Manufacturing method of laminate film

Abstract

To provide a manufacturing method of a laminate film capable of inhibiting inclusion of air bubbles.SOLUTION: A manufacturing method of a laminate film includes a bonding step of bonding a first film and a second film with an adhesive agent. In the bonding step, the first film and the second film are bonded together while passing between a first bonding roll and a second bonding roll. Each of the first bonding roll and the second bonding roll includes an outer rubber tube and an inner shaft. The outer rubber tube has a cylindrical shape. The inner shaft is arranged inside the outer rubber tube. The inner shaft includes a support part. The support part supports a center part in an axial direction of the outer rubber tube. At least one of the first film and the second film satisfies a relation of an expression (1): E×T<100000...(1).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a laminated film. [Background technology]

[0002] Conventionally, laminated films have been widely used in various industrial products. A laminated film is prepared by laminating multiple films. For example, a technique has been proposed in which an active energy ray-curable adhesive is applied to one side of a first film or one or both sides of a second film, and then the first film and the second film are laminated by passing them between a pair of laminating rolls. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-92764 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, as the applications of laminate films have expanded, the configurations and performances required of laminate films have become more diverse. As a result, films with relatively low rigidity are sometimes used for laminate films. However, if a film with relatively low rigidity is used in the method described in Patent Document 1, there is a risk of air bubbles being mixed into the laminate film produced. The present invention has been made to solve the above-mentioned problems of the prior art, and a main object of the present invention is to provide a method for producing a laminated film that can suppress the inclusion of air bubbles. [Means for solving the problem]

[0005] [1] A method for producing a laminated film according to one embodiment of the present invention includes a laminating step of laminating a first film and a second film with an adhesive. In the laminating step, the first film and the second film are laminated together as they pass between a first laminating roll and a second laminating roll. Each of the first laminating roll and the second laminating roll has an outer rubber tube and an inner shaft. The outer rubber tube has a cylindrical shape. The inner shaft is disposed within the outer rubber tube. The inner shaft has a support portion and a small-diameter portion having a smaller diameter than the support portion. The support portion supports a central portion of the outer rubber tube in the axial direction. The small-diameter portions are disposed on both sides of the support portion in the axial direction. At least one of the first film and the second film satisfies the relationship of the following formula (1): E×T<100000 (1) (In formula (1), E represents the tensile modulus at 25°C (unit: MPa); T represents the thickness (unit: μm).) [2] In the method for producing a laminated film according to the above item [1], both the first film and the second film may satisfy the relationship of formula (1). [3] In the method for producing a laminated film according to the above [1] or [2], at least one of the first film and the second film may have a thickness of 45 μm or less. [4] In the method for producing a laminated film according to any one of [1] to [3] above, the tension applied to the first film and / or the second film in the bonding step may be 50 N / m to 400 N / m. [5] In the method for producing a laminated film according to any one of [1] to [4] above, the first laminating roll and the second laminating roll may form a nip between them to sandwich the first film and the second film. The nip may extend in the axial direction. The width of the nip may be 13 mm to 20 mm. [6] In the method for producing a laminated film according to any one of [1] to [5] above, the outer diameter of the central portion of the outer rubber tube in the axial direction may be 1 or less times the outer diameter of the end portion of the outer rubber tube in the axial direction. [7] In the method for producing a laminated film described in [6] above, the outer peripheral surface of the outer rubber tube of the first laminating roll may include a contact area that comes into contact with the first film in the laminating step, and a central angle of the outer rubber tube corresponding to the contact area may be 45° to 90°. [8] In the method for producing a laminated film according to any one of the above [1] to [7], the first film may be a polarizing plate including a polarizer. [Effects of the Invention]

[0006] According to an embodiment of the present invention, a laminated film in which the inclusion of air bubbles is suppressed can be produced. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a method for producing a laminated film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of the first laminating roll and the second laminating roll shown in FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view of a first laminating roll and a second laminating roll according to another embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view of the first film shown in FIG. [Figure 5] FIG. 5 is a schematic cross-sectional view of the second film shown in FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view of a laminated film produced by a method for producing a laminated film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In addition, in order to clarify the explanation, the width, thickness, shape, etc. of each part may be shown schematically in the drawings compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overview of laminated film manufacturing method FIG. 1 is a schematic diagram illustrating a method for producing a laminated film according to one embodiment of the present invention; FIG. 2 is a schematic cross-sectional view of the first laminating roll and the second laminating roll shown in FIG.

[0010] A method for manufacturing a laminated film according to one embodiment includes a laminating step in which a first film 1 and a second film 2 are laminated together with an adhesive. The first film 1 and the second film 2 are laminated together as they pass between a first laminating roll 3a and a second laminating roll 3b. At least one of the first film 1 and the second film 2 satisfies the relationship of the following formula (1). E×T<100000 (1) (In formula (1), E represents the tensile modulus at 25° C. (unit: MPa); T represents the thickness (unit: μm).) As shown in FIG. 2, each of the first laminating roll 3 a and the second laminating roll 3 b has an outer rubber tube 31 and an inner shaft 32 . The outer rubber tube 31 has a cylindrical shape. Hereinafter, the direction in which the axis of the outer rubber tube 31 extends will be referred to as the axial direction. The inner shaft 32 is disposed inside the outer rubber tube 31. The inner shaft 32 has a support portion 321 and two small diameter portions 322. The support portion 321 supports the central portion in the axial direction of the outer rubber tube 31. In one embodiment, the support portion 321 contacts the central portion in the axial direction of the inner circumferential surface of the outer rubber tube 31. In the illustrated example, the support portion 321 has a cylindrical shape extending in the axial direction. The small diameter portions 322 are arranged on both sides of the support portion 321 in the axial direction. Of the two small diameter portions 322, the small diameter portion 322 arranged on one side of the support portion 321 in the axial direction may be referred to as a first small diameter portion 322a, and the small diameter portion 322 arranged on the other side of the support portion 321 in the axial direction may be referred to as a second small diameter portion 322b. Each of the two small diameter portions 322 has a smaller diameter than the support portion 321. With this configuration, even if at least one of the first film 1 and the second film 2 is a film with a relatively low rigidity that satisfies the relationship of formula (1) above, since the first laminating roll and the second laminating roll each have the outer rubber tube and the inner shaft, it is possible to prevent air bubbles from being mixed in between the first film and the second film during the laminating step, and therefore it is possible to smoothly produce a laminated film with reduced air bubbles.

[0011] In one embodiment, the inner shaft 32 further has a first end 323 and a second end 324 . The first end 323 is one end of the inner shaft 32 in the axial direction. The first end 323 is located on the opposite side of the support portion 321 with respect to the first small diameter portion 322a. The second end 324 is the other end of the inner shaft 32 in the axial direction. The second end 324 is located on the opposite side of the support portion 321 with respect to the second small diameter portion 322b. Each of the first end 323 and the second end 324 may protrude from the outer rubber tube 31 in the axial direction. With this configuration, the first and second ends of the inner shaft of either the first laminating roll or the second laminating roll can be smoothly pressed toward the other laminating roll. Since each of the first laminating roll and the second laminating roll has a support portion, deflection of the axial center portion of the first laminating roll and / or the second laminating roll can be sufficiently suppressed. Therefore, the nip described below can be stably formed. As a result, the incorporation of air bubbles between the first film and the second film during the laminating process can be stably suppressed.

[0012] The support part 321 typically includes the central part in the axial direction of the inner shaft 32. In the illustrated example, the outer peripheral surface of the support part 321 is in contact with the central part in the axial direction of the inner peripheral surface of the outer rubber tube 31. The support part 321 may be bonded to the inner peripheral surface of the outer rubber tube 31. The outer diameter of the support portion 321 is, for example, 170 mm to 250 mm, and preferably 180 mm to 200 mm.

[0013] The dimension of the support portion 321 in the axial direction is, for example, 10% to 35%, and preferably 15% to 30%, when the total length (dimension in the axial direction) of the outer rubber tube 31 is taken as 100%. The dimension of the support portion 321 in the axial direction is, for example, 200 mm to 550 mm, and preferably 250 mm to 450 mm.

[0014] Each of the first small diameter portion 322a and the second small diameter portion 322b typically has a cylindrical shape extending in the axial direction. In one embodiment, each of the first small diameter portion 322a and the second small diameter portion 322b is adjacent to the support portion 321 in the axial direction. In the illustrated example, the first small diameter portion 322a, the support portion 321, and the second small diameter portion 322b are continuous with each other and share an axis.

[0015] The difference in outer diameter between the support portion 321 and the first small diameter portion 322a is, for example, 60 mm to 100 mm, and preferably 70 mm to 90 mm. When the difference in outer diameter between the support portion and the first small diameter portion is in this range, deflection of the first laminating roll and / or the second laminating roll can be more stably suppressed in the laminating step. The outer diameter of the first small diameter portion 322a is, for example, 90 mm to 130 mm, and preferably 100 mm to 120 mm.

[0016] The dimension of the first small diameter portion 322a in the axial direction is, for example, 20% to 50%, and preferably 30% to 40%, when the overall length (dimension in the axial direction) of the inner shaft 32 is taken as 100%. The dimension of the first small diameter portion 322a in the axial direction is, for example, 30% to 45%, and preferably 35% to 40%, when the overall length (dimension in the axial direction) of the outer rubber tube 31 is taken as 100%. The dimension of the first small diameter portion 322a in the axial direction is, for example, 480 mm to 720 mm, and preferably 540 mm to 640 mm.

[0017] The range of the outer diameter of the second small diameter portion 322b is typically the same as the range of the outer diameter of the first small diameter portion 322a described above. In one embodiment, the outer diameter of the first small diameter portion 322a and the outer diameter of the second small diameter portion 322b are substantially the same. The range of dimensions of the second small diameter portion 322b in the axial direction is typically the same as the range of dimensions of the first small diameter portion 322a described above. In one embodiment, the axial dimension of the second small diameter portion 322b is substantially the same as the axial dimension of the first small diameter portion 322a.

[0018] Each of the first end 323 and the second end 324 typically has a cylindrical shape with a smaller diameter than the small diameter portion 322. In one embodiment, the first end 323 is adjacent to the first small diameter portion 322a in the axial direction. In the illustrated example, the first end 323 and the first small diameter portion 322a are continuous and share a common axis.

[0019] The difference in outer diameter between the first end 323 and the first small diameter portion 322a is, for example, 50 mm to 80 mm, and preferably 60 mm to 70 mm. The outer diameter of the first end portion 323 is, for example, 30 mm to 60 mm, and preferably 40 mm to 50 mm.

[0020] The axial dimension of the first end 323 is, for example, 7.5% to 15%, and preferably 10% to 12.5%, of the axial dimension of the inner shaft 32. The axial dimension of the first end 323 is, for example, 30 mm to 60 mm, and preferably 40 mm to 50 mm. When the dimension of the first end in the axial direction is within this range, one laminating roll can be stably pressed against the other laminating roll in the laminating step.

[0021] In one embodiment, the second end 324 is adjacent to the second small diameter portion 322b in the axial direction. In the illustrated example, the second end 324 and the second small diameter portion 322b are continuous and share a common axis. That is, in the illustrated example, the inner shaft 32 is a stepped shaft and integrally includes a first end portion 323, a first small diameter portion 322a, a support portion 321, a second small diameter portion 322b, and a second end portion 324, which are arranged in this order in the axial direction. The first end portion 323, the first small diameter portion 322a, the support portion 321, the second small diameter portion 322b, and the second end portion 324 share an axis.

[0022] The range of the difference in outer diameter between second end 324 and second small diameter portion 322b is typically the same as the range of the difference in outer diameter between first end 323 and first small diameter portion 322a described above. The range of outer diameters of second end 324 is typically similar to the range of outer diameters of first end 323. In one embodiment, the outer diameter of second end 324 is substantially the same as the outer diameter of first end 323. The range of dimensions of the second end 324 in the axial direction is typically similar to the range of dimensions of the first end 323 in the axial direction. In one embodiment, the axial dimension of the second end 324 is substantially the same as the axial dimension of the first end 323. When the dimension of the second end in the axial direction is within this range, one laminating roll can be pressed more stably toward the other laminating roll in the laminating step.

[0023] Examples of materials for the inner shaft 32 include metal and carbon, preferably metal. Examples of metals include iron, aluminum, magnesium, stainless steel, and alloys thereof. Among metals, stainless steel is preferred.

[0024] The elastic modulus of the inner shaft 32 is, for example, 50 GPa to 250 GPa at 25° C. The elastic modulus is determined from the tensile stress and the gradient of the strain line according to the metallic material tensile test method in accordance with JIS Z2241.

[0025] The inner shaft 32 may have a solid structure or a hollow structure. As shown in Fig. 3, in one embodiment, the inner shaft 32 has a hollow shape. With such a configuration, the weight of the inner shaft can be reduced. Furthermore, even if the inner shaft has a hollow shape, as long as the inner shaft has a support portion and a small diameter portion, deflection of the laminating roll during the laminating step can be sufficiently suppressed.

[0026] The inner shaft 32 of the first laminating roll 3a and the inner shaft 32 of the second laminating roll 3b may have the same configuration or may have different configurations. In one embodiment, the inner shaft 32 of the first laminating roll 3a and the inner shaft 32 of the second laminating roll 3b have the same configuration.

[0027] As shown in FIG. 2, the above-mentioned inner shaft 32 is inserted into the outer rubber tube 31. The arithmetic mean surface roughness Ra of the outer peripheral surface of the outer rubber tube 31 is, for example, 0.6 μm to 0.9 μm, and preferably 0.7 μm to 0.8 μm. The arithmetic mean surface roughness Ra of the outer peripheral surface of the outer rubber tube is measured, for example, in accordance with JIS B0601. When the arithmetic mean surface roughness Ra of the outer peripheral surface of the outer rubber tube is within this range, the first film and / or the second film can be laminated without slippage during the lamination step, and transfer of irregularities can be suppressed.

[0028] As described above, the central portion of the inner circumferential surface of the outer rubber tube 31 in the axial direction is in contact with the support portion 321 of the inner shaft 32. In the illustrated example, the inner circumferential surface of the outer rubber tube 31, other than the portion in contact with the support portion 321, faces the outer circumferential surface of the small diameter portion 322 at a distance.

[0029] The outer diameter of the outer rubber tube 31 may be substantially constant in the axial direction, or may vary substantially in the axial direction. The outer diameter of the axial center portion of the outer rubber tube 31 is, for example, 1.05 to 0.95 times, preferably 1 time or less, and more preferably less than 1 time the outer diameter of the axial end portion of the outer rubber tube 31. In other words, the outer rubber tube 31 may have a concave shape (inverse crown shape) in which the outer diameter of the central part in the axial direction is less than 1 time the outer diameter of the end part, or may have a crown shape in which the outer diameter of the central part in the axial direction is more than 1 time the outer diameter of the end part. In one embodiment, the outer rubber tube 31 has a concave shape. With this configuration, the outer diameter of the outer rubber tube decreases toward the inside in the axial direction, which creates a difference in peripheral speed between the center and end portions of the outer rubber tube. This allows the film in contact with the outer rubber tube to be stably expanded, effectively preventing wrinkling of the film. As a result, the incorporation of air bubbles into the laminated film can be more stably prevented.

[0030] The range of the inner diameter of the axial central portion of the outer rubber tube 31 is typically the same as the range of the outer diameter of the above-mentioned support part 321. The range of the inner diameter of the axial end portion of the outer rubber tube 31 is, for example, 170 mm to 200 mm, and preferably 180 mm to 190 mm. The outer diameter of the central portion of the outer rubber tube 31 in the axial direction is, for example, 180 mm to 220 mm, and preferably 190 mm to 210 mm. The outer diameter of the end portion of the outer rubber tube 31 in the axial direction is, for example, 180 mm to 220 mm, and preferably 190 mm to 210 mm. The thickness of the outer rubber tube 31 is, for example, 4 mm to 20 mm, and preferably 5 mm to 10 mm.

[0031] The dimension of the outer rubber tube 31 in the axial direction is, for example, 75% to 90%, and preferably 80% to 90%, when the total length (dimension in the axial direction) of the inner shaft 32 is taken as 100%. The dimension of the outer rubber tube 31 in the axial direction is, for example, 1000 mm to 3000 mm, and preferably 1200 mm to 2000 mm.

[0032] The outer rubber tube 31 is made of any suitable rubber material, such as silicon rubber, nitrile rubber, ethylene propylene rubber, butyl rubber, and urethane rubber, with silicon rubber being preferred.

[0033] The hardness of the outer rubber tube 31 at 25° C. is, for example, 50 to 95, and preferably 60 to 90. The hardness of the outer rubber tube is measured, for example, with a type D durometer. The compressive elastic modulus of the outer rubber tube 31 at 25° C. is, for example, 1 MPa to 30 MPa, and preferably 10 MPa to 20 MPa. The compressive elastic modulus of the outer rubber tube is determined from the gradient of the stress and displacement (strain) applied to a rubber test piece when the test piece is compressed at a constant speed using, for example, a Shimadzu Corporation "Precision Universal Testing Machine AG-IS."

[0034] The outer rubber tube 31 of the first laminating roll 3a and the outer rubber tube 31 of the second laminating roll 3b may have the same configuration or may have different configurations. In one embodiment, the outer rubber tube 31 of the first laminating roll 3a and the outer rubber tube 31 of the second laminating roll 3b have the same configuration.

[0035] In the above embodiment, the support portion 321 comes into contact with the central portion of the inner circumferential surface of the outer rubber tube 31 in the axial direction, and supports the central portion of the outer rubber tube 31 . On the other hand, the support part 321 may support the central part of the outer rubber tube 31 via another member. In another embodiment, at least one of the first laminating roll 3a and the second laminating roll 3b may include a stainless steel sleeve in addition to the outer rubber tube 31 and the inner shaft 32. The stainless steel sleeve is typically located between the inner circumferential surface of the outer rubber tube 31 and the outer circumferential surface of the support part 321. In this case, the support part 321 supports the central part of the outer rubber tube 31 in the axial direction via the stainless steel sleeve.

[0036] In one embodiment, the first laminating roll 3a and the second laminating roll 3b form a nip N. In the nip N, the first film 1 and the second film 2 are sandwiched between the first laminating roll 3a (specifically, the outer rubber tube 31) and the second laminating roll 3b (specifically, the outer rubber tube 31). In other words, the nip N refers to the region where the first laminating roll 3a and the second laminating roll 3b sandwich the first film 1 and the second film 2 at a predetermined pressure or higher.

[0037] The nip N extends in the axial direction. The dimension of the nip N in the axial direction is typically substantially the same as the entire length of the outer rubber tube 31. The width of the nip N (in the direction perpendicular to the extending direction) is, for example, 8 mm or more, preferably 12 mm or more, more preferably 13 mm or more, and even more preferably 15 mm or more. When the nip N has such a width, it is possible to more stably prevent air bubbles from being mixed in between the first film and the second film, and it is also possible to prevent streaks from being formed in the laminated film 100 produced. On the other hand, the width of the nip N is, for example, 30 mm or less, preferably 20 mm or less. When the nip N has such a width, the first film and the second film can be prevented from being excessively pinched between the first laminating roll and the second laminating roll (mixing) during the laminating step. As a result, the incorporation of air bubbles between the first film and the second film can be more stably prevented.

[0038] In one embodiment, the width of the axial center of the nip N is larger than the width of the axial end of the nip N. The difference between the width of the axial center of the nip N and the width of the axial end of the nip N is, for example, 5 mm or less, preferably 2 mm or less. When the width difference between the center and end of the nip N is within this range, the first film and the second film can be pressed uniformly in the width direction in the bonding step, and the incorporation of air bubbles between them can be more stably prevented.

[0039] B. Details of the manufacturing method of laminated film The method for producing a laminated film according to one embodiment will be described in more detail below.

[0040] In one embodiment, the manufacturing method of the laminated film 100 includes, in this order, a first preparation step of preparing a first film 1, a second preparation step of preparing a second film 2, an application step of applying an adhesive to the first film 1 and / or the second film 2, and the above-mentioned bonding step.

[0041] B-1. First preparation process As shown in FIG. 4, in the first preparation step, a first film 1 is prepared. The first film 1 may have any appropriate structure. The first film 1 is typically long. The first film 1 may have a single-layer structure or a laminated structure in which two or more layers are laminated. In the illustrated example, the first film 1 has a laminated structure.

[0042] In one embodiment, the first film 1 satisfies the relationship of the above formula (1). The tensile modulus E of the first film 1 at 25° C. is, for example, 1000 MPa to 4000 MPa, and preferably 2000 MPa to 3000 MPa. The thickness of the first film 1 is, for example, 100 μm or less, preferably 45 μm or less, whereas the thickness of the first film 1 is, for example, 10 μm or more, preferably 15 μm or more.

[0043] Examples of such a first film 1 include a polarizing plate, a protective film, a release film, and a retardation film, and preferably a polarizing plate.

[0044] B-1-1. Polarizing plate The polarizing plate 11 includes a polarizer 111 . Any appropriate polarizer can be adopted as the polarizer 111. For example, the polarizer may be made of a single-layer resin film, or may be obtained by using a laminate of two or more layers.

[0045] Specific examples of polarizers made of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, as well as polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Polarizers obtained by dyeing PVA films with iodine and uniaxially stretching them are preferred because of their excellent optical properties.

[0046] The dyeing with iodine is carried out, for example, by immersing the PVA film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA film may be stretched and then dyed. If necessary, the PVA film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents on the surface of the PVA film, and also to swell the PVA film, thereby preventing uneven dyeing.

[0047] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In one embodiment of the present invention, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching can optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. Additionally, in one embodiment of the present invention, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. By introducing auxiliary stretching, it is possible to increase the crystallinity of PVA, even when PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in orientation or dissolution of PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through treatment steps in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction through drying shrinkage treatment.The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such a polarizer manufacturing method are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0048] The thickness of the polarizer is, for example, 1 μm to 80 μm, preferably 1 μm to 15 μm, more preferably 1 μm to 12 μm, still more preferably 3 μm to 12 μm, and particularly preferably 3 μm to 8 μm. When the thickness of the polarizer is within this range, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

[0049] The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0050] The polarizing plate 11 may include a protective layer 112 in addition to the polarizer 111. The protective layer 112 is provided on at least one surface of the polarizer 111. The protective layer 112 is typically attached to the polarizer 111 via any appropriate adhesive layer (not shown).

[0051] The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that can be the main component of the film include cycloolefin (COP) resins such as polynorbornene resins, polyester resins such as polyethylene terephthalate (PET) resins, cellulose resins such as triacetyl cellulose (TAC), and transparent resins such as polycarbonate (PC), (meth)acrylic resins, polyvinyl alcohol resins, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polyolefins, and acetate resins. Other examples include thermosetting or ultraviolet-curable resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, and silicone resins. The term "(meth)acrylic resin" refers to acrylic resins and / or methacrylic resins. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials for this film include resin compositions containing a thermoplastic resin with substituted or unsubstituted imide groups in its side chains and a thermoplastic resin with substituted or unsubstituted phenyl and nitrile groups in its side chains. Examples include a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition. The resin film materials can be used alone or in combination.

[0052] Furthermore, the protective layer 112 may be subjected to surface treatments such as hard coating, anti-reflection, anti-sticking, anti-glare, etc., as needed. Additionally / alternatively, the protective layer 112 may be subjected to treatments to improve visibility when viewed through polarized sunglasses (typically, by imparting (elliptically) circular polarization functionality or ultra-high phase difference).

[0053] The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm.

[0054] B-2.Second preparation process As shown in FIG. 5, in the second preparation step, a second film 2 is prepared. The second film 2 may have any appropriate structure. The second film 2 is typically long. The second film 2 may have a single-layer structure or a laminated structure in which two or more layers are laminated. In the illustrated example, the second film 2 has a single-layer structure.

[0055] In one embodiment, the second film 2 satisfies the relationship of the above formula (1). The tensile modulus E of the second film 2 at 25° C. is, for example, 1500 MPa to 4000 MPa, and preferably 2000 MPa to 3000 MPa. The thickness of the second film 2 is, for example, 5 μm to 60 μm, and preferably 10 μm to 30 μm.

[0056] Examples of such second film 2 include resin films, and more specifically, retardation films, protective films, and surface protective films. Examples of materials for the resin film include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and (meth)acrylic resins. These resins may be used alone or in combination. Of these resin films, (meth)acrylic resins are preferred.

[0057] B-3.Coating process In the coating step, typically, an adhesive is applied to the surface of the first film 1 and / or the second film 2 before being fed between the first laminating roll 3a and the second laminating roll 3b. In one embodiment, the adhesive is applied to the surface of both the first film 1 and the second film 2. In the illustrated example, the adhesive is applied to the surface of the polarizer 111 of the polarizing plate 11 and the surface of the second film 2.

[0058] Any appropriate method can be used to apply the adhesive, for example, gravure coating or slot die coating, preferably gravure coating. The thickness of the adhesive coating is, for example, 0.5 μm to 3.0 μm, and preferably 0.8 μm to 2.0 μm.

[0059] Typically, a curable adhesive is used as the adhesive. Examples of curable adhesives include thermosetting adhesives and ultraviolet curing adhesives, and ultraviolet curing adhesives are preferred. Details of ultraviolet curing adhesives are described in, for example, JP 2013-92764 A. The entire disclosures of these publications are incorporated herein by reference.

[0060] The curable adhesive is in a liquid state before curing. The viscosity of the curable adhesive at 25° C. is, for example, 10 m / Pa·s to 80 m / Pa·s, and preferably 25 m / Pa·s to 50 m / Pa·s.

[0061] B-4.Lamination process As shown in FIG. 2, in the laminating step, the first film 1 and the second film 2 are supplied between a first laminating roll 3a and a second laminating roll 3b.

[0062] In the laminating step, the tension applied to the first film 1 and / or the second film 2 is, for example, 50 N / m to 800 N / m, preferably 50 N / m to 500 N / m, more preferably 50 N / m to 400 N / m, and even more preferably 150 N / m to 250 N / m. In this way, applying an appropriate tension according to the rigidity of the first film and / or the rigidity of the second film in the laminating step can prevent the first film and the second film from wrinkling and curling, and can more stably prevent air bubbles from being mixed in between the first film and the second film.

[0063] The supply speed (line speed) of each of the first film 1 and the second film 2 in the laminating step is, for example, 5 m / min to 30 m / min, and preferably 15 m / min to 25 m / min. The rotation speed of each of the first laminating roll and the second laminating roll in the laminating step is, for example, 7 rpm to 50 rpm, and preferably 23 rpm to 40 rpm.

[0064] When the first film 1 passes between the first laminating roll 3a and the second laminating roll 3b (nip N), it comes into contact with the outer circumferential surface of the outer rubber tube 31 of the first laminating roll 3a. In the illustrated example, the protective layer 112 of the polarizing plate 11 comes into contact with the outer circumferential surface of the outer rubber tube 31 of the first laminating roll 3a. Hereinafter, the region on the outer circumferential surface of the outer rubber tube 31 that comes into contact with the first film 1 is referred to as the contact region. The central angle of the outer rubber tube 31 that corresponds to the contact region is, for example, 30° to 90°, and preferably 45° to 90°.

[0065] When the outer rubber tube 31 of the first laminating roll 3a has the concave shape described above, the central angle of the outer rubber tube 31 corresponding to the contact area is preferably 45° to 90°. When the outer rubber tube 31 has a concave shape, even if the central angle of the outer rubber tube corresponding to the contact area is within the above range, the occurrence of wrinkles in the first film can be stably suppressed. As a result, the first film can be stably conveyed while the occurrence of air bubbles can be sufficiently suppressed. Note that when the outer rubber tube 31 has a crown shape, the first film may be wrinkled if the central angle of the outer rubber tube corresponding to the contact area is 45° to 90°.

[0066] Furthermore, when the second film 2 passes between the first laminating roll 3a and the second laminating roll 3b (nip N), it comes into contact with the outer peripheral surface of the outer rubber tube 31 of the second laminating roll 3b. The range of the central angle of the outer rubber tube 31 corresponding to the contact area with the second laminating roll 3b is typically the same as the range of the central angle of the first laminating roll 3a described above.

[0067] Furthermore, the first film 1 and the second film 2 are appropriately pressed by the first laminating roll 3a and the second laminating roll 3b when they pass between the first laminating roll 3a and the second laminating roll 3b, that is, when they pass through the nip N. This causes the first laminating roll 3a and the second laminating roll 3b to be bonded together by the adhesive.

[0068] The adhesive is then cured by any suitable method, for example, if the adhesive comprises an ultraviolet curable adhesive, the ultraviolet curable adhesive located between the first film 1 and the second film 2 is irradiated with ultraviolet light. In this way, the laminated film 100 is manufactured.

[0069] C. Laminated film As shown in FIG. 6, the laminated film 100 includes a first film 1, an adhesive layer 5, and a second film 2 in this order. The adhesive layer 5 is made of a cured product of the adhesive described above. The thickness of the adhesive layer 5 is, for example, 0.5 μm to 2.0 μm, and preferably 0.8 μm to 1.5 μm. Such a laminate film 100 can be used for any appropriate purpose. In particular, since the inclusion of air bubbles is significantly suppressed in the laminate film 100, it can be suitably used for optical purposes such as image display devices. [Example]

[0070] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0071] The methods for measuring each physical property are as follows. <Measurement of the nip width of the first laminating roll and the second laminating roll> Pressure-sensitive paper (manufactured by Fujifilm Corporation, product name Prescale (ultra-low pressure), thickness 95 μm) was inserted between the first laminating roll and the second laminating roll used in each example and comparative example. As a result, the pressure-sensitive paper was colored in the areas pressurized to 0.1 MPa or more. The colored areas extended in the axial direction of the outer rubber tube. The maximum width of the colored areas is shown in Table 1 as the width of the nip between the first laminating roll and the second laminating roll.

[0072] <Thickness> In each example and comparative example, the thickness of the member to be measured was measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). The thickness T of each of the first film (polarizing plate) and the second film (acrylic resin film) is shown in Table 1.

[0073] Dynamic Mechanical Analysis (DMA) The tensile modulus of elasticity of the first film (polarizing plate) and the second film (acrylic resin film) in each example and comparative example was measured under the following conditions. The tensile modulus E at 25°C is shown in Table 1. The tensile modulus was measured using an autograph. Furthermore, the product (E×T) of the tensile modulus E and the thickness T at 25° C. was calculated for each of the first film and the second film. The results are shown in Table 1.

[0074] <Tension applied to the first and second films> In each example and comparative example, the tension acting on each of the first film and the second film was measured using a tension pickup. The results are shown in Table 1.

[0075] <Air bubble inspection> From the laminated film obtained in each example and each comparative example, 1 m 2 The samples were cut out and the number of bubbles of 70 μm or more in each sample was visually counted. The results are shown in Table 1. 〇: No occurrence (0) △: 1 or more and 5 or less ×:6 or more

[0076] [Preparation Example 1] 1. Preparation of Polarizing Plates A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating liquid) was prepared by dissolving 100 parts by mass of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFFIMER") in a 9:1 ratio, to which 13 parts by mass of potassium iodide was added, in water. The above PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60° C. to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by mass of boric acid with 100 parts by mass of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by mass of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment). Next, the substrate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by mass of potassium iodide with 100 parts by mass of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, the film was dried in an oven maintained at about 90°C, and brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this way, a polarizer having a thickness of about 5 μm was formed on the resin substrate, and a polarizing plate (first film) having a resin substrate / polarizer structure was obtained. The polarizing plate had a long shape.

[0077] [Example 1] A long acrylic resin film (thickness: 20 μm, manufactured by Toyo Kohan Co., Ltd., trade name "Fine Cast Film") was prepared as a second film.

[0078] In addition, a first laminating roll and a second laminating roll were prepared. The first laminating roll had an outer rubber tube and an inner shaft. The material of the outer rubber tube was silicon rubber. The hardness of the outer rubber tube was 85. The outer and inner diameters of the outer rubber tube were constant in the axial direction of the outer rubber tube. The outer diameter of the outer rubber tube was 200 mm. The inner diameter of the outer rubber tube was 192 mm. In other words, the thickness of the outer rubber tube was 8 mm. The inner shaft was a stepped shaft and had, in the axial direction, a first end, a first small diameter portion, a support portion, a second small diameter portion, and a second end portion, in this order. The material of the inner shaft was iron (SUS304). The hardness of the inner shaft was 70HR. The outer diameter of the support portion was 186 mm. The outer diameters of the first small diameter portion and the second small diameter portion were each 110 mm. The outer diameters of the first end and the second end were each 45 mm. The axial dimension of the support portion was 400 mm. The second laminating roll had the same configuration as the first laminating roll described above. Next, the first laminating roll and the second laminating roll were arranged facing each other so that the outer rubber tube of the first laminating roll and the outer rubber tube of the second laminating roll were in contact with each other in the radial direction. In addition, both ends of the inner shaft of the first laminating roll were pressed against the second laminating roll by a cylinder so that the nip width became the value shown in Table 1. Furthermore, each of the first laminating roll and the second laminating roll was rotated at 32 rpm.

[0079] Next, an acrylic ultraviolet-curable adhesive was applied to each of the surface of the polarizer in the polarizing plate obtained in Preparation Example 1 and the surface of the acrylic resin film to form a coating film with a thickness of 1.5 μm.

[0080] Next, the polarizing plate and the acrylic resin film were fed between the first laminating roll and the second laminating roll so that the coating film on the polarizer and the coating film on the acrylic resin film were in contact. The feeding speed (line speed) of the polarizing plate and the acrylic resin film was 20 m / min. On the outer surface of the outer rubber tube of the first laminating roll, a region corresponding to a central angle (embracing angle) of 45° was in contact with the protective layer of the polarizing plate.

[0081] The polarizing plate and the acrylic resin film were bonded together when they passed between the first and second laminating rolls, after which they were irradiated with ultraviolet light to cure the ultraviolet-curable adhesive. In this way, a laminated film having a structure of polarizing plate (first film) / adhesive layer / acrylic resin film (second film) was obtained.

[0082] [Example 2] A laminated film was obtained in the same manner as in Example 1, except that the tension applied to the first film and the tension applied to the second film were changed as shown in Table 1.

[0083] [Examples 3 and 4] A laminated film was obtained in the same manner as in Example 1, except that the nip width between the first laminating roll and the second laminating roll was changed as shown in Table 1.

[0084] [Comparative Example 1] A laminated film was obtained in the same manner as in Example 1, except that the inner shaft (stepped shaft) of the second laminating roll was changed to a normal shaft (unstepped shaft) with a constant outer diameter, and the tension applied to the second film and the nip width were changed as shown in Table 1. The normal shaft (unstepped shaft) was in contact with the entire inner circumferential surface of the outer rubber tube of the second laminating roll. Hereinafter, a laminating roll equipped with a normal shaft may be referred to as a normal roll.

[0085] Comparative Example 2 A laminated film was obtained in the same manner as in Example 1, except that the outer rubber tube of the second laminating roll was changed to a metal tube made of iron, and the tension applied to the second film and the nip width were changed as shown in Table 1.

[0086] [Reference example 1] A laminated film was obtained in the same manner as in Example 4, except that the PET film as the protective layer was changed to a cycloolefin film (thickness 30 μm, manufactured by Zeon Corporation, product name Zeonor) provided with a hard coat layer, the second film was changed to a triacetyl cellulose (TAC) film, the first laminating roll and the second laminating roll were each changed to a normal roll, and the nip width was changed as shown in Table 1.

[0087] [Table 1]

[0088] [evaluation] As is clear from Reference Example 1, when the product of the tensile modulus E and thickness T of the first and second films is 100,000 or more, the generation of air bubbles is suppressed even when the first and second films are bonded together using a normal roll. On the other hand, as is clear from Comparative Example 1, when the product of the tensile modulus E and the thickness T of the first film and / or the second film is less than 100,000, it is confirmed that air bubbles are generated when the first film and the second film are bonded together using a normal roll. In this case, as shown in Examples 1 to 4, it can be seen that the generation of air bubbles can be significantly suppressed by using a first laminating roll and a second laminating roll having a specific configuration to laminate the first film and the second film. [Industrial Applicability]

[0089] The laminated film obtained by the laminated film manufacturing method according to the embodiment of the present invention can be applied to various industrial products, and in particular, can be applied to optical products such as image display devices. [Explanation of symbols]

[0090] 1. Film 1 2. Second Film 3a First laminating roll 3b Second laminating roll 31 Outer rubber tube 32 inner shaft 321 Support part 322 Small diameter section 100 Laminated Film

Claims

1. a bonding step of bonding the first film and the second film together with an adhesive, In the laminating step, the first film and the second film are laminated together when passing between a first laminating roll and a second laminating roll, Each of the first laminating roll and the second laminating roll is an outer rubber tube having a cylindrical shape; an inner shaft disposed within the outer rubber tube, The inner shaft a support portion supporting a central portion of the outer rubber tube in the axial direction; small diameter portions disposed on both sides of the support portion in the axial direction, the small diameter portions having a smaller diameter than the support portion, A method for producing a laminated film, wherein at least one of the first film and the second film satisfies the relationship of the following formula (1): E × T < 100000 ... (1) (In formula (1), E represents the tensile modulus at 25° C. (unit: MPa); T represents the thickness (unit: μm).)

2. The method for producing a laminated film according to claim 1 , wherein both the first film and the second film satisfy the relationship of formula (1) above.

3. The method for producing a laminated film according to claim 1 or 2, wherein at least one of the first film and the second film has a thickness of 45 μm or less.

4. 3. The method for producing a laminated film according to claim 1, wherein in the bonding step, a tension applied to the first film and / or the second film is 50 N / m to 400 N / m.

5. the first laminating roll and the second laminating roll form a nip between them, the nip sandwiching the first film and the second film and extending in the axial direction; The method for producing a laminated film according to claim 1 or 2, wherein the width of the nip is 13 mm to 20 mm.

6. The method for producing a laminated film according to claim 1 or 2, wherein the outer diameter of the central portion of the outer rubber tube in the axial direction is equal to or less than the outer diameter of the end portion of the outer rubber tube in the axial direction.

7. an outer peripheral surface of the outer rubber tube of the first laminating roll includes a contact region that comes into contact with the first film in the laminating step, The method for producing a laminated film according to claim 5, wherein a central angle of the outer rubber tube corresponding to the contact area is 45° to 90°.

8. The method for producing a laminated film according to claim 1 or 2, wherein the first film is a polarizing plate including a polarizer.

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