JP2005081257A - Method and apparatus for drying coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for drying a coating film by which drying nonuniformity in the drying of the coating film formed by applying a coating liquid containing an organic solvent on a web is remarkably reduced. <P>SOLUTION: In the method for drying the coating film formed by applying the coating liquid containing the organic solvent on the travelling long-sized web 12, a drying zone 26 surrounding the coating film surface travelling right after the application is formed. In the drying zone 26, drying wind flowing in one direction from one end side to another side in the web width direction is produced. In the drying method for the coating film, low temperature drying by keeping the temperature of the drying wind to 20-30°C is carried out before 10% organic solvent contained in the coating film is dried until 80% organic solvent contained in the coating film is dried. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for drying a coating film, and in particular, a coating film formed by applying a coating solution containing an organic solvent to a traveling long support (hereinafter referred to as a web) so that there is no unevenness in drying. The present invention relates to a drying method and apparatus for drying.

  When drying a coating film formed by applying an organic solvent-based coating solution containing an organic solvent to a continuously running web, the organic solvent has a high evaporation rate, and thus drying unevenness occurs particularly in the initial drying immediately after coating. There is a problem that it is easy. For example, in the production of an optical compensation sheet using an organic solvent-based coating solution, as shown in FIG. 6, in the drying process of the coating film, a broad patchy drying unevenness A (indicated by a thin line) and a sharp patchy shape. Two types of dry unevenness B (indicated by a thick line) occur, and there is a problem that the yield of the product is lowered in some cases.

  As a general countermeasure against drying unevenness that occurs in the initial drying of such organic solvent-based coating films, the viscosity of the coating solution can be increased by increasing the concentration of the coating solution or adding a thickener. Thus, there is a method of preventing the occurrence of drying unevenness by suppressing the flow of the coating film surface immediately after coating by the drying air. As another method, there is a method of preventing the occurrence of drying unevenness by using a high-boiling solvent and causing a leveling effect even when a flow of the coating film surface immediately after coating occurs due to drying air. However, the method of increasing the viscosity of the coating solution by increasing the concentration of the coating solution or adding a thickener is to apply ultra-thin precision coating that forms an ultra-thin coating film by high-speed coating. There is a disadvantage that it cannot be done. Further, since the limit coating speed (the limit of the coating speed at which stable coating can be performed) decreases as the coating solution viscosity increases, there is a drawback that high-speed coating becomes impossible as the viscosity increases, and production efficiency is extremely deteriorated. On the other hand, the method using a high boiling point solvent has the disadvantage that the drying time is increased and the amount of residual solvent remaining in the coating film is increased, and the production efficiency is deteriorated because the drying time increases accordingly.

  For this reason, in Patent Document 1, as a method for drying an organic solvent-based coating film, the web is rushed into a drying zone having a heating means within 5 seconds after coating, and on the coating film in the space up to the rushing of the drying zone. Although it has been proposed to keep the wind speed at 1 m / second or less, it is not sufficient as a countermeasure against drying unevenness.

Therefore, the present applicant provides a drying zone immediately after coating to surround the coating film surface and dry the coating film with one-direction drying air flowing from one end side to the other end side in the width direction of the support. It was proposed to suppress the above (Patent Document 2).
JP 2000-157923 A JP 2001-170547 A

  However, even the drying method of Patent Document 2 does not satisfy the strict requirement for recent drying unevenness, and further improvement is desired.

  The present invention has been made in view of such circumstances, and a coating film capable of remarkably reducing drying unevenness at the time of drying of a coating film formed by coating a coating liquid containing an organic solvent on a support. It is an object to provide a drying method and apparatus.

  The present inventor provided a drying zone immediately after coating to surround the four directions of the support, and dried the coating film with one-direction drying air flowing from one end side to the other end side in the support width direction. However, drying unevenness may occur especially in the width direction of the support, and the countermeasures have been intensively studied. As a result, until the 80% by weight of the organic solvent contained in the coating film is completely dried, the above-described one-way drying air is not sufficient. It was found that it is important to combine low temperature drying in which the temperature was maintained in the range of 20 ° C to 30 ° C. Further, in conjunction with this low temperature drying, the wind speed of the drying air is gradually reduced as it goes from the upstream side to the downstream side in the running direction of the support, and a surfactant is applied to the coating solution in an amount of 0.05-0. It has been found that the addition in the range of 50% by weight and the rectification of the unidirectional drying air are effective in suppressing the drying unevenness. The present invention has been made based on such findings.

  Claim 1 of the present invention is the drying of a coating film formed by applying a coating solution containing an organic solvent to a traveling long support to achieve the above object, immediately after the coating, A drying method for a coating film, in which a drying zone is formed surrounding four directions of a traveling support, and in the drying zone, a unidirectional flow of drying air flowing from one end to the other end in the width direction of the support is generated. In this case, the drying is performed at a low temperature while maintaining the temperature of the drying air in the range of 20 ° C. to 30 ° C. until 80% by weight of the organic solvent contained in the coating film is completely dried.

  Here, the drying zone surrounding the four directions of the support is a tunnel-shaped drying zone surrounding the four directions of the width direction of the support and the front and back directions of the support. Moreover, the weight% said here is represented with respect to the weight of all the organic solvents, when two or more types of organic solvents are contained. Further, the one-way flow flowing from one end side to the other end side in the support width direction means a value of 80% or more of the total amount of dry air supplied by the wind speed component in the support width direction at any position in the drying zone. Say to show.

  According to the first aspect of the present invention, since the drying zone is provided immediately after the coating, the coating in a state in which the nonuniform wind from the outside of the drying zone contains a large amount of organic solvent and the coating liquid easily flows. A dry environment in which the organic solvent evaporated from the coating film surface covers the coating film surface can be formed while preventing it from hitting the film surface. In this dry environment, when uniform drying air flowing in one direction flowing from one end to the other end in the width direction of the support is generated, the concentration of the organic solvent in the vicinity of the coating film surface is always maintained constant. Since drying is performed, general drying unevenness is suppressed. And until 80 weight% of the organic solvent contained in the coating film is completely dried, the temperature of the drying air in the unidirectional flow in the width direction of the support is maintained at a low temperature of 20 ° C to 30 ° C. Further, it is possible to reduce drying unevenness that occurs in the width direction of the support that cannot be suppressed by only one-direction flow of drying air, particularly sharp drying unevenness. This is because when the temperature of the drying air exceeds 30 ° C., the evaporation rate of the organic solvent is too fast, and thus the distribution (fluctuation) of evaporation of the organic solvent occurs on the coating film surface in the width direction of the support. This is considered to be because the drying distribution is likely to occur, and can be solved by setting the upper limit temperature of the drying air to 30 ° C. In this case, if the temperature of the drying air is 30 ° C. or less, drying unevenness can be suppressed, but if the temperature of the drying air is less than 20 ° C., a brushing failure in which the coating surface is condensed is likely to occur. Therefore, it is important to maintain the temperature of the drying air at a low temperature of 20 ° C to 30 ° C.

  In this case, it is preferable that the coating film reaches the drying zone before 10% by weight of the organic solvent contained in the coating film is dried. This is because even if 10% of the organic solvent contained in the coating film evaporates and the present invention is started, the effect of suppressing drying unevenness is reduced, and the present invention is stopped before 80% of the organic solvent evaporates. This is because there is a possibility that drying unevenness may occur in subsequent drying under different conditions.

  According to a third aspect of the present invention, in the first or second aspect, in the drying zone, the wind speed of the drying air gradually decreases from the upstream side to the downstream side in the support running direction. This is because, in the drying with the drying air, even if the drying air is slightly upstream at the upstream side in the running direction of the support, that is, the first half of the drying zone has a slightly high wind speed, drying unevenness is caused if the drying air is uniform and controlled like a one-way air flow. Since it does not remain, the lack of drying due to the low temperature of the drying wind is compensated for by increasing the wind speed. In the downstream side of the support traveling direction where the drying unevenness is fixed when it occurs, that is, in the latter half of the drying zone, it is important to reduce the drying air so as not to generate drying unevenness due to the drying air. . Therefore, by making the wind speed of the drying air gradually decrease from the upstream side to the downstream side in the support running direction, it is possible to suppress the occurrence of drying unevenness and to generate particularly sharp unevenness among the drying unevenness. Can be suppressed.

  A fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein a surfactant is added to the coating solution in a range of 0.05 to 0.50% by weight (solid content / coating solution). And This is because the addition of the surfactant helps to reduce the rate of change of the surface tension that changes as the temperature of the coating film increases. That is, when a temperature difference occurs in the coating film during drying of the coating film, fluid movement of the coating liquid occurs due to the temperature difference and causes drying unevenness. By containing it in the range of 50% by weight, it is possible to reduce the force that causes fluid motion as a result of the temperature difference, and thus it is possible to suppress drying unevenness. In particular, it is effective in suppressing drying unevenness, particularly broad unevenness, in the initial stage of drying when the content of the organic solvent is large and the coating liquid easily flows. In this case, unless the addition of the surfactant is 0.05% by weight or more, the effect of reducing the change rate of the surface tension that changes as the temperature of the coating film increases is hardly exhibited, and the addition of the surfactant is 0.50. This is because if it exceeds wt%, coating streaks due to foaming of the coating solution tend to occur. The solid content / coating liquid referred to here is the weight ratio of the surfactant solid content to the coating liquid.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the support has a layer that becomes an alignment film by rubbing a previously applied alignment film forming resin. The coating liquid contains a liquid crystalline discotic compound. This is due to the use of the coating film drying method of the present invention, and two types of drying unevenness, which are broad unevenness and sharp unevenness of drying, which are likely to occur when the coating film is dried in the production of an optical compensation sheet. It is because it can suppress effectively.

  According to a sixth aspect of the present invention, in order to achieve the above object, the coating film formed by applying a coating solution containing an organic solvent by a coating machine to a traveling long support is formed immediately after the coating. Forming a drying zone that surrounds the coating film surface of the traveling support, and in the drying zone, a coating film that generates a one-way flow of drying air flowing from one end side to the other end side in the width direction of the support is generated. In the drying apparatus, unidirectional airflow generating means for generating the unidirectionally flowing drying air and air temperature control means for controlling the temperature of the drying air in a range of 20 ° C to 30 ° C were provided. It is characterized by.

  The sixth aspect specifically shows the configuration of the apparatus for carrying out the drying method according to the first aspect.

  A seventh aspect of the present invention is the method according to the sixth aspect, wherein the drying zone is partitioned by a partition plate orthogonal to the traveling direction of the elongated support to form a plurality of divided zones, and the upstream side in the traveling direction of the support is formed. A wind speed control means is provided for controlling the one-way air flow generating means so that the wind speed of the drying air gradually decreases from the divided zone to the downstream divided zone. In this way, by causing the wind speed of the drying air to gradually decrease from the upstream side to the downstream side in the support running direction, it is possible to suppress the occurrence of uneven drying and to partition the drying zone into a plurality of divided zones. By forming, the wind speed can be controlled with high accuracy for each divided zone. As a mode of gradually decreasing the wind speed of the drying wind, it may be continuously decreased or decreased stepwise.

  According to an eighth aspect of the present invention, in the sixth or seventh aspect, at least one of the air supply nozzle and the exhaust nozzle of the one-way airflow generating means is provided with a rectifier that rectifies the dry air supplied or exhausted. It is characterized by. Thereby, since the flow of the drying air which flows through the coating film surface can be made more uniform in one direction, drying unevenness can be further suppressed. With this rectifier, it is preferable that the measured value of the wind speed in the width direction of the support shows a value of 90% or more of the average wind speed of the entire dry air volume supplied at any position in the drying zone.

  As described above, according to the coating film drying method and apparatus of the present invention, it is possible to remarkably reduce drying unevenness when drying a coating film formed by applying a coating liquid containing an organic solvent to a support. it can.

  Hereinafter, preferred embodiments of a coating film drying method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a plan view of a coating / drying apparatus incorporating a coating film drying apparatus of the present invention as viewed from above, and FIG. 2 is a cross-sectional view taken along the line AA of FIG.

  As shown in FIGS. 1 and 2, the coating / drying apparatus 10 is mainly a coating machine 14 that applies a coating solution containing an organic solvent to a traveling long support 12 (hereinafter referred to as “web 12”). And a drying device 16 that passes through the web 12 coated with the coating solution and dries the coating film. The drying device 16 is provided immediately after the coating machine 14.

  For example, a bar coating device including a wire bar 14A can be used as the coating machine 14, and a coating liquid is applied to the lower surface of the web 12 that is supported by a plurality of support rollers 20, 22, and 24 and applied. A film is formed. The thickness of the coating film is a wet thickness in the range of 1 μm to 50 μm, preferably in the range of 2 μm to 40 μm, particularly preferably in the range of 2 μm to 10 μm. The viscosity of the coating solution is preferably 20 mPas / second or less. The traveling speed of the web 12 is preferably in the range of 5 to 100 m / min, particularly preferably in the range of 20 to 80 m / min.

  The drying device main body 18 of the drying device 16 is provided immediately after the coating machine 14 and is formed in a long rectangular box shape along the coating film surface side (the lower surface side of the web) of the traveling web 12. Of each side, the side on the coating film side (the upper side of the box) is cut off. Further, a shielding lid 30 is placed on the opposite side of the drying apparatus main body 18 across the web 12 so that the stable running of the web 12 is not hindered by air from the drying apparatus 16 such as air-conditioning wind. . Then, the web 12 coated with the coating liquid by the coating machine 14 is carried into the drying zone 26 from the inlet opening 18A of the drying device 16, and is carried out from the outlet opening 18B. Thereby, the drying zone 26 surrounding the four directions of the running web 12 is formed. The drying zone 26 divides the drying apparatus main body 18 by a plurality of partition plates 28, 28... Orthogonal to the traveling direction of the web 12, thereby dividing a plurality of divided zones 26 A, 26 B, 26 C, 26 D, 26 E, 26 F, 26 G ( In this embodiment, the image is divided into seven divided zones. In this case, the distance between the upper end of the partition plate 28 dividing the drying zone 26 and the coating film surface formed on the web 12 is preferably in the range of 0.5 mm to 20 mm, more preferably in the range of 1 mm to 15 mm. .

  In addition, as shown in FIG. 1, unidirectional airflow generation means 32 is provided in each of the divided zones 26 </ b> A to 26 </ b> G of the drying zone 26. In the unidirectional airflow generation means 32, an air supply duct 36 is branched and connected to air supply nozzles 34 </ b> A to 34 </ b> G provided on one side of both sides of the drying apparatus main body 18, and an air supply fan 38 is provided in the air supply duct 36. It is done. Further, exhaust nozzles 40A to 40G are provided on the other side of the both sides of the drying apparatus main body 18 so as to face the supply nozzles 34A to 34G, and an exhaust duct 42 is branched and connected to each of the exhaust nozzles 40A to 40G. An exhaust fan 44 is provided in the duct 42. A circulation duct 46 is connected from the middle of the exhaust duct 42 to the suction side of the air supply fan 38, and a fresh dry air introduction duct 48 is provided in the middle of the circulation duct 46. The air supply duct 36 is provided with an air temperature controller 41 for controlling the temperature of the dry air, and the temperature of the dry air blown from the air supply nozzles 34A to 34G is maintained in the range of 20 ° C to 30 ° C. It is controlled so that

  As shown in FIG. 3, each of the air supply nozzles 34 </ b> A to 34 </ b> G has a substantially rectangular shape in which the air outlet 33 is long in the running direction of the web 12, and is formed in a trumpet tubular shape whose diameter increases toward the air outlet 33. Is done. Further, a rectifier 35 is provided inside each of the air supply nozzles 34 </ b> A to 34 </ b> G, and the rectifier 35 is provided with a first perforated plate 35 </ b> A provided at the outlet 33 and a second perforation provided upstream of the outlet 33. And a perforated plate 35B. The opening of the hole of the first porous plate 35A is formed to be smaller than the opening of the hole of the second porous plate 35B, and the air is blown out from the outlet 33 between the first porous plate 35A and the second porous plate 35B. A pressure equalizing chamber 37 for dry air is formed. On the other hand, the exhaust nozzles 40A to 40G arranged to face the supply nozzles 34A to 34G are also provided with a rectifier 35, and a first perforated plate 35A is provided at the exhaust port 39 and on the downstream side of the exhaust port 39. A second porous plate 35B is provided. As a result, by driving the air supply fan 38 and the exhaust fan 44, each of the divided zones 26A to 26G is moved from one end side (air supply side) in the web width direction on the coating film surface as shown in FIG. Uniform drying air in one direction flowing on the other end side (exhaust side) is generated. A part of the exhaust gas containing the evaporated organic solvent from the coating film surface is circulated from the exhaust duct 42 through the circulation duct 46 and mixed with the dry air from the introduction duct 48. Thereby, since the dry wind containing an organic solvent is supplied to each division | segmentation zone 26A-26G, it can prevent that the rapid evaporation of the organic solvent from a coating film surface arises.

  In addition, as shown in FIG. 1, air supply valves 50 </ b> A to 50 </ b> G and air supply valves 52 </ b> A to 52 </ b> G are provided on the branched branch pipe of the air supply duct 36 and the branched branch pipe of the exhaust duct 42, respectively. The opening degree of the air valves 50A to 50G and the exhaust valves 52A to 52G is controlled by the controller 54. Then, the controller 54 controls each of the valves 50A to 50G and 52A to 52G so that the wind speed of the dry air gradually decreases from the upstream divided zone 26A in the web traveling direction to the downstream divided zone 26G. As a mode of gradually decreasing the wind speed of the drying wind, the wind speed may be continuously decreased from the upstream divided zone 26A to the downstream divided zone 26G, or the wind speed may be decreased stepwise.

  Further, the width of the drying apparatus main body 18 is formed so as to be larger than the width of the web 12, and an air conditioning portion in which open portions on both sides of the drying zone 26 are covered with an air conditioning plate 56 is provided. This wind control portion is configured to prevent a rapid flow of drying air from being generated in the drying zone 26 by securing a distance from the air supply port to the coating film end and a distance from the coating film end to the exhaust port. is there.

  Next, the operation of the drying apparatus 10 configured as described above will be described.

  Immediately after the coating liquid is applied to the web 12 supported by the support rollers 20, 22, and 24 with the wire bar 14 </ b> A of the coating machine 14, the coating film surface is dried by the drying device 16. This drying is preferably started immediately after coating and before 10% by weight of the organic solvent is dried. This is because even if 10% of the organic solvent contained in the coating film evaporates, the effect of suppressing drying unevenness is reduced even if the present invention is started.

  In this drying, the coating film surface immediately after coating is in a state sufficiently containing an organic solvent, and in the initial drying immediately after coating a coating solution containing the organic solvent as a solvent, due to the distribution (fluctuation) of evaporation of the organic solvent. A temperature distribution occurs on the coating film surface. This causes a distribution of surface tension, causing the coating liquid to flow within the coating film surface, resulting in uneven drying. Unevenness of drying occurs when the drying air hits the coating film surface, such as when the drying air merges or when a vortex is generated.

  From this, in order to suppress drying unevenness of the coating film surface at the time of drying, particularly at the initial drying, non-uniformity from the outside from the coating to the stop of the flow of the coating liquid on the coating film surface It is important to prevent the wind from hitting the coating film surface and to keep the organic solvent concentration in the vicinity of the coating film surface constant at all times.

  Therefore, in the present invention, the drying device 10 having the above-described configuration is provided to perform initial drying immediately after the coating liquid is applied to the web 12. That is, by forming the drying zone 26 immediately after coating, the nonuniform wind in the strength and direction outside the drying device 16 does not hit the coating film surface in a state where the organic solvent is large and the coating liquid easily flows. it can. Thereby, drying unevenness caused by the coating film surface being disturbed by the force of the wind hitting the coating film surface can be prevented, and uniform drying can be performed.

  Also, by providing the drying zone 26, a dry environment is formed in which the organic solvent evaporated from the coating film surface covers the coating film surface. By driving the air supply fan 38 and the exhaust fan 44 in this dry environment, each of the divided zones 26A to 26G is moved from one end side (supply side) to the other end side (exhaust side) in the web width direction. Dry air that flows in one direction is generated. Accordingly, the dry air containing the evaporated organic solvent is exhausted from the drying zone 26 and gradually dried while the coating film surface is covered with the organic solvent. In this case, if the exhaust amount is too large, the coating film surface is not uniformly covered with the organic solvent. Therefore, it is necessary to adjust the opening degree of the exhaust valves 52A to 52G so that the exhaust amount does not become too large. Thereby, since the organic solvent concentration in the vicinity of the coating film surface can be made uniform, the organic solvent can be uniformly evaporated from each part of the coating film surface. Therefore, drying unevenness caused mainly by the evaporation distribution of the organic solvent from the coating film surface can be prevented, and uniform drying can be performed. In this case, when the web 12 travels in the drying zone 26, the organic solvent concentration in the vicinity of the coating film surface on the inlet side and the outlet side of the drying zone 26 may be different, but the drying zone 26 is divided into a plurality of divided zones 26 </ b> A. It can be solved by dividing the image into ~ 26G. That is, the opening speeds of the supply valves 50A to 50G and the exhaust valves 52A to 52G in the respective divided zones 26A to 26G are controlled to adjust the wind speed of the dry air flowing through the divided zones 26A to 26G. Thus, the difference in the organic solvent concentration in the vicinity of the coating film surface on the inlet side and outlet side of the drying zone 26 can be eliminated.

  In the drying with the unidirectional drying air in the web width direction, the temperature of the drying air is maintained at a low temperature of 20 ° C. to 30 ° C. until 80% by weight of the organic solvent contained in the coating film is completely dried. . As a result, it is possible to reduce drying unevenness, particularly sharp drying unevenness, which occurs in the web width direction, which cannot be suppressed only by the unidirectionally flowing drying air. The unevenness of drying that occurs in the width direction of the web is caused by the distribution of surface tension due to the evaporation distribution (fluctuation) of the organic solvent, and is caused by the flow of the coating solution within the coating film surface. By adding and lowering the surface tension of the coating solution, it is effective in preventing unevenness of drying particularly during the drying period in which the coating film in the first half of the drying zone 26 tends to flow. The addition amount of the surfactant added to the coating liquid is 0.05 to 0.50 wt% (solid content / coating liquid) as a weight ratio of the solid content of the surfactant to the coating liquid (solid content / coating liquid). It is preferable to add in a range. This is because unless the addition of the surfactant is 0.05% by weight or more, the effect of reducing the change rate of the surface tension that changes as the temperature of the coating film increases is hardly exhibited, and the addition of the surfactant is 0.50. This is because if it exceeds wt%, coating streaks due to foaming of the coating solution tend to occur. As the type of the surfactant, a fluorine-based surfactant and a siloxane-based surfactant are particularly preferable.

  Further, drying is performed such that the wind speed of the drying air gradually decreases from the upstream divided zone 32A in the web traveling direction to the downstream divided zone 32C. This is because even in the first half of the drying zone 26 where a large amount of the organic solvent still remains on the coating film surface, the drying air is controlled by a leveling action even if the drying air is controlled like a one-way air flow. This is because unevenness does not remain, and in the first half of the drying zone 26, the lack of drying due to low temperature drying is compensated. In the latter half of the drying zone 26 where the drying unevenness is fixed without exhibiting the leveling action when the organic solvent of the coating film decreases and the drying unevenness occurs, the drying air is reduced in speed to reduce the drying unevenness due to the drying air. It is important not to generate it. As a preferable example of reducing the wind speed of the drying wind, the first half of the drying zone 26, for example, the divided zones 26A to 26D are set to a wind speed of 1.0 m / second, the divided zone 26E is set to a wind speed of 0.5 m / second, The division zone 26F is set to a wind speed of 0.3 m / sec, and the division zone 26G is set to a wind speed of 0.1 m / sec.

As described above, according to the present invention, before 10 wt% of the organic solvent contained in the coating film is dried, the coating film reaches the drying zone 26 to start drying, and 80 wt% of the organic solvent is completely dried. Until the temperature of the drying wind is low-temperature drying with the unidirectional drying wind maintained in the range of 20 ° C. to 30 ° C., the wind speed of the drying wind is gradually decreased from the first half to the second half of the drying zone. Accordingly, it is possible to remarkably reduce drying unevenness of the coating film. The present invention is particularly effective when the amount of organic solvent to be dried is 10 g / m ² or less.

  As the organic solvent of the coating solution used in the present invention, methyl ethyl ketone (MEK), acetone, methyl isobutyl ketone (MIBK), methanol, ethanol, n-propanol, methyl acetate, etc. can be used alone or as a mixed solvent. However, those having a boiling point of 100 ° C. or less are particularly preferable.

  The web 12 used in the present invention is generally polyethylene terephthalate, polyethylene-2,6 naphthalate having a width of 0.3 to 5 m, a length of 45 to 10,000 m, and a thickness of 5 to 200 μm, cellulose diacetate, cellulose triacetate, and cellulose acetate. Coating or laminating α-polyolefins with 2 to 10 carbon atoms such as plastic film such as propionate, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide, polyamide, paper, polyethylene, polypropylene, ethylene butene copolymer Paper, metal foil such as aluminum, copper, tin, or the like, or those obtained by forming a preliminary processing layer on the surface of a belt-like substrate. Further, the above-described web 12 is coated with an optical compensation sheet coating solution, a magnetic coating solution, a photographic photosensitive coating solution, a surface protecting, antistatic or slippery coating solution on the surface, dried, and then desired. Those that are cut into lengths and widths are included, and representative examples thereof include optical compensation sheets, various photographic films, photographic paper, magnetic tapes, and the like.

  In addition to the bar coating method described above, curtain coating method, extrusion coating method, roll coating method, dip coating method, spin coating method, print coating method, spray coating method and slide coating method are used as the coating method for the coating liquid. be able to. In particular, a bar coating method, an extrusion coating method, and a slide coating method can be suitably used.

  In the present invention, the number of coating layers of the coating solution applied simultaneously is not limited to a single layer, and can be applied to a simultaneous multilayer coating method as necessary.

(Example A)
An example of an optical compensation sheet will be described below as an example of drying a coating film containing an organic solvent of the present invention.

  FIG. 4 shows a case where the drying device 16 of the present invention is incorporated into the optical compensation sheet manufacturing process. Then, when the temperature of the drying air and the speed of the drying air in each of the divided zones 26A to 26G (air supply speed and exhaust speed) are changed as shown in FIG. The occurrence of drying unevenness and sharp drying unevenness was investigated.

  5 is divided zone 26A, zone 2 is divided zone 26B, zone 3 is divided zone 26C, zone 4 is divided zone 26D, zone 5 is divided zone 26E, zone 6 is divided zone 26F, zone 7 in FIG. Is a divided zone 26G.

  In Example 1, the temperature of the drying air is 20 ° C., and the air speeds of the supply and exhaust air in each of the divided zones 26A to 26G are 1.0 m / second from zone 1 to zone 4, 0.5 m / second in zone 5, The zone 6 is 0.3 m / sec, the zone 7 is 0.1 m / sec, and the drying speed is decreased in four steps from the upstream side to the downstream side.

  Example 2 is the same as Example 1 except that the temperature of the drying air is 25 ° C.

  Example 3 is the same as Example 1 except that the temperature of the drying air is set to 30 ° C.

  In Example 4, the temperature of the drying air is set to 25 ° C., and the air supply / exhaust speed of each of the divided zones 26A to 26G is set to 1.0 m / second from zone 1 to zone 4, and from zone 5 to zone 7. This is a case where the drying speed is 0.5 m / second and the wind speed is decreased in two steps from the upstream side to the downstream side.

  Comparative Example 1 is the same as Example 1 except that the temperature of the drying air is 15 ° C.

  Comparative Example 2 is the same as Example 1 except that the temperature of the drying air is set to 35 ° C.

  Here, the manufacturing process of the optical compensation sheet will be described. As shown in FIG. 4, the web 12 delivered by the delivery device 57 is supported by a plurality of guide rollers 59, 59. After drying with the drying device 16 of the present invention, the paper passes through the main drying zone 60, the heating zone 62, and the ultraviolet lamp 64, and is taken up by the winder 66.

As the web 12, triacetyl cellulose (Fujitack, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 100 μm was used. A 2 weight percent solution of long-chain alkyl-modified poval (MP-203, manufactured by Kuraray Co., Ltd.) was applied to the surface of the web 12 at a rate of 25 ml per 1 m ² of film, and then dried at 60 ° C. for 1 minute. The web 12 on which the alignment layer resin layer was formed was rubbed on the surface of the resin layer while being transported at 18 m / min to form an alignment layer. The pressing pressure of the rubbing roller 68 in the rubbing treatment was 98 Pa (10 kgf / cm ² ) per cm ² of the alignment film resin layer, and the rotational peripheral speed was 5.0 m / sec.

Next, on the alignment film obtained by rubbing the alignment film resin layer, the coating liquid is 4: 3 by weight ratio of (3) of the discotic compound TE-8 and (5) of TE-8. A coating liquid containing a liquid crystalline compound that is a 40 wt% methyl ethyl ketone solution of a mixture obtained by adding 1 wt% of a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Japan Co., Ltd.) to the above mixture was used as the mixture of No. 1 . While running the web 12 at a running speed of 18 m / min, this coating solution was applied onto the alignment film with a wire bar 14A so that the amount of the coating solution was 5 μm per 1 m ^{2 of} web. And immediately after application | coating, it dried using the drying apparatus of the drying conditions of Examples 1-4 and Comparative Examples 1 and 2 which were shown in FIG.

  Next, the web 12 is passed through the main drying zone 60 adjusted to 100 ° C. and the heating zone 62 adjusted to 130 ° C. to form a nematic phase, and then the alignment film and the liquid crystalline compound are applied. While continuously feeding the web 12, the surface of the liquid crystal layer was irradiated with ultraviolet rays by an ultraviolet lamp 64.

  The results are shown in Table 1. In Table 1, in the state of occurrence of drying unevenness (broad unevenness, sharp unevenness), x indicates that a large amount of unevenness occurred, Δ indicates that the unevenness slightly occurred, and ○ indicates that no unevenness occurred. It shows that.

表１から分かるように、乾燥風の温度が１５°Ｃの比較例１は、ブロードなムラの評価は△でシャープなムラは○であり、ウエブ幅方向の一方向乾燥風に低温乾燥を組み合わせたことで乾燥ムラの抑制効果はあるものの、乾燥温度が２０°Ｃを下回るためにブラッシング故障が発生し、不合格であった。

As can be seen from Table 1, in Comparative Example 1 where the temperature of the drying air is 15 ° C., the evaluation of the broad unevenness is Δ and the sharp unevenness is ○, and the low-temperature drying is combined with the unidirectional drying air in the web width direction. Although there was an effect of suppressing unevenness in drying, a brushing failure occurred because the drying temperature was below 20 ° C., which was unacceptable.

  In Comparative Example 2 where the temperature of the drying air was 35 ° C., no brushing failure occurred, but since the temperature of the drying air exceeded 30 ° C., particularly sharp drying unevenness occurred and it was rejected.

  On the other hand, in Examples 1 to 4, in which the unidirectional drying air in the web width direction is combined with low-temperature drying at a drying air temperature of 20 ° C. to 30 ° C., the evaluation of the broad unevenness is Δ and sharp drying unevenness Were Δ to ○ and passed without occurrence of brushing failure. Among Examples 1 to 4, the sharp dry unevenness evaluation of Example 4 was Δ, which was worse than the other Examples 1 to 3, but in the case of Example 4, this was in the latter half of the drying zone. It is considered that the slowing of the drying wind is caused by the fact that it was not sufficient as compared with Examples 1-3.

  In this way, combining the unidirectional drying air in the web width direction with the low temperature drying at a drying air temperature of 20 ° C. to 30 ° C. is effective in suppressing drying unevenness, particularly in the low temperature drying or upstream of the drying zone. Lowering the wind speed from the side to the downstream zone is effective for sharp drying unevenness.

In addition, after 80% by weight of the organic solvent contained in the coating film had been dried, even if the temperature of the drying air deviated from 20 ° C to 30 ° C, there was no effect on the surface state of the coating film surface. .
(Example B)
Add Megafac F-781-F (manufactured by Dainippon Ink & Chemicals, Inc.), a fluorosurfactant, to the coating solution of Example 1 in Example A to lower the static surface tension of the coating solution. It was investigated how dry unevenness, particularly broad unevenness, can be improved. The results are shown in Table 2. The method for evaluating drying unevenness is the same as in Table 1, but □ is an intermediate evaluation between Δ and ○.

表２の結果から分かるように、フッ素系界面活性剤を添加しない場合、ブロードムラは△の評価であったが、フッ素系界面活性剤を０．０１重量％添加した試験２及び０．０３重量％添加した試験３におけるブロードムラは□の評価であり、添加量を増やすことで多少改善されたが、まだ不十分であった。

As can be seen from the results of Table 2, when no fluorosurfactant was added, broad unevenness was evaluated as Δ, but Test 2 and 0.03 wt% with 0.01 wt% of fluorosurfactant added. The broad unevenness in Test 3 in which% was added was evaluated as □, and it was improved slightly by increasing the amount added, but was still insufficient.

  In contrast, Test 4 with 0.05% by weight of a fluorosurfactant, Test 5 with 0.10% by weight added, Test 6 with 0.30% by weight added, and Test 7 with 0.50% by weight added. The broad unevenness in all was evaluated as “good”, and the product was evaluated as acceptable.

  In Test 8, in which the addition amount of the fluorosurfactant was further increased and 0.55% by weight was added, foaming occurred in the coating solution, and coating stripes due to foaming occurred on the coating film surface. From this, it was found that the addition amount of the fluorosurfactant to the coating liquid is preferably 0.05 to 0.50% by weight (solid content / coating liquid).

  In summary, Example A and Example B are summarized as follows: (1) Drying with unidirectional drying air in the web width direction, (2) Low temperature drying with drying air temperature of 20 ° C to 30 ° C, (3) Drying zone Broad unevenness by combining all four conditions: Drying so that the speed of the drying air gradually decreases as it goes from the upstream side to the downstream side, and (4) addition of surfactant to the coating solution And sharp unevenness of drying can be extremely effectively suppressed.

Plan view of the drying apparatus of the present invention 1 is a longitudinal sectional view taken along line AA in FIG. Process diagram incorporating the drying device of the present invention into the optical compensation sheet manufacturing process Process diagram incorporating the drying device of the present invention into the optical compensation sheet manufacturing process The table showing the conditions of the examples of the present invention and comparative examples Occurrence situation of drying unevenness generated by the conventional drying method

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Application | coating and drying apparatus, 12 ... Web, 14 ... Application | coating machine, 16 ... Drying apparatus, 18 ... Drying apparatus main body, 20, 22, 24 ... Support roller, 26 ... Drying zone, 26A-26G ... Dividing zone, 28 ... Partition plate, 30 ... shielding lid, 32 ... unidirectional airflow generating means, 34A to 34G ... air supply nozzle, 33 ... outlet, 35 ... rectifier, 35A ... first porous plate, 35B ... second porous plate, 36 ... Air supply duct, 38 ... Air supply fan, 39 ... Exhaust port, 40A to 40G ... Exhaust nozzle, 41 ... Air temperature controller, 42 ... Exhaust duct, 44 ... Exhaust fan, 46 ... Circulating duct, 48 ... Exhaust fan, 46 ... Circulating fan, 48 ... Introduction duct, 50A to 50G ... Air supply valve, 52A to 52G ... Exhaust valve, 54 ... Controller, 56 ... Air conditioning plate

Claims (8)

Drying of a coating film formed by applying a coating solution containing an organic solvent to a long supporting body that travels, forming a drying zone that surrounds the four directions of the traveling support immediately after the coating, In the drying zone, in the drying method of the coating film for generating a unidirectional flow of drying air flowing from one end side to the other end side in the support width direction,
The coating film is characterized by performing low-temperature drying while maintaining the temperature of the drying air in the range of 20 ° C. to 30 ° C. until 80% by weight of the organic solvent contained in the coating film is completely dried. Drying method.   2. The coating film drying method according to claim 1, wherein the coating film reaches the drying zone before 10% by weight of the organic solvent contained in the coating film is dried.   The method for drying a coating film according to claim 1 or 2, wherein in the drying zone, the wind speed of the drying air gradually decreases from the upstream side to the downstream side in the running direction of the support.   The method for drying a coating film according to any one of claims 1 to 3, wherein a surfactant is added to the coating solution in a range of 0.05 to 0.50 wt% (solid content / coating solution).   The support body has a layer that becomes an alignment film by rubbing a previously applied alignment film forming resin, and the coating liquid contains a liquid crystalline discotic compound. The drying method of any one of 1-4 coating films. Drying of a coating film formed by applying a coating solution containing an organic solvent to a traveling long support by a coating machine, and immediately after the coating, a drying zone surrounding four directions of the traveling support In the drying zone, in the drying zone of the coating film for generating a one-direction flow of drying air flowing from one end side to the other end side in the support width direction,
Unidirectional airflow generating means for generating the unidirectional flow of drying air;
Air temperature control means for controlling the temperature of the drying air in a range of 20 ° C to 30 ° C;
An apparatus for drying a coating film, comprising:   The drying zone is partitioned by a partition plate perpendicular to the traveling direction of the elongated support to form a plurality of divided zones, and dried as it goes from the upstream divided zone to the downstream divided zone in the support traveling direction. 7. The coating film drying apparatus according to claim 6, further comprising a wind speed control means for controlling the one-way air flow generation means so that the wind speed of the wind gradually decreases.   8. The coating according to claim 6 or 7, wherein a rectifier for rectifying the dry air supplied or exhausted is provided in at least one of the supply nozzle and the exhaust nozzle of the one-way airflow generation means. Membrane drying equipment.

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