JP7308905B2 - OPTICAL FILM MANUFACTURING METHOD AND MANUFACTURING APPARATUS - Google Patents

Description

TECHNICAL FIELD The present invention relates to a manufacturing method and manufacturing apparatus for an optical film formed by laminating a first film and a second film.

In recent years, mobile terminals such as smartphones are rapidly becoming larger and slimmer in terms of design and portability. In order to achieve long-time driving with a limited thickness, the polarizing plate used is also required to have high brightness, thinness and light weight.

Conventionally, as a polarizing plate, a polarizing film made of a polyvinyl alcohol-based resin and a thermoplastic resin film laminated with an adhesive are generally used (for example, Patent Documents 1 and 2).

JP-A-2004-245925 JP-A-2017-9990

A polarizing plate is sensitive to the environment in which it is placed, and depending on the environmental conditions, it is likely to undergo bowing deformation, and this deformation usually occurs in a sheet of polarizing plate. This deformation is also referred to herein as "curling". Curl can be classified according to the in-plane direction of the polarizing plate into “MD curl” that occurs in the MD direction and “TD curl” that occurs in the TD direction. In this specification, MD means the machine flow direction of the film in the production line, and TD means the direction orthogonal to MD.

Curl can also be classified into "positive curl" and "reverse curl". A polarizing plate has a first main surface that is attached to an image display element such as a liquid crystal cell and a second main surface that is opposite to the first main surface. It is a curl that makes the surface side convex, and "reverse curl" is a curl that makes the second principal surface side convex. If the polarizing plate is reversely curled, lamination errors may occur when the polarizing plate is laminated to the image display element via the adhesive layer, or air bubbles may enter the interface between the adhesive layer and the image display element. It becomes easier to cause troubles such as

Patent Document 2 describes a method for manufacturing a polarizing plate with a protective film in which reverse curling is suppressed by correcting MD curling (paragraph 0031, etc.). However, conventionally, a method for adjusting the TD curl of an optical film such as a polarizing plate has not been known.

An object of the present invention is to provide a method and a manufacturing apparatus capable of manufacturing an optical film with adjusted TD curl.

The present invention provides the following optical film manufacturing method and manufacturing apparatus.
[1] A method for producing an optical film in which a first film and a second film are laminated,
an external force applying step of applying an external force in the width direction of the first film;
After the external force applying step, a laminating step of laminating the second film on one side of the first film and passing it between a pair of laminating rolls,
The method for producing an optical film, wherein the first film and the second film are resin films.

[2] A method for producing an optical film in which a first film and a second film are laminated,
an external force applying step of applying an external force in the width direction of the first film;
After the external force applying step, a laminating step of laminating the second film on one side of the first film and passing it between a pair of laminating rolls,
The method for producing an optical film, wherein the external force applying step applies a contractile force in the width direction of the first film.

[3] The method for producing an optical film according to [1] or [2], wherein the first film is a polarizing plate and the second film is a protection film.

[4] An apparatus for manufacturing an optical film in which the first film and the second film are laminated,
an external force applying means for applying an external force in the width direction of the first film;
a pair of bonding rolls that bond together by passing the second film over one side of the first film, after the external force applying means;
The apparatus for manufacturing an optical film, wherein the first film and the second film are resin films.

[5] An apparatus for manufacturing an optical film in which a first film and a second film are laminated,
an external force applying means for applying an external force in the width direction of the first film;
a pair of bonding rolls that bond together by passing the second film over one side of the first film, after the external force applying means;
The optical film manufacturing apparatus, wherein the external force applying means applies a shrinking force in the width direction of the first film.

According to the present invention, an optical film whose TD curl is adjusted can be produced.

It is a side view which shows typically an example of the manufacturing method of the optical film which concerns on this invention. It is the schematic explaining TD curl, (a) is a side view, (b) is a top view. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the manufacturing method of the polarizing plate with a protection film which concerns on one Embodiment of this invention, (a) is a side view, (b) is a top view, (c) is the elements on larger scale. FIG. 4 is a schematic diagram showing the action of force by the expander rolls in the arrangement shown in FIG. 3; BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the manufacturing method of the polarizing plate with a protection film which concerns on one Embodiment of this invention, (a) is a side view, (b) is a top view, (c) is the elements on larger scale. FIG. 6 is a schematic diagram showing the action of force by expander rolls in the arrangement shown in FIG. 5; It is a schematic sectional drawing which shows an example of the layer structure of a polarizing plate. FIG. 4 is a schematic cross-sectional view showing another example of the layer structure of a polarizing plate; FIG. 4 is a schematic cross-sectional view showing another example of the layer structure of a polarizing plate;

The present invention provides a method for manufacturing an optical film in which a first film and a second film are laminated together, comprising: an external force applying step of applying an external force in the width direction of the first film; and a laminating step of laminating the second film on one side of the first film and passing the films between a pair of laminating rolls. The first film and the second film may be single layer films or multilayer films. The first film and the second film are, for example, resin films.

FIG. 1 is a side view schematically showing the method for producing an optical film according to the present invention. Referring to FIG. 1, in the method for manufacturing an optical film according to the present invention, a second film 2 is superimposed on one side of a first film 1, and the first film 1 is passed between a pair of bonding rolls 41 and 42. The optical film 3 is manufactured through a lamination step in which the laminated body of the film and the second film 2 is pressed from above and below to be laminated. The first film 1 to be subjected to the bonding process is introduced between the pair of bonding rolls 41 and 42 after being subjected to the external force applying means 10 .

In the present invention, the first film 1 is subjected to an external force application step of applying an external force in the width direction before the lamination step of laminating the first film 1 on the second film 2 . Thereby, the TD curl in the sheet of the optical film 3 in which the first film 1 and the second film 2 are laminated can be adjusted. In the first film 1, the TD curl of the optical film 3 is adjusted by the stress remaining in the first film 1 by laminating the second film 2 in a state where the stress against the external force applied in the external force applying step remains. It is expected that the

With reference to FIGS. 2(a) and 2(b), when a sheet of optical film 3 that is curled is placed on a flat table with the convex surface facing down, "TD curl" means TD ( It is a curl that lifts the ends (typically both ends) in the direction perpendicular to the machine flow direction), and "MD curl" is the end (typically both ends) in the MD (machine flow direction) It is a curl that lifts up.

Evaluation of the amount of curl that the optical film 3 may have (forward curl, reverse curl, MD curl, TD curl) is performed on sheets cut from the obtained optical film 3 . This sheet is a rectangular sheet with one diagonal parallel to MD or TD, and has a long side length of 50 mm or longer and a short side length of 30 mm or longer. For example, when measuring the TD curl amount, a rectangular sheet with one diagonal line parallel to the TD was cut and placed on a flat table with the convex side of the curled sheet facing down. Occasionally, both corners of a diagonal line parallel to the TD lifted from the flat table and the height from the flat table are measured, and the average value of the heights of these two corners is taken as the TD curl amount.

The manufacturing method according to the present invention is advantageous in adjusting TD curl that occurs in the sheet of the optical film 3 . The manufacturing method according to the present invention includes the adjustment of the TD curl described above, and may or may not include the adjustment of the MD curl. A method for adjusting the MD curl can be adjusted, for example, by adjusting the tension in the MD direction of the first film 1 and the second film 2 which are subjected to the bonding step.

The external force applying means 10 used in the external force applying step is not limited as long as it is means capable of applying an external force in the width direction to the passing first film 1, and examples thereof include expander rolls and pinch expanders. , crown roll, reverse crown roll and the like are exemplified. The external force applied in the width direction of the first film 1 may be an inward shrinking force or an outward stretching force. The external force applied in the width direction of the first film 1 is easier to adjust the magnitude of the applied external force when the external force is directly applied than when the external force is applied in other directions. It is preferable from the point of becoming.

The first film 1 subjected to the external force application step is at least one of i) a film having a greater thickness than the second film 2, and ii) a film having a greater tensile modulus than the second film 2. It is preferable that the conditions are satisfied. Since the first film 1 has such characteristics, it is possible to more effectively adjust the TD curl in the sheet of the optical film 3 . In the following, the first film 1 is a polarizing plate, the second film 2 is a protective film, and the optical film 3 obtained by bonding the first film 1 and the second film 2 is a polarizing plate with a protective film, The present invention will be described in detail by exemplifying an embodiment using an expander roll as the external force applying means 10 . When the first film 1 is a polarizing plate and the second film 2 is a protection film, the above condition ii) is usually satisfied.

[Method for producing polarizing plate with protective film]
3(a), (b), and (c) are diagrams schematically showing a method for manufacturing a polarizing plate with a protective film according to this embodiment. FIG. 3(a) is a side view, FIG. 3(b) is a top view of the transportation process of the polarizing plate 2 in FIG. 3(a) as seen from the bonding surface side of the polarizing plate, and FIG. 4] is a side view showing an enlarged portion of the external force application step shown in Fig. 3(a). [Fig.

3(a), (b), and (c), in the manufacturing method according to the present embodiment, a protective film 2 is superimposed on one side of a polarizing plate 1 and between a pair of bonding rolls 41 and 42. By passing through, the polarizing plate 3 with a protection film is obtained through the lamination process which presses the laminated body of the polarizing plate 1 and the protection film 2 from upper and lower sides, and bonds them. The polarizing plate 1 and the protective film 2 are continuously delivered from a delivery roll (not shown) and continuously transported. The polarizing plate 1 is introduced between a pair of bonding rolls 41 and 42 via a guide roll 11 and an expander roll 12 . An external force in the width direction is applied to the polarizing plate 1 when it is transported in contact with the expander roll 12 (external force application step). The protection film 2 is introduced between the pair of bonding rolls 41 and 42 via the guide roll 21 .

(1) External force applying step In the external force applying step, the polarizing plate 1 is conveyed in contact with the expander rolls 12 to apply an external force in the width direction of the polarizing plate 1 . The external force applied in the width direction of the polarizing plate 1 may be an inward contracting force or an outward stretching force. By subjecting the polarizing plate 1 to the bonding step after subjecting it to the external force applying step, the TD curl in the sheet body of the polarizing plate 3 with the protective film can be adjusted.

The polarizing plate 1 has a laminated structure including a polarizing film, and the first main surface on the side to be bonded to the image display element and the second main surface on the opposite side are determined according to the layer structure and the like. be done. The polarizing plate 1 typically has a reverse curl (a curl in which the second main surface is convex) when formed into a sheet, depending on the layer structure and the like. By applying an inward contraction force as an external force to the polarizing plate 1 that causes reverse curl when formed into a sheet, the TD curl that occurs in the sheet of the polarizing plate 3 with a protective film can be adjusted. More specifically, reverse curling can be suppressed. Therefore, a polarizing plate with a protective film in which TD curl is suppressed or a polarizing plate with a protective film having positive curl in the TD direction can be produced. Therefore, from the viewpoint of laminating the obtained polarizing plate 3 with a protective film to an image display element without problems, it is preferable to apply an inward contraction force to the polarizing plate 1 in the external force applying step.

By applying an inward contraction force as an external force to the polarizing plate 1 that causes reverse curling when formed into a sheet, the reverse curl in the TD direction that occurs in the sheet of the polarizing plate 3 with a protective film is suppressed. Although the mechanism by which this is possible is not clear, since the polarizing plate 1 is subjected to the lamination step in a state in which the elongation force with respect to the inward contraction force applied in the external force applying step remains, the elongation force is applied to the lamination. This is presumed to be due to the force acting to suppress reverse curl in the TD direction in the protective film-attached polarizing plate 3 obtained through the lamination step. This prediction agrees with the experimental result that the closer the position of the pair of laminating rolls used in the laminating step to the expander rolls used in the external force applying step, the greater the reverse curl correcting force. This is because it can be considered that the closer the arrangement position of the pair of laminating rolls to the expander rolls, the greater the magnitude of the remaining stretching force.

For the polarizing plate 1 that causes a positive curl (a curl with the first main surface being convex) when formed into a sheet, the polarizing plate 3 with a protective film is formed by applying an outward stretching force as an external force. TD curl occurring in the sheet can be adjusted, and more specifically, positive curl can be suppressed. Therefore, a polarizing plate with a protective film in which TD curl is suppressed can be produced.

By applying an outward stretching force as an external force to the polarizing plate 1, which causes a positive curl when formed into a sheet, the positive curl in the TD direction that occurs in the sheet of the polarizing plate 3 with a protective film is suppressed. Although the mechanism by which this is possible is not clear, since the polarizing plate 1 is subjected to the bonding process in a state in which the shrinkage force against the outward extension force applied in the external force applying process remains, the shrinkage force is applied to the bonding process. This is presumed to be due to the force acting to suppress positive curl in the TD direction in the protective film-attached polarizing plate 3 obtained through the combining step.

In the external force application step, when the expander rolls 12 are used to apply the external force in the width direction of the polarizing plate 1, the direction of the external force can be adjusted by the arrangement angle of the expander rolls 12, etc., and the magnitude of the external force can be It can be adjusted by the arrangement angle of the rolls 12, the contact angle of the polarizing plate 1 on the expander rolls 12, the degree of curvature (arc height) of the expander rolls 12 to be employed, and the like.

FIGS. 3A, 3B, and 3C show an example in which the expander rolls 12 are arranged so as to apply an inward contraction force to the polarizing plate 1. FIG. As shown in FIG. 3B, the expander roll 12 has a plurality of spools with ball bearings (not shown) arranged on a curved shaft 123 . An expander roll whose spool is covered with a rubber tube is called a rubber expander roll, and an expander roll whose rubber tube is not covered is called a metal expander roll. In this embodiment, the expander roll 12 may be a rubber expander roll or a metal expander roll. The expander roll 12 is generally circular in cross section perpendicular to the axis 123 and has the same area in any perpendicular cross section. A cross section perpendicular to the axis 123 has a diameter of, for example, 50 mm to 400 mm.

A cross section (aa cross section) perpendicular to the central axis of the central portion 122 of the expander roll 12 shown in FIG. 3(b) is indicated by a cross section 122 in FIGS. A cross section perpendicular to the central axis of the portion 121 with which the end portion of 1 contacts is indicated by cross section 121 in FIG. As shown in FIGS. 3(a), 3(b), and 3(c), the expander roll 12 is arranged so that the center C′ of the cross section 122 of the central portion is located downstream of the center C of the cross section 121. In this case, an inward contractive force can be applied to the polarizing plate 1 as an external force. That is, as shown in FIG. 4, since the expander roll 12 is curved, the polarizing plate 1 does not come into contact with the expander roll 12 over the entire width at the same time, and the expander roll 12 first contacts the expander roll 12 depending on the position in the width direction. The timing of contact is different. When the expander rolls 12 are arranged so that the ends in the width direction of the polarizing plate 1 contact the expander rolls 12 before the central portion (indicated by region A1), and then the central portion contacts the expander rolls 12. can apply an inward contraction force (indicated by an arrow D1) to the polarizing plate 1 as an external force.

3(a) and 3(c), the arrow x indicates the incident direction of the edge of the polarizing plate 1 incident on the expander roll 12, and the arrow y indicates the direction from the center C to the center C' of the expander roll 12. In this case, the angle θ of the arrow y with respect to the arrow x is preferably in the range of 50° to 130° from the viewpoint of being able to sufficiently apply an inward contraction force to the polarizing plate 1 as an external force. Hereinafter, as used herein, "arc height of the expander roll" means the distance between the center C and the center C', and "arrangement angle of the expander roll" means the angle θ of the arrow y with respect to the arrow x. The arc height of the expander roll 12 is, for example, 1 mm to 20 mm.

The magnitude of the external force applied to the polarizing plate 1 can also be adjusted by the contact angle α of the polarizing plate 1 on the expander roll 12 . The contact angle α can be adjusted by moving the guide rolls 11 and/or the expander rolls 12 up and down. The contact angle α is preferably 10° to 100° because the magnitude of the external force applied by the expander roll 12 can be easily adjusted.

5(a), (b), and (c) show an example of the arrangement of the expander rolls 12 when applying an outward stretching force to the polarizing plate 1 as an external force. 5(a), (b), and (c) correspond to FIGS. 3(a), (b), and (c), respectively, when an inward contraction force is applied to the polarizing plate 1 as an external force. As shown in FIGS. 5(a), (b), and (c), the expander roll 12 is arranged such that the center C′ of the cross section 122 of the central portion is located upstream of the center C of the cross section 121. In other words, when the center of the polarizing plate 1 in the width direction comes into contact with the expander roll 12 before the ends, an outward stretching force is applied to the polarizing plate 1 as an external force. be able to. That is, as shown in FIG. 6, the central portion in the width direction of the polarizing plate 1 is brought into contact with the expander roll 12 (indicated by region A2) before the end portion thereof, and the rear end portion is brought into contact with the expander roll 12. When the expander roll 12 is arranged, an outward stretching force (indicated by an arrow b2) can be applied to the polarizing plate 1 as an external force.

5(a) and 5(c), the arrow x indicates the incident direction of the edge of the polarizing plate 1 incident on the expander roll 12, and the arrow y indicates the direction from the center C to the center C' of the expander roll 12. In this case, when the angle θ of the arrow y with respect to the arrow x is in the range of 225° to 360°, the polarizing plate 1 can be sufficiently applied with an outward stretching force as an external force.

The magnitude of the external force applied to the polarizing plate 1 can also be adjusted by the contact angle α of the polarizing plate 1 on the expander roll 12 . The contact angle α can be adjusted by moving the guide rolls 11 and/or the expander rolls 12 up and down. The contact angle α is preferably 10° to 100° because the magnitude of the external force applied by the expander roll 12 can be easily adjusted.

The width of the film (polarizing plate 1) in contact with the expander roll 12 is not particularly limited, but the film (polarizing plate 1) preferably exists within the width of the expander roll 12. Since the film (polarizing plate 1) exists within the existing width of the expander roll 12, an external force can be applied to the entire width of the film, and the TD curl control effect can be exerted on the entire film. In addition, since the film does not come into contact with the ends of the expander roll 12, it is possible to suppress appearance defects such as scratches and wrinkles.

(2) Bonding step In the bonding step, the protective film 2 is superimposed on one side of the polarizing plate 1 after being subjected to the external force application step, and passed between a pair of bonding rolls 41 and 42 to obtain a polarizing plate. A laminate of 1 and a protective film 2 is pressed from above and below and bonded to each other to obtain a polarizing plate 3 with a protective film. In the bonding process, the transport direction of the polarizing plate 1 and the protective film 2 is the longitudinal direction of the film, and the transport directions of both are usually parallel.

The distance L (see FIGS. 3A and 5A) between the pair of bonding rolls 41 and 42 and the expander roll 12 can be adjusted as appropriate. It is preferable that the distance L is 3 m or less, because the polarizing plate 1 in which the stress against the external force applied in the external force applying step remains is easily subjected to the bonding step. The distance L is more preferably 1 m or less, and even more preferably 0.5 m or less. Moreover, it is preferable that the distance L is 0.1 m or more, because the polarizing plate 1 in a wrinkle-free state can be easily subjected to the bonding step. More preferably, the distance L is 0.2 m or more. Also, the distance L is preferably four times or less the diameter of the expander roll 12, and more preferably three times or less. Typically, the distance L is 0.7 times the diameter of the expander roll 12 or more.

In the bonding step using the pair of bonding rolls 41 and 42, the pressure (nip pressure) applied to the laminate of the polarizing plate 1 and the protective film 2 is, for example, 0.01 to 0.5 MPa. 0.05 to 0.3 MPa. As the bonding rolls 41 and 42, conventionally known rolls such as rolls having metal surfaces (including alloys such as SUS) or rubber can be used.

According to the present embodiment, the polarizing plate 3 with a protective film is sufficiently suppressed in reverse curling in the TD direction when formed into a sheet, preferably flat without curling, or having positive curling. can be obtained. According to this protective film-attached polarizing plate 3, when it is attached to an image display element via an adhesive layer, an error may occur in attachment, or air bubbles may enter the interface between the adhesive layer and the image display element. Problems can be effectively suppressed, and the bonding of the polarizing plate 3 with the protective film and the image display element can be performed with good productivity. As long as the curl generated in the protective film-attached polarizing plate 3 is a positive curl, even if the amount of curl is relatively large, there is no particular problem in terms of the above problems and productivity. The protective film-equipped polarizing plate 3 obtained by this embodiment may have a reverse curl to the extent that the above problem can be suppressed (preferably, the above problem does not occur).

(3) Protection Film The protection film 2 is usually composed of a base film and an adhesive layer laminated thereon. The protective film 2 is a film for protecting the surface of the polarizing plate 1, and is usually peeled and removed together with the adhesive layer it has after the polarizing plate 3 with the protective film is attached to an image display element, for example. . The base film is a thermoplastic resin, for example, polyolefin resin such as polyethylene resin, polypropylene resin, and cyclic polyolefin resin; polyester resin such as polyethylene terephthalate and polyethylene naphthalate; polycarbonate resin; It can be made of resin or the like. The adhesive layer can be composed of an acrylic adhesive, an epoxy adhesive, a urethane adhesive, a silicone adhesive, or the like. Moreover, it can also be configured with a resin layer having self-adhesiveness such as a polypropylene-based resin or a polyethylene-based resin.

In addition, in this specification, "(meth)acrylic resin" represents at least one selected from the group consisting of acrylic resins and methacrylic resins. The same applies to other terms with "(meta)" attached.

The thickness of the protective film 2 can be, for example, 5 to 200 μm, preferably 10 to 150 μm, more preferably 20 to 120 μm, still more preferably 2
5 to 100 μm (for example, 90 μm or less, further 75 μm or less). If the thickness is less than 5 μm, the protection of the polarizing plate 1 may be insufficient, and handling is also disadvantageous. A thickness exceeding 200 μm is disadvantageous in terms of cost and reworkability of the protective film 2 .

(3) Polarizing plate The polarizing plate 1 is a polarizing element including at least a polarizing film, and usually further includes a thermoplastic resin film such as a protective film laminated on at least one surface of the polarizing film. A protective film is an optical film responsible for protecting the polarizing film.

(3-1) Configuration Example of Polarizing Plate The polarizing plate 1 can include layers or films other than the polarizing film and the protective film, such as optical layers or films having optical functions other than the polarizing film. Examples of the optical layer or optical film having other optical functions are a retardation film (or a retardation layer), a brightness enhancement film, and the like. Various optical films including a protective film can be laminated and pasted on the polarizing film via an adhesive layer or a pressure-sensitive adhesive layer. The polarizing plate 2 may also have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer.

The thickness of the polarizing plate 1 is usually 200 μm or less, preferably 125 μm or less, more preferably 100 μm or less, still more preferably 75 μm or less from the viewpoint of thinning. The smaller the thickness, the more likely the polarizing plate 1 is to curl in its sheet form, but according to the present embodiment, the polarizing plate 1 is so thin that when formed into a sheet form, the polarizing plate 1 is inversely curled in the TD direction. However, the reverse curl can be effectively corrected in the forward curl direction.

Examples of the layer structure of the polarizing plate 1 will be described with reference to FIGS. 7 to 9, but the layer structure is not limited to these examples. The polarizing plate 1a shown in FIG. 7 includes a polarizing film 61; a first thermoplastic resin film 62 bonded to one surface of the polarizing film 61; A resin film 63 ; an adhesive layer 64 laminated on the outer surface of the second thermoplastic resin film 63 ; and a separate film 65 laminated on the outer surface of the adhesive layer 64 . The separate film 65 is a peelable film for protecting the surface (outer surface) of the adhesive layer 64 . The first and second thermoplastic resin films 62, 63 are, for example, protective films.

One of the first and second thermoplastic resin films 62 and 63 may be omitted as in the polarizing plate 1b shown in FIG. The second thermoplastic resin film 63 is omitted in the polarizing plate 1b, and the adhesive layer 64 is directly applied to the outer surface of the polarizing film 61 (the surface opposite to the surface on which the first thermoplastic resin film 20 is laminated). is attached. Such a polarizing plate having a thermoplastic resin film on only one side of the polarizing film 61 is advantageous for thinning the polarizing plate. When a thermoplastic resin film is laminated only on one surface of the polarizing film 61, the polarizing plate 1 tends to curl in the sheet. Even if a reverse curl occurs when the polarizing plate 1 is made into a sheet by laminating and bonding a thermoplastic resin film, the reverse curl can be effectively corrected in the positive curl direction. .

Also, like the polarizing plate 1c shown in FIG. 9, the adhesive layer 64 and the separate film 65 may be omitted. The polarizing plate 1 may previously have a protective film on one side different from the protective film 2 used in the bonding step. In this case, the obtained polarizing plate 3 with a protective film is a polarizing plate having protective films on both sides.

Although not shown in FIGS. 7 to 9, the polarizing film 10 and the first and second thermoplastic resin films 62 and 63 can preferably be attached using an adhesive.

(3-2) Polarizing Film The polarizing film 10 may be a uniaxially stretched polyvinyl alcohol resin film in which a dichroic dye is adsorbed and oriented. As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film, a saponified polyvinyl acetate-based resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

The degree of saponification of the polyvinyl alcohol resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, more preferably 98.0. It is in the range of up to 100.0 mol %. If the degree of saponification is less than 80.0 mol %, the resulting polarizing plate 1 may have reduced water resistance and moist heat resistance.

The degree of saponification is the unit ratio (mol%) of the ratio of the acetic acid group (acetoxy group: -OCOCH ₃ ) contained in the polyvinyl acetate resin, which is the raw material of the polyvinyl alcohol resin, to the hydroxyl group during the saponification process. is represented by the following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic groups)
defined by The degree of saponification can be determined according to JIS K 6726 (1994). A higher degree of saponification indicates a higher proportion of hydroxyl groups, and thus a lower proportion of acetate groups that inhibit crystallization.

The average degree of polymerization of the polyvinyl alcohol resin is preferably 100-10000, more preferably 1500-8000, still more preferably 2000-5000. The average degree of polymerization of the polyvinyl alcohol resin can also be determined according to JIS K 6726 (1994). When the average degree of polymerization is less than 100, it is difficult to obtain preferable polarizing performance, and when it exceeds 10,000, the solubility in solvents deteriorates, making it difficult to form a polyvinyl alcohol-based resin film.

The dichroic dye contained (adsorbed and oriented) in the polarizing film 61 can be iodine or a dichroic organic dye. Specific examples of dichroic organic 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, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Includes Sky Blue, Direct First Orange S, and First Black. A dichroic dye may be used individually by 1 type, and may use 2 or more types together. The dichroic dye is preferably iodine.

The polarizing film 61 is produced by a process of uniaxially stretching a polyvinyl alcohol-based resin film; a process of dyeing the polyvinyl alcohol-based resin film with a dichroic dye to adsorb the dichroic dye; It can be produced through a step of cross-linking the alcohol-based resin film; and a step of washing with water after the cross-linking treatment.

A polyvinyl alcohol-based resin film is formed by forming the polyvinyl alcohol-based resin described above. The film-forming method is not particularly limited, and known methods such as a melt extrusion method and a solvent casting method can be employed. The thickness of the polyvinyl alcohol resin film is, for example, about 10 to 150 μm, preferably 50 μm or less, more preferably 35 μm or less.

The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing with the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before or during the cross-linking treatment. Moreover, you may uniaxially stretch in these several steps.

In the uniaxial stretching, the film may be uniaxially stretched between rolls having different circumferential speeds, or may be uniaxially stretched using hot rolls. The uniaxial stretching may be dry stretching in which the film is stretched in the atmosphere, or wet stretching in which the polyvinyl alcohol resin film is stretched in a solution. The draw ratio is usually about 3 to 8 times.

As a method for dyeing a polyvinyl alcohol resin film with a dichroic dye, for example, a method of immersing a polyvinyl alcohol resin film in an aqueous solution (dyeing solution) containing a dichroic dye is adopted. The polyvinyl alcohol-based resin film is preferably subjected to immersion treatment (swelling treatment) in water before dyeing treatment.

When iodine is used as the dichroic dye, a method of dyeing by immersing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous dyeing solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. Also, the content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing aqueous solution is usually about 20 to 40°C.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of dyeing by immersing a polyvinyl alcohol resin film in a dyeing aqueous solution containing a water-soluble dichroic organic dye is usually adopted. The content of the dichroic organic dye in the aqueous dyeing solution is usually 1×10 ^-4 to 10 parts by weight, preferably 1×10 ^-3 to 1 part by weight, per 100 parts by weight of water. The aqueous dyeing solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dyeing aqueous solution is usually about 20 to 80°C.

The cross-linking treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in a cross-linking agent-containing aqueous solution. A suitable example of a cross-linking agent is boric acid, but other cross-linking agents such as boron compounds such as borax, glyoxal, glutaraldehyde, etc. can also be used. Only one kind of crosslinking agent may be used, or two or more kinds thereof may be used in combination.

The amount of the cross-linking agent in the cross-linking agent-containing aqueous solution is usually 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, the cross-linking agent-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the cross-linking agent-containing aqueous solution is generally 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. The temperature of the aqueous solution containing the cross-linking agent is usually 50°C or higher, preferably 50 to 85°C.

The polyvinyl alcohol-based resin film after cross-linking treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in water. The temperature of water in the water washing process is usually about 1 to 40.degree.

A polarizing film 61 is obtained by performing a drying treatment after washing with water. The drying treatment can be drying with a hot air dryer, drying with contact with a hot roll, drying with a far-infrared heater, or the like. The drying temperature is usually about 30 to 100°C, preferably 50 to 90°C.

The thickness of the polarizing film 61 is usually about 2 to 40 μm. From the viewpoint of thinning the polarizing plate 1, the thickness of the polarizing film 61 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. The thinner the thickness of the polarizing film 61 is, the more likely the polarizing plate 1 is to curl in the sheet. Even if curl occurs, this reverse curl can be effectively corrected in the normal curl direction.

(3-3) First and second thermoplastic resin films The first and second thermoplastic resin films 62 and 63 are each independently made of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin. It is a film made of plastic resin. The thermoplastic resin constituting the first and second thermoplastic resin films 20 and 30 is, for example, a polyolefin-based resin such as a chain polyolefin-based resin (polypropylene-based resin, etc.), a cyclic polyolefin-based resin (norbornene-based resin, etc.). Cellulose-based resins such as triacetyl cellulose and diacetyl cellulose; Polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate-based resins; (meth)acrylic-based resins such as methyl methacrylate-based resins; Polyvinyl chloride resin; acrylonitrile/butadiene/styrene resin; acrylonitrile/styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyethersulfone-based resins; polyarylate-based resins; polyamide-imide-based resins; polyimide-based resins, and the like.

Examples of chain polyolefin resins include homopolymers of chain olefins such as polyethylene resins and polypropylene resins, as well as copolymers composed of two or more chain olefins. More specific examples include polypropylene resins (polypropylene resins that are homopolymers of propylene and copolymers that are mainly composed of propylene), polyethylene resins (polyethylene resins that are homopolymers of ethylene, and ethylene-based resins). and copolymers).

Cyclic polyolefin-based resin is a general term for resins polymerized using cyclic olefins as polymerized units. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically are random copolymers), graft polymers modified with unsaturated carboxylic acids or derivatives thereof, and hydrides thereof. Among them, norbornene-based resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers as cyclic olefins are preferably used.

Cellulose-based resins are obtained from raw material cellulose such as cotton linter and wood pulp (hardwood pulp, softwood pulp) in which some or all of the hydrogen atoms in the hydroxyl groups of cellulose are substituted with acetyl groups, propionyl groups and/or butyryl groups. It also refers to cellulose organic acid esters or cellulose mixed organic acid esters. Examples thereof include cellulose acetate, propionate, butyrate, and mixed esters thereof. Among them, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferred.

Polyester-based resins are resins other than the above cellulose-based resins that have ester bonds, and generally consist of a polycondensate of a polyhydric carboxylic acid or a derivative thereof and a polyhydric alcohol. Divalent dicarboxylic acids or derivatives thereof can be used as polyvalent carboxylic acids or derivatives thereof, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. A divalent diol can be used as the polyhydric alcohol, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol, and the like. Examples of suitable polyester resins include polyethylene terephthalate.

Polycarbonate-based resins are engineering plastics composed of polymers in which monomer units are bonded via carbonate groups, and are resins having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called modified polycarbonate in which the polymer skeleton is modified in order to lower the photoelastic coefficient, or a copolymerized polycarbonate with improved wavelength dependence.

A (meth)acrylic resin is a polymer containing structural units derived from a (meth)acrylic monomer. The polymer is typically a polymer containing a methacrylic acid ester. A polymer containing 50% by weight or more of structural units derived from a methacrylic acid ester is preferred. The (meth)acrylic resin may be a homopolymer of a methacrylic acid ester, or a copolymer containing structural units derived from other polymerizable monomers. In this case, the ratio of structural units derived from other polymerizable monomers is preferably 50% by weight or less with respect to all structural units.

A methacrylic acid alkyl ester is preferable as the methacrylic acid ester that can constitute the (meth)acrylic resin. Methacrylic acid alkyl esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate. and methacrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms such as 2-hydroxyethyl methacrylate. The number of carbon atoms in the alkyl group contained in the methacrylic acid alkyl ester is preferably 1-4. (Meth) acrylic resin WHEREIN: Methacrylic acid ester may be used individually by 1 type, and may use 2 or more types together.

Examples of the other polymerizable monomers that can constitute the (meth)acrylic resin include acrylic acid esters and other compounds having a polymerizable carbon-carbon double bond in the molecule. Other polymerizable monomers may be used alone or in combination of two or more. Alkyl acrylate is preferable as the acrylate. Alkyl acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. , acrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms, such as 2-hydroxyethyl acrylate. The number of carbon atoms in the alkyl group contained in the acrylic acid alkyl ester is preferably 1-4. (Meth)acrylic resin WHEREIN: Acrylic acid ester may be used individually by 1 type, and may use 2 or more types together.

Other compounds having a polymerizable carbon-carbon double bond in the molecule include vinyl compounds such as ethylene, propylene and styrene, and vinyl cyanide compounds such as acrylonitrile. Other compounds having a polymerizable carbon-carbon double bond in the molecule may be used singly or in combination of two or more.

The first and second thermoplastic resin films 62 and 63 can be protective films laminated on one side of the polarizing film 61 to protect the polarizing film 61 . The first or second thermoplastic resin films 62 and 63 can also be protective films having optical functions such as retardation films and brightness enhancement films. For example, by stretching a thermoplastic resin film made of the above materials (such as uniaxial stretching or biaxial stretching), or by forming a liquid crystal layer or the like on the film, a retardation value given an arbitrary retardation value It can be a film. The first and/or second thermoplastic resin films 62 and 63 are laminated on the surface thereof, such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer. layer).

The thickness of the first and second thermoplastic resin films 62 and 63 is usually 1 to 100 μm, preferably 5 to 60 μm, more preferably 5 to 50 μm, from the viewpoint of strength and handleability. A thickness within this range can mechanically protect the polarizing film 61 and suppress shrinkage of the polarizing film 61 when the polarizing plate 2 is exposed to a wet and hot environment. The smaller the thickness of the first thermoplastic resin film 62 or the second thermoplastic resin film 63, the more likely the sheet of the polarizing plate 1 is curled. Even if the thickness of the second thermoplastic resin film 63 is as thin as, for example, 40 μm or less, or even 30 μm or less, and reverse curl occurs when the polarizing plate 1 is formed into a sheet, the reverse curl is directed toward the forward curl direction. can be corrected effectively.

When the first thermoplastic resin film 62 is provided on one side of the polarizing film 61 and the second thermoplastic resin film 63 is provided on the other side, as in the polarizing plates 1a and 1c shown in FIGS. The first thermoplastic resin film 62 and the second thermoplastic resin film 63 may be made of the same kind of thermoplastic resin or different kinds of thermoplastic resins. When the equilibrium moisture content and moisture permeability of the thermoplastic resin films laminated on both sides are different from each other, for example, when the polarizing plate 2 is composed of a plastic resin, the sheets of the polarizing plate 2 tend to curl. In such cases the invention is particularly advantageous.

For example, a film having a higher equilibrium moisture content than the second thermoplastic resin film 63 can be used as the first thermoplastic resin film 62 . The greater the difference in the equilibrium moisture content between the first thermoplastic resin film 62 and the second thermoplastic resin film 63 laminated on both sides of the polarizing film 61, the more likely the polarizing plate 1 will curl in its sheet form. , according to the present invention, the difference in equilibrium moisture content is 0.5% by weight or more, further 1% by weight or more, and furthermore 1.5% by weight or more, and the polarizing plate 1 is a sheet. Even if a reverse curl occurs in the curling direction, the reverse curl can be effectively corrected in the forward curl direction.

As used herein, the equilibrium moisture content of the film is measured by the dry weight method, specifically by the following formula:
Equilibrium moisture content (% by weight) = {(film weight before drying - film weight after drying) / film weight before drying} x 100
required according to Here, the film weight before drying is the weight after storing the film for 24 hours in an environment of 23° C. and 55% relative humidity, and drying means drying the film at 105° C. for 2 hours. Combinations of thermoplastic resin films having a difference in equilibrium moisture content of 0.5% by weight or more include, for example, a combination of a cellulose resin film (such as a TAC film) and a cyclic polyolefin resin film, a cellulose resin film (TAC film, etc.) and a (meth)acrylic resin film, a combination of a cellulose resin film (TAC film, etc.) and a polyester resin film, a cellulose resin film (TAC film, etc.) and a linear polyolefin resin film. , a combination of a (meth)acrylic resin film and a cyclic polyolefin resin, a combination of a (meth)acrylic resin film and a polyester resin film, and the like. The difference in equilibrium moisture content between the first thermoplastic resin film 10 and the second thermoplastic resin film 62 is usually 5% by weight or less, preferably 2.5% by weight or less.

The equilibrium moisture content of the first thermoplastic resin film 62 is, for example, 1.5% by weight or more, and may be 2% by weight or more. The equilibrium moisture content of the first thermoplastic resin film 62 is usually 5% by weight or less.

When a film having a higher equilibrium moisture content than the second thermoplastic resin film 63 is used as the first thermoplastic resin film 62, the equilibrium moisture content of the second thermoplastic resin film 62 is usually 0.1 to 1.5. % by weight, preferably 0.1 to 1% by weight. Examples of thermoplastic resins constituting the second thermoplastic resin film 62 capable of achieving such an equilibrium moisture content include cyclic polyolefin-based resins, (meth)acrylic-based resins, polyester-based resins, chain polyolefin-based resins, and the like.

The equilibrium moisture content of a thermoplastic resin film depends on its material (the type of thermoplastic resin that makes up the film), the thickness of the film, the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface, and the material used. can also be adjusted by

When a film having a higher equilibrium moisture content than the second thermoplastic resin film 63 is used as the first thermoplastic resin film 62, from the viewpoint of correcting the reverse curl that tends to occur in the polarizing plate 1 in the positive curl direction, usually: In the pressing step, the protective film 2 is arranged on the first thermoplastic resin film 62 side of the polarizing plate 1 .

Further, for example, a film having higher moisture permeability than the second thermoplastic resin film 63 can be used as the first thermoplastic resin film 62 . The larger the difference in moisture permeability between the first thermoplastic resin film 62 and the second thermoplastic resin film 63 laminated on both sides of the polarizing film 61, the more likely the polarizing plate 1 will curl in its sheet form. According to the present invention, the difference in moisture permeability is 30 g/(m ² ·24 hr) or more, further 50 g/(m ² ·24 hr) or more, furthermore 100 g/(m ² ·24 hr) or more, and the polarized light Even if the board 1 is reverse curled when it is made into a sheet, the reverse curl can be effectively corrected in the positive curl direction.

In this specification, the moisture permeability of a film is the moisture permeability measured by the cup method defined in JIS Z 0208 at a temperature of 40°C and a relative humidity of 90%. Combinations of thermoplastic resin films having a difference in moisture permeability of 30 g/(m ² ·24 hr) or more include, for example, a combination of a cellulose resin film (such as a TAC film) and a cyclic polyolefin resin film, and a cellulose resin film. Combination of (TAC film, etc.) and (meth)acrylic resin film, combination of cellulose resin film (TAC film, etc.) and polyester resin film, cellulose resin film (TAC film, etc.) and linear polyolefin resin A combination with a film, a combination of a (meth)acrylic resin film and a cyclic polyolefin resin, a combination of a (meth)acrylic resin film and a polyester resin film, and the like can be mentioned. The difference in moisture permeability between the first thermoplastic resin film 62 and the second thermoplastic resin film 63 is usually 5000 g/(m ² ·24 hr).
It is below.

The moisture permeability of the first thermoplastic resin film 62 is, for example, 300 g/(m ² ·24 hr) or more, and may be 400 g/(m ² ·24 hr) or more. Moisture permeability of 300 g/(m ² ·24 hr) or more means that when the first thermoplastic resin film 62 and the polarizing film 61 are laminated using a water-based adhesive, the layer made of the water-based adhesive is effective. It is also advantageous in that it can be dried well and the productivity can be improved. First thermoplastic resin film 6
The moisture permeability of No. 2 is usually 5000 g/(m ² ·24 hr) or less.

When a film having a higher moisture permeability than the second thermoplastic resin film 63 is used as the first thermoplastic resin film 62, the moisture permeability of the second thermoplastic resin film 63 is usually 1 to 350 g/(m ² · 24 hr. ), preferably 5 to 200 g/(m ² ·24 hr). Examples of the thermoplastic resin constituting the second thermoplastic resin film 63 capable of achieving such moisture permeability include cyclic polyolefin resin, (meth)acrylic resin, polyester resin, chain polyolefin resin, and the like.

The moisture permeability of a thermoplastic resin film depends on its material (the type of thermoplastic resin that makes up the film), the thickness of the film, the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface, and the material used. can also be adjusted.

When a film having higher moisture permeability than the second thermoplastic resin film 63 is used as the first thermoplastic resin film 62, from the viewpoint of correcting the reverse curl that tends to occur in the polarizing plate 1 in the positive curl direction, the above In the pressing step, the protective film 2 is arranged on the first thermoplastic resin film 62 side of the polarizing plate 1 .

As described above, the polarizing film 61 and the first and second thermoplastic resin films 62, 63 can be bonded using an adhesive. Prior to laminating and bonding the first and second thermoplastic resin films 62 and 63 to the polarizing film 61, plasma is applied to the bonding surfaces of the polarizing film 61 and/or the first and second thermoplastic resin films 62 and 63. Surface activation treatments such as treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification treatment may also be performed. This surface activation treatment can enhance the adhesiveness between the polarizing film 61 and the first and second thermoplastic resin films 62 and 63 .

As the adhesive, a water-based adhesive, an active energy ray-curable adhesive, or a thermosetting adhesive can be used, preferably a water-based adhesive or an active energy ray-curable adhesive. When the thermoplastic resin films are laminated on both sides of the polarizing film 61, the adhesives on both sides may be of the same type or different types. When a different kind of adhesive is used, the polarizing plate 2 tends to curl in the sheet. Even if a reverse curl occurs, the reverse curl can be effectively corrected in the positive curl direction.

Water-based adhesives are those in which adhesive components are dissolved or dispersed in water. A water-based adhesive that is preferably used is, for example, an adhesive composition using a polyvinyl alcohol-based resin or a urethane resin as a main component.

When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin may be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, or carboxyl group-modified polyvinyl alcohol. , acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, and amino group-modified polyvinyl alcohol. Polyvinyl alcohol-based resins are vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymerization of vinyl acetate with other monomers that can be copolymerized with this. It may be a polyvinyl alcohol-based copolymer obtained by saponifying the combination.

A water-based adhesive containing a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of the polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol resin in the adhesive is 100% water.
It is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight.

Adhesives made from aqueous solutions of polyvinyl alcohol resins are used to improve adhesiveness by adding curable components such as polyhydric aldehydes, melamine compounds, zirconia compounds, zinc compounds, glyoxal, glyoxal derivatives, water-soluble epoxy resins, and the like. It is preferable to contain a cross-linking agent. Examples of water-soluble epoxy resins include polyalkylenepolyamines such as diethylenetriamine and triethylenetetramine, and polyamidepolyamine epoxy resins obtained by reacting epichlorohydrin with polyamidoamine obtained by reacting polyalkylenepolyamines such as diethylenetriamine and triethylenetetramine with dicarboxylic acids such as adipic acid. can be preferably used. Commercial products of such polyamide polyamine epoxy resins include "Sumireze Resin 650" (manufactured by Taoka Chemical Co., Ltd.), "Sumireze Resin 675" (manufactured by Taoka Chemical Co., Ltd.), "WS-525" (Japan PMC Co., Ltd.) and the like. The amount of the curable component and the crosslinking agent added (the total amount when both are added as the curable component and the crosslinking agent) is usually 1 to 100 parts by weight, preferably 1 to 100 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin 1 to 50 parts by weight. If the amount of the curable component or cross-linking agent added is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol resin, the effect of improving the adhesiveness tends to be small. If the amount exceeds 100 parts by weight with respect to 100 parts by weight of the alcohol-based resin, the adhesive layer tends to become brittle.

A suitable example of a case where a urethane resin is used as the main component of the adhesive is a mixture of a polyester-based ionomer-type urethane resin and a compound having a glycidyloxy group. A polyester-based ionomer-type urethane resin is a urethane resin having a polyester skeleton into which a small amount of an ionic component (hydrophilic component) is introduced. Such ionomer-type urethane resins are suitable as water-based adhesives because they can be directly emulsified in water without using an emulsifier.

When a water-based adhesive is used, after bonding the polarizing film 61 and the first and/or second thermoplastic resin films 62 and 63, a drying step is performed to remove water contained in the water-based adhesive. preferably implemented. After the drying step, a curing step of curing at a temperature of, for example, 20 to 45°C may be provided.

Active energy ray-curable adhesives are adhesives that are cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. When using an active energy ray-curable adhesive, the adhesive layer of the polarizing plate 1 is a cured layer of the adhesive.

The active energy ray-curable adhesive can be an adhesive that contains an epoxy compound that cures by cationic polymerization as a curable component, and is preferably an ultraviolet curable adhesive that contains such an epoxy compound as a curable component. is an agent. The term "epoxy-based compound" as used herein means a compound having an average of one or more, preferably two or more epoxy groups in the molecule. Epoxy compounds may be used alone or in combination of two or more.

A specific example of the epoxy compound that can be preferably used is a hydrogenated epoxy compound ( polyol glycidyl ether having an alicyclic ring); aliphatic epoxy compounds such as polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts; one epoxy group bonded to an alicyclic ring in the molecule; It includes alicyclic epoxy compounds which are epoxy compounds having one or more.

The active energy ray-curable adhesive may contain a radically polymerizable (meth)acrylic compound as a curable component instead of or together with the epoxy compound. The (meth)acrylic compound includes a (meth)acrylate monomer having at least one (meth)acryloyloxy group in the molecule; obtained by reacting two or more functional group-containing compounds, and at least two in the molecule. (meth)acryloyloxy group-containing compounds such as (meth)acrylate oligomers having a (meth)acryloyloxy group.

When the active energy ray-curable adhesive contains an epoxy compound that cures by cationic polymerization as a curable component, it preferably contains a photocationic polymerization initiator. Examples of photocationic polymerization initiators include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; and iron-allene complexes. Moreover, when the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth)acrylic compound, it preferably contains a radical photopolymerization initiator. Examples of radical photopolymerization initiators include acetophenone-based initiators, benzophenone-based initiators, benzoin ether-based initiators, thioxanthone-based initiators, xanthone, fluorenone, camphorquinone, benzaldehyde, and anthraquinone.

When using an active energy ray-curable adhesive for laminating and bonding the polarizing film 61 and the first and/or second thermoplastic resin films 62 and 63, a drying process is performed as necessary after lamination and bonding. Next, a curing step is performed in which the active energy ray-curable adhesive is cured by irradiating it with an active energy ray. The light source of the active energy ray is not particularly limited, but ultraviolet rays having a light emission distribution at a wavelength of 400 nm or less are preferable. A wave-excited mercury lamp, a metal halide lamp, or the like can be used.

The irradiation intensity of the active energy ray to the adhesive layer made of the active energy ray-curable adhesive is appropriately determined depending on the composition of the adhesive. It is preferably set to be up to 6000 mW/cm ² . Irradiation intensity is 0
. When it is 1 mW/cm ² or ^more , the reaction time does not become too long. 61 deterioration is less likely to occur.

The irradiation time of the active energy ray ^is also appropriately determined depending on the composition of the adhesive. is preferred. When the integrated light intensity is 10 mJ/cm ² or more, a sufficient amount of active species derived from the polymerization initiator can be generated to allow ^the curing reaction to proceed more reliably. It does not become too much, and good productivity of the polarizing plate 1 can be maintained.

(3-4) Adhesive Layer and Separate Film As shown in FIGS. 7 and 8, the polarizing plate 1 can include an adhesive layer 64 . This adhesive layer 64 can be directly laminated on the surface of the first or second thermoplastic resin films 62, 63 or the polarizing film 61, and the polarizing plate 3 with a protective film can be attached to an image display element (for example, a liquid crystal cell). can be used to match

The adhesive layer 64 for bonding the polarizing plate 3 with a protective film to an image display element (for example, liquid crystal cell) is the main surface (first main surface) of the polarizing plate on the side to be bonded to an image display element such as a liquid crystal cell. face) side. For example, the polarizing plate 1 includes first and second thermoplastic resin films 62 and 63, and the first thermoplastic resin film 62 is a film having a higher equilibrium moisture content and/or higher moisture permeability than the second thermoplastic resin film 63. When used, the adhesive layer 64 can be placed on the second thermoplastic resin film 63 side.

The adhesive layer 64 can be composed of an adhesive composition whose main component (base polymer) is a (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether resin. . Among them, a pressure-sensitive adhesive composition using a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is suitable. The adhesive composition may be active energy ray-curable or heat-curable.

Examples of the (meth)acrylic resin used in the adhesive composition include butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Polymers or copolymers containing one or more of (meth)acrylic acid esters as monomers are preferably used. The (meth)acrylic resin is preferably copolymerized with a polar monomer. Examples of polar monomers include (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, glycidyl ( Monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc., such as meth)acrylates, can be mentioned.

The pressure-sensitive adhesive composition may contain only the above base polymer, but usually further contains a cross-linking agent. The cross-linking agent is a metal ion having a valence of 2 or more, which forms a carboxylic acid metal salt with a carboxyl group; a polyamine compound, which forms an amide bond with a carboxyl group; Examples include epoxy compounds and polyols that form ester bonds with carboxyl groups; and polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable pressure-sensitive adhesive composition has the property of being cured by being irradiated with an active energy ray such as an ultraviolet ray or an electron beam. It is a pressure-sensitive adhesive composition that can be adhered to an adherend such as the adhesive agent, and that can be cured by irradiation with an active energy ray to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably UV-curable. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. Furthermore, if necessary, a photopolymerization initiator, a photosensitizer, and the like may be contained.

The adhesive composition contains fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders). etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives.

The adhesive layer 64 is formed by applying an organic solvent-diluted solution of the adhesive composition to the adhesive layer forming surface of the polarizing plate 1 (that is, the polarizing film 61 or the first or second thermoplastic resin films 62 and 63). and dried. Alternatively, an organic solvent diluted solution of the adhesive composition is applied on a separate film (for example, separate film 65) and dried to form an adhesive layer, which is then transferred to the adhesive layer forming surface of the polarizing plate 1. You may In either method, it is preferable to attach a separate film to the outer surface of the adhesive layer 64 to protect the adhesive layer 64 until use. When an active energy ray-curable pressure-sensitive adhesive composition is used, a cured product having a desired degree of curing can be obtained by irradiating the formed pressure-sensitive adhesive layer with an active energy ray. The thickness of the adhesive layer 64 is usually 1 to 40 μm, but from the viewpoint of making the polarizing plate 1 thinner, it is preferably 3 to 25 μm.

The separate film 65 is a film adhered to protect the surface of the adhesive layer 64 until it is adhered to the image display element (eg liquid crystal cell). The separate film 65 is generally composed of a thermoplastic resin film having one side subjected to a release treatment, and the release-treated surface is attached to the adhesive layer 64 . The thermoplastic resin forming the separate film 65 can be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, or a polyester resin such as polyethylene terephthalate or polyethylene naphthalate. The thickness of the separate film 65 is, for example, 10-100 μm.

(3-5) Other constituent elements of polarizing plate The polarizing plate 1 can contain constituent elements other than those described above. Other constituent elements include optical layers or optical films having optical functions other than the polarizing film 61, and specific examples thereof include optical films such as retardation films and brightness enhancement films. Other optical films can be laminated and pasted via a pressure-sensitive adhesive layer or an adhesive layer.

Moreover, the polarizing plate 1 can include a protective film different from the protective film 2 used in the pressing step. This protective film is arranged on one surface of the polarizing plate 1 . Regarding the structure of this protection film, the description of the protection film 2 mentioned above is cited.

(3-6) Curl of polarizing plate As described above, according to the present invention, the polarizing plate 1 can be corrected in the forward curling direction, thereby sufficiently suppressing reverse curling when formed into a sheet. It is possible to obtain a polarizing plate 3 with a protective film which is preferably flat without curling or has positive curling. The manufacturing method according to the present embodiment is applied when the polarizing plate 1 is formed into a sheet body and causes reverse curling (curling with the main surface side on which the protective film 2 is superimposed being convex) (further reverse curling and causes TD curl).

Above, as one form of the polarizing plate 1 that tends to cause reverse curling when formed into a sheet, the first thermoplastic resin film 62 and the second thermoplastic resin film 63 have different equilibrium moisture contents and/or Although the case of having moisture permeability is mentioned above, reverse curling is likely to occur when the polarizing plate 1 has an asymmetrical layer structure with respect to the polarizing film 61 .

An example of the configuration of the polarizing plate 1 that tends to cause reverse curling is as follows.
(a) A configuration in which a thermoplastic resin film (protective film, etc.) is laminated only on one side of the polarizing film 61,
(b) A configuration in which a protective film is attached to one surface of the polarizing film 61, and an optical film other than the protective film (such as a brightness enhancement film) is attached to the other surface;
(c) The configuration of the thermoplastic resin films (protective films, etc.) bonded to both sides of the polarizing film 61 (resin type, thickness, equilibrium moisture content, moisture permeability, presence or absence of surface treatment layer, etc.) is different from each other, ( d) A configuration in which adhesive layers for bonding thermoplastic resin films (protective films, etc.) to both surfaces of the polarizing film 61 are formed of different adhesives,
(e) A configuration in which thermoplastic resin films (protective films, etc.) are laminated on both sides of the polarizing film 61, and another optical film is laminated on one thermoplastic resin film,
(f) In addition, with the polarizing film 61 as a reference, the total number of films and layers on one side is different from the total number of films and layers on the other side.

(4) Other steps The manufacturing method according to the present invention may further include a step of cutting the polarizing plate 3 with the protective film obtained by the pressing step to obtain a sheet of the polarizing plate 3 with the protective film. can. For cutting, a commonly used cutting device such as a shear cutter can be used.

Although the shape of the sheet is not particularly limited, it is usually rectangular, preferably rectangular with long sides and short sides, more preferably rectangular. This sheet is usually cut so that a pair of opposing sides are parallel to the MD and the remaining pair of opposing sides are parallel to the TD. It may be cut in such a way as to be , or may be a rectangular sheet with one diagonal parallel to MD or TD. Although the length of the long side and the short side of the sheet is not particularly limited, the long side is usually 50 mm or more and the short side is 30 mm or more. Curl is more likely to occur as the sheet size increases. If the size (long side and/or short side) is too small, the problem of curl per se is less likely to occur.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, the equilibrium moisture content, moisture permeability, thickness, film tension and curl amount were measured according to the following methods.

(1) Equilibrium Moisture Content of Film A test piece having a TD length of 150 mm×MD length of 100 mm was cut out. The film weight was measured after storage for 24 hours under an environment of 23° C. and 55% relative humidity. After that, drying treatment was performed at 105° C. for 2 hours, and the film weight after drying treatment was measured. From the film weight before and after drying, the following formula:
Equilibrium moisture content (% by weight) = {(film weight before drying - film weight after drying) / film weight before drying} x 100
Equilibrium moisture content was determined based on.

(2) Moisture Permeability of Film Moisture permeability [g/(m ² ·24 hr)] was measured at a temperature of 40°C and a relative humidity of 90% by the cup method specified in JIS Z 0208.

(3) Thickness of polarizing plate and film Measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(4) Film tension in MD of polarizing plate and protective film Between a pair of laminating rolls for laminating the polarizing plate and protective film and a pair of nip rolls upstream and closest to the laminating rolls The film tension [N/m] of the polarizing plate and the protection film running was measured using a tension detection roll installed between a bonding roll and a pair of nip rolls closest to the bonding roll.

(5) Polarizing plate with protective film and curl amount of polarizing plate From the obtained polarizing plate with protective film, cut out a rectangular test piece with a long side of 300 mm × short side of 200 mm so that one diagonal line is parallel to TD, It was left for 24 hours in an environment of 23° C. temperature and 55% relative humidity. The specimen was placed with its concave side up, ie, on a reference surface (horizontal table) so that the corners of the rectangular specimen were raised. In this state, the height from the reference surface was measured for each of the corners on both ends of the diagonal line parallel to the TD of the test piece, and the TD curl amount [mm] was obtained as the average height of these two corners. If the curl amount is a positive value, it means that the first thermoplastic resin film side is concave (positive curl), and if it is a negative value, the second thermoplastic resin film side is concave. (reverse curl).

<Example 1>
(A) Preparation of polarizing film A long polyvinyl alcohol film (average degree of polymerization: about 2400, degree of saponification: 99.9 mol% or more, thickness: 30 μm) is continuously conveyed and expanded about four times in a dry process. After being uniaxially stretched and further immersed in pure water at 40°C for 1 minute while maintaining the tension, it was then immersed in an aqueous solution with a weight ratio of iodine/potassium iodide/water of 0.1/5/100 at 28°C for 60 seconds. Soaked. Then, it was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 10.5/7.5/100 at 68° C. for 300 seconds. Subsequently, the film was washed with pure water at 5°C for 5 seconds and then dried at 70°C for 180 seconds to obtain a long polarizing film in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. The thickness of the polarizing film was 11.1 μm.

(B) Preparation of polarizing plate The polarizing film obtained in (A) above was continuously conveyed, and a long first thermoplastic resin film [TAC film "KC2UAW" manufactured by Konica Minolta Opto Co., Ltd. was used as a hard film. A film having a coating layer formed thereon, thickness: 32.4 μm, equilibrium moisture content: 1.9% by weight, moisture permeability: 455 g/(m ² 24 hr)] and a long second thermoplastic resin film [JSR (
FEKB015D3, a cyclic polyolefin- ^based resin film manufactured by Co., Ltd.;
is continuously conveyed, and a water-based adhesive is injected between the polarizing film and the first thermoplastic resin film, and between the polarizing film and the second thermoplastic resin film. A laminated film consisting of 1 thermoplastic resin film/aqueous adhesive layer/polarizing film/aqueous adhesive layer/second thermoplastic resin film was obtained. Subsequently, the obtained laminated film was conveyed and passed through a hot air dryer to perform heat treatment at 80° C. for 300 seconds to dry the water-based adhesive layer, thereby obtaining a polarizing plate. The above water-based adhesive had a concentration of 3 wt. % of a polyvinyl alcohol aqueous solution mixed with a cross-linking agent [sodium glyoxylate manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] at a rate of 1 part by weight per 10 parts by weight of the polyvinyl alcohol powder.

The thickness of the polarizing plate was 58.6 μm. When the TD curl amount of the polarizing plate was measured according to the above method, it was −26.0 mm (reverse curl).

(C) Production of polarizing plate with protective film A protective film whose material film is made of polyethylene terephthalate and has a (meth)acrylic pressure-sensitive adhesive layer thereon, total thickness: 57.3 μm] is continuously conveyed, and these are stacked and passed between bonding rolls. A laminate of the protection film and the polarizing plate was pressed from above and below and stuck together to produce a polarizing plate with the protection film. The protective film is attached to the surface of the first thermoplastic resin film (TAC film) of the polarizing plate via the adhesive layer. The contact angle of the polarizing plate on the expander roll was 37.5°, and the distance L between the expander roll and the bonding roll was 350 mm, which was 3.5 times the diameter of the expander roll. The pressure (nip pressure) applied to the laminate of the protective film and the polarizing plate by the bonding roll was 0.1 MPa. The contact angle and nip pressure are approximately the same values in Examples 2 to 5 below, and the nip pressure is approximately the same value in Comparative Examples below. Moreover, the arrangement angle of the expander roll was set to 50°. Table 1 shows the TD curl amount of the obtained polarizing plate with a protective film.

<Examples 2 and 3>
A polarizing plate with a protective film was produced in the same manner as in Example 1 except that the arrangement angle of the expander roll brought into contact with the polarizing plate before lamination was set as shown in Table 1. Table 1 shows the TD curl amount of the obtained polarizing plate with a protective film. The distance L between the expander roll and the lamination roll was 350 mm, which was 3.5 times the diameter of the expander roll.

<Examples 4 and 5>
The arrangement angle of the expander roll in contact with the polarizing plate before lamination was as shown in Table 1, and the distance L between the expander roll and the lamination roll was 274 mm (2.74 times the diameter of the expander roll). A polarizing plate with a protective film was produced in the same manner as in Example 1 except for the above. Table 1 shows the TD curl amount of the obtained polarizing plate with a protective film.

<Comparative Example 1>
A polarizing plate with a protective film was produced in the same manner as in Example 1, except that the polarizing plate was not transported through an expander roll before bonding. Table 1 shows the TD curl amount of the obtained polarizing plate with a protective film.

From the results of Examples 1 to 5, the TD curl amount could be controlled by applying an external force in the width direction of the film (polarizing plate) with the expander roll. Further, from the results of Examples 2 to 5, by changing the distance L between the expander roll and the bonding roll, the TD curl amount could be adjusted even with the same expander roll arrangement angle.

1, 1a, 1b, 1c polarizing plate (first film) 2 protective film (second film) 3 polarizing plate with protective film (optical film) 10 external force applying means 11
Guide Roll 12 Expander Roll 21 Guide Roll 41, 42 Bonding Roll 61 Polarizing Film 62 First Thermoplastic Resin Film 63 Second Thermoplastic Resin Film 64 Adhesive Layer 65 Separate Film.

Claims (7)

A method for manufacturing an optical film in which a first film and a second film are laminated,
an external force applying step of applying an external force in the width direction of the first film;
After the external force applying step, the second film is superimposed on one side of the first film and passed between a pair of bonding rolls to bond them together. Applying shrinkage force in the width direction of the first film,
Regarding the first film, after the external force is applied in the external force applying step, the distance conveyed until passing between the pair of bonding rolls is 3 m or less,
A method for producing an optical film, wherein the first film is passed between the pair of bonding rolls while the external force applied in the external force application step remains. A method for manufacturing an optical film in which a first film and a second film are laminated,
an external force applying step of applying an external force in the width direction of the first film;
After the external force application step, a lamination step of laminating the second film on one side of the first film and passing it between a pair of lamination rolls to bond them together. Applying a stretching force in the width direction of the first film,
Regarding the first film, after the external force is applied in the external force applying step, the distance conveyed until passing between the pair of bonding rolls is 3 m or less,
A method for producing an optical film, wherein the first film is passed between the pair of bonding rolls while the external force applied in the external force application step remains. 3. The method for producing an optical film according to claim 1, wherein the distance is 1 m or less. The method for producing an optical film according to any one of claims 1 to 3, wherein the first film is a polarizing plate and the second film is a protection film. An apparatus for manufacturing an optical film in which a first film and a second film are laminated,
an external force applying means for applying an external force in the width direction of the first film;
a pair of laminating rolls for laminating each other by passing the second film over one side of the first film in a stage subsequent to the external force applying means; Add contractile force in the width direction,
Regarding the first film, after the external force is applied by the external force applying means, the distance conveyed until passing between the pair of bonding rolls is 3 m or less,
An apparatus for manufacturing an optical film, wherein the first film passes between the pair of bonding rolls while the external force applied by the external force applying means remains. An apparatus for manufacturing an optical film in which a first film and a second film are laminated,
an external force applying means for applying an external force in the width direction of the first film;
a pair of laminating rolls for laminating each other by passing the second film over one side of the first film in a stage subsequent to the external force applying means; Adds stretching force in the width direction,
Regarding the first film, after the external force is applied by the external force applying means, the distance conveyed until passing between the pair of bonding rolls is 3 m or less,
An apparatus for manufacturing an optical film, wherein the first film passes between the pair of bonding rolls while the external force applied by the external force applying means remains. 7. The apparatus for producing an optical film according to claim 5, wherein the distance is 1 m or less.

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