TW202413252A - Method of manufacturing polarizer - Google Patents

Abstract

The present invention provides a method of manufacturing a polarizer that is capable of suppressing variation in the length in a direction orthogonal to a stretching direction.

Description

Manufacturing method of polarizer

The present invention relates to a method for manufacturing a polarizing element, and more particularly to a method for manufacturing a polarizing plate, and a roll of a polarizing plate.

Liquid crystal display devices (LCD) are not only used in LCD TVs, but also widely used in mobile terminals such as laptops and mobile phones, and in-vehicle applications such as navigation. Generally, a liquid crystal display device has a liquid crystal panel with polarizing plates including polarizers attached to both sides of the liquid crystal unit, and uses the liquid crystal panel to control the light from the backlight to display images. In recent years, organic EL display devices have also been widely used in mobile terminals such as TVs and mobile phones, and in-vehicle applications such as navigation, just like liquid crystal display devices. In organic EL display devices, in order to prevent external light from being reflected by the metal electrode (cathode) and being seen as a mirror, a circular polarizer (including a polarizer and a λ/4 plate) is sometimes arranged on the viewing side surface of the image display element.

Polarizers are usually manufactured by subjecting a resin film formed of a polyvinyl alcohol-based resin to swelling, dyeing, crosslinking, and stretching. It is known that when manufacturing polarizers, the resin film is immersed in a crosslinking bath and then subjected to stretching (for example, Patent Document 1, etc.).

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] International Publication No. 2017/138551

If the resin film is stretched in the length direction, the resin film will shrink in the width direction (the direction orthogonal to the stretching direction) and will produce a necking phenomenon. It is found that if the resin film is stretched in the length direction in the crosslinking bath, the width of the stretched resin film will vary in the length direction, and it is impossible to obtain a polarizer with a stable width in the length direction.

The purpose of the present invention is to provide a method for manufacturing a polarizer, a method for manufacturing a polarizing plate, and a roll of a polarizing plate that can suppress the change in length in a direction orthogonal to the stretching direction.

The present invention provides a method for manufacturing the following polarizer, a method for manufacturing a polarizing plate, and a roll of a polarizing plate.

[1] A method for manufacturing a polarizing element is to adsorb and orient a dichroic pigment on a resin film formed of a polyvinyl alcohol-based resin, and includes the following steps:

The swelling step is to swell the aforementioned resin film while transporting it;

The dyeing step is to dye while transporting the aforementioned resin film after the aforementioned swelling step; and

The crosslinking and stretching step is to transport the aforementioned resin film after the aforementioned dyeing step while immersing it in a crosslinking bath, and stretch it in the aforementioned crosslinking bath in the transporting direction;

The aforementioned cross-linking extension step is a step of performing an extension treatment in multiple stages, and the first stage of the extension treatment in the aforementioned extension treatment is performed in a manner that satisfies the relationship of the following formula (1).

v×0.3t≦X1≦v×1.2t (1)

[In formula (1),

X1 represents the transport distance of the aforementioned resin film from the beginning to the end of the aforementioned first stage stretching process [m];

v represents the transport speed of the aforementioned resin film in the aforementioned cross-linking and stretching step [m/min];

t represents the time [min] required for the shrinkage of the resin film to reach saturation when the resin film is immersed in the cross-linking bath used in the elongation treatment of the first stage after the dyeing step. ]

[2] A method for manufacturing a polarizing element is to adsorb and orient a dichroic pigment on a resin film formed of a polyvinyl alcohol-based resin, and includes the following steps:

The swelling step is to swell the aforementioned resin film while transporting it;

The dyeing step is to dye while transporting the aforementioned resin film after the aforementioned swelling step; and

The crosslinking and stretching step is to transport the aforementioned resin film after the aforementioned dyeing step while immersing it in a crosslinking bath and stretching it in the transporting direction in the aforementioned crosslinking bath;

The aforementioned cross-linking extension step is a step of performing extension treatment in multiple stages, and the first stage of the aforementioned extension treatment is performed in a manner that satisfies the relationship of the following formula (2);

v×0.4t≦X2≦v×1.2t (2)

[In formula (2),

X2 represents the transport distance [m] of the resin film from the start of immersion of the resin film in the crosslinking bath to the end of the first stage of stretching treatment in the crosslinking and stretching step;

v represents the transport speed of the aforementioned resin film in the aforementioned cross-linking and stretching step [m/min];

t represents the time [min] required for the shrinkage of the resin film to reach saturation when the resin film is immersed in the cross-linking bath used in the elongation treatment of the first stage after the dyeing step. ]

[3] A method for manufacturing a polarizer as described in [2], wherein the cross-linking and extension step further satisfies the relationship of the following formula (1).

v×0.3t≦X1≦v×1.2t (1)

[In formula (1),

X1 represents the transport distance of the aforementioned resin film from the beginning to the end of the aforementioned first stage stretching process [m];

v and t are synonymous with the above. ]

[4] A method for manufacturing a polarizing element as described in [1] or [3], wherein when the transport distance of the resin film from the beginning to the end of the stretching treatment in the first stage is set to X1,

In the aforementioned cross-linking stretching step, the transport distance of the aforementioned resin film from the start to the end of at least one stretching treatment in the stretching treatment performed after the aforementioned first stage is more than 2 times and less than 10 times the aforementioned distance X1.

[5] A method for manufacturing a polarizer as described in any one of [1] to [4], wherein in the crosslinking and stretching step, the first stage stretching treatment and the second stage stretching treatment thereafter are performed in the same crosslinking bath.

[6] A method for manufacturing a polarizer as described in [5], wherein:

In the aforementioned cross-linking bath, the first clamping roller, the second clamping roller, and the third clamping roller are sequentially arranged from the upstream side in the conveying direction.

The aforementioned first stage of stretching is performed between the aforementioned first clamping roller and the aforementioned second clamping roller.

The aforementioned second stage of stretching is performed between the aforementioned second clamping roller and the aforementioned third clamping roller.

[7] A method for manufacturing a polarizing element as described in [6], wherein the second clamping roller is movably arranged in such a manner that the conveying distance of the resin film between the first clamping roller and the second clamping roller is adjustable.

[8] A method for manufacturing a polarizer as described in [6] or [7], wherein the rotation speed of the first clamping roller is set to Rv1 [m/min], and the rotation speed of the third clamping roller is set to Rv3 [m/min], when the width of the resin film after the cross-linking and stretching step becomes the minimum, and the rotation speed of the second clamping roller is set to Rvmin [m/min],

The rotation speed Rv2[m/min] of the aforementioned second clamping roller is within the range of Rvmin±10[m/min].

[9] A method for manufacturing a polarizer as described in [8], wherein the cross-linking stretching step is performed while changing the rotation speed Rv2 [m/min] of the second clamping roller.

[10] A method for manufacturing a polarizing plate comprises the following steps:

The step of obtaining a polarizer by the manufacturing method of a polarizer described in any one of [1] to [9]; and

The polarizer obtained in the step of obtaining the polarizer is not cut in the conveying direction, but a protective film is laminated on one or both sides of the polarizer.

[11] A roll of polarizing plate, which is formed by winding a polarizing plate into a roll, and the polarizing plate comprises a polarizing element and a protective film laminated on one or both sides of the polarizing element;

The difference between the width of the polarizer at the start of the winding of the roll and the width of the polarizer at the end of the winding of the roll is 0.1 mm or more and 3 mm or less in absolute value.

If the manufacturing method of the polarizer of the present invention is used, a polarizer that can suppress the length variation in the direction orthogonal to the stretching direction can be manufactured.

1: Resin film

10: Cross-linking bath

11: 1st clamping roller

12: Second clamping roller

13: The third clamping roller

X1,X2,Xf: distance

FIG1 is a schematic diagram for illustrating the cross-linking and extension step in the manufacturing method of a polarizer in one embodiment of the present invention.

The following describes the implementation of the present invention with reference to the drawings, but the present invention is not limited to the following implementation.

(Manufacturing method of polarizing element)

FIG1 is a schematic diagram for illustrating the cross-linking and extension step in the manufacturing method of a polarizer in one embodiment of the present invention.

The polarizer of this embodiment is a polarizing film formed by adsorbing and orienting the dichroic pigment on a resin film 1 formed of a polyvinyl alcohol resin.

The manufacturing method of the polarizer of this embodiment is to transport the resin film 1 while manufacturing the polarizer, and includes the following steps:

The swelling step is to swell the resin film 1 while transporting it;

The dyeing step is to dye the resin film 1 after the swelling step while transporting it; and

The crosslinking and stretching step is to transport the resin film 1 after the dyeing step while immersing it in the crosslinking bath 10 and stretching it in the transporting direction in the crosslinking bath 10.

In the manufacturing method of the polarizer, for example, the resin film 1 is pulled out from a roll body formed by winding a long resin film 1 into a roll shape, and the above-mentioned swelling step, dyeing step, and cross-linking stretching step are performed while conveying it. The resin film 1 is preferably conveyed by using a known conveying means, and is conveyed along a film conveying path composed of a clamping roller composed of a pair of rollers and a guide roller composed of a single roller.

The manufacturing method of the polarizer may further include: a color correction step, which is to use a color correction liquid to perform color adjustment treatment on the resin film 1 after the cross-linking and stretching step; a cleaning step, which is to use a cleaning liquid for cleaning; and a drying step for drying, etc. The details of each step are as follows.

The polarizer obtained by the treatment in the above steps can be formed into a roll body which is sequentially wound on a winding roll to form a roll, or can be directly supplied to the manufacturing method of the polarizing plate described later without being wound.

In the manufacturing method of the polarizer, the crosslinking stretching step is started by immersing the resin film 1 in the crosslinking bath 10. The crosslinking stretching step is a step of performing a multi-stage stretching treatment in the crosslinking bath 10, and the first stage of the stretching treatment is performed to satisfy at least one of the following equations (1) and (2). Hereinafter, the n-th stage of the stretching treatment performed in the crosslinking stretching step is also referred to as the "n-th stretching treatment".

v×0.3t≦X1≦v×1.2t (1)

v×0.4t≦X2≦v×1.2t (2)

[In formula (1) and formula (2),

X1 represents the transport distance [m] of the resin film 1 from the start to the end of the first stretching process.

X2 represents the transport distance [m] of the resin film 1 from the start of immersion of the resin film 1 in the crosslinking bath 10 to the end of the first stretching treatment in the crosslinking stretching step.

v represents the transport speed of the resin film 1 in the cross-linking and stretching step [m/min].

t represents the time [min] required for the shrinkage of the resin film 1 to reach saturation when the resin film 1 after the dyeing step is immersed in the crosslinking bath 10 used in the first stretching treatment. ]

The multi-stage extension process in the cross-linking extension step can be 2 or more stages, 3 or more stages, or 4 or more stages, and is usually 10 or less stages, 8 or less stages, or 5 or less stages. The cross-linking extension step is preferably a 2-stage or 3-stage extension process.

The distance X1 in formula (1) may be v×0.4t[m] or more, v×0.5t[m] or more, v×0.6t[m] or more, or v×1.1t[m] or less, or v×1.0t[m] or less. When the distance X1 is less than v×0.3t[m], the crosslinking structure of the polyvinyl alcohol resin and the necking of the resin film 1 are simultaneously introduced during the stretching process after the second stage, so the stability of the width is easily reduced. Furthermore, when the distance X1 exceeds v×1.2t[m], the cross-linking of the polyvinyl alcohol resin is excessive, so it will be difficult to shrink the neck during the stretching process after the second stage, which may easily cause the resin film 1 to be cut.

The distance X2 in formula (2) can be greater than v×0.5t[m], greater than v×0.6t[m], greater than v×0.7t[m], less than v×1.1t[m], or less than v×1.0t[m]. When the distance X2 exceeds v×1.2t[m], due to excessive crosslinking, the necking of the resin film 1 will be difficult to adjust during the stretching process after the second stage, which may easily cause the resin film 1 to be cut.

The first extension process in the cross-linking extension step may satisfy one of equation (1) and equation (2), or both. When the first extension process satisfies both equations (1) and (2), the distance X1 may be smaller than the distance X2, or may be the same as the distance X2.

In the crosslinking and stretching step, a crosslinking structure is introduced into the polyvinyl alcohol-based resin constituting the resin membrane 1 by immersing the resin membrane 1 in a crosslinking bath 10. At this time, it is considered that shrinkage occurs in the resin membrane 1 due to the introduction of the crosslinking structure. The first stretching treatment is performed to satisfy at least one of the formula (1) and the formula (2). Therefore, in the step of performing the first stretching treatment, it is inferred that the shrinkage of the resin membrane 1 caused by the introduction of the crosslinking structure can fully suppress the necking effect of the resin membrane 1 caused by the stretching treatment performed after the second stretching treatment. Furthermore, in the second stretching treatment, the shrinkage of the resin film 1 due to the introduction of the cross-linked structure does not substantially occur, and only the shrinkage caused by the necking of the resin film 1 can occur. Therefore, by the stretching treatment after the second stretching treatment, since the length (width) of the resin film 1 in the width direction is easily controlled, the variation of the width of the resin film 1 in the length direction is suppressed, and a polarizer with a stable width can be manufactured. The so-called polarizer with a stable width specifically refers to a polarizer whose variation (standard deviation) of the length (width) in the direction orthogonal to the stretching direction when manufacturing 100,000 meters is less than 3 mm (preferably less than 1 mm).

As described above, by performing the first stretching treatment, in the manufacturing method of the polarizer of this embodiment, by adjusting the stretching ratio after the second stretching treatment, the size of the neck produced in the resin film 1 can be adjusted, and the resin film 1 can be adjusted to the desired width. If the neck produced in the resin film 1 becomes larger, the optical properties of the polarizer (especially the polarization degree) are easily improved. As described above, by performing the first stretching treatment and adjusting the stretching ratio of the stretching treatment after the second stretching treatment, a large neck can be produced in the resin film 1. Therefore, if the manufacturing method of the polarizer of this embodiment is used, a polarizer with excellent optical properties can be easily obtained.

The distance X1 is not particularly limited as long as it satisfies the relationship of formula (1), but is usually 1m or more, 2m or more, or 3m or more, and is usually 10m or less, 8m or less, or 5m or less. The distance X2 is not particularly limited as long as it satisfies the relationship of formula (2), but is usually 1m or more, 2m or more, or 3m or more, and is usually 10m or less, 8m or less, or 5m or less.

In this specification, the conveying speed v [m/min] in equations (1) and (2) is the average of the conveying speed vs [m/min] of the resin film 1 at the position where the first stretching treatment starts and the conveying speed ve [m/min] of the resin film 1 at the position where the first stretching treatment ends. That is, the conveying speed v = (vs + ve) / 2. For example, when the first stretching treatment is performed between the first clamping roller 11 and the second clamping roller 12 shown in Figure 1 described later, the conveying speed vs is the speed at which the resin film 1 is conveyed by the first clamping roller 11 located on the upstream side in the conveying direction. The conveying speed ve is the speed at which the resin film 1 is conveyed by the second clamping roller 12 located on the downstream side in the conveying direction.

The conveying speed v[m/min] is not particularly limited, but is usually 0.1m/min or more, 0.5m/min or more, 1.0m/min or more, 3.0m/min or more, or 5.0m/min or more, and is usually 30m/min or less, 25m/min or less, 20m/min or less, or 15m/min or less.

The time t[min] in formula (1) and formula (2) is the time required for the resin film 1 after the dyeing step to be immersed in the crosslinking bath used in the first stretching treatment until the shrinkage of the resin film 1 reaches saturation. The time t can be determined by the time required for the resin film 1 to be immersed in the crosslinking bath used in the first stretching treatment and the length of the resin film 1 in the width direction to become constant, for example, it can be determined according to the method described in the embodiment described below.

The time t varies depending on the type of resin film 1 used in the manufacturing method of the polarizer, but for example, it can be more than 0.1 min, more than 0.3 min, or more than 0.5 min, or less than 2.0 min, or less than 1.5 min, or less than 1.0 min.

As shown in FIG1 , the crosslinking and stretching step can be performed while the resin film 1 is conveyed in the crosslinking bath 10. For example, in the crosslinking bath 10, the clamping rollers are arranged according to the number of stages of the stretching treatment performed in the crosslinking bath 10. In the crosslinking bath 10 shown in FIG1 , the first clamping roller 11, the second clamping roller 12, and the third clamping roller 13 are arranged in order from the upstream side in the conveying direction. Thus, in the crosslinking bath 10, the first stretching treatment can be performed between the first clamping roller 11 and the second clamping roller 12, and the second stretching treatment can be performed between the second clamping roller 12 and the third clamping roller 13. At this time, the position of the first clamping roller 11 becomes the starting position of the first stretching treatment. The position of the second clamping roller 12 is the end position of the first stretching process and becomes the starting position of the second stretching process. The position of the third clamping roller 13 becomes the end position of the second stretching process.

When the first stretching treatment is performed in the crosslinking bath 10 shown in FIG. 1, the distance X1 is the transport distance of the resin film 1 between the position of the first clamping roller 11 and the position of the second clamping roller 12. The distance X2 is the transport distance of the resin film 1 between the position where the resin film 1 is immersed in the crosslinking bath 10 and the position of the second clamping roller 12. When the distance X1 and the distance X2 are the same, the position where the first clamping roller 11 is located and the clamping position of the first clamping roller 11 is configured to be the position where the resin film 1 starts to be immersed in the crosslinking bath.

In the crosslinking bath 10 shown in FIG1 , when the crosslinking and stretching step is performed, the second clamping roller 12 is preferably movably arranged in the crosslinking bath 10 to adjust the conveying distance of the resin film 1 between the first clamping roller 11 and the second clamping roller 12. At this time, the setting positions of the first clamping roller 11 and the third clamping roller 13 are preferably fixed (set to be immovable). Therefore, by adjusting the setting position of the second clamping roller 12 in the crosslinking bath 10, the first stretching treatment can be performed in a manner that satisfies at least one of the above formulas (1) and (2).

When the crosslinking and stretching step is performed in the crosslinking bath 10 shown in FIG1 , the rotation speed Rv2 [m/min] of the second clamping roller 12 is preferably one that satisfies the following formula (3). The rotation speed Rv2 here refers to the length of the resin film 1 transported by the second clamping roller 12 per unit time.

Rvmin-10≦Rv2≦Rvmin+10 (3)[In formula (3),

Rv2 represents the rotation speed of the second clamping roller 12 [m/min].

Rvmin represents the rotation speed [m/min] of the second clamping roller 12 when the width of the resin film 1 after the cross-linking and stretching step becomes the minimum when the rotation speed of the first clamping roller 11 is set to Rv1 [m/min] and the rotation speed of the third clamping roller 13 is set to Rv3 [m/min]. ]

The above rotation speed Rv1 refers to the length of the resin film 1 transported by the first clamping roller 11 per unit time, and the above rotation speed Rv3 refers to the length of the resin film 1 transported by the third clamping roller 13 per unit time.

The rotation speed Rv2 of the second clamping roller 12 is the rotation speed set when the rotation speed Rv1 of the first clamping roller 11 and the rotation speed Rv3 of the third clamping roller 13 are set to fixed values. The so-called minimum width of the resin film 1 after the cross-linking stretching step refers to the time when the width difference of the resin film 1 before and after the cross-linking stretching step (the value of the width of the resin film 1 after the cross-linking stretching step minus the width of the resin film 1 before the cross-linking stretching step) becomes the maximum, and the necking of the resin film 1 in the cross-linking stretching step becomes the maximum.

Rv2 can be Rvmin-8[m/min] or more, Rvmin-6[m/min] or more, or Rvmin-5[m/min] or more, or Rvmin+8[m/min] or less, Rvmin+6[m/min] or less, or Rvmin+5[m/min] or less, or Rvmin[m/min].

By performing the cross-linking and stretching step in a manner that satisfies formula (3), a large neck can be generated in the resin film 1 in the cross-linking and stretching step. In this way, a polarizer with excellent optical properties can be easily obtained.

The rotation speed Rv1 can be, for example, 2.0 m/min or more, 3.0 m/min or more, or 4.0 m/min or more, or 20.0 m/min or less, or 15.0 m/min or less, or 12.0 m/min or less. The rotation speed Rv3 is preferably greater than the rotation speed Rv1 and the rotation speed Rv2, for example, 5.0 m/min or more, 7.0 m/min or more, or 10.0 m/min or more, or 35.0 m/min or less, or 30.0 m/min or less, or 25.0 m/min or less.

When the rotation speeds Rv1 and Rv3 are within the above ranges, it is preferred that the rotation speed Rv2 is greater than the rotation speed Rv1 and less than the rotation speed Rv3, for example, it can be greater than 4.0 m/min, greater than 5.0 m/min, greater than 6.0 m/min, or greater than 7.0 m/min, and can be less than 30.0 m/min, less than 25.0 m/min, less than 20.0 m/min, or less than 15.0 m/min.

When the stretching treatment is performed in multiple stages after the first stretching treatment, for example, the second stretching treatment and the third stretching treatment are performed after the first stretching treatment, or when multiple stretching treatments are performed after the first stretching treatment, it is also a useful technique to adjust the rotation speed of the second clamping roller and the third clamping roller to be the same as the above Rv2.

In the manufacturing method of the present invention, during the period of transporting the resin film 11 from the beginning of manufacturing the polarizer to the end of manufacturing, the rotation speed Rv2 of the second clamping roller in the crosslinking and stretching step can be controlled to be constant or variable. When changing the rotation speed Rv2, the rotation speed Rv2 can be changed within the range of Rvmin±10[m/min], can be changed within the range of Rvmin±8[m/min], can be changed within the range of Rvmin±6[m/min], and can also be changed within the range of Rvmin±5[m/min]. It is preferred to control the rotation speed Rv2 in such a way that the width variation (standard deviation) of the polarizer covers the length direction of the polarizer and becomes, for example, less than 3 mm, preferably less than 1 mm. When the polarizer obtained by the manufacturing method of the present invention is used to obtain the roll of the polarizing plate described later, it is preferred to control the rotation speed Rv2 in such a way that the difference between the width of the polarizer at the start of the roll and the width of the polarizer at the end of the roll is less than 3 mm in absolute value.

FIG. 1 shows the case where the first stretching treatment and the second stretching treatment are performed in the same crosslinking bath 10, but the first stretching treatment and the second stretching treatment can be performed in another crosslinking bath respectively. When the first stretching treatment and the second stretching treatment are performed in another crosslinking bath respectively, the type of crosslinking bath such as the composition of the crosslinking liquid of each crosslinking bath and the temperature of the crosslinking bath are preferably the same.

When the crosslinking and stretching step includes a stretching treatment after the third stretching treatment, the stretching treatment after the third stretching treatment can be performed in the same crosslinking bath 10 as the first stretching treatment and the second stretching treatment, or in a crosslinking bath different from the first stretching treatment and the second stretching treatment.

The stretching ratio of the resin film 1 in the first stretching treatment is not particularly limited, but is usually more than 1.0 times, may be more than 1.01 times, may be more than 1.05 times, or may be more than 1.1 times, and is usually less than 3.0 times, may be less than 2.5 times, may be less than 2.0 times, or may be less than 1.8 times.

In the cross-linking stretching step, in at least one of the stretching treatments of the stretching treatment after the first stretching treatment and the stretching treatment after the second stretching treatment, the transport distance Xf of the resin film 1 from the start to the end of the stretching treatment preferably satisfies at least one of the following equations (4) and (5).

2×X1≦Xf≦10×X1 (4)

2×X2≦Xf≦12×X2 (5)

In formula (4), the distance Xf can be more than 2 times X1, more than 3 times, or more than 4 times, and can be less than 10 times X1, less than 9 times, or less than 8 times. In formula (5), the distance Xf can be more than 2 times X2, more than 3 times, or more than 4 times, and can be less than 12 times X2, less than 10 times, or less than 9 times.

When the crosslinking treatment step is performed in three or more stages of stretching treatment, all the stretching treatments other than the first stretching treatment can satisfy at least one of the relationships of formula (4) and formula (5), and at least one of the stretching treatments other than the first stretching treatment can satisfy at least one of the relationships of formula (4) and formula (5).

By satisfying at least one of the equations (4) and (5) in the cross-linked stretching step, a sufficient necking can be generated in the resin film 1 in the stretching treatment after the second stretching treatment. In this way, the variation of the width of the resin film 1 in the length direction can be suppressed, and a polarizer with a stable width can be manufactured more easily. By satisfying at least one of the equations (4) and (5) in the cross-linked stretching step, the transport distance of the resin film 1 in the stretching treatment after the second stretching treatment can be fully ensured, so a large necking can be easily generated in the resin film 1, and a polarizer with excellent optical properties can be easily manufactured.

In the crosslinking bath 10 shown in FIG1 , when the second stretching treatment satisfies at least one of equations (4) and (5), the distance Xf becomes the transport distance of the resin film 1 between the position of the second clamping roller 12 and the position of the third clamping roller 13.

In the cross-linking stretching step, the total stretching ratio (cumulative stretching ratio) from the second stretching treatment to the final stretching treatment is not particularly limited, but is preferably greater than the stretching ratio in the first stretching treatment. The total stretching ratio of the stretching treatment after the second stretching treatment is usually 1.1 times or more, 1.5 times or more, 1.8 times or more, 2.0 times or more, or 2.5 times or more, and usually 7.0 times or less, 6.0 times or less, 5.0 times or less, 4.5 times or less, or 4.0 times or less.

The total stretching ratio (cumulative stretching ratio) of all stretching treatments in the cross-linking stretching step can be, for example, 2.0 times or more, 3.0 times or more, or 3.5 times or more, or 7.0 times or less, 6.8 times or less, or 6.5 times or less.

(Polarizing plate manufacturing method)

The polarizing plate of this embodiment is a polarizing element obtained by the above-mentioned polarizing element manufacturing method, and a protective film is laminated on one or both sides. The polarizing element and the protective film are preferably laminated with a bonding layer (adhesive layer or adhesive layer) interposed therebetween.

The manufacturing method of the polarizing plate of this embodiment includes the following steps:

The step of obtaining a polarizer by the above-mentioned method for manufacturing a polarizer; and

The step of not cutting the polarizer obtained in the conveying direction, but laminating a protective film on one or both sides of the polarizer.

When manufacturing polarizing plates, in order to make the width of the polarizer consistent in the length direction, the polarizer is sometimes cut in the conveying direction, or the cut polarizer and the protective film are laminated. If the manufacturing method of the polarizer is used, even if the polarizer is not cut in the conveying direction, a polarizer with suppressed width variation in the length direction can be obtained. Therefore, the polarizer is not cut in the conveying direction, and the protective film can be laminated to obtain a polarizing plate. In addition, the polarizing plate can be cut. That is, after the protective film is laminated on one or both sides of the polarizer, the polarizer can be cut.

The step of laminating the protective film on both sides or one side of the polarizer is performed by applying a laminating agent (adhesive or adhesive) etc. for forming a laminating layer on the laminating surface of at least one of the polarizer and the protective film. When laminating the protective film on both sides of the polarizer, the protective film can be sequentially laminated on one side of the polarizer, while laminating the protective film on one side to the polarizer and laminating the protective film on the other side to the polarizer.

(Polarizing plate roll)

The roll of polarizing plate is made by winding the polarizing plate into a roll. The roll of polarizing plate is usually obtained by winding the polarizing plate on a winding core. The manufacturing method of the above polarizer can obtain a long polarizer. The long strip polarizer obtained by the manufacturing method of the above polarizer is not cut in the conveying direction, and can be made into a long strip polarizing plate by laminating a protective film on one or both sides. For example, by winding the long strip polarizing plate obtained in this way into a roll, a roll of polarizing plate suitable for storage or transfer can be made. There is no special restriction on the length (winding length) of the polarizing plate constituting the roll of polarizing plate, but from the perspective of improving the stability of the width of the polarizer, it can be made to be more than 300m and less than 5000m.

In the roll of polarizing plate, the difference between the width of the polarizer at the start of the roll and the width of the polarizer at the end of the roll can be 3 mm or less in absolute value, or can be 0.1 mm or more and 3 mm or less. The absolute value of the above difference can be 0.1 mm or more and 2 mm or less, 0.1 mm or more and 1 mm or less, or 0.1 mm or more and 0.5 mm or less. The width of the polarizer at the start of the roll can be greater than or less than the width of the polarizer at the end of the roll.

By making the absolute value of the above difference in the roll within the above range, it is easy to obtain a roll with good appearance. On the other hand, when the absolute value of the above difference in the roll exceeds 3mm, it is easy to produce undesirable conditions such as a part of the roll bulging into stripes, and it is easy to form a roll with poor appearance. On the other hand, when the polarizer is cut in the conveying direction, the width of the polarizer becomes approximately constant. In the roll of the polarizing plate, the difference between the width of the polarizer at the beginning of the roll and the width of the polarizer at the end of the roll is easy to be less than 0.1mm in absolute value. However, if the polarizer is cut in the conveying direction, there is a possibility of chip debris or cracks in the polarizer.

The width variation (standard deviation) of the polarizer obtained by the manufacturing method of the present invention is less than 3mm (preferably less than 1mm), so even if it is not cut in the conveying direction, a roll with good appearance can be obtained in which the difference between the width of the polarizer at the winding start part of the polarizing plate roll and the width of the polarizer at the winding end part of the roll is less than 3mm in absolute value.

In addition, the variation (standard deviation) of the polarizer width of the polarizing plate roll of the present invention can be less than 3 mm (preferably less than 1 mm).

The so-called winding start part of the polarizing plate roll refers to the polarizing plate located on the winding start side of the roll core side (the center side of the roll in the radial direction), and the so-called width of the polarizing element at the winding start part of the roll refers to the width of the polarizing element at a position of 1m in the length direction from the end of the polarizing plate where the winding starts. The so-called winding end part of the polarizing plate roll refers to the polarizing plate located on the winding end side of the roll (the outer side of the roll in the radial direction), and the so-called width of the polarizing element at the winding end part of the roll refers to the width of the polarizing element at a position of 1m in the length direction from the end of the polarizing plate where the winding ends.

Below, the various steps of the manufacturing method of polarizers and polarizing plates, as well as the materials used in these manufacturing methods, are described in detail.

(Polarizer)

A polarizer is an absorption-type polarizing film, and the absorption-type polarizing film has the following properties: it absorbs linear polarized light with a vibration plane parallel to its absorption axis, and transmits linear polarized light with a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). A polarizer is a polarizing film formed by adsorbing and orienting a dichroic pigment on a resin film formed of a polyvinyl alcohol resin (hereinafter, sometimes referred to as "PVA resin").

The thickness of the polarizer is not particularly limited, but can be, for example, 3 μm or more, 4 μm or more, 5 μm or more, 35 μm or less, 30 μm or less, or 25 μm or less. By making the thickness of the polarizer less than 35 μm, for example, the effect of polyolefination of PVA resin on the reduction of optical properties in a high temperature environment can be suppressed. By making the thickness of the polarizer more than 3 μm, it is easy to set the structure to achieve the desired optical properties.

(resin film)

The PVA resin constituting the resin film is obtained by saponifying a polyvinyl acetate resin. In addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl acetate resins include copolymers of vinyl acetate and other monomers that can be copolymerized with it. Other monomers that can be copolymerized include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, unsaturated sulfonic acids, etc.

The saponification degree of PVA resin is preferably 85 mol% or more, more preferably 90 mol% or more, and even more preferably 99 mol% or more and 100 mol% or less. The polymerization degree of PVA resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. PVA resin can be modified, for example, it can be polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral, etc. modified by aldehydes.

As dichroic pigments adsorbed and directed on the resin film, iodine or dichroic dyes can be listed. Iodine is preferred as dichroic pigments. As dichroic dyes, red BR, red LR, red R, pink LB, Rubin red BL, date red GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy blue RY, green LG, purple LB, purple B, black H, black B, black GSP, yellow 3G, yellow R, orange LR, orange 3R, scarlet GL, scarlet KGL, Congo red, brilliant purple BK, Supra Blue G, Supra GL, Supra Orange GL, direct sky blue, direct first orange S, first black, etc.

The thickness of the resin membrane used as the embryonic membrane also depends on the thickness of the polarizer to be manufactured, for example, it can be greater than 20μm, greater than 35μm, greater than 40μm, or greater than 45μm, and can be less than 80μm, less than 70μm, or less than 60μm.

(Swelling step)

The swelling step is a step of treating the resin film by, for example, immersing the resin film in a swelling liquid in a swelling bath or spraying the swelling liquid. The swelling step can remove dirt on the surface of the resin film, plasticizers or adhesives in the resin film, and can also impart easy dyeing properties or plasticize the resin film. The swelling liquid can generally be a medium with water as the main component, such as water, distilled water, or pure water. The swelling fluid may also contain an aqueous solution containing boric acid (Japanese Patent Publication No. 10-153709), chloride (Japanese Patent Publication No. 06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohol, etc. in a range of 0.01 mass % to 10 mass %.

The temperature of the swelling liquid is preferably 10°C to 50°C, more preferably 10°C to 40°C, and even more preferably 15°C to 30°C. When immersed in the swelling bath, the immersion time is preferably, for example, 10 seconds to 300 seconds, and more preferably 20 seconds to 200 seconds. When the resin film is stretched in the gas in advance, the temperature of the swelling liquid is, for example, 20°C to 70°C, and preferably 30°C to 60°C. The immersion time when immersed in the swelling bath is preferably 30 seconds to 300 seconds, and more preferably 60 seconds to 240 seconds.

In the swelling bath, the following problems are likely to occur: the resin film swells in the width direction and wrinkles are formed in the resin film. As a means of eliminating the wrinkles while conveying the film, there are examples of using rollers with expansion functions such as expansion rollers, spiral rollers, and convex rollers on the guide rollers used for conveying in the swelling bath, or using other expansion devices such as cross guide rollers, bending rollers, and tenter clamps. Another means to suppress the occurrence of wrinkles is to apply a stretching treatment. For example, a uniaxial stretching treatment can be applied in the swelling bath by utilizing the peripheral speed difference between the clamping rollers.

During the swelling treatment, the resin film also swells and expands in the transport direction of the resin film. Therefore, when the resin film is not actively stretched, in order to eliminate the relaxation of the resin film in the transport direction, it is better to control the speed of the clamping rollers arranged before and after the swelling bath. In addition, for the purpose of stabilizing the transport of the film in the swelling bath, it is also possible to use a water shower to control the water flow in the swelling bath, or use an EPC device (Edge Position Control device: a device that detects the end of the film and prevents the film from bending) in combination.

(Dyeing step)

The dyeing step is performed to adsorb and orient the dichroic pigment on the resin film after the swelling step. The treatment conditions are determined within the range that can achieve the purpose and does not cause undesirable conditions such as excessive dissolution or devitrification of the resin film. The dyeing step is performed by immersing the resin film after swelling treatment in the dyeing bath for a predetermined time and then pulling it out. It can also be performed by spraying the dyeing solution. In order to improve the dyeing property of the dichroic dye, the resin film supplied to the dyeing step is preferably a resin film that has been subjected to at least a certain degree of uniaxial stretching treatment, or preferably, in addition to the uniaxial stretching treatment before the dyeing step, the uniaxial stretching treatment is also performed during the dyeing step to replace the uniaxial stretching treatment before the dyeing step.

When iodine is used as a dichroic pigment, in the dyeing solution of the dyeing bath, for example, an aqueous solution having a concentration of iodine/potassium iodide/water = 0.003 to 3/0.1 to 10/100 in terms of mass ratio can be used. Other iodides such as zinc iodide can also be used to replace potassium iodide, and potassium iodide and other iodides can also be used in combination. Compounds other than iodides, such as boric acid, zinc chloride, and cobalt chloride, can also coexist in the dyeing solution. When boric acid is added, it can be distinguished from the crosslinking extension step and the color-correcting step described later in terms of the inclusion of iodine. As long as the aqueous solution contains 0.003 mass parts or more of iodine relative to 100 mass parts of water, it can be regarded as a dyeing bath. The temperature of the dye bath when immersing the resin film is usually 10℃ to 45℃, preferably 10℃ to 40℃, more preferably 20℃ to 35℃, and the immersion time of the film is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

When a water-soluble dichroic dye is used as a dichroic pigment, an aqueous solution having a concentration of dichroic dye/water = 0.001 to 0.1/100 in terms of mass ratio can be used in the dyeing solution of the dyeing bath. Dyeing aids can coexist in the dyeing solution, for example, inorganic salts such as sodium sulfate or surfactants can be contained. Only one dichroic dye can be used alone, or two or more dichroic dyes can be used in combination. The temperature of the dyeing bath when immersing the resin film is, for example, 20°C to 80°C, preferably 30°C to 70°C, and the immersion time of the resin film is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

During the dyeing step, the resin film can be stretched uniaxially in the dyeing bath. The resin film can be stretched uniaxially by providing a peripheral speed difference between the clamping rollers arranged in the dyeing bath or before and after the dyeing bath.

Even in the dyeing step, in order to remove wrinkles from the resin film, as in the swelling treatment step, the resin film can be transported while using a guide roller with a spreading function such as a spreading roller, a spiral roller, or a convex roller, or other spreading devices such as a cross guide roller, a bending roller, and a tenter clip. Another means to suppress the occurrence of wrinkles is to apply a stretching treatment in the same manner as the swelling treatment.

(Cross-linking extension step)

The crosslinking and stretching step is a step of immersing the resin film dyed in the dyeing step in a treatment bath (crosslinking bath) containing a crosslinking agent and stretching it in the crosslinking bath. The water resistance of the resin film can be improved by the crosslinking treatment. The crosslinking and stretching step can be implemented by stretching the resin film while transporting it along a film transport path constructed by a clamping roller and a guide roller arranged in the crosslinking bath. The stretching treatment performed in the crosslinking and stretching step is as described above. The stretching treatment performed in the crosslinking and stretching step is preferably a stretching treatment that utilizes the peripheral speed difference between the clamping rollers and the clamping rollers to perform uniaxial stretching in the transport direction (length direction).

As the crosslinking liquid, a solution obtained by dissolving a crosslinking agent in a solvent can be used. Examples of the crosslinking agent include boric acid, borax and other boron compounds, or glyoxal, glutaraldehyde and the like. One or more of these can be used. As the solvent, for example, water can be used, but an organic solvent that is compatible with water can be further contained. The concentration of the crosslinking agent in the crosslinking liquid is not limited thereto, but is preferably in the range of 1 mass % to 20 mass %, and more preferably in the range of 6 mass % to 15 mass %.

The crosslinking liquid may be an aqueous solution containing, for example, 1 to 10 parts by mass of boric acid relative to 100 parts by mass of water. When the dichroic pigment contained in the dyeing liquid is iodine, the crosslinking liquid preferably contains, in addition to boric acid, an iodide, the amount of which may be set to, for example, 1 to 30 parts by mass relative to 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. It may contain more than two kinds of iodides. It may coexist with compounds other than iodides, such as sodium thiosulfate, potassium sulfite, sodium sulfate, etc. It may coexist with nitrates. Nitrates may include at least one selected from the group consisting of aluminum nitrate, copper nitrate, sodium nitrate, potassium nitrate, zinc nitrate, and magnesium nitrate. It is preferred that the nitrates include zinc nitrate.

In the crosslinking extension step, the concentration of boric acid and iodide in the crosslinking solution and the temperature of the crosslinking solution can be appropriately changed according to its purpose. The crosslinking solution can be, for example, an aqueous solution having a concentration of boric acid/iodide/water = 3 to 10/1 to 20/100 in terms of mass ratio. As required, other crosslinking agents can be used to replace boric acid, and boric acid and other crosslinking agents can also be used in combination. The temperature of the crosslinking bath when the resin film is immersed is usually 50° C. to 70° C., preferably 53° C. to 65° C., and the immersion time of the resin film is usually 30 seconds to 600 seconds, preferably 40 seconds to 300 seconds, and more preferably 60 seconds to 200 seconds. Furthermore, when the dyeing step and the cross-linking and stretching step are sequentially applied to the pre-stretched resin film before the swelling step, the temperature of the cross-linking bath is usually above 50°C and below 85°C, preferably above 55°C and below 80°C.

(Coloring step)

The color-correcting step is a process for adjusting the color of the resin film after the cross-linking and stretching step. The color-correcting step is a process that is performed on the resin film after the cross-linking and stretching step without accompanying the stretching process. The color-correcting step can be performed by immersing the resin film after the cross-linking and stretching step in a color-correcting bath (color-correcting liquid contained in a color-correcting tank) for a predetermined time and then pulling it out, or by spraying the color-correcting liquid, etc.

The color-correcting solution may be an aqueous solution containing, for example, 1 to 10 parts by mass of boric acid relative to 100 parts by mass of water. When the dichroic pigment contained in the dyeing solution is iodine, the color-correcting solution preferably contains, in addition to boric acid, an iodide, and the amount thereof may be set to, for example, 1 part by mass or more and 30 parts by mass or less relative to 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. Two or more iodides may also be contained. Furthermore, the color-correcting solution may coexist with compounds other than iodides, such as sodium thiosulfate, potassium sulfite, sodium sulfate, etc. Furthermore, the color-correcting solution may coexist with nitrates. The nitrates may include at least one selected from the group consisting of aluminum nitrate, copper nitrate, sodium nitrate, potassium nitrate, zinc nitrate, and magnesium nitrate. The nitrate preferably comprises zinc nitrate.

In the color-replenishing solution, for example, when iodine is used as a dichroic pigment, the concentration can be boric acid/iodide/water = 1 to 5/3 to 30/100 in terms of mass ratio. The temperature of the color-replenishing bath when immersing the resin film is usually above 10°C and below 45°C, and the immersion time of the resin film is usually above 1 second and below 300 seconds, preferably above 2 seconds and below 100 seconds.

The coloring step can be performed multiple times, usually 2 to 5 times. At this time, the composition and temperature of each coloring bath used can be the same or different as long as they are within the above range.

(Washing step)

The cleaning step is performed to remove the resin film after the cross-linking and extension step, or to remove excess boric acid or iodine attached to the resin film after the color touch-up step when the color touch-up step is performed. The cleaning step can be performed by, for example, immersing the resin film after the cross-linking and extension step or the color touch-up step in a cleaning bath (cleaning liquid contained in a cleaning tank), or spraying the cleaning liquid as a spray. The cleaning step can be performed by immersion and spraying.

The temperature of the cleaning solution in the cleaning step is usually above 2°C and below 40°C, and the immersion time of the resin film in the cleaning solution is usually above 2 seconds and below 120 seconds.

Even in the cleaning step, for the purpose of removing wrinkles and conveying the resin film at the same time, a guide roller having a widening function such as a widening roller, a spiral roller, or a convex roller, or other widening devices such as a cross guide roller, a bending roller, and a tenter clip can be used. In addition, in order to suppress the occurrence of wrinkles during the film cleaning process, a stretching process can be applied.

(Drying step)

The drying step is a step of drying the resin film after the crosslinking and extension step, the coloring step, or the washing step. The drying method of the resin film is not particularly limited, but can be performed using, for example, a drying furnace. The drying furnace can be, for example, equipped with a hot air dryer. The drying temperature is, for example, 30°C to 100°C, and the drying time is, for example, 30 seconds to 600 seconds. The treatment of drying the resin film can be performed using a far infrared heater.

(Polarizing plate)

The polarizing plate is formed by laminating a protective film on one or both sides of the polarizing element. The polarizing element and the protective film are preferably laminated with a bonding layer between them. The polarizing plate can be a long strip polarizing plate, and its length can be more than 300m and less than 5000m.

Examples of the protective film include: a film made of acetyl cellulose resins such as triacetyl cellulose or diacetyl cellulose; a film made of polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; a polycarbonate resin film, a cycloolefin resin film; an acrylic resin film; and a film made of a chain olefin resin such as a polypropylene resin.

In order to improve the adhesion between the polarizing film and the protective film, the bonding surface of the polarizing element and/or the protective film can be subjected to surface treatments such as corona treatment, flame treatment, plasma treatment, UV irradiation, primer coating treatment, and saponification treatment.

The bonding layer between the polarizing film and the protective film can be formed by using an adhesive or a sticking agent. Examples of adhesives include: UV-curable adhesives, active energy ray-curable adhesives, aqueous solutions of polyvinyl alcohol resins, or aqueous solutions containing crosslinking agents, such as water-based adhesives such as urethane emulsion adhesives. Zinc compounds such as zinc nitrate can be added to water-based adhesives. UV-curable adhesives can be a mixture of an acrylic compound and a photo-radical polymerization initiator, or a mixture of an epoxy compound and a photo-cation polymerization initiator. In addition, cationically polymerizable epoxy compounds and radically polymerizable acrylic compounds may be used together, and photocationic polymerization initiators and photoradical polymerization initiators may be used together as initiators.

Polarizing plates can be used in image display devices. Image display elements used in image display devices include, for example, liquid crystal display elements, organic EL display elements, etc. When constructing a liquid crystal display device, the polarizing plate can be configured and used on the viewing side, can be configured and used on the backlight side, or can be used on both the viewing side and the backlight side. Display devices can be used for mobile devices such as televisions, personal computers, mobile phones or tablet terminals, and for in-vehicle use. In-vehicle uses include, for example, display devices such as navigation devices, speedometers, air conditioning touch panels, back monitors and rearview monitors, etc.

[Implementation example]

The following presents embodiments to more specifically illustrate the present invention, but the present invention is not limited to these examples.

[Determination of time t in Example 1]

According to the sequence of Example 1, a resin film (width 14.4 mm) was prepared for the swelling step and the dyeing step. The resin film after the dyeing step was immersed in the crosslinking bath used in the crosslinking and stretching step of Example 1, and the change in the width of the resin film was measured every 10 seconds from the start of the immersion. This measurement was performed on 4 resin films. Even in any of the resin films, since the width of the resin film became a constant width of 13.5 mm or 13.6 mm after 30 seconds (0.5 min) from the start of the immersion, it was judged that the shrinkage of the resin film was saturated, and the time t of the above formula (1) and formula (2) was set to 0.5 min.

[Implementation Example 1]

A resin film made of a 45μm thick long polyvinyl alcohol resin [trade name "VF-PE#4500" manufactured by KURARAY Co., Ltd., saponification degree 99.9 mol% or more] was immersed in a swelling bath composed of pure water at a temperature of 23°C for 110 seconds, and uniaxially stretched to 2.1 times in the transport direction of the resin film (swelling step). Thereafter, the film pulled out from the swelling bath was immersed in a dyeing bath at a temperature of 23°C composed of a dyeing solution containing iodine with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio) for 163 seconds, and uniaxially stretched to 1.22 times in the transport direction of the resin film (dyeing step).

Then, the film pulled out from the dyeing bath was immersed in a crosslinking bath composed of a crosslinking liquid of potassium iodide/boric acid/water at a temperature of 59°C for 92 seconds, and a uniaxial stretching treatment in the transport direction of the resin film was performed (crosslinking stretching step). As for the crosslinking bath, a bath in which the first clamping roller, the second clamping roller, and the third clamping roller are arranged in sequence from the upstream side of the transport direction is used, and the uniaxial stretching treatment is performed between the first clamping roller and the second clamping roller (the first stretching treatment), and the uniaxial stretching treatment is performed between the second clamping roller and the third clamping roller (the second stretching treatment).

The distance X1(1) of the resin film conveyance in the first stretching treatment (the distance of the resin film conveyance between the first clamping roller and the second clamping roller) is set to a value calculated by multiplying the above-determined time t by a set value of 0.4 and the resin film conveyance speed v in the crosslinking stretching step (X1(1)=v×0.4t). The distance X2(1) of the resin film conveyance from the start of immersion in the crosslinking bath to the end of the first stretching treatment is set to v×0.46t. In addition, the transport distance of the resin film in the second stretching treatment (the transport distance of the resin film between the second clamping roller and the third clamping roller) Xf(1) is set to 7.0 times the distance X1(1) and 6.1 times the distance X2(1). Rv2 is set to Rvmin+2.7m/min.

Afterwards, drying was performed at a temperature of 38°C (drying step), and a polarizer with a thickness of 18 μm was obtained by adsorbing and orienting iodine on the polyvinyl alcohol resin.

For the polarizer after the drying step, it was confirmed that the length (width) in the direction orthogonal to the stretching direction when 100,000 meters was produced had a change (standard deviation), which was 2.9mm, and had a stable width in the length direction.

[Determination of time t in Example 2]

According to the sequence of Example 2, a resin film (width 14.4 mm) was prepared for the swelling step and the dyeing step. The resin film after the dyeing step was immersed in the crosslinking bath used in the crosslinking and stretching step of Example 2, and the change in the width of the resin film was measured every 10 seconds from the start of the immersion. This measurement was performed on 4 resin films. Even in any of the resin films, since the width of the resin film became a constant width of 13.4 mm or 13.5 mm after 20 seconds (0.33 min) from the start of the immersion, it was judged that the shrinkage of the resin film was saturated, and the time t of the above formula (1) and formula (2) was set to 0.33 min.

[Example 2]

A resin film made of a 45 μm thick strip of polyvinyl alcohol resin [trade name "VF-PE#4500" manufactured by KURARAY Co., Ltd., saponification degree 99.9 mol% or more] was immersed in a swelling bath of pure water at a temperature of 21.5°C for 90 seconds, and the resin film was uniaxially stretched to 2.3 times in the conveying direction (swelling step). Afterwards, the film pulled out from the swelling bath was immersed in a dyeing bath composed of an iodine-containing dyeing solution with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio) at a temperature of 23°C for 180 seconds, and the film was uniaxially stretched to 1.13 times in the transport direction of the resin film (dyeing step).

Then, the film pulled out from the dyeing bath was immersed in a crosslinking bath composed of a crosslinking liquid of potassium iodide/boric acid/water at a temperature of 59°C for 62 seconds, and a uniaxial stretching treatment was performed in the transport direction of the resin film (crosslinking stretching step). As for the crosslinking bath, a bath in which the first clamping roller, the second clamping roller, and the third clamping roller are arranged in sequence from the upstream side of the transport direction, and a uniaxial stretching treatment is performed between the first clamping roller and the second clamping roller (first stretching treatment), and a uniaxial stretching treatment is performed between the second clamping roller and the third clamping roller (second stretching treatment).

The distance X1(2) of the resin film conveyance in the first stretching treatment (the distance of the resin film conveyance between the first clamping roller and the second clamping roller) is set to the value calculated by multiplying the above-determined time t by 0.43 times and the resin film conveyance speed v in the crosslinking stretching step (X1(2)=v×0.43t). The distance X2(1) of the resin film conveyance from the start of immersion in the crosslinking bath to the end of the first stretching treatment is set to v×0.49t. In addition, the transport distance of the resin film in the second stretching treatment (the transport distance of the resin film between the second clamping roller and the third clamping roller) Xf(2) is set to 6.8 times the distance X1(2) and 6.0 times the distance X2(2). Rv2 is manufactured while being controlled to vary between Rvmin+2.3m/min and Rvmin+3.3m/min.

Afterwards, drying was performed at a temperature of 38°C (drying step), and a polarizer with a thickness of 18 μm was obtained by adsorbing and orienting iodine on the polyvinyl alcohol resin.

For the polarizer after the drying step, it was confirmed that the length (width) in the direction orthogonal to the stretching direction when 100,000 meters was produced had a change (standard deviation), which was 0.8mm, and had a stable width along the length direction.

The polarizer prepared above was laminated with saponified cellulose acetic acid ester film TD40 (manufactured by Fuji Film Co., Ltd., thickness 40 μm) on both sides by a water-based adhesive and dried to prepare a long strip polarizing plate. At this time, the polarizer was not subjected to a slicing process to remove the ends in the width direction. 1000 m of the long strip polarizing plate prepared in this way was rolled into a roll to obtain a roll. The difference between the width of the polarizer at the start of the polarizing plate roll (1m in the length direction from the end of the polarizing plate roll) and the width of the polarizer at the end of the polarizing plate roll (1m in the length direction from the end of the polarizing plate roll) is 0.3mm in absolute value. The appearance of the polarizing plate roll is good, and no chip debris is observed.

[Determination of time t in Comparative Examples 1 and 2]

According to the order of Comparative Examples 1 and 2, a resin film (width 14.4 mm) was prepared for the swelling step and the dyeing step. The resin film after the dyeing step was immersed in the crosslinking bath used in the crosslinking and stretching step of Comparative Examples 1 and 2, and the change in the width of the resin film was measured every 10 seconds from the start of immersion. This measurement was performed on 4 resin films. Even in any of the resin films, since the width of the resin film became a constant width of 13.5 mm or 13.6 mm after 30 seconds (0.5 min) from the start of immersion, it was judged that the shrinkage of the resin film was saturated, and the time t of the above formula (1) and formula (2) was set to 0.5 min.

[Comparison Example 1]

A resin film formed of a 45μm-thick strip of polyvinyl alcohol resin [trade name "VF-PE#4500" manufactured by KURARAY Co., Ltd., saponification degree 99.9 mol% or more] was immersed in a swelling bath composed of pure water at a temperature of 23°C for 110 seconds, and the resin film was uniaxially stretched to 2.1 times in the transport direction (swelling step). Thereafter, the film pulled out from the swelling bath was immersed in a dyeing bath composed of iodine-containing dyeing liquid with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio) at a temperature of 23°C for 163 seconds, and the resin film was uniaxially stretched to 1.22 times in the transport direction (dyeing step).

Then, the film pulled out from the dyeing bath was immersed in a crosslinking bath composed of a crosslinking liquid of potassium iodide/boric acid/water at a temperature of 59°C for an immersion time of 92 seconds, and a uniaxial stretching treatment in the transport direction of the resin film was performed (crosslinking stretching step). As for the crosslinking bath, a bath in which the first clamping roller, the second clamping roller, and the third clamping roller are arranged in sequence from the upstream side in the transport direction is used, and the uniaxial stretching treatment is performed between the first clamping roller and the second clamping roller (the first stretching treatment), and the uniaxial stretching treatment is performed between the second clamping roller and the third clamping roller (the second stretching treatment).

The distance X1(c1) of the resin film conveying in the first stretching treatment (the distance of the resin film conveying between the first clamping roller and the second clamping roller) is set to a value calculated by multiplying the time t determined above by 0.2 times and the conveying speed v of the resin film in the crosslinking stretching step (X1(c1)=v×0.2t). The distance X2(c1) of the resin film conveying from the beginning of the immersion of the resin film in the crosslinking bath to the end of the first stretching treatment is set to v×0.26t. In addition, the transport distance of the resin film in the second stretching treatment (the transport distance of the resin film between the second clamping roller and the third clamping roller) Xf(c1) is set to 15.0 times the distance X1(c1) and 11.5 times the distance X2(c1). Rv2 is set to Rvmin+2.7m/min.

Afterwards, drying was performed at a temperature of 38°C (drying step), and a polarizer with a thickness of 18 μm was obtained by adsorbing and orienting iodine on the polyvinyl alcohol resin.

For the polarizer after the drying step, it was confirmed that the length (width) in the direction orthogonal to the stretching direction when 100,000 meters was produced had a change (standard deviation), and the change exceeded 3mm, and it was impossible to produce a stable width in the length direction.

[Comparison Example 2]

A resin film formed of a 45μm-thick strip of polyvinyl alcohol resin [trade name "VF-PE#4500" manufactured by KURARAY Co., Ltd., saponification degree 99.9 mol% or more] was immersed in a swelling bath composed of pure water at a temperature of 23°C for 110 seconds, and the resin film was uniaxially stretched to 2.1 times in the transport direction (swelling step). Thereafter, the film pulled out from the swelling bath was immersed in a dyeing bath composed of iodine-containing dyeing liquid with a mass ratio of iodine/boric acid/water of 1.0/0.5/100 at a temperature of 23°C for 163 seconds, and the resin film was uniaxially stretched to 1.22 times in the transport direction (dyeing step).

Then, the film pulled out from the dyeing bath was immersed in a crosslinking bath composed of a crosslinking liquid of potassium iodide/boric acid/water at a temperature of 59°C for an immersion time of 92 seconds, and a uniaxial stretching treatment was performed in the transport direction of the resin film (crosslinking stretching step). For the crosslinking bath, a bath in which the first clamping roller, the second clamping roller, and the third clamping roller are arranged in sequence from the upstream side in the transport direction is used, and the uniaxial stretching treatment is performed between the first clamping roller and the second clamping roller (the first stretching treatment), and the uniaxial stretching treatment is performed between the second clamping roller and the third clamping roller (the second stretching treatment).

The distance X1(c2) of the resin film conveying distance in the first stretching treatment (the distance of the resin film conveying distance between the first clamping roller and the second clamping roller) is set to a value calculated by multiplying the above-determined time t by 1.4 times and the resin film conveying speed v in the crosslinking stretching step (X1(c2)=v×1.4t). The distance X2(c2) of the resin film conveying distance from the start of the resin film immersion in the crosslinking bath to the end of the first stretching treatment is set to v×1.67t. In addition, the transport distance of the resin film in the second stretching treatment (the transport distance of the resin film between the second clamping roller and the third clamping roller) Xf(c2) is set to 1.3 times the distance X1(c2) and 1.2 times the distance X2(c2). Rv2 is set to Rvmin+2.7m/min.

Afterwards, drying was performed at a temperature of 38°C (drying step), and a polarizer with a thickness of 18 μm was obtained by adsorbing and orienting iodine on the polyvinyl alcohol resin.

For the polarizer after the drying step, it was confirmed that the length (width) in the direction orthogonal to the stretching direction when 100,000 meters was produced had a change (standard deviation), and the change exceeded 3mm, and it was impossible to produce a stable width in the length direction.

1: Resin film

10: Cross-linking bath

11: 1st clamping roller

12: Second clamping roller

13: The third clamping roller

X1,X2,Xf: distance

Claims (11)

A method for manufacturing a polarizing element is to adsorb and orient a dichroic pigment on a resin film formed of a polyvinyl alcohol-based resin, and includes the following steps: The swelling step is to swell the aforementioned resin film while transporting it; The dyeing step is to dye while transporting the aforementioned resin film after the aforementioned swelling step; and The crosslinking and stretching step is to transport the aforementioned resin film after the aforementioned dyeing step while immersing it in a crosslinking bath, and stretch it in the transporting direction in the aforementioned crosslinking bath; The aforementioned cross-linking extension step is a step of performing extension treatment in multiple stages, and the first stage of the aforementioned extension treatment is performed in a manner that satisfies the relationship of the following formula (1); v×0.3t≦X1≦v×1.2t (1) In formula (1), X1 represents the transport distance of the aforementioned resin film from the beginning to the end of the aforementioned first stage stretching process [m]; v represents the transport speed of the aforementioned resin film in the aforementioned cross-linking and stretching step [m/min]; t represents the time [min] required for the shrinkage of the resin film to reach saturation when the resin film is immersed in the cross-linking bath used in the elongation treatment of the first stage after the dyeing step. A method for manufacturing a polarizing element is to adsorb and orient a dichroic pigment on a resin film formed of a polyvinyl alcohol-based resin, and includes the following steps: The swelling step is to swell the aforementioned resin film while transporting it; The dyeing step is to dye while transporting the aforementioned resin film after the aforementioned swelling step; and The crosslinking and stretching step is to transport the aforementioned resin film after the aforementioned dyeing step while immersing it in a crosslinking bath and stretching it in the transporting direction in the aforementioned crosslinking bath; The aforementioned cross-linking extension step is a step of performing extension treatment in multiple stages, and the first stage of the aforementioned extension treatment is performed in a manner that satisfies the relationship of the following formula (2); v×0.4t≦X2≦v×1.2t (2) In formula (2), X2 represents the transport distance [m] of the resin film from the start of immersion of the resin film in the crosslinking bath to the end of the first stage of stretching treatment in the crosslinking and stretching step; v represents the transport speed of the aforementioned resin film in the aforementioned cross-linking and stretching step [m/min]; t represents the time [min] required for the shrinkage of the resin film to reach saturation when the resin film is immersed in the cross-linking bath used in the elongation treatment of the first stage after the dyeing step. The manufacturing method of the polarizer as described in claim 2, wherein the aforementioned cross-linking and extension step further satisfies the relationship of the following formula (1); v×0.3t≦X1≦v×1.2t (1) In formula (1), X1 represents the transport distance of the aforementioned resin film from the beginning to the end of the aforementioned first stage stretching process [m]; v and t are synonymous with the above. A method for manufacturing a polarizer as described in claim 1 or 3, wherein when the transport distance of the resin film from the beginning to the end of the stretching treatment in the first stage is set to X1, In the aforementioned cross-linking stretching step, the transport distance of the aforementioned resin film from the start to the end of at least one stretching treatment in the stretching treatment performed after the aforementioned first stage is more than 2 times and less than 10 times the aforementioned distance X1. A method for manufacturing a polarizer as described in any one of claims 1 to 3, wherein in the aforementioned crosslinking and stretching step, the aforementioned first stage stretching treatment and the subsequent second stage stretching treatment are performed in the same crosslinking bath. A method for manufacturing a polarizer as described in claim 5, wherein: In the aforementioned cross-linking bath, the first clamping roller, the second clamping roller, and the third clamping roller are sequentially arranged from the upstream side in the conveying direction. The aforementioned first stage of stretching is performed between the aforementioned first clamping roller and the aforementioned second clamping roller. The aforementioned second stage of stretching is performed between the aforementioned second clamping roller and the aforementioned third clamping roller. The manufacturing method of the polarizer as described in claim 6, wherein the second clamping roller is movably arranged in such a manner that the conveying distance of the resin film between the first clamping roller and the second clamping roller is adjustable. A method for manufacturing a polarizer as described in claim 6, wherein the rotation speed of the first clamping roller is set to Rv1 [m/min], and the rotation speed of the third clamping roller is set to Rv3 [m/min], when the width of the resin film becomes the smallest after the cross-linking and stretching step, the rotation speed of the second clamping roller is set to Rvmin [m/min], The rotation speed Rv2[m/min] of the aforementioned second clamping roller is within the range of Rvmin±10[m/min]. The manufacturing method of the polarizer as described in claim 8, wherein the cross-linking stretching step is to perform the stretching process while changing the rotation speed Rv2 [m/min] of the second clamping roller. A method for manufacturing a polarizing plate comprises the following steps: The step of obtaining a polarizer by the manufacturing method of a polarizer as described in any one of claims 1 to 3; and The polarizer obtained in the step of obtaining the polarizer is not cut in the conveying direction, but a protective film is laminated on one or both sides of the polarizer. A polarizing plate roll is formed by winding the polarizing plate into a roll, and The aforementioned polarizing plate comprises a polarizing element and a protective film laminated on one or both sides of the aforementioned polarizing element; The difference between the width of the polarizer at the start of the winding of the roll and the width of the polarizer at the end of the winding of the roll is 0.1 mm or more and 3 mm or less in absolute value.

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