Manufacturing method of double-layer film

Abstract

To provide a manufacturing method of a double-layer film which can suppress blushing defects when both a solid content concentration in a coating film and a boiling point of a solvent are low.SOLUTION: The manufacturing method has: a coating process of obtaining an intermediate film including a base film and a coating film by coating the base film with a coating liquid containing a high polymer material and a solvent; a first drying process of drying the coating film of the intermediate film; a second drying process of drying the coating film after the first drying process at a higher temperature than in the first drying process; and a transportation process of transporting the intermediate film at a room temperature to a point before the first drying process after the coating process. In the coating process, a ratio Csol / TAve (μm / °C) of a thickness conversion value Csol (μm) of a solvent amount contained in a coating film immediate after the coating with respect to an average boiling point TAve (°C) of the solvent is a predetermined value or more, and volume absolute humidity in the coating process, a transportation time of the intermediate film in the transportation process and a drying temperature in the first drying process are adjusted at predetermined ranges.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, a method for manufacturing a multilayer film in which a polymeric material layer is provided on a resin base film includes a process of applying a coating liquid containing a polymeric material and a solvent to the base film to form a coating film, and then drying the coating film (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-292291 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-145703 Summary of the Invention [Problem to be solved by the invention]

[0004] In the method for producing a multilayer film using the above-mentioned coating method, blushing defects, such as cloudiness in the polymer material layer, may occur during the drying process of the coating film. In particular, blushing defects tend to occur more easily when the solid concentration in the coating film is low and the boiling point of the solvent is low.

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a multilayer film that can suppress brushing defects. [Means for solving the problem]

[0006] The inventors have conducted extensive research and found that the average boiling point T Ave (℃) vs. the thickness conversion value C of the amount of solvent contained in the coating film immediately after coating sol(μm) is a predetermined value or more, the brushing defect is likely to occur, sol / T Ave The present inventors have found that even in the case of a coating film in which the coefficient of friction (μm / °C) is equal to or greater than a predetermined value, the occurrence of brushing defects can be suppressed by adjusting the humidity conditions in the coating process, the time the coating film is left at room temperature from formation until drying, and the drying temperature, and have completed the present invention.

[0007] The present invention includes the following. <1> The present invention comprises a coating step of applying a coating liquid containing a polymer material and a solvent to a base film to obtain an intermediate film having the base film and a coating film, a first drying step of drying the coating film of the intermediate film, a second drying step of drying the coating film after the first drying step at a temperature higher than that of the first drying step, and a transport step of transporting the intermediate film at room temperature after the coating step until before the first drying step; Ave (°C) versus the thickness equivalent C of the amount of the solvent contained in the coating film immediately after coating sol (μm) ratio C sol / T Ave (μm / °C) is 0.2 or more; and the volume absolute humidity in the coating step is 10.0 g / m 3 the time for which the intermediate film is transported in the transporting step is 4 seconds or less; and the boiling point T sol and drying the coating film at a first drying temperature of (°C)+5°C or higher. <2> In the first drying step, at least a hot air treatment is performed to dry the coating film by blowing hot air onto the surface of the base film opposite to the surface on which the coating film is formed. <1> A method for producing the multilayer film described in claim 1. <3> The boiling point T of the solvent contained in the coating liquid sol (℃) is 80℃ or less, <1> A method for producing the multilayer film described in claim 1. [Effects of the Invention]

[0008] According to the method for producing a multilayer film of the present invention, it is possible to provide a method for producing a multilayer film that can suppress brushing defects. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a side view that schematically shows an example of a manufacturing apparatus used in a method for manufacturing a multilayer film according to one embodiment of the present invention and a manufacturing method using the same. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents. The components of the embodiments shown below can be combined as appropriate.

[0011] In the following description, "room temperature" refers to a temperature within a range of 10°C to 30°C. Preferably, room temperature is about 22°C±5°C.

[0012] In the following description, unless otherwise specified, the terms "upstream" and "downstream" refer to the upstream and downstream, respectively, in the transport direction of the base film.

[0013] In the following description, a "long" film refers to a film having a length that is 5 times or more its width, preferably 10 times or more its width, and specifically refers to a film having a length that can be wound into a roll for storage or transportation. There is no particular upper limit to the length of a long film, and it can be, for example, 100,000 times or less its width.

[0014] In the following description, the term "solvent" refers to a medium that dissolves or disperses a polymeric material.

[0015] <1. Overview of multilayer film manufacturing method> A method for manufacturing a multilayer film according to one embodiment of the present invention includes a coating step in which a coating liquid containing a polymeric material and a solvent is applied to a base film to obtain an intermediate film comprising the base film and a coating film; a first drying step in which the coating film on the intermediate film is dried; a second drying step in which the coating film after the first drying step is dried at a higher temperature than in the first drying step; and a transport step in which the intermediate film is transported at room temperature after the coating step until before the first drying step.

[0016] In the manufacturing method of this multilayer film, the average boiling point T Ave (℃) vs. the thickness conversion value C of the amount of solvent contained in the coating film immediately after coating sol (μm) ratio C sol / T Ave The coating film is formed so that the viscosity (μm / ° C.) is equal to or greater than a predetermined value.

[0017] In this method for producing a multilayer film, the volumetric absolute humidity of the coating environment in the coating step is below a predetermined value. Furthermore, in the conveying step, the time during which the intermediate film is conveyed at room temperature from the coating step to the first drying step is extremely short. In the first drying step, the boiling point T sol The coating is dried at a first drying temperature higher than (°C).

[0018] FIG. 1 is a side view schematically illustrating an example of a manufacturing apparatus used in a multilayer film manufacturing method according to one embodiment of the present invention and a manufacturing method using the same. In FIG. 1, manufacturing apparatus 200 continuously conveys substrate film 1 from upstream to downstream in the conveyance direction of substrate film 1 using conveying rolls 101-108. From upstream in the conveyance direction of substrate film 1, manufacturing apparatus 200 includes, in this order, a payout device 110, conveying roll 101, a corona treatment device 120, conveying roll 102, a coating device 130 including a backup roll 131 and a discharge unit 132, conveying roll 103, a drying oven 140 including a first drying chamber 141 and a second drying chamber 142, conveying rolls 104-107 and conveying roll 108 disposed within drying oven 140, and a winding device 150. The arrows in FIG. 1 indicate the conveyance direction of substrate film 1.

[0019] In the manufacturing apparatus 200 shown in Figure 1, a long substrate film 1 is typically unwound from a unwinding device 110 and transported using transport rolls 101 to 108, becoming an intermediate film 10 with a coating film provided thereon during the transport process.As the coating film on the intermediate film dries, it becomes a multilayer film 20 with a polymer material layer provided thereon, and is then wound up by a winding device 150.

[0020] In such a manufacturing apparatus 200, the base film 1 unwound from the unwinding device 110 is transported to the corona treatment device 120 using the transport roll 101, where corona treatment is performed on the surface of the base film 1 on which the coating film is to be formed. Next, the base film 1 is transported using the transport roll 102 to the coating device 130 which has a backup roll 131 and a discharge section 132.

[0021] In the coating process according to the present embodiment, a coating liquid containing a polymer material and a solvent is applied to the substrate film 1 by a coating device 130 to form a coating film, thereby obtaining an intermediate film 10. In this coating process, the coating film is formed by applying a coating liquid containing a polymer material and a solvent to the substrate film 1 ... Ave (℃) vs. the thickness of the solvent in the coating film C sol (μm) ratio C sol / T Ave The coating process is usually performed so that the volumetric absolute humidity in the coating environment is equal to or less than a predetermined value. The temperature of the coating environment is usually set to room temperature.

[0022] Next, the intermediate film 10 on which the coating film has been formed is transported to the entrance 140E of the drying oven 140 using the transport rolls 103 and 104. In the manufacturing apparatus 200, the section from the coating device 130 to the entrance 140E of the drying oven is usually adjusted to room temperature, and the intermediate film 10 is transported so that its residence time in this room temperature section is 4 seconds or less.

[0023] Next, the intermediate film 10 is transported through a drying oven 140 using transport rolls 104 to 107, and the coating is dried during the transport process. The drying oven 140 typically includes a top section 140a, a bottom section 140b, and a wall section 140c. The drying oven 140 also includes, from upstream, a first drying chamber 141 and a second drying chamber 142. The drying conditions, such as the drying temperature, of each drying chamber can be adjusted independently.

[0024] The first drying chamber 141 is provided with an air inlet s1 on the upstream side of the ceiling 140a and an exhaust port e1 on the downstream side of the ceiling 140a, and air is supplied to and exhausted from the first drying chamber 141 through the air inlet s1 and the exhaust port e1. This air may be heated. The first drying chamber 141 is also provided with hot air nozzles n1 to n3 on its bottom 140b. The hot air nozzles n1 to n3 perform a hot air treatment to dry the coating film by blowing hot air from the surface of the substrate film conveyed by the conveying rolls 104 to 105 opposite to the surface on which the coating film is formed. The first drying chamber 141 is usually heated to a temperature above the boiling point T sol (° C.) The first drying temperature is measured near the exhaust port e1 of the first drying chamber 141.

[0025] The intermediate film 10 dried in the first drying chamber 141 is transported to the second drying chamber 142 using transport rolls 106 and 107. The second drying chamber 142 has an air inlet s2 in its upstream top section 140a and an exhaust outlet e2 in its downstream top section 140a, and air is supplied to and exhausted from the second drying chamber 142 through the air inlet s2 and the exhaust outlet e2. This air may be heated. In the second drying chamber 142, the coating film is dried at a temperature higher than the first drying temperature, and the temperature of the second drying chamber 142 is usually adjusted to be higher than the first drying temperature. The second drying temperature of the second drying chamber is measured near the exhaust outlet e2 of the second drying chamber 142. By drying the coating film in the second drying step, a multilayer film 20 can be obtained, which includes a polymer material layer formed on a substrate film.

[0026] The multilayer film 20 obtained through the second drying step is transported to a winding device 150 using a transport film 108, and is wound into a roll by the winding device 150.

[0027] According to the manufacturing method of this embodiment, by carrying out the coating step, conveying step, and first drying step described above, it is possible to manufacture a multilayer film while suppressing blushing defects.

[0028] Here, the blushing defect is a defect that occurs when moisture in the air condenses on the surface of the coating film in a multilayer film manufacturing method using a coating method, and when moisture is mixed into the coating film, cloudiness is observed due to the difference in refractive index between the resulting polymer material layer and the moisture, or light scattering is observed due to unevenness caused by moisture adhesion on the surface of the polymer material layer. Such blushing defects tend to occur more easily when the solid concentration in the coating film is low and the boiling point of the solvent is low.

[0029] The present inventors have conducted extensive research in light of the above-mentioned circumstances, and have found that in the manufacturing method of a multilayer film using a coating method, blushing defects are likely to occur in the conveying process from the coating step in which a coating film is formed to the early stage of the drying step in which the coating film is dried, and that the ratio C sol / T Ave It has been found that brushing defects are likely to occur when the surface roughness (μm / °C) is equal to or greater than a predetermined value. The inventors speculate that the mechanism behind this is as follows. However, the technical scope of the present invention is not limited to the mechanism described below.

[0030] Condensation, which causes brushing defects, occurs when moisture in the air cools due to the latent heat generated by the evaporation of the solvent in the coating film. Normally, the coating process and the drying process are carried out in a room temperature environment without heating or reducing the pressure, so the more solvent evaporates from the coating film, the more condensation tends to occur. The amount of solvent evaporating from the coating film is correlated with two factors: the amount of solvent in the coating film and the boiling point of the solvent in the coating film, and specifically, the ratio C sol / T AveIt is presumed that when the relationship (μm / °C) is equal to or greater than a predetermined value, the amount of solvent volatilized from the coating film increases, resulting in more condensation and making brushing defects more likely to occur.

[0031] The inventors of the present invention have found that the ratio C sol / T Ave The present inventors have found that in a coating film having a viscosity (μm / °C) of a predetermined value or more, brushing defects can be suppressed by adjusting the volume absolute humidity during the coating process, the transport time from the coating process to the first drying process, and the drying temperature in the first drying process within predetermined ranges, and have completed the present invention.

[0032] One way to suppress brushing defects is to adjust the composition of the coating liquid, for example, by using a coating liquid with a high solids concentration or a solvent with a high boiling point. However, since coating liquids containing polymeric materials tend to have high viscosity, increasing the solids concentration can reduce coatability, and using a solvent with a high boiling point can result in residual solvent in the polymeric material layer of the resulting multilayer film, resulting in a decrease in the quality of the multilayer film or a decrease in the processability of the multilayer film. Furthermore, in terms of the solubility and dispersibility of polymeric materials, usable solvents may be limited to low-boiling point solvents. Therefore, in methods for producing multilayer films using coating liquids containing polymeric materials, it is often necessary to use a coating liquid with a low solids concentration and a low boiling point solvent. In such cases, the method for producing a multilayer film according to this embodiment is useful in that it can suppress brushing defects without changing the composition of the coating liquid.

[0033] <2. Each step in the manufacturing process of multilayer film> The method for producing a multilayer film according to this embodiment includes at least a coating step, a transporting step, a first drying step, and a second drying step.

[0034] <2.1. Coating process> The coating step is a step of applying a coating liquid containing a polymer material and a solvent onto a substrate film to obtain an intermediate film comprising the substrate film and a coating film.

[0035] In this embodiment, prior to the coating step, the main surface of the substrate film may be subjected to a surface treatment such as a discharge treatment using a corona treatment device.

[0036] In the coating process, the average boiling point T Ave (℃) vs. the thickness equivalent value C of the amount of the solvent contained in the coating film immediately after coating sol (μm) ratio C sol / T Ave A coating film having a viscosity of 1000 s / s (μm / °C) or more is formed. Ave When a single solvent is used, the boiling point of the solvent is indicated. When a mixed solvent is used, the average boiling point of the solvent is indicated. Ave The average boiling point (°C) of the mixed solvent is calculated by multiplying the boiling point of each solvent by its weight-based content ratio (boiling point of each solvent x ratio). AVE represents the weighted average of the boiling points of the solvents contained in the mixed solvent. Furthermore, "coating film immediately after coating" means a coating film in which the solvent has not been reduced by evaporation when the coating liquid is applied to the substrate film to form a coating film (a coating film in which the residual solvent ratio in the coating liquid contained in the coating film is 100%), and the "thickness equivalent of the amount of solvent contained in the coating film immediately after coating" can usually be calculated from the amount of coating liquid applied per unit area to the substrate film and the solids concentration of the solvent.

[0037] Said ratio C sol / T Ave (μm / °C) is usually 0.2 μm / °C or more, preferably 0.25 μm / °C or more, and more preferably 0.3 μm / °C or more. sol / T Ave (μm / °C) is usually 1.0 μm / °C or less, preferably 0.9 μm / °C or less, and more preferably 0.8 μm / °C or less. sol / T AveWhen the surface roughness (μm / ° C.) is in the above range, brushing defects are likely to occur. The production method according to this embodiment can effectively suppress the occurrence of brushing defects under conditions in which the coating film is prone to have such defects.

[0038] The amount of solvent contained in the coating immediately after coating converted into thickness C sol (μm) is the ratio C sol / T Ave The thickness (μm / °C) can be appropriately adjusted so that it is a predetermined value or more, but it is usually 8 μm or more, preferably 20 μm or more, more preferably 25 μm or more, and is usually 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less. sol By ensuring that the thickness (μm) is within the above range, brushing defects can be suppressed and a relatively thick polymer material layer can be formed using a coating liquid with a low solid content concentration.

[0039] Average boiling point of the solvent, T Ave (℃) is the ratio C sol / T Ave The average boiling point T of the solvent can be adjusted as needed so that the average boiling point T (μm / °C) is a predetermined value or more, but is usually 85°C or less, preferably 80°C or less, more preferably 75°C or less, and is usually 50°C or more, preferably 55°C or more, more preferably 60°C or more. Ave When the temperature (°C) is in the above range, it is possible to effectively prevent the solvent from remaining in the polymer material layer while suppressing brushing defects.

[0040] The solvent may be a single solvent containing one type of solvent, or a mixed solvent containing two or more types of solvents, but the former is more preferred. When a single solvent is used, brushing defects tend to occur, so the effects of the present invention can be more effectively exhibited. When a single solvent is used, the boiling point T sol (℃) is usually the average boiling point T Ave (℃). On the other hand, in the case of mixed solvents, the boiling point T sol (℃) is usually the average boiling point T Ave (°C), but preferably the average boiling point T Ave(℃)+20℃ or less, more preferably T Ave (°C) + 10°C or less. sol (℃) and the average boiling point T of the solvent Ave (°C) satisfies the above relationship, the solvent in the coating film can be effectively removed in the first drying step described below, and brushing defects can be suppressed. sol "(℃)" refers to the boiling point of a single solvent when a single solvent is used. When a mixed solvent is used, it refers to the boiling point of the solvent with the largest proportion among the multiple solvents. When multiple solvents are used in equal proportions, it refers to the highest boiling point of the multiple solvents used in equal proportions.

[0041] In this embodiment, the boiling point T sol (℃) is the average boiling point T Ave It is particularly preferable that the temperature range in which the solvent can be used is the same as the boiling point T sol (°C) is usually 85°C or lower, preferably 80°C or lower, more preferably 75°C or lower, and can usually be 50°C or higher, preferably 55°C or higher, more preferably 60°C or higher.

[0042] For specific solvents, the average boiling point T Ave (℃) and the boiling point T of the solvent sol (°C) and can be appropriately selected depending on the type of polymer material.

[0043] The volumetric absolute humidity during the coating process is usually 10.0 g / m 3 Less than 9.5 g / m 3 or less, more preferably 9 g / m 3 is usually 7 g / m or less. 3 More preferably, 7.5 g / m 3 More preferably, 8 g / m 3 By having the volume absolute humidity within the above range, the coating film can be formed in an environment with a low amount of water vapor in the air, and therefore the occurrence of brushing defects can be suppressed.

[0044] In this embodiment, the volume absolute humidity is the relative humidity H r is measured using a hygrometer, and can be calculated from the measured value using the following formula. D=(H r / 100)×804e s / {p0(1+0.00366θ)} (1) In the above formula (1), D is the absolute humidity (g / m 3 ), H r is the relative humidity (RH%), θ is the temperature (℃), e s is the saturated water vapor pressure at θ (℃), and p0 is 1 atmosphere (760 mmHg).

[0045] The environmental temperature in the coating process is usually room temperature, preferably within the range of 22°C ± 5°C. The lower the temperature of the coating environment, the more likely blushing defects tend to occur. In this embodiment, by setting the temperature of the coating environment to room temperature, the influence of the temperature of the coating environment, etc., can be reduced, and blushing can be suppressed.

[0046] The solid content concentration (wt%) of the coating liquid used in the coating process is sol / T Ave The amount is not particularly limited as long as it is sufficient to obtain a coating film having a viscosity (μm / °C) of at least the above-mentioned value, and can be adjusted appropriately depending on the viscosity suitable for coating. However, it is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and is usually 50% by weight or less, preferably 45% by weight or less, more preferably 40% by weight or less.

[0047] There are no limitations on the method for applying the coating liquid, and examples of the coating method include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, die coating, and gap coating.

[0048] The thickness of the coating film that can be formed in the coating process is sol / T AveThe thickness is not particularly limited as long as it is sufficient to obtain a coating film having a viscosity (μm / °C) of at least the above-mentioned value, and is appropriately selected depending on the type of desired polymer material layer, but is usually greater than 10 μm, preferably at least 25 μm, more preferably at least 30 μm, and usually not more than 100 μm, preferably not more than 80 μm, more preferably not more than 60 μm. This is because a coating film thickness within the above range can effectively suppress brushing defects.

[0049] <2.2. Transportation process> The transporting step is a step of transporting the intermediate film at room temperature after the coating step described above and before the first drying step described below.

[0050] In the conveying step, the intermediate film is conveyed at room temperature after the coating step and before the first drying step described below. The conveying time of the intermediate film is usually 4 seconds or less, preferably 3.5 seconds or less, and more preferably 3 seconds or less. The conveying time of the intermediate film is usually longer than 0 seconds.

[0051] The transport time of the intermediate film can be adjusted by the distance to the coating device and the drying oven and the transport speed of the base film, which can be adjusted appropriately within the range of usually 14 m / min to 20 m / min.

[0052] In the conveying step, the temperature of the environment in which the intermediate film is conveyed is usually room temperature, and can be preferably adjusted to 22° C.±5° C. In addition, the volumetric absolute humidity in the conveying environment is preferably the same as the volumetric absolute humidity in the coating step described above.

[0053] Furthermore, during the conveying process, the airflow speed above the substrate film on which the coating film is formed can typically be 0 m / s or more and 3 m / s or less. The airflow speed above the substrate film 10 refers to the speed at a position 1 cm away from the surface of the substrate film 10. Brushing defects tend to progress more easily when strong cold wind blows over the coating film, so by keeping the airflow speed in the conveying environment at room temperature at or below the above upper limit, the occurrence of brushing defects can be more effectively suppressed.

[0054] <2.3. First drying process> The first drying step is a step of drying the coating film on the intermediate film.

[0055] The first drying step is usually carried out by continuously transporting the intermediate film through a drying oven. For example, as shown in Figure 1, if the drying oven 140 has multiple compartments (chambers) separated by walls 140c, the first drying step can be carried out in the first drying chamber 141 located most upstream.

[0056] In the first drying process, the boiling point T sol The coating is dried at a first drying temperature of (°C) + 5°C or higher. The first drying temperature is usually the boiling point T sol (℃)+5℃ or higher, preferably T sol (℃)+10℃ or higher, preferably T sol (℃)+15℃ or higher, usually T sol (℃) +30℃ or less, preferably T sol (℃)+25℃ or less, more preferably T sol (°C) + 20°C or less. When the first drying temperature (°C) is in the above range, blushing defects that occur in the early stage of drying of the coating film can be effectively suppressed.

[0057] The first drying temperature is the temperature of the entire drying oven. If the drying oven has multiple compartments, it is the temperature of the entire compartment where the first drying step is performed. For example, in the first drying chamber shown in Figure 1, the first drying temperature is measured near the exhaust port, but this is not limited to this and the temperature is measured at a position that reflects the temperature of the entire drying chamber. Usually, the measurement position of the first drying temperature can be a position away from the heat source.

[0058] The drying method is not particularly limited and any known drying method can be used. However, in the first drying step, it is preferable to perform at least a hot air treatment to dry the coating by blowing hot air from the side opposite to the side on which the coating is formed of the substrate film. This is because blowing hot air from the back side of the coating film can suppress uneven drying of the coating film and dry the coating film uniformly. The heat treatment is usually performed using a hot air nozzle installed at the bottom of the drying chamber. The temperature of the hot air can be about ±10°C of the first drying temperature described above. The hot air speed can be appropriately selected depending on the thickness of the substrate film, the conveying speed, etc.

[0059] Furthermore, as a drying method, a treatment is usually carried out in combination with the above-mentioned hot air treatment, in which hot air is blown onto the side on which the coating film is formed to dry it. In this case, the hot air speed is usually about 0.5 m / s or more and 3.0 m / s or less. When the speed of the hot air blowing directly onto the coating film is within the above range, uneven drying due to localized drying of the coating film can be suppressed, resulting in a coating film with good smoothness. Drying of the coating film side with hot air is usually carried out by circulating hot air into the drying chamber using an air inlet and an exhaust port provided at the ceiling of the drying chamber.

[0060] The first drying chamber is usually kept at normal pressure (1 atmosphere), but may be depressurized as necessary.

[0061] The drying time of the coating film in the first drying step is usually 5 seconds or more, preferably 10 seconds or more, more preferably 15 seconds or more, and can be usually 60 seconds or less, preferably 45 seconds or less, more preferably 30 seconds or less.

[0062] The thickness conversion value of the amount of solvent contained in the coating film after the first drying process and before the second drying process is C d1 (μm), the thickness equivalent value C of the amount of the solvent contained in the coating film immediately after coating sol (μm) d1 (μm) ratio C d1 / C sol is usually 0.6 or less, preferably 0.5 or less, and more preferably 0.4 or less. d1 / C sol is usually 0.15 or more, may be 0.2 or more, or may be 0.3 or more. d1 / C sol When the thickness is in the above range, it is possible to obtain a polymer material layer having good smoothness while suppressing brushing defects that occur in the early stage of drying.

[0063] <2.4.Second drying process> The second drying step is a step of drying the coating film after the first drying step at a temperature higher than that in the first drying step. By including the second drying step, a polymer material layer with a small amount of residual solvent can be obtained, and therefore the quality of the multilayer film can be improved.

[0064] The second drying step is usually carried out by continuously transporting the intermediate film through the drying oven. For example, as shown in Figure 1, if the drying oven 140 has multiple compartments (chambers) separated by walls 140c, the second drying step is carried out in a drying chamber located downstream of the first drying chamber. Therefore, the intermediate film is usually not transported through an environment with a temperature lower than the first drying temperature between the first and second drying steps.

[0065] The drying temperature in the second drying step (second drying temperature) may be any temperature higher than the first drying temperature, and is usually at least 5°C higher than the first drying temperature, preferably at least 10°C higher than the first drying temperature, and more preferably at least 15°C higher than the first drying temperature, and is usually at most 40°C higher than the first drying temperature, preferably at most 35°C higher than the first drying temperature, and more preferably at most 30°C higher than the first drying temperature.

[0066] For example, when the drying furnace has three or more drying chambers, the second drying step may be performed by using two or more drying chambers excluding the first drying chamber, and gradually decreasing the temperature of the drying chambers from the upstream side to the downstream side. In this case, the temperatures of the multiple drying chambers are appropriately adjusted within the range of the second drying temperature described above. An example of a drying method in the second drying step is a method in which hot air is applied to at least one of the front and back sides of the coating film to dry it. In the second drying step, drying may be performed at normal pressure or under reduced pressure.

[0067] The drying time of the coating film in the second drying step is usually 30 seconds or more, preferably 45 seconds or more, more preferably 60 seconds or more, and usually 5 minutes or less, preferably 4 minutes or less, more preferably 3 minutes or less.

[0068] The coating on the intermediate film is dried in the second drying step to obtain a multilayer film including a substrate film and a polymeric material layer. The amount of residual solvent in the polymeric material layer is preferably 10% by mass or less, more preferably 7% by mass or less. The amount of residual solvent can be calculated from the amount of solvent contained in the polymeric material layer that was used in preparing the coating liquid and the amount of solvent in the polymeric material layer measured by an appropriate measurement method such as headspace gas chromatography mass spectrometry.

[0069] <2.5. Optional steps> The method for producing a multilayer film according to this embodiment includes at least the coating step, conveying step, first drying step, and second drying step described above, and may further include optional steps as necessary. Examples of optional steps include a stretching step in which the intermediate film obtained after the second drying step is stretched, and a winding step in which the multilayer film is wound into a roll.

[0070] <3. Preferred examples of multi-layer films> The manufacturing method of this embodiment is typically used in manufacturing a multilayer film including a substrate film and a polymeric material layer containing a polymer material. The materials used for the substrate film and the polymeric material layer are not particularly limited. A preferred example is one in which the substrate film contains a resin having a positive intrinsic birefringence value, and the polymeric material layer contains, as a polymer material, a resin having a negative intrinsic birefringence value. Here, "a resin having a positive intrinsic birefringence value" refers to a resin whose refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to the stretching direction. In the following description, a resin having a positive intrinsic birefringence value may be referred to as resin (A). Furthermore, "a resin having a negative intrinsic birefringence value" refers to a resin whose refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction. In the following description, a resin having a negative intrinsic birefringence value may be referred to as resin (B). The intrinsic birefringence value can be calculated from the dielectric constant distribution.

[0071] The multilayer film has a substrate film containing resin (A) and a polymeric material layer containing resin (B), and by stretching the multilayer film after forming the polymeric material layer, an optically anisotropic laminate can be obtained that includes a first optically anisotropic layer containing resin (A) and a second optically anisotropic layer containing resin (B). When combined with a linear polarizer, this optically anisotropic laminate can constitute a circular polarizing plate that has high anti-reflection performance and high coloring suppression performance.

[0072] The materials for the multilayer film in which the substrate film contains resin (A) and the polymer material layer contains resin (B), and the optically anisotropic laminate obtained by further stretching this multilayer film will be described below.

[0073] In the following description, unless otherwise specified, the in-plane retardation Re is a value expressed as Re = (nx - ny) x d. nx represents the refractive index in the direction perpendicular to the thickness direction (in-plane direction) that gives the maximum refractive index (slow axis direction), ny represents the refractive index in the in-plane direction that is perpendicular to the nx direction, nz represents the refractive index in the thickness direction, and d represents the thickness. The measurement wavelength is 550 nm unless otherwise specified. The in-plane retardation and thickness direction retardation can be measured using a retardation meter (Axometrics' "AxoScan").

[0074] In the following description, symbols such as 1, 2, and T may be used to easily identify the refractive index and in-plane retardation of the optically anisotropic laminate and the refractive index and in-plane retardation of each layer constituting the laminate. For example, Re1, Re2, and ReT correspond to the in-plane retardation of the first optically anisotropic layer, the second optically anisotropic layer, and the entire optically anisotropic laminate, respectively. Furthermore, symbols such as (450), (550), and (650) may be used to easily identify the measurement wavelength of the in-plane retardation. The numbers in parentheses correspond to the measurement wavelength (unit: nm). Therefore, for example, the in-plane retardation of the entire optically anisotropic laminate at wavelengths of 450 nm, 550 nm, and 650 nm are expressed as ReT(450), ReT(550), and ReT(650).

[0075] In the following description, unless otherwise specified, the slow axis of a certain layer refers to the slow axis in the in-plane direction of the layer.

[0076] In the following description, the angle formed by the optical axes (absorption axis, transmission axis, slow axis, etc.) of each layer in a member having multiple layers represents the angle when the layer is viewed from the thickness direction, unless otherwise specified.

[0077] In the following description, unless otherwise specified, the terms "circular polarizer," "plate," and "λ / 4 plate" include not only rigid members but also flexible members such as resin films.

[0078] <3.1. Base film> The substrate film contains a resin (A). The resin (A) is a resin having a positive intrinsic birefringence. A resin having a positive intrinsic birefringence typically contains a polymer having a positive intrinsic birefringence. A "polymer having a positive intrinsic birefringence" refers to a polymer whose refractive index in the stretching direction is greater than that in the direction perpendicular to the stretching direction. Examples of such polymers include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester; polyethersulfone; polysulfone; polyarylsulfone; polyvinyl chloride; alicyclic structure-containing polymers; and rod-shaped liquid crystal polymers. These polymers may be used alone or in combination of two or more in any ratio. Among these, alicyclic structure-containing polymers, cellulose esters, and polycarbonates are preferred, with alicyclic structure-containing polymers being particularly preferred. The alicyclic structure-containing polymer may be a cyclic olefin polymer. The cyclic olefin polymer refers to a polymer having a structural unit obtained by polymerizing a cyclic olefin, or a hydrogenated product thereof. The cyclic olefin may or may not have a substituent.

[0079] The alicyclic structure-containing polymer is a polymer containing an alicyclic structure in the repeating unit, and is usually an amorphous polymer. As the alicyclic structure-containing polymer, either a polymer containing an alicyclic structure in the main chain or a polymer containing an alicyclic structure in the side chain can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, with a cycloalkane structure being preferred from the viewpoint of thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, particularly preferably 6 or more, and preferably 30 or less, more preferably 20 or less, particularly preferably 15 or less.

[0080] In the alicyclic structure-containing polymer, the proportion of repeating units containing an alicyclic structure is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of repeating units containing an alicyclic structure is within the above range, an optically anisotropic laminate having excellent heat resistance can be obtained.

[0081] Examples of polymers containing an alicyclic structure include (1) norbornene-based polymers, (2) monocyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof. Among these, cyclic olefin polymers and norbornene-based polymers are preferred, with norbornene-based polymers being particularly preferred. Examples of norbornene-based polymers include ring-opening polymers of monomers containing a norbornene structure, ring-opening copolymers of monomers containing a norbornene structure and other monomers copolymerizable therewith, and hydrogenated products thereof; addition polymers of monomers containing a norbornene structure, and addition copolymers of monomers containing a norbornene structure and other monomers copolymerizable therewith. Among these, hydrogenated ring-opening polymers of monomers containing a norbornene structure are particularly preferred from the viewpoint of transparency. The alicyclic structure-containing polymer can be selected from the polymers disclosed in, for example, JP 2002-321302 A.

[0082] Examples of cellulose esters include lower fatty acid esters of cellulose (e.g., cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate). Lower fatty acids refer to fatty acids having six or fewer carbon atoms per molecule. Cellulose acetates can include triacetyl cellulose (TAC) and cellulose diacetate (DAC).

[0083] The total acyl substitution degree of the cellulose ester is preferably 2.20 to 2.70, more preferably 2.40 to 2.60. The total acyl substitution degree can be measured according to ASTM D817-91. The weight-average polymerization degree of the cellulose ester is preferably 350 to 800, more preferably 370 to 600.

[0084] Polycarbonates usually have a repeating unit containing a carbonate bond (-O-C(=O)-O-). Examples of polycarbonates include polymers having a structural unit derived from a dihydroxy compound and a carbonate structure (a structure represented by -O-(C=O)-O-). Examples of dihydroxy compounds include bisphenol A. The structural unit derived from a dihydroxy compound contained in a polycarbonate may be one type or two or more types.

[0085] The weight-average molecular weight (Mw) of the polymer contained in the resin having a positive intrinsic birefringence value is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and preferably 100,000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight-average molecular weight is within this range, the mechanical strength and moldability of the optically anisotropic layer are well balanced. The weight-average molecular weight is the weight-average molecular weight in terms of polyisoprene or polystyrene measured by gel permeation chromatography (GPC) using cyclohexane as a solvent. However, if the sample is insoluble in cyclohexane, toluene may be used as the GPC solvent.

[0086] The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer contained in the resin having a positive intrinsic birefringence value is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, and preferably 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. When the molecular weight distribution is at or above the lower limit of the above range, the productivity of the polymer can be increased and production costs can be reduced. On the other hand, when the molecular weight distribution is at or below the upper limit, the amount of low-molecular-weight components is reduced, thereby suppressing relaxation during exposure to high temperatures and improving the stability of the optically anisotropic layer.

[0087] The proportion of the polymer in the resin having a positive intrinsic birefringence value is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and particularly preferably 90% by weight to 100% by weight. When the proportion of the polymer is within the above range, the optically anisotropic layer can have sufficient heat resistance and transparency.

[0088] The resin having a positive intrinsic birefringence value may further contain an optional component in combination with the polymer. Examples of the optional component include stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, and near-infrared absorbers; plasticizers; etc. These components may be used alone or in combination of two or more in any ratio.

[0089] The substrate film is usually obtained by molding the above-mentioned resin (A). The molding method of the resin (A) is not particularly limited, and molding methods such as melt molding and solution casting can be used. Among them, melt molding is preferred. Among the melt molding methods, extrusion molding, inflation molding, and press molding are preferred, and extrusion molding is particularly preferred. According to these methods, the substrate film can be produced as a long film.

[0090] The thickness of the substrate film is not particularly limited and is, for example, 0.5 μm or more, preferably 1 μm or more, more preferably 5 μm or more, and for example, 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less.

[0091] <3.2. Polymer material layer> The polymer material layer includes a resin (B). The resin (B) is a resin having a negative intrinsic birefringence. A resin having a negative intrinsic birefringence typically includes a polymer having a negative intrinsic birefringence. A "polymer having a negative intrinsic birefringence" refers to a polymer whose refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction. Examples of such polymers include aromatic group-containing polymers; polyacrylonitrile polymers; polymethyl methacrylate polymers; and multiple copolymers thereof.

[0092] The aromatic group-containing polymer is a polymer containing an aromatic group-containing unit and is obtained by polymerizing an aromatic group-containing monomer. Examples of the aromatic group contained in the aromatic group-containing monomer include a phenyl group, a naphthyl group (e.g., a 2-naphthyl group), a fluorenediyl group (e.g., a fluorene-9,9-diyl group), and groups having a structure in which hydrogen atoms on the ring of these groups are substituted with substituents.

[0093] One class of examples of aromatic group-containing polymers includes polyesters, polycarbonates, and polyestercarbonates that contain polymerized units that contain fluorene-9,9-diyl groups.

[0094] Another group of examples of aromatic group-containing polymers includes aromatic vinyl polymers. Aromatic vinyl polymers are polymers containing aromatic vinyl units, and the aromatic vinyl units are units having a structure obtained by polymerizing an aromatic vinyl compound. However, in the present application, the polymerized units are not limited by their production method. Examples of aromatic vinyl units include the polymerized unit (A-1) contained in the hydrogenated block copolymer [C] described below and preferred examples thereof.

[0095] The proportion of the polymer in the resin having a negative intrinsic birefringence value is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and particularly preferably 90% by weight to 100% by weight. When the proportion of the polymer is within this range, appropriate optical properties can be exhibited.

[0096] A particularly preferred example of the aromatic vinyl polymer is the hydrogenated block copolymer [C] described below. The hydrogenated block copolymer [C] contains a combination of polymer block [A] and polymer block [B]. The term "hydrogenated" in the term "hydrogenated block copolymer [C]" indicates that the hydrogenated block copolymer [C] contains polymer block [B] containing a hydrogenated linear conjugated diene unit. The hydrogenated block copolymer [C] also includes block copolymers obtained by a production method that does not involve a hydrogenation reaction, so long as it contains polymer block [A] and polymer block [B]. The resin containing this hydrogenated block copolymer [C] is usually a thermoplastic resin.

[0097] The polymer block [A] contains an aromatic vinyl unit. As described above, the aromatic vinyl unit refers to a polymerized unit having a structure obtained by polymerizing an aromatic vinyl compound. The aromatic vinyl compound includes aromatic vinyl compounds and derivatives thereof. The aromatic vinyl compound refers to a hydrocarbon compound having a structure in which a vinyl group is bonded to an aromatic ring. Furthermore, the derivatives of aromatic vinyl compounds include compounds having a structure in which one or more hydrogen atoms of an aromatic vinyl compound are substituted with a substituent. The aromatic vinyl unit includes polymerized units obtained by any production method, so long as they have the structure.

[0098] A preferred example of the aromatic vinyl unit is a polymer unit represented by the following formula (A-1).

[0099] [ka]

[0100] In formula (A-1), R Crepresents a group selected from the group consisting of a phenyl group, a biphenyl group, a naphthyl group, an anthracene group, a phenanthrene group, a naphthacene group, a pentacene group, and a terphenyl group. From the viewpoint of particularly facilitating the production of an optically anisotropic laminate having desired optical properties, R c As the alkyl group, a naphthyl group is preferred.

[0101] In formula (A-1), R 1 ~R 3 each independently represents a group selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 12 carbon atoms. Examples of such an alkyl group include a methyl group, an ethyl group, a propyl group, and a hexyl group. From the viewpoint of particularly facilitating the production of an optically anisotropic laminate having desired optical properties, R 2 and R 3 and R are both hydrogen atoms, more preferably 1 , R 2 and R 3 are all hydrogen atoms.

[0102] A particularly preferred example of the aromatic vinyl-based unit is a polymerized unit represented by the following formula (a-1): The polymerized unit represented by formula (a-1) represents a vinylnaphthalene unit.

[0103] [ka]

[0104] The aromatic vinyl unit can be obtained, for example, by polymerizing an aromatic vinyl compound. Examples of aromatic vinyl compounds include vinylnaphthalene and its derivatives. Examples of vinylnaphthalene include 1-vinylnaphthalene and 2-vinylnaphthalene. Examples of vinylnaphthalene derivatives include α-methyl-1-vinylnaphthalene, α-ethyl-1-vinylnaphthalene, α-propyl-1-vinylnaphthalene, α-hexyl-1-vinylnaphthalene, α-methyl-2-vinylnaphthalene, α-ethyl-2-vinylnaphthalene, α-propyl-2-vinylnaphthalene, and α-hexyl-2-vinylnaphthalene. Among these, 2-vinylnaphthalene is preferred from the viewpoint of industrial availability.

[0105] The aromatic vinyl unit contained in the hydrogenated block copolymer [C] may be of one type or of two or more types. Thus, the aromatic vinyl compound for forming the aromatic vinyl unit may be used alone or in combination of two or more types in any ratio.

[0106] The proportion of aromatic vinyl units in the polymer block [A] is preferably high. Specifically, the proportion of aromatic vinyl units in the polymer block [A] is preferably 50% by weight to 100% by weight, more preferably 75% by weight to 100% by weight, and particularly preferably 100% by weight. When the proportion of aromatic vinyl units in the polymer block [A] is as high as described above, it is particularly easy to produce an optically anisotropic laminate having desired optical properties.

[0107] The polymer block [A] may contain any polymerized unit other than the aromatic vinyl-based unit. Examples of such any polymerized unit include a polymerized unit having a structure obtained by polymerizing any monomer copolymerizable with an aromatic vinyl-based compound, and a polymerized unit having a structure formed by hydrogenating such a polymerized unit.

[0108] The polymer block [B] contains a hydrogenated linear conjugated diene unit. The hydrogenated linear conjugated diene unit refers to a polymerized unit having a structure obtained by polymerizing and hydrogenating a linear conjugated diene compound. The linear conjugated diene compound includes a linear conjugated diene compound and a derivative thereof. The linear conjugated diene compound refers to a linear hydrocarbon compound having a conjugated diene structure. Furthermore, the derivative of the linear conjugated diene compound includes a compound having a structure in which one or more hydrogen atoms of the linear conjugated diene compound are substituted with a substituent. The hydrogenated linear conjugated diene unit includes a polymerized unit obtained by any production method, so long as it has the structure.

[0109] Preferred examples of the hydrogenated linear conjugated diene unit include a polymer unit represented by the following formula (B-1) and a polymer unit represented by the following formula (B-2).

[0110] [ka]

[0111] In formula (B-1) and formula (B-2), R 4 ~R 9 each independently represents a group selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 6 carbon atoms. Examples of such an alkyl group include a methyl group, an ethyl group, a propyl group, and a hexyl group. From the viewpoint of particularly facilitating the production of an optically anisotropic laminate having desired optical properties, R 4 ~R 9 are preferably each independently a hydrogen atom or a methyl group.

[0112] Particularly preferred examples of the hydrogenated linear conjugated diene unit include polymerized units represented by any of the following formulae (b-1) to (b-5). The polymerized units represented by any of formulae (b-1) to (b-3) represent hydrogenated isoprene units. The polymerized units represented by formulae (b-4) or (b-5) represent hydrogenated butadiene units.

[0113] [ka]

[0114] The hydrogenated linear conjugated diene unit can be obtained, for example, by a method including a step of polymerizing a linear conjugated diene compound to obtain a linear conjugated diene unit, and a step of hydrogenating a double bond, if any, present in the linear conjugated diene unit. The linear conjugated diene unit refers to a polymerized unit having a structure obtained by polymerizing a linear conjugated diene compound. The linear conjugated diene unit includes polymerized units obtained by any production method, so long as they have the structure.

[0115] Examples of the chain conjugated diene compound include compounds represented by the following formula (bm).

[0116] [ka]

[0117] A preferred example of the chain conjugated diene compound is butadiene (R in formula (bm)). 4 ~R 9 is a hydrogen atom), isoprene (R in formula (bm) 4 ~R 9 Among R 6 or R 7 where R is a methyl group and the others are hydrogen atoms), 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-hexadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, and 2,4-dimethyl-1,3-pentadiene. Among these, butadiene and isoprene are more preferred from the viewpoint of obtaining an optically anisotropic laminate excellent in transparency, heat resistance, and processability.

[0118] After polymerizing a linear conjugated diene compound to obtain linear conjugated diene units, hydrogenated double bonds of the linear conjugated diene units are obtained to obtain hydrogenated linear conjugated diene units. This hydrogenation may be carried out in a system containing polymer block [A]. For example, after obtaining a block copolymer containing polymer block [A] obtained by polymerizing an aromatic vinyl compound and polymer block [D] obtained by polymerizing a linear conjugated diene compound, the double bonds in polymer block [D] of the block copolymer may be selectively hydrogenated to obtain polymer block [B] containing hydrogenated linear conjugated diene units. In this case, the method for hydrogenating the double bonds of the linear conjugated diene units is usually selected to hydrogenate the aliphatic double bonds of the linear conjugated diene units contained in polymer block [D] without hydrogenating the aromatic unsaturated bonds of the aromatic vinyl units contained in polymer block [A].

[0119] The hydrogenation rate of the double bonds of the chain conjugated diene units is preferably 90% or more, more preferably 95% or more, and particularly preferably 97% or more. When the hydrogenation rate is as high as above, it is particularly easy to produce an optically anisotropic laminate having desired optical properties. The hydrogenation rate is 1 It can be measured by H-NMR.

[0120] The hydrogenated block copolymer [C] may contain one or more types of hydrogenated linear conjugated diene units. Thus, the linear conjugated diene compounds for forming the hydrogenated linear conjugated diene units may be used alone or in combination of two or more types in any ratio.

[0121] The proportion of hydrogenated linear conjugated diene units in the polymer block [B] is preferably high. Specifically, the proportion of hydrogenated linear conjugated diene units in the polymer block [B] is preferably 50% by weight to 100% by weight, more preferably 75% by weight to 100% by weight, and particularly preferably 100% by weight. When the proportion of hydrogenated linear conjugated diene units in the polymer block [B] is as high as described above, it is particularly easy to produce an optically anisotropic laminate having desired optical properties.

[0122] The polymer block [B] may contain any polymerized unit other than the hydrogenated linear conjugated diene unit. Examples of such any polymerized unit include polymerized units obtained by polymerizing a linear conjugated diene compound and having remaining unhydrogenated double bonds (linear conjugated diene unit, etc.), polymerized units having a structure obtained by polymerizing any monomer copolymerizable with a linear conjugated diene compound, and polymerized units having a structure formed by hydrogenating such polymerized units.

[0123] In the hydrogenated block copolymer [C], the ratio wA / wB of the weight fraction wA of the polymer block [A] to the weight fraction wB of the polymer block [B] is usually 50 / 50 or more, preferably 55 / 45 or more, particularly preferably 60 / 40 or more, and usually 85 / 15 or less, preferably 82 / 18 or less, particularly preferably 80 / 20 or less. When the ratio wA / wB is within the above range, it is easy to produce an optically anisotropic laminate having reverse wavelength dispersion characteristics. Furthermore, when the ratio wA / wB is within the above range, it is usually easy to adjust the optical properties other than the wavelength dispersion characteristics of the optically anisotropic laminate to desired values.

[0124] The weight fraction wA of the polymer block [A] refers to the ratio of the weight of the polymer block [A] to the total weight of the polymer block [A] and the polymer block [B]. When the resin used as the material for the optically anisotropic laminate contains multiple types of hydrogenated block copolymers [C], the weight fraction wA of the polymer block [A] referred to here refers to the ratio of the weight of the polymer block [A] to the total weight of the polymer block [A] and the polymer block [B] in the entire multiple types of hydrogenated block copolymers [C] contained.

[0125] The weight fraction wB of the polymer block [B] refers to the ratio of the weight of the polymer block [B] to the total weight of the polymer block [A] and the polymer block [B]. When the resin used as the material for the optically anisotropic laminate contains multiple types of hydrogenated block copolymers [C], the weight fraction wB of the polymer block [B] refers to the ratio of the weight of the polymer block [B] to the total weight of the polymer block [A] and the polymer block [B] in the entire multiple types of hydrogenated block copolymers [C] contained.

[0126] The weight fraction wA of the polymer block [A] and the weight fraction wB of the polymer block [B] are 1 It can be measured by H-NMR.

[0127] The molecular structure of the hydrogenated block copolymer [C] is not particularly limited as long as it has the polymer block [A] and the polymer block [B], and may be a molecular structure having any block configuration. For example, the hydrogenated block copolymer [C] may be a linear block copolymer or a graft block copolymer.

[0128] Examples of linear block copolymers include diblock copolymers having a block structure of [A]-[B] in which a polymer block [A] and a polymer block [B] are linked together; triblock copolymers having a block structure of [A]-[B]-[A] in which a polymer block [A], a polymer block [B], and another polymer block [A] are linked together in this order; and linear block copolymers having a block structure in which a larger number of polymer blocks are linked together. Examples of block structures in which a larger number of polymer blocks are linked together include [A]-([B]-[A]) n -[B]-[A], and [B]-([A]-[B]) n -[A]-[B] (n is an integer of 1 or more) block structure.

[0129] An example of a graft-type block copolymer is a block copolymer having a block structure of [A]-g-[B], in which a polymer block [B] is linked to a polymer block [A] as a side chain.

[0130] From the viewpoint of particularly facilitating the production of an optically anisotropic laminate having desired optical properties, the hydrogenated block copolymer [C] preferably has a molecular structure having two or more polymer blocks [A] and one or more polymer blocks [B] per molecule, and more preferably is a triblock copolymer having an [A]-[B]-[A] block structure.

[0131] The hydrogenated block copolymer [C] contained in the resin as a material for the optically anisotropic laminate may be one type or two or more types.

[0132] The resin having a negative intrinsic birefringence value may further contain an optional component in combination with the polymer. Examples of the optional component include the same optional components as those that may be contained in the resin having a positive intrinsic birefringence value. One type of optional component may be used alone, or two or more types may be used in combination in any ratio.

[0133] The polymer material layer containing the above-mentioned resin (B) is formed by the manufacturing method according to this embodiment. A preferred example of a solvent that can be used together with the resin (B) is 1,3-dioxolane.

[0134] <3.3. Optically anisotropic laminate> When the multilayer film produced by the production method of this embodiment includes a substrate film containing resin (A) and a polymeric material layer containing resin (B), the production method of this embodiment preferably includes a stretching step. By including the stretching step, an optically anisotropic laminate can be obtained in which the substrate film is stretched to form the first optically anisotropic layer and the polymeric material layer is stretched to form the second optically anisotropic layer. As for the stretching method, a known stretching method can be appropriately selected and used.

[0135] The slow axes of the first optically anisotropic layer and the second optically anisotropic layer contained in the stretched multilayer film form a predetermined angle. Since the base film contains a resin (A) having a positive intrinsic birefringence value and the polymer material layer contains a resin (B) having a negative intrinsic birefringence value, by stretching the multilayer film containing the base film and the polymer material layer, the base film usually develops a slow axis in the same direction as the stretching direction, preferably in the same direction, and the polymer material layer usually develops a slow axis in the direction of approximately 90°, preferably 90°, to the stretching direction.

[0136] Therefore, in the stretched multilayer film, the angle between the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer is preferably 85° or more, more preferably 87° or more, even more preferably 88° or more, even more preferably 89° or more, and is preferably 95° or less, more preferably 93° or less, even more preferably 92° or less, even more preferably 91° or less, and most preferably 90°.

[0137] The optically functional laminate is preferably an optically anisotropic laminate that includes a first optically anisotropic layer and a second optically anisotropic layer and satisfies the following formulae (e1) to (e6). nx1>ny1≧nz1 (e1) nz2≧nx2>ny2 (e2) Re1(450) / Re1(550) <Re2(450) / Re2(550) (e3) Re1(550)>Re2(550) (e4) 85°≦θ D ≦95° (e5) 70 / 30 <d1 / d2<99 / 1 (e6)

[0138] however, nx1 represents the refractive index in the in-plane direction of the first optically anisotropic layer that gives the maximum refractive index, ny1 represents the refractive index in an in-plane direction of the first optically anisotropic layer, which is perpendicular to the direction giving nx1; nz1 represents the refractive index of the first optically anisotropic layer in the thickness direction, nx2 represents the refractive index in the in-plane direction of the second optically anisotropic layer that gives the maximum refractive index, ny2 represents the refractive index in an in-plane direction of the second optically anisotropic layer, which is perpendicular to the direction giving nx2; nz2 represents the refractive index of the second optically anisotropic layer in the thickness direction, Re1(450) represents the in-plane retardation of the first optically anisotropic layer at a wavelength of 450 nm, Re1(550) represents the in-plane retardation of the first optically anisotropic layer at a wavelength of 550 nm, Re2(450) represents the in-plane retardation of the second optically anisotropic layer at a wavelength of 450 nm, Re2(550) represents the in-plane retardation of the second optically anisotropic layer at a wavelength of 550 nm, θ D is the angle formed between the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer, d1 is the thickness of the first optically anisotropic layer, d2 is the thickness of the second optically anisotropic layer.

[0139] The formula (e1) indicates that the first optically anisotropic layer can function as a so-called positive A plate or negative B plate. The formula (e2) indicates that the second optically anisotropic layer can function as a so-called negative A plate or positive B plate.

[0140] The formula (e3) indicates that the wavelength dispersion of the second optically anisotropic layer is greater than that of the first optically anisotropic layer.

[0141] The value of "Re2(450) / Re2(550)-Re1(450) / Re1(550)" is usually greater than 0, and preferably satisfies the following formula (e10). Re2(450) / Re2(550)-Re1(450) / Re1(550)≧0.2 (e10) The value of "Re2(450) / Re2(550)-Re1(450) / Re1(550)" is preferably 0.2 or more, more preferably 0.24 or more, and even more preferably 0.28 or more. The larger the value, the better. However, it may be, for example, 0.7 or less. An optically anisotropic laminate including a first optically anisotropic layer and a second optically anisotropic layer having different wavelength dispersion properties in the in-plane retardation can easily obtain reverse wavelength dispersion characteristics in the laminated state. Therefore, the optically anisotropic laminate can be combined with a linear polarizer to form a circular polarizer that functions over a wide wavelength range.

[0142] The value of "Re2(450) / Re2(550)" is preferably 1.05 or more, more preferably 1.10 or more, particularly preferably 1.20 or more, and even more particularly preferably 1.25 or more, and is not particularly limited, and may be, for example, 1.8 or less. When the value of "Re2(450) / Re2(550)" is within the above range, a difference in the wavelength dispersion characteristics of the first optically anisotropic layer and the second optically anisotropic layer is likely to occur, and the retardation required to achieve the desired reverse wavelength dispersion characteristics is reduced, making it possible to obtain a circular polarizing plate that can be made thinner and that can effectively suppress coloring due to reflection of external light.

[0143] The value of "Re1(450) / Re1(550)" is not particularly limited, but may be, for example, 0.8 or more, preferably 1.05 or less, more preferably 1.03 or less, and particularly preferably 1.01 or less. When "Re1(450) / Re1(550)" is within the above range, a difference in wavelength dispersion characteristics between the first optically anisotropic layer and the second optically anisotropic layer is likely to occur, and the retardation required to achieve the desired reverse wavelength dispersion characteristics becomes smaller, making it possible to obtain a circular polarizing plate that can be made thinner and that can effectively suppress coloring due to reflection of external light.

[0144] The value of (Re1(550)-Re2(550)) is usually greater than 0, and preferably a value that allows the optically anisotropic laminate to function as a λ / 4 plate. Specifically, the optically anisotropic laminate preferably satisfies the following formula (e7): 100nm≦(Re1(550)-Re2(550))≦180nm (e7)

[0145] The value of "Re1(550)-Re2(550)" is preferably 100 nm or more, more preferably 110 nm or more, and is preferably 180 nm or less, more preferably 160 nm or less. When "Re1(550)-Re2(550)" is in the above range, a circular polarizing plate that can effectively suppress coloring due to reflection of external light can be obtained.

[0146] The formula (e4) indicates that the magnitude of the in-plane retardation of the first optically anisotropic layer at a wavelength of 550 nm is greater than that of the second optically anisotropic layer.

[0147] The value of Re1(550) preferably satisfies the following formula (e8), provided that the above formulas (e1) to (e6) are satisfied. 250nm ≥ Re1(550) ≥ 180nm (e8)

[0148] More specifically, Re1(550) is preferably 180 nm or more, more preferably 185 nm or more, particularly preferably 190 nm or more, and is preferably 250 nm or less, more preferably 240 nm or less, particularly preferably 230 nm or less. When the in-plane retardation Re1(550) is within the above range, a circular polarizing plate having high antireflection performance and high coloring suppression performance can be constructed, and an optically anisotropic laminate can be produced at low cost.

[0149] The value of Re2(550) preferably satisfies the following formula (e9), provided that the above formulas (e1) to (e6) are satisfied. 110nm ≥ Re2(550) ≥ 40nm (e9)

[0150] More specifically, Re2(550) is preferably 40 nm or more, more preferably 45 nm or more, particularly preferably 50 nm or more, and is preferably 110 nm or less, more preferably 100 nm or less, particularly preferably 90 nm or less. When the in-plane retardation Re2(550) is within the above range, a circular polarizing plate having high antireflection performance and high coloring suppression performance can be constructed, and an optically anisotropic laminate can be produced at low cost.

[0151] The formula (e5) indicates that the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer form a right angle or an angle close to a right angle. D is 85° or more, preferably 87° or more, more preferably 88° or more, even more preferably 89° or more, and is usually 95° or less, preferably 93° or less, more preferably 92° or less, even more preferably 91° or less, and most preferably 90°. When the angle formed by the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer is within the above range, the heat resistance of the optically anisotropic laminate can be effectively improved. Formula (e5) is expressed by θ D If there is no distinction in the direction of rotation of the angle, 85°≦θ D Equivalent to ≦90.

[0152] When the optically anisotropic laminate is long, it is preferable that one of the slow axes of the first optically anisotropic layer and the second optically anisotropic layer forms an angle within a specific range close to 45° with respect to the width direction of the optically anisotropic laminate. Specifically, the angle is preferably 40° or more, more preferably 42° or more, even more preferably 43° or more, and particularly preferably 44° or more, and is preferably 50° or less, more preferably 48° or less, even more preferably 47° or less, and particularly preferably 46° or less. Furthermore, in this case, it is preferable that the other of the slow axes of the first optically anisotropic layer and the second optically anisotropic layer forms an angle within a specific range close to 135° with respect to the width direction of the optically anisotropic laminate. Specifically, the angle is preferably 130° or more, more preferably 132° or more, even more preferably 133° or more, and particularly preferably 134° or more, and preferably 140° or less, more preferably 138° or less, even more preferably 137° or less, and particularly preferably 136° or less. A typical long linear polarizer has an absorption axis parallel or perpendicular to the width direction of the linear polarizer. A long optically anisotropic laminate including a first optically anisotropic layer and a second optically anisotropic layer, each having a slow axis in a direction forming an angle within the above range with respect to the width direction, can be simply attached to the typical linear polarizer with the width direction of the optically anisotropic laminate parallel to the width direction of the linear polarizer to obtain a circular polarizing plate. Therefore, the attachment of the optically anisotropic laminate to the linear polarizer can be performed by roll-to-roll processing, making it particularly easy to produce a circular polarizing plate.

[0153] There are no particular limitations on the thickness of each of the first optically anisotropic layer and the second optically anisotropic layer, and the thickness of each of the first optically anisotropic layer and the second optically anisotropic layer is preferably 0.5 μm or more, more preferably 1 μm or more, and preferably 150 μm or less, more preferably 100 μm or less.

[0154] The formula (e6) indicates that the thickness of the first optically anisotropic layer is greater than the thickness of the second optically anisotropic layer, and the ratio thereof is within a predetermined range.

[0155] The value of d1 / d2 is more than 70 / 30, and preferably 90 / 10 or more. On the other hand, the value of d1 / d2 is less than 99 / 1, and preferably 97 / 3 or less. The present inventors have found that when the value of d1 / d2 is within this range and the requirements of formulas (e1) to (e5) are satisfied, the thickness of the second optically anisotropic layer can be reduced while the retardation of the second optically anisotropic layer can be favorably exhibited. As a result, a circularly polarizing plate having high antireflection performance and high coloring suppression performance can be constructed, and an optically anisotropic laminate that can be produced at low cost can be realized.

[0156] The optically anisotropic laminate preferably has a retardation that allows it to function as a λ / 4 plate. The optically anisotropic laminate has an in-plane retardation ReT(550) at a wavelength of 550 nm of preferably 75 nm or more, more preferably 100 nm or more, and preferably 180 nm or less, more preferably 160 nm or less. When the in-plane retardation ReT(550) of the optically anisotropic laminate is within the above range, a circular polarizing plate that can effectively suppress coloring due to reflection of external light can be obtained.

[0157] The optically anisotropic laminate preferably exhibits reverse wavelength dispersion. When the optically anisotropic laminate has reverse wavelength dispersion, a circular polarizing plate that functions in a wide wavelength range can be obtained from the optically anisotropic laminate. The optically anisotropic laminate preferably satisfies the following formula. ReT(450) / ReT(550) <ReT(650) / ReT(550) Here, ReT(450) represents the in-plane retardation of the optically anisotropic laminate at a wavelength of 450 nm, ReT(550) represents the in-plane retardation of the optically anisotropic laminate at a wavelength of 550 nm, and ReT(650) represents the in-plane retardation of the optically anisotropic laminate at a wavelength of 650 nm.

[0158] The value of ReT(450) / ReT(550) is preferably 0.75 or more, more preferably 0.80 or more, and is preferably 0.95 or less, more preferably 0.92 or less. The value of ReT(650) / ReT(550) is preferably 1.02 or more, more preferably 1.03 or more, and is preferably 1.25 or less, more preferably 1.20 or less.

[0159] The total light transmittance of the optically anisotropic laminate is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The total light transmittance can be measured using an ultraviolet-visible spectrometer in the wavelength range of 400 nm to 700 nm.

[0160] The haze of the optically anisotropic laminate is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. The haze can be measured using a haze meter in accordance with JIS K7361-1997.

[0161] The thickness of the optically anisotropic laminate is not particularly limited. From the viewpoint of thinning, the specific thickness of the optically anisotropic laminate is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 15 μm or more, and is preferably 200 μm or less, more preferably 150 μm or less, particularly preferably 100 μm or less. [Example]

[0162] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents.

[0163] In the following description, the units "%" and "parts" that represent amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out in air at room temperature and normal pressure (23°C, 1 atmosphere) unless otherwise specified.

[0164] [Evaluation method] <Measurement of the area ratio of brushing areas> A backlight unit configuration (size: 450 mm x 300 mm) for observation was prepared by sandwiching the multilayer film obtained in the Examples or Comparative Examples between polarizing plates arranged in a crossed Nicol configuration on a backlight unit. Since linearly polarized light incident on the blushing area of ​​the multilayer film is scattered, the blushing area can be visually recognized as cloudy. Therefore, images of the backlight unit configuration for observation described above were acquired using a USB3 Vision camera CS500-B (manufactured by Shodensha Co., Ltd.) and a C-mount lens (manufactured by Olympus Co., Ltd.) with a focal length of 12.6 mm and an exposure time of 50 ms. The obtained images were then binarized to calculate the area ratio of the blushing area to the total area of ​​the backlight unit configuration.

[0165] <How to calculate absolute humidity> Relative humidity H of the environment in which the coating and drying processes are carried out r was measured using a hygrometer, and the volume absolute humidity D was calculated from the measured value using the following formula. D=(H r / 100)×804e s / {p0(1+0.00366θ)} (1) In the above formula (1), D is the absolute humidity (g / m 3 ), H r is the relative humidity (RH%), θ is the temperature (℃), e s is the saturated water vapor pressure at θ (℃), and p0 is 1 atmosphere (760 mmHg).

[0166] [Manufacturing example: Manufacturing of coating liquid] A fluorene copolymer polyester resin ("OKP-TS22" manufactured by Osaka Gas Chemicals Co., Ltd.) was dissolved in 1,3-dioxolane (boiling point 75°C) as the polymer material to obtain Coating Solution A with a solid content of 15% by weight. The viscosity of the obtained Coating Solution A was measured using an EMS viscometer ("EMS-1000S" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) and found to be 32 mPa·s. The surface tension was also measured using a contact angle meter ("DropMaster500" manufactured by Kyowa Interface Science Co., Ltd.) and found to be 32 m / N.

[0167] [Example 1] A film manufacturing apparatus was prepared, equipped from the upstream side of the film manufacturing equipment with a payout device, a corona treatment device, a backup roll type coating device using a slot die, a vacuum device, a drying device with seven drying ovens, and a winding device. The temperature of the first drying oven, which is the most upstream of the drying equipment, was set to 80°C, and the temperatures of the six drying ovens after the first drying oven were set to 90°C, 110°C, 110°C, 110°C, 110°C, and 100°C, respectively, from the upstream side. The environment during coating of Coating Solution A was a temperature of 22°C and a relative humidity of 36 RH% (volume absolute humidity 7.0 g / m 3 ) The conveying speed of the substrate film (Zeonorfilm ZF12-070 manufactured by Zeon Corporation) was adjusted so that the residence time at room temperature from the coating device to the first drying chamber was 4 seconds, and the corona output of the corona treatment device was set to 0.6 kW. At the above conveying speed, the duration of the first drying step was 15 seconds, and the duration of the second drying step was 100 seconds.

[0168] Coating solution A was applied onto a substrate film to a coating thickness of 20 μm immediately after coating so that the coating thickness after drying would be 3 μm. sol / T Ave The viscosity (μm / ° C.) was 0.23. The multilayer film obtained by drying under the above-mentioned drying conditions was wound up.

[0169] [Example 2] The temperature during coating of coating solution A was 22°C, and the relative humidity was 47 RH% (volume absolute humidity 9.1 g / m 3 A multilayer film was produced under the same conditions as in Example 1, except that

[0170] [Comparative Example 1] The temperature during coating was 22°C, and the relative humidity was 47 RH% (volume absolute humidity 9.1 g / m 3 A multilayer film was produced under the same conditions as in Example 1, except that the temperature was 4.3 seconds and the residence time at room temperature was 4.3 seconds.

[0171] Comparative Example 2 A multilayer film was produced under the same conditions as in Example 1, except that the residence time at room temperature was 6 seconds.

[0172] Comparative Example 3 The temperature during coating was 22°C, and the relative humidity was 47 RH% (volume absolute humidity 9.1 g / m 3 A multilayer film was produced under the same conditions as in Example 1, except that the temperature was 100°C, and the indoor residence time was 6 seconds.

[0173] Comparative Example 4 The temperature during coating was 22°C, and the relative humidity was 47 RH% (volume absolute humidity 9.1 g / m 3 A multilayer film was produced under the same conditions as in Example 1, except that the temperature in the first drying step was 40°C.

[0174] Comparative Example 5 The temperature during coating was 22°C, and the relative humidity was 47 RH% (volume absolute humidity 9.1 g / m 3 A multilayer film was produced under the same conditions as in Example 1, except that the temperature in the first drying step was 60°C.

[0175] The results are shown in Tables 1 and 2. The abbreviations in the tables have the following meanings. Absolute humidity (g / m 3 ): Absolute humidity (g / m) of the coating environment during the coating process 3 ) Room temperature residence time (s): The time the intermediate film is transported through the room temperature section from the coating device to the entrance of the first drying chamber. First drying temperature (℃): The temperature measured at the exhaust port of the first drying chamber. Second drying temperature (°C): The range of drying temperatures that can be assumed in the six drying chambers located downstream of the first drying chamber is stated as 90°C to 110°C. Brushing area ratio (%): The ratio of the area where brushing occurs to the entire area of ​​the backlight unit configuration including the multilayer film obtained in the examples and comparative examples

[0176] [Table 1]

[0177] [Table 2]

[0178] As shown in Tables 1 and 2, in Examples 1 and 2, the ratio C sol / T Ave (μm / ℃) of 0.2 or more, and the coating process is carried out at room temperature and an absolute humidity of 10 g / m 3 It was confirmed that a multilayer film can be obtained without causing brushing defects by forming the multilayer film at a temperature of 1.5°C or less, conveying it to the first drying step with a room temperature residence time of 4 seconds or less, and drying it at a first drying temperature of 80°C (boiling point of 1,3-dioxolane + 5°C). On the other hand, in Comparative Examples 1 to 3, it was confirmed that brushing defects occur when the room temperature residence time exceeds 4 seconds. In particular, in Comparative Example 1, the room temperature residence time was 4.3 seconds, which was slightly more than 4 seconds, but brushing defects were confirmed to occur, and in Comparative Example 2, the absolute humidity in the coating step was 7.0 g / m 3 It was confirmed that brushing defects occurred when the room temperature residence time exceeded 4 seconds even in a low-humidity environment such as below. Furthermore, in Comparative Examples 4 and 5, it was confirmed that brushing defects occurred when the first drying temperature was lower than the boiling point of 1,3-dioxolane. [Explanation of symbols]

[0179] 1. Base film 10 Intermediate Film 20 Multi-layer film 101, 102, 103, 104, 105, 106, 107, 108 Transport roll 110 Payout device 120 Corona treatment device 130 Coating equipment 131 Backup Roll 132 Discharge part 140 Drying oven 141 First drying room 142 Second drying room s1, s2 air supply port e1, e2 exhaust ports n1, n2, n3 hot air nozzles 150 Winding device 200 Multi-layer film manufacturing equipment

Claims

1. a coating step of applying a coating liquid containing a polymer material and a solvent to a substrate film to obtain an intermediate film having the substrate film and a coating film; a first drying step of drying the coating film on the intermediate film; a second drying step of drying the coating film after the first drying step at a higher temperature than in the first drying step; a conveying step of conveying the intermediate film at room temperature after the coating step and before the first drying step; In the coating step, the average boiling point T Ａｖｅ (°C), the thickness conversion value C of the amount of the solvent contained in the coating film immediately after coating ｓｏｌ Ratio C (μm) ｓｏｌ / T Ａｖｅ (μm / °C) is 0.2 or more; The volume absolute humidity in the coating process is 10.0 g / m ３ The following is true: the time during which the intermediate film is transported in the transporting step is 4 seconds or less; In the first drying step, the solvent contained in the coating film is dried at a temperature of 1000 KPa or less. ｓｏｌ and drying the coating film at a first drying temperature of (°C)+5°C or higher.

2. The method for producing a multilayer film according to claim 1, wherein in the first drying step, at least a hot air treatment is performed to dry the coating film by blowing hot air onto the surface of the base film opposite to the surface on which the coating film is formed.

3. The boiling point T of the solvent contained in the coating liquid ｓｏｌ The method for producing a multilayer film according to claim 1, wherein the temperature (°C) is 85°C or lower.

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