MXPA05013036A - Process for processing expandable polymer particles and foam article thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE Process for processing expandable polymer particles e.g. polystyrene (EPS) that eliminates the maturing step between the pre-expander and molding steps. The expandable particles are first over pressurized with gas, e.g. air, carbon dioxide, nitrogen, and mixtures thereof, at a pressure between 500 and 8000kPa and a temperature between -20°C and 130°C for 15 to 7200 minutes to create a gas pressure in the particles. Using the gas pressure in the particles, pre-expanding the particles with a heating medium, e.g. steam at a temperature between 100°C and 120°C and at a pressure ranging above atmospheric pressure and below the gas pressure in said particles, i.e. 50 to 200kPa for 5 to 120 seconds. The pre-expanded particles are air dried in the pre-expander while holding a positive pressure in the particles;are optionally transferred to a pressure silo;and then are transferred to a molding machine where the gas pressure in the particles is used to form a foam article.

Description

Fi? N;? - l, - ??, -? , -ndrs, ?? t i'lhri nfi- -r lo llh- "Guid-? t" i? v / V? > / c "_ i»; / Codt-s jn? bbre-viMons "appt-ai ina i ihc l xin -iiin »? ft-iu-h n-snitar issuc ofilu-Cl G rcth: PROCESS FOR PROCESSING EXPANDABLE POLYMER PARTICLES AND FOAM ARTICLE FROM THEMSELVES Field of the Invention * The invention relates to a process for processing expandable polymer particles, for example expandable polystyrene (EPS) particles. More particularly, the invention relates to a process for processing expandable polymer particles which contain an organic or inorganic blowing agent or mixtures thereof in various amounts. The particles are first over pressurized with gas; pre-expanded and dried; and then fed unripe in a casting mold to form a foam article. BACKGROUND OF THE INVENTION Polymer foam articles molded from expandable polymer particles are well known. According to conventional practice, the conversion of expandable polymer particles to a molded foam article generally occurs in three stages; pre-expansion, maturation and molding. The most commonly known and used expandable polymer particles are expandable polystyrene particles referred to as EPS. These particles Ref .: 168505 expandable are generally made as relatively solid "high density" polystyrene beads of a relatively sticky size, for example, pearls having a diameter of about 0.2 to 4.0 millimeters and a volume density (bundle) of about 600 kg / m3. Typically, these polystyrene beads are impregnated with a blowing agent, for example hydrocarbon, ie, pentane, etc., and then heated with saturated steam to produce "pre-expanded" polystyrene particles, ie larger particles of lower density . If hydrocarbon is used as the blowing agent, the amount is generally in the range of about 3.0 wt% to about 7.0 wt% based on the weight of the polystyrene. The blowing agent boils below the softening point of the polystyrene and causes the beads to expand when heated with saturated steam, which results in particles that are pre-expanded to a lower bulk density of about 8 to 80 kg / m3 . Pre-expanded particles, commonly referred to as "pre-blown" or "pre-foam", must be aged for at least about an hour, and generally about 8 to 24 hours, to allow the particles to mature before they can be molded into a foam article. During the maturation process, the air permeates the particles, and the internal pressure of the particles, which is initially lower than the atmospheric one, gradually * reaches the atmospheric pressure. At the same time, the external and internal moisture in the particles evaporates. If pentane is used as the blowing agent, the condensation of pentane creates a low pressure compared to atmospheric pressure. During maturation, this condition is balanced and is necessary for good molding. For the maturation process, it is known that there is a relatively narrow window (for example, a few hours) of the optimum aging time (maturation) which will produce the highest quality molds in the minimum molding cycle times. The optimum maturation time is determined by trial and error and is a complex function of such variables as bead size, blowing agent level, volume density, pre-expansion conditions and maturation conditions (eg temperature). , ventilation, etc). For the maturation process, the pre-expanded particles are generally stored in large vented bags. In general, a substantial amount of storage space is required, and the scheduling and inventory control of the bags are problematic. further, the maturation process takes time. Also, if pentane is used as in the blowing agent, some pentane vapor is released from the bags. It is difficult to capture and destroy this released pentane vapor since the volume of air is very large and the relative pentane content is low. This presents an environmental and safety hazard, and, provides appropriate ventilation in order to avoid explosive hydrocarbon-air mixtures. A further disadvantage with the conventional practice of maturation or aging of the pre-expanded particles before molding is the reduction in the flexibility of the plant. That is, the pre-expanded particles reguire to be used within two to 24 hours after the maturation process. Therefore, human resources and the mold molding in the plant need to be readily available at this time. It may be desirable to have a process that does not involve a maturation step where the pre-expanded polymer particles can be molded immediately after the particles are pre-expanded. There have been some developments that do not require storage and maturation of an intermediate pre-expanded product.

Collum et al., U.S. Patent No. 5,271,886 issued to Arco Chemical Technology, L.P. and granted on December 21, 1992, it uses a moving stream containing polymer particles impregnated with carbon dioxide and a heating fluid. A pre-expansion unit provides a thermally and hot insulated expansion path through which the polymer particles impregnated with carbon dioxide and the heating fluid in motion flow. The moving steam stream containing the pre-expanded polymer particles leaves the pre-expansion unit and is directed to a molding magneto. The heating fluid in motion is charged to the pre-expansion unit at a temperature of 250 ° to 500 ° F (121 ° to 260 ° C), and preferably, superheated steam at a temperature of 350 ° to 500 ° F ( 176.6 ° to 260 ° C). An additional development that eliminates the maturation process for the pre-expanded particles prior to the molding step is described in AP August et al., United States Patent No. 6,399,665 Bl granted June 4, 2002. This The patent discloses that the pre-expansion of EPS particles has been carried out with heat of condensation from steam which permeates the beads and deposits drops of water inside the expansion cells of the beads. This invention uses dry hot gas, such as air, to pre-expand the unpurified EPS beads through conduction only. The outer layer of the beads is first heated by the hot air and the heat penetrates conductively to the inside thereby forming a more pre-expanded structure (with thinner cell walls) on the peripheral surface of the beads and a less expanded structure (with thicker cell walls) inside the pearls. The pre-expanded beads contain a higher percentage content of blowing agent since the blowing agent is locked within the cells of each bead. The resulting pre-expanded beads are dried and can be used immediately for molding EPS foam articles due to excellent lume characteristics and excellent expansion capacity (due to the high residual pentane content). These resulting pearls differ from pre-expanded steams with steam since thermal conduction enlarges the peripheral cells more than the inner cells in each bead, while the steam acts by convection to permeate each bead (and condense within each cell), by what expands both peripheral and inner cells to substantially the same degree. Detailed information explaining the technical reasons for maturing the impregnated particles, particularly conventional EPS solvents which contains pentane as the blowing agent, is given in the background section of the aforementioned US Patent No. 6,399,665. The maturation period generally allows the internal pentane pressure within the cells and the atmospheric pressure to reach a steady-state equilibrium as well as to dry the pre-expanded beads sufficiently so that the water vapor condensed on the surfaces of The pearls do not cause the pearls to agglomerate into lumps, which can not easily pass through the filling valve used to fill the molding or may not flow in the slits and narrow spaces of the mold by itself. This period of aging also allows some of the water droplets (from the condensed vapor) to escape into the cells through the cell walls in this way by drying the inside of the foam beads. Without internal drying, trapped water droplets sometimes induce local non-uniformities, for example holes in the molded article because each drop requires more heating to vaporize it before the heating and expansion of the surrounding cell can progress. Nevertheless, care must be taken that the aging period is not so great that the remaining blowing agent (eg, pentane) can be lost by diffusion of the cells of the pre-expanded beads, which results in pre-filled beads. They are not expanded anymore when they are heated during molding. When the beads do not expand sufficiently during molding, the molded foam articles tend to be poorly fused, and often break into pieces or filter their contents ie coffee in the case of coffee cups. Thus, for many years, proper aging of pre-expanded beads has been a delicate balance between a sufficiently long time necessary to dry the condensed vapor introduced during pre-expansion, and a time sufficiently short to retain an adequate amount of moisture. blowing agent, for example pentane within the pre-expanded beads. Aging not only allows some of the pentane and water vapor condensed through the cell walls to escape into the surrounding atmosphere, but also allows the air to permeate back into the vacuum left inside the cells after expansion in such a way The particles do not collapse during molding. As set forth hereinabove, the inventions of U.S. Pat. Nos. 5,271,886 and 6,399,665 are directed to a process for processing expandable polymer particles that do not cause maturation or aging of the particles after the pre-treatment stage. -Expansion and before the molding stage. U.S. Patent No. 5,271,886 belongs to particles containing carbon dioxide as a blowing agent, and U.S. Patent No. 6,399,665 belongs to particles containing pentane as a blowing agent. . A further example of expandable polymer particles with carbon dioxide as a blowing agent is Meyer et al. , Patent of the United States of North America NO. 4,911,869. This patent teaches that due to the rapidity with which carbon dioxide diffuses from the polymer particles, it is necessary first to pre-expand the particles and then re-impregnate the particles with the same or different gas just before molding. The above-discussed U.S. Patent No. 5,271,886 solves this problem by expanding the beads to their final density as soon as the beads are en route to the unripe molding operation and without re-inflating the pre-blown before of the molding. The use of carbon dioxide gas as a blowing agent in expandable polymer particles is also described in Meyer et al. Patent of the United States of North America No. 5,049,328. This patent combines the stages of impregnation, purification, and foaming in a simple process, which solves the rapid diffusion of carbon dioxide gas out of the particles. Again, prior US Pat. No. 5,271,886 solves this problem by expanding the beads to their final density as soon as the beads are en route for the unripe molding operation and without re-inflating the pre-blown before to the molding. There is still a need in the art to provide a process which eliminates the maturation step generally associated with conventional expandable polymer particles regardless of the type and / or amount of blowing agent in the particles after the pre-expansion process in such a way The pre-expanded particles can be fed immediately into the mold and foam articles of "good" quality are formed. There is an additional need to provide a process that can eliminate re-impregnation prior to molding. SUMMARY OF THE INVENTION The invention has met these needs. The invention provides a process for processing expandable polymer particles which eliminates the need for a maturation step between the pre-expansion and molding stages. If the expandable polymer particles contain an inorganic blowing agent, for example carbon dioxide or water, or contain a very low amount of organic blowing agent, for example, from about 1.0 to about 3.0% by weight of pentane, the invention allows the particles to be transferred immediately from the stage of pre-expansion to a molding stage. The invention provides a process for processing expandable polymer particles in a foam article. The process comprises the steps of: a) subjecting expandable polymer particles to a pressurization stage where a relatively high pressure is established on the particles; b) pre-expand the particles so as to decrease the density of the particles while retaining a sufficient positive pressure inside the particles and drying the pre-expanded particles while still maintaining a sufficient pressure on the particles; and c) immediately molding the pre-expanded particles to form a molded foam article. More specifically, the process of the invention comprises the steps of: a) pressurizing the expandable polymer particles with compressed gas at a pressure and temperature to create a relatively high gas pressure within the particles; b) using at least the gas pressure in the particles created in the pressurization stage a), pre-expanding the particles with a heating medium while maintaining a sufficient positive pressure in the particles in which the pressure is above the atmospheric pressure and directing a flow of dry hot air for a sufficient time in the particles to dry the particles while maintaining a sufficient positive pressure in the particles in which the pressure is above atmospheric pressure; and c) immediately molding the particles in a foam article using at least the residual gas pressure in the particles. The expandable polymer particles may have a bulk density of about 600 kg / m2 and may contain an organic blowing agent, for example hydrocarbon, ie, pentane, isopentane, and mixtures thereof and / or may contain an agent of inorganic blowing, for example water, air, nitrogen, carbon dioxide, argon, neon and mixtures thereof. The amount of the blowing agent in the expandable particles may be in the range of about 0 weight percent to about 20 weight percent. The expandable particles may be "pre-nucleated", ie particles having a previously established cell or porous structure where the bulk density of the expandable particles has been slightly decreased in this way resulting in the volume being slightly increased. Or the expandable particles can be "non-nucleated", ie, particles having holes and not previously established cell or porous structure. The invention may find particular application for processing expandable polystyrene particles which contain an organic blowing agent, for example pentane, in an amount less than about 3% by weight, or which contain an inorganic blowing agent such as water, carbon dioxide. , air or nitrogen, in which the inorganic blowing agent, for example, carbon dioxide, as discussed hereinabove, generally dissipates rapidly from the cells and therefore from the particles. In this case, the pressurization step a) and the pressure of the heating medium applied to the particles in the pre-expansion stage b) ensures that the particles have sufficient pressure for the expansion required in the molding process to merge properly the particles together for the production of foam articles. In the pressurization step, the expandable particles are overpressured with gas in a pressure range from about 500 kPa to about 8000 kPa and in a temperature range from about -20 ° C to about 130 ° C for about 15 minutes to about 7200 minutes (5 days) . The result is that pressurized gas is created and remains in the particles, that is in the holes or in the cells of the particles. These pressurized particles are then transferred to the pre-expansion unit. The pre-expansion unit contains a heating means for pre-expanding the particles. The heating means can be supplied in a pressure range from about 50 kPa to about 200 kPa and in. a temperature range of about 100 ° C to about 130 ° C. In general, the pressure in the pre-expander will be above the atmospheric pressure and lower than the pressure inside the particles when the s-particles leave the pressurization unit. This creates a pressure differential between the pressure in the particles as a result of the pressurization stage and the pressure in the pre-expansion unit. The heating medium will cause the particles to soften, and the differential pressure in the particles will cause the particles to expand. Within the pressurized atmosphere of the pre-expansion unit the particles can be subjected to a drying process, for example an air drying process, in the pressure that exists in the pre-expansion unit. That is, after the particles are pre-expanded a stream of hot dry air can be transported through the pre-expansion unit and onto the particles. Alternatively, the drying of the particles can be done in a pressurized compartment separated from the pre-expansion unit or in a separate pressurization unit. Preferably, the particles are transferred from the pre-expansion unit directly to the molding tool. However, depending on the production ratio of the plant, it may be necessary to transfer the particles to a maintenance vessel until the molding tool is available. The molding container can be a rigid vacuum pressure silo which maintains the pressure in the particles, or the maintenance container can have a net air flow sticking. As stated hereinabove, the particles are transferred from the pre-expansion unit or from the pressure silo and the molding magneto. The pressure differential between the external part of the particles and the environment will be zero but the pressure inside the particles will be above atmospheric. As soon as the pressurized particles enter the molding chamber, the partial pressure of the gas inside the particles is greater than the air pressure inside the molding chamber. This will allow the particles to expand further and merge with each other when the particles are heated in the casting mag. Now that the pre-expansion unit is in place, the particles have sufficient pressure and the particles are dried, the particles can be fed directly to the molding machine without maturing the particles.

Suitable gases supplied to the pressurization unit to develop a relatively high gas pressure therein include air, carbon dioxide, nitrogen, and mixtures thereof. Preferably, the gas is selected from the group consisting of air, carbon dioxide, and mixtures thereof. It is therefore an object of the present invention to provide a process for processing expandable polymer particles which applies a relatively high gas pressure to the particles and includes maintaining the pressure in the particles whereby the particles are transferred directly from the particles. from the pre-expansion unit to a molding machine without a maturation stage. It is a further object of the present invention to provide a process for processing expandable polymer beads into a molded foam article which overpressures the particles, pre-expands and dries the pressurized particles, and immediately molds the particles pressurized to form a foam article. A still further object of the present invention is to provide a process for processing expandable polymer particles regardless of the amount and / or type of blowing agent in the expandable polymer particles which allows the particles to be molded immediately after the particles are pre-expanded. And still a further object of the present invention is to pressurize the expandable particles such that a sufficient amount of pressure remains in the particles for pre-expansion and molding. These and other objects of the invention will become better appreciated and understood when the following description is read along with the drawings and appended claims. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a sketch of the prior art process where conventional expandable polystyrene particles are pre-expanded, matured and molded. Figure 2 is a diagram of the process of the invention where the expandable, pre-expanded and dried polymer particles are pressurized and then molded. DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a schematic of a conventional process for processing conventional expandable polystyrene particles. The expandable polystyrene particles 8 are fed to the pre-expansion unit 10 where vapor is applied to the particles to decrease the density of the particles. As discussed hereinabove, the lower density particles are transferred from the pre-expansion unit 10 to large vented bags for the maturation process 12, and are then transferred to the molding mag 14 to produce a foam article. finished 16. In the prior art particles, if the blowing agent, for example pentane is very low, the particles are generally placed in a pressure tangue (not shown) before entering and / or after leaving the unit. of pre-expansion 10. Figure 2 is a diagram of the process of the invention. The process of the invention involves over pressurizing the expandable polymer particles in a pressure vessel 18 for a pressurization step, then transferring the polymer particles to a pre-expansion unit 20 for the pre-expansion and drying steps, and then immediately to a molding tool 22 for the molding step to produce a finished foam article 24. "Particles" as used herein designates beads, granules or glued parts. Polymers suitable for use in the process of the invention are thermoplastic polymers. These polymers include, but are not limited to, polystyrene, styrene copolymers, for example, styrenic / maleic anhydride copolymers, xylene <polyphenylene, mixtures of polystyrene-polyphenylene oxide, polyoxymethylene, poly (methyl methacrylate), copolymers of methyl methacrylate, polyethylene, polypropylene, ethylene-propylene copolymers, polyvinyl chloride, polycarbonate, polyethylene terephthalate, cross-linked variations thereof, modified rubber versions thereof, mixtures thereof, and interpenetrating networks thereof, for example, polyethylene and polymerized vinyl aromatic resins, such as polystyrene. While a preferred embodiment will be discussed with reference to expandable polystyrene (EPS) particles, as indicated in the preceding paragraph, other expandable polymer particles, for example expandable polyethylene (EPE), expandable polypropylene (EPP for its acronym in-English), styrenic copolymers, etc. they can be used to carry out the invention. The polymer particles of the invention are expandable since they generally contain a blowing agent. The blowing agent can be incorporated into the particles during the formation of the particles. The blowing agent may be organic or inorganic or mixtures thereof. The organic blowing agents can be hydrocarbon, for example n-pentane (normal pentane), butane, isopentane, and mixtures of pentane, and preferably, n-pentane and mixtures of pentane. Inorganic blowing agents can be carbon dioxide, nitrogen, air, water and other pneumogens and mixtures thereof. The blowing agent, particularly for expandable polystyrene particles, is generally in the range of about 0.1% to about 8% by weight based on the weight of the polymer. Incorporation of the blowing agent into the particles can occur when the particles are formed. This may occur at a stage of the suspension process or the blowing agent may be impregnated into the particles after which the particles are formed where it is generally referred to as a two-stage suspension process. If there is little, no blowing agent in -the. particles, then the pressure of the gas applied to the particles in the pressurization step of the invention will provide sufficient pressure in the particles and the pressure is maintained for the pre-expansion and molding stages. As an example, if 40 bar pressure is applied to the particles for approximately three (3) hours in the pressurization step, the pressure in the beads may be about 22.5 bar. A process has been developed which decreases or eliminates the rate of rapid diffusion of inorganic blowing agents, such as carbon dioxide and / or water. This process can be referred to as "pre-nucleation". The "pre-nucleation" of the particles is achieved by slightly expanding the particles to a density that is not more than 3 times lower than the original density of the particles. The particles used in this pre-nucleation process may contain the inorganic blowing agents discussed hereinabove, ie, carbon dioxide, nitrogen, air, water and other pneumogens and mixtures thereof, or may contain water and / or or a sticky amount, for example about 2 weight percent or less, of an organic blowing agent, for example a hydrocarbon lipid, for example pentane and / or mixtures thereof. In the "pre-nucleation", the initial nuclei of the cells in the particles are formed. The cores of the cells are then used to subsequently further expand the particles with pressurized gas to the final volume density of commercial interest.

The process for preparing the pre-nucleated particles, ie particles which already have a certain cellular structure is described in the following two patent documents. - Application WO 00/15703 (Patent of the United States of America NO. 6,538,042 Bl granted March 25, 2003) relates to porous polyvinylarene particles. The non-expanded particles are slightly expanded to create porous particles having a certain cellular structure and an apparent density in the range between 200 and 600 kg / m2 and containing less than 2% by weight of an organic blowing agent. These porous particles have an increase in volume which is from about 1.5 to less than 3 times compared to the volume of the non-expanded particles. The application WO 00/15704 (US Pat. No. 6,455,599 Bl issued September 24, 2002) relates to a process for the preparation of expanded porous particles by impregnating the particles having a density in the range of 200 to 600 kg / m3 with an inorganic gas and which expands the particles to a density which is not more than 3 times lower than the original density of the unexpanded particles.

A process for preparing expandable polymer particles containing voids in the solid particles is described in the following patent document. Application WO 00 / 157O2 (US Pat. No. 6,573,306 Bl granted June 3, 2003) relates to a process for the preparation of expandable polyvinylarene particles in which solid polyvinyl ane particles containing voids They are impregnated by exposing the solid particles to an inorganic compound selected from the group consisting of gas containing N2 and / or 02 and a temperature below 95 ° C and at a pressure of gauge 100 to 2,000 kPa to maintain the structure and properties of the holes in the solid particles. The inorganic gas contains a low volume of organic compounds and is less soluble in the polymer matrix compared to the organic compounds, and therefore, the inorganic gas remains essentially in the voids of the solid particles for an expansion of the particles. For the process of the invention, the expandable polymer particles can be conventional expandable polymer, for example expandable polystyrene (EPS) particles., expandable polypropylene particles (EPP), expandable polyethylene (EPP) particles, which contain an inorganic or organic blowing agent, as discussed above. The expandable polymer particles can be pre-nucleated particles prepared according to the teachings of the US Pat. No. NO. 6,538,042 (application WO 00/15703) and the Patent of the United States of North America NO. 6,455,599 Bl (application WO 00/15704) or the particles may be aglets prepared in accordance with the teachings of US Pat. No. 6,573,306 Bl (application WO 00/15702), the descriptions of which are all incorporated in the present in its entirety for reference. The blowing agent in the particles of the aforementioned patents, and therefore, the invention can also be carbon dioxide. The expandable polymer particles may contain water which is mixed with the aliphatic hydrocarbon blowing agents or water which can be used as the sole blowing agent as taught in U.S. Patent No. 6,127,439; 6,160,027; and 6,242,540 issued to NOVA Chemicals (International) S.A. In these patents, water retention agents are used. The weight percentage of water for use as the blowing agent may be in the range of 1 to 20%. The disclosures of U.S. Patent Nos. 6,127,439, 6,160,027 and 6,242,540 are hereby incorporated by reference in their entirety. The expandable polymer particles can be produced by means of an extruder having a lower water cutter to form spherical pellets. In the extruder, a guan blowing agent can be used which releases the carbon dioxide gas as the blowing agent where the blowing agent is mixed in the polymer for "pre-nuclear", ie forming cells in the polymer, as soon as it comes out of the mold of the extruder. Additional blowing agents such as gaseous carbon dioxide, pentane, HCFC and CFC can also be added directly to the extruder. Also, the expandable particles can be produced in an extruder with a blowing agent, for example pentane and without foaming in the mold, for example when making non-nucleated particles. The expandable polymer particles can be cellular polymer particles formed as taught in Arch et al. U.S. Patent No. Serial No. 10 / 021,716 issued to NOVA Chemicals Inc. The foamed cellular particles are preferably polystyrene which are pre-expanded at a bulk density in the range of 600 kg / m3 to about 200 kg / m3, and contain a level of organic blowing agent of less than 6.0 weight percent, preferably in the range of between 2.0 wt% to 5 wt% and more preferably in the range of between 2.5 wt% to 3.5 weight percent based on the weight of the polymer. The description of the request from the United States of America? O. of series 10 / 021,716 is hereby incorporated by reference in its entirety. If the expandable polymer particles are foamed cellular polymer particles as described in the preceding paragraph or if the expandable polymer particles are conventional EPS particles, then there may be a sufficient amount of blowing agent in the particles that the pressurization step may not being necessary, for example, if the level of pentane in the particles is at least 2% by weight. The pressurization step of the invention ensures that there is adequate pressure in the particles, regardless of the type and amount of blowing agent in the particles so that the particles can be adequately fused together in the molding step. In broader terms, the invention relates to a process for processing expandable polymer particles comprising a pressurization stage, a pre-expansion stage including a drying step, and a molding step. The particles may contain voids, cells, or cell nucleation sites depending on the process to which the unpurified beads have been subjected prior to being subjected to the process of the invention. For example, if the unpurified beads are pre-nucleated according to the teachings of U.S. Patent No. 6,538,042 (application WO 00/15703) and / or U.S. Patent No. 6,455,599 Bl (application WO 00/15704), the beads used in the process of the invention will generally contain cells. If the unpurified beads are "nucleated", that is processed first according to the teachings of US Pat. No. 6,573,306 Bl (application WO 00/15702), the beads used in the process of the invention they will generally contain cell nucleation sites. In the pressurization stage, the expandable polymer particles may have a volume density in the range of about 600 kg / m3 and in some cases, as low as approximately 16 kg / m3. Preferably, the expandable polymer particles will have a bulk density in the range of from about 200 kg / m3 to about 600 kg / m3 and in some cases, in the range between about 250 kg / m3 and 500 kg / m3. In the pressurization step, the particles are subjected to a compressed gas at a pressure in the range of between about 500 kPa to about 8000 kPa and at a temperature in the range of between -20 ° C to 130 ° C for a period of 15 minutes at about 7200 minutes (5 days), preferably less than 1440 minutes (24 hours) until the gas pressure in the particles, ie voids, cell nucleation sites, or cells, is sufficient for the reduction of regulated density. If the pressure of the gas that is applied to the particles is 2500 kPa, then the particles can be subjected to this gas in this pressure until a pressure of 2500 kPa is obtained in the particles. As stated in the preceding paragraph, the temperature of the gas in the pressurization unit will preferably be in the range of -20 ° C to 130 ° C. However, it has been found by the inventors that for temperatures of greater than 90 ° C for polystyrene expandable particles will tend to soften the polystyrene, and therefore, the temperature for the expandable polystyrene needs to be about 90 ° C or less. Also, it has been found that for the expandable polystyrene particles in the pressurization unit, a period of one hour to about eight hours will be sufficient to achieve the desired pressure on the particles in preparation for the pre-expansion unit. It will be appreciated that a particle of lower density may have a lower pressure so that the gas is supplied to the pressurization unit. That is, if the particles entering the pressurization unit have a density of approximately 16 kg / m3, then the pressure in the pressurization unit may be below 500 kPa (5 bars), ie approximately 50 kPa (0.5 bar). ) at approximately 100 kPa (1.0 bar) since a high pressure of 8000 kPa (80 bar) will tend to compress the foam and break the cels in the particles, etc., especially if the pressure increases very rapidly in the pressurization unit . In order to help maintain a desired and / or regulated pressure in the expandable particles obtained in the pressurization step, the particles can be transported through a suitable medium at a pressure, for example, from about 50 kPa to about 200. kPa, from the pressurization unit to the pre-expansion unit. For the pre-expansion stage, a pressure vessel is generally used. The pressure vessel can be an automatic batch device and the pre-expansion stage can involve a continuous process. For example, the particles may flow into the pressure vessel on one side, * be pre-expanded and dried, and leave the pressure vessel to the mold on another side. The expansion of the particles occurs in the pre-expansion stage by means of a heating medium, which can have a temperature in the range of 100 to 120 ° C (212 ° F to 248 ° F) and a range of pressure between 50 to 200 kPa. The heating medium is applied to the particles for about 5 to 120 seconds to pre-expand the particles at a density in the range between about 193 kg / m3 to about 8 kg / m3 (i.e. about 12 pounds / cubic feet to about 0.5 pounds / cubic foot). For example, if according to conventional practice the density of the particles in the pressurization stage is approximately 600 kg / m3 according to conventional practice,. The density - of the particles as a result of the pre-expansion stage will be approximately 8 kg / m3. The heating means can be any conventional heating means, for example steam, hot air, hot water, radiant heat, convection heat, microwave heat, high frequency radiation, or electromagnetic. Since there is a pressure differential between the pressure in the particles and the pressure in the pre-expansion unit, the particles will expand. The pressure that remains in the particles allows the particles to mold. A generally accepted method for the pre-expansion of impregnated thermoplastic particles is taught in the US Pat. No. NO. 3,023,175 for Rodman who uses steam to pre-expand the particles. In the invention, the particles can be pre-expanded in a similar manner. However, as stated above, a certain pressure will remain in the particles while the vapor is applied for the expansion of the particles. The pressure in the pre-expansion unit can be maintained in the pre-expansion unit for the drying step. The particles can be dried by injecting a flow or stream of dry hot air through the pre-expansion unit and onto the particles. During the drying step, the particles are maintained consistently under a higher pressure in order to maintain an overpressure in the particles. This drying step can continue until the water vapor from the vapor evaporates from the interior of the particles. If the pressure in the pre-expansion unit is between 50 kPa to 200 kPa, then the pressure in the particles may be in the range generally between 50 kPa and 200 kPa. If the pressure in the pre-expander is brought to about 30 kPa, then the particles can remain in the pre-expander until the pressure in the particles equals agüella in the pre-expander. As mentioned above, according to conventional practice, after the particles are pre-expanded, the pressure in the pre-expander is gradually brought to zero and air is injected through the pre-expander and vented from the pre-expander. same. However, in the invention the pressure is maintained in the pre-expansion unit, and for the drying process of the particles, preferably hot dry air is injected into the pre-expander and retained instead of being completely vented in the pre-expander. external environment This hot dry air can have a temperature in the range of about 20 ° to about 90 ° C and a pressure in the range of about 1 kPa to about 10 kPa. The hot dry air can be directed to flow over the particles for about 1 to about 900 seconds without venting all the pressure from the particles and without venting all the air into the environment, the result being little or no residual hydrocarbon, for example pentane, generally used as a blowing agent in the EPS particles, is emitted into the atmosphere. The pre-expanded, dried particles can be transferred immediately to a conventional molding tool. The foam articles are molded under pressure in the presence of steam using any of a number of methods and apparatuses which are well known to those skilled in the art. When the particles leave the pre-expansion unit, the particles will be over pressurized, for example having a pressure in the range of about 30 kPa to about 200 kPa. When the beads enter the casting mag, the partial gas pressure within the particles is greater than the air pressure inside the casting magneal, which allows the particles to expand further and fuse with each other upon further heating. For the molding step, the process of the invention uses the residual gas pressure, and in some cases, the residual blowing agent in the particles to properly fuse the particles together. If there is very little or no residual blowing agent in the particles for the molding stage, then the residual gas pressure in the particles »will be sufficient to properly fuse the particles together. As discussed hereinabove, the production ratio of the molding tool can be such that the particles can not be transferred immediately to the molding tool after the pre-expansion / drying steps. In this case, the particles can be transported to a pressure silo, which can be connected to the molding machine. The pressure silo is constructed in such a way that the pressure will be supported and maintained in the particles. This pressure on the particles may be in the range of about 30 kPa to about 200 kPa. In the invention, a relatively high pressure is first created in the particles and then an adequate pressure is maintained in the particles through the pre-expansion and drying steps such that there is adequate pressure in the particles for the stage of molding From the foregoing, it can be appreciated that the process of the invention provides a sufficient pressure that exists in the particles for the pre-expansion / drying steps and for the molding step regardless of the amount and / or type of the Blowing initially incorporated in the particles or which remains in the particles in the pre-expansion and molding stages. In the pre-expansion, drying and molding stages, the particles are expanded using the residual gas pressure, and in some cases, the residual blowing agent in the particles. Suitable gases for the pressurization unit are air, carbon dioxide, nitrogen, and mixtures thereof. The preferred gas is selected from the group consisting of air, carbon dioxide, and mixtures thereof. The process of the invention can find particular application with water blown expandable polymer particles, preferably expandable water blown polymer particles.

(WEPS), which uses water as the blowing agent, such as particles described in the aforementioned US Patents No. 6,127,439; 6,160,027; and 6,242,540. In order to achieve densities of 20 kg / m3 or less, it has been found that the injection of high pressurized gas, that is in the range of between 500 to 2500 bar for about 15 minutes to about 7200 hours in temperatures in the range between 20 to 90 ° C according to the teachings of the invention creates an eguivalent pressure on the "cell nuclei *". This pressure that exists in the cells of the particles can then be used to expand the polymer of the particles where the high pressure inside the particles causes the cells to expand which results in the desired lower densities of 20 kg / m3 or less. As discussed above, for the pressurization stage, the particles are subjected to highly pressurized gas. This highly pressurized gas, in effect, can be used as the blowing agent. The application of this highly pressurized gas to the particles can occur at the location of the moulder before the particles are pre-expanded and molded in. The application of this highly pressurized gas to the particles in the moulder installation can eliminate the problem of average life generally associated with conventional EPS in which all the blowing agent, for example pentane, is added to the resin supplier's installation.In the pressurization stage, the pressurized gas can be air.If it has been found that the use of Pressurized air can eliminate some of the disadvantages associated with the use of water as the blowing agent.The rate of diffusion of air through polystyrene is less efficient and therefore less rapid than water vapor, and therefore, the air will generally remain in the particles for a longer period of time than the water.The air can be heated at any temperature and still be effective to pressurize the particles, while water and pentane, the most common blowing agents, need to be heated above their boiling point in order to soften and expand the polymer. Another advantage of using pressurized air in the particles is that the air does not condense in the cells after expansion, thus contributing to the elimination of the maturation stage between the pre-expansion and molding stages. Alternatively, for the pressurization step, the pressurized gas can be carbon dioxide. There is an advantage in using carbon dioxide as the pressurized gas in the pressurization step and as a blowing agent in the particles, especially those which are pre-nucleated or non-nucleated particles prepared according to the United States Patents. mentioned above No. 6,455,599, 6,538,042 and 6,573,306 or are solid polystyrene particles which are impregnated with carbon dioxide gas and then pre-nucleated according to US Pat. No. 6,573,306 since the efficiency of the process of The invention can generally be increased. Carbon dioxide is better soluble in the polymer matrix, and a higher charge of pressurizing gas can therefore be obtained for carbon dioxide compared to air or nitrogen. Also, the kinetics of carbon dioxide absorption are better. Finally, a process based on carbon dioxide can allow the recycling of industrial C02, so it makes better use of this greenhouse gas. The process of the invention essentially involves pressurizing expandable polymer particles, pre-expanding and drying the pressurized particles, and directly placing the pre-expanded particles in the casting mag. It is apparent that both the aging bag, which is conventionally used for the processing of EPS particles, and a second pressure vessel, which is conventionally used to process EPP and EPE particles, can be eliminated. As stated hereinabove, the particles may be expandable polyethylene (EPE) or expandable polypropylene (EPP). For these particles, common blowing agents such as pentane, carbon dioxide, or CFC diffuse from the particles very rapidly so that the unexpanded beads impregnated with the blowing agent can not be easily transported to the location of the moulder. for expansion. In turn, a typical process for EPE and EPP particles is first to produce extruded minigranules with suitable additives. These mini-granules are then suspended in water with suspending agents in a manner known to those skilled in the art. Blowing agents are added at high temperatures and pressures in relatively tight pressure vessels. While the granules are still at a high temperature and pressure, the container contents are rapidly discharged at atmospheric pressure where the particles are expanded to final volume densities in the range of about 16 kg / m3 to about 80 kg / m3 (1 at approximately 5 lbs / ft3). The fully expanded particles are aged and dried prior to transportation, packing, and shipping to the molder location. This usually involves the associated costs of "air" shipping, ie large distances of very light weight particles. Once in the location of the moulder, the particles usually need to be re-inflated with a gas, typically air, prior to molding. This "regulates vessels of higher pressure since the volume density of the particles is extremely low.The air pressure must be gradually increased over a period of 4 to 24 hours in order to prevent the particles from collapsing which generally happens If the pressure is excessive and applied quickly, once the particles are inflated, they must be kept under pressure and / or molded quickly before the air within the cell structure dissipates.The process of the invention can be particularly applicable to processing EPP and EPE particles The pressurization unit can be located at the location of the former and used prior to pre-expansion and molding.The invention is further illustrated, but not limited to, the following examples, which belong to the Expandable polystyrene particles Examples 1 This example belongs to pre-nucleated polystyrene beads which contain water as an agent These pearls are produced in accordance with the teachings of US Pat. No. 6,127,439 which describes the use of polar water absorbing polymers as water retention agents, and in accordance with the teachings of the U.S. Patent No. 6,538,042 (application WO 00/15703) and U.S. Patent No. 6,455,599 Bl (application WO 00/15704), which respectively describe the pre-nucleated beads and a process to get these pearls. This example shows that the pre-nucleated beads can be expanded and molded by first pressurizing the beads, and then pre-expanding and molding the beads without maturing the beads between the pre-expansion and molding stages. In order to obtain pre-nucleated beads, approximately 4 liters of beads (size fraction sieved 0.900-1.250 mm) are partially expanded with steam in a pre-expander batch PVD-80 Erlenbach (previously Polytech PVD-80). The initial density of the beads before the pre-nucleation is approximately 600 kg / m3, and the density of the slightly expanded pre-nucleated beads is approximately 419 kg / m3. These four liters of pre-nucleated beads are then pressurized in a batch vessel (which has a volume of four liters) with compressed air at 2250 kPa for 16 hours at room temperature and then transferred under a pressure of 200 kPa to a stirred 100-liter expansion vessel. This expansion vessel has an air pressure of 5 kPa. The beads are treated with steam at a supply pressure of 70 kPa for 20 seconds to expand them to a final density of 34 kg / m3. The resulting wet foamed beads (referred to as "pre-blown" or "pre-foam") are then dried by blowing air at room temperature for 180 seconds through the pre-expansion vessel while a positive pressure of 30 kPa is retained. in the glass. From the expansion vessel, the beads are transported to a conventional molding machine (Kurtz K 5 with a molding cavity measuring 300 mm by 300 mm by 50 mm). The residual air pressure within the beads acts as a blowing agent during the subsequent molding step. In the molding machine, the pressure is released and the magneto is operated in a conventional molding cycle, ie, fixed pressure of 100 kPa; steam time of 8 seconds, and foam pressure release of 15 kPa. The resulting foam molding has a density of 37 kg / m3. From the inspection, visual, the pearls are well fused and virtually no shrinkage of the foam occurs. The cross-breaking strength of the resulting foam is measured according to CEN 12089 with a value of 204 N 'at this density of the foam. EXAMPLE 2 This example involves pre-nucleated polystyrene beads which contain a sticky amount of pentane as a blowing agent. These pre-nucleated beads are produced in accordance with the teachings of the aforementioned US Pat. No. 6,538,042 (application WO 00/15703) and US Pat. No. 6,455,599 Bl (application WO 00 / 15704). The process and group for Example 2 are similar to those used in Example 1. This example shows that the pre-nucleated beads can be expanded and molded by first pressurizing the beads, and then pre-expanding and molding the unripened beads. the pearls between the pre-expansion and molding stages. In order to form the pre-nucleated beads, about 4.0 liters of beads having an initial density of about 600 kg / m3 and containing about 1.9% by weight of pentane as the blowing agent are partially expanded with hot air to a density less than 400 kg / m3. The amount of the blowing agent which remains in the beads after this partial expansion is 1.2% by weight based on the weight of the beads. These four liters of pre-nucleated beads are then pressurized in a batch vessel of Example 1 with compressed air at 2250 kPa for 16 hours at room temperature and then transferred under 200 kPa of pressure to the stirred expansion vessel of Example 1. The Expansion vessel has an air pressure of 5 kPa. The beads are then treated with steam at a supply pressure of 70 kPa for 20 seconds to expand them to a final density of 19 kg / m3. The resulting wet foamed beads are then dried by air blown at room temperature for 180 seconds through the pre-expansion vessel while a positive pressure of 30 kPa is retained in the vessel. From the expansion vessel, the beads are transported to a conventional molding tool of Example 1. In the molding tool the pressure is released and the machine is operated in a conventional molding cycle with the same parameters as in Example 1 The resulting foam has a density of 19.5 kg / m3. from the visual inspection, the pearls are fused well and virtually no foam shrinkage occurs. The resistance to cross-breaking of the resulting foam is measured according to CEN 12089 with a value of 176 N at this density of the foam. This value is comparable with aguel obtained with conventional EPS beads. EXAMPLE 3 The unbleached pearls similar to agells used in Example 2 are pre-nucleated at a density of about 380 kg / m 3, and are processed similarly to agells of Example 2. The pressure in the pre-expander is maintained at 30 kPa . These particles before molding have a density of 17 kg / m3. The particles are transferred to a pressure silo where a pressure of 30 kPa is applied to the particles. The particles are then molded for 23 seconds at a vapor pressure of 90 kPa. The foam produced has a density of 20 kg / m3. - The resistance to cross-breaking according to CEN 12089 is measured with a value in this density of 221 N. Several additional runs are made with the unpurified beads where the pressure in the pre-expander is decreased to 15 kPa for the first run , 10 kPa for the second run, and 8 kPa for the third run. The respective densities of the beads before molding are 15 kg / m3, 16 kg / m3 and 16 kg / m3. Beads are molded for 17 to 19 seconds at a vapor pressure of 90 kPa. The foam produced has a density of 18 kg / m3, 19 kg / m3 and 18 kg / m3, respectively with respective cross-breaking resistances of 183 N, 172 N and 163 N. This example illustrates that the lower the air pressure of the pre-expander, the lower the value of the cross-breaking resistance. In this way, it may be more desirable in most cases to maintain a pressure of 30 kPa or more in the pre-expander for better resistant foam products. Example 4 This example belongs to solid polystyrene beads which are impregnated with carbon dioxide and then pre-nucleated, ie slightly expanded to 400 kg / m 3, similar to the teachings of the aforementioned United States Patent No . 6, 573, 306. This example also uses air as the pressurized gas in the pressurization unit. This example shows that the pearls impregnated with carbon dioxide and then pre-nucleated can be overpressured with air, pre-expanded, and molded without maturing the pearls between the pre-expansion and molding stages. To produce the beads initially used in this example, approximately 20 liters of solid polystyrene beads with a density of 630 kg / m3 are pressurized in a pressure vessel with carbon dioxide for 3 hours at a pressure of 500 kPa at room temperature to So impregnate the pearls with carbon dioxide. This impregnation step is followed by a pre-nucleation step with a batch steam expander (Erlenbach PVD-80). The pre-nucleated beads are then processed with the type and conditions similar to those of Example 1. That is, the pre-nucleated beads are then pressurized in a batch vessel (which has a volume of 4 liters) with compressed air in 2250. kPa for 16 hours at room temperature and then transferred under a pressure of 200 kPa to a stirred 100 liter expansion vessel. This expansion vessel has an air pressure of 5 kPa. The beads are treated with steam at a supply pressure of 70 kPa for 20 seconds to expand them to a final density of 20 kg / m3. The resulting pre-blown beads are dried by blowing air at room temperature for 180 seconds through the pre-expansion vessel while retaining a pressure of 30 kPa in the pre-expansion vessel. Starting from the pre-expansion vessel, the beads are transported to a conventional molding mag (Kurtz K45 used in Example 1). The residual air pressure in the beads helps to expand the beads further in the molding step, the pressure is released and the magic is operated in a conventional molding cycle, ie fixed pressure of 100 kPa; steam in 8 seconds; and 15 kPa foam pressure release. The resulting foam mold has a density of 26 kg / m3. From the visual inspection, the pearls are well fused and virtually no shrinkage of the foam occurs. The resistance to cross-breaking of the resulting foam is measured according to CEN 12089 with a value of 330 N in this foam density. While the present invention has been indicated in terms of the specific embodiments thereof, it will be understood in light of the instant description that numerous variations of the invention are now permitted and still reside within the scope of the invention. For example, it is to be appreciated that both the pre-expansion and the molding units can be eguided with a separate pressure supply source. Accordingly, the invention is to be broadly constructed and limited only by the scope and spirit of the appended claims now attached. 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 (24)

CLAIMS Having described the invention as above, the contents of the following claims are claimed as property:

1. A process for processing expandable polymer particles, characterized by comprising: a) pressurizing the expandable polymer particles with a highly pressurized gas to create a high gas pressure within the particles; b) pre-expanding the particles with a heating medium in a pressure range higher than atmospheric pressure and lower than the gas pressure in the particles as a result of step a) and drying the pre-expanded particles; and c) immediately molding the particles in a foam article using at least the residual gas pressure in the particles.

2. The process according to claim 1, characterized in that the drying of the pre-expanded particles in step b) occurs while the particles are maintained under a pressure in the upper range of atmospheric pressure and lower than the pressure of gas from stage a).

3. The process according to claim 1, characterized in that the gas in the pressurization of the particles of step a) has a temperature in the range of about -20 ° to about 130 ° C and a pressure in the range of about 500 kPa at about 8000 kPa and pressurization occurs for about 15 to about 7200 minutes.

4. The process according to claim 3, characterized in that the polymer is polystyrene and the gas has a temperature of about 90 ° C or less.

5. The process according to claim 4, characterized in that the heating means for the pre-expansion of the particles of step b) has a temperature in the range of about 100 ° C to about 120 ° C and a range of pressure of about 50 kPa to about 200 kPa and applied to the particles for a time in the range of about 5 to about 120 seconds.

6. The process according to claim 2, characterized by the drying of the expanded particles in step b) consists of an air flow which has a temperature in the range of about 20 ° to about 90 ° C and a pressure in the range of about 1 kPa to about 10 kPa and is applied to the particles for a time in the range of "about 1 to about 900 seconds.

The process according to claim 1, characterized by further comprising: after pre-expanding the particles of step b) and before molding the particles of step c), transferring the particles to a pressure silo for Keep the pressure on the particles.

8. The process according to claim 1, characterized by in steps b) and c), the pressure in the particles is maintained at least at a pressure in the range of about 50 kPa to about 200 kPa.

9. The process according to claim 1, characterized in that the pressurized gas in step a) is selected from the group consisting of air, nitrogen, carbon dioxide and mixtures thereof.

10. The process according to claim 1, characterized in that the pressurized gas in step a) is selected from the group consisting of air, carbon dioxide, and mixtures thereof.

11. The process according to claim 1, characterized in that the heating means in step b) is selected from the group consisting of steam, hot air, * hot water, radiant heat, microwave, high frequency radiation, and electromagnetic waves.

12. The process according to claim 1, characterized in that the polymer is selected from the group consisting of polystyrene, polyethylene, polypropylene and an interpenetrating network of polyethylene and polymerized vinyl aromatic resins.

13. The process according to claim 12, characterized by the polymer is polystyrene.

14. The process according to claim 1, characterized in that the expandable polymer particles contain a blowing agent selected from the group consisting of an inorganic blowing agent, an organic blowing agent and mixtures thereof.

The process according to claim 1, characterized in that the expandable polymer particles are polystyrene, are pre-nucleated, and contain an organic blowing agent in an amount less than 3 weight percent based on the weight of the particles .

16. The process according to claim 1, characterized porgue particles of expandable polymer are pre-nucleated and contain an inorganic blowing agent selected from the group gue consisting of carbon dioxide, nitrogen, air, water, and mixtures thereof, and wherein the pressurized gas in step a) is selected from the group consisting of air, nitrogen, carbon dioxide, and mixtures thereof.

17. The process according to claim 1, characterized in that the expandable particles are pre-nucleated and contain carbon dioxide as the blowing agent, and wherein the gas in step a) is selected from air and carbon dioxide.

18. The process according to claim 1, characterized porgue expandable particles are comprised of particles of polystyrene solid gue are impregnated with carbon dioxide and then pre-nucleated, and wherein the pressurized gas in step a) is selected of air and carbon dioxide.

19. A porous foam article is formed from the polymer particles processed in accordance with the process of claim 1.

20. The particles characterized by porgue are processed according to steps a) and b) of the process in accordance with Claim 1

21. An apparatus for processing expandable polymer particles, characterized by comprising: a pressurizing unit for pressurizing the particles with a pressurized gas to create a gas pressure in the particles that is greater than the pressure outside the particles; a pre-expander unit for applying a heating medium at a temperature in the range between about 100 ° C and 120 ° C and a pressure in the range above the atmospheric pressure and lower than the gas pressure in the particles of such form gue the residual gas pressure in the particles is used as the blowing agent and the unit of pre-expander gue it includes a drying means to dry the particles at pressure ranging above atmospheric pressure and less pressure of gas in the particles until the particles are dried, and a molding unit or to form a foam article.

22. The apparatus according to claim 21, characterized in that the pressurized gas in the pressurization unit is selected from the group consisting of air, nitrogen, carbon dioxide and mixtures thereof.

23. The apparatus according to claim 21, characterized in that the pressurized gas in the pressurization unit is selected from the group consisting of air, carbon dioxide and mixtures thereof.

24. The apparatus according to claim 21, characterized in that the heating means in the pre-expander unit is selected from the group consisting of steam, hot air, hot water, radiation, microwave, high frequency radiation and electromagnetic radiation. .