JP5114108B2 - Coating film drying method and apparatus - Google Patents

Description

  The present invention relates to a coating film drying method and apparatus, and in particular, in the production of an optical compensation sheet or the like, a long and wide coating film surface formed by applying a coating liquid containing an organic solvent to a long support. The present invention relates to a drying method and apparatus for drying.

  In order to improve viewing angle characteristics in a liquid crystal display device, an optical compensation sheet is provided as a retardation plate between a pair of polarizing plates and a liquid crystal cell. As a method for producing a long optical compensation sheet, a coating liquid containing an alignment film forming resin is applied to the surface of a long transparent film, and then a rubbing treatment is performed to form an alignment film. And the method of apply | coating the coating liquid containing a liquid crystalline discotic compound on the alignment film and drying the apply | coated coating film is disclosed by the following patent document 1. FIG.

  The method for drying a coating liquid containing a liquid crystalline discotic compound disclosed in Patent Document 1 applies from the application of the coating liquid containing a liquid crystalline discotic compound on the alignment film to drying with a regular drying apparatus. Initial drying is performed under indoor air-conditioning conditions, and the organic solvent in the coating solution is mainly evaporated and dried.

  However, the optical compensation sheet manufactured by the manufacturing method described in Patent Document 1 has a broad spot A (shown by a thin line) as shown in FIG. 9 on the surface of the coating film 101 in the initial drying process. And sharp spots B (indicated by thick lines), two types of spots (unevenness) A and B occur, and there is a problem that the yield of the product is lowered in some cases.

  As a result of analyzing these two types of spots A and B, it was found that the broad spot A had a thin layer of the coating liquid film 102 containing a liquid crystalline discotic compound as shown in FIG. In FIG. 10, reference numeral 103 denotes a long support, and 104 denotes an alignment film layer. On the other hand, the orientation direction 106 of the orientation part 105 (dark color part) where the sharp spots B are generated is shifted from the orientation part 108 in the other normal orientation direction 107 as shown in FIG. I understood.

  As a method generally used as an effective measure against the spots A and B generated by such initial drying, the coating solution can be applied by increasing the concentration of the coating liquid or adding a thickener. Increase the viscosity of the liquid. Accordingly, there is a method for preventing the occurrence of spots 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 spots by using a high-boiling solvent to produce a leveling effect even if the coating surface immediately after coating is flowed by the 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. Moreover, 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, high-speed coating becomes impossible as the viscosity increases, so that 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.

Against this background, the present applicant has proposed a coating film drying method and apparatus described in Patent Document 2. In this coating method and apparatus, a drying zone is provided immediately after coating to surround the coating film surface to be dried of the traveling long support and to one end side in the width direction of the long support in the drying zone. The coating film is uniformly dried without changing the physical properties such as the viscosity of the coating liquid and the type of solvent by generating a one-way flow of drying air flowing from the first to the other end side. It is said that the occurrence of the above-mentioned spots can be suppressed by this drying method and apparatus.
JP-A-9-73081 JP 2001-170547 A

  However, in recent years when the quality of the optical compensation sheet is increasingly demanded, the suppression of spots by the coating method and apparatus of Patent Document 2 is not sufficient, and further improvement is desired.

  In addition, from the viewpoint of improving productivity, it is necessary to increase the traveling speed (also referred to as line speed or coating speed) of the support in the optical compensation sheet production line, and even if the speed is increased, the occurrence of spots can be sufficiently suppressed. There is a demand for a method for drying a coating film.

  The present invention has been made in view of such circumstances, and even when the line speed is increased, spots generated in the initial drying process immediately after coating can be remarkably suppressed, and physical properties such as the viscosity of the coating liquid are obtained. Another object of the present invention is to provide a drying method and apparatus capable of uniformly drying a coating film without changing the kind of solvent.

According to a first aspect of the present invention, in order to achieve the above object, the traveling is performed by providing a drying zone immediately after coating of a coating film formed by applying a coating liquid containing an organic solvent to a traveling long support. In the drying method of surrounding the coating film surface to be dried of the long support and supplying the drying air into the drying zone to dry the coating film, the drying is performed in the first drying zone before the drying zone, By supplying a drying air having a wind speed higher than 0.5 m / s from one end to the other end in the width direction of the long support, a one-way flow of drying air flowing in the width direction is generated on the coating film surface. The first drying step for drying the coating film and the second drying zone after the drying zone are performed, and the long support is run on the coating film surface by not supplying the drying air at all. The coating film generates an accompanying air accompanying the A second drying step for drying; and a support temperature adjusting step for adjusting the temperature of the support so that the temperature of the elongated support is higher than the film surface temperature of the coating film in the second drying step; , And the traveling speed of the long support is a high speed region of 0.4 to 1.2 m / sec (24 to 72 m / min), and the length in the first drying zone of the drying zones is Drying the coating film , wherein the drying zone is divided into the first drying zone and the second drying zone so that the residence time of the scale-like support is in the range of 0.3 to 1.0 seconds. Provide a method.

  According to the first aspect, in the first drying zone among the drying zones surrounding the coating film surface, drying air in one direction from one end to the other end in the width direction of the long support (long support) The first drying step is performed to dry the coating film with a drying air flow perpendicular to the traveling direction. In this way, the coating film surface is surrounded by a drying zone, and a regular drying air flow in one direction from one end to the other end in the widthwise direction of the long support is generated, so that organic matter in the vicinity of the coating film surface is generated. Since the coating film can be dried in a state where the solvent concentration is always kept constant, the occurrence of spots during drying can be suppressed.

  In this case, entrained air is generated on the coating film surface as the long support travels. Therefore, in order to generate the above-described regular dry air having a one-way flow, the air velocity of the dry air is set to 0. Must be greater than 5 m / s. However, conversely, if the wind speed is too high, it will cause spots, so it is possible to overcome the accompanying wind and dry the wind in one direction from the one end to the other end in the width direction of the long support. It is preferable to supply wind.

  However, after the coating film has been dried in the first drying zone, the drying speed is likely to fluctuate remarkably even if the drying air has the same air speed, and this fluctuation causes the occurrence of spots.

  Therefore, in the present invention, the second drying step is performed after the first drying step. That is, in the second drying zone, the accompanying wind accompanying the running of the long support is generated on the coating film surface by setting the wind speed of the drying air to 1/10 or less of the running speed of the long support. The coating film is dried. Further, in the support temperature adjustment step, the temperature of the support was adjusted so that the temperature of the long support in the second drying zone was higher than the film surface temperature of the coating film.

  In this way, the wind speed of the drying air is reduced as much as possible to make the main body of the air flowing on the coating film surface the accompanying air, and the coating film is dried only by this accompanying air and the temperature difference between the elongated support and the coating film surface. By doing so, fluctuations in the drying rate can be effectively prevented, so that the occurrence of spots can be further suppressed. In particular, as the line speed is increased, a larger accompanying wind can be obtained. Furthermore, since the supply amount of dry air can be reduced, it also saves energy.

Moreover , the effect of the present invention is more easily exhibited by setting the traveling speed (line speed) of the long support to a high speed region of 0.4 to 1.2 m / sec (24 to 72 m / min) .

Further , a preferable section of the boundary position between the first drying zone and the second drying zone has a residence time of 0.3 to 1.0 seconds after the elongate support is introduced into the drying zone and drying is started. The part is preferably the first drying zone. This is because the drying rate is likely to fluctuate significantly in the coating film after being dried through the residence time of 0.3 to 1.0 seconds.

It is more preferable not to supply any drying air.

A second aspect of the present invention is characterized in that, in the first support temperature adjustment step, the temperature of the elongated support is adjusted to be 2 ° C. or higher than the film surface temperature of the coating film.

Claim 2 defines a preferable temperature difference between the support temperature and the film surface temperature in the second step, and the temperature of the elongated support is 2 ° C. or more higher than the film surface temperature of the coating film. It is preferable to do so. Thereby, drying can be efficiently assisted by the temperature difference between the temperature of the support and the film surface temperature of the coating film.

A third aspect of the present invention is characterized in that, in the first or second aspect , the thickness of the coating film is a thin film having a wet thickness of 8 μm or less and 1/10 or less of the thickness of the elongated support.

Claim 3 defines the thickness of the coating film suitable for the present invention, and it is easier for the thin coating film having a wet thickness of 8 μm or less to be dried with the accompanying air in the second drying step. Because it becomes. Further, when the thickness of the coating solution is viewed in relation to the support thickness, it is preferably 1/10 or less of the thickness of the long support. By setting the thickness of the coating liquid and the thickness of the support to 1/10 or less, the heat of the support can be efficiently used for drying the coating liquid, and drying can be promoted.

According to a fourth aspect of the present invention , in any one of the first to third aspects, the film surface temperature of the coating film in the second drying zone is 20 ° C. or higher and 23 ° C. or lower.

The fourth aspect defines a preferable film surface temperature of the coating film in the second drying zone. If the film surface temperature of the coating film is too low, the drying efficiency is deteriorated. Therefore, it is preferable to set the film surface temperature of the coating film within the above range.

Claim 5 of the present invention, in order to achieve the above object, in a drying apparatus for drying the coated film formed by coating a coating machine a coating solution containing an organic solvent to the elongate support member to travel, the length A long machine which is provided immediately after the feeding machine and winding machine for running the scale-shaped support body at a running speed of 0.4 to 1.2 m / sec (24 to 72 m / min) and the coating machine, and runs. A drying apparatus main body that forms a drying zone surrounding the coating film surface of the support, and a unidirectional flow that is provided at a front stage of the drying zone and flows from one end to the other end in the width direction of the long support. A first drying zone provided with a unidirectional airflow generating means for generating drying air, and a rear stage portion of the drying zone, accompanied by a long support that travels without supplying drying air. A second drying zone for drying the coating film by the accompanying air generated; Disposed directly in front of the serial coating machine, and a heating means for heating said elongated support before being coated, the residence of the elongate support in the first drying zone of said drying zone There is provided a coating film drying apparatus characterized in that the drying zone is divided into the first drying zone and the second drying zone so that the time is in the range of 0.3 to 1.0 seconds .

Claim 5 constitutes the present invention as an apparatus.

A sixth aspect of the present invention is characterized in that, in the fifth aspect , the second drying zone is provided with a recovery means for recovering the solvent volatilized from the coating film.

Claim 6, the drying of entrained air in the second drying zone, is provided with the collecting means for collecting the solvent volatilized from the coating film, the solvent inhibits the drying fills the second drying zone There is nothing. As the recovery means, a condensing plate that condenses the volatilized solvent, an adsorption plate that adsorbs the solvent, or the like can be suitably used.

  According to the present invention, in the second drying zone, the wind speed of the drying air is set to 1/10 or less of the traveling speed of the support so that the film surface temperature of the elongated support is higher than the film surface temperature of the coating film. The temperature of the support is adjusted. As a result, the coating film can be dried by the accompanying air accompanying the running of the long support and the temperature difference between the support and the coating film surface, so that the speed of the drying wind can be effectively prevented. The occurrence of spots during drying can be suppressed.

  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 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 film drying apparatus 10 of the present invention mainly passes a traveling long support 12 (hereinafter referred to as "web 12") to dry the coating film. And a unidirectional airflow generation means 18 for generating a unidirectional flow of drying air flowing from one end side to the other end side in the width direction of the web 12 in the drying zone 14. Is done. The drying apparatus 10 is provided immediately after a coating machine 20 that applies a coating solution containing an organic solvent to a traveling web 12.

  As the applicator 20, for example, a bar applicator provided with a wire bar 20A can be used, and an application liquid is applied to the lower surface of the web 12 supported by a plurality of backup rollers 22, 24, and 26. A coating film is formed.

  The drying device main body 16 is provided immediately after the coating machine 20, 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, and among the sides of the box body The side of the coated film surface side (the upper side of the box) is cut off. Thereby, the drying zone 14 surrounding the coating film surface to be dried of the traveling web 12 is formed. The drying zone 14 is divided into a plurality of divided zones 14A, 14B, 14C, 14D, 14E, 14F, by partitioning the drying apparatus main body 16 with a plurality of partition plates 28, 28... Orthogonal to the traveling direction of the web 12. It is divided into 14G (seven divided zones in this embodiment). In this embodiment, 14A to 14C constitute the first drying zone 35, and 14D to 14G constitute the second drying zone 36. In this case, the distance between the upper end of the partition plate 28 that divides the drying zone 14 and the coating film surface formed on the web 12 is preferably in the range of 0.5 mm to 12 mm, more preferably in the range of 1 mm to 10 mm. . The first drying zone 35 is provided with unidirectional airflow generation means 18 (see FIG. 2). In the production method of the present invention, in the second drying zone, it is possible to supply a drying air of 1/10 or less of the traveling speed of the long support, and therefore, the unidirectional direction in the second drying zone. It is also possible to provide an airflow generation means. However, it is preferred that the second drying zone be conducted without wind. In the present embodiment, the three divided zones 14A to 14C are the first drying zone 35, and the next four divided zones 14D to 14G are the second drying zone 36. It can be changed as appropriate depending on the factors.

  In FIGS. 1 and 2, the first drying zone and the second drying zone have the same direction of the drying air, but the first drying zone and the second drying zone can have different wind directions. is there.

  The one-way airflow generation means 18 is mainly composed of suction ports 18A, 18B, 18C formed on one side of both sides of the drying apparatus main body 16, and an exhaust port formed on the other side so as to face the suction ports 18A-18C. 18D, 18E, 18F and exhaust means 18G, 18H, 18I connected to the exhaust ports 18D-18F. Thus, by driving the exhaust means 18G to 18I, the air sucked into the divided zones 14A to 14C from the suction ports 18A to 18C is exhausted from the exhaust ports 18D to 18F. Then, dry air is generated that flows in one direction from one end side (suction port side) to the other end side (exhaust port side) in the width direction of the web 12. And since each division | segmentation zone 14A-14C is divided | segmented by the partition plate 28, the drying wind of another division | segmentation zone is not supplied to another division | segmentation zone. Therefore, since the air supplied in one division zone is exhausted in the same division zone, the drying air is supplied in one direction. The unidirectional airflow generation means 18 can individually control the exhaust amount for each of the divided zones 14A to 14C by the exhaust means 18G to 18I. The dry air sucked from the suction ports 18A to 18C is preferably air conditioned air whose temperature and humidity are air conditioned.

  The length of the first drying zone 35 is preferably in the range of 0.3 to 1.0 seconds for the residence time of the elongated support in the first drying zone. Specifically, it is preferably 200 mm or more and 600 mm or less in the running direction of the long support. Moreover, it is preferable that the drying state of the coating film surface is a constant rate drying period in the first drying zone. The constant rate drying period will be described later.

  By setting the length of the first drying zone 35 in the above range, it is possible to sufficiently dry in the first drying step, and thus it is possible to suppress the occurrence of broad spots A. If the drying in the first drying step is short, the drying is insufficient and the drying speed is slow. In addition, if the first drying process is long, the initial drying is completed and the drying speed is easily affected by wind, so that broad spots A are likely to occur.

  In addition, the length of a 1st drying zone and a 2nd drying zone means the length which match | combined all the zones, when each zone is formed by the some division | segmentation zone.

  Moreover, the wind speed of the drying wind of the 1st drying zone 35 is supplied with the wind speed larger than 0.5 m / s. As the long support travels, entrained wind is generated on the surface of the coating film. Therefore, in order to generate regular dry wind having a one-way flow in the drying zone 14, the dry wind is at a speed higher than the above speed. Need to be supplied at.

  In addition, the wind speed of the drying air in the second drying zone is 1/10 or less of the traveling speed of the long support, and it is more preferable that the drying air is dried in an airless state where no drying air is supplied. By slowing down the supply speed of the drying air in the second drying zone, it is possible to perform drying with the accompanying air accompanying the running of the long support, and it is not affected by the drying air of the fine wind. Occurrence can be suppressed.

  The width of the drying device main body 16 is formed to be larger than the width of the web 12, and the wind control portions are provided with the open portions on both sides of the drying zone 14 covered with wind control plates 32. This air conditioning portion secures a distance from the suction port 18A to 18C to the coating film end and a distance from the coating film end to the exhaust port 18D to 18F, and the drying air enters the drying zone 14 only from the suction port 18A to 18C. This is designed to prevent a rapid flow of drying air from being generated in the drying zone 14. The length of the air conditioning portion, that is, the air conditioning plate 32, is preferably in the range of 50 mm or more and 150 mm or less on both the suction port side and the exhaust port side.

  Among the divided zones 14A to 14G, the divided zone 14A closest to the coating machine is a zone where fresh air outside the drying zone 14, for example, the above-described conditioned air is dried immediately after the coating liquid is applied to the web 12. It is important to make it difficult to enter 14. For this purpose, the division zone 14A is arranged so as to be adjacent to the applicator 20, and the position of the wire bar 20A of the applicator 20 and the position of the backup roller 24 are adjusted in addition to the air conditioning plate 32 described above, It is preferable that the web 12 travels in the immediate vicinity of the divided zone 14 </ b> A so that the web 12 covers the open portion of the divided zone 14 </ b> A.

  Further, a shielding plate 34 is provided at a position opposite to the drying apparatus main body 16 with the web 12 interposed therebetween so that the stable running of the web 12 is not hindered by the air such as the air-conditioned air.

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

  The web 12 has a layer that becomes an alignment film by rubbing a previously applied alignment film forming resin, and the coating liquid is an example of an organic solvent-based coating liquid containing a liquid crystalline discotic compound. explain.

  Immediately after the coating liquid is applied to the web 12 supported by the backup rollers 22, 24, and 26 by the wire bar 20 </ b> A of the coating machine 20, the coating film surface is initially dried by the drying device 10. In this initial drying, it is preferable to start drying with a drying air immediately after application, and immediately after application within 5 seconds at the latest.

  In the initial drying in the first drying zone, the coating film surface immediately after coating is in a state that the organic solvent is sufficiently contained. In particular, in the initial drying immediately after coating the coating solution containing the organic solvent, the evaporation of the organic solvent is not performed. Due to the distribution (fluctuation), a temperature distribution is generated on the coating film surface. This causes a distribution of surface tension, causing the coating liquid to flow in the surface of the coating film, and the coating film in the slow-drying portion becomes thin, resulting in broad spots A. Since the broad spots are eliminated by rapid drying, it is effective to increase the drying air in the first drying zone.

  However, in the coating film in the vicinity of the drying change point that changes from the constant rate drying period to the decreasing rate drying period, the drying speed is likely to fluctuate significantly. Therefore, if the speed of the drying air is high, broad spots A are generated. . Therefore, the occurrence of uneven drying can be suppressed by setting the drying air to be a breeze or no air before the drying change point elapses.

  In addition, the alignment direction of the liquid crystalline discotic compound is determined by rubbing the surface of the alignment film forming resin, but in the initial drying, when the wind speed is different from the rubbing direction, When the vortex is generated and the wind hits the coating film surface, a part of the coating film surface is displaced in the orientation direction, which causes sharp spots B.

  From this, in order to prevent spots A and B on the coating film surface during the initial drying, there is no external trouble during the initial drying from the coating to the stop of the flow of the coating liquid on the coating film surface. It is important to prevent the uniform air from hitting the coating film surface and always keep the organic solvent concentration in the vicinity of the coating film surface constant.

  Therefore, in the coating film drying method and coating apparatus of the present invention, drying is performed by supplying a drying air having a wind speed higher than 0.5 m / s in the first drying zone where the drying speed is desired to be increased. Thereby, since the influence of the accompanying wind accompanying driving | running | working of a elongate support body becomes small, a drying rate can be accelerated | stimulated with the drying wind of one direction. On the contrary, in the second drying zone, the speed of the drying air is 1/10 or less of the traveling speed of the long support, so that the drying can be performed by the accompanying air without being influenced by the drying air. The occurrence of uneven drying can be suppressed.

  Here, the drying period will be described. The details are as described in the Drying chapter of the Chemical Engineering Handbook. FIG. 4 shows the temperature change of the film surface temperature with respect to the drying time. In FIG. 4, the horizontal axis represents the drying time, and the vertical axis represents the film surface temperature. When the coating film is dried at a constant air speed and air temperature, the film surface temperature, which is the wet bulb temperature, increases from a certain time as shown in FIG. The period before the rise is referred to as the constant rate drying period, and during the wet bulb temperature, the movement of the volatile matter in the film is sufficiently fast and there is a sufficient liquid that volatilizes from the surface.

  However, when the rate of drying starts to rise, the volatile matter in the film is insufficient on the surface, and even if the same wind is applied, the drying rate becomes slow. The critical point of change in drying is the point at which the solid content is 60 to 80%.

The solid content here means solid content (%) = solid content / (volatile content + solid content) × 100
It is. The solid content and (volatile content + solid content) can be obtained from the following formulas (1) and (2) by weight measurement.
Solid content = [A: Weight of dried film] − [B: Weight of support before coating] (1)
Volatile content + solid content = [C: weight of film sampled in a certain drying zone]-[B: weight of support before coating] (2)
Therefore, when a sample is taken in a certain zone, A: a weight that is completely dried above the boiling point of volatile matter,
B: Weight measured by removing A,
C: Weight measured immediately after sampling,
The solid content can be obtained by measuring each. When the solid content of the sample in the windless zone was measured under the conditions of the examples of the present invention, all were between 60 and 80%.

  In the second drying zone, the temperature of the support is adjusted so that the temperature of the elongated support is higher than the film surface temperature of the coating film. The temperature difference between the temperature of the support and the film surface temperature is preferably 2 ° C. or higher. By increasing the temperature by 2 ° C. or more, drying can be promoted by the temperature difference between the temperature of the support and the film surface temperature.

  Moreover, it is preferable that the film surface temperature of the coating film in a 2nd drying zone is 20 to 23 degreeC. By setting the film surface temperature of the coating film within the above range, the drying efficiency of the coating film can be increased. When the film surface temperature of the coating film is low, the drying speed is slow. Moreover, since it is necessary to make the temperature of a support body higher when film surface temperature is high, manufacturing cost becomes high.

  As shown in FIG. 4, drying is promoted in the constant rate drying period in the initial drying stage where the difference between the air temperature and the film surface temperature is large. In addition, the drying speed is slow in the rate-decreasing drying stage in the latter half of the drying when the film surface temperature rises and the difference between the air temperature and the film surface temperature becomes small. Therefore, drying increases as the difference ΔT between the air temperature and the film surface temperature increases, and drying increases as the wind speed of the drying air increases. When the wind in the latter half is small as in the present invention, drying becomes gradual. However, during evaporation, the coating solution loses the latent heat of evaporation, so the temperature of the remaining coating film decreases. And the temperature of the coating film is an average of the temperature of the adjacent support, but when the heat capacity of the support is large relative to the coating film, that is, when the support is sufficiently thicker than the coating film The film surface temperature during initial drying immediately after coating is governed by the support temperature before coating. This can be explained thermodynamically as follows.

Now, H: latent heat of vaporization, [rho _L: liquid density, [delta] _L: Ekiatsumi, Mw: MEK molecular weight, [rho _B: Base Density, [delta] _B: Base Thickness, Cp: base specific heat, △ T: [before coating base temperature] -[Final film surface temperature], assuming that all of the latent heat of evaporation is absorbed by the coating film, that is, assuming that the coating film and the support are insulated from the outside air,
Hρ _L δ _L / (Mw / 1000) = ρ _B δ _B CpΔT... 1)
1) Organizing the formula,
ΔT = 1000H × (ρ _L δ _L / ρ _B δ _B ) / (MwCp) 2)
For example, when a case where a coating film having a thickness of 5 μm is formed on an 80 μm triacetyl cellulose support using MEK solvent is calculated, H = 35000 (J / mol), ρ _L = 1000 (kg / m ³ ), δ _L = 5 (μm), Mw = 72.1 (g / mol); MEK molecular weight, ρ _B : 1300 (kg / m ³ ), δB = 80 (μm), Cp = 1764 (J / kg · k), Than,
ΔT = 1000 × 35000 × (1000 × 5/1300/80) / (72.1 × 1764) = 13 (° C.)... 3)
It becomes.

  That is, as the drying progresses, the latent heat of vaporization is deprived and the film surface temperature decreases. As the film surface temperature decreases, the temperature difference ΔT between the ambient temperature and the film surface increases. The drying can be progressed by setting the film surface temperature to a low temperature and increasing the temperature difference ΔT between the ambient temperature and the film surface as “drying proceeds”.

  In the case where a thin layer coating of an organic solvent as in the present invention is used to prevent spots caused by turbulence in the drying air, it is necessary to suppress the wind speed of the drying air in the second drying zone to a slight wind of 0.5 m / s or less. . Therefore, there is little influence which contributes to drying by being heated by drying air substantially. That is, the film surface temperature is governed by the support temperature before coating, and indirectly affects the spots.

  FIG. 5 shows a process diagram in which a heating means is incorporated in front of the coating machine. An example of the heating means is the heating roller 81 shown in FIG. Moreover, as a heating means, if the elongate support body before application | coating can be heated, it will not specifically limit, It can use. By heating the elongated support with the heating roller 81 and then applying the coating liquid, the support can maintain the temperature up to the second drying zone, and the temperature of the support can be made higher than the film surface temperature. .

  In the present invention, the “no wind state” means a state in which the wind in the vicinity of the coating film is sufficiently smaller than the wind accompanying the support. Since the line is moving at the time of coating, the wind accompanying the web is generated in the direction of travel of the web, but when the wind speed is measured when the line is stopped, a wind speed of 1/10 or less of the running speed of the support is detected. However, in the present invention, it is referred to as “no wind”.

  6 and 7 show another embodiment of the drying apparatus. The drying device shown in FIGS. 6 and 7 is a drying device provided with a recovery means for recovering the solvent volatilized from the coating film in the second drying zone. In the first drying zone, drying air is supplied and drying is performed, and since the solvent is volatilized by the drying air, it is preferable to provide the recovery means only in the second drying zone.

  FIG. 6 shows a configuration in which the coating surface is on the upper side with respect to the horizontal direction. The drying device 60 includes a condensing plate 62 that is a plate-like member provided substantially parallel to the web 12 at a predetermined distance, a side plate that is provided below the front and rear sides of the condensing plate 62, and the like. 12 application surfaces are surrounded. Thereby, when the solvent in the coating liquid of the coating film is volatilized, the volatilized solvent is condensed on the condenser plate 62 and collected.

  Although the material used for the surface which condenses the condensing plate 62 is not specifically limited, such as a metal, a plastic, wood, etc., it is preferable to use the material resistant to the organic solvent in a coating liquid, or to coat the surface.

  The means for recovering the solvent condensed on the condensing plate 62, for example, provides a groove on the condensing surface of the condensing plate 62 and recovers the solvent using capillary force. The direction of the groove may be the traveling direction of the web 12 or may be a direction perpendicular to the traveling direction. As shown in FIG. 6, when the condensing plate 62 is inclined, it is preferable to provide a groove so that the solvent can be easily recovered.

  Further, instead of the condenser plate 62, a configuration having the same function, for example, a configuration using a perforated plate, a net, a scissors, a roll or the like can be employed.

  A plurality of condensing plates can be arranged in the drying device 60, and the distance between the web 12 and the condensing plate 62 can be changed in the traveling direction of the web 12. As shown in FIG. 6, the distance between the condensing plate 62 and the web 12 may be changed by providing a step in the condensing plate and changing it in a staircase pattern. A configuration may be adopted in which the distance between the condensing plate 62 and the web 12 is changed in a taper shape in the traveling direction of the web 12 by being inclined by a predetermined angle toward the traveling direction.

  FIG. 7 shows another example of the drying apparatus. The drying device 70 is configured such that the coating surface is on the lower side with respect to the horizontal direction, and the coating machine 20 and the condenser plate 72 are disposed on the lower side of the web 12.

  In order to promote evaporation and condensation of the solvent in the coating solution, it is preferable to heat the web 12 and / or the coating film, cool the condensing plates 62 and 72, or both. Furthermore, in order to control the drying speed of the coating film, it is preferable that the temperature is controlled.

  In addition to the drying apparatus described above, a drying apparatus described in Japanese Patent Application Laid-Open No. 2003-170101 can also be used as the drying apparatus of the condensation drying method.

  Moreover, although the example which used the condensing plate as the collection | recovery means was described in FIG.6, 7, an adsorption | suction plate can also be used instead of a condensing plate.

  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 web 12 is coated with an optical compensation sheet coating solution, a magnetic coating solution, a photographic photosensitive coating solution, a surface protection antistatic or slipping coating solution, and the like, after being dried and desired. Those cut into lengths and widths are also included, and typical examples thereof include optical compensation sheets, various photographic films, photographic papers, 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.

  Hereinafter, practical effects of the present invention will be described by way of examples.

  It dried on the conditions of Examples 1-7 of FIG. 8, and Comparative Examples 1-6, and generation | occurrence | production of the spot of a coating film was confirmed. The wind speed was measured at the maximum value when the wind speed was rotated 360 degrees with the line stopped.

  First, the optical compensation sheet manufacturing process will be described. As shown in FIG. 3, the web 12 sent out by the sending machine 40 is supported by a plurality of guide rollers 42, 42. After passing through the drying apparatus 10 of the present invention for performing initial drying, the drying zone 46 for performing main drying, the heating zone 48, and the ultraviolet lamp 50, the film is wound by a winder 52.

As the web 12, triacetyl cellulose (Fujitack, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm was used. Then, the surface of the web 12, the long chain alkyl-modified Poval (MP-203, manufactured by Kuraray Co., Ltd.) 2 weight percent solution after the film 1 m ² per 25ml application was made by drying for 1 minute at 60 ° C 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 30 m / min to form an alignment layer.

And, on the alignment film obtained by rubbing the alignment film resin layer, the coating liquid is 4: 1 by weight ratio of (3) of the discotic compound TE-8 and (5) of TE-8. A coating liquid containing a liquid crystalline compound to be 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 mixture was used. While running the web 12 under various coating speed conditions, this coating solution was applied onto the alignment film with a wire bar 20A so that the amount of the coating solution was 5 ml to 7 ml per 1 m ^{2 of the} web. And the initial drying was performed using the drying apparatus 10 immediately after application | coating.

  The interval between the upper end of the partition plate 28 that divides the drying zone 14 into seven and the coating film surface was set in the range of 5 to 9 mm. The web 12 initially dried by the drying apparatus 10 passes through a drying zone 46 adjusted to 100 ° C. and a heating zone 48 adjusted to 130 ° C. to form a nematic phase. The surface of the liquid crystal layer was irradiated with ultraviolet rays by an ultraviolet lamp 50 while continuously transporting the web 12 coated with the liquid crystalline compound.

The results are shown in FIG. In addition, about the generation | occurrence | production condition of the plaque in FIG. 8, and comprehensive evaluation, it evaluated by the following references | standards.
(Occurrence of spots)
○ ・ ・ ・ No spots were generated. Δ ・ ・ ・ Spots were slightly generated but the quality was not a problem. × ・ ・ ・ Generation of spots was observed.
○: Acceptable as a product and very good surface shape Δ: Acceptable as a product ×… Not acceptable as a product As a result, as can be seen from FIG. 8, the wind speed of the first drying zone is 0.5 m. In the example in which the air velocity was larger than / s and the wind speed in the second drying zone was 1/10 or less of the coating speed, a film in a range acceptable as a product could be formed. However, in Comparative Example 1 and 6, in which the supply speed of the drying air was fast in the second drying zone, the sharp air B was generated because the drying air was supplied even in the reduction drying period. In Example 7 where the temperature difference between the temperature of the support and the film surface was small, the occurrence of drying unevenness was confirmed, but the level was not a problem in terms of quality.

  As described above, the drying air speed in the first drying zone is set to be higher than 0.5 m / s, and drying is performed so as to cancel the entrainment air of the support, and the drying air is made light or no air in the second drying zone. Thus, it was possible to suppress the occurrence of broad spots and sharp spots. Furthermore, by drying the length of the first drying zone, the temperature difference between the film surface and the support, the coating speed, and the speed of the drying air in the first drying zone within an appropriate range, a coating film with even better quality can be obtained. I was able to get it.

It is a side view of the drying apparatus of the present invention. It is a top view of the drying apparatus of the present invention. It is process drawing which integrated the drying apparatus of this invention in the manufacturing process of the optical compensation sheet. It is a figure which shows the temperature change of the film surface temperature with respect to drying time. It is process drawing which integrated the heating means before the coating device. 4 shows another embodiment of a drying device. 4 shows still another embodiment of the drying device. It is a figure which shows the result of an Example. It is a situation figure of the spot (nonuniformity) which generate | occur | produced with the conventional drying system. It is explanatory drawing explaining a broad spot (unevenness). It is explanatory drawing explaining a sharp spot (unevenness).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 60, 70 ... Drying device, 12 ... Elongate support body (web), 14 ... Drying zone, 14A-14G ... Dividing zone, 16 ... Drying device main body, 18 ... Unidirectional airflow generation means, 18A-18C ... Suction port, 18D-18F ... exhaust port, 18G-18I ... exhaust means, 20 ... coating machine, 22, 24, 26 ... backup roller, 28 ... partition plate, 32 ... air conditioning plate, 35 ... first drying zone, 36 ... Second drying zone, 62, 72 ... condensing plate, 81 ... heating roller, A ... broad spots, B ... sharp spots

Claims (6)

Immediately after application of a coating film formed by applying a coating solution containing an organic solvent to a traveling long support, a drying zone is provided to surround the coating film surface to be dried of the traveling long support, In a drying method for drying the coating film by supplying drying air into a drying zone,
It is carried out in the first drying zone preceding the drying zone, and the drying film is supplied onto the coating film surface by supplying drying air having a wind speed of more than 0.5 m / s from one end in the width direction to the other end in the width direction. A first drying step of drying the coating film by generating a unidirectional flow of drying air flowing in the width direction;
It is carried out in the second drying zone after the drying zone, and the coating film is dried by generating accompanying air accompanying the running of the elongated support on the coating film surface by not supplying the drying air at all. A second drying step;
A support temperature adjusting step of adjusting the temperature of the support so that the temperature of the elongated support is higher than the film surface temperature of the coating film in the second drying step ,
A traveling speed of the elongated support is a high speed region of 0.4 to 1.2 m / sec (24 to 72 m / min);
Among the drying zones, the drying zone is divided into the first drying zone and the second drying so that the residence time of the elongated support in the first drying zone is in the range of 0.3 to 1.0 second. A method for drying a coating film, which is divided into zones . Wherein the support temperature adjustment process, drying of the coating film according to claim 1, characterized in that the temperature of the elongated support is adjusted to be higher than 2 ℃ than the surface temperature of the coating film Method. 3. The coating film according to claim 1, wherein the coating film has a wet thickness of 8 μm or less and a thickness of 1/10 or less of the thickness of the elongated support. Method. The method for drying a coating film according to any one of claims 1 to 3, wherein a film surface temperature of the coating film in the second drying zone is 20 ° C or more and 23 ° C or less. In a drying apparatus that dries a coating film formed by applying a coating solution containing an organic solvent to a traveling long support with a coating machine,
A delivery machine and a winder for running the long support at a running speed of 0.4 to 1.2 m / sec (24 to 72 m / min);
A drying apparatus main body that is provided immediately after the coating machine and forms a drying zone that surrounds the coating film surface of the elongate support that travels;
A first drying zone provided with a unidirectional airflow generating means for generating a unidirectional airflow flowing from one end of the elongate support body width direction to the other end, provided at a front portion of the drying zone; ,
A second drying zone that is provided in a subsequent stage of the drying zone, and dries the coating film by an entrained air generated along with the traveling long support without supplying the drying air;
A heating means provided immediately before the coating machine, for heating the elongated support before being coated ,
Among the drying zones, the drying zone is divided into the first drying zone and the second drying so that the residence time of the elongated support in the first drying zone is in the range of 0.3 to 1.0 second. An apparatus for drying a coating film, which is divided into zones . 6. The coating film drying apparatus according to claim 5 , wherein the second drying zone is provided with a recovery means for recovering a solvent volatilized from the coating film.

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