JP4956696B1 - Method for drying coating film formed on the surface of PET film - Google Patents

Abstract

A method for drying a coating film formed on the surface of a PET film, which can dry a coating film containing an organic solvent in a shorter time than before and without causing compressive stress on the dried thin film. I will provide a.
SOLUTION: A PET film 1 having a coating film 2 containing an organic solvent formed on its surface is covered with a plurality of tubes 15 and 16 whose outer periphery of a filament 14 absorbs infrared rays of 3.5 μm or more. An infrared heater 13 having a structure in which a cooling fluid flow path 17 is formed between the tubes is irradiated with infrared light having a principal wavelength of 3.5 μm or less, and the coating film 2 is efficiently maintained while keeping the PET film 1 at a low temperature. Dry well.
[Selection] Figure 2

Description

  The present invention relates to a method for drying a coating film formed on the surface of a PET film.

  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 the base film, dried, peeled off from the base film, and laminated. As a base film for this purpose, a PET film that is excellent in strength and inexpensive is 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 film 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 which received compressive stress deform | transforms when it peels from a base film, there existed a problem of causing the fall of the dimensional accuracy in a lamination process. Further, if the drying temperature is lowered to avoid this problem, it takes a long time to complete the drying, and the productivity is lowered.

Japanese Patent Laid-Open No. 7-251411

  Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art, and to apply a compressive stress to the dried thin film in a shorter time than before, by applying a coating film containing an organic solvent formed on the surface of the base film. It is providing the drying method of the coating film formed in the surface of PET film which can be dried without producing.

  In order to solve the above problems, the present invention provides an infrared ray whose outer periphery of a filament is 3.5 μm or more on a PET film on which a coating film containing an organic solvent having an absorption spectrum of 3.5 μm or less is formed. From an infrared heater having a structure in which a cooling fluid passage is formed between the plurality of pipes and the heater surface temperature is suppressed between the plurality of pipes. The coating film is dried without heating the PET film.

  In preferable embodiment, the said coating film is a coating film containing a ceramic powder, and peels from the surface of PET film 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 PET film at 60 ° C. or less. Furthermore, it is preferable to maintain the temperature of the PET film at 60 ° C. or less by bringing cooling air into contact with the surface on which the coating film of the PET film is formed.

  In the drying method of the coating film formed on the surface of the PET film of the present invention, the outer periphery of the filament is covered with a plurality of tubes that absorb infrared rays of 3.5 μm or more as a heating source, and between these tubes. An infrared heater having a structure in which a flow path of a cooling fluid that suppresses an increase in the heater surface temperature 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 this invention, this problem can be avoided and the temperature rise of the PET film can be prevented.

  Therefore, according to the present invention, the coating film formed on the surface of the PET film is irradiated with infrared light having a principal wavelength of 3.5 μm or less without increasing the temperature in the drying chamber, and has an absorption spectrum of 3.5 μm or less. The organic solvent can be efficiently dried in a short time. Moreover, since the PET film is hardly heated by infrared rays having a wavelength of 3.5 μm or less, the coating film can be dried without heating the PET film. As a result, the PET film is not thermally shrunk after drying as in the prior art, and compressive stress is not generated in the dried thin film. In addition, since it is possible to dry while maintaining a low temperature, it is possible to prevent the diffusion of metal powder used in MLCC and the like, which is also useful in the process of stacking thin films.

  In particular, if the PET film 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 PET film together. In particular, when the cooling air is brought into contact with the surface on which the coating film of the PET 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) which is a base film, and 2 is a coating film formed on the surface thereof. The coating film 2 of this embodiment is obtained by dispersing a solute such as barium titanate powder 3 which is a kind of ceramic powder in an organic solvent together with an organic binder, and terpineol or the like is used as the organic solvent. In addition, it cannot be overemphasized that types, such as these ceramic powder and an organic solvent, can be changed according to the target product.

  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 1.5 to 2.0 μm.

  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. On the ceiling of the drying furnace 10, infrared heaters 13 for irradiating infrared rays having a dominant wavelength of 3.5 μm or less are arranged at appropriate intervals. In this embodiment, the continuous drying furnace 10 is used. However, in the present invention, the type of the drying furnace is not particularly limited, and a batch type drying furnace may be used.

  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 matches the vibration frequency of hydrogen bonds between the solvent or water molecules in the coating film 2, so that the coating film 2 can be efficiently dried.

  On the other hand, 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, the infrared heater 13 having a special structure is used in the present invention, and the absorption spectrum is 3.5 μm or less while suppressing infrared rays having a wavelength longer than 3.5 μm, which may heat the PET film 1. The organic solvent can be efficiently heated and dried.

  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.

  The coated film 2 thus dried is in a state in which the barium titanate powders 3 are firmly bonded to each other by an organic binder as shown on the right side of FIG. 1, and the coating film dried from the surface of the PET film 1 in the next step. The film 2 is peeled off and laminated through a known process such as cutting. Since the temperature of the PET film 1 in the drying process is maintained at 60 ° C. or less, more preferably 45 ° C. or less, the thermal shrinkage in the cooling process is negligibly small, so that a compressive stress may be applied to the coating film 2. In addition, deformation after peeling is also prevented. Therefore, the dimensional accuracy in the subsequent lamination process can be maintained at a high level.

  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 film is efficiently and quickly converted into the dried coating film 2. It can be dried without causing compressive stress. The specific data is shown in the following example.

  Using an experimental furnace in which an infrared heater was placed on the ceiling, the coating film drying rate was measured. The base film used was a PET film having a thickness of 30 μm, and a slurry having a thickness of 80 μm applied on one side was dried. This slurry contains barium titanate, which is a ceramic powder, as a solute, NMP as an organic solvent, and PVDF (polyvinylidene fluoride) as an organic binder.

  The temperature during drying is measured with a thermocouple thermometer affixed to the surface of the coating, and under the constraint that the coating temperature (almost the same as the PET film temperature because it is in close contact) is always kept below 40 ° C. The drying experiment was conducted by the following four methods. In any method, the number of specimens N is two.

  The first method is a conventional hot air drying method, in which hot air of 55 ° C. was passed through the furnace to dry the coating film. In this method, in order to always maintain the coating film temperature at 40 ° C. or less, the air flow must be greatly reduced, and it took 11 minutes to dry the coating film. The completion of drying was confirmed by a method of visually observing the color change of the coating film.

The second method is the method of the present invention, which is a method using heating by the infrared heater shown in FIG. 3 and cooling by cooling air in combination. The cooling air volume is 30 m ³ / hr, and the temperature is room temperature (25 ° C.). The filament temperature was 850 ° C., and the surface temperature of the infrared heater was maintained at 100 ° C. with a cooling fluid (air). In this method, the coating film could be dried in 4 minutes.

  From this experiment, according to the drying method of the present invention, it was confirmed that the drying time could be significantly shortened compared with the conventional method while maintaining the coating film temperature at 40 ° C. or lower.

DESCRIPTION OF SYMBOLS 1 PET film 2 Coating film 3 Barium titanate powder 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 (2)

  A PET film on which a coating film containing an organic solvent having an absorption spectrum of 3.5 μm or less is formed is covered with a plurality of tubes whose outer periphery of the filament absorbs infrared light of 3.5 μm or more. A surface on which a coating film of PET film is formed by irradiating infrared light having a dominant wavelength of 3.5 μm or less from an infrared heater having a structure in which a flow path of a cooling fluid that suppresses an increase in heater surface temperature is formed between tubes A method for drying a coating film formed on the surface of a PET film, characterized in that the temperature of the PET film is maintained at 60 ° C. or lower by bringing cooling air into contact therewith.   2. The coating film formed on the surface of the PET film according to claim 1, wherein the coating film is a coating film containing ceramic powder and is peeled off from the surface of the PET film after drying. Method.

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