is wound out from the web roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and no folding-in was observed at both ends in the film width direction.

< example 10>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 3, except that the winding-out step was carried out for 300 seconds. The curling angle of both ends in the film width direction is 45 ° or less during the period from when the polyvinyl alcohol film is wound out from the raw material roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

< example 11>

Polarizing film production was carried out continuously for 24 hours in the same manner as in example 3, except that the winding-out step was carried out for 150 seconds. The curling angle of both ends in the film width direction is 45 ° or less during the period from when the polyvinyl alcohol film is wound out from the raw material roll 11 to when the polyvinyl alcohol film is immersed in the swelling bath 13. In the 24-hour operation, no film breakage occurred in any of the treatment steps, and folding-in of both ends in the film width direction was not observed.

Description of the reference numerals

10 a base film made of a polyvinyl alcohol resin, 11 base rolls, 13 a swelling bath, 15 a dyeing bath, 17a crosslinking bath, 19 a cleaning bath, 21 a drying oven, 23 a polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 60, 61 guide rolls, 50, 51, 52, 53, 54, 55 nip rolls.

Claims

1. A method of manufacturing a polarizing film, comprising in order:

a swelling treatment step of conveying a long polyvinyl alcohol resin film having a thickness of 30 μm or less while winding the polyvinyl alcohol resin film from a raw material roll, thereby immersing the polyvinyl alcohol resin film in a swelling bath and then taking out the polyvinyl alcohol resin film; and

at least one of both ends of the polyvinyl alcohol resin film in the film width direction has a curl angle of less than 90 DEG when immersed in a swelling bath,

the time from the winding of the polyvinyl alcohol resin film from the log to the immersion of the polyvinyl alcohol resin film in the swelling bath is 10 seconds to 750 seconds,

the polyvinyl alcohol resin film is subjected to a drying treatment during a period from when the polyvinyl alcohol resin film is wound out from a log to when the polyvinyl alcohol resin film is immersed in a swelling bath.

2. A method of manufacturing a polarizing film, comprising in order:

the method for producing a polyvinyl alcohol resin film includes the step of subjecting the polyvinyl alcohol resin film to a widening treatment during a period from when the polyvinyl alcohol resin film is wound out from a log to when the polyvinyl alcohol resin film is immersed in a swelling bath.

3. The manufacturing method according to claim 1,

the drying treatment is performed so that the dryness of the curled surface in the polyvinyl alcohol resin film is lower than the dryness of the surface on the opposite side of the curled surface.

4. The manufacturing method according to any one of claims 1 to 3,

in the swelling treatment step, the polyvinyl alcohol resin film wound from the base material roll is conveyed along two or more rolls selected from a guide roll and a nip roll to immerse the polyvinyl alcohol resin film in a swelling bath,