MXPA01007404A - Process and apparatus for producing foam and foam blocks and boards produced - Google Patents

Abstract

CO2 is used as foaming agent and a first and a second control agent are injected into the plastified mixture. The first agent is used to dissolve and refrigerate the plastified mixture and consists of ethanol while the second agent is solely used to refrigerate the plastified mixture and consists of H2O2. A sufficient amount of ethanol is injected to achieve maximum CO¿2 ?dissolution in the plastified mixture. The amount of H2O2 injected is such that the foaming caused by the ethanol is kept to a minimum. The apparatus includes devices for conditioning and feeding the foaming agent and the control agents to the plastified mixture. The blocks and boards exhibit dimensional stability and good self-extinguishing characteristics.

Description

Procedure and installation to produce foam, and blocks and foam boards produced Description of the invention The invention relates to a process and to an installation for the production of foam polystyrene, as well as to the blocks and plates (such as plates and panels) of foam obtained with them. In this technical field, documents GB-A-1 220 053 and GB-A-1 230 992 from Imperial Chemical Industries Limited (ICI) are particularly relevant. Prior to the date of application of the aforesaid British patents, synthetic resin foaming tests were carried out using substantially inert inorganic gases, especially CO2. These tests did not give the desired results, at least for foam thicknesses greater than a few mm, and the reason for this must be sought, mainly, in the low solubility of the CO2 in the polymer mixture, melt or plastic mixture (" meit ") that must be foamed, which forces to work with high pressures throughout the process (translating into higher costs), resulting in high temperatures, so that at the time of the final extrusion into the atmosphere (in what follows , "final extrusion") the temperature of the plasticized mixture is too high for a correct control of the characteristics of the foam; in addition, the polymer mixture can suffer thermal deterioration. The result is obtaining a very high density foam and only commercial grade foam sheets with thicknesses of a few mm can be achieved, since the amount of CO2, necessary to obtain greater thicknesses, can not be incorporated into the plasticized mixture.

These documents GB-A-1 220 053 and GB-A-1 230 992 established, at the end of the 1960s, the general bases for the production of certain synthetic resin foams, including polystyrene foams. In particular, GB-A-1 220 053 describes "a process for the production of foamed thermoplastic polymers.

Ref: 131552 in which the pressure of a pressurized homogeneous mixture of the molten thermoplastic polymer and a system of foaming agents is relieved, said system comprising a first foaming agent which is completely miscible with the molten thermoplastic polymer at said pressure and which is a solvent of said thermoplastic polymer under the conditions of temperature and pressure of the homogeneous mixture and a second different foaming agent having a solubility of at least 0.01% by weight in the thermoplastic polymer and a critical temperature lower than the temperature of the homogeneous mixture at the point where said pressure is relieved, said first foaming agent having a boiling point lower by 10 or more ° C at said temperature of the mixture "(claim 1). can be applied to the foaming of "polystyrene" (page 1, col.2, line 53), that "the first and second foaming agents and they are chosen to be inert with respect to the thermoplastic polymer under the pressure and temperature conditions of the pressurized container "(page 2, col. 1, lines 40-44), that "the substances most suitable for use as the first foaming agent are liquids whose boiling points at atmospheric pressure are greater than the ambient temperature" (page 2, col.2, lines 69-72) , that "Ethanof can be used as the first foaming agent (page 2, col 2, line 83), it was found that" carbon dioxide "(page 3, col 1, line 17) was a substance that could be used as the second foaming agent, it is preferable to use "as much of the second gaseous foaming agent (CO2) as possible", however, noting that this amount of C02 is usually less than 10% by weight (page 3, col. lines 29-34) and suggesting that, in fact, foaming caused by the first foaming agent (eg, ethanol), on its own, can result in a small number of bubbles or very large cells, to the detriment of the commercial value of the product (page 3, column 1, lines 10-14). In the years following the date of presentation of the aforesaid ICI patents, the industry increasingly turned to the use of carbohalogenated foaming agents (also provided in the aforementioned British patents), either alone or in diverse mixtures. Since the 1980s, however, and for environmental reasons, efforts are being made to reduce the use of carbohalogenated foaming agents and everything points to the growing use of CO2 as the main foaming agent. Among the patent documents which reflect these tendencies, the following may be cited: WO 93/22371, EP-A-0 318 846, EP-A-0 411 923, EP-A-0 464 581, EP-A-0 597 375, DE 39 43 265 A1, US 5,158,986, US 5,244,927, US 5,250,577 and US 5,269,987, some of which also involve the use of ethanol as a "foaming agent". Installations of the general type defined in the preamble of claim 7 hereof are known from EP-A-0 528 536 and US-A-4 436 679. As can be seen from the aforementioned ICI patent documents, the ideal it would be to work with a single foaming agent, in particular CO2. However, its low solubility in the polymer and the other drawbacks mentioned above require the use of CO2 in conjunction with other agents that mitigate these drawbacks. As is evident, any agent other than CO2 which is able to pass from the liquid state to the vapor state at a temperature slightly lower than that of the plasticized polymer mixture at the time of the final extrusion will inevitably and to a greater or lesser extent have a foaming effect and, in this sense, such an agent can be described as a "foaming agent", as is done, for example, in the said ICI patent documents when speaking of the "first foaming agent". But, particularly when the agents used in conjunction with CO2 are lower alcohols, the foaming effects they produce (inevitably) are generally undesirable, since they tend to give bubbles or irregular cells, predominantly large and / or open, in as opposed to the cells of the desired characteristics, produced by the use of the foaming agent itself, that is to say CO2. For this reason, agents other than CO2 will not be referred to as "foaming agents" in the present description, but rather "control agents" since, rather than being used for foaming, they are used to allow the foaming produced basically by the actual foaming agent (CO2). The inventors have experimentally found that ethanol acts as a solvent for polystyrene, thus decreasing the viscosity of the plastic mixture, which allows to work - for the same amount of CO2 incorporated in the plasticized mixture - at lower pressures in the entire production line, including the final extrusion head. The decrease in viscosity also has the effect of reducing both the internal friction of the melt and its friction with the mechanical components with which it comes in contact and, as a result, decreasing the temperature of the plasticized mixture, which It is especially important near the matrix of the final extrusion head. The present inventors have also experimentally verified the beneficial effects of ethanol by absorbing heat from the molten mixture at the time of foaming. However, the experiments of the present inventors with the use of ethanol as a foaming control agent, produced mainly by CO2, have also revealed their disadvantages, which consist, mainly, in that the foams obtained with the The use of ethanol takes a considerable time to reach the final value of some of its physical properties that are considered critical, such as its dimensional stability at high temperatures, its resistance to compression and its behavior to fire or self-extinguishing capacity, and in that (as has been said) ethanol tends to cause foaming with large and open cells. The object of the present invention is to overcome these drawbacks. The inventors have found that, when ethanol is used as a foaming control agent produced by CO2, the optimum characteristics of the foam are obtained if the ethanol is incorporated in a minimum amount and just enough to give the plasticized mixture the necessary viscosity to absorb as much CO2 as possible and to ensure that the foaming caused by ethanol is kept to a minimum. The inventors have also found that this decrease in the amount of ethanol used, by itself, would have the undesirable potential of impairing the necessary temperature drop, since one of the effects of ethanol is to act as a refrigerant of the plasticized mixture. To avoid this drawback, the inventors proposed to use a second control agent, added to the plasticized mixture after the addition of ethanol and constituted by H2O2. The fact that H2O2 does not dissolve polystyrene or modify, therefore, its characteristics makes it maintain or improve the physical properties of the foam and that it can be obtained with greater thickness than with the use of ethanol alone, as a control agent of foaming produced by CO2. The use of a much smaller amount of ethanol makes it possible to reach the aforementioned physical properties more quickly, which are considered critical (dimensional stability, resistance and self-extinguishing capacity). On the other hand, the inventors have also found that the advantages of the invention are optimized if the polystyrene used to make the polymer mixture is a polystyrene of less than about 150. 000, a melt flow rate of approximately 20 g / 10 min (ISO 1133H) and a softening temperature VICAT VST B 50 (according to ISO 306 B 50) higher than 100 ° C. The use of this low molecular weight polystyrene has the main objective of allowing the process to be carried out with a viscosity lower than that conventionally found, which allows dissolving in the plastified mixture a greater amount of CO2, decreasing the amount of ethanol used and, mainly, keeping the temperature rise inevitably produced by friction low. In view of the foregoing, the invention provides, according to a first aspect, a process for the production of foam polystyrene, in the initial stage of which a polystyrene mixture is plasticized with conventional nucleating agents, plasticizers and additives, at a pressure and at a temperature respectively higher than atmospheric pressure and at room temperature to form a "meit" plasticized mixture), which plasticized mixture decompresses and cools sharply at atmospheric pressure and at room temperature, when extruded through a final extrusion die , in which process a foaming agent intended to produce the desired foaming and constituted entirely of CO2, is injected into the plasticized mixture so that said foaming agent dissolves in the plasticized mixture, characterized in that a plasticized mixture is also injected into the plasticised mixture. and a second control agent, the first ag is intended control entity to dissolve and refrigerate the plasticized mixture and being constituted by ethanol, while the second control agent is only intended to cool the plasticized mixture and consists of H2O2, the amount of ethanol being just enough to reach the maximum possible dissolution of CO2 in the plasticized mixture and the injected amount of H2O2 being such that the foaming caused by the ethanol is kept minimal. According to an optional feature, ethanol is injected in the immediate vicinity of the CO2 injection point, and H2O2 is injected downstream from the same point, when injections of the foaming agent and ethanol have already partially cooled the plasticized mixture. According to another optional characteristic, immediately before the final extrusion, the plasticized mixture to be extruded is constituted by 2.25-5% by weight of CO2, by 0.3-3.0% by weight of ethanol and by 0.2- 1, 7% by weight of H2O2, the rest being polystyrene and nucleating agents, plasticizers and conventional additives. According to another optional characteristic, immediately before the final extrusion, the plasticized mixture to be extruded is constituted by 3.0-4.0% by weight of CO2, by 0.6-1, 25% by weight of ethanol and by 0, 25-1% by weight of H2O2, the rest being polystyrene and nucleating agents, plastificant.es and conventional additives. According to another optional characteristic, the temperature and pressure profiles of the process are maintained with decreasing temperature values, in the order of 200 to 100 ° C and with decreasing pressure values in the order of 20 to 7.6 MPa (200 bar and 76 bar, approx.), respectively, always maintaining CO2 in supercritical conditions, until the final extrusion. According to another optional feature, polystyrene has a molecular weight of less than 150,000, a melt index of approximately 20 g / 10 min (ISO 1133H) and a softening temperature VICAT VST B 50 (according to ISO 306 B 50) greater than 100 ° C. According to another aspect, the invention provides an installation for carrying out the process defined above, which includes an extruder-laminator and a dynamic mixer arranged in series, the first of which has means for effecting the initial plasticization of the mixture and the injection of the CO2 and ethanol, and the second of which is provided with a cooling device and feeds the plasticized mixture to an extrusion head that carries the final extrusion die, there being, between the extruder-laminator and the dynamic mixer, means for the injection of H2O2, in which installation, immediately after the extruder-laminator and immediately after the dynamic mixer, are respectively interspersed a first static mixer and a second static mixer, and the means for injecting H2O2 are disposed between the extruder-laminator and the first static mixer. According to another optional feature, upstream of the extruder-laminator, the installation includes a first tank for the reception of C02 from an external source, maintaining the first tank under conditions of pressure and temperature of the same order as those of the external source, a second tank of CO2 in which it is maintained at a pressure of about 7 MPa (70 bar, approx.) and at room temperature, and an injection pump to pump CO2 from the second tank and inject it into the extruder-laminator and capable of raise the CO2 pressure from about 7 MPa (70 bar, approx.) to about 30 MPa (300 bar, approx.). According to another optional characteristic, the passage of CO2 from the first tank and to the second tank is carried out through another pump, downstream from which is provided a heating device that raises the temperature of the C02 leaving the other pump to approximately room temperature. According to another optional feature, the passage of CO2 between the second tank and the injection pump passes through a cooling device that lowers the temperature of the CO2 to prevent its overheating during the pumping operation. According to another optional feature, the injection pump is cooled. According to another optional feature, cooling of the injection pump is effected by cooling its head. According to another optional characteristic, the procedure is carried out in an installation as defined in the immediately preceding paragraphs and includes the steps of: a) initially plasticizing in the extruder-plasticizer a mixture of polystyrene with nucleating agents, plasticizers and conventional additives, being the polystyrene of a molecular weight less than about 150,000, a melt index of about 20 g / 10 min (ISO 1133H) and a softening temperature VICAT VST B 50 (according to ISO 306B50) higher than 100 ° C; b) injecting into the plasticized mixture, in the extruder-laminator, at a pressure in the order of about 20 MPa (200 bar, approx.), on the one hand C02 and on the other hand ethanol; c) passing the plasticized mixture from the extruder-plastifier to the first static mixer and injecting the H2O2 into the plasticized mixture, between both; ) homogenizing the plasticized mixture in the first static mixer; e) passing the plasticized mixture from the first static mixer to the dynamic mixer in which the homogenization is accompanied by a decrease in the temperature and the pressure to which the plasticized mixture is subjected; f) passing the plasticized mixture from the dynamic mixer to the second static mixer, in which the decrease in temperature and pressure to which the plasticized mixture is subjected continues; g) passing the plasticized mixture from the second static mixer to the final extrusion head, where the temperature and pressure are controlled so that they are close to 100 ° C and 7.6 MPa (76 bar, approx.), respectively, always maintaining CO2 under supercritical conditions, until decompression or final extrusion; the operating conditions being such that at the time of final extrusion, the plasticized mixture is constituted by 2.25-5% by weight of CO2, by 0.3-3.0% by weight of ethanol and by 0.2- 1, 7% by weight of H2O2, the remainder being polystyrene and nucleating agents, plasticizers and conventional additives, than the blocks or plates produced, after 42 days of production and after having been subjected for 2 days to 70 ° heating C, have suffered a decrease in each of its linear dimensions (length, width and thickness) less than 5% with respect to the original dimension, and that the test to determine the coefficient of self-extinction, made on said blocks and plates one hour after its extrusion, give a flame height of less than 11 cm. According to another aspect, the invention provides blocks and foam plates produced using the procedure or installation indicated above, characterized because, 42 days after production and after having been subjected to heating at 70 ° C for 2 days, they have suffered a decrease in each of its linear dimensions (length, width and thickness) less than 5% with respect to the original dimension. According to another optional feature of the blocks and plates of the invention, the test for determining the coefficient of self-extinction, carried out on them one hour after extrusion, gives a flame height of less than 11 cm. Other characteristics, objectives and advantages will be evident from the following description complement, when read together with the attached drawings, in which: Fig. 1 represents a very schematic view of an installation in which the procedure of the invention and Fig. 2 represents a schematic view of the conditioning and feeding arrangement of the CO2 in the same installation. Referring first to Fig. 1, the installation includes an extruder-laminator 1 and a dynamic mixer 2, arranged in series or tandem. The extruder-laminator 1 receives the initial charge of polystyrene and nucleating agents, plasticizers and conventional additives, as is ischematized by means of the feed hopper 3, which feeds said initial charge or mixture into the plasticizing extruder-1 and homogenizes to give a plasticized mixture (in fact, the plasticization and homogenization of the plasticized mixture continues throughout the installation until immediately before the final extrusion). The general structure of the extruder-laminator 1 is that of a conventional plasticizing plant and is prepared to work at pressures above 20 MPa (200 bar, approx.) and at temperatures above 225 ° C. In this embodiment of the invention, the extruder-laminator 1 is further provided with injection devices 4 and 5, respectively for CO2 and ethanol, at temperatures close to the ambient and at pressures in the order of 20 MPa (200 bar, approx. .). Between the extruder-laminator 1 and the dynamic mixer 2, there is provided a device 6 for the injection of H2O2, at a temperature close to ambient and at a pressure greater than 20 MPa (200 bar, approx.). The dynamic mixer 2 has the purpose of leaving the plasticized mixture in the optimum conditions for its extrusion and foam- 22 final output, which will occur at the outlet of the matrix 7, provided at the exit end of the final extrusion head 8. In the dynamic mixer 2, the dilution of the plasticized mixture by the ethanol and the C02 solution in the plasticized mixture is continued. Also produced in said dynamic mixer 2 is the cooling of the plasticized mixture by means of a cooling device assisted by exchangers, which is schematized with cooling stages 9, 10, 11 and 12. The final extrusion head 8 and its matrix 7 do not form part of the invention and should therefore be considered conventional, in the same way as the discharge conveyor 13 of the foam 14. In the embodiment shown, immediately after the extruder -plasticizer 1 and the dynamic mixer 2 are respectively interposed a first static mixer 15 and a second static mixer 16, to reinforce the homogenization action of the extruder-laminator 1 and the dynamic mixer 2. In this type of installation, it has been found convenient to use the conditioning and CO2 feeding arrangements of Fig. 2. These provisions include a first tank 20 for receiving CO2 from an external source 21 (the first tank 20 being kept under a condition of pressure and temperature of the same order as those of the external source 21), a second tank 22 of CO2 that is maintained at a pressure of about 7 MPa (70 b) ar, approx.), and a CO2 injection pump 25, through device 4, in the extruder-laminator 1 and capable of raising the CO2 pressure from about 7 MPa (70 bar, approx.) to about 30 MPa (300 bar, approx.). Preferably, the passage of CO2 from the first tank 20 and to the second tank 22 is carried out through another pump 23, downstream from which a heating device 24 is provided which raises the temperature of the CO2 leaving another pump 23 to approximately the environment. The passage of CO2 between the second tank 22 and the injection pump 25 takes place through a cooling device 26 which lowers the temperature of the CO2 to prevent its reheating during the pumping operation of CO2 towards the extruder-laminator 1, a through the device 4. The injection pump 25 is cooled by passing coolant through its head.

EXAMPLES Example 1: Effect of the use of low molecular weight polystyrene on CO2 foaming controlled with ethanol alone In all of the Tests 1-6 which will be indicated below, polystyrene foam is produced by extrusion in the above-described installation. The foam obtained at the outlet of the lips of the matrix 7 with the final extrusion of the plasticized mixture has a width of 630 mm and a thickness of 60 mm. In a first series of tests (Tests 1 and 2), a polystyrene mixture based on conventional polystyrene, of molecular weight (Mw), is introduced in the extruder-laminator 1, with a flow rate of 400 kg / h. 200. 000, with a flow index ("meit flow index", MFI) of 7.5 and with a softening temperature VICAT 50 N (ISO 306 B 50) of 102 ° C. The mixture includes 0.4% talc to regulate cell size and 2.5% hexabromocyclododecane as a flame retardant. Once the polymer mixture is initially plasticized, 3.0 pph (3.0 parts by weight per 100 parts by weight of polymer blend) of the foaming agent, CO2, and 4.1 pph of ethanol as the sole agent are injected therein. of control. The foams obtained are simply acceptable. In a second series of tests (Tests 3 and 4), the conventional polystyrene is replaced by polystyrene of molecular weight (Mw) of 130,000 (SEC), with a melt index (MFI) 200 ° C-5kg (ISO 1133 H) of 23 and a softening temperature VICAT50 N (ISO 306 B 50) of 101 ° C. It is observed that the pressures decrease in the extruder-laminator 1 and in the dynamic mixer 2, but that the pressure in the final extrusion head 8 is maintained - as desired - higher than the critical CO2 pressure. Compared with Tests 1 and 2, the foams of Tests 3 and 4 present a better quality extrusion skin, more uniform on the whole surface and finer, without deterioration of the other technical characteristics. In a third series of tests (Tests 5 and 6), the low molecular weight polystyrene of tests 3 and 4 of the second series will also be used and the amount of control agent (ethanol) is decreased to 3.1 pph. As can be seen in Table 1 (Tests 5 and 6), the pressures increase and reach the same order of magnitude as those observed in Tests 1 and 2. It should be noted that the extrusion reference temperature, taken in the head 8 of final extrusion, remains in the same order of magnitude. With these new conditions (lower amount of control agent) the same good characteristics of the foam (including good quality of the extrusion skin) are obtained that are observed in the tests of the second series. The results obtained in the trials are summarized in Table 1. Table 1 P1 = pressure in the extruder-laminator 1. P2 = pressure in the dynamic mixer 2. P3 = pressure in the final extrusion head 8. Temp. ref. = Extrusion reference temperature, taken at the final extrusion head.

Skin quality: A = Acceptable. Fairly uniform skin without openings. B = Good. Skin uniform and thin. From the results shown in Table 1, it can be deduced that the use of low molecular weight polystyrene produces foams of better quality than those obtained with conventional polystyrene, maintaining lower pressures (Tests 3 and 4) in the extruder-plastifier 1 (P .,), without undesirably lowering the pressures (P3) in the final extrusion head 8.

Example 2: Effect of the use of [CO2 + ethanol] and [CO2 + ethanol + H2O2] All of the Tests 7-13 that will be indicated below were carried out under the same conditions as those described in the first paragraph of the previous Example 1. The products tested have the thicknesses indicated in Table 2 below. A first series of tests (Tests 7-10) was carried out using conventional polystyrene (Tests 7 and 8) and low molecular weight polystyrene (Tests 9 and 10), using only ethanol as a control agent. In a second series of tests (Tests 1 1-13), a mixture of polystyrene of molecular weight (Mw) of 130,000 (SEC), with an MFI 200 ° C-5kg (ISO 1 133 H) of 23 and a temperature of softening VICAT 50 N (ISO 306 B 50) of 101 ° C, with 0.6% of talcum powder to regulate cell size and 2,5% of hexabromocyclododecane as a flame retardant, is introduced into the extruder-laminator 1 with a flow rate of 450 kg / h. Once the polymer mixture is initially plasticized, 3.5 pph (3.5 parts by weight per 100 parts by weight of polymer mixture) of the foaming agent, CO2, is injected between 1 and 1.1 pph of ethanol and between 0, 4 and 0.45 pph of H2O2. The extruded polystyrene foam obtained according to Tests 11-13 has a uniform and good quality extrusion skin, with a percentage of closed cells greater than 95%. The coefficient of self-extinction of the foam thus obtained is much better than in the samples obtained using only ethanol as control agent (Tests 7-10), - 25 as shown in the following Table 2. Likewise, they have a better dimensional stability when the foam is subjected to high temperatures. Table 2 (1) = Molecular weight of polystyrene (2) = Apparatus Micromeritics (3) = dimensional stability measured after 30 days; The specimens are subjected to 2 days at 70 ° C. Ext. = Final extrusion direction; Trans. = Cross direction; Esp. = Direction of thickness (4) = Coefficient of self-extinction measured one hour after production. In the test to determine the coefficient of self-extinction, the following protocol was used: Number and dimensions of the samples: Four specimens were cut from the plate to be tested at the dimensions of 90 mm x 190 mm. The thickness of the specimen is that of the original plate up to 60 mm. Plates thicker than 60 mm are cut to the thickness of 60 mm. Test procedure: The sample is placed on a support. A burner is used and the height of its flame is adjusted to 20 mm, moving the burner in horizontal direction until the flame is at a distance of 15 mm from the rear face of the specimen. After 15 seconds, the burner is removed. Then, the maximum height reached by the flame (on the rear face of the specimen) and the time it takes for the flame to extinguish, both before and after the burner has been removed, is measured.

Example 3: Effect of the supercharging of H2O2 A mixture of low molecular weight polystyrene and additives is fed into the installation as in the previous Example 2 (Tests 11-13). 3.5 pph of foaming agent, CO2, 1 pph of ethanol, as the first control agent, and 1 pph of H2O2 are injected as the second control agent. Once the process has stabilized, the amount of H2O2 is progressively increased. As soon as this amount reaches 3 pph the process begins to destabilize. The pressure in the extruder-laminator 1 begins to oscillate widely, between 10 and 15 MPa (100 and 150 bar, approx.). It is then observed that the current of the motor of the dynamic mixer 2 also oscillates. These variations indicate that the plasticized mixture is not homogeneous because the foaming and control agents are not being incorporated correctly into the plasticized mixture. After adding 3 pph of H2O2 for 30 min, holes begin to appear on the surface of the foam, caused by gas pockets or unmixed control agents. Then the foam is destabilized by varying its width constantly and begin to appear areas of hard material that has solidified quickly, probably also due to gas bags or control agent. The amount of H2O2 is reduced to 2.5 pph and little by little the process stabilizes.

Example 4: Effect of the suppression of H2O2 and ethanol supercharging A mixture of low molecular weight polystyrene and additives is fed into the installation, as in the previous Example 3. Injection into the initially plasticized mixture is 3.5 pph of foaming agent, CO2, and 4.5 pph of control agent, constituted by ethanol. This plasticized mixture is extruded through the lips of the final extrusion die, obtaining a foam of 630 mm. The thickness of said foam at the outlet of the calibrator is 51 mm on average, measured with a vernier caliper at 3 points along its width. When the foam reaches the blade conventionally arranged downstream of the matrix 7 (time elapsed 15 min), the thickness is re-measured over the entire width of the plate, giving an average value of 47 mm on average. Thus, the thickness has decreased 4 mm. The amount of ethanol is increased to 7 pph and the CO2 is decreased to 2.5 pph. The thickness is re-measured at the exit of the calibrator and when the foam reaches the blade. Under these conditions, the thickness has already decreased by 9 mm. The experiment is continued, stopping feeding the CO2 foaming agent and injecting only ethanol, at 9 pph. After 30 min, a change in the structure of the foam is observed. At first glance it is seen that the size of the cells is much larger than in all the previous tests. The thickness of the plate has increased to 55 mm at the outlet of the calibrator. However, when reaching the blade (time elapsed 15 min) the plate has a thickness of 26 mm on average. Thus, the thickness has been reduced 29 mm. In addition, by using only ethanol as a control agent, the walls tend to collapse. Those skilled in the art will understand that many modifications and variants are possible in the execution of the described invention, which are all within the scope of protection defined by the following claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

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1. - Process for the production of foam polystyrene, in whose initial stage a polystyrene mixture is plasticized with nugent agents, plasticizers and conventional additives, at a pressure and a temperature respectively higher than the atmospheric pressure and at room temperature to form a plastic mixture "meit"), which plasticized mixture decompresses and cools sharply at atmospheric pressure and at room temperature, when extruded through a final extrusion matrix, in which process a foaming agent intended to produce the desired foaming and constituted completely by C02, is injected into the plasticized mixture so that said foaming agent dissolves in the plasticized mixture, characterized in that a first and a second control agent are also injected into the plasticized mixture, the first control agent being intended to dissolve and cooling the plasticized mixture and being constituted by tanol, while the second control agent is only intended to refrigerate the plasticized mixture and is constituted by H2O2, the amount of ethanol being just enough to reach the maximum possible dissolution of CO2 in the plasticized mixture and the amount injected of H2O2 such that the foaming caused by ethanol is kept minimal.

2. Method according to claim 1, characterized in that the ethanol is injected in the immediate vicinity of the point of injection of the CO2, and the H2O2 is injected downstream of the same point, when the injections of the foaming agent and the ethanol have already partially cooled the plasticized mixture.

3. Process according to claim 1 or 2, characterized in that, immediately before the final extrusion, the plasticized mixture to be extruded is constituted by 2.25-5% by weight of CO2, by 0.3-3.0% by weight. weight of ethanol and by 0.2-1.7% by weight of H2O2, the rest being polystyrene and nucleating agents, plasticizers and conventional additives.

4. Method according to claim 3, characterized in that, immediately before the final extrusion, the plasticized mixture to be extruded is constituted by 3.0-4.0% by weight of CO2, by 0.6-1, 25% by weight. weight of elanol and by 0.25-1% by weight of H2O2, the rest being polystyrene and nucleating agents, plasticizers and conventional additives.

5. Method according to any of claims 1 to 4, characterized in that the temperature and pressure profiles of the process are maintained with decreasing values of temperature of the order of between 200 and 100 ° C and with decreasing values of pressure of the order of 20 and 7.6 MPa (200 bar and 76 bar, approx.), Respectively, always maintaining CO2 under supercritical conditions, until the final extrusion.

6. Process according to any of claims 1 to 5, characterized in that the polystyrene has a molecular weight of less than 150,000, a melt index of approximately 20 g / 10 min (ISO 1133H) and a softening temperature VICAT VST B 50 (according to ISO 306 B 50) higher than 100 ° C.

7. Installation for performing the method of the preceding claims, which includes an extruder-laminator (1) and a dynamic mixer (2) arranged in series, the first of which has means for effecting the initial plasticization of the mixture and the injection of CO2 and ethanol, and the second of which is provided with a cooling device (9-12) and feeds the plasticized mixture to an extrusion head (8) carrying the final extrusion die (7), there being, between the extruder-laminator (1) and the dynamic mixer (2), means (6) for the injection of H2O2, characterized in that, immediately after the extruder-laminator (1) and immediately after the dynamic mixer ( 2), a first static mixer (15) and a second static mixer (16) are respectively interposed, and the means (6) for the injection of H2O2 are disposed between the extruder-laminator (1) and the first static mixer (15). ).

8. Installation according to claim 7, characterized in that, upstream of the extruder-laminator (1), includes a first tank (20) for receiving CO2 from an external source (21), keeping the first tank (20) under pressure and temperature conditions of the same order as those of the external source (21), a second tank (22) of CO2 in which it is maintained at a pressure of about 7 MPa (70 bar, approx.) and at a temperature environment, and an injection pump (25) for pumping CO2 from the second tank (22) and injecting it into the extruder-laminator (1) and capable of raising the CO2 pressure from about 7 MPa (about 70 bar) to about 30 MPa (300 bar, approx.).

9. Installation according to claim 8, characterized in that the passage of C02 from the first tank (20) and to the second tank (22) is carried out through another pump (23), downstream from which is provided a heating device (24) that raises the temperature of the CO2 leaving another pump (23) to approximately room temperature.

10. Installation according to claim 8 or 9, characterized in that the passage of CO2 between the second tank (22) and the injection pump (25) passes through a cooling device (26) that lowers the temperature of the CO2 to avoid overheating during the pumping operation. 1. Installation according to one of claims 8 to 10, characterized in that the injection pump (25) is cooled. 12. Installation according to claim 11, characterized in that the cooling of the injection pump (25) is effected by cooling its head. 13. Process according to claims 1-6, performed in an installation according to claims 7-12, characterized in that it includes the steps of: a) initially plasticizing in the extruder-plastificadora (1) a mixture of polystyrene with nucleating agents, plasticizers and conventional additives, with polystyrene having a molecular weight of less than 150,000, a melt index of approximately 20 g / 10 min (ISO 1 133H) and a softening temperature VICAT VST B 50 (according to ISO 306B50) greater than 100 ° C;b) injecting into the plasticized mixture, in the extruder-laminator (1), at a pressure of the order of about 20 MPa (200 bar, approx.), on the one hand the CO2 and on the other hand the ethanol; c) passing the plasticized mixture from the extruder-laminator (1) to the first static mixer (15) and injecting H202 into the plasticized mixture (by 6), between both (1 and 15); d) homogenizing the plasticized mixture in the first static mixer (fifteen); e) passing the plasticized mixture from the first static mixer (15) to the dynamic mixer (2) in which the homogenization is accompanied by a decrease in temperature and pressure to which the plasticized mixture is subjected; f) passing the plasticized mixture from the dynamic mixer (2) to the second static mixer (16), in which the decrease in temperature and pressure to which the plasticized mixture is subjected continues; g) passing the plasticized mixture from the second static mixer (16) to the final extrusion head (8), in which the temperature and pressure are controlled so that they are close to about 100 ° C and 7.6 MPa (76) bar, approx.), respectively, always maintaining the CO2 in supercritical conditions, until decompression or final extrusion; the operating conditions being such that at the time of final extrusion, the plasticized mixture is constituted by 2.25-5% by weight of CO2, by 0.3-3.0% by weight of ethanol and by 0.2- 1, 7% by weight of H2O2, the rest being polystyrene and nucleating agents, plasticizers and conventional additives, than the blocks or plates produced, at 42 days of production and after having been subjected for 2 days to 70 ° heating C, have suffered a decrease in each of its linear dimensions (length, width and thickness) less than 5% with respect to the original dimension, and that the test to determine the coefficient of self-extinction, made on said blocks and plates one hour after extrusion, give a flame height less than 11 cm. 14. Blocks or foam plates produced using the method or installation according to any of claims 1-13, characterized because, after 42 days of production and after having been subjected for 2 days to 70 ° C heating, they have suffered a decrease in each of their linear dimensions (length, width and thickness) less than 5% with respect to the original dimension. 15. Blocks and plates according to claim 14, characterized in that the test for determining the coefficient of self-extinction, carried out on them one hour after extrusion, gives a flame height of less than 11 cm. Procedure and installation to produce foam, and foam blocks and boards produced SUMMARY OF THE DJV? NC O CO2 is used as foaming agent and a first agent and a second control agent are injected into the plasticized mixture, the first one being destined to dissolve and cooling the plasticized mixture and being constituted by ethanol, while the second control agent is only intended to refrigerate the plasticized mixture and is constituted by H2O2, the amount of ethanol being just enough to reach the maximum possible dissolution of CO2 in the plasticized mixture and the injected amount of H2O2 being such that the foaming caused by the ethanol is kept minimal. The installation includes provisions for conditioning and feeding the foaming agent and the control agents in the plasticized mixture. The blocks and plates have dimensional stability and good self-extinguishing characteristics.