JPH03131635A - Preexpansion of foamable thermoplastic resin particles - Google Patents

Abstract

PURPOSE:To efficiently obtain expanded particles having few blockings, excellent moldability in a short aging time by stopping heat before target level of preexpansion is attained, introducing cooling air to quench foamable particles and then reexpanding under heating. CONSTITUTION:Steam is introduced into an expanding tank and the tank is maintained at 10-140 deg.C. When foamable thermoplastic resin particles reach 75-95 volume ratio, preferably 90-95 volume ratio based on target level, heating is stopped, cooling air is introduced, for example, at 90 deg.C tank temperature for 30 seconds, at 80-83 deg.C for 1 minute and at 75-78 deg.C for 2 minutes. Then steam is introduced again, the resin particles expanded under heating until the particles reach a target to give the objective expanded particles.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for pre-foaming expandable thermoplastic resin particles, and in particular to the above method suitable for obtaining pre-foam particles having a high expansion ratio, which is currently in demand. The present invention relates to a pre-foaming method.

(Prior art) Methods for pre-foaming (sub-foaming) expandable thermoplastic resin particles can be roughly divided into batch methods and continuous methods, but recently, methods have been developed in which measured raw material particles are placed in a foaming tank and stirred. Steam at normal pressure or 0.1~0.3 kg/afl (
When the foaming progresses and the foamed particles reach a predetermined level, the steam heating is stopped, air is blown in to cool them down, and the pre-foamed particles are foamed. A batch foaming method in which foam is removed from a tank is the most common method used in practice.

By the way, with regard to such batch foaming methods, various efforts have been made in response to the trends of the times as they have been put into practical use, and among them, pre-expanded particles with low apparent specific gravity and good secondary foam moldability have been made industrially advantageous. Various methods have been researched to manufacture foamed particles, including storing material particles in a sealed container, reducing the pressure in the container before blowing steam into the container, and blowing steam into this to heat the particles to soften and expand them, thereby producing foamed material particles. A method of releasing the pressure in the vessel to reduce the pressure to atmospheric pressure before reaching the fusion temperature of , and further expanding by the differential pressure between the pressure in the vessel and the pressure of the blowing agent in the foamed particles (see Japanese Patent Publication No. 4318635) 1 A method of heating expandable resin particles with steam, pre-foaming them while controlling the amount of steam blowing to maintain the foaming speed, and stopping the blowing of steam when a set multiple is reached (Japanese Patent Application Laid-Open No. 56-25424
(Refer to the publication) 2 The expansion ratio of the foamed particles is controlled by the volume of the foamed particle layer, and when the foamed particle layer reaches a certain volume, the blowing of steam is reduced or stopped to accurately stop the foaming at the set value. (Refer to Japanese Patent Publication No. 56-5176) 2. In a foaming tank, foamable resin particles are stirred and heated in a dry atmosphere, and the heated particles are evacuated for a predetermined time to reach a predetermined density. partially inflated,
Afterwards, the pressure is returned to normal and the partially expanded granular foamable resin particles are taken out (see Japanese Patent Publication No. 47-27144). 2. Determine the lower and upper limits of the pressure in the foaming tank, and use these to supply and stop the heating medium. In connection with this, a method of repeatedly increasing and decreasing the pressure in the foaming tank by starting and stopping the supply of the heating medium until the upper surface of the foamed particle layer is detected by a detector installed at a set height of the foaming layer. (Tokuko Showa 62-1016
(see Publication No. 5) have been proposed.

(Problem to be Solved by the Invention) However, in each of the above methods, although the blowing agent and solvent contained in the raw material particles generally differ depending on the heating conditions in order to obtain highly foamed particles, Usually, it has been pointed out that the foam tends to dissipate around 30 seconds after the start of heating, and it is considered that the raw resin particles are rapidly foamed in the initial stage of heating, but little consideration has been given to aging during subsequent molding.

Therefore, currently, when pre-foamed particles are used for secondary molding, aging (curing) takes 4 to 24 hours or more, although this varies slightly depending on the expansion ratio. This is one of the obstacles to streamlining foam molding.

Furthermore, when the particle size is small or the material particles are stored for a long period of time, high-magnification foaming of raw material particles with a small amount of blowing agent causes a problem in that a large amount of blocking occurs due to fusion of the foamed particles.

In view of the above-mentioned circumstances, the present invention introduces intercooling during the pre-foaming process in order to solve these problems, so that even raw material particles with a small amount of blowing agent have less blocking, good moldability, and a shorter heating time. The purpose of this is to shorten the pre-foaming cycle by shortening the process, thereby improving productivity and shortening the aging time.

(Means for Solving the Problems) That is, the feature of the pre-foaming method of the present invention that meets the above-mentioned purpose is that when a predetermined amount of expandable thermoplastic resin particles are put into a foaming tank and heated and foamed while being stirred, As foaming progresses, heating is stopped once at a predetermined level before reaching the target level, and cooling air is blown to cool the foamed particles.

The purpose is to carry out heating and foaming again, and then, when the target level is reached, heating is stopped again, and after cooling, the foamed particles are taken out.

Here, the predetermined level at which the cooling air is blown in the above-mentioned intermediate range is desirably in the range of 75 to 95% volume LLt(r) with respect to the target level, and a range of 90 to 95% volume ratio is particularly effective.

This predetermined level can usually be set by providing a level meter separate from the target level meter within the above range below the target level meter installed in the foaming tank, but instead of providing a level meter, a timer control It is also possible by doing

The invention as claimed in claim 3 specifically shows the practical scope of the invention, and includes blowing steam into a foaming tank to maintain the temperature at 104°C or lower to heat and foam the raw material particles, and to achieve a target level of foaming. Once at the 90-95% capacity ratio level, stop steam blowing and turn on cooling air for 30 seconds.
2 minutes, e.g. 30 seconds at a bath temperature of 90℃, 83~80''
Blow into the tank for 1 minute at 78-75°C for 2 minutes, cool, and then blow steam again to perform heating foaming.
After reaching the target level 1. It is characterized by cooling and taking out.

The expandable thermoplastic resin particles to which the pre-foaming method of the present invention is applied include, for example, polystyrene, styrene, α-methylstyrene, and fluorstyrene.

Acrylonitrile A copolymer with acrylic acid, thermoplastic resin particles such as polyethylene, and aliphatic hydrocarbons such as propane, butane, pentane, hexane, etc.

It contains a blowing agent such as a halogenated hydrocarbon such as methyl chloride or dichlorodifluoromethane, and can have any shape, but a spherical one is most commonly used.

(Function) When the expandable thermoplastic resin particles are pre-foamed by the method described in -1-, heating is stopped by setting a predetermined level below the target level, and cooling air is blown into the raw material particles during heating and foaming. is cooled by contacting the cooling air,
The blowing agent contained inside the particles is accumulated and retained within the particles,
During this time, the foam particles are held more uniformly inside, absorb air, and increase the foaming power during heating, and the cooling air prevents the foam particles from fusing together.

Therefore, when the foam is subjected to heating and foaming again, it is possible to achieve a higher foaming level than when heating and foaming is continued due to expansion due to the accumulated energy dissipation of the accumulated foaming agent and air as described above. , blocking almost no longer occurs.

(Example) Hereinafter, specific embodiments of the pre-foaming method of the present invention will be further described in detail.

The characteristics of the method of the present invention are as described above, and it begins by charging foamable thermoplastic resin particles, which are raw material particles, into a foaming tank for a fixed amount and heating and foaming them while stirring.

In this case, the pre-foaming device is a known foaming tank consisting of a pressure-resistant container with an internal stirring shaft rotated by a drive device, a hopper with an input valve at the top, and a bottom plate with a steam blowing nozzle at the bottom. is used.

When blowing steam for heating and foaming, the inside of the foaming tank is evacuated or purged as in the known method, and cooling air is appropriately added to the steam at a rate of 0.1 to 0.3 kg/c++1 to reach a temperature of 102°C. Adjust the amount and blow in.

At this time, if the temperature exceeds 102°C, blocking will occur and increase, so it is preferable to keep the temperature below 102"C as much as possible. That is, the steam source pressure is 1.2kg/c, and the pressure inside the tank is 0.2~0. Foaming is carried out at a pressure of about 12 kg/c++IG, and the pressurization of this first stage and the second stage described below are carried out under substantially the same conditions.If the tank internal pressure exceeds 0.2 kg/ci, a blocking problem will occur.

In this way, heating and foaming progresses to a predetermined level before reaching the target level, which is the target level of 7.
A capacity ratio of 5 to 95%, preferably 90 to 95%, is set by a separate level meter or by timer control, and once this level is reached, heating is stopped,
Intermediate cooling, which is an important feature of the present invention, is performed. in this case,
If it is less than 75%, it is not preferable because the pressurizing time in the subsequent second stage of heating and foaming will take a long time.

Rather, it is more advantageous to make it 90% or more.

This intercooling generally uses cooling air inside the tank, and the cooling time is 0.5 at 90°C in relation to the temperature inside the tank.
5 minutes, 1 minute at 80-83°C, and about 2 minutes at 78°C. Although there is not much difference in blocking and second stage heating time, considering the temperature inside the tank and the variation, the cooling air source Cooling for about 1 minute at a pressure of 1.5 kg/cry is effective.

After performing the intermediate cooling, the heating and foaming process is performed again, but the final temperature in the tank is set to 104° C. or lower, preferably 103° C. or lower. If the temperature exceeds 104°C, the possibility of blocking increases.

Of course, even if the temperature is 104° C., the shaft will be heated under normal pressure and adhesion to the shaft will occur, so care must be taken.

In this manner, when the target level is reached, the heating is stopped, and after air cooling, etc., the prefoaming of the present invention is completed by taking out the foamed particles.

In the above-mentioned pre-foaming according to the present invention, each temperature indicates the indicated value of the thermometer of the existing steam blowing line and the thermometer in the tank, and even if there is a difference in the indicated value, both can be adjusted by adjusting the steam pressure and air amount. It is possible.

Figures 1 and 2 compare the heating temperature and tank pressure in the pre-foaming process with those in conventional normal foaming, with (a) showing the present invention and (rJ) the conventional foaming process. This is the case.

As can be seen from the figure, in the present invention, the heating temperature decreases once midway through, supporting intermediate cooling, but such a decrease is not observed in the conventional case.

In addition, in the present invention, there is a normal pressure in the tank for about 1 minute between the first stage and the second stage, but such a region does not exist in the conventional case.

That is, the pre-foaming method of the present invention is clearly different from the conventional conventional invention.

Figure 3 shows the increase in foaming ratio between the different methods of the present invention as described above and the conventional normal foaming method. -J- rises and is once in a parallel state during the intermediate cooling process, but the foaming power accumulated during the second stage of heating and foaming rises again, and at this time, a state in which the magnification can be increased is achieved, whereas in the conventional In the case of foaming, the occurrence of blocking increases in the range shown by diagonal lines, and there is no possibility that the foaming ability will deteriorate further, which supports the high magnification in the case of the present invention.

Next, a specific example of preliminary foaming by the method of the present invention will be shown.

(Example 1) Expandable polystyrene resin particles (Kaneka Raw Materials 5GBS) containing 5.1% butane gas as a blowing agent were used as raw material particles, and the original pressure of the blown steam was 1. okglct&, tank pressure 0. 2kg/, ff1. Cooling air pressure 1゜5kg
Preliminary foaming was carried out under the conditions shown in Table 1 below.

Note that the level in intermediate cooling was set to 90% of the target level.

On the other hand, for comparison, ordinary foaming was performed and the results are also listed in Table 1.

The comparison results are as shown below.

As can be seen from the table above in Table 1, in the conventional pressure foaming, there was resin adhered in the tank and there was a lot of blocking, but in the intermediate cooling addition method of the present invention, the heating time was short and the amount of blocking was small.

In addition, when secondary molding was performed using the pre-expanded particles, the product according to the present invention was able to obtain a good product after aging for 2 to 3 hours and had good moldability. It took more than 5 hours to ripen.

(Example 2) Using expandable polystyrene resin particles containing 4.8% butane gas as a blowing agent (Kaneiki raw material 5GBS) as raw material particles, the steam blowing pressure, tank internal pressure, and cooling air pressure were set as in Example 1, and the following Preliminary foaming was performed under the conditions shown in Table 2. Note that the level in intercooling was set at 92% of the target l/bel.

Further, for comparison, normal foaming was performed and the results of comparison between the two are also listed in Table 2.

As shown in Table 2 above, it is understood that in conventional pressurized foaming, a large amount of resin adhered in the tank and there was a lot of blocking, but in the method of the present invention, the heating time is short and there is little blocking.

In addition, although the moldability was good in all cases, the aging time for the pre-expanded particles according to the present invention was extremely short, and whereas the conventional method required 5 to 6 hours, 2 to 3 hours was sufficient, resulting in good quality. of products were obtained.

(Effects of the Invention) As described above, the present invention is capable of charging a predetermined amount of expandable thermoplastic resin particles into a foaming tank, and heating and foaming them while stirring. This is a method that first performs intermediate cooling by blowing cooling air, and then performs the second stage of heating and foaming again.Once heated and foamed to a predetermined level, it is temporarily cooled to give an effect similar to that in ripening. be done. The reason for this effect is that when the raw material particles come into contact with the cooling air, the blowing agent contained inside the particles is accumulated and retained within the particles without escaping, and during this time it is held more uniformly inside the particles, and the blowing agent It is assumed that absorption of 20% of the amount occurs, resulting in an increase in foaming power upon reheating.

However, since it enables heating and foaming without reaching the temperature at which blocking occurs, it has the remarkable effect of achieving high-magnification foaming with almost no blocking even with raw material particles containing a small amount of foaming agent, compared to conventional methods. , it is possible to shorten the aging time and achieve even higher foaming ratio.

Further, as shown in the above-described specific examples, the method of the present invention has an industrial effect of shortening the heating time and contributing to improving productivity by shortening the pre-foaming cycle.

The inventions according to claims 2 and 3 realize further practical effects by specifically implementing the method of the present invention.

[Brief explanation of the drawing]

Figure 1 (() (11)) and Figure 2 (() (D) are charts showing changes in heating temperature and tank pressure in the pre-foaming method. (+7)
is the case of normal pressure foaming for comparison. In addition, Figure 3 (() (+7) is a chart showing the increase in foaming ratio in the case of the method of the present invention and in the case of conventional pressurized foaming for comparison. (A) is for the method of the present invention and (0) is for the comparison. be.

Claims (1)

[Claims] 1. Putting a predetermined amount of expandable thermoplastic resin particles into a foaming tank,
In the method of heating and foaming while stirring, as foaming progresses, heating is temporarily stopped at a predetermined level before reaching the target level, cooling air is blown in to cool the foamed particles, heating and foaming is performed again, and then, When the target level is reached, heating is stopped again and after cooling,
A method for pre-foaming expandable thermoplastic resin particles, characterized by taking out expanded particles. 2. Set the predetermined level before reaching the target level to 75, which is the target level.
The method for pre-foaming expandable thermoplastic resin particles according to claim 1, wherein the volume ratio is ˜95%. 3. Blow steam into the foaming tank to make the inside of the tank 100~1
The foamable thermoplastic resin particles are heated and foamed by maintaining the temperature at 04°C, and the steam blowing is stopped at a volume ratio level of 90 to 95% of the target level, and cooling air is blown for 30 seconds to 2 minutes to heat the inside of the tank to 90 to 95%. 2. The method for pre-foaming expandable thermoplastic resin particles according to claim 1, characterized in that the particles are cooled to 75[deg.] C., and then steam is blown into them again to carry out heating and foaming to reach a target level.