WO2023176716A1

WO2023176716A1 - Method for manufacturing polarizer

Info

Publication number: WO2023176716A1
Application number: PCT/JP2023/009269
Authority: WO
Inventors: 邦智齋藤; 成志中里; 寿和松本
Original assignee: 住友化学株式会社
Priority date: 2022-03-16
Filing date: 2023-03-10
Publication date: 2023-09-21
Also published as: JP2023138399A

Abstract

Provided is a method for manufacturing a polarizer in which variation in length in a direction orthogonal to a stretching direction is suppressed.

Description

Polarizer manufacturing method

The present invention relates to a method for manufacturing a polarizer, and further relates to a method for manufacturing a polarizing plate and a roll body of a polarizing plate.

Liquid crystal display devices (LCDs) are widely used not only in liquid crystal televisions, but also in personal computers, mobile terminals such as mobile phones, and in-vehicle applications such as car navigation systems. Typically, a liquid crystal display device has a liquid crystal panel with polarizing plates including polarizers attached to both sides of a liquid crystal cell, and displays images by controlling light from a backlight with the liquid crystal panel. . In recent years, organic EL display devices, like liquid crystal display devices, have been widely used in televisions, mobile terminals such as mobile phones, and in-vehicle applications such as car navigation systems. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and viewed as a mirror surface, a circularly polarizing plate (a polarizer and a λ/4 plate) is installed on the viewing side surface of the image display element. ) may be placed.

Polarizers are usually manufactured by subjecting a resin film made of polyvinyl alcohol-based resin to swelling treatment, dyeing treatment, crosslinking treatment, and stretching treatment. It is known that in manufacturing a polarizer, a stretching treatment is performed while a resin film is immersed in a crosslinking bath (for example, Patent Document 1, etc.).

International Publication No. 2017/138551

When a resin film is stretched in the length direction, a phenomenon called neck-in occurs in which the resin film contracts in the width direction (direction perpendicular to the stretching direction). It was discovered that when a resin film is stretched in the length direction in a crosslinking bath, the width of the stretched resin film varies in the length direction, making it impossible to obtain a polarizer with a stable width in the length direction. It was done.

An object of the present invention is to provide a method for manufacturing a polarizer, a method for manufacturing a polarizing plate, and a roll body of a polarizing plate, in which variations in length in the direction perpendicular to the stretching direction are suppressed.

The present invention provides the following method for manufacturing a polarizer, method for manufacturing a polarizing plate, and roll body of a polarizing plate.
[1] A method for producing a polarizer in which a dichroic dye is adsorbed and oriented on a resin film made of polyvinyl alcohol resin as a forming material,
a swelling step of swelling the resin film while conveying it;
a dyeing step of dyeing the resin film after the swelling step while conveying it;
A crosslinking and stretching step of immersing the resin film after the dyeing step in a crosslinking bath while transporting it and stretching it in the transporting direction in the crosslinking bath,
The cross-linking and stretching process is a process in which stretching is performed in multiple stages, and the first stage of the stretching is performed so as to satisfy the following formula (1). , a method for manufacturing a polarizer.
v×0.3t≦X1≦v×1.2t (1)
[In formula (1),
X1 represents the distance [m] that the resin film is conveyed from the start to the completion of the first-stage stretching process.
v represents the conveyance speed [m/min] of the resin film in the crosslinking and stretching step.
t represents the time [min] required until the shrinkage of the resin film is saturated when the resin film after the dyeing process is immersed in the crosslinking bath used in the first stage stretching process. ]
[2] A method for producing a polarizer in which a dichroic dye is adsorbed and oriented on a resin film made of polyvinyl alcohol resin as a forming material, comprising:
a swelling step of swelling the resin film while conveying it;
a dyeing step of dyeing the resin film after the swelling step while conveying it;
A crosslinking and stretching step of immersing the resin film after the dyeing step in a crosslinking bath while transporting it and stretching it in the transporting direction in the crosslinking bath,
The cross-linking and stretching process is a process in which a stretching process is performed in multiple stages, and the first stage of the stretching process is performed so as to satisfy the relationship of the following formula (2). , a method for manufacturing a polarizer.
v×0.4t≦X2≦v×1.2t (2)
[In formula (2),
X2 represents the distance [m] that the resin film is transported from the start of immersion of the resin film in the crosslinking bath to the completion of the first stage stretching process in the crosslinking/stretching process.
v represents the conveyance speed [m/min] of the resin film in the crosslinking and stretching step.
t represents the time [min] required until the shrinkage of the resin film is saturated when the resin film after the dyeing process is immersed in the crosslinking bath used in the first stage stretching process. ]
[3] The method for producing a polarizer according to [2], wherein the crosslinking and stretching step further satisfies the relationship of formula (1) below.
v×0.3t≦X1≦v×1.2t (1)
[In formula (1),
X1 represents the distance [m] that the resin film is conveyed from the start to the completion of the first-stage stretching process.
v and t represent the same meanings as above. ]
[4] When the distance that the resin film is conveyed from the start to the completion of the first-stage stretching process is defined as X1,
In the crosslinking and stretching step, the distance that the resin film is conveyed from the start to the completion of at least one of the stretching treatments performed after the first stage is at least 2 times and no more than 10 times the distance X1. The method for producing a polarizer according to [1] or [3], which is
[5] The method according to any one of [1] to [4], wherein in the cross-linking and stretching step, the first-stage stretching treatment and the subsequent second-stage stretching treatment are performed in the same cross-linking bath. Method of manufacturing polarizer.
[6] In the crosslinking bath, a first nip roll, a second nip roll, and a third nip roll are arranged in order from the upstream side in the transport direction,
The first stage stretching process is performed between the first nip roll and the second nip roll,
The method for manufacturing a polarizer according to [5], wherein the second-stage stretching process is performed between the second nip roll and the third nip roll.
[7] The polarized light according to [6], wherein the second nip roll is movably provided so that the conveyance distance of the resin film between the first nip roll and the second nip roll can be adjusted. Method of producing children.
[8] When the rotational speed of the first nip roll is Rv1 [m/min] and the rotational speed of the third nip roll is Rv3 [m/min], the width of the resin film after the crosslinking and stretching step is The rotational speed of the second nip roll when Rvmin [m
/min],
The method for manufacturing a polarizer according to [6] or [7], wherein the rotation speed Rv2 [m/min] of the second nip roll is within the range of Rvmin±10 [m/min].
[9] The method for producing a polarizer according to [8], wherein in the crosslinking and stretching step, the stretching process is performed while varying the rotational speed Rv2 [m/min] of the second nip roll.
[10] Obtaining a polarizer by the method for producing a polarizer according to any one of [1] to [9];
A method for manufacturing a polarizing plate, comprising the step of laminating a protective film on one or both sides of the polarizer without slitting the polarizer obtained in the step of obtaining the polarizer in the transport direction.
[11] A roll body of a polarizing plate obtained by winding a polarizing plate into a roll shape,
The polarizing plate has a polarizer and a protective film laminated on one or both sides of the polarizer,
A roll body of a polarizing plate, wherein the difference between the width of the polarizer at a winding start portion of the roll body and the width of the polarizer at a winding end portion of the roll body is 0.1 mm or more and 3 mm or less in absolute value. .

According to the method for manufacturing a polarizer of the present invention, it is possible to manufacture a polarizer in which variation in length in the direction orthogonal to the stretching direction is suppressed.

FIG. 2 is a schematic diagram for explaining a crosslinking and stretching step in a method for manufacturing a polarizer according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

(Manufacturing method of polarizer)
FIG. 1 is a schematic diagram for explaining a crosslinking and stretching step in a method for manufacturing a polarizer according to an embodiment of the present invention.

The polarizer of this embodiment is a polarizing film in which a dichroic dye is adsorbed and oriented on a resin film 1 made of polyvinyl alcohol resin.

The method for manufacturing a polarizer of this embodiment is a method for manufacturing a polarizer while conveying the resin film 1,
a swelling step of swelling the resin film 1 while conveying it;
a dyeing step of dyeing the resin film 1 after the swelling step while conveying it;
The resin film 1 after the dyeing process is immersed in a crosslinking bath 10 while being conveyed, and is stretched in the conveyance direction in the crosslinking bath 10.

In the method for manufacturing a polarizer, for example, the resin film 1 is unrolled from a roll body in which a long resin film 1 is wound into a roll, and while being conveyed, the above-mentioned swelling step, dyeing step, and crosslinking and stretching step are carried out. I do. The resin film 1 can be conveyed using a known conveyance means, and is carried along a film conveyance path made up of a combination of a nip roll made up of a pair of rolls, a guide roll made up of one roll, etc. It is preferable to do so.

The method for manufacturing a polarizer further includes a complementary color step of performing color adjustment treatment on the resin film 1 after the crosslinking and stretching step using a complementary color solution, a washing step of washing the resin film 1 using a cleaning solution, a drying step of drying the resin film 1, and the like. Good too. Details of each step will be described later.

The polarizer obtained by processing in each of the above steps may be sequentially wound around a take-up roll to form a roll, or it may be used as a polarizing plate as described below without being wound. It can also be used in a manufacturing method.

In the method for manufacturing a polarizer, the crosslinking and stretching step is started by immersing the resin film 1 in the crosslinking bath 10. The crosslinking and stretching process is a process of performing multi-stage stretching in the crosslinking bath 10, and the first stage of the stretching process is performed using the following formula (1) and formula (2). Do this so that at least one of the relationships is satisfied. Hereinafter, the n-th stretching process performed in the crosslinking and stretching process may be referred to as "n-th stretching process".
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 distance [m] that the resin film 1 is transported from the start to the completion of the first stretching process.
X2 represents the distance [m] that the resin film 1 is transported from the start of immersion of the resin film 1 in the crosslinking bath 10 to the completion of the first stretching process in the crosslinking and stretching process.
v represents the conveyance speed [m/min] of the resin film 1 in the crosslinking and stretching process.
t represents the time [min] required until the shrinkage of the resin film 1 is saturated when the resin film 1 after the dyeing process is immersed in the crosslinking bath 10 used for the first stretching process. ]

The multi-stage stretching process performed in the cross-linking and stretching process may be performed in two or more stages, may be three or more stages, may be four or more stages, and is usually 10 stages or less, and 8 stages or less. There may be five levels or less. It is preferable that the crosslinking and stretching process is a process of performing a two-stage or three-stage stretching process.

The distance X1 in formula (1) may be greater than or equal to v x 0.4t [m], may be greater than or equal to v x 0.5t [m], and may be greater than or equal to v x 0.6t [m]. Alternatively, it may be less than or equal to v×1.1t [m], or may be less than or equal to v×1.0t [m]. When the distance X1 is less than v x 0.3 t [m], the introduction of the crosslinked structure into the polyvinyl alcohol resin and the neck-in of the resin film 1 proceed at the same time in the second and subsequent stretching process. Width stability tends to decrease. Furthermore, if the distance X1 exceeds v x 1.2t [m], crosslinking of the polyvinyl alcohol resin will progress too much, making it difficult to adjust the neck-in in the second and subsequent stretching processes. , the resin film 1 is likely to be cut.

The distance X2 in formula (2) may be greater than or equal to v x 0.5t [m], may be greater than or equal to v x 0.6t [m], and may be greater than or equal to v x 0.7t [m]. Alternatively, it may be less than or equal to v×1.1t [m], or may be less than or equal to v×1.0t [m]. If the distance 1 is more likely to be cut.

The first stretching treatment in the crosslinking and stretching step may satisfy one or both of formula (1) and formula (2). When the first stretching process satisfies both formula (1) and formula (2), distance X1 may be smaller than distance X2, or may be the same as distance X2.

In the crosslinking and stretching step, a crosslinked structure is introduced into the polyvinyl alcohol resin that constitutes the resin film 1 by immersing the resin film 1 in a crosslinking bath 10. At this time, it is thought that shrinkage occurs in the resin film 1 due to the introduction of the crosslinked structure. The first stretching process is performed so as to satisfy at least one of Expression (1) and Expression (2). Therefore, in the step of performing the first stretching treatment, the resin film due to the introduction of the crosslinked structure is It is presumed that film 1 is shrinking. Moreover, in the second stretching process, only the contraction due to neck-in of the resin film 1 can be caused without substantially causing the contraction of the resin film 1 due to the introduction of the crosslinked structure. This makes it easier to control the length (width) of the resin film 1 in the width direction through the stretching treatments after the second stretching treatment, thereby suppressing variations in the width of the resin film 1 in the length direction and ensuring stable Polarizers having a width can be manufactured. Specifically, a polarizer having a stable width means that the variation (standard deviation) in the length (width) in the direction orthogonal to the stretching direction when manufactured for 100,000 m is 3 mm or less (preferably 1 mm or less). Refers to a certain polarizer.

Since the first stretching process is performed as described above, in the polarizer manufacturing method of this embodiment, the magnitude of neck-in occurring in the resin film 1 is adjusted by adjusting the stretching ratio after the second stretching process. This allows the resin film 1 to be adjusted to a desired width. The optical properties (particularly the degree of polarization) of the polarizer tend to improve as the neck-in that occurs in the resin film 1 increases. By performing the first stretching process as described above, a large neck-in can be caused in the resin film 1 by adjusting the stretching ratio in the second and subsequent stretching processes. Therefore, according to the method for manufacturing a polarizer of this embodiment, 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 1 m or more, may be 2 m or more, may be 3 m or more, and is usually 10 m or less. , 8 m or less, or 5 m or less. The distance X2 is not particularly limited as long as it satisfies the relationship of formula (2), but is usually 1 m or more, may be 2 m or more, may be 3 m or more, and is usually 10 m or less. , 8 m or less, or 5 m or less.

In this specification, the conveyance speed v [m/min] in formulas (1) and (2) is the conveyance speed vs [m/min] of the resin film 1 at the position where the first stretching process is started, and This is the average value of the transport speed ve [m/min] of the resin film 1 at the position where one stretching process is completed. That is, the conveyance speed v=(vs+ve)/2. For example, when performing the first stretching process between the first nip roll 11 and the second nip roll 12 shown in FIG. This is the speed at which The conveyance speed ve is the speed at which the resin film 1 is conveyed by the second nip roll 12 located on the downstream side in the conveyance direction.

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

The time t [min] in formulas (1) and (2) is the time required for the shrinkage of the resin film 1 to be saturated when the resin film 1 after the dyeing process is immersed in the crosslinking bath used in the first stretching process. It takes time. The time t can be determined as the time required for the length of the resin film 1 in the width direction to become constant after immersing the resin film 1 in the crosslinking bath used in the first stretching process. It can be determined by the method described.

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

The crosslinking and stretching step can be performed while transporting the resin film 1 in a crosslinking bath 10, as shown in FIG. For example, nip rolls are arranged in the crosslinking bath 10 depending on the number of stages of the stretching process performed in the crosslinking bath 10. In the crosslinking bath 10 shown in FIG. 1, a first nip roll 11, a second nip roll 12, and a third nip roll 13 are arranged in order from the upstream side in the transport direction. Thereby, in the crosslinking bath 10, the first stretching process can be performed between the first nip roll 11 and the second nip roll 12, and the second stretching process can be performed between the second nip roll 12 and the third nip roll 13. . At this time, the position of the first nip roll 11 becomes the starting position of the first stretching process. The position of the second nip roll 12 is the completion position of the first stretching process and the start position of the second stretching process. The position of the third nip roll 13 is the completion position of the second stretching process.

When performing the first stretching process in the crosslinking bath 10 shown in FIG. 1, the distance X1 is the distance over which the resin film 1 is transported between the position of the first nip roll 11 and the position of the second nip roll 12. The distance X2 is the distance that the resin film 1 is conveyed between the position where the resin film 1 is immersed in the crosslinking bath 10 and the position of the second nip roll 12. When the distance X1 and the distance X2 are the same, the first nip roll 11 is arranged so that the nip position of the first nip roll 11 is located at the position where the resin film 1 starts immersing in the crosslinking bath.

When performing the crosslinking and stretching process in the crosslinking bath 10 shown in FIG. It is preferable that it be movably provided. In this case, the installation positions of the first nip roll 11 and the third nip roll 13 are preferably fixed (immovable). Thereby, by adjusting the installation position of the second nip roll 12 in the crosslinking bath 10, the first stretching process can be performed so as to satisfy at least one of the above formulas (1) and (2).

When performing the crosslinking and stretching step in the crosslinking bath 10 shown in FIG. 1, it is preferable that the rotational speed Rv2 [m/min] of the second nip roll 12 satisfies the following formula (3). The rotation speed Rv2 here means the length of the resin film 1 conveyed by the second nip roll 12 per unit time.
Rvmin-10≦Rv2≦Rvmin+10 (3)
[In formula (3),
Rv2 represents the rotation speed [m/min] of the second nip roll 12.
Rvmin is the width of the resin film 1 after the crosslinking and stretching process, when the rotational speed of the first nip roll 11 is Rv1 [m/min] and the rotational speed of the third nip roll 13 is Rv3 [m/min]. It represents the rotational speed [m/min] of the second nip roll 12 when it becomes the minimum. ]
The rotation speed Rv1 means the length of the resin film 1 that the first nip roll 11 conveys per unit time, and the rotation speed Rv3 means the length of the resin film 1 that the third nip roll 13 conveys per unit time. means.

The rotational speed Rv2 of the second nip roll 12 is the rotational speed set when the rotational speed Rv1 of the first nip roll 11 and the rotational speed Rv3 of the third nip roll 13 are each fixed values. The time when the width of the resin film 1 after the crosslinking and stretching process is the minimum is the difference in the width of the resin film 1 before and after the crosslinking and stretching process (from the width of the resin film 1 before the crosslinking and stretching process to the width of the resin film 1 after the crosslinking and stretching process). This refers to the time when the value obtained by subtracting the width of the resin film 1) is at its maximum, and this is the time when the neck-in of the resin film 1 in the crosslinking and stretching process is at its maximum.

Rv2 may be Rvmin-8 [m/min] or more, Rvmin-6 [m/min] or more, Rvmin-5 [m/min] or more, and It may be Rvmin+8 [m/min] or less, it may be Rvmin+6 [m/min] or less, it may be Rvmin+5 [m/min] or less, or it may be Rvmin [m/min]. .

By performing the cross-linking and stretching process so as to satisfy formula (3), a large neck-in can be caused in the resin film 1 in the cross-linking and stretching process. This makes it easier to obtain a polarizer with excellent optical properties.

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

When the rotational speeds Rv1 and Rv3 are within the above range, the rotational speed Rv2 is preferably larger than the rotational speed Rv1 and smaller than the rotational speed Rv3, for example, it may be 4.0 m/min or more, 0 m/min or more, 6.0 m/min or more, 7.0 m/min or more, 30.0 m/min or less, 25 The speed may be .0 m/min or less, 20.0 m/min or less, or 15.0 m/min or less.

When performing the stretching process in multiple stages after the first stretching process, for example, performing the second stretching process and the third stretching process after the first stretching process, multiple stretching processes are performed after the first stretching process. In some cases, it is also a useful technique to adjust the rotational speeds of the second nip roll and the third nip roll in the same manner as Rv2 above.

In the manufacturing method of the present invention, the rotational speed Rv2 of the second nip roll in the crosslinking and stretching step may be controlled to be constant or may be varied during the period during which the resin film 11 is conveyed from the start of manufacturing of the polarizer to the completion of manufacturing. may be controlled. When varying the rotational speed Rv2, the rotational speed Rv2 may vary within the range of Rvmin ± 10 [m/min], and may vary within the range of Rvmin ± 8 [m/min]. , Rvmin±6 [m/min] or Rvmin±5 [m/min]. It is preferable to control the rotation speed Rv2 so that the variation (standard deviation) in the width of the polarizer is, for example, 3 mm or less, preferably 1 mm or less over the length of the polarizer. When the polarizer obtained by the manufacturing method of the present invention is used to obtain a roll of a polarizing plate, which will be described later, the width of the polarizer at the beginning of the roll and the width of the polarizer at the end of the roll are determined. It is preferable to control the rotation speed Rv2 so that the difference with the width is 3 mm or less in absolute value.

Although FIG. 1 shows a case where the first stretching process and the second stretching process are performed in the same crosslinking bath 10, the first stretching process and the second stretching process may be performed in different crosslinking baths. . Even when the first stretching treatment and the second stretching treatment are performed in separate crosslinking baths, it is preferable that the composition of the crosslinking liquid in each crosslinking bath and the type of crosslinking bath, such as the temperature of the crosslinking bath, are the same.

When the crosslinking/stretching step includes a stretching process after the third stretching process, the stretching process after the third stretching process may be performed in the same crosslinking bath 10 as the first stretching process and the second stretching process; may be carried out in a separate crosslinking bath.

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 1.01 times or more, may be 1.05 times or more, and may be 1.0 times or more. .1 times or more, and usually 3.0 times or less, 2.5 times or less, 2.0 times or less, 1.8 times or less. It's okay.

In the crosslinking and stretching process, the resin film 1 is transported from the start to the completion of the stretching process in at least one of the stretching processes after the second stretching process, which is a stretching process performed after the first stretching process. It is preferable that the distance Xf 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 may be twice or more of X1, may be three times or more, may be four times or more, and may be no more than 10 times X1, It may be 9 times or less, or it may be 8 times or less. In formula (5), the distance Xf may be twice or more of X2, may be three times or more, may be four times or more, and may be no more than 12 times X2, It may be 10 times or less, or it may be 9 times or less.

When the crosslinking treatment step involves three or more stages of stretching treatment, at least one of the relationships of formula (4) and formula (5) may be satisfied in all of the stretching treatments other than the first stretching treatment. At least one of the stretching treatments other than the first stretching treatment may satisfy at least one of Expression (4) and Expression (5).

By satisfying at least one of formula (4) and formula (5) in the crosslinking and stretching step, sufficient neck-in can be caused in the resin film 1 in the stretching treatment after the second stretching treatment. This suppresses variations in the width of the resin film 1 in the length direction, making it easier to manufacture a polarizer having a stable width. By satisfying at least one of formula (4) and formula (5) in the crosslinking/stretching process, a sufficient distance for the resin film 1 to be transported in the stretching process after the second stretching process can be ensured. This makes it easier to cause large neck-in in the resin film 1, making it easier to manufacture a polarizer with excellent optical properties.

In the crosslinking bath 10 shown in FIG. 1, when the second stretching process satisfies at least one of formula (4) and formula (5), the distance Xf is This is the distance over which the resin film 1 is transported.

Although the total stretching ratio (cumulative stretching ratio) from the second stretching process to the final stretching process in the crosslinking and stretching process is not particularly limited, it is preferably larger than the stretching ratio in the first stretching process. The total stretching ratio of the stretching processes after the second stretching process is usually 1.1 times or more, may be 1.5 times or more, may be 1.8 times or more, and may be 2.0 times or more. It may be 2.5 times or more, and it is usually 7.0 times or less, it may be 6.0 times or less, it may be 5.0 times or less, It may be 4.5 times or less, or it may be 4.0 times or less.

The total stretching ratio (cumulative stretching ratio) in the entire stretching process in the crosslinking and stretching process may be, for example, 2.0 times or more, 3.0 times or more, or 3.5 times or more. It may also be 7.0 times or less, 6.8 times or less, or 6.5 times or less.

(Manufacturing method of polarizing plate)
The polarizing plate of this embodiment is obtained by laminating a protective film on one or both sides of a polarizer obtained by the above-described method for manufacturing a polarizer. The polarizer and the protective film are preferably laminated via a bonding layer (adhesive layer or pressure-sensitive adhesive layer).

The method for manufacturing the polarizing plate of this embodiment is as follows:
Obtaining a polarizer by the above polarizer manufacturing method;
The method includes a step of laminating a protective film on one or both sides of the polarizer without slitting the polarizer obtained in the step of obtaining the polarizer in the transport direction.

When manufacturing a polarizing plate, the polarizer is sometimes slit in the transport direction in order to align the width of the polarizer in the length direction, and the slit polarizer and a protective film are laminated. According to the method for manufacturing a polarizer described above, a polarizer with suppressed width variations in the length direction can be obtained without slitting the polarizer in the transport direction. Therefore, a polarizing plate can be obtained by laminating a protective film without slitting the polarizer in the transport direction. Note that the polarizing plate may be slit. That is, the polarizer may be slit after a protective film is laminated on one or both sides of the polarizer.

The step of laminating a protective film on both sides or one side of a polarizer involves applying a laminating agent (adhesive or pressure-sensitive adhesive) to form a laminating layer on at least one laminating surface of the polarizer and the protective film. This can be done by coating or the like. When laminating protective films on both sides of a polarizer, the protective films may be laminated on one side of the polarizer in order, and while laminating one protective film and polarizer, the other protective film and polarizer may be laminated. You may also perform bonding.

(Polarizing plate roll)
A polarizing plate roll body is a polarizing plate wound into a roll. A roll of a polarizing plate can usually be obtained by winding a polarizing plate around a winding core. With the method for manufacturing a polarizer described above, a long polarizer can be obtained. The long polarizer obtained by the above polarizer manufacturing method can be made into a long polarizing plate by laminating a protective film on one or both sides of the long polarizer without slitting it in the conveying direction. . For example, by winding the long polarizing plate obtained in this way into a roll, it is possible to make a roll of the polarizing plate suitable for storage, transportation, and the like. The length (winding length) of the polarizing plate constituting the roll body of the polarizing plate is not particularly limited, but from the viewpoint of improving the stability of the width of the polarizer, it can be set to 300 m or more and 5000 m or less.

In the roll of the polarizing plate, the difference between the width of the polarizer at the beginning of winding of the roll and the width of the polarizer at the end of winding of the roll can be 3 mm or less in absolute value, and 0.1 mm. It can be greater than or equal to 3 mm. The absolute value of the difference may 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 beginning of winding of the roll body may be larger or smaller than the width of the polarizer at the end of winding of the roll body.

When the absolute value of the difference in the roll body is within the above range, it is easy to obtain a roll body with a good winding appearance. On the other hand, if the absolute value of the above-mentioned difference in the roll body exceeds 3 mm, problems such as a part of the roll body rising in a streak-like manner are likely to occur, and the roll body is likely to have a poor winding appearance. On the other hand, when the polarizer is slit in the transport direction, the width of the polarizer is almost constant, and in the case of a roll of polarizing plate, the width of the polarizer at the beginning of winding of the roll and the width of the polarizer at the end of winding of the roll are the same. The difference between the width and the width is likely to be less than 0.1 mm in absolute value. However, when the polarizer is slit in the transport direction, slit debris may be generated or cracks may occur in the polarizer.

Since the variation (standard deviation) in the width of the polarizer obtained by the manufacturing method of the present invention is 3 mm or less (preferably 1 mm or less), the winding of the roll of the polarizer can be started without slitting in the conveying direction. It is possible to obtain a roll body with a good winding shape in which the difference between the width of the polarizer at a portion and the width of the polarizer at the end of winding of the roll body is 3 mm or less in absolute value.

Further, the variation (standard deviation) in the width of the polarizer in the roll of the polarizing plate of the present invention can be 3 mm or less (preferably 1 mm or less).

The winding start portion of a roll of polarizing plate refers to the polarizing plate at the winding start side on the winding core side of the roll body (the center side in the radial direction of the roll body), and the width of the polarizer at the winding start portion of the roll body. refers to the width of the polarizer at a position 1 m in the length direction from the end of the polarizing plate at the beginning of winding. The winding end portion of the roll body of the polarizing plate refers to the polarizing plate at the winding end side on the outer peripheral side of the roll body (radially outside of the roll body), and the width of the polarizer at the winding end portion of the roll body is , refers to the width of the polarizer at a position 1 m in the length direction from the end of the winding of the polarizing plate.

Hereinafter, each step of the manufacturing method of a polarizer and a polarizing plate, and the materials used in these manufacturing methods will be explained in detail.

(polarizer)
A polarizer is an absorption-type polarizing film that has the property of absorbing linearly polarized light with a vibration plane parallel to its absorption axis and transmitting linearly polarized light with a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). be. A polarizer is a polarizing film in which a dichroic dye is adsorbed and oriented on a resin film made of polyvinyl alcohol resin (hereinafter sometimes referred to as "PVA resin").

The thickness of the polarizer is not particularly limited, but may be, for example, 3 μm or more, 4 μm or more, 5 μm or more, 35 μm or less, 30 μm or less. The thickness may be 25 μm or less. When the thickness of the polarizer is 35 μm or less, for example, it is possible to suppress the influence of polyenization of PVA-based resin on deterioration of optical properties in a high-temperature environment. When the thickness of the polarizer is 3 μm or more, it is easy to achieve a configuration that achieves desired optical characteristics.

(resin film)
The PVA resin constituting the resin film is obtained by saponifying polyvinyl acetate resin. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

The degree of saponification of the PVA-based resin is preferably 85 mol% or more, more preferably 90 mol% or more, and still more preferably 99 mol% or more and 100 mol% or less. The degree of polymerization of the PVA resin is, for example, 1,000 or more and 10,000 or less, preferably 1,500 or more and 5,000 or less. The PVA resin may be modified, such as polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

Examples of the dichroic dye adsorbed and oriented on the resin film include iodine or dichroic dye. Preferably, the dichroic dye is iodine. The dichroic dyes include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Splat Blue G, Splat Blue GL, Splat Orange GL, Direct Sky Blue, Examples include Direct First Orange S and First Black.

The thickness of the resin film as the raw film depends on the thickness of the polarizer to be manufactured, but for example, it may be 20 μm or more, 35 μm or more, 40 μm or more, 45 μm or more. It may also be 80 μm or less, 70 μm or less, or 60 μm or less.

(swelling process)
The swelling process is a process in which the resin film is treated, for example, by immersing the resin film in a swelling liquid in a swelling bath or by spraying the swelling liquid. The swelling process can remove dirt on the surface of the resin film, plasticizers, blocking agents, etc. in the resin film, as well as impart easy dyeability and plasticize the resin film. As the swelling liquid, a medium mainly composed of water, such as water, distilled water, or pure water, is usually used. The swelling liquid contains 0.01% by mass or more of boric acid (JP-A-10-153709), chloride (JP-A-06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc. It is also possible to use an aqueous solution containing 10% by mass or less.

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

In the swelling bath, the problem that the resin film swells in the width direction tends to cause wrinkles in the resin film. One way to transport the film while removing wrinkles is to use rolls with a widening function such as expander rolls, spiral rolls, and crown rolls as guide rolls used to transport the film through the swelling bath, or to use cross guide rolls. , bend bars, and other widening devices such as tenter clips. Another means for suppressing the occurrence of wrinkles is to perform a stretching process. For example, uniaxial stretching can be performed in a swelling bath by utilizing the difference in circumferential speed between nip rolls.

In the swelling treatment, the resin film also swells and expands in the transport direction, so if the resin film is not actively stretched, it is necessary to use a swelling bath, for example, to eliminate slack in the resin film in the transport direction. It is preferable to take measures such as controlling the speed of nip rolls disposed before and after the. In addition, in order to stabilize the transport of the film in the swelling bath, the water flow in the swelling bath is controlled by an underwater shower, and an EPC device (Edge Position Control device: detects the edge of the film and prevents the film from meandering. It is also useful to use a device such as

(dying process)
The dyeing step is performed for the purpose of adsorbing and orienting the dichroic dye to the resin film after the swelling step. The processing conditions are determined within a range in which the objective can be achieved and in which problems such as extreme dissolution and devitrification of the resin film do not occur. The dyeing step may be carried out by immersing the resin film after the swelling treatment in a dyeing bath for a predetermined time and then drawing it out, or may be carried out by spraying a dyeing liquid or the like. In order to improve the dyeability of the dichroic dye, the resin film subjected to the dyeing process is preferably a resin film that has been subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing process. Alternatively, in addition to the uniaxial stretching treatment before the dyeing process, it is preferable to perform the uniaxial stretching process during the dyeing process.

When using iodine as a dichroic dye, the dyeing solution in the dyeing bath contains, for example, an aqueous solution with a mass ratio of iodine/potassium iodide/water = 0.003 to 3/0.1 to 10/100. Can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used together. The staining solution may contain compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, and the like. When adding boric acid, it is distinguished from the later-described cross-linking and stretching process and complementary coloring process in that it contains iodine, and if the aqueous solution contains 0.003 parts by mass or more of iodine per 100 parts by mass of water, It can be considered a dye bath. The temperature of the dyeing bath when dipping the resin film is usually 10 to 45°C, preferably 10°C to 40°C, more preferably 20°C to 35°C, and the immersion time of the film is usually 30°C to 45°C. The duration is at least 60 seconds, preferably at least 60 seconds and at most 300 seconds.

When using a water-soluble dichroic dye as the dichroic dye, the dyeing solution in the dyeing bath contains, for example, an aqueous solution with a concentration of dichroic dye/water = 0.001 to 0.1/100 in mass ratio. Can be used. This dyeing solution may contain a dyeing aid, for example, an inorganic salt such as sodium sulfate, a surfactant, and the like. One type of dichroic dye may be used alone, or two or more types of dichroic dyes may be used in combination. The temperature of the dyeing bath when dipping the resin film is, for example, 20°C or more and 80°C or less, preferably 30°C or more and 70°C or less, and the immersion time of the resin film is usually 30 seconds or more and 600 seconds or less. , preferably 60 seconds or more and 300 seconds or less.

In the dyeing process, the resin film can be uniaxially stretched in a dyeing bath. Uniaxial stretching of the resin film can be carried out by a method such as creating a difference in peripheral speed between nip rolls placed in the dyeing bath or before and after the dyeing bath.

In the dyeing process, as in the swelling process, in order to transport the resin film while removing wrinkles from the resin film, rolls with widening functions such as expander rolls, spiral rolls, and crown rolls are used as guide rolls, and cross guiders are used as guide rolls. , bend bars, tenter clips, etc. may be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment, similar to the swelling process.

(Crosslinking and stretching process)
The crosslinking and stretching step is a step in which the resin film dyed in the dyeing step is immersed in a treatment bath (crosslinking bath) containing a crosslinking agent and stretched in the crosslinking bath. The crosslinking treatment can improve the water resistance, etc. of the resin film. The crosslinking and stretching step can be carried out by stretching and transporting the resin film along a film transport path constructed by nip rolls, guide rolls, and the like arranged in a crosslinking bath. The stretching process performed in the cross-linking stretching process is as described above, and the stretching process performed in the cross-linking stretching process is a stretching process in which uniaxial stretching is performed in the transport direction (longitudinal direction) using the difference in circumferential speed between the nip rolls. It is preferable.

As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. Examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be used alone or in combination of two or more. As the solvent, for example, water can be used, but it may also contain an organic solvent that is compatible with water. The concentration of the crosslinking agent in the crosslinking solution is not limited to this, but is preferably in the range of 1% by mass or more and 20% by mass or less, more preferably in the range of 6% by mass or more and 15% by mass or less. preferable.

The crosslinking liquid can be an aqueous solution containing, for example, 1 part by mass or more and 10 parts by mass or less of boric acid per 100 parts by mass of water. When the dichroic dye contained in the dyeing solution is iodine, the crosslinking solution preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 part by mass or more and 30 parts by mass based on 100 parts by mass of water. It can be less than or equal to parts by mass. Examples of iodides include potassium iodide and zinc iodide. Two or more types of iodides may be contained. Further, compounds other than iodide, such as sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may be present. Further, nitrate may be present together. The nitrate may include at least one selected from the group consisting of aluminum nitrate, copper nitrate, sodium nitrate, potassium nitrate, zinc nitrate, and magnesium nitrate. Preferably, the nitrate includes zinc nitrate.

In the crosslinking and stretching step, the concentrations of boric acid and iodide in the crosslinking liquid and the temperature of the crosslinking liquid can be changed as appropriate depending on the purpose. The crosslinking liquid can be, for example, an aqueous solution having a concentration of boric acid/iodide/water in a mass ratio of 3 to 10/1 to 20/100. If necessary, other crosslinking agents may be used in place of boric acid, or boric acid and other crosslinking agents may be used in combination. The temperature of the crosslinking bath when dipping the resin film is usually 50°C or more and 70°C or less, preferably 53°C or more and 65°C or less, and the immersion time of the resin film is usually 30 seconds or more and 600 seconds or less. , preferably 40 seconds or more and 300 seconds or less, more preferably 60 seconds or more and 200 seconds or less. In addition, when a dyeing process and a crosslinking/stretching process are performed in this order on a resin film that has been stretched in advance before the swelling process, the temperature of the crosslinking bath is usually 50°C or higher and 85°C or lower, preferably 55°C or higher and 80°C. It is as follows.

(Complementary color process)
The complementary color process is a process for adjusting the hue of the resin film after the crosslinking and stretching process. The complementary color process is a treatment process performed on the resin film after the crosslinking and stretching process without any stretching process. The complementary color process may be carried out by immersing the resin film after the cross-linking and stretching process in a complementary color bath (complementary color liquid stored in a complementary color bath) for a predetermined time and then pulling it out, or by spraying the complementary color liquid. It's okay.

The complementary color solution may be an aqueous solution containing, for example, 1 to 10 parts by mass of boric acid per 100 parts by mass of water. When the dichroic dye contained in the dyeing solution is iodine, the complementary color solution preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 part by mass or more and 30 parts by mass based on 100 parts by mass of water. It can be less than or equal to parts by mass. Examples of iodides include potassium iodide and zinc iodide. Two or more types of iodides may be contained. Further, compounds other than iodide, such as sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may be present. Further, nitrate may be present together. The nitrate may include at least one selected from the group consisting of aluminum nitrate, copper nitrate, sodium nitrate, potassium nitrate, zinc nitrate, and magnesium nitrate. Preferably, the nitrate includes zinc nitrate.

In the complementary color solution, for example, when iodine is used as a dichroic dye, a concentration of boric acid/iodide/water in a mass ratio of 1 to 5/3 to 30/100 can be used. The temperature of the complementary color bath when dipping the resin film is usually 10°C or more and 45°C or less, and the immersion time of the resin film is usually 1 second or more and 300 seconds or less, preferably 2 seconds or more and 100 seconds or less. .

The complementary color process may be performed multiple times, for example, 2 to 5 times. In this case, the composition and temperature of each complementary color solution used may be the same or different as long as it is within the above range.

(Washing process)
The cleaning process is performed for the purpose of removing excess chemicals such as boric acid and iodine attached to the resin film after the crosslinking and stretching process, or, if a complementary color process is performed, to the resin film after the complementary color process. The cleaning process can be performed, for example, by immersing the resin film after the crosslinking and stretching process or the complementary color process in a cleaning bath (a cleaning liquid contained in a cleaning tank), or by spraying the cleaning liquid as a shower or the like. The cleaning step may be performed using a combination of dipping and spraying.

The temperature of the cleaning liquid in the cleaning process is usually 2°C or more and 40°C or less, and the immersion time when the resin film is immersed in the cleaning liquid is usually 2 seconds or more and 120 seconds or less.

In the cleaning process, in order to convey the resin film while removing wrinkles, rolls with a widening function such as expander rolls, spiral rolls, and crown rolls are used as guide rolls, and rolls such as cross guiders, bend bars, and tenter clips are used as guide rolls. Other widening devices may also be used. In the washing step, stretching treatment may be performed to suppress the occurrence of wrinkles.

(drying process)
The drying process is a process of drying the resin film after the crosslinking and stretching process, the complementary color process, or the washing process. The method of drying the resin film is not particularly limited, but can be carried out using a drying oven, for example. The drying oven may include, for example, a hot air dryer. The drying temperature is, for example, 30° C. or more and 100° C. or less, and the drying time is, for example, 30 seconds or more and 600 seconds or less. The process of drying the resin film can also be performed using a far-infrared heater.

(Polarizer)
A polarizing plate is a polarizer with protective films laminated on one or both sides. It is preferable that the polarizer and the protective film are laminated via a bonding layer. The polarizing plate may be a long polarizing plate, and its length may be 300 m or more and 5000 m or less.

As a protective film, for example, a film made of acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose; a film made of polyester resin such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; a polycarbonate resin film, cyclo Examples include olefin resin films; acrylic resin films; and films made of chain olefin resins such as polypropylene resins.

In order to improve the adhesion between the polarizer and the protective film, the bonding surface of the polarizer and/or protective film may be treated with corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. Processing may be performed.

The bonding layer interposed between the polarizer and the protective film can be formed using an adhesive or a pressure-sensitive adhesive. Adhesives include active energy ray-curable adhesives such as ultraviolet curable adhesives, aqueous solutions of polyvinyl alcohol resins, aqueous solutions containing crosslinking agents, and water-based adhesives such as urethane emulsion adhesives. Agents can be mentioned. A zinc compound such as zinc nitrate may be added to the water-based adhesive. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a radical photopolymerization initiator, a mixture of an epoxy compound and a cationic photopolymerization initiator, or the like. A cationically polymerizable epoxy compound and a radically polymerizable acrylic compound can be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator can also be used together as an initiator.

Polarizing plates can be used in display devices. Examples of the image display element used in the display device include a liquid crystal display element, an organic EL display element, and the like. In constructing a liquid crystal display device, a polarizing plate may be used by placing it on the viewing side, it may be placed on the backlight side, or it may be used on both the viewing side and the backlight side. Good too. The display device can be used in mobile devices such as televisions, personal computers, mobile phones and tablet terminals, and in-vehicle applications. Examples of in-vehicle applications include display devices used in car navigation devices, speedometers, touch panels for air conditioners, back monitors, rear monitors, and the like.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Determination of time t in Example 1]
According to the procedure of Example 1, a resin film (width 14.4 mm) which was subjected to a swelling process and a dyeing process was prepared. The resin film after the dyeing process was immersed in the crosslinking bath used in the crosslinking and stretching process of Example 1, and changes in the width of the resin film were measured every 10 seconds from the start of immersion. This measurement was performed on four resin films. In either resin film, the width of the resin film reached a constant width of 13.5 mm or 13.6 mm 30 seconds (0.5 min) after the start of dipping, so it was determined that the shrinkage of the resin film was saturated. The time t in the above equations (1) and (2) was set to 0.5 min.

[Example 1]
A resin film made of a long polyvinyl alcohol resin with a thickness of 45 μm [trade name “VF-PE#4500” manufactured by Kuraray Co., Ltd., saponification degree of 99.9 mol% or more] was heated at a temperature of 23°C. The resin film was immersed in a swelling bath made of pure water for 110 seconds and uniaxially stretched 2.1 times in the transport direction of the resin film (swelling step). Thereafter, the film pulled out from the swelling bath was immersed for 163 seconds in a dyeing bath at a temperature of 23°C consisting of a dyeing solution containing iodine with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio). The resin film was immersed in water and uniaxially stretched 1.22 times in the transport direction of the resin film (dying process).

Next, the film pulled out from the dyeing bath was immersed for 92 seconds in a crosslinking bath at a temperature of 59°C consisting of a crosslinking solution containing potassium iodide/boric acid/water at a ratio of 2.3/3.7/100 (mass ratio). The resin film was immersed and uniaxially stretched in the transport direction of the resin film (crosslinking and stretching step). As a crosslinking bath, a bath in which a first nip roll, a second nip roll, and a third nip roll are arranged in this order from the upstream side in the conveying direction is used, and a uniaxial stretching process (first 1 stretching treatment) was performed, and uniaxial stretching treatment (second stretching treatment) was performed between the second nip roll and the third nip roll.

The distance X1 (1), which is the transport distance of the resin film in the first stretching process (the transport distance of the resin film between the first nip roll and the second nip roll), is the value obtained by multiplying the time t determined above by 0.4. and the transport speed v of the resin film in the crosslinking/stretching step (X1(1)=v×0.4t). The distance X2(1) that the resin film was transported from the start of immersion of the resin film in the crosslinking bath to the completion of the first stretching treatment was set to v×0.46t. Further, the transport distance of the resin film in the second stretching process (the transport distance of the resin film between the second nip roll and the third nip roll) Xf(1) is the distance X1(1)
and 6.1 times the distance X2(1). Rv2 was set to Rvmin+2.7 m/min.

Thereafter, it was dried at a temperature of 38° C. (drying step) to obtain a polarizer with a thickness of 18 μm in which iodine was adsorbed and oriented on the polyvinyl alcohol resin.

After the drying process, we checked the variation (standard deviation) in the length (width) in the direction perpendicular to the stretching direction when 100,000 m of polarizers were manufactured, and found that the variation was 2.9 mm. It had a stable width.

[Determination of time t in Example 2]
According to the procedure of Example 2, a resin film (width 14.4 mm) which was subjected to a swelling process and a dyeing process was prepared. The resin film after the dyeing process was immersed in the crosslinking bath used in the crosslinking and stretching process of Example 2, and changes in the width of the resin film were measured every 10 seconds from the start of immersion. This measurement was performed on four resin films. In either resin film, the width of the resin film reached a constant width of 13.4 mm or 13.5 mm 20 seconds (0.33 min) after the start of dipping, so it was determined that the shrinkage of the resin film was saturated. The time t in the above equations (1) and (2) was set to 0.33 min.

[Example 2]
A resin film made of a long polyvinyl alcohol resin with a thickness of 45 μm [trade name “VF-PE#4500” manufactured by Kuraray Co., Ltd., saponification degree of 99.9 mol% or more] was heated at a temperature of 21.5 The resin film was immersed in a swelling bath made of pure water at a temperature of 90 seconds for an immersion time of 90 seconds, and uniaxially stretched 2.3 times in the transport direction of the resin film (swelling step). Thereafter, the film pulled out from the swelling bath was immersed for 180 seconds in a dyeing bath at a temperature of 23°C consisting of a dyeing solution containing iodine with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio). The resin film was immersed in water and uniaxially stretched 1.13 times in the transport direction of the resin film (dying process).

Next, the film pulled out from the dyeing bath was immersed for 62 seconds in a crosslinking bath at a temperature of 59°C consisting of a crosslinking solution containing potassium iodide/boric acid/water at a ratio of 2.3/3.7/100 (mass ratio). The resin film was immersed and uniaxially stretched in the transport direction of the resin film (crosslinking and stretching step). As a crosslinking bath, a bath in which a first nip roll, a second nip roll, and a third nip roll are arranged in this order from the upstream side in the conveying direction is used, and a uniaxial stretching process (first 1 stretching treatment) was performed, and uniaxial stretching treatment (second stretching treatment) was performed between the second nip roll and the third nip roll.

The distance X1 (2), which is the transport distance of the resin film in the first stretching process (the transport distance of the resin film between the first nip roll and the second nip roll), is the value obtained by multiplying the time t determined above by 0.43. and the transport speed v of the resin film in the crosslinking/stretching step (X1(2)=v×0.43t). The distance X2 (2) that the resin film is transported from the start of immersion of the resin film in the crosslinking bath to the completion of the first stretching treatment was set to v×0.49t. Further, the transport distance of the resin film in the second stretching process (the transport distance of the resin film between the second nip roll and the third nip roll) Xf(2) is set to 6.8 times the distance X1(2), and the distance X2 It was set to 6.0 times that of (2). Rv2 was manufactured while being controlled to vary between Rvmin+2.3 m/min and Rvmin+3.3 m/min.

After the drying process, we checked the variation (standard deviation) in the length (width) in the direction perpendicular to the stretching direction when 100,000 m of polarizers were manufactured, and found that the variation was 0.8 mm. It had a stable width along the length.

Saponified cellulose acylate film TD40 (manufactured by Fujifilm Corporation, thickness 40 μm) was laminated on both sides of the polarizer produced above using a water-based adhesive and dried to produce a long polarizing plate. did. At this time, the polarizer was not subjected to slit treatment to remove the ends in the width direction. A long polarizing plate of 1000 m thus produced was wound into a roll to obtain a roll body. The width of the polarizer at the beginning of the winding of the polarizing plate roll (1 m in the length direction from the end of the polarizing plate at the beginning of winding) and the width of the polarizer at the end of the winding of the polarizing plate roll (the position at the end of the winding of the polarizing plate) The difference from the width of the polarizer at a position 1 m from the end in the length direction was 0.3 mm in absolute value. The roll shape of the polarizing plate was good, and no slit debris was observed.

[Determination of time t in Comparative Example 1 and Comparative Example 2]
According to the procedures of Comparative Examples 1 and 2, a resin film (width 14.4 mm) that was subjected to a swelling process and a dyeing process was prepared. The resin film after the dyeing process was immersed in the crosslinking bath used in the crosslinking and stretching process of Comparative Examples 1 and 2, and changes in the width of the resin film were measured every 10 seconds from the start of immersion. This measurement was performed on four resin films. In either resin film, the width of the resin film reached a constant width of 13.5 mm or 13.6 mm 30 seconds (0.5 min) after the start of dipping, so it was determined that the shrinkage of the resin film was saturated. The time t in the above equations (1) and (2) was set to 0.5 min.

[Comparative example 1]
A resin film made of a long polyvinyl alcohol resin with a thickness of 45 μm [trade name “VF-PE#4500” manufactured by Kuraray Co., Ltd., saponification degree of 99.9 mol% or more] was heated at a temperature of 23°C. The resin film was immersed in a swelling bath made of pure water for 110 seconds and uniaxially stretched 2.1 times in the transport direction of the resin film (swelling step). Thereafter, the film pulled out from the swelling bath was immersed for 163 seconds in a dyeing bath at a temperature of 23°C consisting of a dyeing solution containing iodine with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio). The resin film was immersed in water and uniaxially stretched 1.22 times in the transport direction of the resin film (dying process).

The distance X1 (c1), which is the transport distance of the resin film in the first stretching process (the transport distance of the resin film between the first nip roll and the second nip roll), is the value obtained by multiplying the time t determined above by 0.2. and the transport speed v of the resin film in the crosslinking and stretching step (X1(c1)=v×0.2t). The distance X2 (c1) that the resin film was transported from the start of immersion of the resin film in the crosslinking bath to the completion of the first stretching treatment was set to v×0.26t. Further, the conveyance distance of the resin film in the second stretching process (the conveyance distance of the resin film between the second nip roll and the third nip roll) Xf (c1) is set to 15.0 times the distance X1 (c1), and the distance X2 It was 11.5 times that of (c1). Rv2 was set to Rvmin+2.7 m/min.

When we checked the variation (standard deviation) in the length (width) in the direction perpendicular to the stretching direction when 100,000 m of polarizers were manufactured after the drying process, the variation exceeded 3 mm, and the It was not possible to manufacture it with a stable width.

[Comparative example 2]
A resin film made of a long polyvinyl alcohol resin with a thickness of 45 μm [trade name “VF-PE#4500” manufactured by Kuraray Co., Ltd., saponification degree of 99.9 mol% or more] was heated at a temperature of 23°C. The resin film was immersed in a swelling bath made of pure water for 110 seconds and uniaxially stretched 2.1 times in the transport direction of the resin film (swelling step). Thereafter, the film pulled out from the swelling bath was immersed for 163 seconds in a dyeing bath at a temperature of 23°C consisting of a dyeing solution containing iodine with a ratio of iodine/boric acid/water of 1.0/0.5/100 (mass ratio). The resin film was immersed in water and uniaxially stretched 1.22 times in the transport direction of the resin film (dying process).

The distance X1 (c2), which is the transport distance of the resin film in the first stretching process (the transport distance of the resin film between the first nip roll and the second nip roll), is the value obtained by multiplying the time t determined above by 1.4. and the transport speed v of the resin film in the crosslinking/stretching step (X1(c2)=v×1.4t). The distance X2 (c2) that the resin film was transported from the start of immersion of the resin film in the crosslinking bath to the completion of the first stretching treatment was set to v×1.67t. In addition, the transport distance of the resin film in the second stretching process (the transport distance of the resin film between the second nip roll and the third nip roll) Xf (c2) is set to 1.3 times the distance X1 (c2), and the distance X2 It was 1.2 times that of (c2). Rv2 was set to Rvmin+2.7 m/min.

1 resin film, 10 crosslinking bath, 11 first nip roll, 12 second nip roll, 13 third nip roll.

Claims

A method for producing a polarizer in which a dichroic dye is adsorbed and oriented on a resin film made of polyvinyl alcohol resin as a forming material, the method comprising:
a swelling step of swelling the resin film while conveying it;
a dyeing step of dyeing the resin film after the swelling step while conveying it;
A crosslinking and stretching step of immersing the resin film after the dyeing step in a crosslinking bath while transporting it and stretching it in the transporting direction in the crosslinking bath,
The cross-linking and stretching process is a process in which stretching is performed in multiple stages, and the first stage of the stretching is performed so as to satisfy the following formula (1). , a method for manufacturing a polarizer.
v×0.3t≦X1≦v×1.2t (1)
[In formula (1),
X1 represents the distance [m] that the resin film is conveyed from the start to the completion of the first-stage stretching process.
v represents the conveyance speed [m/min] of the resin film in the crosslinking and stretching step.
t represents the time [min] required until the shrinkage of the resin film is saturated when the resin film after the dyeing process is immersed in the crosslinking bath used in the first stage stretching process. ]
A method for producing a polarizer in which a dichroic dye is adsorbed and oriented on a resin film made of polyvinyl alcohol resin as a forming material, the method comprising:
a swelling step of swelling the resin film while conveying it;
a dyeing step of dyeing the resin film after the swelling step while conveying it;
A crosslinking and stretching step of immersing the resin film after the dyeing step in a crosslinking bath while transporting it and stretching it in the transporting direction in the crosslinking bath,
The cross-linking and stretching process is a process in which a stretching process is performed in multiple stages, and the first stage of the stretching process is performed so as to satisfy the relationship of the following formula (2). , a method for manufacturing a polarizer.
v×0.4t≦X2≦v×1.2t (2)
[In formula (2),
X2 represents the distance [m] that the resin film is transported from the start of immersion of the resin film in the crosslinking bath to the completion of the first stage stretching process in the crosslinking/stretching step.
v represents the conveyance speed [m/min] of the resin film in the crosslinking and stretching step.
t represents the time [min] required until the shrinkage of the resin film is saturated when the resin film after the dyeing process is immersed in the crosslinking bath used in the first stage stretching process. ]
The method for manufacturing a polarizer according to claim 2, wherein the crosslinking and stretching step further satisfies the following formula (1).
v×0.3t≦X1≦v×1.2t (1)
[In formula (1),
X1 represents the distance [m] that the resin film is conveyed from the start to the completion of the first-stage stretching process.
v and t represent the same meanings as above. ]
When the distance that the resin film is conveyed from the start to the completion of the first stage stretching process is defined as X1,
In the crosslinking and stretching step, the distance that the resin film is conveyed from the start to the completion of at least one of the stretching treatments performed after the first stage is at least 2 times and no more than 10 times the distance X1. The method for manufacturing a polarizer according to claim 1 or 3.
The polarizer according to any one of claims 1 to 3, wherein in the cross-linking and stretching step, the first-stage stretching treatment and the subsequent second-stage stretching treatment are performed in the same cross-linking bath. Production method.
In the crosslinking bath, a first nip roll, a second nip roll, and a third nip roll are arranged in order from the upstream side in the conveyance direction,
The first stage stretching process is performed between the first nip roll and the second nip roll,
The method for manufacturing a polarizer according to claim 5, wherein the second-stage stretching process is performed between the second nip roll and the third nip roll.
The manufacturing of the polarizer according to claim 6, wherein the second nip roll is movably provided so that the conveyance distance of the resin film between the first nip roll and the second nip roll can be adjusted. Method.
When the rotational speed of the first nip roll is Rv1 [m/min] and the rotational speed of the third nip roll is Rv3 [m/min], the width of the resin film after the crosslinking and stretching step is the minimum. The rotational speed of the second nip roll when
] When
7. The method for manufacturing a polarizer according to claim 6, wherein the rotational speed Rv2 [m/min] of the second nip roll is within a range of Rvmin±10 [m/min].
The method for manufacturing a polarizer according to claim 8, wherein in the crosslinking and stretching step, the stretching process is performed while varying the rotational speed Rv2 [m/min] of the second nip roll.
Obtaining a polarizer by the method for manufacturing a polarizer according to any one of claims 1 to 3;
A method for manufacturing a polarizing plate, comprising the step of laminating a protective film on one or both sides of the polarizer without slitting the polarizer obtained in the step of obtaining the polarizer in the transport direction.
A roll body of a polarizing plate obtained by winding a polarizing plate into a roll shape,
The polarizing plate has a polarizer and a protective film laminated on one or both sides of the polarizer,
A roll body of a polarizing plate, wherein the difference between the width of the polarizer at a winding start portion of the roll body and the width of the polarizer at a winding end portion of the roll body is 0.1 mm or more and 3 mm or less in absolute value. .