JPH0542392B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a high-frequency continuous drying device for ceramic sheets that continuously dries raw ceramic sheets using high-frequency waves. (Prior art) Ceramic substrates used in various electronic components are generally manufactured by extruding a raw ceramic sheet from a mold of a molding machine, drying it and punching it into a predetermined shape, and then firing it in a firing furnace. ing. Conventionally, drying equipment for drying raw ceramic sheets that are continuously extruded from a mold of a molding machine has generally been one that irradiates hot air, infrared rays, or far infrared rays to dry ceramic raw sheets that are continuously conveyed by a belt, etc. Are known. By the way, in a drying device that uses hot air or infrared rays, a difference in moisture content occurs between the inside and the surface of the raw ceramic sheet depending on the thickness of the raw ceramic sheet and other conditions, causing curls and cracks in the dried sheet.
In order to obtain a uniform dried sheet without warping or cracking, it is necessary to slow down the drying speed of the raw ceramic sheet, but slowing down the drying speed increases the drying time, and the drying time is proportional to the drying time. There was a problem that the drying equipment became long and the production efficiency of ceramic substrates decreased. In addition, with drying equipment that uses far infrared rays, when raw ceramic sheets are continuously dried at high speed, the initial drying is slow, and the raw ceramic sheets are likely to be deformed due to tensile force, causing the sheet width and thickness of the dried sheets to deteriorate. There was a problem that variations occurred. By the way, in recent years, drying equipment that uses high frequency waves or microwaves that can uniformly heat the material to be dried in a relatively short period of time has been put into practical use for drying wood, etc., and this type of drying equipment is also used for drying raw ceramic sheets. The use of drying equipment such as However, this type of drying apparatus is for batch processing and cannot be applied to continuous drying of raw ceramic sheets that are continuously extruded from a mold of a molding machine. (Object of the Invention) The present invention has been made in view of the above-mentioned problems in drying raw ceramic sheets. An object of the present invention is to provide a high-frequency continuous drying apparatus for ceramic sheets, which is capable of obtaining dry sheets having the following properties. (Structure of the Invention) Therefore, in the present invention, bar-shaped high-frequency electrodes are arranged at approximately constant intervals in the running direction of the belt so as to be in contact with the lower surface of a continuously running belt on which a raw ceramic sheet is placed, and these high-frequency electrodes It is characterized by continuous drying by passing the green ceramic sheet through the generated high-frequency electric field. That is, the present invention supplies high frequency waves from a high frequency oscillator to each high frequency electrode arranged at approximately constant intervals in the conveyance direction on the lower surface of a belt conveying raw ceramic sheets,
The raw ceramic sheet is dried using dielectric heating using high frequency waves, and according to the present invention, the ceramic sheet conveyed on the belt can be uniformly and continuously dried using high frequency waves. (Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows the overall structure of an embodiment of a high-frequency continuous drying apparatus for ceramic sheets according to the present invention. The high-frequency continuous drying apparatus is of a three-stage type in which a tunnel-shaped upper drying chamber 1, a middle drying chamber 2, and a lower drying chamber 3 are arranged on a base 4 in order from the top. Inside the upper drying chamber 1, an upper belt 6 is provided from the outside of the inlet 1a to the outside of the outlet 1b, on which a raw ceramic sheet 5 is placed and for conveying the raw ceramic sheet 5. The upper belt 6 includes a roller 8a rotatably supported by a support 7a outside the entrance 1a of the upper drying chamber 1, and a roller 8a rotatably supported by a support 7b outside the outlet 1b of the upper drying chamber 1. It is stretched between the roller 8b and the roller 8b. On the upper belt 6, a raw ceramic sheet 5 extruded from a mold of a molding machine (not shown) is attached to a roller 8c rotatably supported by a support 7c outside the entrance 1a of the upper drying chamber 1, and the roller 8a. It is conveyed by a belt 6a stretched between. Similarly, inside the middle drying chamber 2, from the outside of the inlet 2a located below the outlet 1b of the upper drying chamber 1 to the outside of the outlet 2b located below the inlet 1a of the upper drying chamber 1, the upper drying chamber A middle belt 9 is provided for conveying the raw ceramic sheet 5 fed in from 1. The middle belt 9 includes a roller 11a rotatably supported by a support 10a outside the entrance 2a of the middle drying chamber 2, and a roller 11a rotatably supported by a support 10b outside the outlet 2b of the middle drying chamber 2. It is stretched between the roller 11b and the roller 11b. In addition, inside the lower drying chamber 3, there is a middle drying chamber 2.
The lower belt 1 conveys the raw ceramic sheet 5 fed from the middle drying chamber 2 from the outside of the inlet 3a located at the lower part of the outlet 2b to the outlet 3b.
2 is provided. This lower belt 12 is rotatably supported by a roller 14a rotatably supported by a support 13a outside the entrance 3a of the lower drying chamber 3, and by a support 13b outside the outlet 3b of the lower drying chamber 3. It is stretched between the roller 14b and the roller 14b. At the lower part of the upper belt 6, the middle belt 9 and the lower belt 12, as shown in the front view and the top view in FIG. _{2a and} FIG.
and upper belt 6 and lower belt 12 shown by A ₂
Rod-shaped positive (plus) high-frequency electrodes 15 and rod-shaped negative (minus) high-frequency electrodes 16 are alternately arranged at substantially constant intervals d in the running direction of the middle belt 9. The high frequency electrodes 15 and 16 are drawn out from one side and the other side of the upper belt 6, the middle belt 9, and the lower belt 12, respectively, and are connected to the positive (plus) side output terminal and the negative (minus) side of a high frequency oscillator (not shown). are connected to the respective output terminals.
The high frequency electrodes 15 and 16 are both in contact with the lower surfaces of the upper belt 6, the middle belt 9, and the lower belt 12. The upper drying chamber 1, the middle drying chamber 2, and the lower drying chamber 3 are all shielded to prevent radio wave leakage. In the high-frequency continuous drying apparatus having the above configuration, the raw ceramic sheet 5 is continuously extruded from a mold of a molding machine (not shown), is supplied onto the upper belt 6 by the belt 6a, and is fed into the upper drying chamber 1. sent. In the upper drying chamber 1, the raw ceramic sheet 5 passes through a high frequency electric field generated by high frequency electrodes 15 and 16 placed in contact with the lower surface of the upper belt 6, and is dried by dielectric heating. The raw ceramic sheet 5 enters the upper drying chamber 1 through the inlet 1a and passes through the high-frequency electric field until it exits through the outlet 1b, so that the raw ceramic sheet 5 is continuously dried during this period. The raw ceramic sheet 5 coming out of the outlet 1b of the drying chamber 1 is fed onto the middle belt 9 and transferred to the middle drying chamber 2, where it is continuously dried in the same way as above. After that, it is supplied onto the lower belt 12 from the outlet 2b of the middle drying chamber 2. The raw ceramic sheet 5 is dried by passing through a high frequency electric field in the lower drying chamber 3 in the same manner as described above, and is sent out from the outlet 3b of the lower drying chamber 3 as a dry sheet 5a. The high-frequency continuous drying device shown in Fig. 1 uses high-frequency dielectric heating for drying, so the initial drying of the raw ceramic sheet 5 is uniform and fast, and even when the raw ceramic sheet 5 is moved at high speed, it does not deform. Never. Moreover, when the raw ceramic sheet 5 is supplied from the upper drying chamber 1 to the middle drying chamber 2,
When the raw ceramic sheet 5 is supplied from the middle drying chamber 2 to the lower drying chamber 3, the upper and lower surfaces are reversed, so there is no difference in dryness due to the distance between the raw ceramic sheet 5 and the high-frequency electrodes 15 and 16, resulting in more uniform drying. can be done. Next, specific examples of the present invention will be described. In the high-frequency continuous drying device shown in FIG. 1, the total length of the portion where high-frequency electrodes 15 and 16 are arranged at the bottom of the upper belt 6, middle belt 9, and lower belt 12 is 5 meters, and the oscillation frequency is 20 MHz to 50 M.
Using a Hz vacuum tube type high frequency oscillator, the high frequency electrodes 15 and 16 are spaced at 3 cm intervals as shown in Figure 2a.
and alternately arranged as shown in FIG. 2b. Using this apparatus, the moisture content of the dried ceramic sheet 5a was measured for Examples 1 to 4 in which the sheet speed and sheet thickness of the raw ceramic sheet 5 were changed, and the results shown in Table 1 below were obtained.

[Table] As can be seen from this Table 1, in all of Examples 1 to 4, the moisture content of the drying sheet 5a has a substantially constant value of 4.5 to 5.5, and the moisture content of the drying sheet 5a is approximately constant. The quality is also good. In addition, when the sheet moisture content and the total evaporated water content during drying of the raw ceramic sheet 5 with a sheet thickness of 0.35 mm were measured while changing the sheet speed from 6 m/min to 16 m/min, the curve h ₁ in Fig. 3 was measured.
The results shown in and _h2 were obtained. As can be seen from the curve _h2 in FIG. 3, as the sheeting speed increases, the high frequency energy applied to the entire green ceramic sheet 5 to be dried increases, and the amount of water to be treated also increases. As a result, the final moisture content of the dry sheet 5a remains approximately constant, as can be seen from the curve _h1 . For comparison with the above embodiment, far-infrared heaters (not shown) are placed above the upper belt 6, middle belt 9, and lower belt 12 in place of high-frequency heating in the high-frequency continuous drying apparatus shown in FIG. When the moisture content and sheet properties of the dry sheet 5a were examined, the results shown in Table 2 below were obtained.

[Table] When drying the raw ceramic sheet 5 using far infrared rays, unlike drying using dielectric heating, the temperature locally increases in the area irradiated with far infrared rays, and the binder contained in that area increases. It gets burnt. Therefore, it is not possible to increase the heater atmosphere temperature of the far-infrared heater in accordance with the sheet speed. Therefore, as can be seen from Table 2 above, the moisture content of the dry sheet 5a varies greatly from 5.5 to 10.2 depending on the sheet speed and sheet thickness.
Warping and cracks also occur. The present invention is not limited to the three-stage type explained in FIG. 1, but can also be applied to a one-stage type or an arbitrary number of stages. Additionally, it should be noted that the meaning of the high frequency in the high frequency continuous drying apparatus in the present invention includes the microwave region. (Effects of the Invention) As is clear from the detailed description above, in the present invention, the raw ceramic sheet conveyed by the belt is continuously dried by dielectric heating using high frequency, so that the raw ceramic sheet is uniformly dried. When heated, it is possible to obtain a good dry sheet with stable dryness, good dimensional accuracy, strong sheet strength, and no sheet breakage or bending. Further, according to the present invention, it is possible to continuously dry ceramic green sheets by high-frequency heating, and the productivity of ceramic substrates used in various electronic components can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the entire high-frequency continuous drying device for ceramic sheets according to the present invention, and FIGS. A front view and a plan view showing the arrangement relationship, and FIG. 3 are actual measurement diagrams of sheet moisture content and total evaporated moisture content with respect to sheet speed in a specific example of the present invention. 5... Ceramic raw sheet, 5a... Dry sheet, 6... Upper belt, 9... Middle belt, 12
...Lower belt, 15, 16...High frequency electrode.

Claims (1)

[Claims] 1. A high-frequency continuous drying device for ceramic sheets that continuously dries raw ceramic sheets placed on a continuously running belt by passing them through a high-frequency electric field, in which a rod-shaped high-frequency electrode contacts the lower surface of the belt and 1. A high-frequency continuous drying device for ceramic sheets, characterized in that the devices are arranged at approximately constant intervals in the running direction of the ceramic sheets.