JPS62183311A - Prefoaming method of foamable thermoplastic resin particle - Google Patents

Abstract

PURPOSE:To enable excellent batch type prefoaming, by changing the number of revolutions of an agitating blade on the inside of a foaming tank in a batch foaming process. CONSTITUTION:Agitation by agitating blade 3 is performed by increasing the number of revolutions comparatively high at the beginning, a level meter 10 is kept controlled so as not to actuate even if a surface wave of a large-sized particle abuts against the blade 3 and at a stage after the particle has arrived at a certain foam magnification the agitation by the agitating blade 3 is shifted to the comparatively low number of revolutions. Blowing in of steam is suspended and foaming of more than that is suspended by actuating the level meter 10 when the surface wave of a particle layer has arrived at a preset height obtained when the same has arrived at the certain foam magnification which has been established beforehand by making the surface wave of the particle layer small.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a method for pre-foaming expandable thermoplastic resin particles, and a method for pre-foaming the resin particles to a predetermined expansion ratio before using them for foam molding, etc. It's about.

<Prior Art> In conventional pre-foaming of expandable thermoplastic resin particles, a batch-type pre-foaming method is often employed as disclosed in Japanese Patent Publication No. 56-5176.

This pre-foaming method involves supplying and storing a certain amount of expandable thermoplastic resin particles in a foaming tank, and blowing a heating medium from the bottom of the foaming tank while stirring the particles, and when the particles reach a predetermined set magnification. , the method was to stop blowing in the heating medium and take out the particles.

In addition, in order to reduce the variation in foaming of particles, a large amount of heating medium is supplied at the start of foaming, the amount of heating medium is reduced just before foaming is completed, and when a predetermined setting position is reached, the heating medium is stopped. 'ltta particles were extracted.

Therefore, in implementing the conventional method, a level meter (tuning fork type, phototube type, etc.) was installed above the foaming tank to determine the setting position.

However, in the case of the conventional method, (1) Since the stirring by the stirring blade is constant stirring, if the heating medium is supplied from the bottom of the foaming tank, excessive foaming will occur in the lower part of the foaming tank, resulting in uneven foaming between the upper and lower parts of the foaming tank. There were drawbacks that occurred.

(2) In an attempt to eliminate vertical variations in the foaming tank, the rotation speed of the stirring blade is increased to improve the stirring effect.
As the high stirring effect continues, when the top surface of the particle reaches the level meter at the set position, the undulations on the top surface of the particle become larger, and one is detected at the crest of the wave and the other is detected at the trough of the wave. This results in a difference in the foaming ratio of the entire foaming tank, and even though the variation in foaming of particles within the same foaming tank is relatively small, there is a There was a drawback that the foaming variation increased.

Purpose> Therefore, in this invention, by changing the rotation speed of the stirring blade in the foaming tank during one batch foaming process,
An attempt is made to overcome the drawbacks of the conventional methods described above and to realize excellent batch-type prefoaming.

Composition> The method for achieving the above objective is to supply and store a predetermined amount of expandable thermoplastic resin particles in a foaming tank, and blow a heating medium from the bottom of the foaming tank while stirring the particles. In the method of pre-foaming particles by heating and expanding them, a stirring blade installed in a foaming tank is initially stirred at a relatively high rotational speed, and when the particles reach a certain expansion ratio, , the stirring blade is lowered to a relatively low rotational speed, and the upper surface of the particle diagram drawn into the foaming tank is
When the set height is reached when foaming to the set foaming ratio,
The purpose is to stop blowing the heating medium and stop foaming.

<Example> Next, an example of the present invention will be described with reference to the drawings.

The figure shows an example of a pre-foaming chamber for carrying out the pre-foaming method of the present invention. (1) is a foaming tank, which, like the conventional pre-foaming tank, is a cylindrical tube made of a steel plate or the like. It is tank-shaped. (2) is the stirring motor, and the foaming tank (
The shaft portion (31) of the stirring blade (3) in 1) is connected. (4) is an inverter that can change the rotation speed of the stirring blade (3) using a control signal. (5) is a measuring instrument,
A valve (51) is installed below it and can be opened and closed by a control signal so that expandable thermoplastic resin particles can be supplied into the foam 4fi [11]. (61
is for taking out the pre-foamed particles from the take-out port (61), and is opened and closed by an advancing/retracting mechanism such as an air cylinder (62). (7) is a hot plate through which steam passes as a heating medium, and has pores (not shown) through which steam passes from the steam chamber (81). (8)
(9) shows a solenoid valve for supplying steam, and (9) shows an air valve for air cooling the particles.

(g)) is a level meter using a tuning fork type or phototube type, etc. When the particle surface reaches this position, heating is stopped, air cooling is performed, the lid (6) is oiled, and the particles are discharged from the outlet (61). It is now possible to do so. In order to particularly improve the evacuation of particles, an evacuation air valve (11) is provided in the upper part of the foaming tank (1). (12) is a steam trap, (13) is a bearing, (14) and (15) are operating valves for air cylinders, (1
6) is a control box, and this control box (16)
In addition to controlling the opening and closing of the valves in each part, the level meter ω) is also controlled.

The pre-foaming method of the present invention using the pre-foaming device as described above will be explained.

The expandable thermoplastic resin particles are transferred from the meter (5) to the valve (51).
) and foam! A predetermined amount is supplied and stored within +1+. Then, while the particles are stirred by the rotation of the stirring blade (3), steam as a heating medium is passed from the steam valve (8) through the steam chamber (81) and through the hot plate (7) (foaming tank C1). °Blow into the air. In particular, in the method of the present invention, stirring by the stirring blade (3) is initially performed at a relatively high rotational speed, and the level meter (a) is controlled so that it does not operate even if the top wave of large particles hits it. After the particles reach a certain expansion ratio (expansion ratio of about 80 to 90% of the final expansion ratio), the stirring by the stirring blade (3) is changed to a relatively low rotation speed. . When the top wave of the particle layer becomes smaller and reaches the preset height when foaming at the preset 'R foaming ratio, the level meter ω
) to stop blowing steam and stop further foaming.

In the above example, the rotation speed of the stirring blade (3) was controlled by the foaming characteristics, but since the level meters were installed at two locations, high and low, stirring was not possible until the top surface of the particle layer reached the level h1 at the lower position. The blade (3) is rotated at high speed to achieve a high stirring effect.
After the level wound at the lower position is detected, the stirring blade (
It is also possible to reduce the rotation of step 3) and then stop steam heating when a level meter at a high position detects the detection.

It is preferable to convert the rotational speed of the stirring blade (3) using the inverter (4) as described above, but this is somewhat inferior in terms of cost and accuracy; It is also possible to carry out the operation by using a motor or the like and communicating with a level meter so that it can be remotely controlled.

Among the pre-foaming mentioned above, the expandable thermoplastic resin particles are polystyrene, polypropylene, polyethylene, and other various thermoplastic resins containing an easily volatile foaming agent and molded into pellets, etc. Various materials similar to those used for pre-foaming can be used.

Effects> The method of the present invention as described above has the following effects in terms of preliminary foaming.

(1) By controlling the rotation of the stirring blades, first, a high stirring effect is achieved at the beginning of pre-foaming, and when a certain expansion ratio is reached, the stirring effect is reduced to a low one for pre-foaming, so that the upper surface of the particle layer is It is possible to detect when the set height is reached when foaming to a preset foaming ratio (when the wave on the top of the particle layer is small, when the stirring effect is low), and the foaming variation between batches can be reduced. The length can be controlled.

(2) At the beginning of preliminary foaming, it is possible to achieve a high stirring effect, and this high stirring effect does not cause any adverse effects.

Experimental example> Expandable polystyrene particles were used as the raw material particles.
Injected into the tcy light bubble, blowing pressure 0.2Kfl
/ ci! Perform steam heating. The rotation speed of the stirring blades is 65r, p, n, and 125r, p, i in 20 seconds after charging.
Increase the number of continuous rotations, keep it constant, and hold for 75 seconds. At this stage, the waves on the top of the particle layer are large, but the level meter is not activated. Next, after the expansion ratio of the particles reached about 53 times, the speed was gradually reduced to 65r, p after 20 seconds.

m, the waves on the top of the particle layer become smaller,
When it comes into contact with the level meter (g), steam heating is stopped, the air valve (11) is opened, air cooling is performed for 10 seconds, and n (6
1, and the expanded particles were taken out. According to such batch Seiko Mii foaming, the conventional method had foaming variations of 60@±4@, but the degree of variation could be halved to 60 times ±2 times.

[Brief explanation of drawings]

The figure is a schematic cross-sectional view of a pre-foaming WA device used in carrying out the present invention.

Claims (1)

[Claims] 1. Place a specified amount of foaming thermoplastic resin in the foaming tank. Supply and store fat particles, and stir the above particles. While blowing the heating medium from the bottom of the foaming tank. By heating and expanding the particles, In the pre-foaming method, the Initially, the comparison was made with the stirring blades Stir at high speed and mix the above grains. When the foam reaches a certain foaming ratio, the above Reduce the stirring blade to a relatively low rotation speed. Stir and top surface of the particle layer in the foaming tank is the setting when foaming to the set foaming ratio. When the height is reached, blow in the heating medium. It is characterized by stopping foaming. Pre-expanding method for expandable thermoplastic resin particles Law.