DE1294663B - Process for the production of pre-expanded polystyrene granulate - Google Patents

Description

The subject of the invention is a process for the production of pre-expanded polystyrene granules by briefly heating polystyrene granulate containing propellant at increased pressure through action of vapors of a boiling liquid inert towards polystyrene 5 to a temperature in which the polymer only weakly softens, and cooling, which is characterized in that one the granulate under pressure reduction in the steam atmosphere, optionally with simultaneous introduction of air and / or the gases inert to polystyrene.

British patent specification 715 100 describes "a process for the production of polystyrene foam, in which granulated polystyrene containing a blowing agent, e.g. B. a volatile, organic liquid, contains, heated in a closed mold to such a temperature that the propellant evaporates and the polystyrene is foamed so that it fills the mold. If with this and other acquaintances Process a foam of low density is desired, the granulated Polystyrene are subjected to a pre-expansion, in which the granulate is partially foamed by it is brought to a temperature of 80 to 95 ° C in a closed mold for about 4 to 8 minutes. The heating is generally carried out in hot water or steam. Before use for the actual molding process, the pre-expanded granulate must be depending on the particle size Matured for 16 to 24 hours.

Molded parts which are produced from granulate according to the above-described process, which has been subjected to a single pre-expansion, have a density of about 16 kg / m ³ , but it is possible to add molded parts with densities down to about 8 kg / m ³ for 3s obtained when the granulate is subjected to two or more prefoams with the inclusion of appropriate maturing times.

From the German patent specification 1074 854 a method for prefoaming of propellant-containing Known plastic particles in which the pre-expansion is carried out in a steam atmosphere under pressure will. It is emphasized there that this process for the production of foam bodies with low Volume weight is not suitable and that when prefoaming to achieve the greatest possible Degree of expansion of the expansion no substantial counter pressure may be opposed. Tn the Therefore, it is recommended to use the pre-expansion at atmospheric pressure or at one of these to apply only slightly excessive pressure.

The process according to the invention results in pre-expanded polystyrene granules which can be used for production of molded parts with a very low density without it maturing for a long time must become.

The granules are expediently placed in a closed container above a boiling one Liquid and lets the pressure rise for a certain time and then relaxes through a drain valve, so that the pressure in the device falls to normal pressure. The material then cools in , an atmosphere made up of the steam and air that were in the vessel is sucked in.

In general, the pressures in the pressure vessel are allowed to rise to 0.35 to 1.05 atmospheres and the mixture is turned a heating time of 30 to 100 seconds. The exact values of the pressure and the heating time depend on the desired density of the end product, but pressures and heating times can be outside these ranges are used as long as the temperature in the container is so high that the polymer softens, but is below the limit at which the polymer softens so much that the blowing agent can escape from it.

The liquid used to heat the granulate in the pressure vessel is preferably used Water, however any other liquid inert to polystyrene can be used. the Liquid can be miscible or immiscible with the propellant.

The pressure vessel is preferably depressurized in air, but any number can optionally be used Gases that have diffusion properties similar to air and are inert to polystyrene are used will. For example, it is possible to put oxygen, nitrogen or carbon dioxide in the vessel initiate.

Customary volatile organic liquids, such as petroleum ether, with a boiling range are used as propellants between 30 and 70 ° C, pentane, hexane, heptane, cyclopentane, cyclohexane and cyclopentadiene in question.

example

The values in the following tables illustrate the dependency of the density of the finished product on the size of the granules of the foamable material, the pressure in the vessel and the time until this pressure is reached and the cooling time.

Tabel

attempt Grain size
of the granules Vapor pressure
in the autoclave Time to reach
of pressure, starting
of normal pressure Cooling time Mass density Appearance mm atü Seconds kg / m » 1 0.7 to 2.4 0.35 30th 50 minutes 24.83 no shrinkage 2 0.7 to 2.4 0.7 70 50 minutes 10 no shrinkage 3 0.7 to 2.4 1.05 100 50 minutes 5.45 no shrinkage 4th 0.7 to 2.4 1.05 100 10 mins 12.18 greatly shrunk 5 0.7 to 2.4 1.05 100 20 minutes 9.55 slightly shrunk 6th 0.7 to 2.4 1.05 100 30 minutes 9.55 slightly shrunk 7th 0.7 to 2.4 1.05 100 40 minutes 7.85 no shrinkage

Table 1 (continued)

attempt Grain size
of the granules Vapor pressure
in the autoclave Time to reach
of pressure, starting
of normal pressure Cooling time Mass density Appearance mm atü Seconds kg / m ³ 8th 0.7 to 2.4 1.05 100 16 hours 7.69 no shrinkage 9 3.4 1.05 100 50 minutes 8.49 no shrinkage 10 2.4 to 3.4 1.05 100 50 minutes 7.85 no shrinkage 11 2.05 to 2.4 1.05 100 50 minutes 6.73 no shrinkage 12th 1.2 to 2.04 1.05 100 50 minutes 5.61 no shrinkage 13th 0.85 to 1.2 1.05 100 50 minutes 5.61 no shrinkage 14th 0.75 1.05 100 50 minutes 17.62 no shrinkage

The following temperatures prevail in the autoclave during cooling:

Tabel' 2 Temperature in the air Time after relaxing space in the autoclave of the autoclave to normal pressure OC Minutes 82 4th 79 8th 75 12th 73 15th 69 21 66 25th 61 31 52 40 51 45 48 50

In the known methods, if a petroleum ether with a molecular weight of about 72 is used in an amount of about 6 percent by weight as a propellant, a cell body with an absolute specific volume of the order of 26 cm ³ / g would have to be obtained when at 100 ° C is foamed. In practice, foaming to about 40 cm ^s / g is achieved.

^{In the process according to the invention, an absolute specific volume of the order of 180 cm 3} / g is obtained in a single operation by foaming at a temperature of 108 to 120 ° C. (vapor pressure 0.35 to 1.05 atmospheric pressure). This number is considerably higher than the calculated value based on the evaporation of the petroleum ether.

The products obtained according to the invention can be processed by any known method into foam articles which have a much lower density than the previously known articles. For example, it is possible to produce molded parts with a density of 4.8 kg / m ³ by molding a material which has been produced by the method according to the invention with a relaxation time of the pressure vessel of about 50 minutes.

Claims (1)

Claim: Process for the production of pre-expanded polystyrene granulate by brief heating of propellant-containing polystyrene granulate at increased pressure by the action of Steaming a polystyrene inert boiling liquid to a temperature at which softens the polymer only slightly, and cooling, characterized in that the granules are reduced in pressure in the steam atmosphere, optionally with the simultaneous introduction of air and / or opposite Polystyrene inert gases, cools.