Manufacturing method of long-sized laminate

Abstract

To provide a manufacturing method of a long-sized laminate having a resin layer with a variation of an orientation angle prevented.SOLUTION: A manufacturing method of a long-sized laminate includes: a first dry drawing contraction step including heating and dry-drawing, in a longer direction, a long-sized intermediate laminate including a resin base material and a resin layer, and contracting in a width direction; a second dry drawing contraction step of dry-drawing the intermediate laminate in a longer direction while heating at a temperature lower than the highest heating temperature of the first dry drawing contraction step and contracting in the width direction; and a wet drawing step in this order. A film change rate in the second dry drawing contraction step is 5% to 20%. A variation of an orientation angle in a width direction of the resin base material after the second dry drawing contraction step is 30° or less. A variation of an orientation angle in a width direction of the resin layer after the second dry drawing contraction step is less than 0.5°. A variation of an orientation angle in the width direction of the resin layer after the wet drawing is less than 0.3°.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a long laminate, and a long laminate obtained by this production method. [Background technology]

[0002] By stretching a resin film, various properties such as physical strength, heat resistance, surface properties, and moisture permeability can be imparted to the film, and thus stretched resin films are used in a variety of applications (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 120642 [Patent Document 2] Patent No. 7168115 Summary of the Invention [Problem to be solved by the invention]

[0004] Resin films with a specific orientation angle (the orientation direction of polymer molecules contained in the film) are used as heat-shrinkable films that have heat shrinkability in a specific direction and as films used in easy-open packaging materials. It is known that the orientation angle of such resin films can be adjusted by stretching. Furthermore, the film stretching process may be performed multiple times depending on the purpose. When multiple stretching processes are performed in the film production process, deviations in the orientation angle occur between each stretching process, making it difficult to adjust the orientation angle. It is also known that a laminate formed by laminating a film-forming material on a substrate is stretched to prevent problems such as breakage due to stretching. When such a laminate is subjected to the stretching process, a film with the desired orientation angle may not be obtained. Therefore, a manufacturing method that suppresses variations in the orientation angle even when multiple stretching processes are performed is needed. [Means for solving the problem]

[0005] 1. A method for producing a long laminate according to an embodiment of the present invention includes, in this order: a first dry stretching / shrinking step, which involves dry-stretching a long intermediate laminate having a resin substrate and a resin layer in the longitudinal direction while heating it and shrinking it in the width direction; a second dry stretching / shrinking step, which involves dry-stretching the intermediate laminate in the longitudinal direction while heating it at a temperature lower than the maximum heating temperature of the first dry stretching / shrinking step and shrinking it in the width direction; and a wet stretching step. The film change rate in the second dry stretching / shrinking step is 5% to 20%, and the variation in the width direction orientation angle of the resin substrate after the second dry stretching / shrinking step is 30° or less, and the variation in the width direction orientation angle of the resin layer after the second dry stretching / shrinking step is less than 0.5°. The variation in the width direction orientation angle of the resin layer after the wet stretching is less than 0.3°. 2. In the method for producing a long laminate described in 1 above, the maximum heating temperature in the first dry stretching shrinking step may be 140°C to 170°C. 3. In the method for producing a long laminate according to the above 1 or 2, the polyvinyl alcohol-based resin layer of the long laminate may have a crystallinity of 45% to 55%. 4. In the method for producing a long laminate described in any one of 1 to 3 above, the first dry stretching shrinkage step and the second dry stretching shrinkage step may be carried out using a tenter stretching device equipped with a plurality of clips as holding means. 5. In the method for producing a long laminate according to any one of 1 to 4 above, the total stretching ratio in the longitudinal direction in the first dry stretching and shrinking step and the second dry stretching and shrinking step may be 3.5 times or less. 6. In the method for producing a long laminate according to any one of 1 to 5 above, the total shrinkage rate in the width direction in the first dry stretching and shrinking step and the second dry stretching and shrinking step may be less than 50%. 7. In the method for producing a long laminate described in any one of 1 to 6 above, the total stretching ratio in the first dry stretching shrinking step, the second dry stretching shrinking step, and the wet stretching step may be 4.0 times or more. 8. In another aspect of the present invention, a long laminate is obtained. The long laminate of an embodiment of the present invention is obtained by the manufacturing method described in any one of 1 to 7 above. [Effects of the Invention]

[0006] According to an embodiment of the present invention, a long laminate having a resin layer in which variations in orientation angle are suppressed can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic view illustrating an example of a first dry stretching-shrinking step and a second dry stretching-shrinking step in the manufacturing method according to the embodiment of the present invention. [Figure 2] FIG. 3 is a partially enlarged view of a schematic diagram illustrating an example of a second dry stretching and shrinking step in the manufacturing method according to the embodiment of the present invention. [Figure 3] 1 is a schematic plan view illustrating the overall configuration of an example of a stretching device that can be used in the production method of the present invention. [Figure 4] FIG. 4 is a schematic plan view of the main part of the stretching device of FIG. 3. [Figure 5] FIG. 4 is a schematic plan view of the main part of the stretching device of FIG. 3. [Figure 6] FIG. 1 is a schematic diagram illustrating an example of an MD stretching / TD shrinkage process. [Figure 7] FIG. 10 is a schematic diagram illustrating another example of the MD stretching / TD shrinkage process. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Manufacturing method of long laminate A method for producing a long laminate according to an embodiment of the present invention includes a first dry stretching / shrinking step (hereinafter also referred to as the first in-air stretching / shrinking step) in which a long intermediate laminate having a resin substrate and a resin layer is dry-stretched in the longitudinal direction while being heated and then shrunk in the width direction; a second dry stretching / shrinking step (hereinafter also referred to as the second in-air stretching / shrinking step) in which the intermediate laminate is dry-stretched in the longitudinal direction while being heated at a temperature lower than the maximum heating temperature of the first dry stretching / shrinking step and then shrunk in the width direction; and a wet stretching step (hereinafter also referred to as the underwater stretching step). The film change rate in the second dry stretching / shrinking step is 5% to 20%, and the variation in the width direction orientation angle of the resin substrate after the second dry stretching / shrinking step is 30° or less, and the variation in the width direction orientation angle of the resin layer after the second dry stretching / shrinking step is less than 0.5°. The variation in the orientation angle of the resin layer in the width direction after wet stretching is less than 0.3°. The resin layer is a layer containing any appropriate resin. The resin layer can be formed, for example, by applying a solution containing any resin to a resin substrate. Examples of the resin include polyvinyl alcohol-based resins. Hereinafter, a laminate having a polyvinyl alcohol (hereinafter also referred to as PVA)-based resin layer formed thereon will be specifically described as an example.

[0009] FIG. 1 is a schematic diagram illustrating an example of the first dry stretching-shrinking step and the second dry stretching-shrinking step of the manufacturing method according to an embodiment of the present invention. A continuous intermediate laminate 50 having a resin substrate and a PVA-based resin layer is subjected to a first in-air stretching-shrinking step and a second in-air stretching-shrinking step while being transported in the longitudinal direction (MD) of the intermediate laminate. The first in-air stretching-shrinking step and the second in-air stretching-shrinking step can be performed using any appropriate device. Preferably, they are performed using a tenter stretching device equipped with a plurality of clips as gripping means. In the illustrated example, both ends of the intermediate laminate 50 in the width direction are gripped by clips 20. The intermediate laminate 50 transported in the longitudinal direction passes through a first in-air stretching-shrinking step zone SS1 and a second in-air stretching-shrinking step zone SS2 in that order, and is then subjected to the first and second in-air stretching-shrinking steps. Details of the longitudinal stretching process and the widthwise shrinking process will be described later. In the illustrated example, the in-air stretching in the longitudinal direction and shrinking in the width direction are performed simultaneously. In the first in-air stretching-shrinking step and the second in-air stretching-shrinking step, the in-air stretching in the longitudinal direction and the shrinking in the width direction may be performed first, or the shrinking in the width direction may be performed first. In the first in-air stretching-shrinking step zone SS1, the intermediate laminate 50 is stretched in the longitudinal direction (MD direction) of the intermediate laminate 50 while being heated, and then shrunk in the width direction. The maximum heating temperature in the first in-air stretching-shrinking step zone SS1 (i.e., the maximum heating temperature in the first in-air stretching-shrinking step) is, for example, 140°C to 170°C. In the in-air stretching-shrinking step zone SS, the intermediate laminate 50 can be heated to the highest temperature in the first in-air stretching-shrinking step. In one embodiment, a preheating step zone PH may be included before the first in-air stretching-shrinking step. Next, the intermediate laminate 50 is stretched in the longitudinal direction (MD direction) of the intermediate laminate 50 at a temperature lower than the maximum heating temperature in the first in-air stretching shrinking step zone SS1, and shrunk in the width direction. The film change rate in the second in-air stretching shrinking step is 5% to 20%. After the second in-air stretching shrinking step, the variation in the orientation angle in the width direction of the resin substrate is 30° or less, and after the stretching step following the second in-air stretching, the variation in the orientation angle of the polyvinyl alcohol-based resin layer is less than 0.5°.After the second in-air stretching / shrinking step, the intermediate laminate 50 is subjected to an in-water stretching step (not shown). The variation in the width direction orientation angle of the polyvinyl alcohol-based resin layer after in-water stretching is less than 0.3°. According to the manufacturing method of the present invention, a long laminate having a PVA-based resin layer with reduced variation in orientation angle can be obtained. By using an intermediate laminate having a resin substrate and a PVA-based resin layer, for example, stretchability during in-water stretching can be improved. On the other hand, in the PVA-based resin layer obtained by in-water stretching of an intermediate laminate, even if the variation in orientation angle is reduced in the intermediate laminate before in-water stretching, the resulting PVA-based resin layer may have a large variation in orientation angle. In the manufacturing method of the embodiment of the present invention, the first in-air stretching / shrinking step and the second in-air stretching / shrinking step are performed, and the film change rate during the second in-air stretching / shrinking step is set to 5% to 20%. If the film conversion rate in the second in-air stretching / shrinking step, which is performed at a temperature lower than the maximum heating temperature in the first in-air stretching / shrinking step, is within the above range, the variation in the width direction orientation angle of the resin substrate and the width direction orientation angle of the PVA-based resin layer in the intermediate laminate after the first in-air stretching / shrinking step and the second in-air stretching / shrinking step can be suppressed. If the variation in the orientation angle of the resin substrate is large, the orientation axis of the PVA-based resin may experience axial misalignment similar to that of the resin substrate in the subsequent underwater stretching step, resulting in poor axial accuracy of the resulting PVA-based resin layer and increased variation in the orientation angle of the resulting PVA-based resin layer. According to the method for producing a long laminate of an embodiment of the present invention, the axial accuracy of the resin substrate and the PVA-based resin layer in the intermediate laminate before the underwater stretching step can be improved. As a result, the axial accuracy of the PVA-based resin layer obtained after underwater stretching can also be improved, and the variation in the orientation angle of the resulting PVA-based resin layer can be suppressed. In this specification, the width direction refers to the direction perpendicular to the longitudinal direction of the intermediate laminate.

[0010] As described above, in the manufacturing method of a long laminate according to an embodiment of the present invention, the film conversion rate in the second in-air stretching shrinkage step is 5% to 20%, preferably 7% to 18%, and more preferably 8% to 15%. When the film conversion rate is within the above range, the variation in the orientation angle between the resin substrate and the PVA-based resin layer in the intermediate laminate can be suppressed. As a result, the variation in the width direction orientation angle of the PVA-based resin layer in the long laminate obtained after underwater stretching can be suppressed. Note that, in this specification, the film conversion rate refers to the average value of the values measured at both ends of the long laminate. FIG. 2 is a partially enlarged schematic diagram illustrating an example of the second dry stretching shrinkage step of the manufacturing method according to an embodiment of the present invention. In this specification, the film conversion rate refers to the transport change rate L of the intermediate laminate 50 in the second in-air stretching shrinkage step SS2. SS2 (%) and the shrinkage change rate W on one side in the second air-stretching shrinkage process SS2 The value calculated from the following formula: SS2 is the absolute value of the change in the stretching ratio in the SS2 process (the conveying change rate L SS2 = the stretch ratio at the time of introducing the SS2 process (i.e., 1 (times)) - the stretch ratio (times) in the SS2 process). SS2 is the absolute value of the change in shrinkage rate in the SS2 process, and the shrinkage change rate W SS2 = Transport change rate L SS2 = The value calculated by subtracting the shrinkage rate (times) at the time of introducing the SS2 step from the shrinkage rate (times) at the SS2 step.

[0011]

number

[0012] A-1. Preparation of intermediate laminate The intermediate laminate is produced by forming a resin layer on a resin substrate. The resin substrate may have any suitable structure as long as it can support the resin layer from one side. Hereinafter, an intermediate laminate in which a PVA-based resin layer is formed as the resin layer will be specifically described.

[0013] Examples of materials for forming the resin substrate include ester resins such as polyethylene terephthalate resins, cycloolefin resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Among these, preferred are cycloolefin resins (e.g., norbornene resins) and amorphous polyethylene terephthalate resins. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid as a dicarboxylic acid and copolymers further containing cyclohexanedimethanol as a glycol. The thickness of the resin substrate is preferably 20 μm to 300 μm, and more preferably 50 μm to 200 μm.

[0014] The resin substrate may be previously subjected to a surface modification treatment (e.g., corona treatment, etc.), or an easy-adhesion layer may be formed on the resin substrate. By performing such treatment, the adhesion between the resin substrate and the PVA-based resin layer can be improved. The surface modification treatment and / or the formation of the easy-adhesion layer may be performed before or after stretching the resin substrate, which is performed as needed.

[0015] Any appropriate method can be used to form the PVA-based resin layer. Preferably, the PVA-based resin layer is formed by applying a coating liquid containing a PVA-based resin onto a resin substrate that has been subjected to a stretching treatment, followed by drying. The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

[0016] Any appropriate resin can be used as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined in accordance with JIS K 6726-1994. By using a PVA-based resin with such a saponification degree, a PVA-based resin layer with excellent durability can be obtained. If the saponification degree is too high, the coating liquid is likely to gel, making it difficult to form a uniform coating film.

[0017] The average degree of polymerization of the PVA resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

[0018] The coating liquid is typically a solution in which the PVA resin is dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Of these, water is preferred. The concentration of the PVA resin in the coating liquid is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. Such a resin concentration allows the formation of a uniform coating film that adheres closely to the resin substrate.

[0019] Additives may be blended into the coating solution. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. These can be used to further improve the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

[0020] Any appropriate method can be used to apply the coating liquid, such as roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (such as comma coating).

[0021] A-2. Dry stretching and shrinking process A long intermediate laminate having a resin substrate and a PVA-based resin layer is subjected to a first dry stretching / shrinking step, which includes dry stretching the intermediate laminate in the longitudinal direction while heating and shrinking it in the width direction, and a second dry stretching / shrinking step, which includes dry stretching the intermediate laminate in the longitudinal direction while heating at a temperature lower than the maximum heating temperature in the first dry stretching / shrinking step and shrinking it in the width direction.

[0022] The total longitudinal stretch ratio of the intermediate laminate in the first in-air stretching and shrinking step and the second in-air stretching and shrinking step is preferably 3.5 times or less, more preferably 2.0 to 3.5 times, and more preferably 2.4 to 3.0 times. When the total longitudinal stretch ratio of the intermediate laminate in the first in-air stretching and shrinking step and the second in-air stretching and shrinking step is within the above range, a long laminate having a polyvinyl alcohol-based resin layer with reduced variation in orientation angle can be obtained. In this specification, the total longitudinal stretch ratio of the intermediate laminate in the first in-air stretching and shrinking step and the second in-air stretching and shrinking step refers to the sum of the longitudinal stretch ratios in each in-air stretching and shrinking step.

[0023] The total shrinkage ratio in the width direction in the first in-air stretching and shrinking step and the second in-air stretching and shrinking step is preferably less than 50%, more preferably 32% to 42%, and even more preferably 35% to 40%. When the total shrinkage ratio in the width direction in the first in-air stretching and shrinking step and the second in-air stretching and shrinking step is within the above range, a long laminate having a polyvinyl alcohol-based resin layer with reduced variation in orientation angle can be obtained. Herein, the total stretch ratio in the width direction of the intermediate laminate in the first in-air stretching and shrinking step and the second in-air stretching and shrinking step refers to the sum of the shrinkage ratios in the width direction in each in-air stretching and shrinking step.

[0024] The first in-air stretching-shrinking step and the second in-air stretching-shrinking step can be performed using any appropriate method. The first in-air stretching-shrinking treatment and the second in-air stretching-shrinking treatment are preferably performed using a tenter stretching apparatus equipped with multiple clips as gripping means. A production method using a tenter stretching apparatus will be specifically described below.

[0025] A-2-1. First dry stretching and shrinking treatment In the first dry stretching shrinkage treatment, an intermediate laminate having a resin substrate and a PVA-based resin layer is stretched in the longitudinal direction (hereinafter also referred to as MD stretching) and shrunk in the width direction (hereinafter also referred to as TD shrinkage) while being heated using a tenter stretching device equipped with multiple clips as gripping means. Specifically, both side edges of the intermediate laminate are gripped with a clip spacing L1 in the conveyance direction, and the intermediate laminate is stretched in the longitudinal direction by expanding the clip spacing from L1 to L2, and the intermediate laminate is shrunk in the width direction by decreasing the clip spacing in the width direction. The order of MD stretching and TD shrinkage can be appropriately set depending on the purpose. For example, MD stretching may be performed first, TD shrinkage may be performed first, or MD stretching and TD shrinkage may be performed simultaneously.

[0026] The tenter stretching device may be, for example, a stretching device equipped with a pair of rails having a straight section where the rail-to-rail distance is constant and a tapered section where the rail-to-rail distance continuously decreases, and multiple clips that can run on each rail while changing the clip spacing. With such a stretching device, the intermediate laminate can be stretched and shrunk by holding both side edges of the intermediate laminate with the clips and changing the clip spacing in the conveyance direction (the distance between the clips on the same rail) and the clip spacing in the width direction (the distance between the clips on different rails).

[0027] FIG. 3 is a schematic plan view illustrating the overall configuration of an example of a stretching device that can be used in the manufacturing method of the present invention. A stretching device that can be used in the manufacturing method of the present invention will be described with reference to FIG. 3. The stretching device 100 has endless rails 10L and 10R symmetrically arranged on both the left and right sides in a plan view. In this specification, the left endless rail, as viewed from the entrance side of the intermediate laminate, is referred to as the left endless rail 10L, and the right endless rail is referred to as the right endless rail 10R. A number of clips 20 for holding the laminate are disposed on each of the left and right endless rails 10L and 10R. The clips 20 move circulating in a loop, guided by their respective rails. The clips 20 on the left endless rail 10L move circulating counterclockwise, and the clips 20 on the right endless rail 10R move circulating clockwise. In the illustrated stretching device, a gripping zone A, an MD stretching zone B, a TD shrinkage zone C, and a release zone D are provided in this order from the entrance side of the intermediate laminate to the exit side. Note that these zones refer to zones where the intermediate laminate is substantially gripped, stretched in the MD, contracted in the TD (or contracted in the TD and stretched in the MD), and released, and do not refer to mechanically or structurally independent compartments. It should also be noted that the length ratio of each zone in the stretching device in Figure 3 differs from the actual length ratio.

[0028] In the illustrated example, in the gripping zone A and the MD stretching zone B, the left and right endless rails 10R, 10L are straight sections with a constant rail-to-rail distance. Typically, the left and right endless rails 10R, 10L are configured to be approximately parallel to each other with a rail-to-rail distance corresponding to the initial width of the intermediate laminate to be processed. In the TD shrinking zone C, the left and right endless rails 10R, 10L are tapered sections with a continuously decreasing rail-to-rail distance. Typically, the left and right endless rails 10R, 10L are configured so that the rail-to-rail distance gradually decreases from the MD stretching zone B side toward the release zone D side until it corresponds to the post-shrinkage width of the intermediate laminate. In the release zone D, the left and right endless rails 10R, 10L are straight sections with a constant rail-to-rail distance, typically configured so that they are approximately parallel to each other with a rail-to-rail distance corresponding to the post-shrinkage width of the intermediate laminate.

[0029] The clip 20 on the left endless rail 10L (left clip) and the clip 20 on the right endless rail 10R (right clip) can move circumferentially independently. For example, the drive sprockets 30a and 30b of the left endless rail 10L are driven to rotate counterclockwise by electric motors 40a and 40b, and the drive sprockets 30a and 30b of the right endless rail 10R are driven to rotate clockwise by electric motors 40a and 40b. As a result, a running force is applied to the clip support members (not shown) of the drive rollers (not shown) engaged with the drive sprockets 30a and 30b. This causes the left clip 20 to move circumferentially in the counterclockwise direction, and the right clip 20 to move circumferentially in the clockwise direction. By independently driving the left electric motor and the right electric motor, the left clip 20 and the right clip 20 can be moved circumferentially independently.

[0030] The clip size is preferably 12 mm to 40 mm, and more preferably 15 mm to 35 mm. If the clip size is less than 12 mm, the stretching tension may not be maintained and the laminate may break, or the strength of the clip conveying section may be insufficient, resulting in drive malfunction. If the clip size exceeds 40 mm, the area that is not stretched near the clip may become large, causing unevenness at the edge, or cracks may occur on the surface of the resin film due to local stretching of the non-gripped section. Here, the clip size refers to the width of the gripped area.

[0031] Furthermore, the left clip 20 and the right clip 20 are each a variable pitch type. That is, the clip spacing (clip pitch) between the left and right clips 20, 20 in the conveying direction (MD) can change independently as they move. Variable pitch clips can be realized by any appropriate configuration, such as the configuration described in JP 2008-23775 A.

[0032] 4 and 5 are schematic plan views of the main parts of the stretching device of FIG. 3. FIG. 4 is a schematic plan view of the rails of the stretching device of FIG. 3, at the transition from the MD stretching zone B to the TD contraction zone C. FIG. 5 is a schematic plan view of the rails of the stretching device of FIG. 3, at the transition from the TD contraction zone C to the release zone D. As shown in FIGS. 4 and 5, both ends of the tapered section are bent sections 11 and 12, respectively, at a predetermined angle (θ1), which allows connection to a straight section with a constant rail-to-rail distance. The bend angle can be appropriately set depending on the desired shrinkage rate and productivity. The bend angle θ1 can be, for example, 1° to 20°.

[0033] The stretching device illustrated in FIG. 5 is configured to perform MD stretching and TD shrinkage in this order, and MD stretching can also be performed during TD shrinkage. Specifically, the longitudinal stretching and widthwise shrinkage (MD stretching / TD shrinkage steps) can include gripping both side edges of the intermediate laminate with clips at a clip spacing of L1 in the conveyance direction (gripping step), stretching the intermediate laminate in the longitudinal direction by expanding the clip spacing in the conveyance direction from L1 to L2 while passing the intermediate laminate through a straight section (MD stretching step), and shrinking the intermediate laminate in the width direction by passing the intermediate laminate through a tapered section (TD shrinkage step). If necessary, the process may further include releasing the clips gripping the intermediate laminate (releasing step).

[0034] 6 and 7 are schematic diagrams showing an example of a shrinkage-stretching process including these steps. Each step in the shrinkage-stretching process will be described in more detail below with reference to these figures. First, in the gripping step (gripping zone A), left and right clips 20 grip both side edges of an intermediate laminate 50 taken into a stretching device at a fixed gripping interval (clip interval), and the intermediate laminate 50 is transported to the MD stretching zone B by the movement of each clip 20 guided by left and right endless rails. The gripping intervals (clip intervals) of both side edges in gripping zone A are typically equal to each other. The clip interval is the distance between the centers of adjacent clips.

[0035] Next, in the MD stretching step (MD stretching zone B), the intermediate laminate 50 held by the left and right clips 20 is stretched in the longitudinal direction (MD stretching) while being conveyed. The MD stretching of the intermediate laminate 50 is performed by gradually increasing the moving speed of the clips 20 in the conveying direction and expanding the clip spacing in the conveying direction from L1 to L2. The longitudinal stretch ratio N (L2 / L1) can be controlled by adjusting the clip spacing in the conveying direction (clamping spacing in the gripping step) L1 at the entrance of the MD stretching zone B and the clip spacing in the conveying direction L2 at the exit of the MD stretching zone B.

[0036] The stretch ratio in the longitudinal direction is calculated by L2 / L1. The stretch ratio in the longitudinal direction in the first in-air stretching / shrinking step is preferably 1.8 to 3.3, and more preferably 2.1 to 2.7. When the stretch ratio in the longitudinal direction in the first in-air stretching / shrinking step is within the above range, the stretchability (total stretch ratio) of the intermediate laminate is further improved, and good stretching can be achieved even at high temperatures.

[0037] If the clip spacing L1 is too large, stress that causes the intermediate laminate 50 to shrink in the width direction will be generated in the portions not held by the clips 20, which may result in unevenness in the properties of the resulting long laminate. Therefore, the clip spacing L1 is typically set to a spacing that is equal to or smaller than the spacing that prevents such unevenness from occurring.

[0038] The clip distance L1 is preferably 100 mm or less, more preferably 60 mm or less, and even more preferably 40 mm or less. L1 is not limited as long as the clip distance L2 described below can be achieved after stretching, and can be, for example, 25 mm or more.

[0039] On the other hand, if the clip spacing L1 is set to a predetermined value or less as described above, the clip spacing L2 after MD stretching may also be small depending on the stretch ratio, causing interference such as contact between the clips 20 in the tapered portion (particularly in the bent portion), making it impossible to achieve the desired shrinkage ratio (as a result, the total stretch ratio may not be sufficiently high). Therefore, typically, the clip spacing L2 is set to a spacing that is greater than or equal to the spacing that prevents the clips 20 from interfering with each other when the intermediate laminate 50 passes through the tapered TD shrinkage zone C (particularly in the bent portion). By setting L2 in this manner, L1 can be reduced without being limited to the spacing that prevents clips from interfering with each other in the bent portion. Note that "no interference between the clips" means that the clips, their supporting members, and spacing adjustment mechanisms can move through the bent portion as set without coming into contact with each other.

[0040] The clip spacing L2 can be appropriately set depending on the bending angle, the size and shape of the clip, etc. The clip spacing L2 is preferably 25 mm to 300 mm, and more preferably 35 mm to 150 mm. If the clip spacing L2 is within the above range, interference between the clips 20 at the tapered portion (especially the bending portion) can be avoided in the TD shrinking step, and a sufficient bending angle can be achieved, and more uniform shrinkage can be achieved.

[0041] Next, in the width direction (TD) shrinkage process (TD shrinkage zone C), the intermediate laminate 50 held by the left and right clips 20 is transported in the longitudinal direction and shrunk in the width direction (TD shrinkage). In the TD shrinkage zone C, the left and right endless rails 10R, 10L are tapered so that the rail-to-rail distance continuously decreases, and the intermediate laminate 50 shrinks in the width direction by passing through this zone. The TD shrinkage rate can be controlled by adjusting the amount of change in the rail-to-rail distance. Specifically, the smaller the ratio of the rail-to-rail distance at the exit of the TD shrinkage zone C to the rail-to-rail distance at the entrance (end on the MD stretching zone B side) of the TD shrinkage zone C, the greater the shrinkage rate obtained.

[0042] The shrinkage rate (%) in the width direction in the first in-air stretching-shrinking step ({1-(width of laminate at the exit of the TD shrinkage zone: W2) / (width of laminate at the entrance of the TD shrinkage zone: W1)} x 100) can be set to any appropriate value. The shrinkage rate in the width direction in the first in-air stretching-shrinking step is preferably 30% to 40%, more preferably 32% to 38%, and even more preferably 34% to 36%. When the shrinkage rate in the width direction in the first in-air stretching-shrinking step is within the above range, the intermediate laminate can be stretched at a higher draw ratio.

[0043] In the embodiment illustrated in FIG. 6, only the width direction of the intermediate laminate 50 is shrunk in the TD shrinkage step. In this case, the intermediate laminate 50 passes through the TD shrinkage zone C while maintaining the clip distance (L2) in the conveying direction. On the other hand, in the embodiment illustrated in FIG. 7, MD stretching and TD shrinkage are performed simultaneously. When MD stretching and TD shrinkage are performed simultaneously, for example, the rails in the MD stretching zone may be tapered so that the rail-to-rail distance continuously decreases. That is, in the stretching device, an MD stretching / TD shrinkage zone BC is provided between the gripping zone A and the release zone D, and in the MD stretching / TD shrinkage zone BC, the rail-to-rail distance (the width of the laminate) is reduced from W1 to W2 while the clip distance in the conveying direction is expanded from L1 to L2. By performing MD stretching in multiple stages in the MD stretching step and the TD shrinkage step, the final stretch ratio can be increased. Furthermore, by simultaneously performing TD shrinkage and MD stretching, the occurrence of warping and wrinkles can be suppressed. Details of such a method of longitudinal stretching and widthwise shrinking are described, for example, in Japanese Patent No. 6563201. The entire disclosures of these publications are incorporated herein by reference.

[0044] The heating temperature of the intermediate laminate in the first in-air stretching and shrinking step can be set to any appropriate value depending on the material forming the resin substrate, etc. The heating temperature is typically equal to or higher than the glass transition temperature (Tg) of the resin substrate, preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate + 10°C, and more preferably equal to or higher than Tg + 15°C. In one embodiment, the maximum heating temperature in the first in-air stretching and shrinking step is preferably 140°C to 170°C, more preferably 145°C to 165°C, more preferably 150°C to 160°C, and even more preferably 152°C to 158°C. In this embodiment, heating may be performed so that the maximum temperature in the first in-air stretching and shrinking step falls within the above range. The method for producing a long laminate according to an embodiment of the present invention suppresses the occurrence of defects such as breakage of the laminate even at the above temperatures, and allows stretching at a high draw ratio even at high temperatures. Furthermore, by performing an in-air stretching / shrinking step while heating so that the maximum temperature is within the above range, and then performing a second in-air stretching / shrinking step, it is possible to finally obtain a long laminate having a polyvinyl alcohol-based resin layer with reduced variation in orientation angle.

[0045] Heating in the first in-air stretching / shrinking step can be performed by any appropriate method. For example, the intermediate laminate may be stretched in the longitudinal direction and / or shrunk in the width direction while being transported through a furnace set at the above-mentioned heating temperature, or may be stretched in the longitudinal direction and / or shrunk in the width direction while being exposed to hot air set at the above-mentioned heating temperature. The heating temperature may be set to a constant temperature throughout the first in-air stretching / shrinking step, or may be increased in stages.

[0046] A-2-2. Second dry stretching and shrinking process A second dry stretching / shrinking step may be carried out following the first dry stretching / shrinking step. The second dry stretching / shrinking step may enable stretching / shrinking at a higher temperature in the first dry stretching / shrinking step. The first and second in-air stretching / shrinking steps may be carried out continuously or stepwise. The longitudinal stretching and widthwise shrinking in the second in-air stretching / shrinking step may be carried out in any suitable order. Specifically, the intermediate laminate may be stretched in the longitudinal direction and then shrunk in the width direction, or the intermediate laminate may be shrunk in the width direction and then stretched in the longitudinal direction, or the longitudinal stretching and widthwise shrinking of the intermediate laminate may be carried out simultaneously. The same method as in the first in-air stretching / shrinking step may be used for the longitudinal stretching and widthwise shrinking of the intermediate laminate. The second in-air stretching / shrinking step is carried out so that the film change rate is 5% to 20%. By carrying out the second in-air stretching and shrinking so that the film change rate falls within the above range, axial misalignment of the resin substrate and the PVA-based resin layer can be suppressed.

[0047] As described above, in the second in-air stretching / shrinking step, in-air stretching / shrinking treatment is performed at a temperature lower than the maximum heating temperature in the first in-air stretching / shrinking step. By further including an in-air stretching / shrinking step performed at a temperature lower than the maximum heating temperature in the first in-air stretching / shrinking step, variations in the orientation angle of the resin substrate and the orientation angle of the PVA-based resin layer in the intermediate laminate after the first in-air stretching / shrinking step and the second in-air stretching / shrinking step can be suppressed. As a result, variations in the orientation angle of the final PVA-based resin layer can be suppressed even when another stretching step (e.g., an underwater stretching step) is performed. As a result, a long laminate having a PVA-based resin layer with better axial accuracy can be obtained.

[0048] The heating temperature in the second in-air stretching / shrinking step may be lower than the maximum heating temperature in the first in-air stretching / shrinking step. The heating temperature in the second in-air stretching / shrinking step is preferably lower than 140°C, more preferably 120°C or lower, and even more preferably 110°C or lower. The heating temperature in the second in-air stretching / shrinking step is, for example, 90°C or higher. When the heating temperature in the second in-air stretching / shrinking step is within the above range, variations in the orientation angle of the resin substrate and the orientation angle of the PVA-based resin layer in the intermediate laminate after the first in-air stretching / shrinking step and the second in-air stretching / shrinking step can be suppressed. As a result, variations in the orientation angle of the PVA-based resin layer obtained as a final product can be suppressed even when another stretching step (e.g., an underwater stretching step) is further performed. As a result, a long laminate having a PVA-based resin layer with better axial accuracy can be obtained.

[0049] The difference between the maximum heating temperature in the first in-air stretching-shrinking step and the heating temperature in the second in-air stretching-shrinking step is preferably 20°C to 80°C, more preferably 30°C to 70°C, and even more preferably 35°C to 65°C. When the difference between the maximum heating temperature in the first in-air stretching-shrinking step and the heating temperature in the second in-air stretching-shrinking step is within the above range, the variation in the orientation angle of the resin substrate and the orientation angle of the PVA-based resin layer in the intermediate laminate after the first in-air stretching-shrinking step and the second in-air stretching-shrinking step can be further suppressed. As a result, even when another stretching step (e.g., an underwater stretching step) is further performed, the variation in the orientation angle of the final PVA-based resin layer can be further suppressed. As a result, a long laminate having a PVA-based resin layer with better axial accuracy can be obtained.

[0050] Heating in the second in-air stretching / shrinking step can be performed by any appropriate method. For example, the intermediate laminate may be stretched in the longitudinal direction and / or shrunk in the width direction while being transported through a furnace set at the above-mentioned heating temperature, or may be stretched in the longitudinal direction and / or shrunk in the width direction while being exposed to hot air set at the above-mentioned heating temperature. The heating temperature may be set to a constant temperature throughout the second in-air stretching / shrinking step, or may be increased in stages.

[0051] The variation in the orientation angle of the resin substrate of the intermediate laminate after the first in-air stretching and shrinking process and the second in-air stretching process (hereinafter also referred to as the orientation angle of the resin substrate after the second in-air stretching and shrinking process) is 30° or less, preferably 25° or less, and more preferably 20° or less. If the variation in the orientation angle of the resin substrate after the second in-air stretching and shrinking process is within the above range, the variation in the orientation angle of the PVA resin layer formed on the resin substrate can be suppressed even when the resin substrate is subsequently subjected to an underwater stretching process. The smaller the variation in the orientation angle of the resin substrate after the second in-air stretching and shrinking process, the better, and it may even be 0°. In this specification, the variation in the orientation angle of the resin substrate after the second in-air stretching and shrinking process refers to the absolute value of the difference between the maximum and minimum orientation angles in the width direction of the resin substrate of the intermediate laminate after the first in-air stretching and shrinking process and the second in-air stretching and shrinking process. The orientation angle of the resin substrate can be measured by any appropriate method. The orientation angle can be measured by any suitable method, for example, using an "Axoscan" product manufactured by Axometrics.

[0052] The variation in the orientation angle of the PVA-based resin layer of the intermediate laminate that has undergone the first in-air stretching and shrinking process and the second in-air stretching process (hereinafter also referred to as the orientation angle of the PVA-based resin layer after the second in-air stretching and shrinking process) is less than 5°, preferably 3° or less, more preferably 1° or less, and particularly preferably 0.5° or less. When the variation in the orientation angle of the PVA-based resin layer after the second in-air stretching and shrinking process is within the above range, the variation in the orientation angle of the final PVA-based resin layer can be suppressed. The smaller the variation in the orientation angle of the PVA-based resin layer after the second in-air stretching and shrinking process, the better, and it may even be 0°. In this specification, the variation in the orientation angle of the PVA-based resin layer after the second in-air stretching and shrinking process refers to the absolute value of the difference between the maximum and minimum orientation angles in the width direction of the PVA-based resin layer peeled from the intermediate laminate that has undergone the first in-air stretching and shrinking process and the second in-air stretching and shrinking process. The orientation angle of the PVA-based resin layer can be measured by any appropriate method. The orientation angle can be measured by any suitable method, for example, using an "Axoscan" product manufactured by Axometrics.

[0053] A-3.Release process After the first in-air stretching / shrinking step and the second in-air stretching / shrinking step, the clips 20 gripping the intermediate laminate 50 are released in a release step (release zone). In the release step, the inter-clip distance and the clip spacing are typically both kept constant. If necessary, the clips are released after the intermediate laminate 50 has been cooled to a desired temperature.

[0054] A-4. Preheating process In one embodiment, a preheating zone (e.g., PH in FIG. 1) may be provided before the first in-air stretching and shrinking treatment, and the intermediate laminate 50 may be subjected to a preheating step. If the film undergoes the preheating step, the occurrence of wrinkles, folds, sagging, and the like due to a sudden change in film temperature can be suppressed. The temperature of the preheating zone may be set to any appropriate value. The temperature of the preheating zone is, for example, 70°C to 140°C, preferably 80°C to 130°C, and more preferably 90°C to 130°C.

[0055] A-5.Wet stretching process The intermediate laminate 50 that has been subjected to the first dry stretching / shrinking step and the second dry stretching / shrinking step is then subjected to a wet stretching step. Examples of the stretching method include roll stretching. If the process further includes an underwater stretching step, the total stretch ratio in the manufacturing process of the long laminate can be further improved.

[0056] Wet stretching is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid solution). Using an aqueous boric acid solution as a stretching bath can impart to the PVA-based resin layer rigidity sufficient to withstand the tension applied during stretching and water resistance that prevents dissolution in water. Specifically, boric acid generates tetrahydroxyborate anions in the aqueous solution, which can crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer is imparted with rigidity and water resistance, allowing it to be stretched well, resulting in a polarizing film with excellent optical properties.

[0057] The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and even more preferably 3 to 5 parts by weight, per 100 parts by weight of water. By adjusting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, allowing for the production of a polarizing film with better properties. In addition to boric acid or a borate, aqueous solutions obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

[0058] Preferably, an iodide is added to the drawing bath (boric acid aqueous solution). Adding an iodide can prevent iodine adsorbed in the PVA resin layer from leaching out. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of the iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

[0059] The wet stretching temperature (liquid temperature of the stretching bath) is preferably 40°C or higher, more preferably 60°C or higher. At such a temperature, the film can be stretched at a high ratio while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, good stretching may not be possible, even taking into account the plasticization of the thermoplastic resin substrate by water. On the other hand, the stretching temperature is, for example, 70°C or lower, preferably 67°C or lower, and more preferably 65°C or lower. The higher the stretching temperature, the higher the solubility of the PVA-based resin layer, which may result in poor optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0060] The total stretching ratio in the first dry stretching / shrinking step, the second dry stretching / shrinking step, and the wet stretching step is preferably 4.0 times or more, more preferably 5.0 to 6.0 times, and even more preferably 5.2 to 5.8 times. In this specification, the total stretching ratio refers to the sum of the stretching ratios in the first dry stretching / shrinking step, the second dry stretching / shrinking step, and the wet stretching step.

[0061] The variation in the orientation angle of the PVA-based resin layer of the intermediate laminate that has undergone the first in-air stretching / shrinking step, the second in-air stretching / shrinking step, and the underwater stretching step (hereinafter also referred to as the orientation angle of the PVA-based resin layer after the underwater stretching step) is less than 0.3°, preferably less than 0.2°, and more preferably 0.18° or less. If the variation in the orientation angle of the PVA-based resin layer after the underwater stretching step is within the above range, a PVA-based resin layer with excellent axial accuracy can be obtained. The smaller the variation in the orientation angle of the PVA-based resin layer after the underwater stretching step, the better, and it may even be 0°. In this specification, the variation in the orientation angle of the PVA-based resin layer after the underwater stretching step refers to the absolute value of the difference between the maximum and minimum orientation angles in the width direction of the PVA-based resin layer peeled from the intermediate laminate that has undergone the first in-air stretching / shrinking step, the second in-air stretching / shrinking step, and the underwater stretching step. The orientation angle of the PVA-based resin layer can be measured by any appropriate method. For example, the measurement can be performed using a product called "Axoscan" manufactured by Axometrics.

[0062] B. Long laminate According to the manufacturing method of the long laminate of the embodiment of the present invention, a long laminate having a resin layer (e.g., a PVA-based resin layer) with excellent axial accuracy can be obtained. The crystallinity of the PVA-based resin layer of the long laminate is preferably 45% to 55%, more preferably 48% to 53%. According to the manufacturing method of the long laminate of the embodiment of the present invention, it is possible to stretch and shrink the intermediate laminate at a high stretch ratio and a high shrinkage percentage even at a high temperature. As a result, a long laminate having a PVA-based resin layer with a high crystallinity can be obtained. The long laminate obtained by the manufacturing method of the long laminate of the embodiment of the present invention can be suitably used in applications requiring a PVA-based resin layer with a high crystallinity. Herein, the crystallinity of PVA refers to a value measured by the following evaluation method. Herein, the crystallinity of PVA refers to a value calculated by X-ray diffraction (XRD) analysis as a percentage of the crystalline peak area relative to the sum of the crystalline peak area and the amorphous peak area.

[0063] (Method for evaluating the crystallinity of PVA) Any appropriate analytical device can be used for the X-ray analysis, including, for example, the "SmartLab" X-ray diffraction device manufactured by Rigaku Corporation and the "HyPix3000" 2D detector manufactured by Rigaku Corporation. A 150 μm thick PVA-based resin layer is used as the sample. If the PVA-based resin layer is less than 150 μm thick, the PVA-based resin layers are stacked to a total thickness of approximately 150 μm. X-rays with a wavelength of 1.5406 Å are transmitted through the sample perpendicular to the thickness direction, and scattered light is detected using a two-dimensional detector placed on the opposite side of the sample from the light source, resulting in a two-dimensional scattering image. After background correction, the obtained scattering image is integrated over the entire azimuthal angle (360°) around the beam center to obtain a one-dimensional profile of the integrated X-ray intensity versus the scattering angle 2θ. Next, waveform separation of the crystalline and amorphous peaks is performed on the obtained one-dimensional profile within the scattering angle 2θ range of 14° to 28.5°, and the crystallinity (%) is calculated using the following formula: Crystallinity (%) = crystalline peak area / (crystalline peak area + amorphous peak area) × 100

[0064] The thickness of the PVA resin layer of the long laminate is, for example, 12 μm or less, preferably 8 μm or less, and may be 6 μm or less, while the thickness of the PVA resin layer is preferably 1 μm or more, more preferably 2 μm or more.

[0065] C. Other processes As described above, the method for producing a long laminate according to an embodiment of the present invention can suppress variations in orientation angle and produce a long laminate having a polyvinyl alcohol-based resin layer with excellent axial accuracy. The method for producing a long laminate according to an embodiment of the present invention may further include any other appropriate steps in addition to the step described in section A above, depending on the intended use of the long laminate. In one embodiment, the long laminate according to an embodiment of the present invention may be a long laminate having a PVA-based resin layer that can function as a polarizing film. The longitudinal direction, which is the stretching direction, essentially corresponds to the absorption axis direction of the resulting polarizing film. The method for producing a long laminate having a PVA-based resin layer that can function as a polarizing film will be described in detail below.

[0066] When producing a long laminate having a PVA-based resin layer capable of functioning as a polarizing film, any appropriate steps may be included as other steps. Examples of such steps include an insolubilizing step, a dyeing step, a crosslinking step, a stretching step other than the above-mentioned stretching steps (the first and second in-air stretching and shrinking steps and the underwater stretching), a washing step, and a drying step (adjusting the moisture content and drying shrinkage). These steps may be performed at any appropriate timing.

[0067] The dyeing step is typically a step of dyeing the PVA-based resin layer with a dichroic substance. Preferably, the dyeing step is carried out by adsorbing the dichroic substance into the PVA-based resin layer. Examples of the adsorption method include immersing the PVA-based resin layer (laminate) in a dyeing solution containing the dichroic substance, applying the dyeing solution to the PVA-based resin layer, and spraying the dyeing solution onto the PVA-based resin layer. Preferably, the laminate is immersed in a dyeing solution containing the dichroic substance, because this method allows for good adsorption of the dichroic substance. Both sides of the laminate may be immersed in the dyeing solution, or only one side may be immersed.

[0068] Examples of the dichroic substance include iodine and organic dyes. These may be used alone or in combination of two or more. The dichroic substance is preferably iodine. When iodine is used as the dichroic substance, the dye solution is preferably an iodine aqueous solution. The amount of iodine to be added is preferably 0.1 to 1.0 part by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide salt to the iodine aqueous solution. Examples of iodide salts include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide and sodium iodide are preferred. The amount of iodide salt to be added is preferably 0.3 to 15 parts by weight per 100 parts by weight of water.

[0069] The temperature of the dye solution during dyeing is preferably 20° C. to 40° C. When the PVA-based resin layer is immersed in the dye solution, the immersion time is preferably 5 to 300 seconds. Under these conditions, the dichroic substance can be sufficiently adsorbed into the PVA-based resin layer.

[0070] The insolubilizing step and the crosslinking step are typically carried out by immersing the PVA resin layer in an aqueous solution of boric acid. The washing step is typically carried out by immersing the PVA resin layer in an aqueous solution of potassium iodide. The drying temperature in the drying step is preferably 30°C to 100°C.

[0071] The separate stretching step may be any appropriate stretching step. The separate stretching step may be dry stretching or wet stretching. Examples of the stretching method include roll stretching. By performing the separate stretching step, the final stretching ratio can be further increased. Preferably, the separate stretching step includes a wet stretching step. If the separate stretching step is further included, the total stretching ratio in the process of producing the long laminate can be further improved, and as a result, a polarizing film with excellent optical properties can be obtained. The separate stretching step may be performed simultaneously with the dyeing step, the insolubilizing step, and / or the crosslinking step, or may be performed separately. If performed separately, the separate stretching step may be performed at any appropriate timing.

[0072] Drying is carried out by any appropriate method. In one embodiment, it is preferable to further include a drying shrinkage treatment in which the film is heated while being transported in the longitudinal direction, thereby shrinking the film by 2% or more in the width direction. The drying shrinkage treatment is preferably carried out in the order of dry stretching, dyeing, wet stretching, and drying shrinkage treatment. In this embodiment, the PVA-based resin layer preferably contains a halide. Any appropriate halide can be used as the halide. Examples of halides include iodide and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred. The content of the halide in the PVA-based resin solution used to form the PVA-based resin layer (and consequently the PVA-based resin layer) is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out using a heated roll, and the temperature of the heated roll is preferably 60 to 120°C. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 2% or more.

[0073] D. Polarizing film The polarizing film (PVA-based resin layer of the long laminate) produced by the manufacturing method including the above-mentioned other steps is essentially a PVA-based resin film in which a dichroic material is adsorbed and aligned. The polarizing film preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single-layer transmittance (Ts) of the polarizing film is preferably 39% or more, more preferably 40% or more, even more preferably 41% or more, and particularly preferably 42% or more. The theoretical upper limit of the single-layer transmittance is 50%, and the practical upper limit is 46%. The single-layer transmittance (Ts) is the Y value measured using a 2-degree visual field (C light source) according to JIS Z8701 and corrected for luminous efficiency. It can be measured, for example, using a product named "V-7100" manufactured by JASCO Corporation. The polarization degree of the polarizing film is preferably 99% or more, more preferably 99.90% or more, and even more preferably 99.95% or more.

[0074] The thickness of the polarizing film is, for example, 12 μm or less, preferably 8 μm or less, and may be 6 μm or less, while the thickness of the PVA-based resin layer is preferably 1 μm or more, more preferably 2 μm or more.

[0075] The polarizing film may be used in any appropriate manner. Specifically, the polarizing film may be used as a single-layer PVA-based resin film, as a laminate of a resin substrate and a PVA-based resin film, or as a laminate in which a protective film is disposed on at least one of the PVA-based resin film and the PVA-based resin film (i.e., a polarizing plate).

[0076] E. Polarizing plate The polarizing plate has a polarizing film and a protective film disposed on at least one side of the polarizing film. Examples of materials for forming the protective film include cellulose-based resins such as diacetyl cellulose and triacetyl cellulose, (meth)acrylic resins, cycloolefin-based resins, olefin-based resins such as polypropylene, ester-based resins such as polyethylene terephthalate-based resins, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof.

[0077] The thickness of the protective film is preferably 10 μm to 80 μm. The protective film is typically laminated on the polarizing film via an adhesive layer (specifically, an adhesive layer or a pressure-sensitive adhesive layer). The adhesive layer is typically formed of a PVA-based adhesive or an activation energy ray-curable adhesive. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive. When a laminate of a resin substrate / PVA-based resin film (polarizing film) is used, the resin substrate can preferably be peeled off after laminating a protective film on the surface of the polarizing film opposite to the resin substrate. If necessary, another protective film can be laminated on the peeled surface. By peeling off the resin substrate, curling can be more reliably suppressed.

[0078] In practice, polarizing plates have a pressure-sensitive adhesive layer as their outermost layer. This pressure-sensitive adhesive layer is typically the outermost layer on the image display device side. A release liner is temporarily and removably attached to the pressure-sensitive adhesive layer to protect the pressure-sensitive adhesive layer until actual use and to enable roll formation.

[0079] The polarizing plate may further include any appropriate optically functional layer depending on the purpose. Representative examples of optically functional layers include a retardation film (optical compensation film) and a surface treatment layer. For example, a retardation film may be disposed between the protective film and the pressure-sensitive adhesive layer (not shown). The optical properties of the retardation film (e.g., refractive index ellipsoid, in-plane retardation, thickness retardation) may be appropriately set depending on the purpose, characteristics of the image display device, etc. For example, when the image display device is an IPS-mode liquid crystal display device, a retardation film having a refractive index ellipsoid of nx>ny>nz and a retardation film having a refractive index ellipsoid of nz>nx>ny may be disposed. The retardation film may also serve as a protective film. In this case, the protective film disposed on the image display device side may be omitted. Conversely, the protective film may have an optical compensation function (i.e., it may have a refractive index ellipsoid, in-plane retardation, and thickness retardation appropriate for the purpose). Here, "nx" is the refractive index in the direction in which the refractive index within the film plane is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis within the film plane, and "nz" is the refractive index in the thickness direction.

[0080] The surface treatment layer may be disposed further outside the outer protective film (not shown). Typical examples of the surface treatment layer include a hard coat layer, an anti-reflection layer, and an anti-glare layer. The surface treatment layer is preferably a layer with low moisture permeability, for example, for the purpose of improving the humidity durability of the polarizing film. The hard coat layer is provided for the purpose of preventing scratches on the polarizing plate surface. The hard coat layer can be formed, for example, by adding a cured film made of an appropriate ultraviolet-curable resin such as an acrylic or silicone resin, which has excellent hardness and slip properties, to the surface. The hard coat layer preferably has a pencil hardness of 2H or more. The anti-reflection layer is a low-reflection layer provided for the purpose of preventing reflection of external light on the polarizing plate surface. Examples of anti-reflection layers include a thin-layer type, as disclosed in JP 2005-248173 A, which prevents reflection by utilizing the cancellation effect of reflected light due to light interference, and a surface structure type, as disclosed in JP 2011-2759 A, which imparts a microstructure to the surface to achieve low reflectance. Anti-glare layers are provided for purposes such as preventing external light from reflecting off the polarizing plate surface and impairing the visibility of light transmitted through the polarizing plate. Anti-glare layers are formed by imparting a micro-convex / concave structure to the surface using appropriate methods, such as surface roughening methods such as sandblasting or embossing, or incorporating transparent fine particles. The anti-glare layer may also function as a diffusion layer (e.g., a viewing angle widening function) to diffuse light transmitted through the polarizing plate and widen the viewing angle. Instead of providing a surface treatment layer, a similar surface treatment may be applied to the surface of the outer protective film. [Example]

[0081] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0082] [Example 1] <Intermediate laminate manufacturing process> As a resin substrate, an amorphous PET substrate (100 μm thick) was prepared, and an aqueous PVA solution was applied thereto and dried at a temperature of 60°C. As a result, a PVA-based resin layer with a thickness of 13 μm was formed on the amorphous PET substrate to produce a laminate.

[0083] <MD stretching and TD shrinking process> The obtained laminate was subjected to MD stretching and TD shrinking using a stretching device similar to that shown in Fig. 1. Specifically, in the gripping zone, both side edges of the intermediate laminate were gripped and conveyed in the longitudinal direction, and passed through a preheating zone (set temperature: 90°C). Next, in the stretching and shrinking treatment zone SS including the first air stretching and shrinking treatment zone SS1 and the second air stretching and shrinking treatment zone SS2, the temperature was raised in the first stretching and shrinking treatment zone so that the maximum temperature in the first stretching and shrinking treatment became 150°C, and then the temperature was lowered from 150°C to 105°C in the second stretching treatment zone. The temperature lowering was performed by blowing warm air at 105°C in the second air stretching and shrinking treatment zone SS2. The film change rate in the second air stretching and shrinking process was 8.90%. Thereafter, in the release zone, the clip gripping the laminate was released. The clip size was 15 mm. The total stretching ratio in the first air stretching and shrinking treatment and the second air stretching and shrinking treatment was 2.7 times, and the total shrinkage rate was 38%. The variation in the orientation angle of the resin substrate after the first air stretching and shrinking treatment and the second air stretching and shrinking treatment was 19.49°, and the variation in the orientation angle of the PVA-based resin layer was 0.16°. Also, the crystallinity of the PVA-based resin layer was 51%.

[0084] Next, the long laminate was immersed in an insolubilization bath (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment). Next, it was immersed in a dyeing bath (an aqueous iodine solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight 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 became a desired value (dyeing treatment). Next, the sample was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight 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 64°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 3 parts by weight of potassium iodide with 100 parts by weight 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 stainless steel (SUS) heated roll whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this way, a laminate having a 5 μm-thick PVA-based resin layer (polarizer) on a resin substrate was obtained. The variation in the orientation angle of the PVA-based resin layer was 0.06°. An HC-TAC film was attached to the surface of the polarizer obtained above (the surface opposite to the resin substrate) via a UV-curable adhesive. The HC-TAC film was a film in which a hard coat (HC) layer (7 μm thick) was formed on a triacetyl cellulose (TAC) film (25 μm thick), and the TAC film was attached to the polarizer side. Next, the resin substrate was peeled off to obtain a polarizing plate having a configuration of HC layer / TAC film (protective layer) / polarizer.

[0085] [Example 2] A long laminate (polarizing plate) having a PVA-based resin layer functioning as a polarizer was obtained in the same manner as in Example 1, except that the maximum heating temperature in the first stretching and shrinking treatment was set to 160°C and the film change rate was adjusted to the value shown in Table 1.

[0086] [Example 3] A long laminate (polarizing plate) having a PVA-based resin layer functioning as a polarizer was obtained in the same manner as in Example 1, except that the total stretching ratio in the first in-air stretching and shrinking treatment and the second in-air stretching and shrinking treatment was set to 2.4 times, the total shrinkage rate was set to 32%, the maximum heating temperature in the first in-air stretching and shrinking treatment was set to 140°C, and the film change rate was adjusted to the value shown in Table 1.

[0087] (Comparative Example 1) A long laminate (polarizing plate) having a PVA-based resin layer functioning as a polarizer was obtained in the same manner as in Example 1, except that the film change rate was adjusted to the value shown in Table 1.

[0088] (Comparative Example 2) A long laminate (polarizing plate) having a PVA-based resin layer functioning as a polarizer was obtained in the same manner as in Example 1, except that the second in-air stretching and shrinking treatment was not carried out.

[0089] (Comparative Example 3) An attempt was made to produce a long laminate in the same manner as in Example 1, except that the first air-stretching and shrinking treatment and the second air-stretching and shrinking treatment were carried out at the same temperature, but the laminate broke and it was not possible to produce a long laminate.

[0090] [evaluation] The long laminates obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 1. 1. Thickness Thicknesses of 10 μm or less were measured using an interference film thickness meter (Otsuka Electronics Co., Ltd., product name "MCPD-3000"), and thicknesses of more than 10 μm were measured using a digital micrometer (Anritsu Corporation, product name "KC-351C").

[0091] 2. Crystallinity of PVA The X-ray diffraction device used was a Rigaku Corporation product called "SmartLab," and the two-dimensional detector used was a Rigaku Corporation product called "HyPix3000." The PVA-based resin layer was peeled from the polarizing plate obtained in the Examples and Comparative Examples. Next, PVA-based resin layers were stacked to a total thickness of approximately 150 μm to prepare a sample. X-rays with a wavelength of 1.5406 Å were transmitted through the sample perpendicular to the thickness direction, and scattered light was detected using a two-dimensional detector placed on the opposite side of the sample from the light source, resulting in a two-dimensional scattering image. The obtained scattering image was subjected to background correction, and then integrated over the entire azimuthal angle (360°) with the beam center as the axis to obtain a one-dimensional profile of the integrated X-ray intensity versus scattering angle 2θ. Next, waveform separation of the crystalline and amorphous peaks was performed on the obtained one-dimensional profile within the scattering angle 2θ range of 14° to 28.5°, and the crystallinity (%) was calculated using the following formula: Crystallinity (%) = crystalline peak area / (crystalline peak area + amorphous peak area) × 100

[0092] 3. Orientation angle For the resin substrate (PET) and PVA-based resin layer of the long laminate after the first and second in-air stretching and shrinking treatments, the film to be measured was cut out in the width direction to obtain test pieces. These test pieces were measured in the width direction using an Axoscan manufactured by Axometrics, and the orientation angle at a wavelength of 550 nm was measured. The orientation angle of the obtained polarizer was also measured in the same manner. The absolute value of the difference between the maximum and minimum values of the widthwise orientation angle after the first and second air-stretching and shrinking processes was taken as the orientation angle variation after the first and second air-stretching and shrinking processes, and the absolute value of the difference between the maximum and minimum values of the widthwise orientation angle of the polarizer was taken as the orientation angle variation of the polarizer.

[0093] [Table 1]

[0094] The PVA resin layer of the long laminate obtained by the manufacturing method of the embodiment of the present invention had a high degree of crystallinity, and the variation in orientation angle was suppressed. [Industrial Applicability]

[0095] According to the manufacturing method of the present invention, a long laminate having a PVA-based resin layer with excellent axial accuracy can be obtained. According to the manufacturing method of the embodiment of the present invention, a long laminate having a PVA-based resin layer with high crystallinity can be obtained. [Explanation of symbols]

[0096] 10 Rail 20 clips 50 Intermediate laminate 100 Stretching equipment

Claims

1. A method for producing a long laminate, the method comprising: a first dry stretching and shrinking step, which includes dry stretching a long intermediate laminate having a resin substrate and a resin layer in a longitudinal direction while heating the intermediate laminate and shrinking the intermediate laminate in a width direction; a second dry stretching and shrinking step, which includes dry stretching the intermediate laminate in the longitudinal direction while heating the intermediate laminate at a temperature lower than the maximum heating temperature in the first dry stretching and shrinking step, and shrinking the intermediate laminate in the width direction; and a wet stretching step, in this order, wherein the film change rate in the second dry stretching and shrinking step is 5% to 20%, the variation in the width direction orientation angle of the resin substrate after the second dry stretching shrinkage step is 30° or less, and the variation in the width direction orientation angle of the resin layer after the second dry stretching shrinkage step is less than 0.5°; The method for producing a long laminate, wherein the variation in orientation angle of the resin layer in the width direction after the wet stretching is less than 0.3°.

2. The method for producing a long laminate according to claim 1, wherein the maximum heating temperature in the first dry stretching and shrinking step is 140°C to 170°C.

3. The method for producing a long laminate according to claim 2, wherein the polyvinyl alcohol-based resin layer of the long laminate has a crystallinity of 45% to 55%.

4. 2. The method for producing a long laminate according to claim 1, wherein the first dry stretching and shrinking step and the second dry stretching and shrinking step are carried out using a tenter stretching device having a plurality of clips as holding means.

5. The method for producing a long laminate according to claim 1 , wherein a total stretching ratio in the longitudinal direction in the first dry stretching and shrinking step and the second dry stretching and shrinking step is 3.5 times or less.

6. The method for producing a long laminate according to claim 1 , wherein a total shrinkage rate in the width direction in the first dry stretching and shrinking step and the second dry stretching and shrinking step is less than 50%.

7. The method for producing a long laminate according to claim 1 , wherein a total stretching ratio in the first dry stretching / shrinking step, the second dry stretching / shrinking step, and the wet stretching step is 4.0 times or more.

8. A long laminate obtained by the manufacturing method according to any one of claims 1 to 7.

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