JP5842220B2 - Resin film heating method - Google Patents

Description

  The present invention relates to a method for heating a resin film using an infrared heater, and more particularly to a method for efficiently heating a polyethylene film or a polypropylene film used for a separator of a lithium ion battery. .

  Heating may be required to perform heat treatment such as annealing on the molded resin film. For this purpose, for example, as shown in Patent Document 1, a method of heating a resin film by hot air blowing and infrared irradiation while running in a furnace by a roll-to-roll method is common. As the infrared heater, one having a structure in which a filament is housed inside a glass protective tube (for example, Patent Document 2) is widely used.

In order to increase the productivity of the heating process, it is necessary to radiate a large amount of heat from the infrared heater to the resin film. Therefore, conventionally, it has been common to increase the radiant energy by increasing the filament temperature of the infrared heater. It is known that when the filament temperature increases, the peak of the emission spectrum shifts to the short wavelength side. Especially when the filament temperature is set to 700 ° C. or higher, the main wavelength of the emission spectrum is in the near infrared region as shown in FIG. 3.5 μm or less. Such near infrared rays act on the covalent bond in the molecular structure of a polyethylene film or a polypropylene film, and can advance heating efficiently.

  However, when the filament temperature of the infrared heater is raised, the temperature of the protective tube surrounding the periphery gradually increases, and the protective tube itself becomes a radiator and emits infrared rays. For example, when the temperature of the protective tube reaches 300 ° C., the furnace wall is heated together with the resin film by radiating infrared rays having a dominant wavelength of 5 μm into the furnace as shown in FIG. However, since the radiation energy in the near-infrared region of 3.5 μm or less, which is the target under such conditions, is a slight amount, the heating efficiency is insufficient.

  Therefore, if an attempt is made to increase the radiant energy of 3.5 μm or less, the radiant energy in the far infrared region also increases, and the resin film and the furnace wall are overheated. Thus, when the furnace temperature rises too much and exceeds the softening point of the resin film, heat treatment such as annealing cannot be appropriately performed. For this reason, conventionally, the resin film could not be efficiently heated while suppressing an increase in film temperature and furnace temperature.

JP 2004-299216 A JP 2006-294337 A

  Therefore, the object of the present invention is to solve the above-mentioned conventional problems, while radiating near infrared rays acting on the covalent bond intensively while suppressing the rise in the furnace temperature and the film temperature, and efficiently heating the resin film It is to provide a method for heating a resin film.

The method for heating a resin film of the present invention made to solve the above-mentioned problem is to provide a resin film having a covalent bond in the molecular structure and having an absorption spectrum of electromagnetic waves having a wavelength of 3.5 μm or less inside the furnace body. in while traveling, covered with inner tube outer periphery of the filament absorbs infrared radiation having a wavelength greater than 3.5 [mu] m, the double by an outer tube that absorbs infrared radiation having a wavelength greater than 3.5 [mu] m, these It is heated by an infrared heater having a structure in which a cooling air flow path that suppresses the rise in the heater surface temperature is formed between the two tubes, and the filament temperature of the infrared heater is set to 700 to 1200 ° C. and acts on the covalent bond . while irradiating infrared rays dominant wavelength below 3.5μm suitable for the surface temperature of the infrared heater is suppressed to 200 ° C. or less by the cooling air, to suppress an increase in the furnace temperature And it is characterized in heating the One resin film.

  In a preferred embodiment, the resin film is a separator used as an electrode partition of a lithium ion battery. The resin film is a polyethylene film or a polypropylene film. It is preferable to run these resin films in the furnace by a roll-to-roll method.

In the resin film heating method of the present invention, as the resin film heating means, the outer periphery of the filament is covered with a plurality of tubes that absorb infrared rays having a wavelength exceeding 3.5 μm, and infrared rays are interposed between the plurality of tubes. An infrared heater having a structure in which a flow path of a cooling fluid that suppresses an increase in the surface temperature of the heater is formed is used. This infrared heater raises the filament to a high temperature of 700 to 1200 ° C., selectively radiates infrared rays having a short wavelength of 3.5 μm or less, which acts on the covalent bond in the molecule, and moves the resin film running in the furnace by the conveying means. It can be heated efficiently. Moreover, because the cooling fluid suppresses the increase in the surface temperature of the infrared heater, the increase in the furnace temperature due to the long wavelength infrared light having a wavelength of 3.5 μm or more can be suppressed, and waste of energy can be eliminated. And the rise of the resin film which is a drying target object, or the temperature in a furnace can be suppressed.

It is a graph which shows the radiation spectrum of an infrared heater. It is sectional drawing which shows the drying furnace of embodiment of this invention. It is sectional drawing of the infrared heater used for this invention. It is a graph which shows the radiation spectrum of the infrared heater used for this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is a schematic sectional view showing a drying furnace used in the present invention, where 1 is a tunnel-like furnace body, 2 is a discharge roll provided on the inlet side of the furnace body 1, and 3 is on the outlet side. It is the winding roll provided. The resin film F travels rightward in the furnace by a so-called roll-to-roll method.

The resin film F is, for example, a polyethylene film or a polypropylene film used for a separator of a lithium ion battery, and both have a covalent bond in the molecular structure and have an electromagnetic wave absorption spectrum with a wavelength of 3.5 μm or less. Specifically, polyethylene has an absorption region at 2.7 to 3.5 μm, and polypropylene has an absorption region at 2.5 to 3.3 μm.

A large number of infrared heaters 4 are arranged on the ceiling of the furnace body 1 to irradiate the traveling resin film F with infrared rays. As shown in FIG. 3, these infrared heaters 4 have a structure in which the outer periphery of the filament 5 is covered with a plurality of tubes 6 and 7 that absorb infrared rays having a wavelength exceeding 3.5 μm. The inner tube 6 is a protective tube for the filament 5 and is an infrared ray transmitting glass tube such as quartz glass. The outer tube 7 is made of quartz glass or borosilicate crown glass that absorbs infrared rays having a wavelength exceeding 3.5 μm, and functions as a low-pass filter.

  In the heating furnace where the upper limit temperature resulting from the product physical properties is defined, infrared radiation with a short wavelength (3.5 μm or less) considered to be effective for heating a resin film having a covalent bond becomes dominant. It is not really easy to control. The reason for this is that the temperature of a radiator mainly composed of the wavelength region becomes a high temperature exceeding 700 ° C. at least according to Planck's radiation law. As a result, when the furnace temperature rises, the resin film F softens and the intended annealing cannot be performed. Even if allowed, the following problems can be inferred from the theoretical aspect of radiation.

  First, short wavelength radiation is preferentially radiated from the high temperature radiator, but the radiation energy per unit area is enormous due to Stefan-Boltzmann law. As a result, an unnecessarily high temperature rise is caused in each part of the furnace, and it is impossible to establish a drying process for mass production, particularly from the viewpoint of energy saving and heat resistance of the product when transport is stopped. It was.

  On the other hand, in the heater having the shape shown in FIG. 3, since the radiator has a thin filament shape, both the radiation area and the heat capacity are small. When viewed from one heater, “a small amount of short wavelength infrared radiation is emitted. It means having the characteristics as a radiation source. That is, the temperature of the filament itself can be easily increased, the temperature of the filament can be changed, and the radiation area (total energy generation) in the unit volume in the furnace can be controlled by adjusting the number of heaters installed (pitch). Easy. In addition, since the temperature of the filament energized at 700 ° C. to 1200 ° C. is instantaneously reduced when the energization is stopped, the safety when the conveyance is stopped is extremely high. By introducing a tube cooling mechanism in addition to the above features, each of the above-mentioned problems can be solved, and the wavelength of radiation in the drying furnace can be controlled assuming a wide range of applications.

The filament 5 is heated to 700 to 1200 ° C. and emits infrared light having a peak near 3 μm as shown in FIG. 4, but quartz glass, borosilicate crown glass, and the like have infrared wavelengths of 3.5 μm or less. Because the tube 6 and the tube 7 have a function as a low-pass filter that absorbs infrared rays having a wavelength exceeding 3.5 μm indicated by hatching, the tube 6 and the tube 7 have a wavelength of 3.5 μm or less among the electromagnetic waves radiated from the filament 5. supplied into the furnace through the infrared selectively. Since the infrared energy in this wavelength region matches the vibration frequency of the covalent bond in the molecule of the resin film F, the resin film F can be efficiently heated.

  However, the tube 6 and the tube 7 become radiation absorbers in the wavelength region longer than 3.5 μm, and rise in temperature by absorbing infrared energy. Since a considerable amount of infrared rays having a wavelength longer than 3.5 μm is radiated from the filament 5 at the above-described temperature, there is a concern that the tube temperature will rise as it is. As a result, the tube itself also becomes an infrared radiator, and the infrared radiation having a wavelength longer than 3.5 μm is mainly emitted into the furnace as described above. Such long-wavelength infrared rays can be considered not only to reduce the contribution to the heating effect compared to infrared rays around 3 μm, but also to increase the fluid temperature in the furnace via the increase in wall temperature due to the absorption of the infrared rays on the inner wall of the furnace. The temperature of the resin film F may be excessively increased.

  Therefore, in the present invention, the space between the pipe 6 and the pipe 7 is used as a cooling fluid flow path 8 that suppresses an increase in the surface temperature of the infrared heater, and the cooling fluid is allowed to flow. As a result, the infrared energy in the long wavelength region once absorbed by the tubes 6 and 7 can be converted in the form of convection heat transfer, transmitted to the cooling fluid, and removed outside the system. As a result, the wavelength of the infrared rays finally supplied into the furnace is limited to a short wavelength region, and even in a situation where the filament 5 is continuously energized and heated at a high temperature, It becomes possible to maintain the tube 7 at 200 ° C. or lower, more preferably 150 ° C. or lower.

  The cooling fluid is, for example, air or an inert gas. In this embodiment, air is blown from the fluid supply port 9 and heated air is taken out from the fluid discharge port 10. In addition, since the air taken out from the fluid discharge port 10 may become hot air of 100 ° C. or higher, it is preferable to make effective use such as supplying into the furnace.

The infrared heater 4 having such a structure can selectively supply infrared rays having a wavelength of 3.5 μm or less into the furnace, and the surface temperature of the infrared heater 4 is kept at a low temperature. Can be suppressed. For this reason, overheating of the resin film F is also prevented. Further, if the inner wall of the furnace body 1 is made of a reflective material having a small infrared emissivity, the temperature rise of the furnace wall can be more effectively suppressed. As such a material, for example, a glossy stainless steel plate can be used.

  In addition to the infrared heater 4 described above, it is preferable that a large number of hot air blowing means 11 for blowing hot air toward the resin film F are arranged at the bottom of the furnace, and drying with hot air is used in combination. These hot air blowing means 11 also function as means for supporting the resin film F in the furnace. These hot air blowing means can also be formed on the ceiling surface of the furnace body 1 so that hot air can be blown from the upper and lower surfaces of the resin film F running in the furnace. However, this point is not an essential part of the present invention and can be changed as appropriate.

  Table 1 shows a typical heater setting example for heating the separator polyethylene film. The set temperature of the heater surface temperature is not the filament temperature but the temperature of the outer tube 7. Since the main part of the radiant infrared rays is emitted from the central filament and passes through the tube 7 and exits to the outside, there is no problem in the heating effect even if the temperature of the tube 7 is low. In actual operation, it is also possible to control by the energization amount (w) to the heater and the gas flow rate.

  In the above-described embodiment, as shown in FIG. 2, the furnace body 1 is divided into three zones from the inlet side, and a different number of infrared heaters 4 are arranged. Such a layout is appropriately determined according to the properties of the heating object. For example, the entire furnace can be a single zone, or the pitch of the infrared heaters 4 can be changed within the same zone. In the above-described embodiment, as shown in FIG. 2, the lower surface of the resin film F is supported by hot air from the hot air jetting means 11, but can be appropriately changed such as being supported by a roll.

  As described above, according to the present invention, near-infrared rays that act on covalent bonds between molecules are intensively radiated and the resin film is efficiently dried while suppressing an increase in furnace temperature and workpiece surface temperature. can do.

  A conventional infrared heater and an infrared heater according to the present invention were installed in the same heating device, and the effects of annealing were compared. The film is transported in a heating device with the heating conditions of each heater adjusted so that the keep temperature on the film surface is 120 ° C., the keep time is 30 seconds, the temperature rise time is 10 seconds, and the cooling time is 5 seconds. Annealed. The annealing effect is quantified by assuming that the state where the keep time stays for 3 minutes is 100 and the state before annealing is 1. As a result, the conventional infrared heater showed an annealing effect of 90, and the infrared heater according to the present invention showed an annealing effect of 97. Even with the same temperature history, the effect of the infrared heater according to the present invention was confirmed.

DESCRIPTION OF SYMBOLS 1 Furnace body 2 Discharge roll 3 Winding roll 4 Infrared heater 5 Filament 6 Inner pipe | tube 7 Outer pipe | tube 8 Flow path of cooling fluid 9 Fluid supply port 10 Fluid discharge port 11 Hot-air ejection means

Claims (4)

Absorbs infrared rays having a wavelength of more than 3.5 μm on the outer periphery of the filament while running inside the furnace body with a resin film having a covalent bond in the molecular structure and an electromagnetic wave absorption spectrum with a wavelength of 3.5 μm or less Of the cooling air, which is covered by a double layer by an inner tube that absorbs infrared light having a wavelength exceeding 3.5 μm, and that suppresses the rise in the heater surface temperature between these double tubes. Heating with an infrared heater having a structure in which a flow path is formed, and cooling the infrared heater while irradiating infrared light having a main wavelength of 3.5 μm or less suitable for acting on the covalent bond with a filament temperature of 700 to 1200 ° C. A method for heating a resin film, characterized in that the surface temperature of an infrared heater is suppressed to 200 ° C. or less by air and the resin film is heated while suppressing an increase in furnace temperature.   The method for heating a resin film according to claim 1, wherein the resin film is a separator used as an electrode partition of a battery.   The method for heating a resin film according to claim 2, wherein the resin film is a polyethylene film or a polypropylene film.   The method for heating a resin film according to claim 1, wherein the resin film is caused to travel in a furnace by a roll-to-roll method.

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