JP2011251265A - Substrate drying method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drying method for a substrate to prevent a coated film from whitening while drying regardless of the substrate using a coating composition having low solid content amount with high viscosity.SOLUTION: When a coating liquid is dried which contains two or more types of solvents whose drying speed and solubility are different and which has a combination of a good solvent having a low viscosity and a poor solvent having a high viscosity, the high-viscosity solvent is added in a coating step up to just lower a concentration at which the coating liquid coagulates in order to focus on the viscosity of the coating liquid; and the good solvent is added to a coating film in order to focus on the solubility of the solvent in a drying step, to thereby suppress the whitening of the coating film generated in the drying step.

Description

  The present invention relates to a method and an apparatus for drying a coating film applied on a substrate.

  In recent years, development and manufacture of thin flat display devices called flat panel displays (FPD) have been actively conducted. There are many types of flat panel displays, but the main ones include a liquid crystal display (LCD), a plasma display (PDP), and organic electroluminescence (organic EL).

  In the manufacturing process of these display devices, a method of forming a thin film of a target material on a substrate is frequently used. Several film formation processes can be selected depending on whether the thin film to be formed is a solid film or a film patterned into a desired shape.

  In general, when a solid film is formed, it can be formed by using various coating means such as slit coat, spin coat, dip coat, roll coat, etc. In many cases, a patterned thin film is used for formation, and development of a patterning thin film forming means with higher performance and higher productivity is being developed. As a means for forming a patterned thin film, attention has been paid to a method of combining photolithography with the above-described solid film forming means, an inkjet method, a printing method, or the like.

  For example, Patent Document 1 discloses the following method as patterning of a coating film in an organic EL display manufacturing process.

  First, an element isolation structure for forming a target pattern in advance on a substrate is provided using a photolithography method. Next, a method is disclosed in which an ink obtained by dissolving a target material in a solvent is dropped from a coating nozzle onto a substrate and separated by an element isolation structure to obtain a desired patterned thin film.

  In addition to the method of patterning the coating liquid with the structure formed on the substrate as in the above-mentioned Patent Document 1, the coating nozzle side is processed so that the desired pattern can be applied and applied as in the hole die coating method. There is also a technique of directly patterning the material.

  In the hole die coating method, the coating nozzle side is processed in such a manner, and a row of holes is processed in advance according to a target pattern (stripe pattern), and the coating liquid is applied onto the substrate using the nozzle. It is a technique. The hole die coating method is attracting attention because of the simplicity of the device structure and high material utilization efficiency.

  The outline of the conventional hole die coating method will be described below.

  3 and 4 are diagrams schematically showing a hole die coater used in the hole die coating method, FIG. 3 is a perspective view showing a die head of the hole die coater, and FIG. 4 is a state in which a pattern is formed on the substrate by the hole die coater. It is a perspective view shown.

  3 and 4, 201 is a pipe, 202 is a manifold, 203 is a nozzle plate, 204 is a die head, 205 is a nozzle, 301 is a substrate, and 302 is a coating liquid pattern.

  As shown in FIGS. 3 and 4, a die head 204 including a pipe 201 for supplying a coating liquid, a manifold 202 and a nozzle plate 203 is arranged at a fixed interval (coating gap) with respect to the substrate 301, and the die head 204 or the substrate is arranged. The coating liquid is applied by horizontally moving 301 in the direction of the coating pattern.

  As a result, a coating liquid pattern 302 corresponding to the interval between the nozzles 205 is formed on the substrate 301. Thus, the board | substrate with which the coating liquid pattern 302 was apply | coated progresses to a drying process, and a desired pattern is obtained by removing the solvent in a coating liquid.

JP 2001-351777 A

  By the way, in the hole die coating method, when the stripe width and dry film thickness of the pattern to be obtained are determined, the wet film thickness is also determined, and the dry film thickness ÷ wet film thickness, that is, the solid content of the coating solution is also determined. However, when trying to obtain a thin coating film in a high-definition pattern such as that used in flat panel displays, it is necessary to reduce the amount of solids and the viscosity of the coating liquid becomes low, which stabilizes the liquid column. May become difficult.

  When such a coating solution is applied by the hole die coating method, it is necessary to prepare the coating solution so as to obtain a high viscosity at a low solid content. In order to obtain a coating solution having a low solid content and a high viscosity, if the material to be used as a coating film is a resin, the viscosity can be increased to some extent by increasing the molecular weight. However, there are cases where an increase in molecular weight adversely affects the physical properties of the coating film. In this case, it is necessary to increase the viscosity of the coating liquid without changing the material that becomes the coating film in the coating liquid.

  In order to increase the viscosity of the coating solution by changing the solvent part of the coating solution, increase the viscosity of the solvent, decrease the solubility of the solvent, add a high-viscosity solid as a thickener, etc. There is a way. Among these methods, the thickener addition method for adding a high-viscosity solid content as a thickener is carried out when the thickener added in the coating film remains, so that the coating film is adversely affected. I can't.

  In the case of a coating solution in which a resin-based material is dissolved, by reducing the solubility of the solvent, the polymer of the resin may be in a semi-aggregated state and entangled, thereby increasing the viscosity. However, if the solubility is lowered too much, it completely aggregates and the solid content becomes insoluble.

  In the case of increasing the viscosity of the coating liquid by increasing the viscosity of the solvent itself, a solvent having a high molecular weight or a solvent having a high polarity tends to have a relatively high viscosity, and thus can be used. However, since the solvent having a large molecular weight is slow to dry, there is a possibility that the drying is slow in the drying process after coating, or the solvent cannot be completely dried. In addition, if the solid content in the coating solution is low polarity, the highly polar solvent becomes a poor solvent, so if added too much, the solid content may aggregate and become insoluble. There is also. Therefore, it is necessary to prepare the coating liquid in consideration of the balance between the polarity of the solid content and the drying speed of the original solvent.

  As described above, in the hole die coating method, it is important to optimize the physical properties of the coating liquid with respect to the target coating material and pattern.

  In addition, since the solute of the coating solution is nonpolar, the high-viscosity solvent also acts as a poor solvent, the ratio of the high-viscosity solvent increases, and the solubility is insufficient when a certain component ratio is exceeded. It is also known that the coating solution aggregates or whitens. As described above, in the coating solution used for the hole die coating method, a high-viscosity solvent of a certain amount or more, that is, a poor solvent cannot be added, and thus a high-viscosity solvent having a higher viscosity with the same addition amount is used. There is a need.

  As described above, the viscosity of a solvent generally depends on the molecular weight and polarity of the solvent. Molecules with very large polarities (for example, polyhydric alcohols) act as strong antisolvents for nonpolar solutes and cause the coating liquid to aggregate even in small amounts.

  Here, when considering the drying step of the coating solution, the solvent of the coating solution is a low polarity and good solvent, but a solvent having a low viscosity and a poor solvent having a high viscosity but low solubility are mixed. Yes. For this reason, when only the viscosity is increased without increasing the polarity of the high-viscosity solvent, a higher molecular weight is used as the high-viscosity solvent, so that the good solvent is dried first in the drying step.

  Here, when considering the drying process of the coating film, it can be divided into the first period of drying in which the coating film behaves as a liquid and the latter period of drying in which the solvent evaporates to some extent and the coating film does not flow, and the coating film behaves as a solid. . In the first stage of drying, since the coating film is flowing, convection occurs in which the temperature of the surface decreases due to the heat of vaporization of the solvent molecules evaporated on the coating film surface, and the solvent at the bottom rises to the coating film surface. it seems to do. This is also indicated by the occurrence of Benard cell (dry unevenness in which a fine hexagonal matrix is formed on the dried coating film) when the composition of the coating solution is inappropriate.

  Thus, since the coating film is constantly stirred by the flow of the solution inside the coating film in the first drying stage, there is a difference in the drying speed between the good solvent and the poor solvent that is highly polar and slow to dry. Even if only the good solvent side is evaporated, it is considered that the distribution of the ratio of the solvent in the coating film in the film thickness direction is relaxed by stirring.

  However, at the end of drying, most of the solvent disappears from the coating film, so the solid content ratio in the coating film increases, and the coating film is considered to have increased viscosity and lost fluidity. In this state, the movement of the solvent molecules inside the coating film depends not on convection but on diffusion inside the coating film. However, compared with convection, the diffusion process has a lower moving speed, and the distribution of the solvent ratio of the coating film generated from the difference in the evaporation rate of the solvent on the coating film surface is difficult to be relaxed. Therefore, the ratio of the poor solvent that is slow to dry tends to increase on the coating film surface.

  In this case, if the concentration of the poor solvent in the coating film increases while the fluidity of the coating film is low, the concentration of the poor solvent in the solvent component of the coating solution is too high. Aggregation occurs in the solidified coating film. However, since the coating film has almost no fluidity, huge agglomerates are not formed, and the surface of the coating film appears to be fine and rough. The film becomes cloudy. Such a phenomenon is called whitening of the coating film. Thus, whitening of the coating film tends to occur when drying of the poor solvent component in the composition of the coating solution is slow, but in order to increase the viscosity of the coating solution with a low solid content, there is polarity. It is necessary to use a solvent having a large molecular weight and slow drying as a high viscosity solvent, and as a result, there is a problem that whitening is likely to occur when the coating solution is dried.

  The present invention solves the above problems, and a substrate drying method that hardly causes whitening of a coating film during drying, even if the substrate is coated using a coating composition having a low solid content and a high viscosity. An object is to provide an apparatus.

  In order to achieve the above object, a substrate drying method and apparatus according to the present invention is a liquid mixture comprising at least a solute and two or more solvents having a difference in solubility with respect to the solute. In the drying step of drying the coating film of the composition, drying is performed while supplying a solvent having a relatively high drying rate and high solubility to the solute among the two or more solvents. It is characterized by that.

  Even if the substrate is coated using a coating composition having a low solid content and a high viscosity by the drying method and the drying apparatus, whitening of the coating film hardly occurs during drying.

  According to this invention, even if it is the board | substrate which applied using the coating composition with a solid content and high viscosity, it can make it hard to raise | generate whitening of a coating film at the time of drying.

Schematic configuration diagram of a substrate drying apparatus in an embodiment of the present invention Flow chart related to substrate drying in this embodiment A perspective view showing an example of a die head of a conventional hole die coater The perspective view which shows the state which forms the pattern in a board | substrate with the hole die coater of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic view of a substrate drying apparatus according to an embodiment of the present invention.

  In FIG. 1, 101 is a vacuum chamber when the substrate drying apparatus has a pressure reducing mechanism, 102 is a solvent spraying mechanism for spraying a solvent onto a substrate being dried, 103 is a substrate to be dried by the substrate drying apparatus, and 104 is a substrate 103. A solvent and a solvent holder 105 disposed around the substrate 103 are hot plates as a heating mechanism for drying the substrate 103 while heating.

  As described above, in the hole die coating method, in order to form a pattern with high definition and a very thin dry film thickness, a coating solution having a low solid content and a high viscosity is required.

  For example, when considering a process of forming a stripe pattern of a nonpolar resin material with a line width of 50 to 200 μm and a dry film thickness of 15 to 150 nm on a glass substrate by a hole die coating method, in-plane thickness unevenness of the glass substrate Considering the board thickness variation between the substrates, it is essential that the coating gap between the nozzle tip and the substrate when coating by the hole die coating method is 50 μm or more. Considering the process margin, the coating gap of 70 μm or more is required. Preferably there is.

  On the other hand, in the hole die coating method, in order to carry out the coating process as described above, the viscosity of the coating liquid is 70 mPa · s or more, preferably 100 mPa · s or more in order to ensure the stability of the liquid column. It is desirable. Further, the solid content of the coating liquid is essential to be 1.5% or less, and preferably 1.0% or less.

  If the solid content is a resin, for example, by increasing the molecular weight of the resin, the viscosity of the coating solution can be increased even with the same solid content. However, when the resin has a high molecular weight, the physical properties of the coated / dried pattern change, which may adversely affect the characteristics of the created pattern. Also, depending on the type of resin and the polymerization method, it may be difficult to polymerize the resin.

  If it is difficult to increase the viscosity of the coating liquid due to the change in the solid material, a highly viscous liquid is added to the solvent of the coating liquid.

  For example, the viscosity of the coating solution is increased by adding a highly polar solvent having a hydroxyl group in the molecule, but when the resin material is nonpolar as described above, the amount of the highly viscous solvent having a high polarity is increased. Has an upper limit, and if an amount larger than the upper limit is added, the coating solution will aggregate. Therefore, the viscosity of the coating solution is increased to the target 70 to 100 mPa · s by adding to the limit amount. However, when a coating liquid prepared at 70 to 100 mPa · s is used and a wet pattern of a coating film is formed on a substrate by a hole die coater and then a drying process is performed, as described above, the high-viscosity solvent is originally Since the drying is slower than the good solvent which is the solvent, whitening of the coating film is likely to occur in the drying process.

  Therefore, in the present embodiment, when performing the drying step, it is possible to suppress the whitening of the coating film by supplying a good solvent that dries faster than the high viscosity solvent to the coating liquid pattern on the substrate. Yes.

  The means for supplying the good solvent is not particularly limited as long as the object can be achieved. For example, a solvent is sprayed inside the substrate drying device, a cloth-like solvent holding body soaked with the solvent is placed inside the drying device, and the drying atmosphere is made rich in the good solvent by evaporation of the solvent. It is possible to adopt a technique such as supplying to the coating film by the method.

  In this case, if the supply amount of the solvent is too small, whitening of the coating film cannot be prevented, and if it is too much, whitening can be suppressed, but a problem that the drying time becomes long occurs. Must be set to

  In the present embodiment, a drying process of a coating liquid composed of two or more kinds of solvents having a difference in drying speed and solubility is employed. In particular, in the hole die coating method, a good solvent having a low viscosity and a poor viscosity having a high viscosity are used. When drying a coating solution consisting of a combination of solvents, add a high-viscosity solvent to the concentration just before agglomeration in the coating process to emphasize the viscosity of the coating solution, and focus on solvent solubility in the drying step. Therefore, whitening of the coating film that occurs during the drying process can be suppressed by supplying a good solvent to the coating film.

  Although the drying process of this Embodiment may be performed under a normal pressure, by performing under a reduced pressure, it becomes possible to shorten drying time by using a high-viscosity solvent with slow drying for a coating liquid. The pressure at the time of depressurization is not particularly specified. However, if the pressure is lowered too rapidly in the first drying step, the solvent boils and the coating film is disturbed, which is not preferable.

  In addition, the pressure profile in the present embodiment is not particularly limited as long as the object of the present invention can be achieved, and the pressure is applied in the early drying stage in which the coating film is liquid and in the late drying stage in which the coating is solid. It may be changed. Further, the substrate may be heated during the drying process in order to promote drying, and the substrate temperature profile is not particularly limited.

  In order to carry out the drying process of the present embodiment, a substrate drying apparatus having a mechanism for supplying a good solvent to the coating film on the substrate during the drying process is provided.

  This substrate drying apparatus has a mechanism for supplying a good solvent to the coating film on the substrate during the drying process, but the supply mechanism for the good solvent is not particularly limited, and the solvent spray mechanism 102 shown in FIG. A mechanism for supplying a good solvent directly to the coating film by spraying a solvent onto the coating film on the substrate 103, or a drying furnace by vaporizing the sprayed good solvent , A mechanism in which the atmosphere in the chamber 101 is made rich in a good solvent and a mechanism for supplying it to the coating film by evaporation equilibrium, or a cloth-like solvent in which a solvent for making the atmosphere in the drying furnace rich in the solvent is soaked by the evaporated solvent The holding body 104, a holding body, a solvent supply mechanism, and the like can be given.

  In addition, a mechanism for performing the substrate drying process under reduced pressure can be provided. In this case, a vacuum chamber 101 and a vacuum pump (not shown) are provided in addition to the solvent spray mechanism 102 which is a solvent supply means.

  In addition, the substrate drying apparatus may have a substrate heating mechanism for promoting drying of the coating film regardless of whether or not the decompression mechanism is included. Specific examples of the substrate heating mechanism include a hot plate 105 that directly heats the substrate 103, a hot air blowing mechanism, a lamp that heats by infrared irradiation, and a mechanism that circulates a heating medium in the heating device itself.

  Next, the coating / drying process in the present embodiment will be described based on the flowchart of FIG.

  First, a glass substrate on which a coating solution is patterned is placed on the stage of a hole die coater (S1). The alignment mark formed on the glass substrate is recognized by the alignment camera provided in the hole die coater, and the position of the substrate is finely adjusted in order to align the coating position with the hole die nozzle (S2).

  Next, since the thickness of each substrate is uneven, the surface of the substrate is measured with a laser displacement meter or the like, and the height of the substrate is measured (S3). From this height data, the coating height of the die head is determined in accordance with the coating gap. During application, pressure is applied to the manifold through the piping, and the application liquid is discharged from the nozzle at an appropriate discharge amount to obtain the desired film thickness, and the stage or die head is moved horizontally while maintaining the set gap. A pattern of the coating solution is formed on the substrate (S4).

  The set value of the gap or the set value of the discharge pressure may be the same value from the start of application to the end of application, or may be changed during the application process.

  The substrate after the coating process is moved to the drying chamber, and the drying process is performed (S5). The drying pressure may be performed under atmospheric pressure, but it is preferable to perform the pressure reduction under reduced pressure because drying becomes faster and tact time is improved. In order to shorten the drying time, it is preferable to install a heating mechanism on the stage of the substrate drying apparatus (S6). A solvent supply means is provided in the chamber for performing vacuum drying. In this way, the first substrate is dried (S7).

  In addition, the substrate drying apparatus of the present embodiment is provided with a shower nozzle that sprays a solvent as means for supplying a good solvent among the solvents of the coating solution, and sprays the solvent onto the substrate (S8). Next, the second substrate is dried on the substrate (S9), the vacuum pump of the decompression chamber is operated to decompress the inside of the drying chamber, and the heating is finished (S10), and the drying is performed at a decompression rate that does not cause bumping. I do.

  In step S8, a good solvent is sprayed from the shower nozzle onto the substrate when the fluidity of the coating film surface has been lost to some extent. If the spray amount is too small, the good solvent sprayed before reaching the substrate is vaporized, and if it is too large, the substrate surface is so wet that the pattern is blurred. By setting the solvent supply rate, pressure, and temperature to appropriate values, a coating pattern without whitening can be obtained.

  By using the substrate drying method and apparatus of the present invention, the application range of the patterning process by the hole die coating method can be expanded. In particular, in the fields of patterning of color filter materials for liquid crystal displays, patterning of phosphor materials for plasma displays, patterning of light emitting layer materials for organic EL displays, and light emitting auxiliary layer materials, patterning processes by the hole die coating method are more extensive. It becomes possible to use for.

101 Chamber 102 Solvent Spray Mechanism 103 Substrate 104 Solvent and Solvent Holder 105 Hot Plate

Claims (4)

  In the drying step of drying a coating film of a liquid mixture composition applied on a substrate and comprising at least a solute and two or more kinds of solvents having a difference in solubility with respect to the solute, the two or more kinds A substrate drying method characterized in that drying is performed while supplying a solvent having a high drying rate and a high solubility relative to the solute in the solvent.   The solvent is composed of a solvent having a relatively high drying rate and a high solubility with respect to the quality, and a solvent having a relatively slow drying rate and a low solubility. 2. The substrate drying method according to claim 1, wherein the viscosity of the liquid mixture composition increases as the content rate of the solvent having a low drying rate and low solubility increases.   3. The substrate drying method according to claim 1, wherein the substrate drying step is performed under reduced pressure and / or under heating.   A substrate drying apparatus for performing the substrate drying process according to claim 1.

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