JPS6359363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film forming apparatus, and more particularly to an apparatus for producing a uniform polymer film with good reproducibility by a solution casting method.

Polymer membranes are used for various purposes such as substance separation, packaging, information conversion and recording. Forming polymeric materials into membranes is also important as a means of preparing samples for investigating the optical, electrical, mechanical, and thermal properties of polymers and the small molecules mixed therein.

Among the methods for manufacturing polymer films, the so-called solution casting method, in which a polymer is dissolved in a suitable solvent, the solution is applied onto a substrate, and the solvent is evaporated to form a film, is used at room temperature. Being able to form a film using pressure;
It does not require large-scale equipment, it is easy to process the polymer solution during film formation, such as immersion in water, there is less wasted polymer sample, and the film thickness can be thicker than when applied using a spinner. It is a method that is widely used, especially for making films with dimensions of several tens of centimeters square or less, because it is easy to predict.

Conventionally, in order to manufacture a polymer film by this casting method, a pre-prepared polymer solution is poured onto a part of a substrate such as a flat glass plate, and then the solution is poured onto the substrate using an appropriate tool. An upward spread method was used. [For example, see "New Experimental Chemistry Course, Vol. 19-2" (Maruzen, 1978), page 974, edited by the Chemical Society of Japan.] Tools for spreading the solution include a blade called a doctor blade, and a wire of the required thickness on both ends. There is a known metal round rod that can be rolled up to create a gap between it and the board equal to the thickness of the wire. Another method is to attach tape to both ends of the board to raise it higher, and then slide a glass rod across the tape at both ends. Application has been performed by moving these tools by hand.
Some literature describes a so-called applicator for making a substrate for thin layer chromatography as a tool for making a film by the casting method, but in this case, a polymer solution is poured into the center of the applicator and the substrate is A polymer solution of a certain thickness was spread on the substrate by pushing it by hand and passing it under it.

When the thickness of the membrane produced by these methods is precisely measured using the weight per unit area and the permeation rate of gas/liquid, there is a fluctuation or dispersion of ±10 to 20% every time it is produced. , or depending on the location in the film prepared at the same time.

In all of the above methods, the solution is applied manually, so the application speed and the positional relationship of the tool for application with respect to the polymer solution are not always strictly constant. As described below, we actually cast the film using several constant and variable coating speeds.
When measuring the thickness of the resulting film, the film thickness tends to vary with the coating speed. Furthermore, it is well known that, for example, membrane transmittance changes in inverse proportion to membrane thickness. In other words, in order to produce a film that is uniform and always has the same thickness and properties, the film-forming solution must be applied at a constant speed, and the shape and angle of the part where the application tool and the solution come into contact must be adjusted. , mutual relative positions, etc. must also remain constant throughout.

Furthermore, the rate of solvent evaporation after the film-forming solution is applied has a large relationship to the properties of the resulting film. The so-called phase conversion method uses a mixed solvent of a good polymer solvent and a poor solvent to cause polymer precipitation during film formation by evaporating the good solvent more rapidly. It is widely used as a manufacturing method. For example, when making a film using this method, it is natural that the approach to the solvent composition in which precipitation occurs must be as constant as possible over the entire coated surface. For evaporation to occur at a constant rate at all points on the substrate, the substrate must be smooth and have a constant thickness and temperature, and the temperature and temperature of the surrounding atmosphere through which the vapor will diffuse is required.
It is important that not only the vapor pressure and wind speed be constant, but also that the temperature and thermal conditions of the surface holding the substrate be homogeneous. This is because solvent evaporation inevitably removes evaporation heat from the film-forming solution and lowers its temperature, but since the heat conduction of solids is generally much greater than that of liquids and gases, the heat that compensates for the temperature drop is This is because it is mainly supplied from the surface directly below that is in contact with the substrate. However, in the conventional method used for film formation, insufficient consideration was given to the smoothness of the surface on which the substrate is placed after coating the polymer solution and the homogeneity of the thermal environment at each point within the surface. For example, if the board is made uneven to prevent it from sticking to the stand on which it is placed, part of the board will be in contact with the stand and other parts will be in contact with the air, which will reduce heat conduction to the board. becomes different.
As will be described later, a film produced on such a table actually has non-uniformity corresponding to the unevenness of the table. Furthermore, if there is a frame that comes close to the substrate at the end of the surface on which the substrate is placed, the thermal environment of that portion will be different from that of the center. The same applies to the structure below the table on which the board is placed to support it. In order to produce homogeneous films, it is particularly important that equal heat conduction and movement of solvent molecules occur at each point in the solution layer on a line parallel to the blades simultaneously formed on the substrate. .

The present inventors have researched a method of using a casting method to create a polymer film that is homogeneous and whose properties do not change each time the film forming operation is performed.However, as long as conventional methods are used, homogeneous films can be produced with good reproducibility. It is difficult to
We discovered that the reason for this is as described above, and based on that knowledge, we completed this invention.

That is, the present invention includes a blade for applying a polymer solution onto a substrate, the blade having a notch of a predetermined length and width in the center, and a blade for pushing the substrate to pass under the blade at a constant speed. and a substrate drying section designed so that the solution layer formed on the substrate by the blade receives uniform heat conduction at least in all lines parallel to the blade. This is a film forming apparatus characterized by having the following.

In order to achieve the above-mentioned uniform heat conduction, the substrate drying section has a sufficiently smooth surface and is seamless.
A table having a sufficiently large width and length and a sufficient thickness compared to the substrate is used, and the solution layer coated on the substrate is dried on the table. Furthermore, the structure to support the table is designed to prevent uneven distribution of heat to the table surface. The platform may also be covered to prevent uneven heat transfer due to wind during drying and to control the vapor pressure of the water or solvent.

Embodiments of the present invention will be described below based on the drawings. 1 and 2 are a plan view and an elevation view showing an embodiment of the invention. Film forming device main body 1
is equipped with a blade 3 for applying a polymer solution onto a substrate 2 in a uniform thickness. As shown in FIG. 3, the blade 3 is made by carving a notch with a width equal to the desired coating thickness d and a length b in the center. In addition, the dimension a is smaller than the width of the substrate 2 used for film formation, and both ends 12 and 1 of the blade are
2 so that they both rest on the board, and the length b
shall be determined to match the width of the desired film. For example, the width d is 50, 100, 150,
You can choose from 200, 250, 300, 400, 500, 600, 800, 1000 microns, etc. The blade 3 can process the width d accurately, has little variation in dimensions,
It is also best to make it from a material that is easy to clean and store, such as stainless steel. Also, both ends 12, 12 of the blade 3
is pressed against the substrate 2 by the weight of the blade 3 itself, and has the role of applying the solution to a thickness of exactly d, so
It is desirable that the blade 3 has a certain degree of self-weight.

The polymer solution prepared for film formation is poured onto the substrate 2 placed on the horizontal surface 4 of the apparatus main body so as to be in contact with the blade 3, but in this example, the solution is prevented from spreading unnecessarily. , and another holding plate 5 close to the blade 3 to facilitate processing after coating is completed.
is provided in the direction opposite to the direction in which the substrate advances during solution application, and the solution is injected between it and the blade 3. In order to fix the blade 3 and the holding plate 5, clamps 6, 6 are provided on the film forming apparatus main body 1,
The structure is such that fixtures 7, 7 having the shape shown in FIG. 4 are inserted therein, and then the blade 3 and presser plate 5 are inserted into the fixtures 7, 7. Blade 3, holding plate 5, fixture 7,
7 and the substrate 2 (referred to as a solution reservoir), a film forming solution is poured in an amount that will not run out during film forming. Since the fixtures 7, 7 become dirty with the polymer solution in this way, they are designed to be removable so that they can be easily cleaned.

In the main body of the film forming apparatus, push the substrate 2 further and insert the blade 3.
A push metal fitting 8 is provided to uniformly apply the film-forming solution onto the substrate by passing it under the film at a constant speed, and the push metal fitting 8 is a belt (both not shown) connected to the rotating shaft of a motor. move back and forth as one. While riding on the horizontal surface 4 of the apparatus main body 1, the substrate 2 is pushed by the pusher 8, slides thereon, and is transferred to the substrate drying section 9. To form a film, first pour the polymer solution into the solution reservoir, immediately move the pusher 8 from right to left in FIG.
Apply the solution evenly on the substrate. By changing the diameter of the gear that transmits the rotation of the motor to the belt, the voltage supplied to the motor, etc., the moving speed of the pusher 8, that is, the coating speed of the polymer solution, can be set arbitrarily within a certain range. can do. The range of movement speed is, for example, 2 to 2 per second.
Just choose a speed of 30cm. The length C of the horizontal plane is selected so that a substrate having the maximum length of the desired film can be sufficiently mounted thereon.

To evaporate the solvent from the applied solution,
A substrate drying section 9 for keeping the substrate stationary is provided with a stand 10 for placing the substrate on it. 10 units
is from the immediate vicinity of the blade 3 for applying the solution,
The top surface of the stand 10 and the surface 4 are arranged on the same horizontal plane. The stand 10 has a smooth surface, is made of a seamless plate of sufficient thickness, and has a sufficiently larger area than the substrate 2. That is, as the stand 10, for example, a single plate of stainless steel with a thickness of 3 cm or more and having a smooth surface is used, and its size is such that when the substrate 2 is placed on it, it can be used in both the length and width directions. It is determined that there is a margin of 10 cm or more compared to the board 2. The structure that supports the table 10 also prevents the heat from being transmitted unevenly to the surface of the table 10, and ensures that the solution layer formed on the substrate by the blade is spread over at least all lines parallel to the blade. The structure is configured to receive uniform heat conduction. For this purpose, the structure for supporting the stand 10 is to support the four corners of the stand 10 with four pillars.
A stand 10 that grips and holds the left and right opposing sides of the stand 10
The thickness can be increased to begin at the bottom of the device. In any case, it goes without saying that no other auxiliary structure that would locally change the heat transfer to the platform 10 should be attached. By doing so, the solution layer can always have a uniform temperature distribution at each point on all lines parallel to the blade. It is desirable that the heat conduction in the direction perpendicular to the blade is also uniform, but since this direction is the direction in which the substrate moves during solution application, differences in the elapsed time after application at each point on the line in this direction exists,
A strictly constant temperature distribution cannot be expected. As the material of the stand 10, various thermally homogeneous materials can be used, such as a heat insulating material or a thick iron plate.

The substrate drying section may be further provided with a cover 11 to prevent air from blowing during drying and to control water vapor pressure and solvent vapor pressure. In this case, blade 3
The part into which the substrate passes under is left open by the thickness of the substrate and the applied solution, or a lid that can be opened and closed is provided using an appropriate mechanism. It is also convenient to make the opening for taking out the substrate after drying with a mechanism that can be opened and closed freely. The substrate drying section can also be equipped with a mechanism that further controls the temperature and performs heating or cooling.

In addition, in order to remove the end effect at the end after coating starts and to create a uniform rectangular film, line up short rectangular plates with the same thickness in front and behind the substrate of the desired length, and It is best to first pour the film-forming solution onto the top, move the three plates at the same time to uniformly coat the central substrate, and then dispose of the remaining film-forming solution by placing it on the latter plate.

Furthermore, by making blades with different lengths b (see FIG. 3) of the cutout portions of the blades 3, films with various widths can be made. When the length b is considerably smaller than the dimension a, the film-forming solution does not need to be poured into the entire solution reservoir, and when the substrate is moved during film-forming, at least the area of the length b is filled with the polymer. Just touch the solution. Therefore, the solution reservoir can be partitioned with appropriately shaped metal fittings so that the amount of consumption of the film-forming solution can be minimized.

Figure 5 shows that using the apparatus described in the above example, a solution of cellulose acetate in acetone (weight ratio 1.0:3.0) was applied onto a 10 x 20 x 0.2 cm ³ glass plate at three different speeds. It shows the weight of the film formed per unit area when applied to a thickness of 300 microns.

According to this figure, the film weight, that is, the film thickness, changes with the coating speed, and there is a difference of more than 10% between the maximum and minimum speeds used in the test. This result shows the necessity and importance of coating at a constant speed in producing a film with a constant thickness.

Figure 6 shows the weight of the film formed per unit area when the same solution was applied to five different thicknesses using the same equipment at a speed of 2.4 cm per second. It can be seen that the film thickness increased almost in proportion to the width engraved on the blade.

In other words, the film thickness is determined and controlled only by the width engraved on the blade, and the above-mentioned variations and variations in film thickness that are common in conventional film forming methods are not observed. From FIG. 6, it can be seen that the reproducibility of the film thickness obtained when using the apparatus of the present invention is high.

Figure 7 shows an experiment in which a mixed solution of cellulose acetate, acetone, and water (weight ratio 1.0:5.6:1.2) was applied to a thickness of 100 microns, the solvent was evaporated for 30 seconds, and then immersed in water. Using a conventional device that uses a table with a 0.5 mm step in a plane parallel to the blade, evaporation was performed on an uneven surface and when it was performed on a thermally homogeneous surface. This is the difference in the optical density of the film.

The non-uniformity of the optical density is a reflection of the non-uniformity of the film structure, and as in this device, the solution layer formed on the substrate has a configuration in which heat conduction is uniform at least in all lines parallel to the blade. This example illustrates the non-uniformity of the film structure that occurs due to differences in evaporation rate depending on location when using a device that does not have this. On the other hand, when the apparatus of the present invention is used, as can be seen from FIG. 7, a film with a uniform structure can be produced. This uniformity of structure is one advantage of the present invention, which pays particular attention to achieving uniformity of heat conduction through the substrate to the coating solution. It goes without saying that the uniformity of the structure within the film also contributes to improving the reproducibility of the properties of films produced at different times. Furthermore, the presence of the above-mentioned fixed blade with a constant shape and a mechanism that can move the substrate at a constant speed also greatly contributes to improved reproducibility. High reproducibility is another advantage of the present invention.

The present invention is an apparatus configured as described above, and by using the apparatus, a film whose thickness and properties do not change depending on the location can be produced in the same manner at any time as intended.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention, and FIG.
The figure shows an elevational view thereof, FIG. 3 a perspective view of the blade section, and FIG. 4 a perspective view of the fixture section. Furthermore, FIG. 5 is a graph showing the relationship between the coating speed and film weight of the film produced using the apparatus of the present invention, FIG. 6 is a graph showing the relationship between the width of the blade and the film weight, and FIG. FIG. 4 is an optical density distribution diagram of films obtained by an apparatus having and not having an uneven structure in the drying section. In the figure, reference numerals 1...film forming apparatus main body, 2...substrate,
3...blade, 4...horizontal surface, 5...presser plate, 6...
Clamp, 7... Fixture, 8... Push metal fitting, 9...
...Substrate drying section, 10...stand, 11...cover, 12
...Both ends of the blade, a...Dimensions of the blade, b...Length of the cutout of the blade, c...Length of the horizontal surface, d...Width of the cutout of the blade.

Claims (1)

[Claims] 1 (a) A blade with a notch of a predetermined length and width in the center for applying a polymer solution onto the substrate;
(b) a pusher driven by a motor for pushing the board to pass under the blade at a constant speed; and (c)
and a substrate drying section designed so that the solution layer formed on the substrate by the blade receives uniform heat conduction at least in all lines parallel to the blade. .