JP2008190841A - Coated film drying method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drying method and device capable of notably suppressing unevenness occuring in an initial drying process immediately after application, and uniformly drying a coated film without changing material properties such as viscosity of coating liquid and the kind of a solvent. <P>SOLUTION: This coated film drying method is characterized by providing a drying zone 14 immediately after application to surround a coated film surface to be dried of a traveling web 12, and in the drying zone 14, sequentially carrying out a first drying process for drying the coated film surface by allowing the web 12 to travel a first drying air zone 35 supplied with drying air of unidirectional flow flowing from one end side to the other end side in the width direction of the web 12, an airless drying process for drying the coated film surface by allowing the web 12 to travel an airless zone 36 with no blowing of drying air; and a second drying process for drying the coated film surface by allowing the web to travel a second drying air zone 36 supplied with drying air of unidirectional flow flowing from the one end side to the other end side in the width direction of the web 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

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. 10 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 spots A had a thin layer of the coating liquid film 102 containing a liquid crystalline discotic compound as shown in FIG. In FIG. 11, 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.

  The present invention has been made in view of such problems, and can remarkably suppress spots generated in the initial drying process immediately after application, and also changes physical properties such as the viscosity of the coating solution and the type of solvent. An object of the present invention is to provide a drying method and apparatus capable of uniformly drying a coating film without any problems.

  According to a first aspect of the present invention, in order to achieve the above object, in the method for drying a coating film formed by applying a coating solution containing an organic solvent to a traveling long support, a drying zone is formed immediately after the coating. A one-way flow that flows from one end side to the other end side in the width direction of the long support in the drying zone and surrounds the coating film surface to be dried of the long support that travels. A first drying step for drying the coating film surface by running the elongate support in a first drying air zone for supplying wind; and the elongate support in a non-winding zone that does not blow dry air. A windless drying step of running and drying the coating film surface, and a second drying air zone for supplying a one-way flow of drying air flowing from one end side to the other end side of the elongated support width direction, A second dryer that dries the coated film surface by running a long support. When, it provides a method for drying a coating film, which sequentially performed.

  According to the first aspect, the drying zone is provided immediately after coating, and the unidirectional flow of drying air flowing from one end side to the other end side in the width direction of the support is blown on the coating film surface of the traveling long support. When drying, a windless drying process is performed by providing a windless zone in the middle of the drying zone that does not blow dry wind. That is, in the first drying process in the initial stage of drying, a large amount of organic solvent remains on the coating film surface, and fluctuations due to the distribution of the organic solvent evaporated from the coating film surface are likely to occur, and this fluctuation promotes the occurrence of spots. Accordingly, in the first drying step, the generation of spots is suppressed by quickly removing the evaporated organic solvent from the surface of the coating film by blowing a unidirectional flow of drying air onto the surface of the coating film.

  However, if the drying air is continuously blown on the surface of the coating film while the organic solvent concentration in the coating film is reduced and the drying speed is slowed down by the first drying step, it becomes a cause of spots. For this reason, after the first drying step, a non-air drying step in which no drying air is supplied is performed once, and then the coating film surface is again sprayed with a one-way flow of drying air to dry, thereby generating spots throughout the drying zone. Can be suppressed.

  According to a second aspect of the present invention, in the first aspect, the airless drying step is provided at a position where the dry state of the coating film surface changes from a constant rate drying period to a decreasing rate drying period.

Claim 2 shows at what point it is preferable to perform the windless drying process through the drying of the entire drying zone, and the drying state of the coating film surface changes from the constant rate drying period to the decreasing rate drying period. It is preferable to be provided at the position of the drying change point. Thereby, generation | occurrence | production of the spot in drying of a coating film can be suppressed further.

  A third aspect of the present invention according to the first aspect is characterized in that the windless drying step is provided at a position where the solid content in the coating film dried in the drying zone is 60 to 80% by mass.

  The third aspect of the present invention is another aspect of the time when it is preferable to perform the windless drying process through the drying in the entire drying zone, and the solid content in the coating film dried in the drying zone is 60 to 80% by mass. It is preferable to be provided at a position. This is because the drying change point is located in a range where the solid content in the coating film is 60 to 80% by mass. Therefore, if the solid content in the coating film is measured by test drying or the like, it can be determined at which position in the drying zone the airless drying process should be performed.

  A fourth aspect of the present invention is the method according to the first aspect, wherein the length of the first dry wind zone is 80 mm or more and 1600 mm or less in the running direction of the long support, and the length of the non-wind zone is the long shape. It is 20 mm or more and 1000 mm or less in the running direction of the support.

  The fourth aspect of the present invention is still another aspect of the time when it is preferable to perform the windless drying process through the drying of the entire drying zone. The length of the first drying wind zone and the length of the windless zone are as described above. Therefore, the above-mentioned drying change point can be located in the windless drying process.

  A fifth aspect according to any one of the first to fourth aspects, wherein the average wind speed of the drying air in the first drying step is 0.3 m / s or more and 0.6 m / s or less, and the drying air in the second drying step. The average wind speed is from 0.1 m / s to 0.3 m / s.

  According to the fifth aspect, since the average wind speed of the drying air in the second drying process is made smaller than the average wind speed of the drying air in the first drying process, the occurrence of spots can be further suppressed.

  A sixth aspect of the present invention provides the liquid crystal layer coating liquid according to any one of the first to fifth aspects, wherein the dried coating film is a liquid crystal layer coating liquid coated on an alignment film that has been subjected to a rubbing process when an optical compensation sheet is manufactured. It is characterized by being.

  This is because the drying method of the present invention is particularly effective in drying a coating film formed by applying a coating liquid for a liquid crystal layer applied on a rubbing-treated alignment film to a long support.

  A seventh aspect according to any one of the first to sixth aspects, wherein the coating liquid contains a fluoroaliphatic group-containing polymer containing a repeating unit derived from the monomer (i) below, and the fluoroaliphatic group-containing polymer: It satisfies the following condition (ii).

(I) a first fluoroaliphatic group-containing monomer having a terminal structure represented by — (CF ₂ CF ₂ ) ₃ F; and a second fluoro having a terminal structure represented by — (CF ₂ CF ₂ ) ₂ F And an aliphatic group-containing monomer.

  (Ii) The product C × F of the concentration C% by mass of the fluoroaliphatic group-containing polymer in the coating solution and the fluorine content F% in the fluoroaliphatic group-containing polymer is 0.05 to 0.12. The surface tension ratio (surface tension at 10 milliseconds after coating / surface tension at 1000 milliseconds after coating) of the coating liquid measured by the maximum bubble pressure method is 1.00 to 1.20. It is.

  According to the seventh aspect, the fluoroaliphatic group-containing polymer containing the monomer repeating unit (i) and satisfying the above (ii) is added to the coating solution. As a result, in the initial drying after coating, the fluoroaliphatic group-containing polymer quickly moves to the air interface of the coating solution and stabilizes the coating film air interface. Even if it dries at high speed under conditions, it is possible to suppress the occurrence of drying unevenness. Further, when C × F is less than 0.05, there is a problem that the liquid crystal compound is not sufficiently controlled at the air interface, and the appearance characteristics (degree of unevenness) of the optical film is deteriorated, and exceeds 0.12. When the liquid crystal composition is applied to a transparent support, the coating properties are not sufficient, and the appearance characteristics of the optical film (repel failure occurs) are problematic. When C × F is within the above range, there is no such problem, and unevenness during initial drying can be further reduced.

The surface tension ratio of (ii) above is mainly a value at room temperature (25 ° C.), and the surface tension of the coating solution is determined using a dynamic surface tension measuring device (MPT2: manufactured by LAUDA) by the maximum bubble pressure method. Can be measured. Moreover, as for the application quantity of a coating liquid, 5.0-6.4 mL / m < ² > is more preferable. The maximum bubble pressure method is a method in which nitrogen gas is blown out from a thin tube inserted into a liquid to expand the bubbles, thereby expanding the interface between the liquid and gas and measuring the surface tension from the maximum pressure at that time.

  An eighth aspect of the present invention provides the coating film according to any one of the first to seventh aspects, wherein the coating film formed has an air interface when the fluorine atom abundance (F / C) measured by the ESCA method is 100 at the air interface of the coating film. The fluorine atom abundance (F / C) at a position of 10 nm in the depth direction from 2 to 10.

  According to the eighth aspect, since the fluorine concentration on the surface of the coating film is high and fluorine exists also in the coating film, a coating film having excellent appearance characteristics can be formed.

  According to a ninth aspect of the present invention, there is provided a coating film drying apparatus formed by applying a coating solution containing an organic solvent to a traveling long support by a coating machine in order to achieve the above object, and is provided immediately after the coating machine. A drying apparatus main body forming a drying zone surrounding a coating film surface to be dried of the long support that travels, and one end side in the width direction of the long support formed on the first half side of the drying zone A first drying air zone having unidirectional airflow generating means for generating a unidirectional flow of drying air flowing from the other end side to the other end side, and one side of the elongated support body width direction formed on the second half side of the drying zone Formed between a second drying air zone and a second drying air zone having a unidirectional airflow generating means for generating a unidirectional airflow flowing from one end side to the other end side; And no wind zone, before supplying dry air The first drying air zone, to provide a drying apparatus of the coating film, characterized in that and a partition plate for dividing said second dry air zone, and the calm zone together.

According to the ninth aspect, the first drying zone having the unidirectional airflow generating means for generating the drying wind is provided on the first half side of the drying zone formed in the drying apparatus main body, and then the non-winding zone in which the drying wind is not supplied. It has. Therefore, in the initial stage of drying that sufficiently contains an organic solvent, it is possible to dry quickly by supplying wind. Also, when the drying progresses and the organic solvent is low, the distribution of the drying rate becomes large and the spots are more likely to occur, so the generation of spots is suppressed by slowing the drying speed without supplying wind. can do.

  Further, after the no-air zone, a second drying zone having a unidirectional airflow generating means for generating drying air is provided. After passing through the no-air zone, the distribution of the drying speed is reduced again, so that the drying speed can be improved by supplying the drying air in the second drying zone. Since each zone is divided by the partition plate, the drying air flows from one end side to the other end side in each zone and does not flow to the other zones. Therefore, one-way drying air can be supplied.

  ADVANTAGE OF THE INVENTION According to this invention, the spot which generate | occur | produces in the initial drying process immediately after application | coating can be suppressed by adjusting the supply position and wind speed of the drying air during drying, and uniform drying can be performed.

  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. The drying apparatus main body 16 that forms the drying zone 14 and the unidirectional airflow that is formed on the front half side of the drying zone 14 and that generates the unidirectionally flowing drying air that flows from one end side to the other end side in the width direction of the web 12. A first drying air zone 35 including the generating means 18, a non-air blowing zone 36 that does not supply drying air, and a one-way direction that flows from one end side to the other end side in the width direction of the web 12. It is comprised with the 2nd drying wind zone 37 provided with the unidirectional airflow generation means 18 which generates the drying wind of a flow. The inside of the drying zone 14 is divided by a partition plate 28 into a first drying air zone 35, a no-air zone 36, and a second drying air zone 37. The drying device 10 is provided immediately after the coating machine 20 that applies a coating liquid containing an organic solvent to the traveling web 12.

  In the present invention, the “no wind zone” refers to a zone in which dry air is not supplied. Since the line moves at the time of application, a wind accompanying the web is generated in the web traveling direction. If no drying air is supplied, the drying zone is referred to as a “no wind zone” in the present invention. When the wind speed in this windless zone is measured with an anemometer when the line is stopped, a wind speed of 0.1 m / s or less may be detected, but even if the wind speed is detected, it will be referred to as a “windless zone” in the present invention.

  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 and 14B constitute the first dry air zone 35, 14C constitutes the no-air zone 36, and 14D to 14G constitute the second dry air zone 37. 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 air zone 35 and the second drying air zone 37 are provided with unidirectional airflow generation means 18 (see FIG. 2). However, in the windless zone, if the wind is not supplied, the drying method of the present invention can be used for drying, and therefore it is possible to provide a unidirectional airflow generating means in the windless zone. In the present embodiment, the two divided zones 14A and 14B are the first dry wind zone 35, the next one divided zone 14C is the non-wind zone 36, and the next four divided zones 14D to 14G are the second dry wind zone. However, it can be appropriately changed depending on the type of coating liquid, easiness of drying, and the like.

  The one-way airflow generation means 18 mainly faces the suction ports 18A, 18B, 18C, 18D, 18E, and 18F formed on one side of both sides of the drying device main body 16, and the suction ports 18A to 18F on the other side. The exhaust ports 18G, 18H, 18I, 18J, 18K, and 18L formed in this manner and the exhaust means 18M, 18N, 18P, 18Q, 18R, and 18S connected to the exhaust ports 18G to 18L. Accordingly, by driving the exhaust means 18M to 18S, the air sucked into the divided zones 14A, 14B and 14D to 14G from the suction ports 18A to 18F is exhausted from the exhaust ports 18G to 18L. , 14B, 14D to 14G generate dry air flowing in one direction from one end side (suction port side) to the other end side (exhaust port side) in the web 12 width direction. And since each division | segmentation zone 14A-14G 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, 14B, and 14D to 14G by the exhaust means 18M to 18S. The dry air sucked from the suction ports 18A to 18F is preferably air conditioned air whose temperature and humidity are air conditioned.

  The length of the first drying air zone 35 is preferably 80 mm or more and 1600 mm or less, and more preferably 50 mm or more and 200 mm or less in the running direction of the long support. Further, the length of the windless zone 36 is preferably 20 mm or more and 1000 mm or less, more preferably 100 mm or more and 500 mm or less in the traveling direction of the long support.

  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 it is shorter than 80 mm, the drying is insufficient and the drying speed is slow. On the other hand, if the length is longer than 1600 mm, 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, by setting the length of the windless zone 36 in the above range, the drying speed of the coating liquid can be slowed, and the drying change point at which the drying state changes from the constant rate drying period to the reduced rate drying period is set in the no wind zone. Can be located. If it is shorter than 80 mm, it is difficult to position the drying change point in the windless zone, and if it exceeds 1000 m, a wind with a wind direction different from the rubbing direction is generated due to running of the web at the end of drying, resulting in sharp spots. B tends to occur.

  In addition, the 1st dry wind zone and a non-wind zone say the length which match | combined all the zones, when it is formed by the some division | segmentation zone.

  Moreover, it is preferable that the average wind speed of the drying wind of a 1st drying wind process is 0.3 m / s or more and 0.6 m / s or less, More preferably, it is 0.5 m / s or more and 0.6 m / s or less. . By setting it as the said range, since it can fully dry in a 1st drying process, generation | occurrence | production of the broad spot A can be suppressed. When it is slower than 0.3 m / s, the drying is insufficient and the drying speed becomes slow. Moreover, when it is faster than 0.6 m / s, since the drying change point is located in the first drying zone, broad spots A are likely to occur.

  Moreover, it is preferable that the average wind speed of the drying wind of a 2nd drying process is 0.1 m / s or more and 0.3 m / s or less, More preferably, it is 0.1 m / s or more and 0.15 m / s or less. At the end of drying, sharp spots B are generated by a wind having a wind direction different from the rubbing direction of the rubbing treatment applied to the alignment film under the coating film. Generation | occurrence | production of this sharp spot B can be suppressed by supplying the drying wind weaker than the drying wind of a 1st drying process to a fixed direction. Therefore, it is preferable to supply the drying air within the above range.

  In the present invention, the average wind speed is obtained by multiplying the absolute value of the wind speed of each divided zone by the length in the conveyance direction of the web of the divided zone, and dividing by the total length of the zone for obtaining the total. Can be obtained.

  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 18G to the coating film end and a distance from the coating film end to the exhaust port 18H to 18N, and the drying air is only in the drying zone 14 from the suction ports 18A to 18G. 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 this initial drying, 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 distribution (fluctuation) of the organic solvent. As a result, 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 quick drying, it is effective to increase the initial drying wind. However, the inventors have discovered that, if no wind is blown in a dry zone where broad spots can occur, broad spots do not occur. This means that a windless zone is provided.

  That is, it is possible to suppress the occurrence of broad spots A by increasing the initial drying wind or not blowing any wind. However, since the distribution of the drying speed becomes large at the drying change point, the drying speed changes significantly due to the influence of the drying air, and broad spots A are generated. Further, when drying is performed without supplying any wind from the beginning, the problem that the drying time increases and the production efficiency deteriorates cannot be solved.

  In order to avoid this, it is possible to suppress the occurrence of broad spots A by making the wind in the drying zone corresponding to the drying change point no air and extremely slowing the drying.

  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. Accordingly, it is important to blow a weak wind so that sharp spots do not occur after passing through a dry zone where broad spots occur. This is the effect of drying by blowing air again when the entire film has changed from the constant rate drying period to the decreasing rate drying period.

  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.

  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%.

  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.

[Coating solution]
Next, the coating solution used in the present invention will be described. The coating liquid used for the coating film drying method of the present invention is not particularly limited and can be used. However, preferably, the product C × F of the concentration C mass% of the fluoroaliphatic group-containing polymer in the coating solution and the fluorine content F mass% attributable to the fluoroaliphatic group-containing polymer is 0.05 to 0.12. The surface tension ratio (surface tension at 10 msec after application / surface tension after 1000 msec after application) measured by the maximum bubble pressure method of the coating solution is 1.00 to 1 .20 is preferably satisfied. By appropriately adjusting the surface tension of the coating liquid, the leveling property of the coating liquid can be improved. Therefore, by setting the surface tension ratio within the above range, the coating liquid can be suitably used.

  That is, if the surface tension ratio is greater than 1.20, the moving speed to the air interface immediately after coating is slow, the stability of the coating surface at the air interface is poor, and the effect of reducing unevenness during initial drying is sufficient. Not. If the surface tension ratio is in the range of 1.00 to 1.20, there is no such inconvenience, and unevenness during initial drying can be further reduced.

  The content of the fluoroaliphatic group-containing polymer according to the present invention relative to the coating composition mainly comprising a liquid crystal compound (coating component excluding the solvent) is preferably in the range of 0.05 to 1% by mass. A range of 1 to 0.5% by mass is more preferable. When the addition amount of the fluoroaliphatic group-containing polymer is less than 0.05% by mass, the effect of improving the leveling property is insufficient, and when it exceeds 1% by mass, the performance as an optical film (for example, uniform retardation) For example, adversely affecting sex etc.).

  In addition, the present inventors have determined that the surface tension of the coating solution is a chemical structure of the fluoroaliphatic group-containing polymer added to the coating solution, specifically, at least one fluoroaliphatic group constituting the fluoroaliphatic group-containing polymer. It was found to be closely related to the terminal structure of the contained monomer.

That is, the terminal structure of the fluoroaliphatic group-containing monomer constituting the fluoroaliphatic group-containing polymer is changed from the conventional — (CF ₂ CF ₂ ) _n H to — (CF ₂ CF ₂ ) _n F, whereby the organic solvent The surface tension of a coating solution containing a large amount of can be reduced. N is preferably 2 to 4, and more preferably 2 or 3.

In addition, the terminal structure of the fluoroaliphatic group-containing monomer is, _- and (CF 2 _{CF 2)} a first fluoroaliphatic group-containing monomer is _{3 F, - (CF 2 CF} 2) a second fluoro is ₂ F More preferably, the copolymer contains an aliphatic group-containing monomer.

  In the fluoroaliphatic group-containing polymer, the portion other than the terminal structure is not particularly limited, and various repeating units can be adopted.

  Next, the fluoropolymer will be described. The fluoropolymer preferably used in the drying method of the present invention comprises at least one repeating unit derived from a fluoroaliphatic group-containing monomer represented by the following general formula [1] and poly (oxyalkylene) acrylate and / or poly A fluoroaliphatic group-containing polymer containing at least one repeating unit derived from a monomer of (oxyalkylene) methacrylate.

R ₁ represents a hydrogen atom or a methyl group, X represents an oxygen atom, a sulfur atom or —N (R ₂ ) —, m represents an integer of 1 to 6, and n represents an integer of 2 to 4. R ₂ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, specifically a methyl group, an ethyl group, a propyl group or a butyl group, preferably a hydrogen atom or a methyl group. X is preferably an oxygen atom.

  M in the general formula [1] is preferably an integer of 1 to 6 and particularly preferably 2. Moreover, n is 2 or more and 4 or less, 2 or 3 is particularly preferable, and a mixture thereof may be used.

  Next, poly (oxyalkylene) acrylate and / or poly (oxyalkylene) methacrylate, which are other components constituting the fluoroaliphatic group-containing polymer, will be described (hereinafter, when referring to both acrylate and methacrylate, both (Sometimes called (meth) acrylate).

Polyoxyalkylene group can be represented by _{(OR) X,} R is an alkylene group having 2 to 4 carbon atoms, such as _{-CH 2 CH 2 -, - CH} 2 CH 2 CH 2 -, - CH (CH ₃ ) CH ₂ — or —CH (CH ₃ ) CH (CH ₃ ) — is preferred.

  The oxyalkylene units in the poly (oxyalkylene) group may be the same as in poly (oxypropylene), or two or more different oxyalkylenes may be randomly distributed. It may be a linear or branched oxypropylene or oxyethylene unit, or a linear or branched oxypropylene unit block and an oxyethylene unit block.

  In this poly (oxyalkylene) chain, a plurality of poly (oxyalkylene) units are linked to each other by one or more chain bonds (for example, -CONH-Ph-NHCO-, -S-, etc., where Ph represents a phenylene group). (Represented) can also be included. If the chain bond has a valence of 3 or more, this provides a means for obtaining branched oxyalkylene units. When this copolymer is used in the present invention, the molecular weight of the poly (oxyalkylene) group is suitably from 250 to 3,000.

  Poly (oxyalkylene) acrylates and methacrylates are commercially available hydroxypoly (oxyalkylene) materials such as “Pluronic” (Pluronic (Asahi Denka Kogyo Co., Ltd.)), “Adeka Polyether” (Asahi Denka Kogyo Co., Ltd.). "Carbowax" [Carbowax (Glyco-Products)], "Triton" (Toriton (Rohm and Haas)) and "PEG" (Daiichi Kogyo Seiyaku Co., Ltd.) Can be produced by reacting the product with acrylic acid, methacrylic acid, acrylic chloride, methacrylic chloride or acrylic acid anhydride in a known manner. Apart from this, poly (oxyalkylene) diacrylate produced by a known method can also be used.

  As one aspect of the fluoroaliphatic group-containing polymer used in the present invention, a copolymer of a fluoroaliphatic group-containing monomer represented by the general formula [1] and polyoxyalkylene (meth) acrylate is used.

As a preferable aspect of the fluoroaliphatic group-containing polymer used in the present invention, a first fluoroaliphatic group-containing monomer in which the terminal structure is represented by — (CF ₂ CF ₂ ) ₃ F in the general formula [1] A copolymer containing a second fluoroaliphatic group-containing monomer represented by — (CF ₂ CF ₂ ) ₂ F and polyoxyalkylene (meth) acrylate is used.

  In this case, the total amount of the fluoroaliphatic group-containing monomer represented by the general formula [1] in the fluoroaliphatic group-containing polymer is preferably 20 to 50% by mass of the total constituent monomers of the fluoroaliphatic group-containing polymer, About 40 mass% is more preferable. In addition, (first fluoroaliphatic group-containing monomer) / (first fluoroaliphatic group-containing monomer + second fluoroaliphatic group-containing monomer) is preferably 20 to 80% by mass.

  The amount of the fluoroaliphatic group-containing monomer represented by the general formula [1] in the fluoroaliphatic group-containing polymer used in the present invention is 5 to 60% by mass of the total constituent monomers of the fluoroaliphatic group-containing polymer. It is preferable that it is about 35 to 45% by mass.

  The amount of poly (oxyalkylene) acrylate and / or poly (oxyalkylene) methacrylate is preferably 40 to 95% by mass of the total amount of constituent monomers of the fluoroaliphatic group-containing polymer, and is 55 to 65% by mass. Is more preferable.

  3000-100000 are preferable and, as for the preferable weight average molecular weight of the fluoro aliphatic group containing polymer used by this invention, 6000-80000 are more preferable.

  The fluoroaliphatic group-containing polymer used in the present invention can be produced by a known and conventional method. For example, a general-purpose radical polymerization initiator is added and polymerized in an organic solvent containing monomers such as the above-mentioned (meth) acrylate having a fluoroaliphatic group and (meth) acrylate having a polyoxyalkylene group. It is manufactured by. Further, in some cases, other addition-polymerizable unsaturated compounds can be further added and produced by the same method as described above. Depending on the polymerizability of each monomer, a dropping polymerization method in which a monomer and an initiator are added dropwise to a reaction vessel is also effective for obtaining a polymer having a uniform composition.

  Next, materials for coating solutions other than the above-described fluoroaliphatic group-containing polymer will be described.

(Liquid crystal compound)
Examples of liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.

  The liquid crystal compound includes a metal complex. A liquid crystal polymer containing a liquid crystal compound in a repeating unit can also be used as the liquid crystal compound. In other words, the liquid crystal compound may be bonded to a (liquid crystal) polymer.

(Discotic liquid crystalline compounds)
Examples of discotic liquid crystalline compounds include C.I. Benzene derivatives described in a research report of Destrade et al. (Mol. Cryst. 71, 111 (1981)), C.I. Destrode et al. (Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990)). The cyclohexane derivatives described in the research report of Kohne et al. (Angew. Chem. 96, 70 (1984)) and M.M. Lehn et al. (JCS, Chem. Commun., 1794 (1985)), J.C. Azacrown-type and phenylacetylene-type macrocycles described in the research report of Zhang et al. (J. Am. Chem. Soc. 116, 2655 (1994)) are included.

  In the composition for forming an optically anisotropic layer, an optional additive can be used in combination with the liquid crystalline compound and the fluoroaliphatic group-containing polymer as described above. Examples of additives include an anti-repellent agent, an additive for controlling the tilt angle of the alignment film (tilt angle of the liquid crystalline compound at the optically anisotropic layer / alignment film interface), a polymerization initiator, and an alignment temperature. Additives (plasticizer) to be reduced, polymerizable monomers and polymers, surfactants and the like can be mentioned.

(Anti-repellent agent)
In order to prevent repellency at the time of application, a repellency inhibitor can be used together with a liquid crystal compound, particularly a discotic liquid crystal compound. The repellency inhibitor is not particularly limited as long as it is compatible with a liquid crystal compound and is a polymer compound (polymer) that does not significantly inhibit the tilt angle change or orientation of the liquid crystal compound.

  Examples of the polymer that can be used as the repellency inhibitor are described in JP-A-8-95030, and examples of particularly preferred specific polymers include cellulose esters. Examples of cellulose esters include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose, and cellulose acetate butyrate.

  The amount of the polymer that can be used as a repellency inhibitor is generally in the range of 0.1 to 10% by mass with respect to the liquid crystal compound so as not to inhibit the alignment of the liquid crystal compound. It is more preferably in the range of 1 to 8% by mass, and still more preferably in the range of 0.1 to 5% by mass.

(Orientation film side tilt angle control agent)
As an additive for controlling the tilt angle of the alignment film side surface, a compound having both a polar group and a nonpolar group in the molecule can be added to the optically anisotropic layer.

Examples of polar groups include R—OH, R—COOH, R—O—R, R—NH ₂ , R—NH—R, R—SH, R—S—R, R—CO—R, R—COO—. R, R—CONH—R, R—CONHCO—R, R—SO ₃ H, R—SO ₃ —R, R—SO ₂ NH—R, R—SO ₂ NHSO ₂ —R, R—C═N— _{R, HO-P (-R)} 2, (HO-) 2 P-R, P (-R) 3, HO-PO (-R) 2, (HO-) 2 PO-R, PO (-R) ₃ , R—NO ₂ , R—CN, etc. are examples. Moreover, organic salts (for example, ammonium salt, pyridinium salt, carboxylate, sulfonate, phosphate) may be used.

Examples of polar groups include R—OH, R—COOH, R—O—R, R—NH ₂ , R—SO ₃ H, HO—PO (—R) ₂ , (HO—) ₂ PO—R, PO ( -R) ₃ or an organic salt is preferred. Here, R contained in the polar group represents a nonpolar group, and examples thereof include the following nonpolar groups.

  Examples of the nonpolar group include an alkyl group (preferably a linear, branched or cyclic substituted or unsubstituted alkyl group having 1 to 30 carbon atoms) and an alkenyl group [preferably a linear, branched or cyclic group having 1 to 30 carbon atoms]. Substituted or unsubstituted alkenyl group], an alkynyl group [preferably a linear, branched, or cyclic substituted or unsubstituted alkenyl group having 1 to 30 carbon atoms], an aryl group [preferably a substituted or unsubstituted alkenyl group having 6 to 30 carbon atoms] Examples thereof include an unsubstituted aryl group] and a silyl group [preferably a substituted or unsubstituted silyl group having 3 to 30 carbon atoms].

  These nonpolar groups may further have a substituent. Examples of the substituent include a halogen atom, an alkyl group (including a cycloalkyl group and a bicycloalkyl group), an alkenyl group (a cycloalkenyl group and a bicycloalkenyl group). ), Alkynyl group, aryl group, heterocyclic group, cyano group, hydroxyl group, nitro group, carboxyl group, alkoxy group, aryloxy group, silyloxy group, heterocyclic oxy group, acyloxy group, carbamoyloxy group, alkoxycarbonyl Oxy group, aryloxycarbonyloxy group, amino group (including anilino group), acylamino group, aminocarbonylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfamoylamino group, alkylsulfonylamino group, arylsulfonyl Mino group, mercapto group, alkylthio group, arylthio group, heterocyclic thio group, sulfamoyl group, sulfo group, alkylsulfinyl group, arylsulfinyl group, alkylsulfonyl group, arylsulfonyl group, acyl group, aryloxycarbonyl group, alkoxycarbonyl group And carbamoyl group, arylazo group, heterocyclic azo group, imide group, phosphino group, phosphinyl group, phosphinyloxy group, phosphinylamino group, silyl group and the like.

  An alignment film tilt control agent can also be added to the composition for forming an optically anisotropic layer. By orienting the molecules of the liquid crystalline compound in the presence of the alignment film tilt control agent, the tilt angle of the liquid crystalline molecules at the alignment film side interface can be adjusted. The amount of change in tilt angle at this time is related to the rubbing density. If an alignment film having a high rubbing density is compared with an alignment film having a low rubbing density, the tilt angle is more likely to change in the alignment film having a low rubbing density even if the amount of the alignment film tilt control agent added is the same. Therefore, the preferred range of the added amount of the alignment film tilt control agent varies depending on the rubbing density of the alignment film to be used, the desired tilt angle, and the like. The content is preferably 0001% by mass to 30% by mass, more preferably 0.001% by mass to 20% by mass, and still more preferably 0.005% by mass to 10% by mass. The tilt angle refers to an angle formed by the normal line between the major axis direction of the liquid crystal compound molecule and the interface (alignment film interface or air interface).

(Polymerization initiator)
It is preferable to form an optically anisotropic layer by fixing the molecules of the liquid crystal compound in an aligned state. As a method for fixing the alignment state, it is preferable to use a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. In order to prevent deformation of the support and the like due to heat, the photopolymerization reaction is performed. preferable.

  Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin compounds ( US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), acridine, and Phenazine compounds (described in JP-A-60-105667 and US Pat. No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970) are included.

  The amount of the photopolymerization initiator used is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution. It is preferable to use ultraviolet rays for light irradiation for polymerization of liquid crystalline molecules.

The irradiation energy ^is preferably in the range of ^{20mJ / cm 2 ~50J / cm 2} , more preferably in the range of ^{20mJ / cm 2 ~5000mJ / cm 2} , a range of 100mJ / cm ² ~800mJ / cm 2 More preferably, In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. A protective layer may be provided on the optically anisotropic layer.

(Polymerizable monomer)
The composition for forming an optically anisotropic layer may contain a polymerizable monomer together with the liquid crystalline compound. The polymerizable monomer that can be used in the present invention is not particularly limited as long as it is compatible with the liquid crystal compound and does not cause a significant change in tilt angle or inhibition of alignment of the liquid crystal compound. Among these, compounds having a polymerization active ethylenically unsaturated group such as a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group are preferably used. The addition amount of the polymerizable monomer is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the liquid crystal compound. In addition, it is particularly preferable to use a monomer having two or more reactive functional groups because an effect of improving the adhesion between the alignment film and the optically anisotropic layer can be expected.

(polymer)
Although the composition for forming an optically anisotropic layer contains the fluoroaliphatic group-containing polymer according to the present invention, another polymer may be used together with the discotic liquid crystalline compound. The polymer preferably has a certain degree of compatibility with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound.

  Examples of such polymers include cellulose esters. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose, and cellulose acetate butyrate.

  The addition amount of the polymer is preferably in the range of 0.1 to 10% by mass with respect to the discotic liquid crystalline compound so as not to inhibit the orientation of the discotic liquid crystalline compound, and 0.1 to 8% by mass. More preferably, it is in the range of 0.1 to 5% by mass. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.

(Coating solvent)
The composition for forming an optically anisotropic layer can be prepared as a coating solution. As a solvent used for preparation of a coating liquid, an organic solvent is preferable.

  Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, chloroform). , Dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

(Coating film)
The coating film formed by the drying method of the present invention has a position of 10 nm in the depth direction from the air interface when the fluorine atom abundance (F / C) measured by the ESCA method is 100 at the air interface of the coating film. It is preferable that the fluorine atom abundance ratio (F / C) is 2-10. By increasing the fluorine concentration on the surface of the coating film and further including fluorine inside the coating film, a coating film having good appearance characteristics can be formed.

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

[Test Example 1: Drying device]
Using the drying apparatus of the present invention, drying was performed under the conditions of Tables 1 to 11 and Comparative Examples 1 to 5 at a wind speed of 0.2 to 0.7 m / s, and the occurrence of coating spots was confirmed. . The wind speed was measured at the maximum value when the anemometer 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. 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 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 solution containing a liquid crystalline compound that was 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 at a running speed of 30 m / min, this coating solution was applied onto the alignment film with a wire bar 20A so that the amount of the coating solution was 5 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 wind direction in the drying apparatus 10 is shown in FIG. (A) shows the wind direction of the conventional drying apparatus. (B) shows the wind direction of the drying air of the drying apparatus of the present invention. As shown in the figure, the drying apparatus of the present invention is provided with a non-wind zone after the first dry wind ventilation zone, and then with a second dry wind ventilation zone.

The results are shown in FIG. In addition, about the generation | occurrence | production condition of the plaque in FIG. 6, and comprehensive evaluation, it evaluated by the following references | standards.
(Generation 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 shown in FIG. 6, in Comparative Example 1 in which no windless zone was provided Since the wind is supplied when changing from the constant rate drying period to the decreasing rate drying period, a distribution is seen in the drying speed, and broad spots are generated. In Example 5 with a long windless zone, although the wind was not supplied, the web was running, so that wind was generated in the running direction of the web, and sharp spots were slightly generated. Also in Example 8 with a long first drying wind zone and Example 12 with a fast wind speed in the first drying wind zone, since the drying in the first drying process is fast, the drying wind in the subsequent first drying process sharpens. There were slight spots. Moreover, in Example 10 where the speed of the drying air in the first drying process is weak, since the supply of the drying air is insufficient, the drying is not uniformly performed, and broad spots are slightly confirmed.

  From the above, it was possible to suppress the occurrence of broad spots and sharp spots by providing a windless zone after the first drying zone. Further, by drying the length of the drying zone and the wind speed of the drying air within an appropriate range, a coating film with even better quality could be obtained.

[Test Example 2: Coating liquid (surface tension)]
Using the composition shown in FIG. 7, it was dissolved in methyl ethyl ketone to prepare a coating solution. The following discotic liquid crystal compound (1) was used as the discotic liquid crystal compound. Moreover, the fluoroaliphatic group containing polymer prepared the coating liquid using the compound of the following compounds (P-0) to (P-4).

Compound (P-0): acidic group-containing monomer

Compound (P-1): ωHC6 type polymer

Compound (P-2): ωFC6 type polymer

Compound (P-3): ωF (C6 + C4) type polymer

Compound (P-4): ωF (C6 + C4) type polymer

  Thus, about the coating liquid from which compositions, such as a fluoro aliphatic group containing polymer, differ, it apply | coated on the transparent support body by the extrusion coating system (E type). And the relationship between the time change of the surface tension of the coating liquid immediately after coating and the appearance characteristics was evaluated.

  The surface tension of the coating solution was measured using a dynamic surface tension measuring device (MPT2: manufactured by LAUDA) by the maximum bubble pressure method. In this method, a certain amount of coating liquid containing a fluoroaliphatic group-containing polymer is placed in a beaker, nitrogen gas is blown out from a thin tube inserted into the beaker, bubbles are expanded, and the maximum pressure when expanding the interface between the liquid and gas is increased. The surface tension was determined. The result is shown in FIG.

As shown in FIG. 8, in Examples 16 and 17 using ωF (C4 + C6) type polymer as the fluoroaliphatic group-containing polymer, from Comparative Examples 2, 4 and 5 using ωFC4 type polymer or ωFC6 type polymer alone. Also, the surface tension was low immediately after application. In Examples 16 and 17, as shown in FIG. 8, the surface tension ratio (surface tension after 10 msec / surface tension after 1000 msec) was as small as 1.1 mN / m ² .

  Therefore, in Examples 16 and 17 using the ωF (C4 + C6) type polymer as the fluoroaliphatic group-containing polymer, immediately after application, compared with Comparative Examples 2, 4 and 5 using the ωFC4 type polymer or the ωFC6 type polymer alone. It can be seen that the adsorption speed at the air interface is high and the effect of stabilizing the coating surface is high. As a result, it was found that unevenness failure caused by initial drying can be prevented and the appearance characteristics of the optical film can be improved.

  Further, in Comparative Example 3 using the ωH type polymer as the fluoroaliphatic group-containing polymer, the surface tension immediately after coating is low and the adsorption rate to the air interface is high, but the ωH type polymer has H groups in part. It was found that the air interface stabilization effect was low and the appearance characteristics were inferior. Moreover, the same tendency was obtained as a result of carrying out the same test for the bar coating method.

[Test Example 3: Coating liquid (fluorine atom abundance ratio)]
A coating film was formed and dried using the coating solutions of Example 16 and Comparative Examples 2 and 3 using the drying apparatus of the present invention. The conditions for forming the coating film were such that the amount of the coating solution was 5 ml to 7 ml per 1 m ^{2 of the} web while running the web at a running speed of 30 m / min. The fluorine atom abundance ratio after drying was measured by ESCA analysis. The results are shown in FIG. The fluorine concentration was measured by ESCA analysis. The measurement was performed using JPS-9000MX made by JEOL. Further, the appearance characteristics in FIG. 9 were evaluated according to the following criteria.

(Preparation of polarizing plate)
The produced optical film was affixed on one side of the polarizer on the polymer substrate (TAC film) surface using a polyvinyl alcohol-based adhesive. Moreover, the saponification process was performed to the 80-micrometer-thick triacetylcellulose film (TD-80U: Fuji Photo Film Co., Ltd. product), and it affixed on the other side of the polarizer using the polyvinyl alcohol-type adhesive agent.

  The transmission axis of the polarizer and the slow axis of the polymer substrate were arranged in parallel. The transmission axis of the polarizer and the slow axis of the triacetyl cellulose film were arranged so as to be orthogonal to each other. In this way, a polarizing plate was produced.

(Evaluation of unevenness on a flat high-intensity light source)
The polarizing plate was bonded to a planar high-intensity light source (FP901 high-intensity planar light source manufactured by Gunma Ushio Electric Co., Ltd.) and compared with a level sample serving as a judgment standard, and unevenness was evaluated with the naked eye.
○ ... Excellent or better than level sample.
X: Inferior to the level sample.

  As a result, in Example 16 using the coating liquid containing the compound (P-3) as the fluoroaliphatic group-containing polymer, the fluorine concentration on the surface of the formed coating film was 100%, and in the depth direction On the other hand, the coating film contained fluorine in the coating film, and a coating film having good appearance characteristics was obtained. In Comparative Example 2 using Compound (P-2) and Comparative Example 3 using Compound (P-1), since fluorine is present only on the surface or the surface fluorine concentration is not 100%, appearance characteristics Was not good.

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 a figure which shows the wind direction (A) of the drying wind of the conventional drying apparatus, and the wind direction (B) of the drying wind of the drying apparatus of this invention. It is a table | surface figure which shows the result of a present Example. It is a table | surface figure which shows the result of a present Example. It is a table | surface figure which shows the result of a present Example. It is a table | surface figure which shows the result of a present 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 ... Drying device, 12 ... Web, 14 ... Drying zone, 14A-14G ... Dividing zone, 16 ... Drying device main body, 18 ... Unidirectional airflow generation means, 18A-18F ... Suction port, 18G-18L ... Exhaust port, 18M -18S ... exhaust means, 20 ... coating machine, 22, 24, 26 ... backup roller, 28 ... partition plate, 32 ... air conditioning plate, 35 ... first drying air zone, 36 ... no wind zone, 37 ... second drying air zone A ... Broad spots, B ... Sharp spots

Claims (9)

In the drying method of the coating film formed by applying a coating solution containing an organic solvent to the long support that travels,
Immediately after the application, a drying zone is provided to surround the coating film surface to be dried of the elongated support that travels, and in the drying zone,
The long support is run to dry the coating film surface in a first drying air zone that supplies a one-way flow of drying air flowing from one end side to the other end side in the width direction of the long support. A first drying step,
A windless drying step of drying the coating film surface by running the elongated support in a windless zone that does not blow dry air;
The long support is run to dry the coating film surface in a second drying air zone that supplies a one-way flow of drying air flowing from one end side to the other end side in the width direction of the long support. And a second drying step of sequentially performing the coating film drying method.   2. The method of drying a coating film according to claim 1, wherein the non-air drying step is provided at a position including a drying change point at which the drying state of the coating film surface changes from a constant rate drying period to a decreasing rate drying period. .   2. The method of drying a coating film according to claim 1, wherein the airless drying step is provided at a position where the solid content in the coating film dried in the drying zone is 60 to 80% by mass.   The length of the first dry wind zone is 80 mm or more and 1600 mm or less in the running direction of the long support, and the length of the windless zone is 20 mm or more and 1000 mm in the running direction of the long support. The method for drying a coating film according to claim 1, wherein:   The average wind speed of the drying air in the first drying process is 0.3 m / s or more and 0.6 m / s or less, and the average wind speed of the drying air in the second drying process is 0.1 m / s or more and 0.3 m / s. The method for drying a coating film according to any one of claims 1 to 4, wherein the drying method is s or less.   6. The dried coating film is a liquid crystal layer coating liquid coated on an alignment film that has been subjected to a rubbing process when an optical compensation sheet is manufactured. The drying method of the coating film as described. The coating solution contains a fluoroaliphatic group-containing polymer containing a repeating unit derived from the monomer (i) below, and the fluoroaliphatic group-containing polymer satisfies the following condition (ii) The drying method of the coating film in any one of Claim 1 to 6.
(I) a first fluoroaliphatic group-containing monomer having a terminal structure represented by — (CF ₂ CF ₂ ) ₃ F; and a second fluoro having a terminal structure represented by — (CF ₂ CF ₂ ) ₂ F And an aliphatic group-containing monomer.
(Ii) The product C × F of the concentration C% by mass of the fluoroaliphatic group-containing polymer in the coating solution and the fluorine content F% in the fluoroaliphatic group-containing polymer is 0.05 to 0.12. The surface tension ratio (surface tension at 10 msec after application / surface tension at 100 msec after application) measured by the maximum bubble pressure method of the coating solution is 1.00-1.20. It is.   The formed coating film has fluorine atoms existing at a position of 10 nm in the depth direction from the air interface when the fluorine atom abundance (F / C) measured by the ESCA method is 100 at the air interface of the coating film. 8. The method for drying a coating film according to claim 1, wherein the rate (F / C) is 2 to 10. In a coating film drying apparatus formed by applying a coating solution containing an organic solvent to a long supporting body traveling by a coating machine,
A drying apparatus main body that is provided immediately after the coating machine and forms a drying zone that surrounds the coating film surface to be dried of the elongated support that runs;
A first drying air zone provided with unidirectional airflow generating means for generating a unidirectional airflow flowing from one end side to the other end side in the widthwise direction of the elongated support, which is formed on the first half side of the drying zone. When,
A second drying air zone formed on the second half side of the drying zone and provided with a unidirectional airflow generating means for generating a unidirectional airflow flowing from one end side to the other end side in the width direction of the elongated support. When,
An airless zone that is formed between the first drying air zone and the second drying air zone and does not supply drying air;
A coating film drying apparatus comprising: a partition plate that divides the first drying air zone, the second drying air zone, and the no-air zone from each other.

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