JPS61192524A - Prefoaming of expandable thermoplastic resin particle - Google Patents

Abstract

PURPOSE:To permit to form the pre-expanded particles of lowest magnification efficiently with a good quality by a method wherein the expandable thermoplastic resin particles are heated from outside indirectly through the bulkhead of a prefoaming tank under mixing them in the prefoaming tank to effect the pre-expanding of the particles. CONSTITUTION:The expandable thermoplastic resin particles are supplied into the prefoaming tank 1 through a supplying port 2. The resin particles are mixed by the rotation of a mixing rod 4 and, at the same time, the resin particles in the prefoaming tank 1 are mixed continuously and evenly by operating a vibrating mechanism to vibrate the particles of resin. On the other hand, high- temperature heated steam is introduced into a heating chamber 5 to heat the resin particles in the prefoaming tank 1 indirectly through the bulkhead 11. When the resin particles are expanded by heating and are expanded in the same tank 1 to a given level, the resin particles are pre-expanded with a predetermined magnification of foaming.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a method for pre-foaming expandable thermoplastic resin particles, in which the resin particles are pre-foamed to a certain expansion ratio before being used for foam molding, etc. It relates to a method for producing pre-expanded granules.

<Prior art> Conventionally, as the above pre-foaming method, resin particles made of a thermoplastic resin containing an easily volatile blowing agent are put into a tank-shaped pre-foaming chamber, and the resin particles are stirred with a stirring rod or the like. A method has been adopted in which high-temperature heated steam is jetted and supplied into a pre-foaming tank, and the heated steam is brought into contact with resin particles to directly heat them.

However, in the above conventional method, heated steam is allowed to penetrate into the resin particles, and a portion of the steam also acts as a blowing agent. Although this is suitable, when pre-expanded particles with an extremely low expansion ratio of about 3 to 10 times are subjected to yJ molding, the entire resin particle cannot be heated evenly, and uneven heating tends to occur, resulting in high temperature heating. The resin particles in the portions that are in direct contact with the steam are foamed to a high magnification of 10 times or more due to the action of the foaming agent caused by the steam. On the contrary, since some resin particles do not come into contact with steam etc., they may remain unfoamed at all, resulting in variations in expansion ratio and the disadvantage that pre-expanded particles of stable quality cannot be produced.

In order to prevent the above drawbacks, a method has been used in which resin particles are stored in a cloth bag or the like and then heated in a boiling water tank to perform pre-foaming, but this method is cumbersome and requires time and effort. At the same time, the use of boiling water was dangerous, and the pre-expanded grains immersed in boiling water contained water and became damp, making it impossible to use them for foam molding unless they were dried. .

Therefore, the purpose of the present invention is to provide a method that eliminates the drawbacks of the above-mentioned conventional techniques and can efficiently produce pre-expanded granules with a very low expansion ratio of about 3 to 10 times with good quality. was developed.

<Structure> In order to achieve the above object, the resin particles are indirectly heated from outside C1 through the partition wall of the pre-foaming tank while stirring the expandable thermoplastic resin particles in the pre-foaming tank. It is characterized by pre-foaming.

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

The figure shows an example of a pre-foaming device for carrying out the pre-foaming method of the present invention, and (1) is a pre-foaming tank;
Like conventional pre-foaming devices, it has a cylindrical tank shape made of steel plate or the like. A supply port (2) for the expandable thermoplastic resin particles and a discharge port (3) for the produced pre-expanded particles are provided at the lower part of the pre-expanded tank (1).

(4) is a stirring rod, and a plurality of stirring rods (4) are vertically spaced apart from each other along the central axis of the pre-foaming tank (1) and protrude radially in the horizontal direction. 40) is a motor for rotating the stirring rod (4). And pre-foaming If
f (On the inner wall surface of 11, there is a stirring rod (
4) are formed alternately with baffle rods (10) that protrude horizontally toward the center, and the rotation of the stirring rod (4) stirs the resin particles supplied into the pre-foaming tank (1). Mixing is effective for improving the heating effect described later and for equalizing the expansion ratio.

Next, a heating chamber (5) is provided at the bottom of the pre-foaming tank (1) via a partition wall (11) made of a steel plate, etc., and a heating medium such as steam is supplied to this heating chamber (51). A port (50) and a discharge port (51) are formed to allow introduction of a heating medium such as high-temperature heated steam.

Generally speaking, (6) is a vibration mechanism, which is installed at the lower end of the pre-foaming tank (1) and forcibly vibrates the area near the bottom of the pre-foaming tank (1) during pre-foaming. It is designed to be able to give vibration to the resin particles.

A pre-foaming method using the above-mentioned pre-foaming device will be explained.

The expandable thermoplastic resin particles are supplied into the pre-foaming tank (1) from the supply port ('2J).Then, the resin particles are stirred by the rotation of the stirring rod (4), and at the same time, the vibration mechanism is operated. The resin particles are vibrated and the entire resin particles in the pre-foaming tank (1) are constantly stirred and mixed without any separation. On the other hand, high temperature heated steam is introduced into the heating chamber (5), and the partition wall (
11) indirectly heat the resin particles in prefoaming 1 (1). Then, when the resin particles are heated and foamed and expanded to a certain height in the pre-foaming tank (1), the resin particles have been pre-foamed to a predetermined expansion ratio1.
If the manufactured pre-expanded grains are taken out from the discharge port (3),
Pre-foaming ends.

Among the pre-foaming methods described above, the expandable thermoplastic resin particles include polystyrene, polypropylene, polyethylene, and other various thermoplastic resins containing an easily volatile foaming agent and molded into a pellet shape or the like. , similar to those used for conventional prefoaming can be used.

As a pre-foaming device, if heating medium such as steam does not come into direct contact with the resin particles, it can be applied to the bottom of the pre-foaming tank (1) shown in the figure as well as a part of the wall surface such as the lower side of the tank through a partition wall (11). A heating means may be provided as appropriate.

As a heating means, as shown in the figure, in addition to introducing heated steam, heated gas such as air, heated liquid such as heated water or heated oil, or other heating medium into the heating chamber (5), a pre-foaming tank ( It is also possible to use various known heating means, such as one in which a heat generating means such as an electric heater is installed outside the partition wall (11) in 1).

Next, in order to stir the resin particles without mutual selection in the pre-foaming tank (1), in addition to installing a stirring rod (4) and a baffle bar (10), an S movement mechanism (6) is used to stir the resin particles in the pre-foaming tank (1). It is effective to forcefully vibrate (1). That is, by forcibly vibrating the pre-foaming tank (1), the unfoamed particles, which have a higher specific gravity than the foamed resin particles, tend to fall below the pre-foaming tank (1), and the steam The heat will be concentrated at the bottom of the chamber (8).Therefore, the unfoamed particles will be heated and foamed sequentially with high efficiency, so there is little possibility that unexpanded particles will remain in the produced pre-expanded particles. This makes it possible to produce pre-expanded granules with stable quality and less uneven foaming.As for the specific structure of the camera mechanism (6), a normal electromagnetic type or air set vibrator can be used as appropriate. The vibration mechanism (6) is installed at the bottom of the pre-foaming tank (1), etc., and the pre-foaming 4* (11
If vibration can be applied effectively to the resin particles near the lower part of the resin particles, the generation of the unfoamed particles can be effectively prevented.

The illustrated pre-foaming device is of a batch type in which resin particles are pre-foamed in fixed amounts, but in the method of the present invention, resin particles are continuously supplied, pre-foamed, and then sequentially discharged. It is also applicable to a continuous type Y-equipment foaming device. In the case of this continuous pre-foaming device, the outlet (3) is installed at the top of the pre-foaming Iff (11).

<Effects> According to the method of the present invention configured as described above, when heating the expandable thermoplastic resin particles in the pre-foaming tank (1), a heating medium such as heated steam is brought into direct contact with the resin particles. First, heating is performed indirectly via the partition wall (11) of the pre-foaming tank (1).

In the conventional pre-foaming method using beating, there is a problem in that steam or the like penetrates into the interior of the resin particles, acts as a foaming agent, and causes the resin particles to become highly foamed. In particular, the progress of foaming is extremely different between resin particles that are in direct contact with steam, etc. and resin particles that are not in contact with steam, etc., and heating unevenness is likely to occur. The problem of uneven heating mentioned above does not occur at all because the heating is performed and the foaming is performed relatively slowly, with only the thermal expansion of the foaming agent and the softening of the resin particles due to heat.
It has an extremely large effect because it averages out the expansion ratio of the pre-expanded grains.

In addition, since steam does not come into contact with the resin particles, the problem of moisture adhering to the resin particles and making them wet can be solved, and the pre-expanded granules produced are completely dry and of good quality. It will be done.

<Experimental Example> In order to demonstrate the effects of the present invention described above, pre-foaming was carried out specifically using resin particles.

First, an iron pre-foaming tank (capacity: 1,800 mJ) was placed on an electric heater and heated to a constant temperature, and 8q of expandable polystyrene beads were added as resin particles into the pre-foaming tank and stirred by hand. While heating and foaming for 1 minute,
The foaming ratio after foaming was measured and shown in the table below.

Table 1 The above experiment demonstrated that even indirect heating by the pre-foaming method of the present invention can sufficiently avoid pre-foaming.

Next, 50 g of expanded polystyrene beads were placed in the above device, and while being heated to 120° C., vibrations were applied, and as the heating time elapsed, the expansion ratio of the expanded beads was measured, and is shown in the table below.

Table ■ In the table, the accuracy is given by the formula below, which indicates the variation in the expansion ratio of the foam particles.

χ Here, (lyn-1: Standard deviation of foaming ratio measurement value χ:
Average Value of Expansion Ratio Measurements From the above results, it was demonstrated that by applying vibration, foaming progresses faster and variation in expansion ratio is reduced.

[Brief explanation of the drawing]

The figure is a sectional view of a pre-foaming device showing an embodiment of the present invention. (1)...Pre-foaming tank, (11)...
Partition wall, (4)...Stirring bar, (5)...
Heating chamber, (6)... Vibration mechanism.

Claims (1)

[Claims] 1. Pre-foaming tank for foamable thermoplastic resin particles While stirring inside the pre-foaming tank, The resin particles are indirectly applied from the outside through the It is characterized by heating and pre-foaming. A method for pre-expanding expandable thermoplastic resin particles. 2. Vibrate the resin particles in the pre-foaming tank. Claim 1 of the above-mentioned claim Preparation of expandable thermoplastic resin particles as described in section Foaming method. 3. Addition of foaming material installed adjacent to the wall of the pre-foaming tank. Supply the heating medium to the heat chamber and heat the resin particles. Heating described in claim 1 above A method for pre-expanding expandable thermoplastic resin particles. 4. Prepare resin particles at a foaming ratio of 3 to 10 times. Foaming as described in claim 1 above A method for pre-expanding expandable thermoplastic resin particles.