JPS6364294B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a foam molded article. Conventionally, foam molded products are produced by filling a mold with pre-foamed particles of expandable thermoplastic resin, heating and expanding them, and then rapidly cooling them to a sufficient temperature that the molded product will not be deformed due to the internal expansion pressure. It is manufactured by removing the product from the mold after it has been left to cool. This method has the disadvantage that it consumes a lot of energy because the mold is repeatedly heated and cooled from low temperature to high temperature to low temperature. In addition, because of the rapid cooling, a thin skin layer is formed on the surface of the molded product, which impedes the dissipation of internal volatile matter and requires a longer cooling time, resulting in the drawback that the cycle time for one step is extremely long. In addition, special public service in Showa 54
-15301, the mold is filled with pre-expanded particles, heated, the internal pressure of the mold increases the volume of the mold cavity under high pressure, and after expansion, compression and
We have proposed a cooling method, but in this case, the internal pressure of the mold is high, so rapid release will cause the internal pressure to radiate explosively, which is extremely dangerous, and the molded product will have a matte surface. , and a flexible molded product with no firmness as a structure of the molded product. The method of the present invention is essentially different from the above-mentioned method, in that after heating and expansion welding, the cavity surface temperature is
After slow cooling using high-temperature water at 55 to 80℃ to prevent the temperature from dropping below 60℃, the mold is opened, the molded product expands with the remaining internal expansion pressure, and the mold is clamped again to remove residual volatilization. forcibly discharged from the molded body,
At the same time, the beads on the surface of the molded product in contact with the mold are hardened compared to the internal beads, so this compression pressure and internal pressure further narrow the gap between the surface beads, creating a strong skin with dense parallel orientation. can be formed. Since the balance between skin strength and internal pressure can be easily achieved, one cycle time can be shortened, the process is safe, and the surface of the molded product is glossy.
Moreover, a molded product with firmness can be obtained. As described above, the present invention can solve the drawbacks of the conventional method using a simple method, and since the temperature drop in the mold is much smaller than in the conventional method, the heating energy for the mold can be saved. can. Furthermore, since the one cycle time required for molding is also shortened, it can be said that this molding method can produce foam molded articles in the most advantageous and economical way compared to conventional methods. Furthermore, the molded product produced according to the present invention has a thick and tough skin, and is therefore physically superior. The method of the present invention is as follows: (1) Cooling water is circulated between the mold and the water collection open bath using, for example, high-pressure air, and is uniformly sprayed onto the inner mold wall by a large number of wide-angle sprayers installed in the mold steam chamber to increase the cavity surface temperature. 60-95
℃, preferably 70 to 85℃. Preferably, spray cooling is performed for 5 to 20 seconds. Furthermore, since the circulating high-temperature water is added only in the amount of water that has been reduced due to evaporation or scattering, a very small amount only needs to be replenished. (2) After the spraying is completed, drain the mold with compressed air so that no cooling water remains in the mold, and after completely draining the cooling water, open the mold to a gap of, for example, 5 to 20 mm, so that the internal molded product is not in the mold. The mold is kept open for a sufficient amount of time so that it does not protrude from the gap, and then the mold is completely clamped. After the mold clamping is completed, the molded product is left for 0 to 15 seconds, preferably 5 to 10 seconds, so that no deformation occurs after the mold is opened, and then the mold is opened to take out the molded product. This is a foam molding method. A more detailed explanation will be given below. In the conventional molding process, expandable thermoplastic resin particles are pre-foamed, left for an appropriate curing time (usually 24 to 48 hours), then filled into a mold, and the raw material is heated and expanded using a heating medium such as steam. After the particles are fused together, cooling water at, for example, 20°C is released into the mold to rapidly cool the mold and stop the expansion of the foaming gas remaining inside the mold, thereby preventing expansion and deformation of the mold after the mold is opened. can be stopped. If there is a large amount of foaming gas remaining inside the molded product, it is necessary to lengthen the time for discharging the cooling water into the mold. Also,
When the residual foaming gas content inside the pre-foamed beads is small, the heating energy required for heating expansion during molding and integral fusion between particles increases. On the other hand, as the molded product inside the mold is rapidly cooled, the surface of the molded product in contact with the mold hardens and forms a skin layer, which prevents the internal residual foaming gas from dispersing. Since the cooling effect is poor, low-temperature cooling for a considerable period of time is required. If the strength of the hardened skin of the molded product is less than the expansion pressure of the internal residual foaming gas, the mold cavity surface supports the expansion pressure, so if the mold is opened at that time, the molded product will immediately expand and deform. In addition, when the cooling effect progresses and the strength of the skin increases and balances with the expansion pressure of the residual foaming gas or becomes lower than the strength, the mold can be opened and expansion deformation of the molded product can be suppressed. In the present invention, the mold is cooled with high-temperature water of 55 to 80 °C so that the mold surface temperature where the mold and the molded product come into contact is 60 to 95 °C, preferably 70 to 85 °C, and then The cooling water is drained using compressed air, and the mold is opened. The surface of the molded product expands in a flexible state due to the expansion pressure of the foaming gas remaining inside the molded product. After slightly opening the mold (preferably 5 to 20
mm), when the mold is clamped again, the expanded molded product will
While the foaming gas remaining inside the mold is forcibly dissipated to the outside, the expandable beads in contact with the mold can be oriented in parallel in a regular manner. Further, due to the forced discharge of the internal residual foaming gas, a difference in distribution of the residual foaming gas occurs between the skin and the interior, and the interior re-expands due to adiabatic compression, thereby forming a thick layered skin on the surface of the molded product. This strong skin balances the expansion pressure of the residual foaming gas, or the strength of the skin is greater than the internal expansion pressure, so even if the mold is opened while the cavity surface temperature remains high, it will not expand and deform. It will be in a state where it will not occur. However, since the thickness of each part of the molded product is different, it is necessary to compensate for the local time difference. It is necessary to do this. The molded product produced according to the present invention has better cushioning properties and surface hardness than molded products obtained by conventionally known methods, and has excellent strength and fusion bonding. In addition, the molding cycle can be shortened by 20 to 30%, and since the temperature drop in the mold is small, the heating energy required for heating the mold during continuous automatic operation, such as steam, can be reduced by 20 to 30%. As for the mold, there are no particular problems with conventional molds, but if the contact pilot part of the cavity mold and core mold is lengthened so that there is no problem in filling the pre-foamed beads, Furthermore, the effects of the present invention can be enhanced. The molded product of the present invention can be applied to conventionally molded fish boxes, packaging cushioning materials in general, and other molded articles in general, and can exhibit functions superior to conventional products. Cost reduction effects such as simplification can be expected. The synthetic resin used in the present invention can be applied to all resins used in foamed bead molding, such as foamed polystyrene resin and foamed polyolefin resin used in foamed bead molding. The effects of the present invention are listed below. (1) There is no need to preheat the mold, and the temperature range for heating and cooling is small, so heating energy such as steam is saved. (2) The molding cycle is greatly shortened because residual volatile matter in the molded product is forcibly dissipated. (3) The molded product has better cushioning properties. (4) The skin of the molded product has a regularly oriented structure of foamed beads, improving surface hardness and other physical properties. (5) Improved molded products can be obtained using conventional molds. Next, the present invention will be explained with reference to Examples. Example Using an automatic foam molding machine SC-10B (manufactured by Toyo Kikai Kinzoku Co., Ltd.), two fish boxes (510 mm x 294 mm x 85 mm) were prepared.
Fill the mold with 55 times pre-expanded polystyrene foam beads with mold cracking of 3 mm, and after filling, heating, cooling, and draining according to the conditions in Table 1, open the mold by 10 mm, and then close the mold. The mold was opened, the mold was released, and the molded product was removed. Comparative Example Using the same foam molding machine and mold as in the example (cracking 3 mm), the mold was filled with 55x pre-expanded polystyrene beads and molded under the conditions shown in Table 1.

[Table] As shown in Figure 1, the skin of the molded product according to the example had excellent strength and had particles arranged side by side regularly. There was no orientation at all.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of an example of a molded product (fish box) according to the present invention. 1... Skin part of the molded product, 2... Inside of the molded product.

Claims (1)

[Claims] 1. A method for obtaining a foamed molded product by filling the cavity of a mold with pre-expanded particles of a thermoplastic resin and heating and expanding the particles using a heating medium such as steam, in which the pre-expanded particles are heated, expanded and fused. After that, the surface temperature of the cavity is slowly cooled using high temperature water of 55 to 80℃ to prevent it from dropping below 60℃.
A method for producing a foamed molded product, which comprises draining water, then opening the mold, maintaining that state, clamping the mold, and then taking out the molded product.