JP4369773B2 - Drying method of coating film - Google Patents

Description

  The present invention relates to a technique for continuously drying a coating liquid applied to a traveling long support, and in particular, a drying method and a structure in which optical function layers formed by the method are laminated. The present invention relates to an optical film having a polarizing plate, a polarizing plate having the optical film, and an image display device including the polarizing plate.

  As a method for continuously drying a coating film formed by coating a coating solution on a traveling long support, there is a method of sending air conditioned air from one direction to a coating surface (for example, Patent Documents). 1). In addition, there are drying methods such as spraying hot air on the coated surface in a drying apparatus after coating, or irradiating far infrared rays.

  By the way, in recent years, in the field of films for optical applications such as liquid crystal display devices, there are severe demands on the appearance after coating depending on the intended use. In particular, in products to which a thin layer coating of 10 μm or less is applied, unevenness in appearance caused by unevenness (unevenness) in the coating film tends to appear very remarkably, but it is desired to reduce such unevenness in appearance.

JP 2001-170547 A

  However, in the conventional drying method, there is a section that is exposed to the ambient environment around the device after the coating liquid is applied to the long support running on the coating device and before it is dried in the drying device. However, for example, the drying speed varies due to the influence of disturbance factors such as winds of irregular speed and direction from the surrounding environment. As a result, a difference occurs in the surface tension of the coating film and the coating liquid flows, so that there is a problem that the thickness of the coating film is uneven, which causes uneven appearance.

  The present invention has been made in view of the above-described problems, and provides a coating film drying method capable of stably producing a coating film with little variation in thickness, and an optical formed by the method. An object of the present invention is to provide an optical film having a structure in which functional layers are laminated, a polarizing plate having the optical film, and an image display device including the polarizing plate.

When drying the coating film formed by applying the coating liquid to the traveling long support, the inventors set the evaporation rate (drying rate) of the coating liquid immediately after coating to 0.1 g / m ² · It was found that the coating film can be dried in a uniform state by setting it to s or less, and a coating film having a uniform thickness can be formed.

Accordingly, the present invention provides a method for drying a coating film formed by applying a coating liquid to a traveling long support, and is parallel to the long support on the downstream side of the coating liquid coating apparatus. A gap is provided between the coating film and the plate provided with fins on the surface of the long support , and the long support is applied after the coating liquid is applied to the long support. The present invention relates to a method for drying a coating film in which drying is performed while maintaining the evaporation rate of the solvent at 0.1 g / m ² · s or less before entering the drying apparatus. As a result, it is possible to stably manufacture a coating film with little variation in thickness. More preferably, the pitch of the fins is shorter than the central portion of the plate at the end of the plate in the running direction of the elongated support.

In the present invention, in order to set the evaporation rate to 0.1 g / m ² · s or less, the long support from when the coating liquid is applied to when the long support enters the drying apparatus. A plate parallel to is disposed with a gap of 10 mm or less between the plate and the coating film. This prevents wind from the surrounding environment from entering the gap between the plate and the coating film, almost fills the gap with solvent vapor, and makes the evaporation rate 0.1 g / m ² · s or less. be able to.

In addition, by controlling the temperature of the plate above the vapor dew point of the coating solution, the evaporation rate can be controlled within a range of 0.1 g / m ² · s or less, and condensation of vapor is prevented and stable. Drying can be performed.

  In addition, by providing fins on the surface of the plate on the long support side, it is possible to prevent the air flow associated with the running of the long support from affecting the coating film in an undried state, and to have a uniform thickness. A coating film can be obtained.

  Moreover, if the viscosity of a coating liquid is 300 mPa * s or less, more stable drying can be performed. Furthermore, if it is 50 mPa * s or less, especially stable drying can be performed.

  In addition, by forming the coating film as an optical functional layer having an optical function, it is possible to obtain a coated product with less appearance unevenness even in the case of a coated product for optical applications that require a severe appearance in recent years. Can do.

  Moreover, the film suitable for the optical use with few external appearance nonuniformities can be obtained by manufacturing the optical film which has the structure which laminated | stacked the optical function layer with the above drying methods. Furthermore, by laminating such optical films to form a polarizing plate, it is possible to obtain a polarizing plate suitable for optical applications with little appearance unevenness.

  Further, when an image display device is manufactured using the polarizing plate, a high-quality device with little appearance unevenness can be realized.

Furthermore, the present invention provides a method for drying a coating film formed by applying a coating liquid to a traveling long support, and a plate having a plate width equal to or larger than the width of the long support is applied to the coating liquid. together with our Ku disposed along the travel path of the elongate support member on the downstream side of the factory unit, a plurality of convex structures extending substantially perpendicular to the traveling direction of said elongated support, the traveling direction Along the bottom surface of the plate, and apply the long support from the time when the coating film is formed to the time when the long support enters the drying device. A coating film drying method is provided in which at least a part of the coating film is dried in the gap by running the film along a traveling path while facing the plate surface of the plate with a gap of 10 mm or less. Is. Thereby, drying can be performed while reducing the influence of wind or the like from the surrounding environment, and it becomes possible to stably produce a coating film with little variation in thickness. It is more preferable that the pitch of the convex structure is shorter than the central portion at the end portion in the traveling direction of the long support in the plate.

According to the present invention, in a method for drying a coating film formed by applying a coating liquid to a traveling long support , the long side is parallel to the long support on the downstream side of the coating liquid coating apparatus. A space is provided between the plate provided with fins on the surface of the long support and the coating film, and the long support enters the drying apparatus after the coating liquid is applied to the long support. In the meantime, since the evaporation rate of the solvent is kept at 0.1 g / m ² · s or less, the coating film is dried in a uniform state to stably produce a coating film with little variation in thickness. can do. Therefore, the appearance with the coating film formed can be obtained as good.

Further, according to the present invention, in a method for drying a coating film formed by applying a coating liquid to a traveling long support, a plate having a plate width equal to or greater than the width of the long support is applied to the coating liquid. along with your Ku disposed along the travel path of the elongate support member on the downstream side of the coating apparatus, a plurality of convex structures extending substantially perpendicular to the traveling direction of the elongate support member, the direction of travel Along the bottom surface of the plate, and apply the long support from the time when the coating film is formed to the time when the long support enters the drying device. At least a part of the coating film is dried in the gap by running the film along a running path while facing the plate surface of the plate with a gap of 10 mm or less. For this reason, it is possible to perform drying while reducing the influence of wind or the like from the surrounding environment, and it becomes possible to stably manufacture a coating film with little variation in thickness.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments in which the present invention is configured to be applicable to a manufacturing process for a polarizing plate of an image display device will be described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration in which a plate is provided on the coating film forming side of a long support. The long support 10 serves as a substrate for forming a coating film. For example, in the production of a polarizing plate, a flat long flexible planar substrate composed of a web-like film or sheet or the like. Thus, the vehicle travels at a substantially constant speed in the right direction on the paper surface while being supported by a plurality of rollers 35 and the like. The running path of the long support 10 is provided with a coating device 30 such as a die coater for applying a coating liquid on at least one side of the long support 10 (the upper surface side in FIG. 1 and the other figures are the same). When the elongate support 10 travels through the coating apparatus 30, the coating liquid 11 is applied in a uniform state on the upper surface side to form the coating film 11. A coating liquid is for forming the protective sheet and optical function layer of a polarizing plate, for example (a specific example is mentioned later).

In the traveling path of the long support 10, the long support is provided immediately after the coating device 30 (on the downstream side in the manufacturing process) so as to face the coating film 11 applied to the long support 10. A plate 20 substantially parallel to the main surface (surface to be coated) of the body 10 is provided, and a certain gap G is provided between the plate 20 and the coating film 11. The surface 20s side of the plate 20 facing the coating film 11 is finished as smooth as possible, and the plate 20 has a plate width so as to cover the coating film 11 in the width direction (perpendicular to the paper surface) of the long support 10. And disposed along the travel route of the elongated support 10. The plate 20 is mainly intended to suppress the coating film 11 formed on the long support 10 from being affected by wind or the like from the environment around the traveling path in an undried state. The gap G between 20 and the coating film 11 is preferably 10 mm or less. As a result, the gap between the plate 20 and the coating film 11 is almost filled with the vapor of the solvent, and the evaporation rate of the solvent can be reduced to 0.1 g / m ² · s or less, and the uniform state Thus, the coating film is dried to form a coating film having a uniform thickness.

  Therefore, the plate 20 applies the solvent evaporation environment of the coating film 11 in the gap G (instead of forced ventilation as in Patent Document 1) while preventing the coating film 11 from being exposed to an external air flow. It functions as an evaporation environment control plate that autonomously and uniformly controls the vapor pressure of the solvent evaporated from the film 11 itself.

Further, in order to control the evaporation rate of the solvent, the plate 20 is formed so as to exhibit uniform thermal conductivity, and the temperature of the plate 20 (particularly the temperature of the surface 20s facing the coating surface) is controlled by a temperature control unit 25 including a heat source. ) Is controlled to a temperature above the dew point of the solvent. In this case, however, the temperature is adjusted so that the evaporation rate of the solvent is 0.1 g / m ² · s or less. As a result, it is possible to arbitrarily adjust the evaporation rate within a range of 0.1 g / m ² · s or less while preventing condensation of the solvent vapor in the gap G between the plate 20 and the coating film 11. Become.

  The plate 20 can be, for example, a metal plate or a plate material whose lower surface 20s is covered with a metal layer, and the temperature control unit 25 can have, for example, an electric heater as a heat source. Preferably, a temperature sensor 26 that detects the temperature of the plate material 20 or the gap G is provided, and the temperature control value of the plate 20 is controlled more precisely by using the temperature detection value of the temperature sensor 26 to perform feedback control. Can be done.

  The drying process using the plate 20 as described above is preferably performed immediately after application of the coating liquid and before the elongate support 10 enters the drying apparatus 40, and is performed at such timing. As a result, it is possible to satisfactorily prevent the influence of the wind from the surrounding environment before the undried coating liquid enters the drying device 40.

  Thereafter, the elongated support 10 on which the coating film 11 is formed and passed below the plate 20 enters a conventional drying apparatus 40, and is heated or irradiated with ultraviolet rays to completely dry or cure the coating film 11. Is called. However, since the temperature of the plate 20 provided immediately after the coating apparatus 30 is adjusted, the gap G below the plate 20 has a temperature higher than room temperature, and has an effect of accelerating the drying of the coating film 11. Therefore, the coating film 11 may be completely dried by the action of the plate 20, and in that case, it is not necessary to provide the drying device 40.

In addition, after the elongate support body 10 passes under the board 20, when a drying process is separately performed in the drying apparatus 40, the evaporation rate of the solvent is controlled to be 0 g / m ² · s. May be. In this case, since the elongated support 10 on which the coating film 11 is formed is guided to the drying device 40 in a state where it is not dried at all by the surrounding environment, a coating film having a good and uniform film thickness is formed. On the other hand, when the drying device 40 is not provided, it is necessary to perform complete drying while the elongate support 10 passes under the plate 20, so that the solvent evaporation rate is at least 0 g. It is controlled to a value higher than / m ² · s. In this case, a specific lower limit value of the evaporation speed is determined to a speed at which complete drying is possible based on the length of the plate 20 in the traveling direction, the moving speed of the long support 10, and the like.

  In order to produce a stable coating film 11 with no unevenness as described above, the viscosity of the coating solution used is preferably 300 mPa · s or less. More preferably, when the viscosity of the coating solution is 50 mPa · s or less, particularly stable drying is possible.

  Next, FIG. 2 shows a configuration different from that in FIG. 1, and shows a configuration in which plates are provided on both the coating film forming side and the non-forming side of the long support. Immediately after the coating device 30 in the travel path of the long support 10, the long support 10 is substantially parallel to the long support 10 so as to face the coating film 11 on the coating film forming side of the long support 10. A first plate 20a is provided, and a second substantially parallel to the long support 10 is provided so as to face the long support 10 on the coating film non-formation side of the long support 10. Plate 20b is provided. Also in this case, constant gaps G1 and G2 are provided between the first plate 20a and the coating film 11 and between the second plate 20b and the elongated support 10, respectively.

By providing the first plate 20a on the side facing the coating film 11, the gap G1 between the first plate 20a and the coating film 11 is almost filled with the vapor of the solvent, and the evaporation rate of the solvent is increased. The coating film can be reduced to 0.1 g / m ² · s or less, and the coating film is dried in a uniform state to form a coating film having a uniform thickness.

  In addition, by providing the plates 20a and 20b on both the coating film forming side and the non-forming side of the long support 10, it becomes possible to more effectively prevent the influence of wind and the like from the surrounding environment.

In order to control the evaporation rate of the solvent, each of the plates 20a and 20b is formed so as to exhibit uniform thermal conductivity, and the temperature of each of the plates 20a and 20b (particularly by the temperature control units 25a and 25b including the heat source). The temperature of the coating surface or the surface facing the support surface) is individually controlled so that the temperature is equal to or higher than the dew point of the solvent. By controlling the plates 20a and 20b separately, fine adjustment is possible when controlling the evaporation rate of the solvent, and a stable state with an evaporation rate of 0.1 g / m ² · s or less is realized with high accuracy. can do.

  When the temperatures of the plates 20a and 20b are independently controlled, temperature sensors 26a and 26b for measuring the temperatures of the plates 20a and 20b or the gaps G1 and G2 are separately provided, and the temperature controllers 25a and 25b are respectively provided. Although it is preferable to perform feedback control, referring to the temperature detection value of one of these (for example, the temperature sensor 26a on the side facing the coating surface), feedback control of both of the two temperature control units 25a and 25b is performed. Also good.

  Next, FIG. 3 shows a configuration different from that described above, in which a surrounding plate (flat tunnel structure) 20c is provided so as to surround the long support immediately after the coating liquid is applied. FIG. FIG. 3 is a cross-sectional view perpendicular to the traveling direction of the long support 10, and the long support 10 travels in a direction perpendicular to the paper surface.

In the configuration of FIG. 3, the surrounding plate 20c is disposed immediately after the coating apparatus 30 in the travel path of the long support 10, and the long support 10 immediately after the coating film 11 is formed is separated by the surrounding plate 20c. It enters the tunnel-like internal space 21 to be formed. That is, the surrounding plate 20c has a structure in which a plate is provided not only on the coating film forming side and the non-forming side of the long support 10 but also on the side. While the vehicle 11 travels in the inner space 21 of the surrounding plate 20c, the influence of wind from the surrounding environment can be remarkably reduced. The constant gap G1 described above is provided between the coating film 11 and the surrounding plate 20c on the side of the surrounding plate 20c facing the coating film 11, and the evaporation rate of the solvent is 0.1 g / m ² · s. It becomes as follows.

In addition, in order to control the evaporation rate of the solvent, the surrounding plate 20c is formed so as to exhibit uniform thermal conductivity, and the temperature of the surrounding plate 20c (particularly the temperature on the inner surface side) is set by the temperature control unit 25 including the heat source. The temperature is controlled to be above the dew point. This prevents evaporation of the solvent vapor in the gap G1 between the surrounding plate 20c and the coating film 11 and the internal space 21 of the surrounding plate 20c, and the evaporation rate is within a range of 0.1 g / m ² · s or less. It becomes possible to adjust arbitrarily.

  Next, FIG. 4 is a diagram showing a configuration in which a plurality of flat fins 22a to 22d are provided on the plate 20 in the configuration of FIG. As shown in FIG. 4, the fins 22 a to 22 d are suspended from the surface of the plate 20 facing the coating film 11 so as to cross the running path of the long support 10. In addition, a certain gap G is provided between the lower ends of the fins 22 a to 22 d and the coating film 11 so that the lower ends of the fins 22 a to 22 d do not come into contact with the coating film 11.

  Thus, by providing the fins 22a to 22d on the surface of the plate 20 facing the coating film 11, the irregular airflow 8 generated as the long support 10 coated with the coating liquid travels is the solvent. It is possible to reduce the influence of uneven evaporation rate. That is, the air flow 8 generated in the traveling direction is prevented from entering the gap space G between the plate 20 and the coating film 11 by the fins 22a, and stable drying is performed without being affected by the air flow 8. Can do. In addition, it is assumed that an air flow is generated in the gap space G between the plate 20 and the coating film 11, but they are prevented from affecting a wide range by the fins 22 b and 22 c, and stable drying is achieved. It can be carried out. Further, by providing the fins 22a to 22d, it is possible to satisfactorily reduce the influence of the space G between the plate 20 and the coating film 11 from the surrounding environment.

  The fins 22a to 22d may be arranged at equal intervals in the traveling direction of the elongated support 10, and an arrangement interval in the vicinity of the end portion of the plate 20 and an arrangement interval in the vicinity of the center portion of the plate 20 are set. It may be different. That is, in the vicinity of these end portions (particularly, in the vicinity of the inlet corresponding to the left side of the drawing), the surrounding air is easily trapped when each portion of the elongated support 10 having the coating film 11 enters the lower space of the plate 20. However, by arranging the fins at a relatively short pitch in the vicinity of the end portion, the effect of preventing the entrainment of the airflow can be enhanced. Further, as shown in FIG. 4, it is preferable that the fins 20 a and 20 d on the end side among the plurality of fins 22 a to 22 d are provided in alignment with the position of the end surface 20 e of the plate 20. As a result, the intrusion of the airflow 8 can be prevented at the end of the plate 20.

As in the configuration of FIG. 1, in order to control the evaporation rate of the solvent, the plate 20 is formed so as to exhibit a uniform thermal conductivity, and the temperature of the plate 20 (particularly the coating) is controlled by a temperature control unit 25 including a heat source. The temperature of the surface facing the surface) is controlled to be equal to or higher than the dew point of the solvent. Accordingly, the evaporation rate can be arbitrarily set within a range of 0.1 g / m ² · s or less while preventing condensation of the solvent vapor in the gap space G between the plate 20, the coating film 11, and the fins 22 a to 22 d. It becomes possible to adjust. Moreover, it can also comprise so that the temperature of the board 20 may be controlled separately for every partial space | gap space partitioned off by each fin 22a-22d, In that case, it is possible to adjust the drying state of a coating liquid more highly. is there. In the case of such divided control, the temperature sensor 26 is also provided for each partial space (divided space), and the temperature adjustment function is particularly enhanced by performing temperature feedback control for each zone. Further, the lower surface of the plate 20 may be formed in a wave shape instead of the fin. In this case, a plurality of wave structures each extending in a direction substantially perpendicular to the traveling direction of the long support 10 are formed in a long shape. What is necessary is just to make it arrange in parallel with the running direction of the support body 10. That is, although the formation of fins as shown in FIG. 4 is a preferred embodiment, generally, a plurality of convex structures extending in a direction substantially perpendicular to the running direction of the elongated support 10 are substantially parallel to the lower surface of the plate 20. By arranging, it is possible to obtain the effect of preventing the entrainment of airflow.

  By the coating / drying process as described above, the coating film 11 can be formed as an optical functional layer having an optical function, for example. And the optical film and polarizing plate used for an image display apparatus can be formed as a structure where the said optical functional layer was laminated | stacked. That is, the drying step described above is particularly useful for forming an optical functional layer laminated on an optical film or a polarizing plate.

  A polarizing plate is comprised as a structure which provided the protective sheet and the other optical film on the single side | surface or both surfaces of the polarizer which consists of a dichroic substance containing polyvinyl alcohol film etc., for example.

  Various types of polarizers can be used without any particular limitation. For example, hydrophilic materials such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, ethylene / vinyl acetate copolymer partially saponified films, etc. Uniaxially stretched by adsorbing a dichroic substance such as iodine or a dichroic dye on a conductive polymer film, polyene-based blended films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride . Among these, a polarizer comprising a polyvinyl alcohol film and a dichroic substance such as iodine is preferable.

  When the protective sheet provided on one or both sides of the polarizer is formed as the coating film 11 in the embodiment of the present invention, the material thereof is transparency, mechanical strength, thermal stability, moisture shielding, isotropic The thing excellent in etc. is preferable. For example, polyester polymers such as polyethylene terephthalate (PET) and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene copolymer (AS resin) And styrene-based polymers such as the above, and polycarbonate-based polymers. Polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like are also examples of the polymer that forms the protective sheet.

  The protective sheet can also be formed as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylurethane, epoxy, or silicone. In this case, the above-described drying method is performed immediately after the coating liquid exhibiting the thermosetting action or the ultraviolet curing action is applied to the elongated support (polarizer) 10 by the coating apparatus 30 and before entering the drying apparatus 40. By using it, a stable cured layer without unevenness can be obtained.

  Moreover, the above polarizing plates are used by laminating various optical functional layers in practical use. And the drying method mentioned above can be used also when laminating | stacking an optical function layer.

  The optical functional layer is not particularly limited. For example, the surface of the protective sheet on which the polarizer is not provided is a surface intended for hard coat treatment, antireflection treatment, sticking prevention, diffusion or antiglare. For example, the alignment liquid crystal layer may be laminated for the purpose of processing or viewing angle compensation. In addition, an optical functional layer used for forming an image display device such as a reflection plate, a semi-transmission plate, a retardation plate (including a wave plate (λ plate) such as 1/2 or 1/4), a viewing angle compensation layer, and the like is provided. A layer or a laminate of two or more layers can be mentioned. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is laminated on a polarizing plate, an elliptical polarizing plate or a circular polarizing plate in which a retardation plate is laminated, and a viewing angle compensation layer are laminated. A polarizing plate formed by laminating a wide viewing angle polarizing plate or a brightness enhancement layer is preferable.

  The viewing angle compensation layer is an optical functional layer for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the image display device is viewed from a slightly oblique direction rather than perpendicular to the screen. Examples of the wide viewing angle polarizing plate in which such a viewing angle compensation layer is laminated include a retardation plate, an alignment film such as a liquid crystal polymer, and a transparent substrate on which an alignment layer such as a liquid crystal polymer is supported. A normal retardation plate uses a birefringent polymer film uniaxially stretched in the plane direction, whereas a retardation plate used as a viewing angle compensation film has a biaxially stretched biaxially stretched film. Refractive polymer film, biaxially stretched film such as a polymer with birefringence with a controlled refractive index in the thickness direction, or a uniaxially stretched in the plane direction and also stretched in the thickness direction, etc. Is used. Examples of the inclined alignment film include a film obtained by bonding a heat shrink film to a polymer film and stretching or / and shrinking the polymer film under the action of the contraction force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. As the raw material polymer for the phase difference plate, an appropriate material for the purpose of preventing coloring or the like due to a change in the viewing angle based on the phase difference of the liquid crystal cell or expanding the viewing angle for good viewing can be used.

  In addition, an optical compensation position in which a liquid crystal polymer alignment layer, in particular an optically anisotropic layer composed of a discotic liquid crystal polymer gradient alignment layer, is supported by a triacetylcellulose film because it achieves a wide viewing angle with good visibility. A phase difference plate can be preferably used. The drying method can be applied to the formation of a viewing angle compensation layer exhibiting this type of optical compensation function. For example, when a coating liquid containing a liquid crystalline discotic compound is applied to a long triacetyl cellulose film and the coating film is dried, the above-described drying method can be applied, thereby reducing the appearance unevenness. A phase difference plate can be obtained.

  The polarizing plate on which the brightness enhancement layer is laminated is usually provided on the back side of the liquid crystal cell. The brightness enhancement layer reflects linearly polarized light with a predetermined polarization axis or circularly polarized light in a predetermined direction when natural light is incident due to the backlight of an image display device such as a liquid crystal display device or reflection from the back side, and transmits other light. As shown in the figure, a polarizing plate with a brightness enhancement layer is made to receive light from a light source such as a backlight to obtain transmitted light in a predetermined polarization state, and to reflect light without transmitting light other than the predetermined polarization state. . The light reflected from the film surface of such a brightness enhancement layer is further inverted through a reflective layer or the like provided behind the brightness enhancement layer and re-incident on the brightness enhancement layer, and part or all of the light is reflected in a predetermined polarization state. In addition to increasing the amount of light that is transmitted and transmitted through the brightness enhancement layer, the polarized light that is difficult to be absorbed by the polarizer is supplied to increase the amount of light that can be used for image display, thereby improving the brightness. That is, when light is incident through the polarizer from the back side of the liquid crystal cell with a backlight or the like without using a brightness enhancement layer (brightness enhancement film), the polarization direction does not coincide with the polarization axis of the polarizer. Most of the light is absorbed by the polarizer and does not pass through the polarizer. That is, although depending on the characteristics of the polarizer used, approximately 50% of the light is absorbed by the polarizer, and the amount of light that can be used for image display is reduced accordingly, resulting in a dark image. In the brightness enhancement layer, light having a polarization direction that is absorbed by the polarizer is not incident on the polarizer, but is reflected once by the brightness enhancement layer, and further inverted through a reflection layer provided on the rear side thereof. Repeatedly re-enter the brightness enhancement layer, and only the polarized light whose polarization direction is reflected and reversed between the two is allowed to pass through the polarizer is transmitted to the polarizer. Therefore, light such as a backlight can be efficiently used for image display, and the screen can be brightened.

  In addition, a diffusion plate can be provided between the brightness enhancement layer and the reflective layer. The light in the polarization state reflected by the brightness enhancement layer goes to the reflection layer or the like, but the installed diffuser plate diffuses the light passing therethrough at the same time and simultaneously cancels the polarization state to make it a non-polarization state. That is, the original natural light state is restored. The light in the non-polarized state, that is, the natural light state is directed toward the reflection layer and the like, is reflected through the reflection layer and the like, and passes through the diffusion plate again and reenters the brightness enhancement layer. By providing the diffusion plate that returns to the original natural light state, the brightness of the display screen can be maintained, and at the same time, the unevenness of the brightness of the display screen can be reduced and a uniform bright screen can be provided. By providing the diffuser plate that returns to the original natural light state, the number of repetitions of the initial incident light is moderately increased, and a uniform bright display screen can be provided in combination with the diffusion function of the diffuser plate.

  As the brightness enhancement layer exhibiting the optical function as described above, for example, a cholesteric liquid crystal polymer alignment film or a circularly polarized light that is either counterclockwise or clockwise, such as a film substrate on which the alignment liquid crystal layer is supported. Appropriate ones such as those showing a characteristic of reflecting other light and transmitting other light can be used. The above drying method can also be applied to the formation of this type of brightness enhancement layer. For example, when applying a coating liquid for forming an oriented liquid crystal layer on a long film substrate and drying the coating film, the above-described drying method can be applied, thereby reducing appearance unevenness. A brightness enhancement layer can be formed.

  In addition, as a brightness enhancement layer, for example, a dielectric multilayer thin film or a multilayer laminate of thin film films having different refractive index anisotropy exhibits characteristics of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light. In this type of brightness enhancement layer, the transmitted light can be efficiently transmitted while suppressing the absorption loss due to the polarizing plate by allowing the transmitted light to enter the polarizing plate without changing the polarization axis. become. Therefore, this type of brightness enhancement layer may be laminated on the optical functional layer formed by the drying method described above to form a multilayer structure polarizing plate.

  On the other hand, a brightness enhancement layer of a type that transmits circularly polarized light, such as a cholesteric liquid crystal layer, can be directly incident on a polarizer, but from the point of suppressing absorption loss, the circularly polarized light is linearly polarized through a retardation plate. It is preferable to make it enter into a polarizing plate. Note that circularly polarized light can be converted to linearly polarized light by using a quarter wave plate as the retardation plate.

  A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region exhibits, for example, a retardation layer that functions as a quarter-wave plate for monochromatic light with a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superposing a retardation layer, for example, a retardation layer functioning as a half-wave plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement layer may be composed of one or more retardation layers. Further, such a retardation layer can also be formed by forming a coating film by applying a coating liquid and then drying the coating film, thereby forming a retardation layer with less appearance unevenness. Can do.

  When forming various optical functional layers in this manner, a coating solution is formed by applying a coating solution to a long support (film or the like) serving as a base material, and the coating film is dried by the drying method described above. Thus, an optical functional layer without unevenness is formed. Therefore, a high-quality optical film without unevenness can be obtained by laminating such an optical functional layer on the optical film. Furthermore, when this optical film is laminated on the polarizing plate, a high-quality polarizing plate without unevenness can be obtained.

  Moreover, the polarizing plate may consist of what laminated | stacked the polarizing plate and the optical function layer of 2 layers or 3 layers or more. Therefore, a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which a reflective polarizing plate, a semi-transmissive polarizing plate and a retardation plate are combined may be used. Further, the optical film or the polarizing plate may be provided with at least one optical functional layer formed by the drying method described above. Therefore, in an optical film or polarizing plate having a multilayer structure, a polarizing plate in which at least one layer is formed by the above-described drying method and the other layers are formed by a conventional method may be used.

  Moreover, when laminating | stacking the above optical function layers on a protective sheet, the lamination | stacking timing may be before bonding a protective sheet to a polarizer, and may be after bonding. When laminating an optical functional layer by applying a coating solution to a protective sheet, the protective sheet alone or a laminate of a polarizer and a protective sheet is used as a long support 10, and this long support is used. Immediately after the coating liquid having an optical function is applied to the coating apparatus 30 with respect to 10 and before the coating film enters the drying apparatus 40, the drying method described above can be employed. And by the drying method, stable drying can be performed and an optical functional layer without unevenness is formed.

  Further, when the optical film having the optical functional layer as described above is laminated on the polarizing plate, the optical film and the polarizing plate are separately produced, and these are mutually connected in the manufacturing process of the image display device such as a liquid crystal display device. It can also be formed by a method of laminating by laminating, but the one in which the optical film is laminated on the polarizing plate in advance has excellent quality stability and assembly work, etc. There is an advantage of improving efficiency.

  The polarizing plate obtained as described above can be preferably used for forming a liquid crystal display device. For example, it can be used in a reflection type, semi-transmission type, or transmission / reflection type liquid crystal display device in which a polarizing plate is disposed on one or both sides of a liquid crystal cell. The liquid crystal cell substrate may be a plastic substrate or a glass substrate. The liquid crystal cell forming the liquid crystal display device is arbitrary, for example, an active matrix drive type typified by a thin transistor type, a simple matrix drive type typified by a twist nematic type or a super twist nematic type, etc. Any type of liquid crystal cell may be used. A polarizing plate having a structure in which optical function layers formed by the drying method are laminated is used in a liquid crystal display device, whereby high-quality image display without unevenness is realized in the liquid crystal display device.

  Further, the polarizing plate obtained as described above is not limited to the liquid crystal display device, and can be preferably used for an image display device such as an organic EL display device or a plasma display device.

  And by using the polarizing plate which laminated | stacked the optical function layer formed by the drying method mentioned above for an image display apparatus, while being able to implement | achieve an image display apparatus without an external appearance nonuniformity, such an image display apparatus is It can be obtained stably. In addition, high-quality image display without unevenness is realized in the image display device.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples and comparative examples.

Example 1.
Viscosity 6 mPa · s (measuring device: Rheometer RS manufactured by Haake Co., Ltd.) obtained by diluting an ultraviolet curable liquid crystal monomer to a solid content of 30% on a PET film (thickness 75 μm) with a die coater. The coating solution of -1) is applied so that the thickness after drying is 4.0 μm, and this coating film is arranged in a plate 20 provided with a certain gap G between the coating film and the coating film as shown in FIG. The sheet having the optical functional layer was obtained by passing through the formed zone, drying with hot air at 70 ° C., and curing by ultraviolet irradiation (integrated light amount 300 mJ / cm ² ). At this time, when the evaporation rate of the coating liquid in the zone where the plate 20 was arranged was measured based on the gas concentration distribution of the generated steam and the air volume (wind speed), it was 0.03 g / m ² · s.

Here, in the batch-type drying method, the inventors have confirmed that there is a correlation between the evaporation rate and the gas concentration distribution of the generated steam. By applying the coating solution onto the electronic balance in batch mode and measuring the change in weight over time while monitoring the gas concentration and wind speed, the relationship (calibration curve) between the gas concentration and wind speed and the drying speed is calculated in advance. In this embodiment, the evaporation rate was calculated using this relationship. Specifically, a hole is formed in the central portion of the plate 20 in the flow direction of the base material and in the central portion in the width direction of the base material, and a gas concentration measuring device (portable VOC monitor manufactured by Yokogawa Electric Corporation) is provided in the hole. In addition, the gas concentration and wind speed are measured by arranging each sensor of the wind speed measuring apparatus (Anemo Master manufactured by Nippon Kanomax Co., Ltd.), and the evaporation rate of 0.03 g / m ² · s is obtained from the relationship obtained in advance by the above method. I was asked.

  In this example, the wind direction was the same direction (forward direction) as the base material traveling direction, and the measured wind speed was 0.1 m / s.

Comparative Example 1
In Example 1, a coating film was formed under the same conditions as above except that the plate 20 was removed. At this time, when the evaporation rate of the coating liquid in the portion where the plate 20 was removed was measured in the same manner as described above, it was 0.12 g / m ² · s.

  In this comparative example, each sensor of the gas concentration measuring device and the wind speed measuring device was installed so as to be at the same position as in Example 1, and was installed at a position of 5 mm from the coating film surface. And when the wind speed at this time was confirmed, it was the same as that of Example 1.

Evaluation 1.
FIG. 5 shows the average value of the coating film thickness of Example 1 and Comparative Example 1, and FIG. 6 shows the dispersion of the coating film thickness. As shown in FIG. 5, the average value of the coating film does not change between Example 1 and Comparative Example 1. However, as shown in FIG. It was found that an optical functional layer having a small thickness variation can be formed. Therefore, immediately after the application of the coating liquid, the drying is performed in a state where the evaporation rate is kept at 0.1 g / m ² · s or less. An optical functional layer having a small size is formed.

Further, when the thickness dispersion is 0.03 μm or less, the uneven appearance of the film becomes inconspicuous. Therefore, a good optical film can be obtained by drying at an evaporation rate of 0.1 g / m ² · s or less as in Example 1. Can be obtained.

Example 2
After drying a coating solution (viscosity 250 mPa · s), which is obtained by diluting a thermosetting resin to a solid content of 10% with an organic solvent (MIBK (methyl isobutyl ketone)) on a TAC film (thickness 85 μm) with a die coater. The coating film is applied so as to have a thickness of 3.0 μm, and this coating film is passed through a zone in which a plate 20 having a certain gap G is provided between the coating film and the coating film as shown in FIG. It dried with the hot air of 100 degreeC with the apparatus 40, and the sheet | seat which has an optical function layer was obtained. At this time, when the evaporation rate of the coating liquid in the zone where the plate 20 is arranged is measured in the same manner as in Example 1 based on the gas concentration distribution of the generated steam and the air volume (wind speed), 0.06 g / m ² · s.

  In this example, the apparatus for measuring the viscosity of the coating solution was the same as in Example 1, and when the wind speed at this time was confirmed, it was the same as in Example 1.

Comparative Example 2
In Example 2, a coating film was formed under the same conditions as above except that the plate 20 was removed. At this time, when the evaporation rate of the coating liquid in the portion where the plate 20 was removed was measured in the same manner as described above, it was 0.15 g / m ² · s.

  In this comparative example, each sensor of the gas concentration measuring device and the wind speed measuring device was installed at the same position as in Example 2. And when the wind speed at this time was confirmed, it was 0.1 m / s.

Evaluation 2.
FIG. 7 shows the average value of the coating film thickness of Example 2 and Comparative Example 2, and FIG. 8 shows the dispersion of the coating film thickness. As shown in FIG. 7, the average value of the coating film does not change between Example 2 and Comparative Example 2. However, as shown in FIG. It was found that an optical functional layer having a small thickness variation can be formed. Therefore, immediately after the application of the coating liquid, the drying is performed in a state where the evaporation rate is kept at 0.1 g / m ² · s or less. An optical functional layer having a small size is formed. Moreover, also in Example 2, thickness dispersion is 0.03 micrometer or less, and it is a good optical film with which appearance nonuniformity is not conspicuous.

It is a figure which shows the structure which provided the board in the coating film formation side of the elongate support body. It is a figure which shows the structure which provided the board in both the coating film formation side and non-formation side of a elongate support body. It is a figure which shows the structure which provided the surrounding board so that a elongate support body might be enclosed immediately after a coating liquid was apply | coated. It is a figure which shows the structure which provided the flat fin in the board in the structure of FIG. It is a figure which shows the average value of the coating film thickness of Example 1 and Comparative Example 1. It is a figure which shows dispersion | distribution of the coating film thickness of Example 1 and Comparative Example 1. FIG. It is a figure which shows the average value of the coating film thickness of Example 2 and Comparative Example 2. It is a figure which shows dispersion | distribution of the coating film thickness of Example 2 and Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Elongate support body 11 Coating film 20, 20a, 20b Plate 20c Enclosure plate 22a-22d Fin 25, 25a, 25b Temperature control part 30 Coating apparatus 40 Drying apparatus

Claims (10)

In a method for drying a coating film formed by applying a coating solution to a traveling long support,
On the downstream side of the coating liquid coating apparatus, a gap is provided between the coating film and a plate parallel to the long support and provided with fins on the surface of the long support, and the long film During the period from when the coating solution is applied to the long support until the elongate support enters the drying apparatus, the solvent evaporation rate is kept at 0.1 g / m ² · s or less for drying. The drying method of the coating film to perform. The method for drying a coating film according to claim 1, wherein a pitch of the fins is shorter than a central portion at an end portion in the traveling direction of the elongated support in the plate. The plate is disposed with a gap of 10 mm or less between the coating film and the elongated support in parallel with the elongated support from when the coating solution is applied until the elongated support enters the drying apparatus. The method for drying a coating film according to claim 1, wherein the drying is performed while the coating film travels through the gap. The method for drying a coating film according to any one of claims 1 to 3, wherein the temperature of the plate is controlled to be equal to or higher than the dew point of the vapor of the coating solution.   The method for drying a coating film according to claim 1, wherein the coating film is formed as an optical functional layer having an optical function. In a method for drying a coating film formed by applying a coating solution to a traveling long support,
A plate having a width more than the plate width of said elongated support, together with our Ku disposed along the travel path of said elongated support downstream of the coating apparatus of the coating liquid, the long A plurality of convex structures extending in a direction substantially perpendicular to the traveling direction of the shaped support are arranged substantially parallel to the lower surface of the plate along the traveling direction ,
The long support from the time when the coating film is formed by the coating apparatus to the time when the long support enters the drying apparatus, the coating film is spaced from the plate surface of the plate by 10 mm or less. A method of drying a coating film, wherein the coating film is dried at least in part in the gap by running along the running path while being opposed to each other. The method for drying a coating film according to claim 6, wherein the pitch of the convex structure is shorter than the central portion at the end portion of the plate in the traveling direction of the elongated support. The plate is provided as a first plate, and a second plate facing the surface opposite to the side where the coating film is present on both surfaces of the elongated support member with a gap therebetween is the first plate. Provided approximately parallel to the plate,
The elongate support from the formation of the coating film until the elongate support enters the drying device is caused to travel through the gap between the first and second plates. The drying method of the coating film of Claim 6.   7. The method for drying a coating film according to claim 6, wherein the plate is provided as one surface of a flat tunnel structure surrounding a travel path of the elongated support.   The method for drying a coating film according to claim 6, wherein the temperature of the plate is adjusted to be equal to or higher than a dew point of the vapor of the coating solution.

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