JP2009221238A - Method for producing porous film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a porous film having uniformly arranged pores. <P>SOLUTION: A solution 15 containing a polymer and a solvent is cast onto a flow casting band 57 with a surface roughly adjusted to a constant temperature. A cast film 68 is formed on the flow casting band 57. Then, determination process is carried out for determining whether a Rayleigh number Ra of the solution 15 in the cast film 68 is less than 5,000 or not. Thirdly, when the Rayleigh number Ra is less than 5,000, moist air 400 having a temperature, a dew point and a condensation point of a solvent adjusted respectively is brought into contact with an exposed face 68a of the cast film 68 to form and grow water drops on the exposed face 68a by dew condensation while evaporating the solvent. When the Rayleigh number Ra is 5,000 or more, determination processing is performed repeatedly. Fourthly, dry air 410 is brought into contact with the exposed face 68a to evaporate the water drops penetrating into the cast film 68. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a porous film having uniformly arranged micropores.

  Today, in the optical field and the electronic field, demands for higher integration, higher information density, and higher definition of image information are increasing. Therefore, it is strongly required to form a finer structure (fine pattern structure) (fine patterning) for films used in these fields. In research in the field of regenerative medicine, a membrane having a fine structure on the surface is effective as a material for cell culture.

  Various methods such as vapor deposition using a mask, photochemical reaction and photolithographic technique using a polymerization reaction, and laser ablation technique have been put to practical use for fine patterning of a film.

It is known that a porous film such as a porous film having a large number of micropores can be obtained by casting a dilute solution of a predetermined polymer under high humidity (for example, see Patent Document 1). An outline of the method for producing the porous film will be briefly described. First, a solution containing a hydrophobic solvent and a polymer is cast on a support to form a cast film on the support. Next, wet air whose temperature, dew point, solvent condensation point, etc. are adjusted within a predetermined range is applied to the exposed surface (hereinafter referred to as an exposed surface) of the cast film, and is included in the cast film. While evaporating the solvent to be evaporated, water droplets are formed on the exposed surface by condensation and grown (hereinafter referred to as a water droplet formation growth step). By this water droplet formation growth process, the water droplets on the exposed surface enter the cast film while maintaining the shape or growing. Finally, dry air is applied to the cast film from which the solvent has been sufficiently removed to evaporate the water droplets. As a result of evaporation of water droplets that have entered the cast membrane, traces of the water droplets become pores and remain in the cast membrane. As a result, a porous film having a large number of micropores can be obtained.
JP 2001-157574 A

  In the water droplet formation growth process described in Patent Document 1, the dimensions and arrangement of the water droplets formed on the exposed surface are expressed by the temperature of the exposed surface of the cast film and the dew point of the air in the vicinity of the exposed surface. Controlled by condensation conditions. Therefore, in order to produce a porous film that is uniformly arranged and has pores with uniform individual dimensions, it is desirable to perform the water droplet formation growth process under conditions that satisfy this dew condensation condition. However, in the water droplet formation growth process, evaporation of the solvent accompanying the endotherm of the system and condensation of the water droplets accompanying the heat generation of the system are mixed. Therefore, it is very difficult to maintain appropriate atmospheric conditions in the water droplet formation growth process.

  Furthermore, even when the water droplet formation and growth step is performed in an environment having the dew condensation conditions, variations in the water droplet arrangement may occur. As a result of intensive studies by the present inventors, it has been found that not only the condensation conditions but also other conditions are required in the water droplet formation and growth process in order to suppress variations in the water droplet arrangement.

  The present invention solves the above-described problem, and in the water droplet formation and growth step, a porous film having fine pores having a substantially uniform formation pitch, in which water droplets are uniformly arranged on the exposed surface of the cast film. An object of the present invention is to provide a method for producing a porous film.

The present invention includes a forming step of casting a solution containing a polymer and a solvent on a support whose surface temperature is adjusted to be substantially constant to form a cast film on the support, and the temperature, dew point and the solvent. Water droplets are formed on the exposed surface of the cast film by condensation while evaporating the solvent contained in the cast film while applying wet air, each of which has its condensation point adjusted, to the exposed surface of the cast film. In a method for producing a porous film comprising: a water droplet formation growth step for growing a water droplet; and a water droplet evaporation step for evaporating the water droplets that have entered the cast film by applying dry air to the exposed surface. The cast film satisfying 1) is characterized by performing the water droplet formation growth step.
(Expression 1) Ra = (g · β · x ³ · | T1-T2 |) / (ν · α) <5000
(However, the acceleration of gravity is g, the temperature of the exposed surface of the cast film is T1, the temperature of the support surface side of the cast film in contact with the surface of the support is T2, the film thickness of the cast film is x, (The thermal expansion coefficient, kinematic viscosity, and temperature conductivity of the solution in the cast film are β, ν, and α.)

  It is preferable to perform a determination step of determining whether or not the Rayleigh number Ra in the cast film satisfies the formula (1) before performing the water droplet formation growth step. In the determining step, the temperature T1 of the exposed surface is measured, and the temperature of the regulated air is determined based on the value of the temperature T1 of the exposed surface so that the Rayleigh number Ra satisfies the formula (1). Preferably, the dew point, the condensation point, and the temperature of the surface of the support are adjusted, and the adjusted air is applied to the exposed surface.

  By adjusting at least one of the temperature of the conditioned air or the wet air, the dew point, the condensation point of the solvent, and the temperature of the surface of the support, the value of | T1-T2 | It is preferable to keep substantially constant in the following range. Further, when the temperature of the surface of the support before the solution is cast is T3 and the temperature of the solution before the solution is cast is T4, the value of | T3−T4 | It is preferable that it is below ℃. Further, the value of | T1-TA1 | is preferably 40 ° C. or less.

  In the water droplet formation growth step, it is preferable that the film thickness x of the cast film is 300 μm or more. Furthermore, it is preferable that the residual solvent amount of the solution in the water droplet formation growth step is 400% by mass or more on a dry basis.

  According to the present invention, since the water droplet formation growth process is performed for the cast film having the Rayleigh number Ra satisfying the formula (1), the variation in the arrangement of the water droplets on the exposed surface due to the convection of the solution in the cast film. Can be suppressed. Therefore, according to the present invention, it is possible to produce a porous film having water droplets formed on the exposed surface of the cast film and having fine pores with a substantially uniform formation pitch.

  As shown in FIG. 1, the porous film manufacturing process 10 includes a casting process 11, a determination process 12, a water droplet formation growth process 13, and a water droplet evaporation process 14. The porous film 16 can be manufactured from the polymer solution (hereinafter referred to as a solution) 15 by the porous film manufacturing process 10.

  As shown in FIG. 2A, in the casting step 11, the solution 15 (see FIG. 1) is cast on the support 21 to form a film-like cast film 22. This solution 15 is obtained by dissolving a polymer that is a raw material of the porous film 16 in a solvent. The method for casting the solution 15 includes a method in which the solution is placed on a stationary support and spread (hereinafter referred to as a batch type), and a method in which the solution flows out from the casting die on the traveling support. Yes, any method can be used in the present invention. In general, the former is suitable for producing a variety of products with a small production volume, and the latter is suitable for mass production. In the latter method, by continuously or intermittently discharging the solution from the casting die, it is possible to continuously produce a long porous film or a porous film having a predetermined length. .

  In the determination step 12, it is determined whether or not the cast film 22 is suitable for the water droplet formation growth step 13. Details of the determination step 12 will be described later.

  As shown in FIG. 2B and FIG. 2C, in the water droplet formation and growth step 13, air that has been adjusted to a desired condition for the main purpose of evaporation and condensation of the solvent on the exposed surface 22a of the cast film 22. (Hereinafter referred to as wet air) 400. As a result, while the solvent 23 contained in the cast film 22 evaporates, water droplets 25 are formed or grown on the exposed surface 22a due to condensation. Due to the evaporation of the solvent 23, the fluidity of the solution 15 in the cast film 22 is lost, and the water droplet 25 enters the cast film 22. In the water drop formation growth step 13, any case may be employed in which the evaporation of the solvent and the formation of the water drop 25 on the exposed surface 22 a are started simultaneously, or one of them is started first.

  Then, as shown in FIG. 2D, when the water droplet 25 has a desired size, the water droplet evaporation step 14 is performed. In the water droplet evaporation step 14, for the main purpose of evaporation of the water droplets, the water droplets that have entered the cast film 22 from which the solvent 23 has been sufficiently removed by applying air 410 adjusted to a desired condition (hereinafter referred to as dry air). Evaporate 25. The porous film 16 can be generated from the cast film 22 by evaporation of the water droplets 25. In the case where the solvent 23 remains in the cast film 22, the conditions are such that the water droplet 25 is evaporated after the solvent 23 is evaporated as much as possible. As this condition, for example, a compound having a lower boiling point than water is used as a solvent, or the vapor pressure of water or solvent contained in the atmosphere of the cast film 22 is adjusted to a desired range. If the support 21 is unnecessary, the support 21 may be peeled after or during the formation of the porous film 16.

  As shown in FIG. 3, very many holes 31 are formed densely in the porous film 16 obtained by the porous film manufacturing process 10 (see FIG. 1). As shown in FIG. 3A, the holes 31 are arranged on the porous film 16 so as to form a honeycomb structure, that is, a so-called honeycomb structure. And as shown to FIG. 3 (B) and (C), the hole 31 is formed so that it may penetrate through the both surfaces of the porous film 16. FIG. As shown in FIG. 3D, a porous film 33 in which a recess 33a is formed on one side instead of the hole 31 is also included in the porous film of the present invention.

  The arrangement of the holes 31 corresponds to the number of water droplets formed per unit area, the size of the water droplets, the type of water droplets to be formed, the drying speed, the residual solvent amount of the solution, and the degree of water droplet growth in the water droplet formation and growth step 13. It varies depending on the timing of evaporation of the solvent 23 and the like. The form of the porous film 16 produced according to the present invention is not particularly limited, but the present invention has, for example, a thickness L1 of the porous film 16 of 0.05 μm or more and a diameter D1 of the holes 31 of 0.05 μm. As described above, it is particularly effective when producing a porous film in which the formation pitch L2 of the holes 31 is 0.1 μm or more and 120 μm or less.

  As described above, the honeycomb structure means a structure in which holes having a fixed shape and a fixed size are arranged continuously and regularly. This regular arrangement is two-dimensional in the case of a single layer and regular in three dimensions in the case of a multilayer. This regularity is two-dimensionally arranged so that a plurality of (for example, six) holes surround one hole, and three-dimensionally a structure such as a face-centered cubic or hexagonal crystal structure. In many cases, close packing is performed, but regularity other than these may be exhibited depending on manufacturing conditions. Note that the number of holes formed around one hole on the same plane is not limited to six, and may be three to five or seven or more.

  Next, FIG. 4 shows a schematic diagram of a film production facility 40 for producing a porous film 38 from a solution 15 containing a polymer as a raw material and a solvent. The film production facility 40 includes a tank 41 for storing the solution 15, a stirring blade 41 a provided in the tank 41, a casting chamber 42, and a pump 43 for feeding the solution 15 stored in the tank 41 to the casting chamber 42. And a winder 44 that winds up the porous film 38 sent out from the casting chamber 42. The tank 41 is provided with a jacket 41b. By sending a heat transfer medium adjusted to a predetermined temperature to the jacket 41b, the temperature of the solution 15 in the tank 41 can be kept substantially constant within a predetermined range.

  The casting chamber 42 has a first zone 51 to a third zone 53. In the first zone 51, the casting step 11, the discrimination step 12, and the water droplet formation and growth step 13 are performed, in the second zone 52, the water droplet evaporation step 14 is performed (see FIG. 1), and in the third zone 53, each step is performed. The cast film that has passed through 11 to 14 is peeled off from the support, becomes a porous film 38, and is sent out to the casting chamber 42.

  In the casting chamber 42, rotating rollers 55 and 56 are provided. The casting band 57 is stretched around the rotating rollers 55 and 56. The rotating roller 56 is connected to a driving unit (not shown). By this drive unit, the rotation roller 56 is driven to rotate, and the rotation of the rotation roller 56 causes the casting band 57 to travel in the first zone 51 to the third zone 53 in an endless manner. Note that a drive unit (not shown) may be connected to the rotation roller 56 instead of the rotation roller 55 to rotate the rotation roller 56.

  It is preferable that the conveying direction of the casting band 57 is adjusted to be within ± 10 ° with respect to the horizontal direction. Similarly, the transport direction of the casting band 57 in the width direction substantially orthogonal to the transport direction is also preferably within ± 10 ° with respect to the horizontal direction. By adjusting the inclination of the casting band 57 in the transport direction and the width direction, the form of the water droplet 25 (see FIGS. 1 and 2) formed in the water droplet formation growth step 13 can be adjusted.

  Further, the first zone 51 is provided with a casting die 60 and a wet air supply device 61, the second zone 52 is provided with a dry air supply device 64, and the third zone 53 is stripped. A roller 66 is provided. The casting die 60 is provided in the vicinity of the upper portion of the casting band 57 and is connected to the tank 41 via the pump 43. The solution 15 sent from the tank 41 flows out onto the casting band 57 by the casting die 60, and forms a cast film 68 on the surface 57 a of the casting band 57. The stripping roller 66 strips the cast film 68 from the casting band 57 as the porous film 38 and sends it to the winder 44.

  The finishing accuracy of the inner wall surface of the slit provided in the casting die 60 is preferably 1 μm or less in terms of surface roughness, and the straightness is preferably 1 μm / m or less in any direction. In order to keep the temperature of the solution 15 passing through the slit substantially constant within a predetermined range, it is preferable to attach a temperature controller (for example, a heater, a jacket, etc.) to the casting die 60. Furthermore, it is preferable to use a slit whose average value is adjustable within a range of 0.05 mm to 3.5 mm by automatic adjustment. And it is preferable to provide a thickness adjusting bolt (heat bolt) in the casting die 60 at a predetermined interval. As a method of adjusting the film thickness x of the cast film 68, feedback control is performed based on the amount of the pump 43 fed or a profile of a thickness gauge (not shown) (for example, an infrared thickness gauge) to adjust the clearance to a predetermined value. You may do it.

  As shown in FIG. 5, the humid air supply device 61 includes a blower port 71, a suction port 72, and an infrared radiation thermometer 73 provided so as to face the exposed surface 68 a of the cast film 68. The infrared radiation thermometer 73 measures the temperature T1 of the exposed surface 68a of the cast film 68. The number of infrared radiation thermometers 73 is not limited to one, and a plurality of infrared radiation thermometers 73 may be provided. When providing a plurality of infrared radiation thermometers 73, for example, they may be arranged in the transport direction of the cast film 68 or in a direction perpendicular to the transport direction.

  The control unit 80 is connected to the humid air supply device 61 and the temperature controller 75. The control unit 80 starts and stops the blowing process for sending the wet air 400 adjusted to a predetermined condition from the blower port 71, and starts and stops the suction process for sucking the wet air 400 and the like in the vicinity of the suction port 72, respectively. Do. Further, the control unit 80 reads the temperature T1 of the exposed surface 68a measured by the infrared radiation thermometer 73, and independently sets the temperature TA1, the dew point TW1, and the condensation point TY1 of the solvent in a desired range. Adjust to a substantially constant with. Further, the control unit 80 adjusts the temperature of the rotary rollers 55 and 56 via the temperature controller 75 attached to the rotary rollers 55 and 56, and the temperature T3 of the surface 57a of the casting band 57 is within a predetermined range. Adjust to approximately constant. Examples of the temperature adjustment method include a method in which a liquid flow path is provided inside the rotary rollers 55 and 56 and the heat transfer medium is fed into the liquid flow path for adjustment.

  As shown in FIG. 4, the dry air supply device 64 includes a blower opening and a suction opening provided so as to face the exposed surface 68 a and an infrared radiation thermometer. Since the structure of the dry air supply machine 64 is the same as that of the wet air supply machine 61, the detailed description is omitted. The water droplet evaporation process 14 is performed by applying the dry air 410 adjusted to a predetermined condition to the exposed surface 68a by a control unit (not shown).

  Next, the detail of the porous film manufacturing process 10 (refer FIG. 1) in the porous film manufacturing equipment 40 is demonstrated.

  Solution 15 is placed in tank 41. As the stirring blade 41a rotates, the solution 15 is uniformly mixed. The temperature of the solution 15 in the tank 41 is maintained so as to be substantially constant in the range of 0 ° C. or more and 50 ° C. or less. The pump 43 sends the solution 15 from the tank 41 to the casting die 60. The casting band 57 travels at a predetermined speed by driving the rotating rollers 55 and 56. The temperature controller 75 holds the temperature T3 of the surface 57a of the casting band 57 so as to be substantially constant.

  The lower limit of the preferable range for the temperature T3 of the surface 57a is preferably not less than the freezing point of water, that is, 0 ° C. or more under 1 atm. On the other hand, the upper limit of the temperature T3 of the surface 57a is preferably not more than the boiling point YBP (° C.) of the solvent contained in the solution 15, and more preferably not more than [YBP-3] (° C.). This prevents water condensed on the exposed surface 68a from solidifying and prevents the solvent of the solution 15 from rapidly evaporating, thereby obtaining a porous film 38 having excellent shape, particularly surface smoothness. be able to.

  Furthermore, it is preferable to make the distribution of the temperature T3 on the surface 57a substantially uniform in the width direction of the cast film 68. Thereby, the distribution of the temperature T1 of the exposed surface 68a in the width direction of the cast film 68 can be made substantially uniform. By reducing the temperature distribution in the width direction of the cast film 68, the anisotropy of the pore arrangement of the porous film 38 can be suppressed, so that the homogeneous porous film 38 can be manufactured. Specifically, the distribution of the temperature T3 on the surface 57a is preferably within ± 3 ° C. Thereby, the distribution of the temperature T1 of the exposed surface 68a in the width direction of the cast film 68 can be within ± 3 ° C.

  In the first zone 51, the casting step 11, the discrimination step 12, and the water droplet formation and growth step 13 are performed, and in the second zone 52, the water droplet evaporation step 14 is performed.

  In the casting step 11, the solution 15 passes through the slit provided in the casting die 60 and flows out onto the casting band 57 from the outlet. The temperature controller provided in the casting die 60 holds the temperature T4 of the solution 15 passing through the slit and the outlet in a range of 0 ° C. or more and 50 ° C. or less. Then, the solution 15 that has flowed out onto the casting band 57 forms a cast film 68. Then, as the casting band 57 travels, the cast film 68 is sequentially conveyed to the zones 51 to 53. In order to keep | T1-T2 | within a predetermined range, the value of | T3-T4 | is preferably 30 ° C or lower, more preferably 20 ° C or lower, and 10 ° C or lower. Is particularly preferred.

  In the determination step 12, a determination process by the control unit 80 is performed. Details of the discrimination processing will be described later.

  In the water droplet formation and growth step 13, the control unit 80 adjusts the temperature TA1, the dew point TW1, and the solvent condensation point TY1 of the wet air 400 so as to be substantially constant within a predetermined range. The wet air supply device 61 applies the wet air 400 adjusted to a predetermined condition under the control of the control unit 80 to the exposed surface 68a of the cast film 68 through the air blowing port 71 and through the suction port 72. The wet air 400 is recovered.

  The temperature TA1 of the humid air 400 is preferably 5 ° C. or higher and lower than 100 ° C. If the temperature TA1 of the humid air 400 is less than 5 ° C., evaporation of the liquid, particularly water is difficult to occur, and the porous film 38 having a good shape may not be obtained. Further, if the temperature TA1 of the wet air 400 exceeds 100 ° C., water droplets may be evaporated before water droplets are generated in the cast film 68. In order to suppress the convection of the solution 15 in the cast film 68, the value of | T1-TA1 | is preferably 40 ° C. or less, more preferably 30 ° C. or less, and particularly preferably 20 ° C. or less. preferable.

(Condensation conditions)
The difference between the dew point TW1 of the wet air 400 and the temperature T1 of the exposed surface 68a of the cast film 68, that is, the value of (TW1-T1) is preferably 0 ° C. or higher, and preferably 0 ° C. or higher and 80 ° C. or lower. More preferably, 5 ° C. or more and 60 ° C. or less is more preferable, and 10 ° C. or more and 40 ° C. or less is particularly preferable. If the value of (TW1-T1) is less than 0 ° C., condensation may be difficult to occur, and if it exceeds 80 ° C., condensation and drying become steep, and it is difficult to control the pore size and make it uniform. May be.

  The condensation point TY1 of the solvent in the humid air 400 is at least lower than the temperature T1 of the exposed surface 68a. This is because the larger the value of (T1-TY1) (° C.), the easier the solvent evaporates from the cast film 68.

  The blowing direction of the humid air 400 is a follow-up wind of a flow (parallel flow) parallel to the transport direction of the cast film 68. When the humid air 400 is blown as a countercurrent, the exposed surface 68a of the cast film 68 is disturbed, and the growth of water droplets may be hindered. Further, the blowing speed of the wet air 400 is preferably 0.02 m / s or more and 2 m / s or less, more preferably 0.05 m / s or more and 1.5 m / s or less, relative to the moving speed of the cast film 68. More preferably, it is 0.1 m / s or more and 1 m / s or less. If the air blowing speed is less than 0.02 m / s, the cast film 68 may be transported to the second zone 52 without water droplets on the exposed surface 68a growing sufficiently in the cast film 68. If it exceeds 2 m / s, the exposed surface 68a of the cast film 68 may be disturbed, or condensation or water droplet growth may not proceed sufficiently.

  The time for the cast film 68 to pass through the first zone 51 is preferably 0.1 seconds or more and 1000 seconds or less. If the passage time is less than 0.1 seconds, the water droplets formed on the cast film 68 evaporate without sufficiently growing, and therefore it may be difficult to form a hole with a desired size. If it exceeds 1, the size of the water droplet becomes too large, and there is a possibility that the porous film 38 having fine pores cannot be obtained.

  In the water droplet evaporation step 14, a control unit (not shown) adjusts the temperature TA2, the dew point TW2, and the solvent condensation point TY2 of the dry air 410 so as to be substantially constant within a predetermined range. Then, the dry air supply unit 64 collects the dry air 410 while applying the adjusted dry air 410 to the exposed surface 68a of the cast film 68 under the control of the control unit.

(Drying conditions)
The difference between the temperature T1 of the exposed surface 68a of the cast film 68 and the dew point TW2 of the dry air 410, that is, the value of (T1−TW2) is preferably 1 ° C. or more. This makes it possible to evaporate the water droplets as water vapor while stopping the growth of the water droplets on the cast film 68 in the second zone 52.

  The blowing speed of the dry air 410 for drying the cast film 68 in the second zone 52 is preferably 0.02 m / s or more and 20 m / s or more, more preferably 0.1 m / s or more and 10 m / s or less, and 0.5 m / s. More preferably, it is s or more and 5 m / s or less. If the blowing speed is less than 0.02 m / s, the evaporation of water from the water droplets may not proceed sufficiently, and the productivity may be inferior. If it exceeds 20 m / s, the water evaporation from the water droplets may occur. May occur abruptly and the shape of the hole to be formed may be disturbed.

  The cast film 68 that has been dried is peeled off from the casting band 57 while being supported by the peeling roller 66, and the porous film 38 is taken up by the winder 44. In addition, although the conveyance speed of the porous film 38 is not specifically limited, It is preferable that they are 0.1 m / min or more and 60 m / min or less. When the conveyance speed is less than 0.1 m / min, the productivity is inferior and the cost is not preferable. On the other hand, when it exceeds 60 m / min, when the porous film 38 is conveyed, an excessive tension is applied and it is torn and the formed honeycomb structure is disturbed. The porous film 38 can be continuously produced by the above method. In addition, it can also manufacture so that the length of the porous film 38 obtained may be shortened by casting the solution 15 on the casting belt 57 intermittently, ie, intermittently.

(Determination process)
Next, details of the discrimination process will be described. The controller 80 determines whether or not the cast film 68 satisfies (Equation 1). In the determination process, when it is determined that the cast film 68 satisfies Expression 1, the water droplet formation growth process 13 is performed on the cast film 68. On the other hand, if it is determined that the cast film 68 does not satisfy (Expression 1), the determination is repeated without performing the water droplet formation growth step 13 until it is determined that the cast film 68 satisfies (Expression 1). Process.
(Expression 1) Ra = (g · β · x ³ · | T1−T2 |) / (ν · α) <5000
(However, the gravitational acceleration is g, the temperature of the exposed surface 68a is T1, the temperature of the support surface 68b of the cast film 68 in contact with the surface 57a of the casting band 57 is T2, the thickness of the cast film 68 is x, and (The thermal expansion coefficient, kinematic viscosity, and temperature conductivity of the solution 15 are β, ν, and α.)

  In (Expression 1), since the gravitational acceleration g, the thermal expansion coefficient β and the temperature conductivity α of the solution 15 in the cast film 68 are substantially constant in each step, at least the values of the variables T1, T2, x, and ν are If it can be detected, the control unit 80 can perform the determination process based on Equation 1.

  Here, the control unit 80 can detect the temperature T 1 of the exposed surface 68 a of the cast film 68 in the first zone 51 via the infrared radiation thermometer 73. Alternatively, the temperature T3 of the surface 57a of the casting band 57 adjusted through the temperature controller 75 may be set as the temperature T2 of the support surface 68b of the cast film 68 in contact with the surface 57a.

  The thickness x of the cast film 68 can be adjusted to a predetermined range by adjusting the clearance of the slit of the casting die 60 and the like. Further, the kinematic viscosity ν of the solution 15 can be adjusted from the polymer, the composition of the solvent, the residual solvent amount ZY and the like contained in the solution 15. The transition of the thickness x of the cast film 68 and the residual solvent amount ZY in each step 12 to 13 can be obtained in advance from the manufacturing experiment in each step 12 to 13. The residual solvent amount ZY indicates the amount of solvent remaining in the cast film 68 on a dry basis, and after taking a sample from the target film or the like, the mass of this sample is x, and the sample is dried Is represented by {(xy) / y} × 100.

  In the present invention, the determination step 12 is performed, and the water droplet formation growth step 13 is performed when the convection of the solution 15 in the cast film 68 is suppressed to a certain amount under the condition that satisfies Equation 1, that is, the solution 15 It is possible to suppress variations in the formation pitch of water droplets caused by convection. Therefore, according to the present invention, the porous film 38 having pores with a uniform formation pitch can be easily manufactured. Note that in (Equation 1), the Rayleigh number Ra is less than 5000, which is a condition for performing the water droplet formation growth step 13. However, it is preferable that the Rayleigh number Ra is less than 2000. More preferably, Ra is less than 1500.

  In the porous film manufacturing step 10 (see FIG. 1), before the water droplet evaporation step 14, water droplets are formed on the exposed surface 68a at a constant formation pitch, or water droplets formed on the exposed surface 68a are It is desirable to rearrange so that the formation pitch becomes more uniform. The former can be adjusted by conditions such as the conditions of the humid air 400 and the temperature of the casting band 57, but for the latter, it is necessary to ensure the fluidity of the solution 15 in the cast film 68.

  In order to ensure the fluidity of the solution 15, the polymer concentration of the solution 15 is lower than that of the polymer solution used in the solution casting method or the like. Since the solution 15 having a low polymer concentration has a low viscosity, convection is likely to occur. Further, when the polymer concentration of the solution 15 is lowered, the film thickness x of the cast film 68 in the water droplet formation and growth step 13 is increased, so that convection easily occurs. Therefore, the Rayleigh number Ra of the solution 15 in the cast film 68 in the method for producing a porous film as in the present invention is larger than that in the solution film forming method or the like, and the convection of the solution 15 in the cast film 68 is increased. It tends to become more prominent.

  The film thickness x of the cast film 68 in the water droplet formation growth step 13 is preferably 300 μm or more, and preferably 350 μm or more and 2000 μm or less. Furthermore, the residual solvent amount of the solution 15 in the water droplet formation growth step 13 is preferably 400% by mass or more, and preferably 500% by mass or more and 5000% by mass or less on a dry basis.

  Therefore, in the porous film manufacturing process 10 (see FIG. 1) for forming water droplets for forming micropores on the exposed surface 68a of the cast film 68, the determination process 12 is performed before the water droplet formation growth process 13. Is significant, and a porous film 38 having uniformly arranged pores can be produced.

  In the said embodiment, although the porous film 38 was manufactured by the online system using the casting band 57 which runs endlessly, this invention is not restricted to this, The manufacturing method which performs each process 11-14 by a batch type is carried out. It is also possible to apply. In the case of a batch type, a Peltier element may be used as the support, or a support having a Peltier element may be used.

  In the above-described embodiment, when it is determined in the determination process that the cast film 68 does not satisfy (Expression 1), the water droplet formation growth process is performed until it is determined that the cast film 68 satisfies (Expression 1). However, the present invention is not limited to this, and when it is determined in the determination process that the cast film 68 does not satisfy (Equation 1), the cast film 68 is used. The main object is to satisfy (Equation 1), and it is possible to repeatedly perform the discrimination process while applying air adjusted to a desired condition (hereinafter referred to as adjusted air) to the exposed surface 68a. At this time, the temperature T1 of the exposed surface 68a may be measured, and the regulated air may be adjusted based on the temperature T1. In the so-called on-line type porous film manufacturing facility 40 shown in FIG. 4, a plurality of wet air supply devices 61 are arranged in the first zone 51, and each wet air supply device 61 performs a discrimination process. If the control unit 80 determines that the cast film 68 does not satisfy Expression 1, the control unit 80 may repeatedly perform the determination process while applying the adjusted air to the exposed surface 68a using the wet air supply unit 61. Good. On the other hand, when the control unit 80 determines that the cast film 68 satisfies Expression 1, the wet air supply unit 61 is used to measure the temperature T1 of the exposed surface 68a, and the wet air 400 is applied to the exposed surface 68a. The water droplet formation and growth step 13 may be performed. On the other hand, in the case of the batch type, after casting the solution on a traveling support or a stationary support, the water droplet formation growth step 13 is performed only for the cast film that satisfies the formula 1, and the cast film that does not satisfy the formula 1 The water droplet formation and growth step 13 may be performed after waiting in another zone until Equation 1 is satisfied, or after applying conditioned air to the exposed surface of the cast film.

  In the present invention, the difference between the temperature T1 of the exposed surface 68a and the temperature T2 of the support surface 68b, that is, the value of | T1-T2 | The temperature of the surface 57a of the casting band 57 is preferably adjusted. If the value of | T1−T2 | exceeds 5 ° C., the convection of the solution 15 in the cast film 68 becomes significant, so that the formation pitch of water droplets formed on the exposed surface 68a varies.

  In the above embodiment, the determination step 12 for holding the value of | T1-T2 | within a predetermined range is performed before the water droplet formation growth step 13. However, the present invention is not limited to this, and instead of the determination step 12, The water droplet formation and growth step 13 may be performed after stopping the blowing process and the suction process for a certain time, or a combination of these conditions may be used. This is because the temperature difference | T1-T2 | between the exposed surface 68a of the cast film 68 and the support surface 68b can be reduced by stopping the blowing process and the suction process for a certain time. Although the specific conditions of the said fixed time are based also on other manufacturing conditions, it is preferable to set it as 10 seconds or more, for example.

  In the above embodiment, in the determination process, when it is determined that Expression 1 is not satisfied, the determination step 12 is repeatedly performed. However, when the determination step 12 is repeatedly performed, the number of Rayleigh calculated in the determination process and the target are set. Based on the difference from the Rayleigh number, the controller 80 may appropriately adjust the conditions of the wet air 400, the temperature of the surface 57a of the casting band 57, and the like.

  In the above embodiment, the control unit 80 may adjust the temperature of the solution 15 in the tank 41 and the casting die 60 and the clearance of the slit of the casting die 60.

  In the above embodiment, the water droplet formation growth step 13 is performed on the film-like cast film 68, but the present invention is not limited to this, and the water droplet formation growth step 13 may be performed on the plate-like or bulk solution 15. In the case of forming a plate-like or bulk-like solution, the water droplet formation growth step 13 may be performed on the solution stored in a container having a certain depth, instead of casting. Thereby, a plate-shaped or bulk-shaped porous structure can also be manufactured.

  In the above embodiment, three wet air supply devices 61 are provided in the first zone 51 and four dry air supply devices 64 are provided in the second zone 52. However, the present invention is not limited to this, and the first zone 51 includes One, two, or four or more wet air supply units 61 may be provided, and one to three, or five or more dry air supply units 64 may be provided in the second zone 52.

  In the above embodiment, the infrared radiation thermometer 73 is provided between the air blowing port 71 and the suction port 72. However, in the present invention, the infrared radiation thermometer 73 is not limited to this, and the infrared radiation thermometer 73 is located upstream of the air blowing port 71. May be provided. In addition to the infrared radiation thermometer 73, a known non-contact type thermometer (for example, FT-H30 manufactured by Keyence Corporation) may be used.

  Using one of the infrared radiation thermometers 73, the temperature of the exposed surface 68a at the side edge of the cast film 68 is measured, and this is designated as T1, and the other one of the infrared radiation thermometers 73 is measured. It is also possible to measure the temperature of the surface 57a of the casting band 57 in the vicinity of the side edge, and use this as T2 to perform the discrimination process.

  Instead of the humid air supply device 61, a wet air supply device including a blower port and a suction port, which are two-dimensional nozzles, may be used together with an infrared radiation thermometer. The cast film 68 can also be dried by a reduced pressure drying method that reduces the atmospheric pressure of the cast film 68. By performing the drying under reduced pressure, it becomes easier to adjust the evaporation rate of the solvent and the water droplets, and the size and shape of the water droplets formed on the cast film 68 can be changed as appropriate.

  Also, a method of drying by a reduced pressure drying method, or a condenser cooled from the membrane surface and having a groove on the surface at a position about 3 to 20 mm away from the membrane surface, water vapor (volatile organic solvent is also on the surface of the condenser) In addition, a method of condensing and drying can also be applied. By applying any one of the above drying methods, it is possible to reduce the dynamic influence on the exposed surface of the cast film 68 and to dry it, so that a smoother film surface can be obtained.

  As a raw material for the porous film, it is preferable to use a polymer compound (hereinafter referred to as “hydrophobic polymer”) that is soluble in a water-insoluble solvent. Moreover, although a porous film can be formed only with the said hydrophobic polymer, it is preferable to use an amphiphilic polymer together.

  As the solvent for preparing the solution 15 by dissolving the respective polymer compounds, the above-mentioned solvents can be appropriately selected and used.

(solvent)
The solvent is not particularly limited as long as it is a solvent that can dissolve the polymer, such as an organic solvent. For example, chloroform, dichloromethane, carbon tetrachloride, cyclohexane, methyl acetate and the like can be mentioned.

  Further, the concentration of the polymer compound in the solution 15 when casting may be any concentration that can form a cast film, and is preferably in the range of 0.01% by mass to 30% by mass, for example. When the concentration of the polymer compound is less than 0.01% by mass, the productivity of the film is inferior and may not be suitable for industrial mass production. Further, if the concentration of the polymer compound is more than 30% by mass, the polymer compound is dried before the water droplets are sufficiently grown in the condensation drying process described later, so that it has a fine pore size. It may be difficult to create a pore structure.

  The cast film in the present invention may be a laminated cast film in which a plurality of solutions form layers in the film thickness direction. When the laminated cast film is composed of an exposed layer located on the exposed surface side and a base layer located between the exposed layer and the support, the concentration of the polymer compound in the solution forming the exposed layer is, for example, The range is preferably 0.01% by mass or more and 30% by mass or less. Such a laminated cast film is formed by simultaneous lamination co-casting in which two or more types of solutions are simultaneously co-cast and laminated, or sequential lamination co-casting in which a plurality of solutions are co-cast and laminated sequentially. can do. In addition, you may combine both casting. When performing simultaneous lamination and co-casting, a casting die to which a feed block is attached may be used, or a multi-manifold casting die may be used. However, in the laminated film consisting of multiple layers by co-casting, the thickness of the exposed layer is preferably 0.5 to 30% of the total thickness of the laminated film. In addition, when performing simultaneous lamination and co-casting, it is preferable that the high-viscosity dope is enveloped by the low-viscosity dope when the dope is cast from the die slit to the support, and is formed from the die slit to the support. Of the casting beads, the dope in contact with the outside world preferably has a higher alcohol composition ratio than the inner dope.

(Hydrophobic polymer)
There is no restriction | limiting in particular as said hydrophobic polymer, According to the objective, it can select suitably according to the objective, For example, vinyl polymer (For example, polyethylene, polypropylene, polystyrene, polyacrylate, polymethacrylate, polyacrylamide) , Polymethacrylamide, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyhexafluoropropene, polyvinyl ether, polyvinyl carbazole, polyvinyl acetate, polyvinyl carbazole, polytetrafluoroethylene, etc., polyester (for example, polyethylene terephthalate, polyethylene) Naphthalate, polyethylene succinate, polybutylene succinate, polylactic acid, etc.), polylactone (eg polycaprolactone, etc.), polyamide or poly Imides (such as nylon and polyamic acid), polyurethane, polyurea, polybutadiene, polycarbonate, polyaromatics, polysulfone, polyethersulfone, polysiloxane derivatives, cellulose acylate (triacetyl cellulose, cellulose acetate propionate, cellulose acetate) Butyrate). From the viewpoints of solubility, optical physical properties, electrical physical properties, film strength, elasticity, and the like, these may be homopolymers as necessary, or may take the form of copolymers or polymer blends. In addition, you may use these polymers as a mixture of 2 or more types of polymers as needed. For use in optical applications, for example, cellulose acylate and cyclic polyolefin are preferred.

  The amphiphilic polymer is not particularly limited and may be appropriately selected depending on the intended purpose.For example, polyacrylamide is a main chain skeleton, a dodecyl group is a hydrophobic side chain, and a carboxyl group is a hydrophilic side chain. Examples thereof include an amphiphilic polymer and a polyethylene glycol / polypropylene glycol block copolymer.

  The hydrophobic side chain is a non-polar linear group such as an alkylene group or a phenylene group, and has a hydrophilic group such as a polar group or an ionic dissociation group up to the terminal except for a linking group such as an ester group or an amide group. It is preferable that the structure does not branch. As the hydrophobic side chain, for example, when an alkylene group is used, it is preferably composed of 5 or more methylene units. The hydrophilic side chain preferably has a structure having a polar part, an ionic dissociation group, or a hydrophilic part such as an oxyethylene group at the end via a linking part such as an alkylene group.

  The ratio between the hydrophobic side chain and the hydrophilic side chain differs depending on the size, nonpolarity, polarity strength, hydrophobic strength of the hydrophobic organic solvent, etc. The ratio (hydrophobic side chain / hydrophilic side chain) is preferably 3/1 to 1/3. In the case of a copolymer, a block copolymer in which a hydrophobic side chain and a hydrophilic side chain form a block as long as it does not affect the solubility in a hydrophobic solvent, rather than an alternating polymer of hydrophilic side chains of hydrophobic side chains. It is preferable that

  The number average molecular weight (Mn) of the hydrophobic polymer and the amphiphilic polymer is preferably 1,000 to 10,000,000, and more preferably 5,000 to 1,000,000.

  A porous film can be produced using only the hydrophobic polymer, but it is preferably used together with an amphiphilic polymer.

  The composition ratio (mass ratio) between the hydrophobic polymer and the amphiphilic polymer is preferably 99: 1 to 50:50, and more preferably 98: 2 to 70:30. When the ratio of the amphiphilic polymer is less than 1% by mass, a uniform porous film may not be obtained. On the other hand, when the ratio of the amphiphilic polymer exceeds 50% by mass, the stability of the cast film, particularly the mechanical stability, may not be sufficiently obtained.

  The hydrophobic polymer and the amphiphilic polymer are also preferably polymerizable (crosslinkable) polymers having a polymerizable group in the molecule. In addition, a polymerizable polyfunctional monomer is blended together with the hydrophobic polymer and / or the amphiphilic polymer, and after forming a honeycomb film with the blend, a thermosetting method, an ultraviolet curing method, an electron beam curing method, etc. It is also preferable to perform a curing treatment by a known method.

  The polyfunctional monomer used in combination with the hydrophobic polymer and / or the amphiphilic polymer is preferably a polyfunctional (meth) acrylate from the viewpoint of reactivity. Examples of the polyfunctional (meth) acrylate include dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, dipentaerythritol caprolactone adduct hexaacrylate or a modified product thereof, epoxy acrylate oligomer, polyester acrylate oligomer, Urethane acrylate oligomer, N-vinyl-2-pyrrolidone, tripropylene glycol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, or a modified product thereof can be used. These polyfunctional monomers are used singly or in combination of two or more from the balance of scratch resistance and flexibility.

  When the hydrophobic polymer and the amphiphilic polymer are a polymerizable (crosslinkable) polymer having a polymerizable group in the molecule, they react with the polymerizable group of the hydrophobic polymer and the amphiphilic polymer. It is also preferable to use a polymerizable polyfunctional monomer in combination.

  Polymerization of the monomer having an ethylenically unsaturated group can be carried out by irradiation with ionizing radiation or heating in the presence of a photo radical initiator or a thermal radical initiator. Accordingly, a coating liquid containing a monomer having an ethylenically unsaturated group, a photo radical initiator or a thermal radical initiator, mat particles and an inorganic filler is prepared, and the coating liquid is applied on a transparent support and then ionizing radiation or heat is applied. It can be cured by a polymerization reaction to form an antireflection film.

  Examples of the photo radical initiator include acetophenones, benzoins, benzophenones, phosphine oxides, ketals, anthraquinones, thioxanthones, azo compounds, peroxides, 2,3-alkyldione compounds, disulfides Examples include compounds, fluoroamine compounds and aromatic sulfoniums.

  Examples of the acetophenones include 2,2-ethoxyacetophenone, p-methylacetophenone, 1-hydroxydimethylphenyl ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-4-methylthio-2-morpholinopropiophenone, 2 -Benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone and the like.

  Examples of the benzoins include benzoin benzene sulfonate, benzoin toluene sulfonate, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether.

  Examples of the benzophenones include benzophenone, 2,4-chlorobenzophenone, 4,4-dichlorobenzophenone, p-chlorobenzophenone, and the like.

  Examples of the phosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

  Various examples of the photo radical initiator are also described in the latest UV curing technology (P.159, issuer; Kazuhiro Takasawa, publisher; Technical Information Association, Inc., published in 1991). Further, as a commercially available photocleavable photoradical polymerization initiator, Irgacure (651, 184, 907) manufactured by Ciba Specialty Chemicals Co., Ltd. and the like are preferable examples.

  The photo radical initiator is preferably used in the range of 0.1 to 15 parts by mass and more preferably in the range of 1 to 10 parts by mass with respect to 100 parts by mass of the polyfunctional monomer.

  In addition to the photopolymerization initiator, a photosensitizer may be used. Specific examples of the external photosensitizer include n-butylamine, triethylamine, tri-n-butylphosphine, Michler's ketone, and thioxanthone.

  As said thermal radical initiator, an organic peroxide, an inorganic peroxide, an organic azo compound, an organic diazo compound, etc. can be used, for example.

  Specific examples of the organic peroxide include benzoyl peroxide, halogen benzoyl peroxide, lauroyl peroxide, acetyl peroxide, dibutyl peroxide, cumene hydroperoxide, and butyl hydroperoxide. Examples of the inorganic peroxide include hydrogen peroxide, ammonium persulfate, and potassium persulfate. Examples of the azo compound include 2,2'-azobis (isobutyronitrile), 2,2'-azobis (propionitrile), 1,1'-azobis (cyclohexanecarbonitrile), and the like. Examples of the diazo compound include diazoaminobenzene, p-nitrobenzenediazonium, and the like.

It is process drawing which shows the outline | summary of the manufacturing method of a porous film. (A)-(C) show the outline | summary of a water droplet formation growth process, (D) is explanatory drawing which shows the outline | summary of a water droplet evaporation process. (A) is a top view which shows the outline | summary of the porous film which has a some through-hole, (B) is BB sectional drawing, (C) is CC sectional drawing. (D) is a top view of a porous film having a plurality of indentations. It is explanatory drawing which shows the outline | summary of the manufacturing equipment of a porous film. It is explanatory drawing which shows the outline | summary in a 1st zone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Porous film manufacturing process 11 Casting process 12 Discriminating process 13 Water drop formation growth process 14 Water drop evaporation process 15 Solution 16 Porous film 61 Wet air supply machine 68 Cast film 68a Exposed surface 68b Support surface 71 Blower 72 Suction port 73 Infrared Radiation thermometer 75 Temperature controller 80 Control unit

Claims (8)

A forming step of casting a solution containing a polymer and a solvent on a support whose surface temperature is adjusted to be substantially constant to form a cast film on the support, a temperature TA1, a dew point, and a condensation point of the solvent Is applied to the exposed surface of the cast film, and while the solvent contained in the cast film is evaporated, water droplets are formed on the exposed surface of the cast film by condensation to grow the water droplets. In a method for producing a porous film, comprising: a water droplet formation growth step; and a water droplet evaporation step in which dry air is applied to the exposed surface to evaporate the water droplets submerged in the cast film.
A method for producing a porous film, comprising performing the water droplet formation growth step on the cast film having a Rayleigh number Ra satisfying the formula (1).
(Expression 1) Ra = (g · β · x ³ · | T1-T2 |) / (ν · α) <5000
(However, the acceleration of gravity is g, the temperature of the exposed surface of the cast film is T1, the temperature of the support surface side of the cast film in contact with the surface of the support is T2, the film thickness of the cast film is x, (The thermal expansion coefficient, kinematic viscosity, and temperature conductivity of the solution in the cast film are β, ν, and α.)   The porous film according to claim 1, further comprising a determination step of determining whether or not the Rayleigh number Ra in the cast film satisfies the formula (1) before performing the water droplet formation growth step. Manufacturing method.   In the determining step, the temperature T1 of the exposed surface is measured, and based on the value of the temperature T1 of the exposed surface, the temperature of the adjusted air, so that the Rayleigh number Ra satisfies the formula (1), The method for producing a porous film according to claim 2, wherein the dew point, the condensation point, and the temperature of the surface of the support are adjusted, and the adjusted air is applied to the exposed surface. Adjusting at least one of the temperature of the conditioned air or the humid air, the dew point, the condensation point of the solvent, the temperature of the surface of the support,
The method for producing a porous film according to any one of claims 1 to 3, wherein the value of | T1-T2 | is kept substantially constant in a range of 0 ° C or higher and 5 ° C or lower.   When the temperature of the surface of the support before the solution is cast is T3 and the temperature of the solution before the solution is cast is T4, the value of | T3−T4 | The method for producing a porous film according to any one of claims 1 to 4, wherein:   The method of producing a porous film according to any one of claims 1 to 5, wherein a value of | T1-TA1 | is 40 ° C or lower.   The method for producing a porous film according to any one of claims 1 to 6, wherein in the water droplet formation growth step, the film thickness x of the cast film is 300 µm or more.   The method for producing a porous film according to any one of claims 1 to 7, wherein a residual solvent amount of the solution in the water droplet formation growth step is 400% by mass or more on a dry basis.

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