JPS6235375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for thermoforming synthetic resin foam sheets.

Conventionally, when manufacturing food containers, cups, etc. by thermoforming a synthetic resin foam sheet, the foam sheet is taken out from a winding roll, heated and softened in a heating furnace, and then shaped into a predetermined shape using a mold. The product was obtained by thermoforming and punching out the molded body. However, foamed sheets undergo secondary foaming when heated, increasing the thickness of the sheet, but it is difficult to control the thickness of the sheet with radiant heating or convection heating in a heating furnace. There were problems such as scratches, etc. caused by the molding, and the molding itself became impossible. In addition, this heating method uses radiation or convection for heating, which has the disadvantage of poor thermal efficiency and large energy loss.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for thermoforming a synthetic resin foam sheet, which eliminates the drawbacks of the prior art and makes it possible to obtain a synthetic resin foam molded product of good quality.

That is, in the present invention, when a synthetic resin foam sheet is heated, it is brought into direct contact with a pair of heating plates having portions with different temperatures to perform non-uniform heating with partially different heating temperatures, and after being heated and softened, it is molded. In the method of thermoforming a synthetic resin sheet, the non-uniform heating is performed by heating the portion of the synthetic resin sheet that will not be finally trimmed to form a molded product to a high temperature and keeping the other portions to a low temperature. The gist of this paper is the characteristic thermoforming method for synthetic resin foam sheets.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a schematic diagram of each step of a thermoforming method according to an embodiment of the present invention. Here, 1 is a synthetic resin foam sheet wound around a winding roll 2;
3 is a pair of heating plates for heating and softening the synthetic resin foam sheet 1.

This heating plate 3 has parts with different temperatures when heated, and using such a heating plate 3, parts with different temperatures can be provided on the sheet 1, and the heating temperature of the sheet 1 can be changed. This method performs so-called non-uniform heating in which the heating conditions are partially different.

As such a heating plate having parts with different temperatures when heated, for example, as shown in FIGS. 2 and 3, recesses are formed at appropriate positions on the opposing surfaces of the upper and lower heating plates 3. 5 can be used.
Using such a heating plate 3, a high temperature area and a low temperature area can be provided on the sheet 1, thereby making it possible to make the thickness of the molded body uniform. In other words, the recesses 5 in FIGS. 2 and 3 have low thermal conductivity, so the heating temperature is lower than that of the protruding parts of the heating plate 3 other than the recesses 5, and the sheet portion corresponding to the recess 5 is lower than other parts. In comparison, the fluidity of the resin is also reduced. That is, when molding the deep drawn container molded body 13' shown in FIG. 9, in the conventional molding method, the upper part A of the side wall near the opening and the part C near the bottom
was forcibly stretched, and the thickness of the upper part A of the side wall and the vicinity of the bottom part C became thinner than the thickness of the bottom part B, resulting in a problem that the thickness of the molded container became uneven. In addition, there was a drawback that the A part and the C part were easily damaged by friction with the mold. but,
In the present invention, the sheet 1 is heated using the heating plate 3 as described above.
In order to make the E part that is not finally trimmed and make up the container molded body into a high temperature part and the other parts as a low temperature part, the resin is heated to other parts than the E part where the resin has high fluidity during molding. The resin is supplied, smooth molding is performed, and the thicknesses of A, B, C, and D are uniform, and a good molded product can be obtained.

Further, the heating plates 3 are arranged vertically at intervals, and are configured such that the vertical interval can be adjusted as desired. Furthermore, when secondary foaming occurs in the sheet 1 during heating, the spacing between the heating plates 3 may be varied in accordance with the foaming thickness within a range that conforms to the molding allowable dimensions. clearance control). Each heating plate 3 has a built-in heater, and its opposing surfaces are coated with Teflon or the like to prevent sheet adhesion. 4 is a mold 4 consisting of a male mold 4a and a female mold 4b.
It is.

Examples of the synthetic resin foam sheet 1 that can be used in the present invention include sheets of polystyrene foam, polyethylene foam, polypropylene foam, etc., and the thickness thereof is usually 0.5 to 7.0 mm.

When thermoforming the synthetic resin foam sheet 1 with the above configuration, the synthetic resin foam sheet 1 wound around the winding roll 2 is taken out and held between the heating plates 3 in direct contact with each other, Normally 100~170℃
It softens when heated to a certain extent. When heated, the synthetic resin foam sheet 1 softens and undergoes secondary foaming to maintain a thickness within a moldable size range. Next, the molded body 13 is obtained by molding using a mold 4 consisting of a male mold 4a and a female mold 4b. The molded product 13 thus obtained has a secondary foaming thickness of the foamed sheet 1' within the moldable size range, and is free from damage such as scratches due to friction with the mold 4 during molding. It is of good quality as there are no cracks. In addition, by controlling the clearance between the heating plates and utilizing the pressing effect of the heating plates, it is possible to set a more precise moldable size range, and the molded body 13 obtained thereby has even better quality. Become. Next, the molded body 13 is punched out to obtain a final product.

4 to 8 show a heating plate 3 used in another embodiment of the present invention.

FIGS. 4 and 5 show a heating plate 3 having recesses 5 at appropriate opposing positions, and a heat insulating material 6 filled in the recesses 5. FIG. In this heating plate 3, a portion 3a where the heat insulating material 6 is not loaded
becomes high temperature, and the heat insulating material 6 becomes low temperature, so that the foam sheet 1 can be provided with a high temperature part and a low temperature part, similar to the heating plate 3 in FIG.
A molded body 13' having a uniform thickness can be obtained as in the case where the heating plate 3 shown in the figure is used.

6 and 7, the opposing surfaces of the heating plate 3 main body made of a heat insulating material are partially protruded 3b, and a heater 8 is provided in the non-protruding part (recess 7).
It is shown loaded with. In this heating plate 3, the loaded part of the heater 8 becomes a high temperature part, and the non-heater loaded part 3b becomes a low temperature part, so that the foamed sheet 1 can be provided with a high temperature part and a low temperature part, similar to the heating plate 3 in FIG. During molding, a molded body 13' having a uniform thickness can be obtained as in the case where the heating plate 3 shown in FIG. 2 is used.

The heating plate 3 shown in Figure 8 is a heater 8.
A heating aid 11 made of a thermal conductor having a recess 10 on its surface is attached to a heating main body 9 having a built-in heating element, and a heat insulator 12 is loaded into the recess 10. In this heating plate 3, the part loaded with the heat insulating material 12 becomes the low temperature part, and the part 3a not loaded with the heat insulating material becomes the high temperature part, and when the heated sheet 1 is molded using the heating plate, the same thickness can be obtained as described above. A molded body 13' having the following properties is obtained. When the heating auxiliary tool 11 is attached in this manner, there is no need to perform complicated processing on the heating plate main body, and the heating plate is highly versatile. In this embodiment, a heat insulating material 12 is provided in the recess 10 of the heating aid 11.
Although the explanation has been given on the case where the heat insulating material 12 is loaded, it can be used without being loaded with the heat insulating material 12.

The molded body 2 obtained by the method of the present invention can be used, for example, as a food container.

As explained above, according to the present invention, it is possible to perform molding by suppressing the increase in thickness of a synthetic resin foam sheet due to secondary foaming using a heating plate to maintain a moldable thickness, and in particular, by using a compressed air During molding, the molded product will not be damaged due to friction with the mold due to the excessively thick secondary foaming of the sheet, and molding can be performed reliably. In addition, since the heating plate directly contacts and heats the foam sheet, even if there are variations in the thickness of the material sheet, it will be pressed by the heating plate, making it possible to obtain a molded product with a uniform thickness and good quality. Since it is heated, it has good thermal efficiency. Furthermore, since the heating plate is configured so that the temperature differs between parts, the part that is ultimately trimmed and does not form the container is used as the high temperature part, and resin is supplied from this part to the part that makes up the container, and the molding is completed. This method has various advantages, such as being able to produce a molded product of good quality without any variation in thickness by performing the molding process smoothly.

Next, the present invention will be explained in more detail by referring to specific examples.

Specific Example 1 A polystyrene foam sheet with a thickness of 30 mm was sandwiched between a pair of heating plates that were made by providing a recess of 80 mm diameter on the surface of the foam sheet side and filling the recess with a heat insulating material, which could be moved up to a vertical distance of 5 mm. 120 in the wood part
℃, 12 at a temperature of 155℃ in areas without insulation
heated for seconds. As the sheet underwent secondary foaming due to heating, the heating plates were moved so that the interval between the heating plates became 5 mm. After heating, the foamed sheet was molded using a mold to obtain a cup-shaped container. The resulting cup-shaped container was uniform with no variation in thickness.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a thermoforming process for a synthetic resin foam sheet according to an embodiment of the present invention, and FIGS. 2 and 3 are longitudinal cross-sectional views and plan views showing a heating plate used in an embodiment of the present invention. 4 to 8 are a vertical sectional view and a plan view showing a heating plate used in another embodiment of the present invention, and FIG. 9 is a vertical sectional view showing a state in which a container is molded. 1...Synthetic resin foam sheet, 3...Heating plate, 4
...Mold for molding.

Claims (1)

[Claims] 1. A synthetic resin sheet that is softened by non-uniform heating by bringing the synthetic resin foam sheet into direct contact with a pair of heating plates that have portions with different temperatures when heated, softening the sheet, and then molding the sheet. In the thermoforming method, the non-uniform heating is carried out by heating a portion of the synthetic resin sheet that will not be finally trimmed to form a molded article to a high temperature and keeping the other portions to a low temperature. Thermoforming method for resin foam sheets.