JPS6121815B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for pre-foaming expandable resin particles, and an object of the present invention is to industrially advantageously produce pre-foam beads having a uniform expansion ratio. When heat molding is performed using expandable resin particles as a raw material, a foamed molded product is obtained by pre-foaming by heating and then further heat foaming molding. Pre-foaming methods are classified into two types: batch method and continuous method, and the present invention belongs to the batch method. In the conventional batch pre-foaming method, a certain amount of raw material beads is put into a foaming tank and then steam is blown into the foaming tank to produce pre-foamed beads. In this case, the method of controlling the amount of steam blowing is to blow a predetermined amount of steam for a set time, blow a predetermined steam flow rate until the top surface of the pre-foamed beads corresponds to a set multiple, and blow a predetermined steam flow rate into the pre-foam beads. There are three methods: blowing steam until the upper surface reaches a position corresponding to the set multiple, then reducing the amount of steam blowing by a predetermined amount and stopping the blowing of steam at the position corresponding to the set multiple. In the method described above, there are many variations and it is difficult to obtain pre-expanded beads with a constant expansion ratio due to fluctuations in the steam source pressure and differences in the foaming agent content of the raw beads. In this method, the expansion ratio is detected by the volume of pre-expanded beads, but in order to increase efficiency, the amount of steam blowing must be increased, and when the set position is reached, the steam blowing must be stopped. Also, over-foaming occurs and it is difficult to obtain pre-foamed beads with a predetermined expansion ratio. Method (2) is an improved method of (2), in which the foaming speed is slowed just before the pre-expanded beads reach the set multiple, but in this case, due to the difference in the foaming agent content of the raw beads, if the foaming agent content is low. It takes a long time to reach the set multiple. Furthermore, even if it is noticed that the content of the blowing agent is low, it is necessary to adjust the amount of steam blown, which is disadvantageous in that it requires labor. As a characteristic of expandable polystyrene beads, the blowing agent content decreases over time, and raw beads with a low blowing agent content have a slow foaming speed.In this case, even if deceleration foaming is not performed, there will be variations in the foaming ratio from batch to batch due to overfoaming. Although this is not a problem, it is difficult to measure the blowing agent content when producing pre-expanded beads in practice, and the blowing agent content of the raw beads to be foamed is often unknown. The present invention solves the above-mentioned problems, and even in such cases, it is possible to obtain pre-foamed beads with a uniform expansion ratio. The present invention provides methods and devices. That is, the first invention is a method for pre-foaming foamable resin particles by heating them with steam, in which the foaming speed is detected and the amount of steam blown is controlled so as to achieve a preset foaming speed. The present invention relates to a method for pre-foaming expandable resin particles, which is characterized by pre-foaming and stopping the blowing of steam when a set multiple is reached. According to the present invention, while continuously or intermittently detecting the foaming speed, the amount of steam blown is controlled so as to reach a preset foaming speed. That is, when the foaming speed is higher than the set value, the amount of steam blown is decreased, and when the foaming speed is lower than the set value, the amount of steam blown is increased. Therefore, regardless of the amount of blowing agent in the expandable resin particles, for example, the foaming speed can be made constant by adjusting the amount of steam, and the foaming speed can be set in advance according to the content of the blowing agent. Therefore, there is no need to worry about over-foaming, and the steam blowing time, that is, the pre-foaming time, can be shortened and kept constant. A second invention relates to an apparatus for carrying out the first invention, the gist of which is a foaming tank having an internal stirrer and a device connected to the foaming tank through a steam inlet at the bottom of the foaming tank. In a pre-foaming device for foamable resin particles consisting of a steam blowing device, a level meter for measuring the position (height) of the upper surface of the expandable resin particle layer is installed in the foaming tank, and the level meter measures the level of the foamed resin particle layer after steam blowing. A foamable resin connected to a steam blowing device so as to detect a change in the position of the upper surface of the foamable resin particle layer and continuously or continuously control the amount of steam blowing so that the change in position becomes a set value. The present invention relates to a device for pre-foaming particles. The level meter that detects the foaming speed, that is, the change in the position of the top surface of the foamable resin particle layer in the foaming tank, is an ultrasonic type or radiation type that can continuously or step-by-step detect the position of the top surface of the foamable resin particle layer. There are level meters such as The level meter detects the foaming speed based on the rising speed of the top surface of the foamable resin particle layer at any given time, and when the rising speed is greater than the set value, the amount of steam blown is adjusted so that the rising speed is higher than the preset value. and when the rising speed is smaller than the set value, the amount of steam blown is reduced. The rising speed detected by the level meter is an electrical signal,
After converting into signals such as pneumatic pressure, oil pressure, mechanical quantities, etc., and processing them such as amplification, the signals are converted into electrical signals, pneumatic pressure, hydraulic pressure, mechanical quantities, etc., and then sent to the steam amount control mechanism in the steam blowing device. , for example, to an on-off valve provided in a steam conduit, and the mechanism operates to control the amount of steam blown. One level meter may be installed at the top of the foaming tank so that the above-mentioned rate of rise can be detected, but
Two or more level gauges are installed on the side of the foaming tank, and the rate of rise is controlled by controlling the amount of steam blown until the next upper level gauge detects it, depending on the time it takes for the lower level gauge to detect it. is also possible. In this case, the time from the start of foaming until the level meter at the lowest level detects it, the time until the level meter at the next upper position detects it, and so on, are set in sequence, and the time is determined in sequence from the time when the level meter at the lowest level detects the foaming, and the time after that is determined in order. If the foaming time is slow compared to the foaming time, increase the amount of steam blown up to the next upper level meter, and if it is faster than the foaming time, conversely reduce the amount. In this method, if multiple level meters are provided, the position of the upper surface of the foamable resin particle layer can be continuously detected. However, considering the economical aspect, the limit is 4 or 5. The present invention will be explained using the drawings. FIG. 1 is a schematic diagram of an apparatus according to the invention. Raw material beads (expandable resin particles) are transported to a measuring device 3 by a pneumatic transport device 1 . The measuring device is of a variable volume type, and automatic gate valves 2 and 4 are installed at the front and rear of the measuring device, so that a set volume of raw material beads can be measured. A predetermined amount of raw material beads is introduced into a foaming tank 6 through an automatic gate valve 5. The foaming tank has a stirring motor 7 at the top, stirring blades 8 inside, and a fixed rod 9 placed between the stirring blades to enable stirring.A steam chamber 10 is connected to the bottom plate of the foaming tank, and a porous bottom plate 11 is installed. Steam is ejected into the foaming tank 6 through the foaming tank 6. After charging the raw material beads, the steam inlet valve 12 is opened to supply steam into the steam chamber. Steam enters the steam chamber and is blown into the foaming tank, causing the raw material beads to foam and increase in volume. The top surface of the foamable resin particle (pre-foamed beads) layer is detected by a level meter 13 installed at the top of the foaming tank 6, and the distance between the top surface of the pre-foamed bead layer and the level meter is set to 0% of the bottom of the tank, which corresponds to the set foaming ratio. The position is converted to 100% and inputted to the program controller 14. The program controller constantly compares whether the foaming speed is at a preset value and if it is fast, outputs a signal to throttle the steam inlet valve 12 and vice versa. In this case, feedback control is performed during foaming by issuing an output signal to close the steam inlet valve 12. When the position of the upper surface of the pre-foamed bead layer reaches a position preset by the program controller 14, the steam inlet valve 12 is closed to stop the blowing of steam to cool the foamed beads, and then the automatic discharge gate valve 1 is activated.
Discharge the pre-foamed beads from Step 5. Note that heated air may be blown in together with steam, and in this case, the air inlet valve 16 may be adjusted. Examples 1 to 4 In the apparatus shown in Fig. 1 (internal volume of foaming tank 810),
A certain amount of expandable polystyrene beads was charged, the expansion rate was set, and the test was conducted. In addition, when the set multiple was reached, the steam injection was stopped. The results are shown in Table 1. As the expandable polystyrene beads, HiBeads MB (trade name, Hitachi Chemical Co., Ltd.) from the same lot was used. FIG. 2 shows a graph of the relationship between the change in the foaming ratio and the steam blowing time in Example 1.

[Table] As is clear from Table 1, when the foaming ratio is kept constant, the amount of steam is controlled by the foaming speed, so the time required for pre-foaming is not influenced by the foaming agent content and is therefore shortened. You can set the time. Comparative Examples 1 to 4 Similar to Example 1, however, the steam injection amount was kept constant and the steam injection amount was reduced just before the set foaming ratio (later stage of foaming: after the foaming ratio 90%) to avoid over-foaming. Summer. The results are shown in Table 2.
In FIG. 3, the relationship between the change in expansion ratio and the steam blowing time is shown by a curve 16 for Comparative Example 1 and a curve 17 for Comparative Example 2.

[Table] As is clear from the results in Table 2, when the amount of steam blowing is kept constant, the steam blowing time is affected by the content of the blowing agent, resulting in poor productivity. As is clear from the above, according to the present invention, since the foaming speed is detected and the amount of steam blown is controlled, the pre-foaming time can be shortened regardless of the amount of blowing agent in the expandable resin particles. By setting the foaming speed appropriately, over-foaming can be prevented and variations in the foaming ratio can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a pre-foaming device used in carrying out the present invention. FIG. 2 is a graph showing the relationship between the change in the foaming ratio and the steam blowing time in Examples 1 and 2, and FIG. 3 is a graph showing the relationship between the change in the foaming ratio and the steam blowing time in Comparative Examples 1 and 2. Explanation of symbols, 1... Air transport device, 2... Meter inlet gate valve, 3... Meter, 4... Meter outlet gate valve, 5... Foaming tank inlet gate valve, 6...
Foaming tank, 7... Stirring motor, 8... Rotating blade, 9...
... Fixed rod, 10 ... Steam chamber, 11 ... Porous bottom plate, 12 ... Steam inlet valve, 13 ... Level meter, 14 ... Program controller, 15 ... Automatic discharge gate valve, 16 ... Air inlet valve.

Claims (1)

[Claims] 1. In a method for pre-foaming foamable resin particles by heating them with steam, the foaming speed is detected,
A method for pre-foaming expandable resin particles, characterized in that pre-foaming is performed while controlling the amount of steam blown so as to achieve a preset foaming speed, and the blowing of steam is stopped when a set multiple is reached. 2. In a pre-foaming device for foamable resin particles comprising a foaming tank having an internal stirrer and a steam blowing device connected to the foaming tank through a steam blowing port at the bottom of the foaming tank, the foamable resin is placed in the foaming tank. A level meter is installed to measure the position (height) of the top surface of the particle layer, and the level meter detects a change in the position of the top surface of the foamable resin particle layer after steam injection, and the change in position becomes the set value. A pre-foaming device for foamable resin particles which is connected to a steam blowing device so as to continuously or continuously control the amount of steam blowing. 3. The pre-foaming device for expandable resin particles according to claim 2, wherein a level meter is provided at the upper part of the foaming tank, and the level meter is connected to an on-off valve provided in a steam conduit of a steam blowing device. 4 Claims 2 and 3 in which the level meter is an ultrasonic level meter or a radiation level meter
A pre-foaming device for expandable resin particles as described in 1.