JPS6220221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides low density foamed (highly foamed)
The present invention relates to a method for producing pre-expanded styrenic resin particles.

Conventionally, the widely used method for primary foaming (pre-foaming) of expandable styrenic resin particles involves contacting the particles with steam in an open system under atmospheric pressure, and then blowing the foamed particles continuously or intermittently. Some things are discharged to the outside of the foaming tank. In this method, the foaming and expansion of styrenic resin particles depends on the size of the particles.
Although it depends on the composition, in order to finally obtain a good foamed molded product, it is not possible to pre-foam to a high degree of foaming.

On the other hand, if the system is not open to atmospheric pressure, but is closed, and the air inside the foaming tank is first reduced in pressure using a vacuum pump, etc., and then foaming particles and steam are introduced for primary foaming, an open system is created. It is known that it is easier to obtain a higher degree of foaming than by (Japanese Patent Publication No. 43-18635) However, even with this method, pre-expanded particles having a sufficiently high degree of expansion (low density) could not be obtained.

As mentioned above, it is not possible to obtain pre-expanded particles with a high degree of expansion using existing techniques, but as a result of the inventors' extensive research to elucidate the cause of this,
It was found that this is due to the effect of air present when styrene resin particles come into contact with steam. The presence of air (more precisely, a gas whose permeation rate through a styrene resin membrane is significantly lower than that of steam) around the foam particles inhibits foam expansion. In order to eliminate only the influence of air, the above-mentioned method of reducing the pressure inside the foaming tank and increasing the degree of pressure reduction would be sufficient, but this would be disadvantageous in terms of equipment and operation, and furthermore, it would be a closed system. Therefore, the styrene resin particles cannot escape the influence of the blowing agent that they spit out themselves during the foaming process.

The present inventors conducted research on a method for efficiently obtaining pre-expanded particles with a high degree of foaming by preventing the foaming inhibiting effect of the blowing agent escaping from the air and particles, and as a result, the present invention was achieved.

That is, in the present invention, expandable styrenic resin particles containing an organic blowing agent containing 50% by weight or more of a gaseous organic compound at normal temperature and normal pressure are brought into contact with substantially only steam under a pressure greater than atmospheric pressure. The present invention relates to a method for producing pre-expanded styrenic resin particles characterized by heating and foaming them.

In the present invention, expandable styrenic resin particles are particles of styrenic resin containing 50% by weight or more of styrene impregnated with an organic foaming agent.

The styrene resin is polystyrene, a copolymer of styrene and other vinyl monomers,
Here, other vinyl monomers include acrylonitrile, butadiene, acrylic acid, acrylic acid esters such as ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate,
methacrylic acid esters such as cetyl methacrylate;
Styrene derivatives such as α-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene,
Examples include maleic anhydride, maleic acid, and maleic acid monoalkyl ester. In addition, the styrene resin may be a blend of polystyrene and a homopolymer or copolymer of the other vinyl monomers, or a blend of polystyrene or a styrene copolymer with another thermoplastic resin (for example, polyethylene, polypropylene, polyphenylene, etc.). The styrene resin may also contain fine inorganic powder such as talc or calcium carbonate.

The styrenic resin of the present invention contains 50% by weight of styrene.
If the content is less than that, it is difficult to balance the steam permeability of the resin with the strength of the cell partition walls after heat treatment and foaming, and a low-density (highly foamed) foam cannot be obtained.

The above-mentioned organic blowing agents are organic compounds that are gaseous at room temperature and pressure, and include aliphatic hydrocarbons such as butane and propane, and halogenated hydrocarbons such as dichlorodifluoromethane.
℃ or less is preferable.

In the present invention, other organic compounds can be used as the organic blowing agent, such as those that are liquid at normal temperature and pressure, but the amount used is 50% by weight or less, preferably 30% by weight or less based on the total amount of the blowing agent. Ru. If such a blowing agent exceeds 50% by weight, it is difficult to obtain pre-expanded particles with a practically low density (highly expanded). The blowing agent is usually 1% per styrene resin.
~20% by weight.

The above-mentioned blowing agent styrenic resin particles can be produced by a conventionally known method such as using aqueous suspension polymerization.
When using aqueous suspension polymerization, the blowing agent can be impregnated into the styrenic resin particles during polymerization, after polymerization, or by suspending the obtained styrenic resin particles in water again and press-fitting the resulting styrenic resin particles. .

The heating and foaming of the expandable styrenic resin particles is as follows:
It is carried out using almost only steam and at a pressure higher than atmospheric pressure.

Here, "substantially only steam" means that steam accounts for 2/3 or more of the heating medium for the expandable styrene resin particles. Preferably, the heating medium is 100% or nearly 100% steam. Heating media other than steam include heated air, nitrogen, etc. However, if the amount of such heating media increases, foaming of the expandable styrenic resin is inhibited, so highly expanded pre-expanded styrenic resin particles cannot be obtained. It becomes difficult and undesirable.

The heating and foaming is carried out at a pressure higher than atmospheric pressure, but a pressure higher than atmospheric pressure by 1 Kgf/cm ² or less is sufficient. In other words, 1Kg in gauge pressure
f/cm ² or less is sufficient. Further, in order to obtain the effects of the present invention, the gauge pressure is preferably 0.05 Kgf/cm ² .
If the pressure is too high, it will be easier to obtain a high degree of foaming, and the time required to reach the desired degree of foaming will be shortened, but more foam particles will adhere to the walls of the foaming tank, and it will be difficult to adjust the degree of foaming. . The standard for setting the pressure is the degree of dissipation of the blowing agent to the outside of the particle, which is determined by the softening point of the base resin and the affinity between the blowing agent contained inside and the styrene resin. However, the accuracy of setting the internal pressure of the foaming tank is not a decisive requirement. The fact that it is maintained at a pressure higher than atmospheric pressure in an atmosphere consisting essentially of only steam produces surprising effects that could not be obtained with conventional foaming systems. The optimum pressure setting can be easily determined by trial and error a few times.

To create this pressurized state of almost steam only, first blow steam into the foaming tank,
The air is expelled, and then steam is blown in to create a pressurized state (pressure higher than atmospheric pressure). In order to create a pressurized state of almost only steam, a more efficient method is to install a steam inlet to the foaming tank at the bottom and an exhaust port at the top, so that the steam is mixed inside the foaming tank and the stagnation area is minimized. This can be achieved by controlling the amount of steam blown into the foaming tank and the amount of mixed gas discharged from inside the foaming tank.

The heating and foaming can be stopped by stopping the blowing of steam when a predetermined foaming degree is reached, and discharging the pre-foamed styrenic resin particles into the atmosphere as quickly as possible.

In carrying out the present invention, the foaming tank may be made pressure resistant and closed to the extent that it can withstand pressurized conditions, and may be partially open.

An example of a foaming device that can be used to implement the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a foaming device that can be used for the present invention.

A stirring blade 2 in the foaming tank 1, a shaft 3 to which the stirring blade 2 is attached, a power 4 for rotating the shaft 3, and further,
A baffle bar 5 is provided. When foaming under pressure,
It is preferable that the foaming tank 1 has a pressure-resistant structure that can be sealed. Expandable styrene resin particles weighed in advance are introduced into the foaming tank from the hopper 6. An injector valve 7 is provided at the bottom of the hopper 6 and is closed after the particles are injected. Then, the steam valve 8 is opened and steam is blown into the foaming tank 1 from the steam blower 9. At the beginning of steam blowing, the exhaust valve 10 is operated while being opened to exhaust the air in the foaming tank 1. After a certain period of time (usually about 10 to 60 seconds),
Exhaust valve 10 is closed. At this time, the exhaust valve 10 is not completely closed to prevent the foaming tank 1 from being deformed due to depressurization due to erroneous operation, and to completely exhaust the remaining air in the foaming tank and the gas (foaming agent) escaping from the particles. It can be left slightly open so that it can be opened.

By blowing the steam, the particles in the foaming tank 1 are expanded and the upper surface of the particle layer rises. During this time, if pressurized foaming is performed, check the pressure inside the foaming tank 1 with a pressure gauge.
1 and manually or by controller 1 if necessary.
2, the degree of opening and closing of the steam valve 8 is adjusted. Level detector 1 indicates that the degree of foaming has reached a predetermined value.
3 is designed to detect the upper surface of the foamed particle layer. This signal is sent to the controller 12, and the exhaust valve 10 is fully opened, the steam valve 8 is closed, and the foamed particle discharge valve 14 is further opened to cause the foamed particles to fall into the receiver 15 and be stored therein. Ru. After the foamed particles are discharged, the foamed particle discharge valve 14 is closed, and the above operation is repeated.

Confirmation that the degree of foaming has reached a predetermined value can also be carried out by using a timer or by observing with the naked eye through a peephole. Opening can be done manually.

Next, examples of the present invention will be shown.

Example 1 Expandable polystyrene particles with an average particle diameter of 1.05 mm [Hibeads SB-TK (trade name, Hitachi Chemical Co., Ltd.); blowing agent composition: 60% by weight of n-butane, 40% by weight of i-butane; contains blowing agent 5.3% by weight; cyclohexane content 1.5% by weight] using the foaming device shown in Figure 1 (however, a peephole was used instead of a detector).
Foaming was carried out using

Steam of 7 kgf/cm ² is depressurized into the foaming tank 1 (effective internal volume 1200) while rotating the stirring blade 3.
Kgf/cm ² was blown through the steam valve 8 to preheat and replace the air in the tank with steam. Next, 17 kg of the expandable polystyrene particles were put into the foaming tank 1 from the hopper 6, and steam was blown into the foaming tank 1 by opening the steam valve 8 while leaving the discharge valve 10 open. After 20 seconds had elapsed after the steam was blown, the opening degree of the discharge valve 10 was reduced to approximately 1/2. The pressure inside the foaming tank 1 begins to rise and rises to 0.2Kgf/cm ² for about 20 seconds.
As a result, the pressure gauge 11 operates, and the controller 12 starts repeating activation and deactivation until the pressure inside the foaming tank 1 reaches 0.2.
It became constant at Kgf/ ^cm2 . After approximately 40 seconds, the introduced particles expanded and the top surface of the foamed particle layer reached the preset height inside the viewing window (volume 1000 below the set position), so the steam valve 8 was closed. Subsequently, the exhaust valve 10 was fully opened to stop foaming. Next, the foamed particle discharge valve 14 was opened and the foamed particles were taken out. The degree of foaming of this product was measured and found to be 71 ml/g. After drying this and leaving it in an atmosphere at 25° C. for about 20 hours, the degree of foaming was measured again and it was 71 ml/g. Using this, we performed steam foam molding of a box-like object with a wall thickness of 20 mm and an internal volume of 20 mm, and the shape and dimensions were accurate, and the appearance was smooth and beautiful.

Comparative Example 1 Hibeads SB-TK used in Example 1 with the blowing agent (n-butane, i-butane) reduced to 1.8% was impregnated with pentane (a mixture of n-pentane and i-pentane). A sample was prepared that differed only in the foaming agent from the expandable polystyrene used in Example 1.
Other than polystyrene, this product contains 0.7% by weight of i-butane, 1.0% by weight of n-butane, 0.7% by weight of i-pentane, 3.3% by weight of n-pentane, and 1.5% by weight of cyclohexane.
% by weight. This was foamed under the same operation and conditions as in Example 1, but the degree of foaming after 1 hour of foaming was 63 ml/g, and the foamed particles had clearly shrunk. When this was left in an atmosphere at 25° C. for 20 hours, the shrinkage state of the expanded particles disappeared. The foamed particles had a degree of foaming of 71 ml/g. Next, when a molding experiment was carried out using the expanded particles in the same manner as in Example 1, the product was so deformed that it could not be put to practical use.

According to the present invention, practical highly expanded (low density) pre-expanded styrenic resin particles can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a foaming device that can be used in the present invention. Explanation of symbols, 1... Foaming tank, 2... Stirring blade, 3
... shaft, 4 ... power, 5 ... baffle bar, 6 ... hopper, 7 ... feeder valve, 8 ... steam valve, 9 ...
...Steam blower, 10...Exhaust valve, 11...Pressure gauge, 12...Controller, 13...Level detector,
14...Discharge valve, 15...Receiver.

Claims (1)

[Claims] 1 50% by weight of organic compounds that are gaseous at room temperature and pressure
A method for producing pre-expanded styrenic resin particles, which comprises heating and foaming expandable styrenic resin particles containing the above-mentioned organic blowing agent by bringing them into contact with substantially only steam under pressure equal to or higher than atmospheric pressure.