JP4513293B2 - Drying method of coating film - Google Patents

Description

The present invention relates to a dry how the coating film, in particular, elongate a running support (hereinafter, referred to as web) so as not coating film formed by coating a coating solution containing an organic solvent drying unevenness about the dry how to dry.

  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 manufacture of an optical compensation sheet using an organic solvent-based coating solution, as shown in FIG. 5, in the drying process of the coating film 1, a broad spotted drying unevenness A (indicated by a thin line) is sharp. Two types of dry unevenness of spotted 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. It is disclosed that the wind speed is maintained at 1 m / second or less. Patent Document 2 discloses that a drying zone is provided immediately after coating to surround the coating film surface, and the coating film is dried with one-direction drying air flowing from one end side to the other end side of the enclosed drying zone. is doing.
JP 2000-157923 A JP 2001-170547 A

  However, even the drying methods disclosed in Patent Document 1 and Patent Document 2 do not satisfy the strict requirements for recent drying unevenness, and further improvements are 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. an object of the present invention is to provide a dry how.

In order to achieve the above object, the coating film drying method of the present invention comprises a step of applying a coating solution containing an organic solvent to a traveling long support, and forming a coating film on the surface of the coating film. A step of passing the support on which the coating film is formed through a drying zone that surrounds the four directions of the support including the opposing zone wall surfaces, the drying zone being downstream from the upstream side in the support running direction To the side, a windless drying zone for drying the coating film without blowing dry air, a buffer zone in which the distance between the zone wall surface and the coating film surface is larger than the windless drying zone, and blowing air to blow the air e Bei dry air zone for drying the coated film, in the windless drying zone, the coating solution viscosity of the coating film drying the coating film to a least 1.5 times the viscosity of the coating solution during the coating, the windless The zone of the drying zone The distance between the wall and the coating film surface is 5mm or more and 20mm or less, the distance between the zone wall and the coating film surface of the buffer zone is equal to or more than 20mm.
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.
According to the present invention, the buffer zone is formed as a space recessed from the windless drying zone, so that the flow of the drying air and the evaporated organic solvent from the drying air zone can be blocked in this space.
Viscosity of the coating solution of the coating film without wind drying zone is gradually dried to at least 1.5 times the viscosity of the coating solution during the coating. In this case, the accompanying air is in the same direction as the traveling direction of the support and does not cause drying unevenness. Thereby, generation | occurrence | production of the drying nonuniformity in the drying initial stage of the state which contains many organic solvents and a coating liquid flows easily can be suppressed effectively. This airless drying is particularly effective for suppressing the occurrence of broad unevenness among the unevenness of drying.
In no wind drying zone, by narrowing the 20mm below the zone wall opposite the coated film surface against the coating film surface, tends to become entrained air laminar flow formed by the running of the support, the laminar flow coating This is in order not to disturb the film surface. Further, in the buffer zone, the distance between the coating film surface and the zone wall surface facing the coating film surface is more than 20 mm, so that the drying air in the drying air zone and the organic solvent evaporated from the coating film are It can be prevented from flowing into the windless drying zone. As a result, it is possible to prevent the coating film surface of the windless drying zone from being adversely affected.
In the method for drying a coating film of the present invention, in the above invention, the length of the buffer zone in the running direction of the support is preferably 100 to 500 mm.
In the method for drying a coating film of the present invention, in the above-described invention, in the drying air zone, it is preferable that the wind speed of the drying air gradually decreases from the upstream side to the downstream side in the support running direction. Thereby, generation | occurrence | production of especially sharp nonuniformity can be suppressed among dry nonuniformity.
In the method for drying a coating film of the present invention, in the above invention, it is preferable not to supply and exhaust air in the buffer zone.

As described above, according to the dry how the coating film of the present invention, it is possible to significantly reduce the drying unevenness during the drying of the coating film formed by coating a coating solution containing an organic solvent to a support .

  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 side view of a coating / drying apparatus incorporating a coating film drying apparatus of the present invention, and FIG. 2 is a plan view of FIG. 1 viewed from above.

  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 18 that passes through the web 12 coated with the coating solution and dries the coating film. The drying device 18 is provided immediately after the coating machine 14, and the web 12 is preferably carried into the drying device 18 within 1 second after coating.

  For example, a bar coating apparatus having a wire bar 14A shown in FIG. 1 can be used as the coating machine 14, and the coating liquid is applied to the lower surface of the web 12 supported by a plurality of support rollers 20, 22, and 24. It is applied to form a coating film. 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 26 of the drying device 18 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, and the coating film surface side of each side of the box body. Side (the upper side of the box) is cut out. Further, a shielding lid 28 is placed on the opposite side of the drying apparatus main body 26 across the web 12 so that the stable running of the web 12 is not hindered by air from the drying zone 16 such as air-conditioning wind. . Thereby, the tunnel-shaped drying zone 16 surrounding the four directions of the running web 12 is formed.

  The drying zone 16 is formed in the front half of the drying zone 16 and is a non-air drying zone 30 having a distance L1 to a zone wall surface 26A (bottom plate) facing the coating film surface of 5 mm or more and 20 mm or less, and a drying zone 16 is formed by a dry air zone 32 that is dried by blowing dry air onto the coating film surface, and a buffer zone 33 provided between the no-air drying zone 30 and the dry air zone 32. An inlet opening 13 of the web 12 is formed on the surface of the drying apparatus body 26 on the coating machine 14 side, and an outlet opening 15 is formed on the opposite surface. The length L2 in the web running direction of the windless drying zone 30 is only required to ensure a distance sufficient to dry until the coating solution viscosity of the coating film is at least 1.5 times the coating solution viscosity at the time of coating. Although there is a tradeoff with speed, the range of 2500 to 3000 mm is preferable.

  The drying air zone 32 is divided into a plurality of divided zones 32A, 32B, 32C (in the present embodiment, three zones) by partitioning the drying apparatus main body 26 with a plurality of partition plates 34, 34... Orthogonal to the traveling direction of the web 12. Divided into divided zones). In this case, the distance L3 between the upper end of the partition plate 34 that divides the dry air zone 32 and the coating film surface of the web 12 is preferably in the range of 0.5 mm to 20 mm, and more preferably in the range of 1 mm to 15 mm.

  As shown in FIG. 2, unidirectional airflow generation means 36 is provided in each of the divided zones 32 </ b> A to 32 </ b> C of the dry air zone 32. In the unidirectional airflow generation means 36, an air supply duct 38 is branched and connected to air supply ports 36 </ b> A, 36 </ b> B, 36 </ b> C formed on one side of both sides of the drying apparatus main body 26, and an air supply fan 40 is connected to the air supply duct 38. Is provided. Further, exhaust ports 36D, 36E, and 36F are formed on the other side of the both sides of the drying apparatus body 26 so as to face the air supply ports 36A to 36C, and an exhaust duct 42 is branched and connected to each of the exhaust ports 36D, 36E, and 36F. In addition, an exhaust fan 44 is provided in the exhaust 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 40, and a drying air introduction duct 48 heated to a predetermined temperature is provided in the middle of the circulation duct 46. Thus, by driving the air supply fan 40 and the exhaust fan 44, each of the divided zones 32 </ b> A to 32 </ b> C is formed on the coating film surface from one end side (air supply port side) to the other end side (exhaust port) on the web width direction. Unidirectional dry air flowing to the side). 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 dry air containing an organic solvent is supplied to each of the divided zones 32A to 32C, it is possible to prevent the organic solvent from rapidly evaporating from the coating film surface. Further, valves 50A to 50F are respectively provided in the branch pipe branched from the air supply duct 38 and the branch pipe branched from the exhaust duct 42, and the opening degree of each valve 50A to 50F is controlled by the controller 52. Then, the controller 52 controls the valves 50A to 50F so that the wind speed of the drying air gradually decreases from the upstream divided zone 32A in the web traveling direction toward the downstream divided zone 32C. The length L6 of the dry wind zone 32 in the web running direction is preferably in the range of about 1/2 to 1/1 of the length L2 (see FIG. 1) of the windless dry zone 30.

  Further, the width of the drying apparatus main body 26 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 16 are covered with an air conditioning plate 54 is provided. This air conditioning portion creates a rapid flow of drying air in the drying zone 16 by securing a distance from the air supply ports 36A to 36C to the coating film end and a distance from the coating film end to the exhaust ports 36D to 36F. It is something that is not.

  As shown in FIG. 1, in the buffer zone 33, a distance L4 to the zone wall surface 26A (bottom plate) facing the coating film surface is more than 20 mm, and the length L5 of the zone wall surface 26A in the web running direction is separated. Is formed to be 100 to 500 mm. This is because the buffer zone 33 needs to be formed as a space recessed from the windless drying zone 30 in order to stop the flow of the drying wind and the evaporated organic solvent from the drying wind zone 32. If the thickness is less than 100 mm, the buffering capacity is extremely reduced. If the thickness exceeds 500 mm, the passage time of the web 12 through the buffer zone 33 becomes longer, and on the contrary, the coating film surface is disturbed.

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

  Immediately after the coating liquid containing the organic solvent is applied to the web 12 supported by the support rollers 22, 24, and 26 with the wire bar 14 </ b> A of the coating machine 14, that is, within 1 second after the coating, the coating film surface in the windless drying zone 30 No wind drying, which is the initial drying of, is performed. In this no-air drying zone 30, the organic solvent is removed from the entrained air and the coating film surface by conveying the web 12 until the coating liquid viscosity of the coating film is at least 1.5 times the coating liquid viscosity at the time of coating without blowing dry air. The coating film surface is gradually dried only by convection due to natural evaporation of the coating. The organic solvent evaporated from the coating film surface by the accompanying air or convection is naturally discharged mainly from the inlet opening 13 of the web 12. In this windless drying, since the zone wall surface 26A facing the coating film surface is close to 5 mm or more and 20 mm or less with respect to the coating film surface, the entrained air described above becomes a laminar flow along the web running direction, and the coating film It can be dried without disturbing the surface. In addition, since the lower limit of the distance from the coating film surface to the zone wall surface 26A is set to 5 mm, the coating film surface does not come into contact with the zone wall surface 26A.

  The web 12 on which the coating film has been subjected to the windless drying in the windless drying zone 30 is carried into the drying wind zone 32 through the buffer zone 33. In the drying air zone 32, the coating film surface is dried with a unidirectional drying air flowing from one end side to the other end side in the web width direction on the coating film surface. As a result, a dry environment is formed in which the organic solvent evaporated from the coating film surface covers the coating film surface, and in this drying environment, a unidirectional flow of drying air flowing in the web width direction is generated on the coating film surface. While the coating film surface is covered with the organic solvent, the dry air containing the evaporated organic solvent is exhausted from the exhaust ports 36D to 36F and gradually dried. In this case, if the exhaust amount from the exhaust ports 36D to 36F is too large, the organic solvent is not evenly covered on the coating film surface, so the opening amount of the valves 50D to 50F is adjusted so that the exhaust amount does not become too large. It is necessary to. 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 by the evaporation distribution of the organic solvent from the coating film surface can be suppressed, and uniform drying can be performed. In this case, 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, in the first half of the drying air zone 32 where a large amount of organic solvent still remains on the coating film surface, even if the drying air has a slightly high wind speed, if the drying air is controlled like a unidirectional air flow, the drying unevenness is caused by the leveling action. In the first half of the dry air zone 32, strong dry air is used to compensate for insufficient drying in the no-air drying zone. In the second half of the drying air zone 32 where the drying unevenness is fixed without exhibiting the leveling action when the organic solvent of the coating film is reduced and the drying unevenness is generated, the drying air is slowed down and drying unevenness due to the drying air is fixed. It is important not to generate Moreover, in the drying air zone 32 by this drying air, it is preferable to dry with 20 degreeC-30 degreeC low temperature drying air until 80% of the organic solvent contained in a coating film evaporates. This is because if the drying air is less than 20 ° C., a brushing failure is likely to occur due to condensation on the coating film surface, and if it exceeds 30 ° C., drying is likely to occur due to rapid drying. In addition, the drying air in forced drying is not limited to being controlled in one direction from one end to the other end in the web width direction, and uses a uniform air controlled to dry the coating film surface. be able to.

As described above, the present invention performs windless drying when the coating film surface immediately after coating is easy to flow, and when the coating solution viscosity is at least 1.5 times that at the time of coating, the coating film is dried at once with no wind. While making up for insufficient drying during drying, the wind speed of the drying air is gradually reduced, thereby making it possible to remarkably reduce unevenness in drying 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.

  Moreover, it is preferable to contain a surfactant in the coating solution, and in particular, a fluorine-based surfactant and a siloxane-based surfactant are preferable. The addition amount of the surfactant is preferably in the range of 0.05% by weight to 0.50% by weight with respect to the coating solution.

  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. 3 shows an embodiment of the present invention in which the drying device 18 including the no-air drying zone 30, the drying air zone 32, and the buffer zone 33 is incorporated in the optical compensation sheet manufacturing process. Further, the comparative example is a case where a drying zone of a type in which the entire drying device blows drying air to dry instead of the drying device 18 of the embodiment, and is divided into seven divided zones. In addition, the drying path length of the drying apparatus 18 of an Example and the drying apparatus of a comparative example was made the same.

  Further, the windless drying zone 30 provided only in the embodiment represents the first half as zone 1, the middle as zone 2, and the second half as zone 3, and the buffer zone 33 includes the windless drying zone 30 and the drying wind zone 32. Since it is arranged between them, it is represented as zone 4. Accordingly, the remaining three zones 5 to 7 become the dry air zone 32 and correspond to the three divided zones 32A to 32C in FIG.

  Then, for each of the drying device 18 of the example and the drying device of the comparative example, the air supply speed and the exhaust speed of the drying air in each zone in the drying air zone 32 are adjusted as shown in FIG. The occurrence of drying unevenness (broad unevenness, sharp unevenness) was investigated.

  In Example 1, the buffer zone 33 is not provided, and after the coating film is airlessly dried in the airless drying zone 30, the air supply / exhaust air velocity in each of the zones 5 to 7 in the airflow zone 32 is 2.0 m / sec. This is the case when dried with wind. Since Example 1 did not provide the buffer zone 33, the zones 1 to 4 are the windless drying zone 30.

  The second embodiment is a case where the buffer zone 33 is provided, and other conditions are the same as those of the first embodiment.

  In the third embodiment, the buffer zone 33 is provided, and after the coating film is air-dried in the airless drying zone 30, the air supply / exhaust speed of each divided zone in the air-drying zone 32 is set to 2.0 m / second in the zone 5 6 is 0.5 m / sec, and zone 7 is 0.1 m / sec. The drying speed is such that the drying speed gradually decreases from the upstream zone 5 to the downstream zone 7.

  Comparative Example 1 is a case where the air supply / exhaust air velocity in the zones 1 to 4 is 1.0 m / sec and the air supply / exhaust air velocity in the zones 5 to 7 is 0.5 m / sec.

  Comparative Example 2 is a drying process in which the air velocity of the supply and exhaust air in zones 1 to 4 is 1.0 m / sec, zone 5 is 0.5 m / sec, zone 6 is 0.3 m / sec, and zone 7 is 0.1 m / sec. This is the case when dried with wind.

  Here, the manufacturing process of the optical compensation sheet will be described. As shown in FIG. 3, the web 12 sent out by the sending machine 55 is supported by a plurality of guide rollers 56, 56. After drying with the drying device 18 of the present invention (Example) or the drying device of the comparative example, the material passes through the main drying zone 60, the heating zone 62, and the ultraviolet lamp 64 and is wound 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 solution 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 18 of this invention, or the drying apparatus of a comparative example.

  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 has occurred, Δ indicates that a slight amount of unevenness has occurred, and □ indicates that a slight unevenness has occurred. ◯ indicates that no unevenness occurred.

表１の乾燥ムラの評価うち、ブロードなムラについて見てみると、無風乾燥ゾーン３０のない比較例１及び２の乾燥装置は共に△の評価であったが、無風乾燥ゾーン３０を有する実施例１〜３は□又は□〜○の評価であった。実施例１〜３のうち実施例１のみが少し悪い評価であったが、実施例１の場合には、無風乾燥ゾーン３０と乾燥風ゾーン３２との間に緩衝ゾーン３３を設けていないために、乾燥風ゾーン３２の乾燥風や塗布膜面から蒸発した有機溶剤が無風乾燥ゾーン３０に多少悪影響を及ぼしているものと推察される。

Of the dry unevenness evaluations in Table 1, when looking at the broad unevenness, both the drying apparatuses of Comparative Examples 1 and 2 without the windless drying zone 30 were evaluated as Δ, but the examples having the windless drying zone 30 were. 1-3 was evaluation of (square) or (square)-(circle). Although only Example 1 was a little bad evaluation among Examples 1-3, in the case of Example 1, since the buffer zone 33 was not provided between the no-air drying zone 30 and the drying wind zone 32, it is. It is presumed that the drying air in the drying air zone 32 and the organic solvent evaporated from the coating film surface have some adverse effects on the airless drying zone 30.

  In addition, in the evaluation of wind unevenness in Table 1, when looking at sharp unevenness, the wind speed of the drying wind gradually decreased from the upstream zone to the downstream zone in the second half of drying after zone 5. The comparative example 2 and Example 3 are good evaluation with (circle). On the other hand, Comparative Example 1 having the same drying wind speed in the latter half of the drying was evaluated as x, and Examples 1 and 2 were evaluated as Δ. The reason why Examples 1 and 2 were better than Comparative Example 1 was that the coating film surface was dried in a windless drying zone until the coating liquid viscosity was at least 1.5 times the coating liquid viscosity at the time of coating, and the coating film surface It is considered that the forced drying after the stabilization became effective.

Thus, the windless drying zone 30 is particularly effective in suppressing the occurrence of broad unevenness, and the drying wind zone 32 is dried so that the wind speed of the drying wind gradually decreases from the upstream zone to the downstream zone. In particular, the result was effective in suppressing the occurrence of sharp unevenness.
(Example B)
Add Megafac F-781-F (manufactured by Dainippon Ink & Chemicals, Inc.), a fluorosurfactant, to the coating solution of Example 3 in Example A to lower the static surface tension of the coating solution. It was investigated how dry unevenness, particularly broad unevenness, was improved. The results are shown in Table 2. The method for evaluating drying unevenness is the same as in Table 1.

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試験１及び添加濃度が０．０３重量％の試験２は、ブロードムラの評価が□であった。これに対し、添加濃度が０．０５重量％の試験３、添加濃度が０．１０重量％の試験４、添加濃度が０．５０重量％の試験５は、ブロードムラの評価が何れも○で良い結果となった。更に、フッ素系界面活性剤の添加濃度を０．５５重量％まであげた試験６は、塗布液に泡立ちが生じ、塗布スジが発生してしまった。

As can be seen from the results in Table 2, the broad unevenness evaluation was □ in Test 1 in which no fluorosurfactant was added and Test 2 in which the addition concentration was 0.03% by weight. In contrast, Test 3 with an addition concentration of 0.05% by weight, Test 4 with an addition concentration of 0.10% by weight, and Test 5 with an addition concentration of 0.50% by weight are all evaluated as ◯. It was a good result. Furthermore, in Test 6 in which the addition concentration of the fluorosurfactant was increased to 0.55% by weight, foaming occurred in the coating solution, and coating stripes were generated.

From this, broad unevenness can be improved by setting the concentration of the fluorosurfactant added to the coating solution in the range of 0.05 wt% to 0.50 wt%. From the above results, it is possible to reduce the occurrence of broad unevenness by setting the addition concentration of the surfactant to the coating liquid in the range of 0.05 wt% to 0.50 wt% and providing the windless drying zone 30. It is considered to be more effective.
[Appendix]
The present specification discloses the following invention as a method and apparatus for drying a coating film. Invention (1) is a drying method of a coating film formed by applying a coating solution containing an organic solvent to a long supporting body that travels, and is a drying method that surrounds four directions of the traveling support immediately after the coating. A zone is formed, and in the drying zone, the coating film is dried without blowing the drying air until the coating film viscosity of the coating film is at least 1.5 times the coating liquid viscosity at the time of coating. Next, the coating film is dried by blowing dry air.
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.
According to the present invention (1), by providing a drying zone immediately after coating, a drying environment is formed in which non-uniform wind from outside the drying zone does not hit the coating film surface. First, airless drying is performed to dry the coating film without blowing dry air until the coating liquid viscosity of the coating film is at least 1.5 times the viscosity of the coating liquid at the time of coating. In this non-air drying, drying with the drying air is not performed, but the coating film surface is dried only by the accompanying wind generated by the traveling of the support and the convection due to the evaporation of the organic solvent from the coating film surface. The coating solution is gradually dried until the coating solution viscosity of the coating film is at least 1.5 times the coating solution viscosity at the time of coating. In this case, the accompanying air is in the same direction as the traveling direction of the support and does not cause drying unevenness. Thereby, generation | occurrence | production of the drying nonuniformity in the drying initial stage of the state which contains many organic solvents and a coating liquid flows easily can be suppressed effectively. This airless drying is particularly effective for suppressing the occurrence of broad unevenness among the unevenness of drying.
If the coating film viscosity is increased by airless drying and it becomes difficult for the coating film to flow, then the drying zone forms a drying environment in which uneven wind from outside the drying zone does not hit the coating film surface. In addition, the coating film is dried at once by drying with a drying wind. Thereby, while being able to make up for the shortage of drying in the windless drying, the coating film is less likely to flow due to the increase in the viscosity of the coating liquid in the windless drying, so that drying unevenness due to the drying wind can also be suppressed.
Invention (2) is characterized in that it is within 1 second after coating immediately after the coating. This is because, if it takes a long time for the support to be carried into the drying zone, the coating film surface is disturbed before being carried into the drying zone, and the effect of windless drying in the drying zone is reduced. It is preferable to carry the support into the drying zone within 1 second after coating.
Invention (3) is characterized in that, in the windless drying zone in which the windless drying is performed among the drying zones, the zone wall surface facing the coating film surface is brought close to the coating film surface at 5 mm or more and 20 mm or less. To do. This is because by making the zone wall surface facing the coating film surface narrower to 20 mm or less with respect to the coating film surface, the entrained wind formed by the running of the support tends to be laminar, This is not to disturb. On the other hand, if the zone wall surface facing the coating film surface exceeds 20 mm with respect to the coating film surface, the accompanying air tends to be turbulent (a vortex is generated) and the coating film surface is likely to be disturbed. The lower limit of 20 mm or less with respect to the coating film surface is preferably 5 mm or more so that the zone wall surface does not contact the coating film surface.
Invention (4) 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 in the drying air zone that blows drying air out of the drying zone to dry the coating film. It is characterized by making it. This is a state in which the organic solvent concentration in the vicinity of the coating film surface is always kept constant when a regular drying air having a unidirectional flow flowing from one end to the other end in the width direction of the support is generated in the drying by the drying air. This is because the coating film can be dried. Thereby, since the coating film surface can be uniformly dried, the occurrence of drying unevenness can be further suppressed. Here, the unidirectional flow flowing from one end side to the other end side in the support width direction is 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.
The invention (5) is such that, in the drying air zone in which drying air is blown to dry the coating film, the wind speed of the drying air gradually decreases from the upstream side to the downstream side in the support running direction. It is characterized by. Thereby, generation | occurrence | production of especially sharp nonuniformity can be suppressed among dry nonuniformity.
In the invention (6), a buffer zone in which the distance between the coating film surface and the zone wall surface facing the coating film surface is separated by more than 20 mm is provided between the no-air drying zone and the drying air zone. It is characterized by being. This is to prevent the drying air in the drying air zone and the organic solvent evaporated from the coating film from flowing into the windless drying zone and adversely affecting the coating film surface of the windless drying zone.
Invention (7) is characterized in that a surfactant is contained in the coating solution. This is because by reducing the surface tension of the coating solution with the surfactant, it is useful for reducing 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, but by adding a surfactant to the coating liquid, Since the force causing the fluid motion generated as a result of the difference can be reduced, drying unevenness can be suppressed. In particular, there is an effect in the initial stage of drying, ie, windless drying, in which the content of the organic solvent is large and the coating liquid easily flows.
The invention (8) is characterized in that the concentration of the surfactant is 0.05 to 0.50% by weight (solid content / coating liquid). This is because unless the surfactant concentration is 0.05% by weight or more, the effect of reducing the rate of change of the surface tension that changes as the temperature of the coating film decreases is hardly exhibited. This is because if it exceeds 50% by weight, coating streaks due to foaming of the coating solution are likely to occur. The surfactant solid content / coating liquid is a ratio of the surfactant solid content to the coating liquid.
In the invention (9), the support has a layer to be an alignment film by rubbing a previously applied alignment film forming resin, and the coating liquid contains a liquid crystalline discotic compound. It is characterized by. 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.
The invention (10) is a coating film drying apparatus formed by applying a coating solution containing an organic solvent to a traveling long support by a coating machine. The drying support is provided immediately after the coating machine. A drying apparatus main body that forms a drying zone that surrounds the four directions of the body, and a windless drying that is a space that is formed in the first half of the drying zone and has a distance of 5 mm or more and 20 mm or less to the zone wall surface facing the coating film surface And a drying air zone that is formed in the latter half of the drying zone and blows drying air on the surface of the coating film.
The invention (10) specifically shows the apparatus configuration for carrying out the drying method of the invention (1).
In the invention (11), the distance to the zone wall surface facing the coating film surface exceeds 20 mm between the no-air drying zone and the drying wind zone, and the length of the zone wall surface in the support running direction is 100. It is characterized by comprising a buffer zone, which is a space formed at ˜500 mm.
This shows the preferred structure of the buffer zone so that the dry wind in the dry wind zone and the organic solvent evaporated from the coating film do not flow into the windless drying zone and adversely affect the coating film surface of the windless drying zone. First, the distance to the zone wall surface facing the coating film surface needs to exceed 20 mm. As a result, the buffer zone is formed as a space recessed from the windless drying zone, so that the flow of the drying air and the evaporated organic solvent from the drying air zone is blocked in this space. In this case, if the length of the zone wall surface in the support running direction is less than 100 mm, there is almost no buffering capacity, and if it exceeds 500 mm, the time required for the support to pass through the buffer zone becomes long, and the coating film surface is disturbed.
According to the invention (12), in the dry air zone, a unidirectional air flow generating means for generating a unidirectional flow of dry air flowing from one end side to the other end side in the long support width direction is provided. It is characterized by. As a result, the coating film can be dried while the organic solvent concentration in the vicinity of the coating film surface is always kept constant, so that the coating film surface can be uniformly dried and the occurrence of wind unevenness is further suppressed. it can.
In the invention (13), the dry air 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 downstream side from the upstream divided zone in the support traveling direction The unidirectional airflow generating means is controlled by the control means so that the wind speed of the drying air gradually decreases as it goes to the divided zones. This is because in the drying by 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 air zone has a slightly high wind speed, the drying unevenness does not remain if the drying air is controlled like a one-way air flow. Therefore, the lack of drying in the no-air drying zone is compensated for in the first half of the drying air zone. And it is important to reduce the drying air so that drying unevenness due to the drying air does not occur on the downstream side of the support running direction where the uneven drying is fixed when it occurs, that is, in the latter half of the drying air zone. Become.

Side view of the drying apparatus of the present invention Plan view of the drying apparatus of the present invention Process diagram incorporating the drying device of the present invention into the optical compensation sheet manufacturing process Table showing conditions of Examples and Comparative Examples of the present invention Spots (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 zone, 18 ... Drying apparatus, 20, 22, 24 ... Support roller, 26 ... Drying apparatus main body, 28 ... Shielding lid, 30 ... No wind drying Zone, 32 ... Dry air zone, 33 ... Buffer zone, 34 ... Partition plate, 36A, 36B, 36C ... Air supply port, 36D, 36E, 36F ... Exhaust port, 38 ... Air supply duct, 40 ... Air supply fan, 42 ... exhaust duct, 44 ... exhaust fan, 46 ... circulation duct, 48 ... introduction duct, 50A, 50B, 50C, 50D, 50E, 50F ... valve, 52 ... controller, 54 ... air conditioning plate, 55 ... sending machine, 58 ... rubbing Processing unit 60 ... main drying zone 62 ... heating zone 64 ... ultraviolet lamp 66 66winder 68 ... rubbing roller

Claims (3)

Forming a coating film by applying a coating liquid containing an organic solvent to a long supporting body that travels;
Including a step of passing the support on which the coating film is formed through a drying zone surrounding four directions of the support including the zone wall surface facing the coating film surface,
The drying zone has an airless drying zone that dries the coating film without blowing dry air from the upstream side to the downstream side in the support traveling direction, and the distance between the zone wall surface and the coating film surface is e Bei a buffer zone is not performed supply and exhaust rather greater than windless drying zone, the drying air zone for drying the coating film blowing drying air,
In the windless drying zone, the coating film is dried until the coating liquid viscosity of the coating film is at least 1.5 times the coating liquid viscosity at the time of coating,
The distance between the zone wall surface of the windless drying zone and the coating film surface is 5 mm or more and 20 mm or less, and the distance between the zone wall surface of the buffer zone and the coating film surface exceeds 20 mm. How to dry the membrane. The method for drying a coating film according to claim 1 , wherein the buffer zone has a length in the running direction of the support of 100 to 500 mm. 3. The coating film drying method according to claim 1, wherein in the drying air 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.

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