JPH0684453B2 - Pre-expanding method for expandable polystyrene resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for pre-expanding expandable polystyrene resin particles,
In particular, the present invention relates to the above-mentioned pre-foaming method technology suitable for satisfying the required small particle size and high foaming.

(Prior Art) There are methods such as a batch method and a continuous method for pre-expanding (primary foaming) the expandable thermoplastic resin particles, but recently, the expandable thermoplastic resin particles are batchwise in the foaming tank. A batch method in which a fixed amount is supplied, the particles are heated and expanded by a heating medium such as steam at a temperature of ° C, and the pre-expanded particles are taken out in a batch method is put to practical use as the most general method.

By the way, in the batch type pre-expansion method, various methods have been studied in the past in order to produce the pre-expanded particles having a low apparent specific gravity and good secondary expansion moldability in a mining industrially advantageous manner, and the material particles were sealed. The inside of the vessel is decompressed in advance before the steam is blown, and steam is blown into the vessel to heat and soften and expand the particles while raising the pressure inside the vessel below the fusion temperature of the foam particles to reach the fusion temperature. Before reaching the internal pressure, the internal pressure is released and reduced to atmospheric pressure, and the pressure is further expanded by the differential pressure between the internal pressure and the foaming agent pressure in the expanded particles (Japanese Patent Publication No. Sho 43).
-18635 gazette), in heating the expandable resin particles with steam, pre-foaming is performed while controlling the blowing amount of steam so that the foaming speed is achieved, and when the set multiple is reached, the blowing of steam is stopped. (JP-A-56
-25424), the expansion ratio of the expanded particles is controlled by the volume of the expanded particle layer, and when the expanded particle layer reaches a certain volume, the blowing of water vapor is reduced or stopped so that the expansion is accurately performed at the set value. A method of stopping (see Japanese Patent Publication No. 56-5176), stirring and heating the expandable resin particles in a foaming tank in a dry atmosphere, and applying vacuum to the heated particles for a predetermined time and a predetermined density. Partially expanded, and then returned to normal pressure to take out the partially expanded granular expandable resin particles (see Japanese Patent Publication No. 47-27144), the lower limit and upper limit set values of the pressure in the foaming tank were determined and heated. Supply of media,
In association with the stop, the supply of the heating medium is started and stopped, and the pressure in the foaming tank is increased and decreased repeatedly until the upper surface of the foamed particle layer is detected by a detector provided at the set height of the foaming tank. Methods (see Japanese Patent Publication No. 62-10165) have been proposed.

And, in each of these methods, it can be said that the foaming agent and the solvent contained in the expandable thermoplastic resin particles in order to obtain expanded particles that are more highly expanded as a general aspect are slightly different depending on heating conditions, After the start, it dissipates violently in about 30 seconds, so there is a limit to foaming even if the particles are foamed for a long time unless it is rapidly foamed in the early stage of heating, and if heated more than necessary, it shrinks rather Therefore, rapid foaming of the resin particles in the early stage of heating has been considered.

However, the expanded particles obtained by each of the above-mentioned methods are currently 0.2 to 0.3 mmφ and 30 to 40 times as much as possible, and it has not been possible to obtain expanded particles expanded uniformly and at high magnification.

Moreover, immediately after supplying the expandable resin particles to the foaming tank, when steam is immediately blown to rapidly foam the resin particles, the temperature of the resin particles is lower than the steam temperature, so that part of the steam drains and forms a water droplet film on the particle surface. However, because of the mischief of the drain, it takes a long time to foam, and in fact, rapid heating cannot be performed, which hinders uniform heating of the particles.

On the other hand, recently, with the progress of the full mode method (putting the molten metal directly into the styrene type), the demands for small particle size and high foaming were inevitably increased, and the current foaming ratio was further increased to 0.2-0.3 mmφ.
There is a strong demand for pre-expanded particles having an expansion ratio of about 60 times.

(Problems to be Solved by the Invention) The present invention deals with the actual situation as described above, and takes into consideration the difficulties of each method and the demands of the times, and has an object to obtain a further smaller particle size and higher foaming. , The expandable polystyrene resin particles are pre-heated prior to the heat-foaming, and the temperature difference with the heating medium, steam, is reduced to minimize the draining of steam on the surface of the resin particles and to achieve uniform foaming in a short time. Therefore, the purpose is to achieve high magnification.

(Means for Solving the Problems) That is, the feature of the present invention that meets the above-mentioned object is that first, when the expandable polystyrene resin particles are heated and pre-expanded, the resin particles are previously prepared. , Preheating at a temperature that does not lead to melting of the resin particles, then temporarily reducing the pressure inside the tank, and then blowing steam to maintain the pressure inside the tank at atmospheric pressure or higher to heat and foam it,
Further, in a second aspect of the invention, following the heat-foaming according to the first aspect of the invention, after the above predetermined foaming, the pressure in the tank is rapidly reduced to atmospheric pressure or lower, and further foaming is performed by the differential pressure between the pressure inside the tank and the pressure inside the expanded particles. Then, hot air is again introduced into the tank, and the inside of the tank is kept in a pressurized state for a predetermined time to allow air to rapidly permeate into the expanded particles, and then hot air introduction is stopped and the inside of the tank is returned to atmospheric pressure for foaming. To take out the used particles.

Here, the expandable polystyrene resin particles to which the present invention is applied include polystyrene resin particles such as polystyrene, styrene and α-methylstyrene, and fluorostyrene, and aliphatic hydrocarbons such as propane, butane, pentane, and hexane. It contains a foaming agent such as a halogenated hydrocarbon such as methyl or dichlorodifluoromethane, and can have any shape, but a spherical shape is most commonly used.

Further, the preheating performed by blowing the steam and performing heating and foaming may be performed after supplying a certain amount of the particles in the foaming tank and then injecting the steam in the same tank, but is otherwise restricted. Alternatively, a preheating step may be separately performed and the preheated resin particles may be used.

However, as in the first and second inventions, it is industrially advantageous to carry out the heat-foaming by preheating and steam blowing in the same foaming tank into which a constant amount of resin particles are supplied.

As the preheating means, preferably, heating is performed at a temperature not lower than 80 ° C. at which the resin particles are not melted, specifically, 80 ° C. to 120 ° C., and any heating medium or means such as hot air or indirect heating may be used. Further, it may be under vacuum, under pressure, or under normal pressure. However, most commonly, hot air preheating under normal pressure is used.

(Function) By preheating the expandable polystyrene resin particles in advance as described above, the temperature difference between the steam and the steam becomes small when the steam is blown, and the steam does not drain on the surface of the resin particles. Without being hindered, the heating by steam blowing becomes uniform, the heating rate is shortened, rapid heating is advanced, high magnification is achieved, and small particle size and high foaming can be approached.

In addition, after preheating, the first invention in which the pressure in the tank is once reduced and the steam is blown allows the foaming at a low-pressure steam pressure much lower than the blow-in steam pressure by the usual method because the steam is blown in under the reduced pressure. Become.

For this reason, in combination with the above preheating, the expansion of the foaming agent contained in the resin particles is small and the foamed particles are expanded to a higher degree.

Further, after the completion of foaming following the above steps, the pressure in the tank is rapidly reduced, and further foaming is performed by the pressure difference between the pressure inside the tank and the pressure inside the expanded particles, and hot air is introduced into the expanded particles by pressurizing with hot air. In the second invention in which air is rapidly permeated, it becomes easy to remove the remaining water vapor in the tank to obtain dried pre-expanded particles, and it becomes possible to adjust the residual blowing agent in the expanded particles. The dimensional accuracy after molding can be improved and the aging time can be significantly shortened.

However, although each of the above inventions is extremely effective for a small particle size of the raw material particle size of 0.2 to 0.3 mmφ, it goes without saying that it is similarly effective for the raw material particle having a particle size of 0.5 mmφ or more. .

(Example) Hereinafter, the method of the present invention will be described in more detail based on an example apparatus shown in the accompanying drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention, in which (1) is a foaming tank and a steam injection nozzle (7).
A pressure-resistant container having a bottom plate having a stirrer shaft (2) rotatably driven by a driving device (3), and a hopper (8) provided with a charging valve (9) at the top. .

Further, a pressure regulating valve (1
A pipe that is open to the atmosphere via 0) and a pipe that connects to the vacuum pump (12) via a valve (11) are connected to each other, and a level meter (5) is installed at a required side wall position. Incidentally, (6) is a pressure gauge, and (4) is an exhaust valve.

Therefore, in the apparatus having the above-mentioned structure, in the present invention, in order to carry out the method, the steam introduction pipe and the hot air pipe further having the steam valve (13) and the hot air supply valve (14) under the foaming tank (1), respectively. The introduction pipes are connected by a common pipe so that steam or hot air can be selectively supplied into the foaming tank (1).

Therefore, hereinafter, a concrete embodiment of the pre-foaming method of the present invention will be described with reference to the state diagram shown in FIG.

First, in the foaming tank (1), the stirring shaft (2) is driven and rotated by the drive device (3). Then, pre-measured expandable polystyrene resin particles (hereinafter simply referred to as resin particles) are supplied from the hopper (8) into the foaming tank (1) by opening the charging valve (9), and then the hot air supply valve (14). Open and introduce hot air. (FIG. 2a) At this time, the pressure regulating valve (10) that is open to the atmosphere above the foaming tank (1) is in an open state and is in communication with the atmosphere.

Thus, when hot air is passed for a predetermined time, and when the resin particles reach a predetermined temperature by this, the hot air supply valve (14) and the pressure regulating valve (10) on the upper side are closed to make the valve (1
1) is opened, and the inside of the tank is decompressed by the vacuum pump (12) until a predetermined vacuum degree is obtained (Fig. 2b), and then the steam valve (13) is opened to continuously supply steam into the tank. Flow into.
(FIG. 2c) Then, when the pressure in the tank reaches a preset pressure (upper limit pressure), the pressure regulating valve (10) is opened to reduce the pressure, while when the preset pressure (lower limit pressure) is reached. Regulator valve (10)
Is closed, and the pressure in the tank is raised to keep the inside of the tank within a constant pressure range. (Fig. 2d) In this state, the resin particles continue to foam in the foaming tank, and when it is detected by the level meter (5) that the resin particles have foamed to the predetermined volume, the steam valve (13) is closed and the tank is sealed. After that, the valve (11) is opened again, the pressure is reduced by the vacuum pump (12), the steam remaining in the tank is exhausted to dry the particles, and the secondary foaming remaining in the expanded particles Except for the amount required for molding. (Fig. 2e) Thus, when the pressure is reduced to a predetermined vacuum level (100 to 500 mmHg), the hot air supply valve (14) is opened and hot air is blown in (Fig. 2f), and the chamber is pressurized again and held for a certain period of time. (Second
Fig. G), air is rapidly permeated into the expanded particles, then the hot air supply valve (14) is closed and the pressure regulating valve (10) is opened,
Return the atmospheric pressure to the atmospheric pressure (Fig. 2h), open the exhaust valve (4),
The pre-expanded particles are taken out.

The above is one cycle process from the addition of resin particles to the completion of foaming, and this is repeated as necessary.

In the above description, when the level meter detects that the foaming ratio has reached a predetermined expansion ratio due to heat foaming, the inside of the tank is decompressed again, the remaining steam and unnecessary foaming agent are discharged, and the inside of the tank is pressurized again with hot air. However, these are not particularly and essential in the present invention, but it is necessary to bring air into the expanded particles (which is in a depressurized state at this point) by bringing hot air into the vessel to pressurize the vessel again. This is because it is rapidly permeated, which is effective in greatly shortening the aging time thereafter, and once the pressure in the tank is reduced from the pressure increased by steam heating, the expanded particles Since the internal pressure is higher than the internal pressure of the tank, it is suitable for re-expanding the expanded particles.

In addition, in the foaming step, decompression in the tank and pressure application by hot air into the tank have the advantage that the amount of residual gas in the expanded particles can be easily adjusted by adjusting the degree of decompression in the tank and the pressure by hot air. To have.

Further, in the preheating, in the figure, a hot air introducing pipe is provided in the lower part of the foaming tank (1) to preheat the resin particles in the tank, but it is not necessarily limited to the same tank, but is preheated in another tank. It is also possible to send the resin particles into the foaming tank.

Specific examples will be described below.

Example 1 Diameter 0.2-0.3mm with butane gas 5.7% as a foaming agent
Using the expandable polystyrene resin particles of φ (brand name, full-mold grade for bell molding) as a material, pre-expansion was performed using the apparatus shown in FIG. 1 according to the following steps and conditions.

(1) Preheat hot air 110 ℃ × 3 minutes (2) Vacuum decompression −300mmHg (3) Injection steam pressure 0.6kg / cm ² G × 3 minutes (4) Tank pressure 0.15 to 0.2kg / cm ² G (5) Foaming After the completion of the drying, the foamed particles obtained after drying at 70 ° C. for 30 seconds showed high foaming with a foaming ratio of 62 times, the residual gas content of the foamed particles was 2.9%, and the water content was 2.3%.

Then, when the foamed particles were aged for 3 to 5 hours and then molded, a good product could be obtained.

For comparison, the same material as above was used, but the same pressure was used for the pressure of the steam, the pressure inside the tank, and the conditions for drying after foaming were the same, but preheating with hot air was not performed and the vacuum pressure was reduced to -100 mmHg. When the foaming results of the pre-foamed product were examined, the expansion ratio was 38 times, the water content was 4.0%,
The residual gas amount was 3.2, and the subsequent aging took 6 to 8 hours.

On the other hand, although preheating with hot air was not performed, blowing conditions were examined in the same manner, except that the blowing steam pressure, the tank internal pressure, the vacuum depressurization, and the respective conditions at the time of drying after the completion of foaming were the same as in the above-mentioned Example.
The expansion ratio was 41 times, the water content was 2.7%, the residual gas amount was 3.0%, and the aging time was 4 to 6 hours.

Example 2 Using the expandable polystyrene resin particles containing a blowing agent butane gas of 5.7% as a raw material, each step of preheating, vacuum decompression and steam blowing in Example 1 described above using the foaming apparatus shown in FIG.
In addition to the conditions, after the required foaming is completed, the tank pressure is further reduced
The pressure was reduced to 300 mmHg, the hot air supply valve (14) was opened, followed by hot air drying at 70 ° C., then hot air at 110 ° C. was blown in and kept under pressure for 90 seconds, and then the expanded particles were taken out.

The obtained expanded particles had an expansion ratio of 65 times, the residual gas content of the expanded particles was 2.4%, and the water content was 1.5%. After expansion, molding was performed with almost no aging time (0 to 1 hour). Done,
We were able to obtain good quality products.

On the other hand, using the same resin particles as above, except that preheating with hot air was not carried out, pre-foaming was carried out in the same process and conditions, and the expansion ratio of the obtained expanded particles was 58 times and the residual gas amount was
The water content was 2.6% and the water content was 1.6%.

And, this product required aging time of 1 to 2 hours to obtain a good quality product.

In addition, when the preheating with hot air was not carried out and the vacuum decompression prior to the foaming step was not carried out, the foamed particles had a foaming ratio of 39 times, a water content of 1.5% and a residual gas content of 2.9%. But,
The expanded beads were forcibly cured and required almost no aging time.

Example 3 Foaming polystyrene resin particles having a diameter of 0.8 mm and containing 6% of butane gas as a foaming agent were used as raw materials, and pre-foaming was performed using the foaming apparatus shown in FIG. 1 under the following steps and conditions.

That is, the pressure inside the tank was reduced to -300 mmHg in advance, and the vapor pressure
Blow in steam at 0.6kg / cm ² G, and in about 3 minutes the tank pressure will be 0.1
When the amount reached 5 to 0.2 kg / cm ² G, steam blowing was stopped and pre-expanded particles were obtained.

This product has a foaming ratio of 58 times, a water content of 4.3%, and a residual gas content of 3.7.
% Required 5 hours for aging. On the other hand, prior to the decompression in the tank, hot air at 110 ° C was passed through and preheated for 3 minutes, the expansion ratio increased to 65 times, and the residual gas content was 3.0% water content.
The aging time was about 3 hours at 3.1%.

(Effects of the Invention) As described above, the present invention reduces the temperature difference between the particles and steam during heat-expanding by preheating the expandable polystyrene resin particles prior to the heat-expanding, so that the drainage of steam on the surface of the resin particles is reduced. Has a remarkable effect of making the expansion of small-sized resin particles more advanced and minimizing the formation of uniform expanded particles by minimizing or completely reducing the formation of the resin particles. It is extremely effective in achieving a high magnification that the uniform heating during the foaming of (2) is promoted and the shortening of the heating rate can be expected.

Further, in combination with the above preheating, the initial stage of the heating and foaming which is continuously performed is depressurized, and by blowing steam in this state, it is possible to foam with low-pressure steam, and as a result, low-temperature foaming is possible and the particles are contained in the resin particles. Less dispersal of foaming agent,
It is possible to expect further high-magnification foaming.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a foaming agent for carrying out the pre-foaming method of the present invention, and FIG. 2 is a state explanatory view in the pre-foaming method. (1) …… Bubbling tank, (2) …… Stirring shaft, (7) …… Steam injection nozzle, (10) (11) …… Valve, (12) …… Vacuum pump, (13) …… Steam valve , (14) …… Hot air supply valve,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Tsuneto, 3-3-12 Daikai, Fukushima-ku, Osaka City, Osaka Prefecture (56) References Japanese Patent Publication No. 52-37498 (JP, B2)

Claims (6)

[Claims] 1. A method of heating expandable polystyrene resin particles to pre-expand them, after supplying and storing a predetermined amount of the particles in a foaming tank, preheating the particles with hot air at a temperature that does not result in melting of the particles, Thereafter, the tank is hermetically closed and decompressed, and steam is continuously blown in this state, the tank pressure is kept at atmospheric pressure or higher and heated, and preliminary expansion of the expandable polystyrene resin particles is carried out. Foaming method. 2. The pressure in the tank after preheating is set to a vacuum degree of 50 mmHg to 500 mmHg, and then steam is blown in to maintain the tank internal pressure at a gauge pressure of 0.15 to 0.3 kg / cm ² G. A method for pre-expanding expandable polystyrene resin particles. 3. A method of heating expandable polystyrene resin particles to pre-expand them, after supplying and storing a predetermined amount of the particles in a foaming tank, preheating the particles at a temperature which does not result in melting of the particles, and thereafter, The inside of the tank is closed and decompressed, and steam is continuously blown in that state to maintain the pressure inside the tank at atmospheric pressure or higher to heat it, and to pre-foam it and after the prescribed foaming, the inside of the tank is rapidly reduced to atmospheric pressure or less. The pressure is reduced, and further foaming is performed by the pressure difference between the pressure inside the tank and the pressure inside the expanded particles, and then hot air is again introduced into the tank to keep the inside of the tank in a pressurized state for a predetermined time to allow air to rapidly permeate into the expanded particles. After that, the introduction of hot air is stopped, the inside of the tank is returned to atmospheric pressure, and the expanded particles are taken out, thereby pre-expanding the expandable polystyrene resin particles. 4. The method for pre-expanding expandable polystyrene resin particles according to claim 3, wherein the preheating temperature is 80 to 120 ° C. 5. The pressure inside the tank after preheating is set to a vacuum degree of 50 mmHg to 500 mmHg, and then steam is blown in to maintain the tank pressure at a gauge pressure of 0.15 to 0.3 kg / cm ² G, and after the required foaming, the inside of the tank is kept. The method for prefoaming expandable polystyrene resin particles according to claim 3 or 4, wherein the pressure is again reduced to 50 to 500 mmHg. 6. The method for pre-expanding expandable polystyrene resin particles according to claim 3, wherein the temperature of hot air introduced into the tank again after the required expansion is 50 to 120 ° C.