JP5776082B2 - How to dry the coating - Google Patents

Description

  The present invention relates to a method for drying a coating film formed on the surface of a substrate that transmits near infrared rays, such as a PET film or glass.

  In the manufacturing process of multilayer electronic components such as MLCC (Multilayer Ceramic Capacitor), Chip Inductor, LTCC (Low Temperature Co-fired Ceramic) etc., as shown in Patent Document 1, for example, ceramic powder, metal powder, organic binder and organic A method is adopted in which a coating film containing a solvent is formed on the surface of a substrate, dried, peeled off from the substrate, and laminated. As a base material for this purpose, PET film and glass excellent in strength are widely used.

  In general, an infrared heater or hot air is used as a heating means in order to increase the productivity of the drying process. However, in such a conventional method, the base material heated and expanded during drying shrinks in the cooling step after drying, and compressive stress is generated in the coating film formed on the surface. Since the coating film that has received the compressive stress is deformed when peeled from the substrate, there is a problem in that the dimensional accuracy in the laminating process is lowered.

  Further, in the conventional technique, when the coating film formed on the surface of the substrate has a thickness of 100 μm or more, the temperature of the upper and lower surfaces of the coating film becomes uneven during the drying process, and distortion due to thermal stress occurs. There was a problem.

JP 2003-279245 A

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to form a coating film containing an organic solvent formed on the surface of a base material without causing compressive stress on the dried film. Provided is a method for drying a coating film that can be dried without causing distortion due to thermal stress even when the coating film formed on the surface of the material has a thickness of about 100 μm or more. It is.

  The method for drying a coating film of the present invention made to solve the above-described problem is to transmit infrared rays having a dominant wavelength of 3.5 μm or less through a coating film containing an organic solvent having an absorption spectrum of 3.5 μm or less. After forming 100 μm to 2 mm on the surface of the base material, irradiate infrared rays with a dominant wavelength of 3.5 μm or less only from the back side of the base material to uniformly diffuse energy in the coating film without drying the coating film Subsequently, the coating film is dried by irradiating infrared rays having a dominant wavelength of 3.5 μm or less from the surface side of the substrate on which the coating film is formed.

  The infrared irradiation is preferably performed through a short-pass filter that absorbs infrared light of 3.5 μm or more, and in particular, the outer periphery of the filament is covered with a plurality of tubes that absorb infrared light of 3.5 μm or more. It is preferable to use an infrared heater having a structure in which a cooling fluid flow path that suppresses an increase in the heater surface temperature is formed between a plurality of tubes.

  In preferable embodiment, a base material is a PET film or glass, The said coating film is a coating film containing a ceramic powder, and peels from the surface of a base material after drying. Moreover, it is preferable to irradiate infrared rays having a dominant wavelength of 3.5 μm or less while maintaining the temperature of the substrate at 60 ° C. or less. Furthermore, it is preferable to maintain the temperature of the substrate at 60 ° C. or less by bringing cooling air into contact with the surface on which the coating film of the substrate is formed.

  In the present invention, a coating film containing an organic solvent having an absorption spectrum of 3.5 μm or less is formed on the surface of a substrate that transmits infrared rays having a dominant wavelength of 3.5 μm or less. Irradiate infrared rays having a dominant wavelength of 3.5 μm or less only from the back side, and then irradiate infrared rays having a dominant wavelength of 3.5 μm or less from the surface side of the substrate on which the coating film was formed. Even if it is a case where the film thickness is formed to 100 μm or more by drying, in the stage before drying occurs, energy is uniformly diffused in the coating film without drying the coating film, and in the state before drying begins, The in-film temperature can be made uniform. This makes it difficult for the temperature difference to be applied to the upper and lower surfaces of the coating film during the drying process, so that the thermal stress in the film is reduced, and the phenomenon of distortion due to the thermal stress can be effectively avoided.

  Moreover, since the base material used for this invention is hardly heated with the infrared rays whose wavelength is 3.5 micrometers or less, a coating film can be dried, without heating a base material. As a result, the base material is not thermally contracted after drying as in the prior art, and compressive stress is not generated in the dried thin film.

  In the invention described in claim 2, the cooling fluid that suppresses the rise in the heater surface temperature between the plurality of tubes, the outer periphery of the filament being covered with a plurality of tubes that absorb infrared rays of 3.5 μm or more as a heating source. An infrared heater having a structure in which a flow path is formed is used. The infrared heater having this structure can maintain the temperature of the outer surface of the heater at a low temperature by the cooling fluid, although it can irradiate infrared rays having a dominant wavelength of 3.5 μm or less by increasing the filament temperature. In general, when the temperature of an infrared heater is increased, the temperature of the outer peripheral protective tube of the filament also increases, and the outer peripheral protective tube becomes a secondary heating element, which emits long-wave infrared light and raises the temperature in the drying chamber. However, in the invention according to claim 2, this problem can be avoided and the temperature rise of the substrate can be prevented. Therefore, without increasing the temperature in the drying chamber, the coating film formed on the surface of the substrate is irradiated with infrared light having a dominant wavelength of 3.5 μm or less, and an organic solvent having an absorption spectrum of 3.5 μm or less is applied for a short time. Can be dried efficiently.

  In particular, if the substrate is dried while maintaining the temperature at 60 ° C. or lower, the effect of thermal shrinkage during cooling can be suppressed to a level that does not cause any practical problems. For this purpose, it is preferable to use cooling of the base material in combination, and particularly when the cooling air is brought into contact with the surface of the base material on which the coating film is formed, the vapor of the evaporated organic solvent is quickly exhausted to the outside. Therefore, it is possible to further increase the drying efficiency.

It is a typical expanded sectional view of a coating film. It is sectional drawing of the drying furnace which shows embodiment of this invention. It is sectional drawing of the infrared heater used for this invention.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic enlarged cross-sectional view of a coating film, wherein 1 is a PET film (polyethylene terephthalate film) as a substrate, and 2 is a coating film formed on the surface thereof. The base material only needs to transmit infrared rays having a dominant wavelength of 3.5 μm or less, and glass or the like can be used in addition to the PET film.

  Generally, an organic solvent has an absorption spectrum of 3.5 μm or less, so it absorbs infrared light with a main wavelength of 3.5 μm or less and efficiently heats and evaporates. Has the property of being hardly heated. In addition, in the state before drying shown on the left side of FIG. 1, the thickness of the PET film 1 of this embodiment is 10 to 100 μm, and the thickness of the coating film 2 is 100 μm to 2.0 mm.

  In this embodiment, the PET film 1 on which the coating film 2 is formed is dried by a drying furnace 10 as shown in FIG. The drying furnace 10 is a so-called roll-to-roll furnace in which the PET film 1 is moved at a predetermined speed between an inlet-side dispensing roll 11 and an outlet-side winding roll 12. In the front stage of the drying furnace 10, infrared heaters 13 for irradiating infrared light having a dominant wavelength of 3.5 μm or less are arranged on the floor at an appropriate interval. Subsequently, in the rear stage of the drying furnace 10, the floor and ceiling are arranged. Similarly, infrared heaters 13 for irradiating infrared rays having a dominant wavelength of 3.5 μm or less are arranged at appropriate intervals. Note that the infrared heater 13 may be disposed only on the ceiling in the subsequent stage of the drying furnace 10. Furthermore, although the continuous drying furnace 10 is used in this embodiment, the type of the drying furnace is not particularly limited in the present invention, and may be a batch type drying furnace.

  In these infrared heaters 13, as shown in FIG. 3, the outer periphery of the filament 14 is concentrically covered by a plurality of tubes 15, 16, and a cooling fluid flow path 17 is provided between the plurality of tubes 15, 16. It is of the formed structure. The inner tube 15 is a protective tube for the filament 14 and is an infrared ray transmissive protective tube such as quartz glass or borosilicate crown glass. The outer tube 16 is a tube for flowing a cooling fluid around the outer periphery of the inner tube 15. These tubes 15 and 16 have a function as an electromagnetic short-pass filter and absorb infrared rays of 3.5 μm or more. As described above, quartz glass, borosilicate crown glass, or the like can be used, but it is preferable to use a quartz glass tube in view of heat resistance, thermal shock resistance, economy, and the like.

  The filament 14 is heated to 700 to 1200 ° C. and emits infrared light having a peak at a wavelength of about 3 μm. Quartz glass, borosilicate crown glass, and the like transmit infrared light having a wavelength of 3.5 μm or less. It has a function as a short pass filter that absorbs infrared rays having a wavelength of 5 μm or more. For this reason, the pipe | tube 15 and the pipe | tube 16 selectively permeate | transmit the infrared rays with a wavelength less than 3.5 micrometers among the electromagnetic waves radiated | emitted from the filament 14, and supply them in a furnace. The infrared energy in this wavelength region is directly absorbed by the organic solvent in the coating 2 and easily converted into heat, and also matches the frequency of hydrogen bonding between the solvent or water molecules. The membrane 2 can be efficiently dried.

  However, since the thickness of the coating film 2 of the present invention is 100 μm to 2.0 mm, the infrared heater 13 is disposed only on the ceiling portion of the drying furnace 10, and infrared irradiation is performed on the upper surface of the coating film 2. When done only from the side, the irradiated energy is lost as volatile energy of solvent and moisture on the irradiated surface before it is uniformly dispersed in the coating film, so the temperature of the upper and lower surfaces of the coating film during the drying process Becomes non-uniform and may cause distortion. On the other hand, in the present invention, in the former stage of the drying furnace 10, first, the coating film is applied without drying by irradiating infrared light having a dominant wavelength of 3.5 μm or less only from the back side of the PET film 1. The energy is uniformly diffused in the film, and the temperature in the film is made uniform in a state before the drying is started. Thereafter, the energy is uniformly diffused in the coating film, and from the surface side of the PET film 1, By irradiating with an infrared ray having a wavelength of 3.5 μm or less to dry, the temperature of the upper and lower surfaces of the coating film in the drying process is made uniform, thereby generating thermal stress in the coating film and distortion caused by it. Can be effectively avoided.

  Since the PET film 1 has physical properties that are hardly heated by near infrared rays having a wavelength of 3.5 μm or less, the temperature does not rise while passing through the drying furnace 10. For this reason, it does not shrink in the cooling process as in the prior art.

  However, the tube 15 and the tube 16 become radiation absorbers in the wavelength region longer than 3.5 μm, and the temperature of the tubes 15 and 16 is increased by absorbing the infrared energy. Since a considerable amount of infrared rays having a wavelength longer than 3.5 μm is emitted from the filament 14 at the above-described temperature, the surface temperature of the tube 16 rises as it is, and as a result, the tube itself becomes an infrared radiator, There is a risk that infrared rays having wavelengths longer than 3.5 μm are mainly emitted into the furnace. Such long-wavelength infrared rays increase the temperature in the furnace and heat the PET film 1, which may cause the same problem as in the past.

  Therefore, in the present invention, a cooling fluid is passed through the flow path 17 between the pipe 15 and the pipe 16, and the long-wavelength infrared energy once absorbed by the pipe 15 and the pipe 16 is converted into convective heat transfer. It is converted and transmitted to the fluid and removed from the system. As a result, the wavelength of the infrared rays finally supplied into the furnace is limited to the short wavelength region, and the temperature of the tube 15 and the tube 16 is set to 200 even in a state where the filament 14 is continuously energized and heated at a high temperature. It becomes possible to maintain at ℃ or lower, more preferably 150 ℃ or lower. Accordingly, it is possible to reliably prevent an increase in the furnace temperature and heating of the PET film 1 due to secondary radiation of long-wavelength infrared rays.

  In addition, although the fluid supplied to the flow path 17 is air, an inert gas, etc., in this embodiment, air is blown in from the fluid supply port 18, and the heated air is taken out from the fluid discharge port 19, respectively.

  As described above, according to the present invention, an organic solvent having an absorption spectrum of 3.5 μm or less is efficiently heated and dried while suppressing infrared rays having a wavelength longer than 3.5 μm, which may heat the PET film 1. Can be made.

  However, since it is difficult to completely eliminate infrared rays having a wavelength longer than 3.5 μm, there is a possibility that the temperature of the PET film 1 is slightly increased. Therefore, in the present embodiment, as shown in FIG. 2, the surface on which the coating film 2 of the PET film 1 is formed by arranging the cooling air jet pipe 20 and the intake pipe 21 in the vicinity of the inlet and the outlet of the drying furnace 10. The PET film 1 is cooled by bringing cooling air into contact therewith.

  Further, the inside of the furnace is also cooled by this cooling air, and the temperature of the PET film 1 can be maintained at 60 ° C. or lower, more preferably 45 ° C. or lower. In addition, since the cooling air has a function of discharging the vapor of the organic solvent evaporated from the surface of the coating film 2 to the outside, the drying of the coating film 2 can be further promoted. It is of course possible to combine cooling from the lower surface of the PET film 1.

  As described above, according to the present invention, the coating film 2 containing the organic solvent formed on the surface of the PET film 1 as the base material can be efficiently and quickly formed into the dried coating film 2. It can be dried without causing thermal stress or compressive stress.

  The effect of the said content was confirmed by evaluating a coating-film drying speed using an experimental furnace. Specifically, a thick film is coated on a PET film, and as a drying means, A: by air drying, B: an infrared heater having no short pass filter function and air drying, C: short of the present application Evaluation was carried out by selecting any one of three types of infrared heaters having a pass filter function and those using air drying together. As a result of the evaluation, the drying time of C is shortened by using the drying means of C (the infrared heater having the short-pass filter function of the present application and air drying) in comparison with the case of using other means (AB). It was confirmed that the temperature and drying temperature could be reduced.

DESCRIPTION OF SYMBOLS 1 PET film 2 Coating film 10 Drying furnace 11 Dispensing roll 12 Winding roll 13 Infrared heater 14 Filament 15 Pipe 16 Pipe 17 Flow path 18 Fluid supply port 19 Fluid discharge port 20 Jet pipe 21 Intake pipe

Claims (7)

After forming a coating film containing an organic solvent having an absorption spectrum of 3.5 μm or less on the surface of a substrate that transmits infrared rays having a dominant wavelength of 3.5 μm or less, 100 μm to 2 mm,
Irradiating infrared rays having a dominant wavelength of 3.5 μm or less only from the back side of the substrate to uniformly diffuse energy in the coating without drying the coating, and subsequently forming the coating The coating film is dried by irradiating infrared rays having a dominant wavelength of 3.5 μm or less from the surface side of the coating film.   The method for drying a coating film according to claim 1, wherein the irradiation with infrared rays is performed through a short pass filter that absorbs infrared rays of 3.5 µm or more.   The infrared irradiation is covered with a plurality of tubes that absorb infrared rays of 3.5 μm or more on the outer periphery of the filament, and a cooling fluid flow path that suppresses the rise in the heater surface temperature is formed between these tubes. 3. The method for drying a coating film according to claim 2, wherein the method is performed using an infrared heater having a structure as described above.   The method for drying a coating film according to any one of claims 1 to 3, wherein the coating film is a coating film containing ceramic powder and is peeled off from the surface of the substrate after drying.   The method for drying a coating film according to any one of claims 1 to 4, wherein an infrared ray having a dominant wavelength of 3.5 µm or less is irradiated while maintaining the temperature of the substrate at 60 ° C or lower.   6. The method for drying a coating film according to claim 5, wherein the temperature of the substrate is maintained at 60 [deg.] C. or less by bringing cooling air into contact with the surface of the substrate on which the coating film is formed.   The method for drying a coating film according to claim 1, wherein the substrate is a PET film or glass.