JPS5919805B2 - Rapid molding method for plastic film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Generally, a high frequency welder or a so-called impulse heater is used for molding plastic films.

The former method generates heat inside the film to be heated and can rapidly raise the temperature to form the film, but it cannot be applied to Mylar films, etc., which have small dielectric loss. On the other hand, in the latter method, high power is rapidly applied to the heater for a short period of time to form the mold by external heating, but due to the external heating, the mold cannot be formed unless it is tightened with a molding jig until it cools down. It collapses. This has the disadvantage that the molding time becomes longer. An object of the present invention is to provide a method for molding such a plastic film, which is normally difficult to mold, in a short period of several seconds.

The drawing is a sectional view showing an example of an apparatus for carrying out the molding method of the present invention.

A plastic film 1 to be formed is sandwiched between an upper forming jig 2 and a lower forming jig 3. The lower forming jig 3 is thinly made of stainless steel or the like to reduce its heat capacity.A spiral coil 4 for induction heating is attached to the back side of the jig 3 using heat-resistant paint or electrically insulating adhesive 5, and water is poured into the coil. Drain and cool. This lower forming jig system is embedded in a lower table 7 via an electrical insulating layer 6, and this table T and upper forming jig 2 are made of a metal with good thermal conductivity (high heat capacity) such as brass or stainless steel. It is best to make them with water and bury water pipes (not shown) inside them for water cooling. Note that the symbols "+" and "•" written in the cross section of the coil 4 indicate the current direction. After the plastic film to be formed is tightened between the above-mentioned forming jigs 2 and 3, a high-frequency current generating sufficiently larger energy than the cooling energy is passed from the high-frequency heating device 8 to the spiral coil 4, and the lower forming jig is heated. 3 has a small heat capacity, so the temperature rises rapidly and softens the plastic film.

When the high-frequency current is stopped when the film has adapted to the jig, the temperature of jigs 2 and 3 is rapidly lowered by the cooling water, so the film solidifies in a short time of 2 to 3 seconds and molding is completed. , the film can be taken out. In the molding method of the present invention, one cycle of heating and cooling can be shortened as described above, increasing productivity.Since external heating is used, high-quality film such as Mylar film with low dielectric loss can be rapidly molded. This also makes automatic molding possible. Up until now, it has been difficult to create automatic machines with good productivity when molding small speaker cones or bellows from Mylar film or polyester film, but according to the present invention, the heating time is 1. It has become possible to manufacture an automatic machine with a cooling time of 5 seconds and a solidification time of 0.5 seconds.

[Brief explanation of drawings]

The drawing is a sectional view showing an example of an apparatus for carrying out the molding method of the present invention. 1 is a film to be formed, 2 is an upper forming jig, 3 is a lower low heat capacity forming jig, 4 is a high frequency coil, 5 is an adhesive, 6 is an electrical insulation layer, 7 is a lower metal stand, and 8 is a high frequency induction heating device.

Claims (1)

[Claims] 1 Among a set of molding jigs for thermoforming a plastic film, one of the molding jigs is small and thin with a small heat capacity, and a water-cooled high-frequency heating coil or high-frequency heating Attach the wire ring and the cooling water pipe, place it in a stand with a large heat capacity, use the other forming jig with a large heat capacity or cool it with a cooling water pipe, etc., sandwich the film to be formed between the forming jigs, A method for rapidly forming a plastic film, characterized in that the film is formed by rapidly raising the temperature of a forming jig while being cooled by a high-frequency current, and is rapidly cooled and solidified when the high-frequency heating is stopped.