Polarizing plate manufacturing method

Abstract

Provided is a method for producing a polarizing plate capable of suppressing curl. A method for manufacturing a polarizing plate including a polarizer, the method including, in this order: a first step in which the polarizing plate is placed in an environment having a temperature of 35-65 DEG C and a humidity of 70% or more; and a second step in which the laminate is placed in an environment having a temperature lower than the temperature in the first step and a humidity of 70% or more. The moisture absorption rate of the protective layer represented by formula (1) is 0.5% or more. In formula (1), A is the mass of the protective layer after the protective layer is left to stand for 10 minutes in an environment with a temperature of 35 DEG C and a humidity of 80%, and B is the mass of the protective layer after the protective layer is left to stand for 60 minutes in an environment with a temperature of 23 DEG C and a humidity of 55%: Hygroscopicity (%) = {(A / B)-1} * 100 (1).

Description

Methods for manufacturing polarizers Technical Field

[0001] This invention relates to a method for manufacturing polarizers. Background Technology

[0002] In recent years, image display devices, represented by liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have become increasingly widespread. Optical components with optical properties, such as polarizers and retardation layers (retardation films), are used in these image display devices. Polarizers, for example, can be unwound from a wound roll and cut or punched into any appropriate shape and size according to the image display device or optical laminate to be used, and processed into, for example, chip-like shapes (e.g., Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-108400 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, polarizers cut (punched out) as described above sometimes curl (warp).

[0008] The main objective of this invention is to provide a method for manufacturing a polarizer that can suppress curling.

[0009] means for solving problems

[0010] [1] The polarizer manufacturing method of the embodiment of the present invention is a method for manufacturing a polarizer including a polarizer, and the manufacturing method includes, in sequence: a first step, in which a laminate having a polarizer and a protective layer is placed in an environment with a temperature of 35°C or higher and 65°C or lower and a humidity of 70% or higher; and a second step, in which the laminate is placed in an environment with a temperature lower than that of the first step and a humidity of 70% or higher. The moisture absorption rate of the protective layer shown in the following formula (1) is 0.5% or higher.

[0011] Moisture absorption rate (%) = {(A / B) - 1} × 100 (1)

[0012] In formula (1), A is the mass of the protective layer after it has been placed in an environment with a temperature of 35°C and a humidity of 80% for 10 minutes, and B is the mass of the protective layer after it has been placed in an environment with a temperature of 23°C and a humidity of 55% for 60 minutes.

[0013] [2] In the above [1], in the aforementioned method for manufacturing polarizers, the temperature of the second step is above 20°C and below 30°C.

[0014] [3] In the above [1] or [2], in the aforementioned method for manufacturing polarizers, the thickness of the aforementioned protective layer is 10 μm or more.

[0015] [4] In any of the above [1] to [3], in the aforementioned method for manufacturing polarizers, the time spent in the environment of the first process and the time spent in the environment of the second process are both 2 minutes or more.

[0016] [5] In any of the above [1] to [4], in the aforementioned method of manufacturing polarizer, the aforementioned laminate has an additional protective layer on the side of the aforementioned polarizer opposite to the aforementioned protective layer.

[0017] Invention Effects

[0018] According to embodiments of the present invention, it is possible to obtain polarizers that can suppress curling. Detailed Implementation

[0019] A. Overall Structure of Polarizing Film Manufacturing Method

[0020] The polarizer manufacturing method of the present invention is a method for manufacturing a polarizer including a polarizer. The manufacturing method sequentially includes: a first step in which a laminate having a polarizer and a protective layer is placed in an environment with a temperature of 35°C or higher and 65°C or lower and a humidity of 70% or higher; and a second step in which the laminate is placed in an environment with a temperature lower than that of the first step and a humidity of 70% or higher. In this manufacturing method, the moisture absorption rate of the protective layer shown in the following formula (1) is 0.5% or higher:

[0021] Moisture absorption rate (%) = {(A / B) - 1} × 100 (1)

[0022] In formula (1), A is the mass of the protective layer after it has been placed in an environment with a temperature of 35°C and a humidity of 80% for 10 minutes, and B is the mass of the protective layer after it has been placed in an environment with a temperature of 23°C and a humidity of 55% for 60 minutes.

[0023] In existing polarizers, sometimes even with humidification, sufficient moisture cannot be introduced into the polarizer. As a result, sometimes the polarizer curls (warps) when processed into a chip shape, and sometimes it fails to meet standards (non-compliant) during the inspection process of chip-shaped polarizers. Even if it does not fail to meet standards during the inspection process, when applied to image display panels, sometimes the entire panel curls (panel bends). The inventors conducted in-depth research and found that polarizers that do not introduce sufficient moisture absorb moisture from their ends, causing the cut polarizers to curl.

[0024] Furthermore, the inventors considered that, in order to introduce the desired moisture into the polarizer, when conditioning the laminate (essentially a polarizer) containing the polarizer and protective layer, moisture absorption by the polarizer and protective layer can be achieved at higher temperatures and higher humidity levels compared to a conventional environment (e.g., temperature 23°C and humidity 55%). On the other hand, it was found that if the conditioned polarizer is returned to its conventional state, the amount of moisture released from the protective layer and polarizer is large, and further research is needed to achieve the desired moisture content in the polarizer. It was also found that if the temperature is increased while maintaining the conditioned humidity at the same level as the conventional environment, the polarizer dries out; if the humidity is increased, the moisture inside the polarizer will also evaporate due to the temperature increase, sometimes resulting in a decrease in moisture absorption. Therefore, the inventors conducted in-depth research and conceived of the configuration of the polarizer manufacturing method according to the embodiments of the present invention.

[0025] In other words, the polarizer manufacturing method of the present invention, during the conditioning of a laminate having a polarizer and a protective layer having a moisture absorption rate of a specified value (0.5%) or higher, performs a first step of placing the laminate in an environment with a specified temperature (35°C or higher and 65°C or lower) and humidity (70% or higher) that is higher than the conventional environment. This ensures that moisture in the aforementioned environment is well absorbed into the protective layer and the polarizer while maintaining a state that minimizes the release of absorbed moisture. Next, by performing a second step of placing the laminate in a specified environment (humidity 70% or higher and temperature lower than the temperature of the first step), the moisture absorption of the protective layer can be increased while the release of moisture from the polarizer can be suppressed, creating a state where moisture can easily move from the protective layer absorbed in the first and / or second steps to the polarizer. Thus, while suppressing the release of moisture from the polarizer, a portion of the moisture absorbed by the protective layer in the first and / or second steps can be introduced into the polarizer. As a result, the desired moisture can be fixed within the polarizer.

[0026] Therefore, according to an embodiment of the present invention, a polarizer containing a polarizer that has absorbed the desired amount of moisture can be obtained by performing the first and second steps as described above. The polarizer obtained by the manufacturing method of the embodiment of the present invention, as described above, forms a state in which excessive moisture absorption can be suppressed when the polarizer is used, since the polarizer has absorbed moisture to the desired degree. Therefore, the polarizer obtained by the embodiment of the present invention can suppress moisture absorption at the ends of the polarizer and suppress curling. As a result, non-conformity can be suppressed in the polarizer itself and in optical laminates (e.g., polarizers with retardation layers) such as those bonded to a retardation layer, and panel bending can also be suppressed when the polarizer is applied to an image display device.

[0027] B. Details of the manufacturing process for polarizers

[0028] The manufacturing method of the polarizer according to the embodiments of the present invention will be described below, with each step described in detail below.

[0029] B-1. Preparation of laminated bodies

[0030] First, prepare a laminated body with a polarizer and a protective layer.

[0031] The laminate may also include any suitable layers other than the polarizer and the protective layer. For example, the laminate may have an additional protective layer on the side of the polarizer opposite to the protective layer. With the additional protective layer, the resulting polarizer can be a double-sided protected polarizer. It should be noted that without the additional protective layer, the resulting polarizer can be a single-sided protected polarizer. For example, during transport (essentially after the second process), the laminate may have a surface protective film on the side of the protective layer opposite to the polarizer. The laminate may also have an additional surface protective film on the side of the additional protective layer opposite to the polarizer. The additional protective layer, surface protective film, and additional surface protective film are arbitrary components and may be omitted appropriately.

[0032] The laminate can have any suitable shape. In one embodiment, the laminate can be elongated. Such a laminate can be wound into a roll. For example, the rolled laminate can be unwound from the raw material roll and conveyed to a heating and humidifying section such as an oven. It should be noted that in this specification, "elongated" means a slender shape with a length sufficiently long relative to its width, such as a slender shape with a length of 10 times or more, preferably 20 times or more, relative to its width.

[0033] B-1-1. Polarizer

[0034] A polarizer is typically constructed from a resin film containing a dichroic substance (typically iodine). Any suitable resin film suitable for use as a polarizer can be used. A typical resin film is a polyvinyl alcohol (PVA) based resin film. The resin film can be a single layer or a laminate of two or more layers.

[0035] As a specific example of a polarizer composed of a single-layer resin film, a PVA-based resin film subjected to iodine-based dyeing and stretching treatment (typically uniaxial stretching) can be cited. The aforementioned iodine-based dyeing is performed, for example, by immersing the PVA-based resin film in an aqueous iodine solution. The stretching ratio of the aforementioned uniaxial stretching is preferably 3 to 7 times. Stretching can be performed after dyeing or during dyeing. Furthermore, stretching can be performed before dyeing. Depending on the needs, the PVA-based resin film can be subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc. For example, by immersing the PVA-based resin film in water for washing before dyeing, not only can contaminants and anti-blocking agents on the surface of the PVA-based resin film be washed away, but the PVA-based resin film can also swell to prevent uneven dyeing.

[0036] Specific examples of polarizers obtained using laminates include those using a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or those using 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 manufactured, for example, by coating a PVA-based resin solution onto a resin substrate and drying it to form a PVA-based resin layer on the resin substrate, thus obtaining a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to form a polarizer from the PVA-based resin layer. In one embodiment, it is preferable to form a polyvinyl alcohol (PVA) resin layer comprising a halide and a polyvinyl alcohol resin on one side of the resin substrate. Stretching typically includes stretching by immersing the laminate in an aqueous boric acid solution. Furthermore, stretching may, if necessary, also include air stretching of the laminate at a high temperature (e.g., above 95°C) before stretching in the aqueous boric acid solution. Based on this, in one embodiment, it is preferable to subject the laminate to a drying shrinkage treatment in which it shrinks by more than 2% in the width direction by heating while being conveyed longitudinally along the edge. Typically, one embodiment includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment on the laminate. By introducing assisted stretching, even when PVA is coated on a thermoplastic resin, the crystallinity of PVA can be improved, resulting in high optical properties. Furthermore, by simultaneously improving the orientation of PVA beforehand, problems such as reduced orientation and dissolution of PVA can be prevented when immersed in water during subsequent dyeing and stretching processes, further achieving high optical properties. Moreover, when the PVA-based resin layer is immersed in liquid, compared to the case where the PVA-based resin layer does not contain halides, orientation disorder and reduction of orientation of polyvinyl alcohol molecules can be suppressed. Therefore, the optical properties of the polarizer obtained by immersing the laminate in liquid through dyeing and underwater stretching treatments can be improved. Furthermore, by utilizing the drying shrinkage treatment to shrink the laminate in the width direction, optical properties can be improved. It should be noted that the resulting resin substrate / polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer for the polarizer), or the resin substrate can be peeled off from the resin substrate / polarizer laminate, and any suitable protective layer conforming to the purpose can be laminated on the peeled surface to form a laminate for use. Details of such a polarizer manufacturing method are described, for example, in Japanese Patent Application Publication No. 2012-73580 (Japanese Patent No. 5414738) and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0037] The thickness of the polarizer is preferably 1 μm or more and 30 μm or less, more preferably 1 μm or more and 25 μm or less, even more preferably 1 μm or more and 15 μm or less, even more preferably 1 μm or more and 10 μm or less, particularly preferably 1 μm or more and 8 μm or less, and most preferably 2 μm or more and 5 μm or less. If the thickness of the polarizer is within the above range, the polarizer can be made thinner.

[0038] The polarizer preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The single-unit transmittance Ts of the polarizer is preferably 40% to 48%, more preferably 41% to 46%. The polarization degree P of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. The aforementioned single-unit transmittance is representative of the Y value measured using a UV-Vis spectrophotometer and corrected for visibility. The aforementioned polarization degree is representatively calculated based on the parallel transmittance Tp and orthogonal transmittance Tc measured using a UV-Vis spectrophotometer and corrected for visibility, using the following formula.

[0039] Degree of polarization (%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0040] B-1-2. Protective layer

[0041] The moisture absorption rate of the protective layer, as described above, is typically 0.5% or more, preferably 0.75% or more, more preferably 1.0% or more, and even more preferably 1.5% or more. The upper limit of the moisture absorption rate of the protective layer can, for example, be 20%. Within such a range, the moisture absorption of the protective layer in the first and second processes can be significantly improved.

[0042] The moisture permeability of the protective layer is, for example, 300 g / m². 2 • More than 24 hours, preferably 500g / m 2 • More than 24 hours, preferably 600g / m 2 • After 24 hours or more, it can be further optimized to 800g / m 2 • More than 24 hours. The upper limit of moisture permeability of the protective layer is, for example, 3000 g / m². 2 • 24h. With this configuration, the moisture absorption of the protective layer in the first and second processes can be further improved. Furthermore, with this configuration, the moisture absorbed by the protective layer can move more efficiently towards the polarizer. The permeability can be obtained by measurement according to JIS Z0208. Specifically, unless otherwise specified, "permeability" in this specification refers to permeability at a temperature of 40°C and a humidity of 92%.

[0043] The protective layer, provided it meets the above-mentioned characteristics, can be formed from any suitable film that can be used as a protective layer for a polarizer. The protective layer is preferably a cellulose triacetate (TAC) based film. If the protective layer is made of such a resin film, the moisture absorption of the protective layer in the first and / or second steps can be significantly improved, and the moisture absorbed by the protective layer can be particularly well introduced into the polarizer.

[0044] In one embodiment, the thickness of the protective layer is typically 10 μm or more, preferably 15 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, and particularly preferably 30 μm or more. The upper limit of the protective layer thickness can be, for example, 100 μm. If the thickness of the protective layer is above the aforementioned lower limit, the hygroscopicity of the protective layer can be further improved. As a result, the introduction of moisture from the protective layer to the polarizer can be more significantly achieved.

[0045] B-2. Heating and humidifying the laminate (humidification process)

[0046] Next, the prepared laminate is sequentially fed to the first and second processes to condition the laminate. Hereinafter, the processes that sequentially include the first and second processes are sometimes referred to as the "conditioning process". However, the conditioning process may include processes other than the first and second processes.

[0047] In the humidification process, specifically, the rolled-up laminate is unwound from the raw material roll and conveyed through a heating and humidification unit such as an oven, thereby performing the first and second processes in sequence.

[0048] The heating and humidifying unit can be, for example, a housing with an internal space capable of controlling temperature and humidity. In the first step, the temperature of the heating and humidifying unit can typically be adjusted to 35°C or higher and 65°C or lower; the humidity can typically be adjusted to 70% or higher. In the second step, the temperature of the heating and humidifying unit can typically be adjusted to the temperature of the first step; the humidity can be adjusted to 70% or higher.

[0049] The heating and humidifying unit can be configured in the same space for both the first process and the second process. Alternatively, the first process and the second process can be configured separately.

[0050] The heating and humidifying unit can be configured to control the environment except for temperature and humidity. Examples of environments other than temperature and humidity include pressure and atmosphere (e.g., atmospheric atmosphere, inert gas atmosphere). The environment other than temperature and humidity can be appropriately set according to the purpose.

[0051] B-2-1. First Process

[0052] In the first step, as described above, the laminate is placed in an environment with a temperature of 35°C or higher and 65°C or lower, and a humidity of 70% or higher. The temperature of the first step (first conditioning temperature) is preferably 37°C or higher and 63°C or lower, more preferably 40°C or higher and 60°C or lower. The humidity of the first step (first conditioning humidity) is preferably 75% or higher, more preferably 80% or higher. The upper limit of the first conditioning humidity can be 100%. By keeping the first conditioning temperature and first conditioning humidity within such ranges, the polarizer and protective layer effectively absorb moisture in the first step, and the release of moisture can be suppressed.

[0053] In one embodiment, the time for which the laminate is placed in the environment of the first process (the first conditioning time) is typically 2 minutes or more, preferably 5 minutes or more, and more preferably 7 minutes or more. The upper limit of the first conditioning time can be, for example, 120 minutes. If the first conditioning time is above the aforementioned lower limit, moisture absorption into the protective layer can be performed more efficiently while maintaining the balance between moisture absorption and release in the protective layer. As a result, the introduction of moisture from the protective layer to the polarizer can be performed more effectively.

[0054] An additional process may be included between the first process and the second process, preferably the second process is performed immediately after the first process. The travel time from the first process to the second process can be, for example, more than 0 minutes and less than 30 minutes.

[0055] B-2-2. Second process

[0056] Next, the laminate from the first process is subjected to a second process. Specifically, in the second process, the laminate is transported and placed in an environment with a temperature lower than that of the first process and a humidity of 70%. The second process performs a humidity conditioning treatment on the laminate under the aforementioned environment.

[0057] The temperature of the second process (second conditioning temperature) can be any suitable temperature as long as it is lower than the first conditioning temperature. Specifically, for example, when the first conditioning temperature is 40°C to 70°C, the second conditioning temperature can typically be less than 70°C, preferably 5°C or more and 60°C or less, more preferably 10°C or more and 50°C or less, further preferably 15°C or more and 40°C or less, and particularly preferably 20°C or more and 35°C or less, whichever is lower than the first conditioning temperature. The humidity of the second process (second conditioning humidity) can be any suitable humidity as long as it is 70% or more. The second conditioning humidity can preferably be 75% or more, more preferably 80% or more. The upper limit of the second conditioning humidity can be 100%. The second conditioning humidity can be the same as or different from the first conditioning humidity. By having the second conditioning temperature and the second conditioning humidity within such a range, the moisture absorption of the protective layer is increased compared to the moisture absorption in the first process, which further improves the introduction of moisture from the protective layer to the polarizer.

[0058] In one embodiment, the time the laminate is placed in the environment of the second process (the second conditioning time) is typically 2 minutes or more, preferably 5 minutes or more, and more preferably 7 minutes or more. The upper limit of the second conditioning time can be, for example, 120 minutes. If the second conditioning time is above the lower limit mentioned above, it further contributes to an increase in the moisture absorption of the protective layer, which in turn can help the moisture to move more effectively toward the polarizer.

[0059] After the second process (i.e., after the humidification process), the laminate is removed from the heating and humidification unit. Specifically, the laminate can be removed from the heating and humidification unit while being conveyed to obtain a strip-shaped polarizer, or the strip-shaped polarizer after the humidification process can be wound into a roll while being conveyed to obtain a rolled polarizer. In this embodiment, the polarizer obtained fixes the desired moisture in the polarizer after the second process, and as a result, the polarizer absorbs moisture to the desired degree.

[0060] The environment after the second process (after the humidification process) can be any suitable environment.

[0061] The temperature after the conditioning process can be the same as or different from the temperature in the second process (the second conditioning temperature). After the conditioning process, the laminate can typically be placed in a normal environment (e.g., temperature 25°C and humidity 55%). Specifically, for example, after the conditioning process, the laminate is removed from the heating and humidification section, so the environment after the conditioning process can be a normal environment.

[0062] After the humidification process, the laminate can be cured. Curing the laminate allows for efficient introduction of moisture from the protective layer to the polarizer. Curing can be performed, for example, in any suitable environment and using any suitable method after the humidification process. Curing can be performed, for example, by storing the laminate in its laminated state. Specifically, the laminate can be rolled up and stored in a roll in any suitable environment. In this case, the laminate can be cured over time in its stored state. The laminate can be stored, for example, in a normal environment or in a specified temperature and / or humidity environment. The temperature can be, for example, 15°C to 30°C; the humidity can be, for example, 50% to 65%.

[0063] Curing can be performed directly in a long strip after the humidification process, in a manner that produces the same effect on the laminate during transport. For example, after the humidification process, transporting the laminate under appropriate temperature and humidity conditions can produce the same effect as curing described above.

[0064] The above steps will produce a polarizer.

[0065] B-3. ​​Variation Example

[0066] Hereinafter, a modified example of the method for manufacturing a polarizer according to an embodiment of the present invention will be described.

[0067] As described above, the laminate supplied for the humidity conditioning process can have any suitable layer other than the polarizer and the protective layer.

[0068] B-3-1. Additional protective layer

[0069] In one embodiment, the laminate may have an additional protective layer on the side of the polarizer opposite to the protective layer. With this configuration, the characteristics of the polarizer can be maintained and / or improved when the polarizer available in this embodiment is applied, for example, to an image display device. The additional protective layer, when the polarizer is in use, may be, for example, a protective layer disposed on the identification side. In this case, the aforementioned protective layer may constitute an inner protective layer.

[0070] The additional protective layer, without impairing the aforementioned effects of the present invention, can be formed of any suitable resin film that can be used as a protective layer for a polarizer. The additional protective layer can have any suitable moisture permeability. For example, the moisture permeability of the additional protective layer can be 0.1 g / m³. 2 • More than 24 hours and 2000g / m 2 • Less than 24 hours. The moisture permeability of the additional protective layer can be the same as, greater than, or less than that of the protective layer.

[0071] In one embodiment, the moisture permeability of the additional protective layer is preferably 100 g / m². 2 • 24 hours or more, preferably 200g / m 2 • More than 24 hours, preferably 500g / m 2 • 24 hours or more, with a preferred concentration of 700g / m 2 • 24 hours or more. If the permeability of the additional protective layer is above the aforementioned lower limit, the laminate can easily absorb moisture from both sides of the protective layer and the additional protective layer during the conditioning process. As a result, the conditioning effect of the obtained polarizer can be further improved. This effect is particularly significant when no additional surface protective layer is temporarily bonded to the additional protective layer.

[0072] In another embodiment, the moisture permeability of the additional protective layer is preferably 500 g / m². 2 • Less than 24 hours, more preferably 100g / m 2 • Less than 24 hours, preferably 50g / m 2 • Less than 24 hours. If the permeability of the additional protective layer is below the above-mentioned upper limit, the release of moisture introduced into the polarizer from the protective layer to the outside of the polarizer can be further suppressed after the conditioning process. As a result, it is easier to maintain the moisture content of the polarizer after the conditioning process.

[0073] Regarding resin films used as additional protective layers, examples include polyolefin resins (e.g., cycloolefin resins), acrylic resins, and cellulose triacetate (TAC) resins. For these additional protective layers, surface treatments can be applied as needed. Examples of surface treatments include hard coating, anti-reflective treatment, anti-blocking treatment, and anti-glare treatment.

[0074] The thickness of the additional protective layer is preferably 10 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less. It should be noted that when a surface treatment is performed on the additional protective layer, the thickness of the additional protective layer includes the thickness of the surface treatment layer.

[0075] In the case where the other protective layer is an outer protective layer (i.e., the protective layer constitutes an inner protective layer), in one embodiment, the protective layer (inner protective layer) is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0 nm to 10 nm, and the thickness-direction phase difference Rth(550) is -10 nm to +10 nm. It should be noted that the in-plane phase difference "Re(λ)" is the in-plane phase difference measured at 23°C using light with a wavelength of λ nm. For example, "Re(550)" is the in-plane phase difference measured at 23°C using light with a wavelength of 550 nm. Re(λ) is calculated using the formula: Re(λ) = (nx - ny) × d when the thickness of the layer (thin film) is d (nm). The thickness-direction phase difference "Rth(λ)" is the thickness-direction phase difference measured at 23°C using light with a wavelength of λ nm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23℃ using light with a wavelength of 550nm. Rth(λ) is calculated using the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (thin film) is d (nm).

[0076] B-3-2. Surface protective film

[0077] In one embodiment, after the conditioning process, a surface protective film can be temporarily bonded to the protective layer on the side opposite to the polarizer. This surface protective film can suppress the release of moisture from the protective layer that has absorbed moisture during the conditioning process. That is, after the second process, by temporarily bonding the surface protective film to the protective layer of the laminate, the release of moisture absorbed by the protective layer during the conditioning process from the protective layer (essentially the side opposite to the polarizer of the protective layer) out of the laminate can be further suppressed.

[0078] The protective film can typically be temporarily bonded to the laminate while it is being conveyed after the second process. Specifically, the temporary bonding of the protective layer and the protective film can be performed, for example, after the second process, by laminating the strip-shaped laminate (essentially the protective layer) and the strip-shaped protective film in a roll-to-roll manner. It should be noted that roll-to-roll refers to a method of continuously bonding the strip-shaped films together by continuously conveying them to each other and aligning them along their length.

[0079] The surface protective film can be peeled off at any appropriate time. For example, the surface protective film can be peeled off when the polarizer is ready for use.

[0080] The moisture permeability of the surface protective film can preferably be 100 g / m². 2 • Less than 24 hours, preferably 75g / m 2 • Less than 24 hours, preferably 50g / m 2 • Less than 24 hours, preferably 25g / m2 • Less than 24 hours. The lower limit of moisture permeability of the surface protective film can be, for example, 0.1 g / m³. 2 • 24h. The moisture permeability of the surface protective film is preferably lower than that of the protective layer. The moisture permeability difference between the protective layer and the surface protective film is preferably 300 g / m². 2 • More than 24 hours, preferably 400g / m 2 • More than 24 hours, preferably 500g / m 2 • More than 24 hours. The upper limit of this moisture permeability difference can be, for example, 1000 g / m². 2 ·24h.

[0081] Surface protective films can be, for example, films comprising a substrate layer and an adhesive layer, or self-adhesive films. "Self-adhesive film" refers to a film that possesses the property of adhering to an object without the need for adhesives or other adhesion methods, relying solely on its own adhesiveness. It should be noted that the moisture permeability of a surface protective film refers to the overall moisture permeability of the surface protective film. For example, in the case of a film comprising a substrate layer and an adhesive layer, it is the overall moisture permeability including both the substrate layer and the adhesive layer; in the case of a self-adhesive film, it is the moisture permeability of the self-adhesive film itself.

[0082] In one embodiment, the surface protective film may have a substrate layer and an adhesive layer. The surface protective film may, for example, be temporarily bonded to the laminate (essentially a protective layer) in a peelable manner by means of the adhesive layer.

[0083] The substrate layer is, for example, a resin film. The resin film can be composed of any suitable resin material. Examples of materials constituting the resin film include polyester, polyolefin, polyamide, polyimide, polycarbonate, polyacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and polyvinyl fluoride. Examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. Examples of polyolefins include polyethylene, polypropylene, polybutene, polymethylpentene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylate copolymer, and ethylene-vinyl alcohol copolymer. Examples of polyamides include nylon 6, nylon 6,6, and some aromatic polyamides. The substrate layer can be composed of one material or two or more materials. The substrate layer can have a single-layer structure or a multi-layer structure. Furthermore, when the substrate layer is a resin film, it can be a stretched film or a non-stretched film.

[0084] The adhesive layer can be formed from any suitable adhesive. Specific examples include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, polyurethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, quantity, combination, and mixing ratio of the monomers of the base resin forming the adhesive, as well as the amount of crosslinking agent, reaction temperature, and reaction time, an adhesive with desired properties can be prepared. Only one type of base resin can be used, or two or more types can be used in combination. The base resin is preferably an acrylic resin (i.e., the adhesive layer is preferably composed of an acrylic adhesive).

[0085] In another embodiment, the surface protective film can be a self-adhesive film. Polyolefin films are representative examples of self-adhesive films. Specifically, the self-adhesive film is preferably composed of polyethylene, polypropylene, or mixtures thereof. Here, polyethylene contains homopolymers of ethylene and copolymers of ethylene with other olefins. Polypropylene contains homopolymers of propylene and copolymers of propylene with other olefins.

[0086] Specific examples of the aforementioned polyethylene include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (L-LDPE).

[0087] Examples of other olefins mentioned above include ethylene, propylene, butene, pentene, hexene, heptene, octene, nonene, and decene. Among these, ethylene, propylene, and butene are preferred. In the preparation of copolymers of ethylene or propylene with other olefins, the blending ratio of other olefins is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 20 parts by weight or less, relative to 100 parts by weight of the total ethylene or propylene with other olefins.

[0088] The thickness of the surface protective film is, for example, 5 μm or more and 200 μm or less, preferably 10 μm or more and 150 μm or less, more preferably 15 μm or more and 100 μm or less, and even more preferably 20 μm or more and 75 μm or less. It should be noted that the thickness of this surface protective film is the combined thickness of the substrate layer and the adhesive layer when they are included. If the thickness is within the above range, the strength of the support in the surface protective film can be ensured, and it can be used as a surface protective film with moderate flexibility in the manufacture of polarizers.

[0089] When a temporary protective film is applied to the surface, curing can be performed after the temporary bonding. Specifically, after the conditioning process, curing can be performed on the laminate after the temporary protective film is applied. Curing can be performed using the same method described in section B-2-2. The curing period after temporary bonding and before peeling can be any appropriate period between the temporary bonding process and the peeling process. The curing period is preferably 1 hour or more, more preferably 12 hours or more, further preferably 24 hours or more, further more preferably 36 hours or more, and particularly preferably 48 hours or more. The upper limit of the curing period can be 1000 hours. If the curing period is within such a range, the effects of the present invention can become particularly significant.

[0090] B-3-3. Additional surface protective film

[0091] In one embodiment, the laminate may have an additional surface protective film on the side opposite to the polarizer of the additional protective layer. This additional surface protective film can be provided from the perspective of preventing scratches and damage to the surface of the polarizer during the polarizer manufacturing process. The additional surface protective film typically includes a substrate layer and an adhesive layer. For example, the additional surface protective film can be a film with a substrate layer and an adhesive layer, or it can be a self-adhesive film. The additional surface protective film can be temporarily adhered to the laminate (essentially the polarizer or the additional protective layer) in a peelable manner by means of the adhesive layer or the self-adhesive film. Like the aforementioned surface protective film, the additional surface protective film can be peeled off at any appropriate time. For example, the additional surface protective film can be peeled off from the laminate when the polarizer is supplied for use. Furthermore, for example, the additional surface protective film can be peeled off while the laminate is being transported after the conditioning process. The specific configuration of the additional surface protective film can be the same as that of the surface protective film in item B-3-2 above. It should be noted that, in another embodiment, an additional surface protective film can be temporarily bonded to the polarizer (on the side opposite to the protective layer) or another protective layer of the laminate after the conditioning process. For example, the temporary bonding of the additional surface protective film to the polarizer or another protective layer can be achieved by laminating the strip-shaped laminate (essentially the polarizer or another protective layer) with the strip-shaped additional surface protective film in a roller-to-roll manner.

[0092] C. Polarizing plate

[0093] The polarizer obtained in this embodiment, as described above, fixes the desired moisture in the polarizer after the second process, resulting in the polarizer absorbing moisture to the desired degree. The absorbance of the polarizer in this polarizer is preferably 29.0 or higher, more preferably 29.5 or higher, and even more preferably 29.8 or higher. The upper limit of this absorbance can be, for example, 31.0. This absorbance is an indicator of the moisture content of the polarizer; a high absorbance indicates that the polarizer contains a large amount of moisture. If the absorbance is within the above range, the polarizer is well-conditioned, which greatly helps to suppress curling. The absorbance can be measured using the method described in "(3) Moisture Content (Absorbance)" of the embodiment described later.

[0094] The polarizer obtained by embodiments of the present invention can be configured as a polarizer with a phase retardation layer by laminating it with a phase retardation layer. The polarizer with a phase retardation layer can be manufactured, for example, by laminating a strip-shaped phase retardation film onto the polarizer. Lamination can be performed by roller-to-roll lamination or by cutting the polarizer and phase retardation film into single pieces. The polarizer with a phase retardation layer can also be manufactured, for example, by transferring a liquid crystal alignment curing layer formed on a resin substrate onto a protective layer of the polarizer. Transfer can also be performed by roller-to-roll lamination of a strip-shaped film, or by cutting the polarizer and the liquid crystal alignment curing layer formed on the resin substrate into single pieces.

[0095] Example

[0096] The present invention will be specifically described below through examples, but the present invention is not limited to these examples. The measurement and evaluation methods in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0097] (1) Moisture absorption rate of the protective layer

[0098] Approximately 10 mg of the protective layer used in the examples and comparative examples was measured to prepare a sample, which was then mounted on a dynamic moisture adsorption (DVS) apparatus. After standing for 60 minutes at 23°C and 55% humidity, the weight of the sample was measured and recorded as B [mg]. Next, the sample was further stood for 10 minutes at 35°C and 80% humidity, and the weight of the sample was measured and recorded as A [mg]. Using the obtained weights A and B, the moisture absorption rate of the protective layer was calculated using the following formula (1).

[0099] Moisture absorption rate (%) = {(A / B) - 1} × 100 (1)

[0100] (2) Moisture permeability

[0101] Samples were prepared by cutting the layers and films used in the examples and comparative examples into 10cm φ circular shapes. Using a water vapor transmission rate measuring device manufactured by Hitachi, Ltd., according to the JIS Z0208 water vapor transmission rate test (cup method), the samples were allowed to pass through the water vapor for 24 hours at a temperature of 40°C and a humidity of 92% RH, and the water vapor content [g] was measured. This value was taken as the water vapor transmission rate [g / m]. 2 ·24h).

[0102] (3) Moisture content (absorbance)

[0103] The absorbance of the polarizers fabricated in the examples and comparative examples was measured using a positive reflection infrared film thickness gauge (RX-1000) manufactured by Kurabo Industries Ltd. The obtained absorbance was used as an indicator of the amount of moisture introduced into the polarizer.

[0104] (4) Evaluation of Curl

[0105] The polarizers obtained in the examples and comparative examples were cut into rectangular shapes with a length of 148 mm and a width of 70 mm along a direction orthogonal to the length direction of the polarizer to prepare samples. It should be noted that when cutting the samples, the length direction of the polarizer (the absorption axis of the polarizer) was made at a 45° angle with respect to the long and short sides of the polarizer.

[0106] The sample is placed on the stage with the layer on the identification side (surface side) (the layer opposite to the surface protective film) facing upwards when used as a polarizer. If the four corners of the sample lift off the stage due to warping, it is considered "positive" curling. For each of the four corners of the sample, the vertical distance from the top surface of the stage to the corner is measured using a ruler, and the reading is recorded. The measurement value of the corner with the largest warping is directly recorded as curl H0.

[0107] On the other hand, when the sample is placed on the stage as described above, if the four corners of the sample do not float off the stage, but the center of the sample floats off the stage due to warping, this is judged as "negative" curl. Next, the sample is repositioned on the stage with the layer on the identification side (surface side) (the layer opposite to the surface protective film) facing down when used as a polarizer. For each of the four corners of the sample, the vertical distance from the top surface of the stage to the corner is measured using a ruler, and the reading is recorded. The value obtained by multiplying the measured value of the corner with the largest warping by -1 is recorded as curl H0.

[0108] After measuring the curl H0, the sample was placed at 23℃ and 55% humidity for one week. After one week, the curl was measured again using the same method, and the obtained value was recorded as curl H1. The change in curl ΔH was calculated by subtracting curl H0 from the value of curl H1 (H1-H0). The change in curl was evaluated according to the following criteria.

[0109] A (Best): 1.5mm or less

[0110] B (Good): Greater than 1.5mm and less than 3.0mm

[0111] C (Acceptable): Greater than 3.0mm and less than 4.0mm

[0112] D (Unacceptable): Greater than 4.0mm and less than 6.0mm

[0113] E (Defect): Greater than 6.0mm

[0114] [Manufacturing Example 1] Fabrication of a Polarizer

[0115] As a thermoplastic resin substrate, a strip-shaped, amorphous polyethylene terephthalate copolymer film (thickness: 100 μm) with a Tg of about 75°C is used to perform corona treatment on one side of the resin substrate.

[0116] 13 parts by weight of potassium iodide were added to 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetyl-modified PVA (trade name "GOHSEFIMER" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) in a ratio of 9:1, and the mixture was dissolved in water to prepare a PVA aqueous solution (coating solution).

[0117] The above-mentioned PVA aqueous solution is coated on the corona-treated surface of the resin substrate and dried at 60°C, thereby forming a PVA-based resin layer with a thickness of 13 μm, and a laminate is produced.

[0118] The resulting laminate was uniaxially stretched to 2.4 times its original length in an oven at 130°C (air-assisted stretching treatment).

[0119] Next, the laminate was immersed in an insoluble bath (an aqueous solution of boric acid prepared by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment).

[0120] Next, the polarizer is immersed in a staining bath at 30°C (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) for 60 seconds (staining treatment) while adjusting the concentration to achieve the desired value of the final polarizer's monomer transmittance (Ts).

[0121] Next, it is immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous solution of boric acid prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) for 30 seconds (crosslinking treatment).

[0122] Then, the laminate is immersed in a boric acid aqueous solution (boric acid concentration 4 wt% and potassium iodide concentration 5 wt%) at a liquid temperature of 70°C, while being uniaxially stretched along the length direction (longitudinal direction) between rollers with different circumferential speeds until the total stretch ratio reaches 5.5 times (water stretching treatment).

[0123] Then, the laminate is immersed (washing treatment) in a washing bath at a liquid temperature of 20°C (an aqueous solution of 4 parts by weight of potassium iodide mixed with 100 parts by weight of water).

[0124] Then, while drying in an oven maintained at approximately 90°C, it comes into contact with heated rollers made of SUS, whose surface temperature is maintained at approximately 75°C (drying shrinkage treatment).

[0125] This process forms a polarizer with a thickness of approximately 5 μm on the resin substrate, resulting in a laminate consisting of a resin substrate and a polarizer. The polarizer has a single-unit transmittance, Ts, of 43.3%.

[0126] [Example 1]

[0127] An HC-ZD film, serving as an additional protective layer, is laminated onto the surface of the polarizer in Example 1 (the side opposite to the resin substrate). It should be noted that the HC-ZD film is a cyclic olefin resin (COP) film (25 μm thick) manufactured by ZEON CORPORATION in Japan, on which an HC layer (4 μm thick) is formed, laminated with the COP film positioned on the polarizer side. To protect the polarizer, an additional surface protective film (a polyolefin film (model A-521) manufactured by Toray Film Advanced Processing Co., Ltd., 25 μm thick) is laminated onto the HC layer.

[0128] Next, the resin substrate is peeled off, and a cellulose triacetate (TAC) film (20 μm thick) is bonded to the peeled surface as a protective layer using a UV-curable adhesive. The TAC film used is "0-TAC" manufactured by Fujifilm Corporation. This results in a long strip of laminate consisting of an additional surface protective film / HC layer / COP film (an additional protective layer) / polarizer / TAC film (protective layer). The long strip of laminate is then wound into a roll.

[0129] The long, laminated body is unwound from the roll (raw material roll) and conveyed for 5 minutes in an oven (heating and humidification section) set at 40°C and 80% humidity. This process is repeated to perform the first step of placing the laminated body in an environment of 40°C and 80% humidity for 5 minutes.

[0130] Next, the laminate after the first process is conveyed for 5 minutes in an oven (heating and humidification section) set at 25°C and 80% humidity. This process is repeated for the second process, where the laminate is placed in an environment of 25°C and 80% humidity for 5 minutes. The laminate is then conditioned through the first and second processes.

[0131] Next, while conveying the laminate, the roll of surface protective film (polyethylene film manufactured by Toray Film Advanced Processing Co., Ltd.: model A-521, 25μm thickness) is unwound from the laminate after passing through the oven, and a temporary adhesive film is temporarily bonded to the TAC film side of the laminate (the side of the TAC film opposite to the polarizer) in a roll-to-roll manner. This process is repeated to obtain a laminate consisting of an additional surface protective film / HC layer / COP film (an additional protective layer) / polarizer / TAC film (protective layer) / surface protective film, which is then wound into a roll. The wound laminate is then cured under normal conditions (23°C, 50%) for 48 hours.

[0132] Next, the wound laminate is unwound, and the surface protective film on the TAC film side is peeled off. Before evaluation, another surface protective film on the HC layer is peeled off. Thus, a polarizer with the structure of HC layer / COP film (another protective layer) / polarizer / TAC film (protective layer) is obtained.

[0133] The resulting polarizers were evaluated in (3) and (4) above. The results are shown in Table 1.

[0134] [Examples 2-7, Comparative Examples 1-5]

[0135] The type of protective layer and the humidity conditioning conditions (temperature, humidity, and time in the first and second processes) were changed as shown in Table 1, but the polarizer was obtained in the same manner as in Example 1. The resulting polarizer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0136] In Table 1, under the "Temperature, Humidity, Time" section of the humidity conditioning conditions, Comparative Examples 1-4 are listed in one column because the temperature, humidity, and time were not changed between the first and second processes (the second process was not actually performed).

[0137] The details of the "Types" column for protective layers in Table 1 are as follows.

[0138] <Protective Layer>

[0139] • TAC: Cellulose triacetate film (manufactured under the brand name "0-TAC" by Fujifilm Corporation). Moisture permeability: 1488 g / m³ 2 ·24h)

[0140] • COP: Cycloolefin film (manufactured by ZEON CORPORATION in Japan under the brand name "ZD-HC" (a film with an HC layer formed on top of a COP film). Moisture permeability: 9 g / m³ 2 ·24h)

[0141] Table 1

[0142]

[0143] Industrial availability

[0144] The polarizers obtained by the embodiments of the present invention can be suitably used for optical applications such as optical components and image display devices.

Claims

1. A method for manufacturing a polarizer, the polarizer comprising a polarizer, and the manufacturing method comprising, in sequence: In the first step, the laminate containing the polarizer and the protective layer is placed in an environment with a temperature of 35°C or higher and 65°C or lower and a humidity of 70% or higher. In the second step, the laminate is placed in an environment with a temperature lower than that of the first step and a humidity of 70% or higher. The moisture absorption rate of the protective layer shown in the following formula (1) is 0.5% or higher: Moisture absorption rate (%) = {(A / B)-1}×100 (1), where A is the mass of the protective layer after it has been placed in an environment with a temperature of 35°C and a humidity of 80% for 10 minutes, and B is the mass of the protective layer after it has been placed in an environment with a temperature of 23°C and a humidity of 55% for 60 minutes.

2. The method for manufacturing a polarizer according to claim 1, wherein, The temperature of the second process is above 20°C and below 30°C.

3. The method for manufacturing a polarizer according to claim 1 or 2, wherein, The thickness of the protective layer is 10 μm or more.

4. The method for manufacturing a polarizer according to claim 1 or 2, wherein, The environmental placement time in the first process and the environmental placement time in the second process are both 2 minutes or more.

5. The method for manufacturing a polarizer according to claim 1 or 2, wherein, The laminated body has an additional protective layer on the side of the polarizer opposite to the protective layer.

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