Method for producing expanded polyolefin resin particles

Abstract

The present invention relates to a method for producing plastic foam particles, comprising the steps of providing a plastic material in the form of plastic material pre-expanded particles, filling the plastic material pre-expanded particles with a blowing agent under the influence of pressure and expanding the blowing agent filled plastic material pre-expanded particles to produce plastic foam particles, more particularly plastic foam particles having low density under the influence of temperature, in which the expansion of the blowing agent filled plastic material particles is carried out under the influence of temperature by irradiating the blowing agent filled plastic material particles with high-energy thermal radiation, in particular infrared radiation.

Description

[Technical field]

[0001] The present invention relates to a method for producing expanded polyolefin resin beads. [Background technology]

[0002] Methods for producing expanded polyolefin resin beads and for further processing them to produce expanded bead moldings are known per se in the related art.

[0003] Known methods for producing expanded polyolefin-based resin particles are based on a two-stage process. In the first stage, the thermoplastic polyolefin-based resin material is melted in an extruder and filled with the melt of the thermoplastic polyolefin-based resin material. In this way, the expanded polyolefin-based resin particles are produced in the extruder with a blowing agent. In the second stage, the thermoplastic polyolefin-based resin material emerging from the extruder in the form of strands, expanded or being expanded by the blowing agent, is granulated or ground.

[0004] In the first stage of the corresponding method, the blowing agent is dissolved in the melt of the thermoplastic resin material due to the pressure and temperature conditions in the extruder. After the thermoplastic polyolefin resin material filled with the blowing agent leaves the extruder, the pressure drop causes the blowing agent to transfer to the gas phase, resulting in the expansion of the polyolefin resin material.

[0005] The polyolefin resin material coming out of the extruder in the form of strands, for example through granulation or crushing by a cutting device, is immediately expanded by a blowing agent in the second step of the corresponding method after coming out of the extruder as described above, to form polyolefin resin foam particles, which can be further processed into foamed bead moldings in a separate processing step.

[0006] Firstly, the known methods are relatively complicated in terms of both system technology and processing technology. Moreover, the polyolefin-based resin expanded particles that can be produced using the known methods have room for improvement in terms of properties such as, for example, size, morphology and distribution of bubbles. From the viewpoint of system or processing technology, the possibilities of influencing the corresponding properties of the polyolefin-based resin expanded particles are significantly limited in the known methods.

[0007] Furthermore, in the known methods, it is difficult to produce polyolefin-based resin expanded particles starting from polyolefin-based resin pre-expanded particle material which are prevented from such damage or destruction, since the described extrusion-based processes damage or destroy the structure of the polyolefin-based resin pre-expanded particles, in particular due to the input of mechanical and thermal energy.

[0008] This applies in particular to the autoclave process known per se, in which polyolefin-based resin pre-expanded particles are expanded batchwise discontinuously to form foam beads using superheated steam in an autoclave (so-called postexpander / continuous expander). Here, the following problems need to be improved: poor energy efficiency, infrastructure requirements for steam generation and supply, risk of morphological deterioration of the foam beads produced over the entire volume, scattering of the foam beads due to different thermal conditions in different areas of the autoclave, and the subsequent drying process required to remove the water from the superheated steam. Summary of the Invention [Problem to be solved by the invention]

[0009] Based on this, the present invention also makes it possible to produce expanded polyolefin-based resin beads from pre-expanded polyolefin-based resin beads, and more specifically, it is an object of the present invention to provide an improved method for producing expanded polyolefin-based resin beads having properties that can be set in a targeted manner for subsequent processing into expanded bead moldings and their intended use or usage characteristics. [Means for solving the problem]

[0010] This object is achieved by a method according to claim 1. The dependent claims relate to possible embodiments of the method.

[0011] The first aspect of the present invention relates to a method for producing expanded polyolefin resin particles. Thus, the method described herein is generally used for producing expanded polyolefin resin particles. Thus, the particles of polyolefin resin that can be produced or produced according to the method are polyolefin resin particles that have at least a partial, typically an overall, cellular structure. The expanded polyolefin resin particles can also have a certain (further) expansion capacity due to a certain blowing agent content. This may be a residue from the described method or may be introduced in a separate processing step afterwards. Thus, the expanded polyolefin resin particles that can be produced or produced according to the method can be expandable and / or (mechanically) compressible due to their cellular structure. In any case, the expanded polyolefin resin particles that can be produced or produced according to the method can be called or considered as "expanded particles" or "expanded beads". As will be described later, the method is described as a method for radiation-based modification, i.e., more specifically, for the subsequent expansion or further expansion of pre-expanded polyolefin resin particles. The radiation-based modification is more specifically effected by targeted radiation that affects the particle structure and cell properties of the corresponding polyolefin-based resin pre-expanded particles, which, as mentioned, is more specifically understood to mean the subsequent expansion or further expansion of the pre-expanded particles.

[0012] The polyolefin resin foam particles, which can be produced or have been produced according to the method and are hereinafter also referred to as "plastic particles" or "plastic foam particles" for short, can be further processed into foamed bead moldings in one or more independent subsequent processes. The further processing of the resin foam particles into foamed bead moldings can be carried out using steam or superheated steam (steam-based) or without using steam or superheated steam (non-steam-based or dry).

[0013] The process steps for producing the plastic foam particles are described in further detail below.

[0014] In the first step of the method, the plastic material is provided in the form of polyolefin-based resin pre-expanded particles. The polyolefin-based resin pre-expanded particles provided according to the method are also referred to below simply as "pre-expanded particles of plastic material", but also optionally as "plastic pre-expanded particles". The plastic material considered as starting material is therefore an expanded particle material of polyolefin-based resin, and thus already a cellular polyolefin-based resin material, which is provided in the form of pre-expanded particles in the first step of the method. The pre-expanded plastic material provided is therefore in particulate form, i.e. more specifically in loose or disintegrated form. In the first step, therefore, at least one measure is generally carried out to provide the pre-expanded resin material in the form of particles, i.e. more specifically in loose or disintegrated form, in the form of the corresponding pre-expanded resin particles. Depending on the composition or modification of the material, the density of the plastic material pre-expanded particles provided in the first step of the method is usually less than 1 g / cm 3 Less than 0.05 to 1.5 g / cm, more specifically depending on the particle structure 3 This results in the expansion properties of the provided plastics material pre-expanded particles. The provided plastics material pre-expanded particles therefore have a porous or cellular structure.

[0015] Despite their cellular structure, the pre-expanded particles of plastic material can, if desired, contain at least one additive or auxiliary material, such as, for example, an elongated, spherical or platelet-shaped filler. More specifically, in the case of pre-expanded particles of plastic material containing additives or auxiliary materials, depending on the concentration of the additive or auxiliary material, the density can optionally be 1 g / cm 3 Corresponding additives or auxiliary materials may optionally be present in the resin which form bubbles, and may also have a nucleating effect.

[0016] The first step of the method can be carried out, optionally at least partially automatable or partially automated, by a feeding device arranged to continuously or discontinuously feed the plastic material corresponding to the form of the plastic pre-foamed material. The corresponding feeding device can be, for example, a conveying device, by means of which the plastic material pre-foamed particles to be processed into the corresponding plastic foamed particles can be conveyed to or into a filling device carrying out the second step of the method. The corresponding conveying device can be designed, for example, as or include a belt conveyor device or a flow conveyor device. Thus, conveying the plastics material pre-expanded particles to or into a filling device performing the second step of the method can include receiving the plastics material pre-expanded particles in a conveying stream. Thus, the plastics material pre-expanded particles can be conveyed by a conveying stream to or into a filling device performing the second step of the method.

[0017] In the second stage of the method, the plastic material pre-expanded particles are filled with the blowing agent at least under the influence of pressure. Thus, in the second stage, the plastic material pre-expanded particles are filled with the blowing agent at least under the influence of pressure. Optionally, depending on the material, in addition to a certain temperature, a certain (higher) temperature can also be applied. Thus, in the second stage, at least one means for filling the plastic material pre-expanded particles with the blowing agent is generally carried out at least under the influence of pressure, i.e. at least under pressure. Phenomenologically, in the second stage of the method, the blowing agent is typically enriched in the respective plastic material pre-expanded particles. The enrichment of the blowing agent in the respective plastic material pre-expanded particles is, for example, from or through the absorption and / or dissolution process of the blowing agent in the respective plastic material pre-expanded particles, more specifically depending on the chemical structure of the plastic material pre-expanded particles, the blowing agent and the additives or auxiliary materials optionally contained, and, as mentioned above, depending on the pressure or temperature conditions, which are usually selected depending on the material. The cellular structure of the plastic material pre-expanded particles may also result in concentration or accumulation of the blowing agent within the cellular spaces provided by the cellular structure, i.e. the internal volume of each pre-expanded plastic material defined by the cellular spaces may be utilized as receiving space for receiving the blowing agent in the second step of the method.

[0018] The pressure level in the second stage of the method is usually selected, in particular depending on the material, such that the cell structure of the plastics material pre-expanded particles is not damaged. More specifically, the pressure level in the second stage of the method is selected such that the cell structure of the plastics material pre-expanded particles is not damaged in an undesirable way by the pressure, i.e. is not plastically deformed or even, for example, completely collapsed. In this connection, the effective difference between the external load pressure and the internal cell pressure is of particular importance.

[0019] The same applies more specifically to the pressure rise rate, i.e. the rate at which the external pressure increases from the initial level to the target level in the second stage. Typically, the pressure rise rate will be in the range of 0.001 bar / min to 1000 bar / min. More specifically, between 0.01 bar / min to 1000 bar / min, even more specifically, between 0.1 bar / min to 1000 bar / min, even more specifically, between 1 bar / min to 1000 bar / min, even more specifically, between 2, 3, 4, 5, 6, 7, 8, 9 or 10 bar / min to 1000 bar / min, even more specifically, between 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 89, 85, 9 0, 95 or 100 bar / min to 1000 bar / min, even more specifically 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525, 550, 575, 600, 625, 650, 675, 700, 735, 750, 775, 800, 825, 850, 875, 900, 925, 950 or 975 bar / min to 1000 bar / min. All intermediate values ​​not explicitly listed here are also acceptable.

[0020] Gases such as carbon dioxide, or mixtures containing carbon dioxide and / or nitrogen, such as air, can be used as the blowing agent. In general, flammable or non-flammable organic gases, in particular butane or pentane; or inert gases, such as noble gases, i.e. more specifically helium, neon, argon, etc.; nitrogen, or mixtures thereof, can be used. The term "blowing agent" can therefore also include mixtures of chemically and / or physically different blowing agents. The selection of a blowing agent typically takes into account its absorption capacity in the plastics material pre-expanded particles, i.e. the chemical and / or physical constitution or composition of the plastics material pre-expanded particles. If the plastics material pre-expanded particles contain additives or auxiliary materials, the properties such as the chemical and / or physical constitution of the additives or auxiliary materials can also be taken into account when selecting the blowing agent.

[0021] The second stage of the method can be at least partially automated or partially automated, as required, and can be carried out by a filling device that is configured to fill the plastic material pre-expanded particles with a blowing agent under the influence of at least a pressurized pressure or to carry out a corresponding filling process. The corresponding filling device can, for example, be designed as or include an autoclave device, i.e. generally as a pressure vessel device including an optionally temperature-controllable pressure or treatment space. The corresponding filling device can also have a temperature control device that is configured to control the temperature of the corresponding pressure or treatment space. The corresponding filling device can in any case have a control and / or regulation unit implemented in hardware and / or software, which is configured for control and / or regulation, i.e. generally for setting certain dynamic and / or static pressure and / or temperature parameters in the corresponding pressure or treatment space.

[0022] In the third stage of the method, the plastic material pre-expanded particles filled with the blowing agent are expanded to generate cellular resin particles under the influence of temperature, i.e. more specifically, at high temperature. As a result, the plastic material pre-expanded particles filled with the blowing agent are typically exposed to high temperature in the third stage of the method, i.e. generally to thermal energy, which leads to outgassing and / or expansion of the blowing agent contained in the plastic material pre-expanded particles. This is typically done in the dry state, i.e. without external influence of a fluid, such as, for example, water vapor or water. More specifically, the outgassing or expansion of the blowing agent in the cellular and matrix regions of the thermally softened or softened plastic material pre-expanded particles causes the plastic material particles to expand again or further, which, after cooling or "freezing", leads to the formation of plastic particles with a permanent cellular structure that may have changed compared to the starting material, for example, in terms of the number and / or shape and / or size of the bubbles, and thus leads to the formation of the cellular plastic particles to be produced. Thus, in the third step of the method, at least one means is carried out to release or expand the blowing agent gas from the cellular and matrix regions of the plastic material pre-expanded particles that have been thermally softened or softened by the influence of temperature, thereby producing plastic foam particles. Phenomenologically, in the third stage of the method, more specifically, outgassing or desorption of the blowing agent from the cell and matrix regions of the softened or mushy plastic material pre-expanded particles causes further cell growth and possibly new cell formation and subsequent cell growth within the plastic material pre-expanded particles, resulting in plastic foam particles having, if desired, a significantly lower density compared to the plastic pre-expanded particles. Where bubble formation occurs, it is typically based on the aforementioned detachment of the blowing agent at the nucleation points of the plastic material particles which soften or have been softened under the influence of temperature, whereas bubble growth is usually based on the positive pressure-associated expansion of the blowing agent within already formed or existing bubbles. As also mentioned, the cellular structure thus formed or the further expansion state thus achieved is permanently "frozen" or fixed by lowering the temperature of the resin foam particles thus produced, i.e., by cooling them, for example, by the environment.

[0023] As a result, it is in principle true that after completion of the pressurization carried out in the second stage of the method, i.e. more particularly in the case of pressure reduction to normal or standard conditions, a degassing or desorption process takes place within each pre-expanded plastic material particle filled with blowing agent and typically thermally softened. The blowing agent outgassing or desorption process is an essential prerequisite for the bubble growth process, and optionally for the bubble formation process within the respective plastic material particle, which is necessary for the production of the plastic foam particles. In a third step of the method, more specifically by a corresponding outgassing or desorption process, the plastic foam particles produced according to the method are formed from the blowing agent-filled, typically heat-softened, pre-expanded plastic material particles present after the second step of the method.

[0024] As mentioned above, the plastic foam particles to be produced or produced according to the present method have a lower density than the plastic pre-expanded particles. Therefore, the present method serves to produce lower density plastic foam particles as mentioned above. Therefore, the present method can also be referred to as a method for radiation-based modification of plastic pre-expanded particles, i.e., more specifically, radiation-based post-expansion or further expansion.

[0025] As described below, by controlling the cell formation and cell growth processes associated with the corresponding gas release or desorption, it is possible in some cases to achieve cell structures with locally different cell properties and thus graded plastic foam particles.

[0026] In general, it is true that according to the method, more specifically, plastic foam particles can be produced with bubble sizes ranging from 0.5 to 250 μm. As a result, the actual bubble size (of course, typically referring to the average value) can be set over a very wide range. It can therefore be adjusted according to the process depending on the selected processing conditions. The same applies to the distribution of bubble sizes within the respective plastic foam particles.

[0027] More specifically, the methods described herein can provide a thickness of less than 250 μm, more specifically less than 240 μm, even more specifically less than 230 μm, even more specifically less than 220 μm, even more specifically less than 210 μm, even more specifically less than 200 μm, even more specifically less than 190 μm, even more specifically less than 180 μm, even more specifically less than 170 μm, even more specifically less than 160 μm, even more specifically less than 150 μm, even more specifically less than 140 μm, even more specifically less than 130 μm, even more specifically less than 120 μm, even more specifically less than 110 μm, even more specifically less than 100 μm, even more specifically less than 90 μm, even more specifically less than 80 μm, even more specifically less than 70 μm, even more specifically less than 60 μm, even more specifically less than 50 μm, and even more specifically less than 100 μm. In some embodiments, the plastic foam particles may have an (average) cell size of less than 45 μm, even more specifically less than 40 μm, even more specifically less than 35 μm, even more specifically less than 30 μm, even more specifically less than 25 μm, even more specifically less than 24 μm, even more specifically less than 23 μm, even more specifically less than 22 μm, even more specifically less than 21 μm, even more specifically less than 20 μm, even more specifically less than 19 μm, even more specifically less than 18 μm, even more specifically less than 17 μm, even more specifically less than 16 μm, even more specifically less than 15 μm, even more specifically less than 14 μm, even more specifically less than 13 μm, even more specifically less than 12 μm, even more specifically less than 11 μm, even more specifically less than 10 μm, or even smaller. All intermediate values ​​not explicitly listed here are also contemplated.

[0028] The third step of the method can be carried out, optionally at least partially automatable or partially automated, by an expansion device configured to radiatively expand the blowing agent for producing plastic foam particles, at least under the influence of temperature, in order to carry out a corresponding radiation-based expansion process. The corresponding expansion devices are typically designed as or include radiation-based heating devices, i.e., generally as temperature-controlled devices that include a temperature-controlled or processing space whose temperature is controllable or at least controlled based on radiation. The corresponding temperature control device may also have a conveying device, which is configured to convey the plastic material particles to be expanded along a conveyor line through the corresponding temperature control or treatment space. In any case, the corresponding expansion device may have a control and / or adjustment unit implemented in hardware and / or software, which control and / or adjustment unit is set for controlling and / or regulating, i.e. generally for setting certain dynamic and / or static transport and / or temperature and / or radiation parameters in the corresponding temperature control or treatment space.

[0029] More specifically, the third stage of the process can optionally be carried out continuously, which is advantageous compared to the batchwise autoclave-based process mentioned at the beginning.

[0030] The density of the plastic foam particles produced in the third step of the method is typically significantly lower than the initial density of the plastic material pre-expanded particles provided in the first step, resulting in the cellular properties of the plastic particles producible or produced according to the method. Thus, the bulk density of the plastic foam particles produced in the third stage of the process is significantly lower than the bulk density of the plastic material pre-expanded particles provided in the first stage of the process.

[0031] The plastic foam particles produced in the third step of the method are typically further or subsequently expandable, as described above, which may represent an essential property for the described, more particularly steam-based or non-steam-based, further processing of the plastic foam particles for the production of foamed bead moldings.

[0032] The method is therefore distinguished from known methods by a special dynamic process control which requires the softening necessary for expansion but, in contrast to extrusion processes, does not require complete melting of the pre-foamed plastic material filled with foaming agent and therefore does not require pressure- and temperature-intensive filling of the foaming agent into the plastic material melt. Dynamic process control, i.e., more specifically, the ability to rapidly (volumetric) heat, as opposed to the convective and conductive energy transport in steam-based post-foaming, is also important for high energy efficiency (due to the lack of time for bubble fusion) and also for the significantly finer bubble morphology mentioned below. The method is therefore associated with a (greatly) simplified technical effort and system required for its implementation, in which plastic material pre-expanded particles are filled with a blowing agent, and the corresponding plastic material particles filled with the blowing agent can be converted into plastic expanded particles at least under the influence of temperature, more particularly under the influence of temperature and pressure.

[0033] Furthermore, the properties of the plastic foam particles producible or produced according to the present method, more particularly those relating to the number, size, shape and distribution of the bubbles, are improved, resulting from the easily settable and very well controllable processing conditions as part of the loading occurring in the second stage of the method and as part of the expansion occurring in the third stage of the method.

[0034] In contrast to the autoclave-based foaming process described at the beginning, this method allows a continuous foaming process of the corresponding plastic pre-foamed particles filled with foaming agent and does not require subsequent drying due to the absence of superheated steam.

[0035] The method therefore allows for significantly expanded processing methods which can be precisely set or adjusted for each plastic material and in principle makes it possible to produce plastic foam particles with the desired properties from any (thermoplastic) plastic material pre-expanded particles.

[0036] As mentioned above, the impregnation of the plastics material pre-expanded particles with the blowing agent can be carried out under the influence of pressure and temperature. Thus, the parameters which can be varied in order to impregnate the plastic material pre-expanded particles with the blowing agent and subsequently target specific properties of the produced or produced plastic foam particles are, first of all, the pressure and temperature conditions prevailing in the second stage of the method. Of course, time is also important, that is to say, more specifically, the course and duration of the pressure and temperature conditions in the second stage of the method, i.e. parameters which influence the loading of the plastics material pre-expanded particles with the blowing agent, more specifically, the absorption of the blowing agent in the plastics material pre-expanded particles.

[0037] Specific parameters for carrying out the second step of the method are given by way of example below:

[0038] The impregnation of the plastics material pre-expanded particles with the blowing agent can be carried out, for example, under a pressure in the range of 1 to 200 bar, more particularly in the range of 1 to 190 bar, even more particularly in the range of 1 to 180 bar, even more particularly in the range of 1 to 170 bar, even more particularly in the range of 1 to 160 bar, even more particularly in the range of 1 to 150 bar, even more particularly in the range of 1 to 140 bar, even more particularly in the range of 1 to 130 bar, even more particularly in the range of 1 to 150 bar, even more particularly in the range of 1 to 160 bar, even more particularly in the range of 1 to 170 bar, even more particularly in the range of 1 to 180 bar, even more particularly in the range of 1 to 190 bar, even more particularly in the range of 1 to 180 bar, even more particularly in the range of 1 to 190 bar, even more particularly in the range of 1 to 190 bar, even more particularly in the range of 1 to 20 ... It can be carried out in the range of 120 bar, more particularly in the range of 1 to 110 bar, more particularly in the range of 1 to 100 bar, more particularly in the range of 1 to 90 bar, more particularly in the range of 1 to 80 bar, more particularly in the range of 1 to 70 bar, more particularly in the range of 1 to 60 bar, more particularly in the range of 1 to 50 bar, more particularly in the range of 1 to 40 bar, more particularly in the range of 1 to 30 bar, more particularly in the range of 1 to 20 bar, more particularly in the range of 1 to 10 bar. Instead of 1 bar, 2, 3, 4, 5, 6, 7, 8, 9 or 10 bar can also be used as lower limit values. The aforementioned pressures mentioned as examples refer more specifically to the pressure of the corresponding filling device or to the pressure in the processing space when the second stage of the method is carried out. All intermediate values ​​not explicitly listed here are also conceivable.

[0039] As mentioned above, the pressure level, and more particularly the rate of pressure increase in the second stage of the method, depends more particularly on the material and is usually selected so that the cellular structure of the plastic material pre-expanded particles is not damaged. More specifically, the pressure level, more specifically the rate of pressure rise, in the second stage of the method is selected such that the cellular structure of the plastic material pre-expanded particles is plastically deformed and does not collapse due to the pressure (effective difference between the external load pressure and the internal cellular pressure).

[0040] Filling the plastic material pre-expanded particles with a blowing agent can be carried out, for example, at a temperature in the range of 0 to 250°C, even more specifically in the range of 0 to 240°C, even more specifically in the range of 0 to 230°C, even more specifically in the range of 0 to 220°C, even more specifically in the range of 0 to 210°C, even more specifically in the range of 0 to 200°C, even more specifically in the range of 0 to 190°C, even more specifically in the range of 0 to 180°C, even more specifically in the range of 0 to 170°C, even more specifically in the range of 0 to 160°C, even more specifically in the range of 0 to 180°C, even more specifically in the range of 0 to 170°C, even more specifically in the range of 0 to 170°C, even more specifically in the range of 0 to 160°C, even more specifically in the range of 0 to 19 ...60°C, even more specifically in the range of 0 to 160°C, even more specifically in the range of 0 to 160°C, even more specifically in the range of 0 to 160°C, even more specifically in the range of 0 to The heating can be performed in the range of 0 to 150°C, more specifically, in the range of 0 to 140°C, even more specifically, in the range of 0 to 130°C, even more specifically, in the range of 0 to 120°C, even more specifically, in the range of 0 to 110°C, even more specifically, in the range of 0 to 100°C, even more specifically, in the range of 0 to 90°C, even more specifically, in the range of 0 to 80°C, even more specifically, in the range of 0 to 70°C, even more specifically, in the range of 0 to 60°C, even more specifically, in the range of 0 to 50°C, even more specifically, in the range of 0 to 40°C, even more specifically, in the range of 0 to 30°C, and even more specifically, in the range of 0 to 20°C. The aforementioned temperatures given as examples refer more specifically to the pressure or temperature in the processing space of the corresponding filling device when the second stage of the method is carried out. All intermediate values ​​not explicitly listed here are also conceivable.

[0041] Filling the plastic material pre-expanded particles with the blowing agent can be carried out, for example, more specifically, depending on the chemical composition of the plastic material pre-expanded particles and / or the blowing agent, for a period of time in the range of 0.1 to 1000 hours, more specifically, in the range of 0.1 to 950 hours, even more specifically, in the range of 0.1 to 900 hours, even more specifically, in the range of 0.1 to 850 hours, even more specifically, in the range of between 0.1 to 800 hours, even more specifically, in the range of 0.1 to 750 hours, even more specifically, in the range of 0.1 to 700 hours, even more specifically, in the range of 0.1 to 650 hours, even more specifically, in the range of 0.1 to 600 hours, even more specifically, in the range of 0.1 to 550 hours, even more specifically, in the range of 0.1 to 500 hours, even more specifically, in the range of 0.1 to 450 hours, even more specifically, , 0.1 to 400 hours, more specifically, 0.1 to 350 hours, more specifically, 0.1 to 300 hours, more specifically, 0.1 to 250 hours, more specifically, 0.1 to 200 hours, more specifically, 0.1 to 150 hours, more specifically, 0.1 to 100 hours, more specifically, 0.1 to 90 hours, more specifically, 0.1 to 80 hours, more specifically, 0.1 to 70 hours, more specifically, 0.1 to 60 hours, more specifically, 0.1 to 50 hours, more specifically, 0.1 to 40 hours, more specifically, 0.1 to 30 hours, more specifically, 0.1 to 20 hours, and more specifically, 0.1 to 10 hours. The aforementioned durations given as examples refer more specifically to the pressure or temperature exposure of the plastic material particles in the pressure or processing space of the corresponding filling device when the second stage of the method is carried out. All intermediate values ​​not explicitly listed here are also conceivable.

[0042] Specific parameters for carrying out the third step of the method are given by way of example below:

[0043] The expansion of the blowing agent-filled plastic particle material under the influence of temperature, more specifically depending on the chemical composition of the blowing agent and / or the blowing agent, to produce plastic foam particles can take place, for example, at normal pressure, i.e. at ambient pressure of about 1 bar. Thus, a particular pressure level, e.g., a positive or negative pressure level, can simplify the process of expanding the blowing agent filled plastic material pre-expanded particles to produce plastic foam particles, but is not absolutely necessary.

[0044] The expansion of the blowing agent-filled plastic particle material to produce plastic foam particles under the influence of temperature can be carried out, for example, more specifically in the range of 20-300°C, more specifically in the range of 20-290°C, even more specifically in the range of 20-280°C, even more specifically in the range of 20-270°C, even more specifically in the range of 20-260°C, even more specifically in the range of 20-250°C, even more specifically in the range of 20-240°C, even more specifically in the range of 20-230°C, even more specifically in the range of 20-220°C, even more specifically in the range of 20-210°C, even more specifically in the range of 20-200°C, even more specifically in particular in the range of 20-190°C, even more specifically in the range of 20-210°C, even more specifically in the range of 20-200°C, even more specifically in particular ...00°C, even more specifically in particular in the range of 20-200°C, even more specifically in particular in the range of 20-200°C, even more specifically in particular More specifically, at temperatures in the range of 20-180° C., even more specifically in the range of 20-170° C., even more specifically in the range of 20-160° C., even more specifically in the range of 20-150° C., even more specifically in the range of 20-140° C., even more specifically in the range of 20-130° C., even more specifically in the range of 20-120° C., even more specifically in the range of 20-110° C., even more specifically in the range of 20-100° C., even more specifically in particular in the range of 20-90° C., even more specifically in the range of 20-80° C., even more specifically in the range of 20-70° C., even more specifically in the range of 20-60° C., even more specifically in the range of 20-50° C., even more specifically in the range of 20-40° C., even more specifically in the range of 20-30° C. All intermediate values ​​not explicitly listed here are also contemplated.

[0045] The aforementioned temperatures may more specifically refer to the inlet temperature when the plastic material pre-expanded particles filled with the blowing agent enter the corresponding expansion device, and / or the outlet temperature when the plastic foam particles leave the corresponding expansion device. The corresponding inlet and outlet temperatures may be the same, similar, or different. In case the corresponding expansion device comprises a conveying device configured to convey the plastic particle material filled with foaming agent along the corresponding temperature control device, the aforementioned temperatures refer to the temperature at which the plastic pre-expanded particle material filled with foaming agent enters the corresponding expansion device or temperature control device, i.e. in the initial region of the corresponding conveying device (inlet temperature) and / or the outlet temperature at which the plastic particles leave the corresponding expansion device or temperature control device, i.e. in the end region of the corresponding conveying device (outlet temperature). Typically, the inlet temperature will be lower than the outlet temperature.

[0046] The expansion of the plastic material pre-expanded particles filled with a blowing agent under the influence of temperature is carried out by irradiating the plastic material pre-expanded particles filled with a blowing agent with high-energy thermal radiation, i.e., more specifically, infrared radiation. More specifically, infrared radiation having a wavelength in the range of 1 μm to 15 μm, more specifically 1.4 μm to 8 μm, and even more specifically 1.4 μm to 3 μm is considered. The wavelength of the infrared light is typically selected depending on the material. The temperature control, i.e. more specifically the heating of the plastic material pre-expanded particles filled with a foaming agent, can be carried out in a very targeted manner, more specifically by selecting and / or setting the properties of the high-energy radiation used, i.e. more specifically its wavelength, depending on the material, without melting or fusion, which is undesirable for the expansion process of the plastic material particles filled with a foaming agent, i.e. softening of the plastic material pre-expanded particles filled with a foaming agent upon heating and insufficient stability of the softened plastic material particles. Research has shown that infrared light is particularly suitable in this case, as it allows a very easily controllable volumetric heating, a controllable softening process and therefore a controllable expansion process (which is essential for setting the properties of the produced plastic foam particles) of the plastic material pre-expanded particles filled with foaming agent in conjunction with a conveyor device.

[0047] More specifically, the expansion of the plastic material particles filled with a foaming agent can be carried out under the influence of temperature by irradiating the pre-expanded particles of the plastic material filled with a foaming agent with high-energy thermal radiation, more specifically infrared radiation, which are continuously transported on at least one conveyor line defined by a transport device, more specifically along at least one radiation generating device generating corresponding high-energy radiation, more specifically infrared radiation. The corresponding radiation generating device can be more specifically designed as or can include an infrared oven, more specifically an infrared continuous oven, which can include one or more infrared emitters arranged or formed along the corresponding conveyor line. A corresponding infrared emitter can have, for example, an arbitrarily variable radiation output in the range of 1 to 500 kW, even more specifically in the range of 1 to 450 kW, even more specifically in the range of 1 to 400 kW, even more specifically in the range of 1 to 350 kW, even more specifically in the range of 1 to 250 kW, even more specifically in the range of 1 to 200 kW, even more specifically in the range of 1 to 150 kW, even more specifically in the range of 1 to 100 kW, even more specifically in the range of 1 to 50 kW. Instead of 1 kW, 2, 3, 4, 5, 6, 7, 8, 9, or 10 kW may also be used as lower limits. All intermediate values ​​not explicitly listed here are also possible.

[0048] The aforementioned power output can more specifically refer to area power output per square meter. Studies have focused on power output in the range of 5 to 100 kW / m 2 It has been shown that good results can be obtained with an area output of 10 ...

[0049] According to the method, after the expansion of the plastic material particles filled with the blowing agent to produce the plastic foam particles, the produced plastic foam particles can be cooled under the influence of temperature (more specifically, a lower temperature compared to the previously carried out expansion process), as described above. Cooling, which is expediently rapid, makes it possible to "freeze" the cell structure of the plastic foam particles present after the expansion process. In this way, further, global or merely localized expansion of the plastic particles, which may be undesirable after the expansion treatment, can in particular be prevented, for example maintaining the cell structure of the plastic particles which is desirable after the expansion treatment. Cooling can occur, more specifically, from a processing temperature above a reference temperature (more specifically, room temperature can be used as the reference temperature) to a cooling temperature below the processing temperature or the reference temperature (more specifically, room temperature). Therefore, a separate temperature control device for cooling the plastic particles is not necessarily required, but it is sufficient to cool the plastic particles to room temperature or store them at room temperature after the foaming process.

[0050] According to this method, as described above, at least one, in particular functional, additive or auxiliary material, For example, fibres or fibre materials and / or dyes or colour materials and / or nucleating substances or nucleation materials and / or For example, to targetably influence or control the softening properties of the plastic material particles filled with the blowing agent, a pre-expanded plastic particle material can be provided or used that includes substances or materials such as additives for adjusting the melt viscosity, e.g., chain extenders, or additives for increasing the absorption coefficient, e.g., graphite, carbon black, etc. Alternatively or additionally, a plastic pre-expanded particle material may be provided or used which contains at least one additive from the group consisting of antioxidants, UV stabilizers, antistatic agents, flow or non-stick additives, flame retardant additives, pigments, dyes and mixtures thereof. The antioxidant can be present, for example, in the range of 0 to 2.5 wt %, and more specifically, in the range of 0 to 1 wt %; UV stabilizers, for example amine or nickel-based UV stabilizers, for example in a proportion of 0-5% by weight, more particularly 0-2.5% by weight (in the case of amine or nickel-based UV stabilizers, more particularly a proportion of 0-5% by weight applies, even more particularly 0-2.5% by weight applies); antistatic agents in a proportion of 0-5% by weight, more specifically 0-1% by weight to 2.5% by weight; Flowable or non-sticky additives in a proportion of 0-5% by weight, more specifically 0-2.5% by weight; antiblocking additives in a proportion between 0 and 5% by weight, more particularly between 0 and 2.5% by weight; the nucleating additive in a proportion of 0 to 5% by weight, more particularly 0 to 2.5% by weight, and The flame retardant additive may be present in a proportion of 0 to 65% by weight, more particularly 0 to 20% by weight, even more particularly 0 to 5% by weight, and even more particularly 0 to 2.5% by weight. For example, pigments such as carbon black or dyes may be present in amounts of 0-15% by weight (each).

[0051] Thus, according to this method, the pre-expanded plastic material particles, which are compounded with these and filled with a blowing agent, can also be expanded, so that plastic foam particles with special properties are obtained. More specifically, tailor-made plastic particles can be produced for a specific application or area of ​​use through the targeted selection and concentration of corresponding additives or auxiliary materials, which may have been introduced into the pre-expanded plastic material particles as part of their production.

[0052] More specifically, the fibers or fiber materials (which in principle can be organic or inorganic fibers or fiber materials, so that mention should be made, for example, of aramid, glass, carbon or natural fibers) can be used in further processes in order to realize the special material properties of the plastic foam particles producible or produced according to the method or of the foamed bead moldings producible or produced from the plastic foam particles produced according to the method. The corresponding plastic foam particles or the foamed bead moldings produced therefrom are characterized, on the one hand, by a particular density due to their cell structure and, on the other hand, more particularly, according to the method, by the mechanical bonding of adjacent cells within each plastic foam particle and / or between each adjacent plastic foam particle due to special mechanical properties. During subsequent processing of the particle foam into molded articles, these special mechanical properties can be utilized or even modified locally or integrally. Regardless of their chemical composition, the same applies in principle to non-fibrous or non-fibrous shaped additives or auxiliary materials, for example spherical or globular or platelet-shaped organic and / or inorganic additives or auxiliary materials.

[0053] In addition to influencing the mechanical properties of the plastic particles in a targeted manner, the electrical and / or thermal properties of the plastic particles can be influenced in a targeted manner using corresponding additives or auxiliary materials. Thus, plastic particles with special electrical and / or thermal conductivity can be produced, for example, by means of electrically and / or thermally conductive additives or auxiliary materials, such as metal and / or carbon black particles.

[0054] The concentrations of the corresponding additives or auxiliary materials usually vary depending on the material but can in principle be freely selected. It is thus mentioned merely by way of example that plastic material pre-expanded particles can be provided or used which contain one (or more) additives or auxiliary materials in a concentration between 0.01% by weight (applies in particular to chemically active additives) and 60% by weight (applies in particular to fibrous additives). As indicated, the concentrations usually depend on the specific chemical and / or physical properties of the additives or auxiliary materials or combinations thereof.

[0055] According to this method, it has been stated that in principle any thermoplastic material can be provided or used as starting material. Thus, merely by way of example, polypropylene, mixtures of polypropylene, polyethylene, mixtures of polyethylene, polyethylene-polypropylene mixtures, copolymers of ethylene and at least one other olefin monomer, copolymers of propylene and at least one other olefin monomer, and / or mixtures of the above are provided or used as particles of polyolefin-based resin materials. Thus, mixtures of different thermoplastic polyolefin-based resin materials can also be used. Modified polyolefins (mPO) are mentioned in this context only as examples.

[0056] When polyolefin-based blends are used that contain at least two (poly)olefin components differing in at least one chemical and / or physical parameter and / or parameter relating to molecular structure, these blends can essentially be present in any proportional composition, the respective percentages adding up to 100%. Thus, the first component can be present in any weight percentage between 1 and 99% by weight, the second component can be present in any weight percentage between 99 and 1% by weight, the respective percentages adding up to 100% by weight. Of course, percentages below 1% and above 99% by weight are also conceivable.

[0057] For example, copolymers of propylene and at least one other olefin component can be used, the proportion of the at least one olefin monomer being in the range of 0.5-50% by weight, more particularly in the range of 1-10% by weight. In addition to ethylene / propylene, the corresponding olefin monomers can be butene, hexene, octene, etc. The same applies to copolymers of ethylene and at least one other olefin component.

[0058] The corresponding copolymers may have a melting temperature in the range of 100 to 140°C, more specifically in the range of 120 to 140°C, and even more specifically greater than 140°C.

[0059] Likewise, a mixture of at least two different copolymers can be used. Merely by way of example, reference is made to a mixture of a first copolymer (copolymer A) of propylene and at least one olefin component having a melting temperature above 140° C., and another copolymer (copolymer B) of propylene and at least one olefin component having a melting temperature between 120° C. and 140° C. The proportion of copolymer B relative to the total mixture can range from 0.1 to 50% by weight, more particularly from 0.1 to 25% by weight. The percentages of copolymer A are such that the sum of the percentages equals 100% by weight.

[0060] As mentioned above, any plastic materials used may contain one or more additives, such as fibers, etc. Any plastic materials used may be recyclable or contain a certain percentage of recycled content.

[0061] It has been stated that the properties of the low density plastic foam particles producible or produced according to the present method can be influenced more particularly by the processing conditions during the filling and expansion processes.

[0062] Thus, depending on the selected processing conditions, for example, the method makes it possible to produce foamed plastic particles having a uniformly or non-uniformly distributed cell structure. The properties, and more particularly the distribution of the cell structure within the respective plastic foam particle, can therefore be influenced, in addition to material-specific parameters, also by the pressure, temperature and time during filling or expansion, the transport or residence times or conditions between the individual processing steps.

[0063] When plastic foam particles having a non-uniformly distributed cell structure are produced by this method, each plastic foam particle in the edge region can have a different number, shape, and / or size of cells than in the core region. Thus, graded plastic foam particles can be produced with different distributions of cell count, cell shape, and / or cell size, resulting in a special range of properties. As a result, graduated plastic foam particles may have different cell properties in the (outer) edge region and the (inner) core region, for example core-shell particles.

[0064] Correspondingly configured plastic foam particles can be obtained, more specifically, by filling the compressed starting material with foaming agent for a (very) short time, after which the foaming agent accumulates only near the edges and therefore, more specifically, expansion takes place at the edges. Conversely, a (very) long storage period between blowing agent filling and expansion can result in plastic foam particles with a predominantly expanded "core".

[0065] It is true that in general, this method makes it possible to produce plastic foam particles, more specifically having bubble sizes in the range of 0.5 to 250 μm. This method therefore allows the actual bubble size (which of course in this context usually refers to the average) to be set over a very wide range and can be adjusted depending on the selected processing conditions. The same applies to the cell size distribution within each plastic foam particle.

[0066] In general, it is also true that, more specifically, depending on the degree of expansion and optionally the filler content, plastic foam particles having a bulk density in the range of 5 to 1000 g / l can be produced according to the present process. The actual bulk density (which of course also in this context usually refers to an average) can therefore be set over a very wide range and can be adjusted depending on the selected processing conditions.

[0067] Below, purely by way of example, plastics material pre-expanded particles which can be or have been treated in particular as part of the method and the relevant parameters for carrying out the second and third steps of the method are given.

[0068] In the context of this example, in a first step of the process, a pre-expanded expandable polypropylene plastic material, i.e. polypropylene-based resin material particles, having a bulk density of about 75 g / l, was provided. In the second stage of the method, the plastic material pre-expanded particles were filled with air as a foaming agent in a pressure vessel at a pressure of about 8 bar for 100 hours without any special temperature control. The pressure rise rate was about 0.2 bar per hour. In the third stage of the method, more specifically, the plastic material pre-expanded particles filled with a foaming agent were expanded by continuously or discontinuously conveying the plastic material pre-expanded particles filled with a foaming agent through an infrared continuous oven containing several infrared emitters, i.e. by conveying the plastic material particles along a temperature-controlled line of about 5 m in length formed by a conveyor and several temperature-controlled elements in the form of infrared emitters with a total radiator power of about 20 kW. The temperature of the conveyor belt at the entrance to the conveyor line was approximately 85°C. The temperature of the conveyor belt at the exit of the conveyor or temperature controlled line was approximately 160°C. The conveying speed was about 450 mm / s. The bulk density of the plastic foam particles produced by this method was about 35 g / l.

[0069] A second aspect of the invention relates to a particle foam material formed by or comprising plastic foam particles produced according to the method according to the first aspect.

[0070] A third aspect of the invention relates to a method of processing plastic particle material according to the second aspect for producing expanded bead moulded bodies.

[0071] A fourth aspect relates to an apparatus for producing plastic foam particles, more specifically according to the method according to the first aspect, comprising: - a first device arranged for filling the thermoplastic pre-expanded particles with a blowing agent under the influence of pressure, more particularly a device comprising a filling device, for example in the form of a pressure vessel device; and - a second device set up for expanding the foaming agent for producing plastic foam particles under the influence of temperature, more specifically the second device comprises an expansion device in the form of a radiation generator for generating high-energy radiation, in particular infrared radiation.

[0072] The second device may therefore more particularly be designed as or include a radiation-based heating device.

[0073] The second device may include a conveying device, more specifically a combination of a conveyor and a temperature control device. The corresponding combined conveyor and temperature control device may be designed as at least a continuous oven, more specifically an infrared continuous oven including one or more infrared emitters.

[0074] Furthermore, the second device can be associated with a relaxation device, such as, for example, a relaxation space in which the produced plastic foam particles are stored (relaxed) under defined chemical and / or physical conditions, more particularly at defined temperature conditions, for a defined time. A corresponding relaxation device can, for example, be designed as or include a pressure reducing device.

[0075] It is conceivable that the apparatus further comprises a conveying device, by means of which the produced plastic foam particles are conveyed continuously or discontinuously through the corresponding relaxation spaces.

[0076] The apparatus may further comprise suitable handling equipment for handling the plastics material pre-expanded particles to provide and / or remove the produced plastics material pre-expanded particles. The corresponding handling devices can be designed as or can include conveying devices. More specifically, conveying devices suitable for conveying bulk material, for example pneumatic conveying devices set up to form a conveying flow, come into consideration.

[0077] The apparatus can essentially comprise a conveying device, by means of which the plastics material pre-expanded particles, and also the plastic expanded particles, can be conveyed continuously or discontinuously through the individual devices of the apparatus.

[0078] Any statements made regarding the method according to the first aspect equally apply to the particle expansion material according to the second aspect, the method according to the third aspect and the apparatus according to the fourth aspect.

[0079] The invention is again explained below by way of example using exemplary embodiments with reference to the drawings. [Brief description of the drawings]

[0080] [Figure 1] FIG. 1 shows a flow chart illustrating a method according to an exemplary embodiment. [Diagram 2] FIG. 2 shows a schematic diagram of an apparatus for carrying out a method according to an exemplary embodiment. [Diagram 3] FIG. 3 shows a schematic diagram of a plastic foam particle produced according to a method according to an exemplary embodiment. [Figure 4] FIG. 4 shows a schematic diagram of a plastic foam bead produced according to a method according to an exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0081] FIG. 1 shows a flow chart illustrating a method according to an exemplary embodiment.

[0082] The method is a method for producing plastic foam particles. The method is therefore used for producing plastic foam particles. The plastic particles which can be produced or have been produced according to the method and have a lower density compared to the starting material are plastic particles which have at least a partial, possibly even a total, cellular structure. The plastic particles can also have a certain (further) expansion capacity due to a certain blowing agent content. The blowing agent can be a residue from the described method or can be introduced later in another process step. The density of the plastic foam particles which can be produced or have been produced according to the method can therefore be expandable and / or (mechanically) compressible.

[0083] The low-density plastic foam particles which can be produced or which have been produced according to the present method can be further processed in one or more separate subsequent processes to give foamed bead moldings. The further processing of the plastic particles to foamed particle moldings can take place with steam or superheated steam (steam-based) or without the use of steam or superheated steam (non-steam-based or dry).

[0084] The processing steps for producing the plastic foam particle density are described in more detail below with reference to FIGS.

[0085] In a first step S1 of the method, a plastic material is provided in the form of plastic material pre-expanded particles. The provided plastic material pre-expanded particles are sometimes also called "pre-expanded plastic particles". Thus, plastic material pre-expanded particles, which are typically thermoplastic plastic material particles and are regarded as starting material, are provided in the first step of the method. The provided starting material is therefore in particulate form, i.e. more specifically in loose or disintegrated form. Thus, in a first step, at least one measure is carried out to provide a (thermoplastic) plastic material in particulate form, more particularly in loose or disintegrated form, in the form of corresponding plastic material pre-expanded particles. Depending on the composition and modification of the material, the density of the pre-expanded particles of plastic material provided in the first step of the process is usually less than 1 g / cm due to the cellular structure. 3 Less than 0.05 to 1.5 g / cm 3 , which results in the pre-expanded properties of the provided plastics material pre-expanded particles. The provided plastics material pre-expanded particles therefore have a porous or cellular structure. The provided plastic material pre-expanded particles therefore have a porous or cellular structure. Despite their cellular structure, the plastics material pre-expanded particles can, if desired, comprise at least one additive or auxiliary material, such as, for example, elongated, spherical or platelet-shaped fillers. More specifically, for plastic material pre-expanded particles containing additives or auxiliary materials, the density is optionally 1 g / cm depending on the concentration. 3 It can exceed. Corresponding additives or auxiliary materials can optionally be present themselves in the cellular form and can also have the effect of nucleating agents.

[0086] The first step S1 of the method can optionally be at least partially automatable or can be carried out in a partially automated manner by a supply device 2, which is only diagrammatically shown in Figure 2. This device is set up to supply the corresponding plastics material pre-expanded particles continuously or discontinuously. The corresponding feed device 2 can be, for example, a conveying device, by means of which the plastics material pre-expanded particles to be processed into the corresponding plastics foam particles can be conveyed to or into a filling device 3 performing the second step of the method. The corresponding conveying device can, for example, be designed as or include a belt conveyor device or a flow conveyor device. The conveying of the plastics material pre-expanded particles to or into a filling device 3 performing the second step of the method can thus include receiving the plastics material pre-expanded particles in a conveying flow. The plastics material pre-expanded particles can thus be conveyed by a conveying flow to or into a filling device 3 which carries out the second stage of the method.

[0087] In a second step S2 of the method, the plastics material pre-expanded particles are filled with a blowing agent at least under the effect of pressure. In the second step, the plastics material pre-expanded particles are filled with a blowing agent at least under the effect of pressure, optionally, depending on the material, a certain pressure plus a certain (higher) temperature can be applied. In the second step, at least one measure for filling the plastics material pre-expanded particles with a blowing agent is generally carried out at least under the effect of pressure, i.e. at least with pressure. Phenomenologically, the second stage of the process typically results in an enrichment of the blowing agent in each pre-expanded particle of plastic material. The concentration of the blowing agent in the respective plastic material pre-expanded particles may result for example from or through absorption and / or dissolution processes of the blowing agent in the respective plastic material pre-expanded particles, more specifically depending on the chemical structure of the plastic material pre-expanded particles, the blowing agent and, if necessary, any additives or auxiliary materials contained. As mentioned above, the pressure or temperature conditions are usually selected depending on the material. The cellular structure of the plastic material pre-expanded particles may also result in a concentration or accumulation of the blowing agent within the cell spaces provided by the cellular structure, i.e. the internal volume of each pre-expanded plastic material defined by the cell spaces is available as receiving space for receiving the blowing agent in the second step of the method.

[0088] The pressure level and the pressure rise rate in the second stage of the method are usually selected, in particular depending on the material, so that the cell structure of the plastic material pre-expanded particles is not damaged. More specifically, the pressure level and the pressure rise rate in the second stage of the method are selected so that the cell structure of the plastic material pre-expanded particles is not plastically deformed or collapsed by the pressure (effective difference between the external load pressure and the cell internal pressure).

[0089] Gases such as carbon dioxide or mixtures containing carbon dioxide and / or nitrogen, such as air, can be used as blowing agents. In general, combustible or non-combustible organic gases, in particular butane or pentane; or inert gases, such as noble gases, i.e. more specifically helium, neon, argon, etc.; or nitrogen, or mixtures thereof can be used. The term "blowing agent" can therefore also include mixtures of chemically and / or physically different blowing agents. The selection of the blowing agent typically takes into account its absorption capacity in the plastics material pre-expanded particles, ie the chemical and / or physical make-up or composition of the plastics material pre-expanded particles. If the plastics material pre-expanded particles contain additives or auxiliary materials, the properties, such as the chemical and / or physical makeup of the additives or auxiliary materials may also be taken into consideration when selecting the blowing agent.

[0090] A second step S2 of the method can optionally be or is at least partially automatable and can be carried out by a filling device 3, which is only diagrammatically shown in Fig. 2. This device is set up to fill the plastics material pre-expanded particles with a blowing agent at least under the effect of pressure or to carry out a corresponding filling process. The corresponding filling device 3 can for example be designed as or to include an autoclave device, ie generally as a pressure vessel device 3.1 which includes a pressure or treatment space. The corresponding filling device 3 may also have a temperature control device 3.2 which is set up to control the pressure or temperature of the corresponding treatment space. The corresponding loading device may in any case have a control and / or regulation unit 3.3 implemented in hardware and / or software, configured for control and / or regulation, i.e. in general for setting certain dynamic and / or static pressure and / or temperature parameters in the pressure or treatment space.

[0091] In a third step of the method, the plastic material pre-expanded particles filled with the blowing agent are expanded under the influence of temperature, i.e. more specifically, elevated temperature, to produce plastic foam particles. The plastic material pre-expanded particles filled with the blowing agent are therefore typically exposed to elevated temperature in the third step of the method, i.e. typically subjected to thermal energy, which results in the release of gas and / or the expansion of the blowing agent contained in the plastic material pre-expanded particles. More specifically, the outgassing of the blowing agent in the cell and matrix regions of the heat-softened or softened plastic material pre-expanded particles causes the plastic material particles to expand again or further, resulting in the formation of plastic particles having a permanent cell structure that may have changed, for example, in terms of cell number, cell shape, and / or cell size, as compared to the starting material after cooling or "freezing". The same is true in the formation of the produced plastic foam particles. Thus, in a third step of the method, at least one measure is carried out for degassing or expanding the blowing agent contained in the plastic material pre-expanded particles, at least by the influence of temperature, and thus at least thermally softening, to produce plastic foam particles. Phenomenologically, in the third stage of the method, more specifically, outgassing or desorption of the blowing agent from the cell and matrix regions of the softened or softened plastic material pre-expanded particles optionally results in further cell growth, and optionally new cell formation and subsequent cell growth within the plastic material pre-expanded particles to produce plastic foam particles. If bubble formation occurs, it is typically based on the aforementioned detachment of the blowing agent at the nucleation points of the plastic material particles, which soften or become soft under the influence of temperature. On the other hand, bubble growth is usually based on the expansion associated with the positive pressure of the blowing agent in already formed or existing cells. As also mentioned, the cellular structure formed in this way, or the further expanded state realized in this way, is permanently "frozen" or fixed by a decrease in temperature of the plastic foam particles produced in this way, i.e., by cooling by the environment, for example.

[0092] In principle, therefore, after completion of the pressurization carried out in the second stage of the method, i.e. more specifically, when a pressure drop occurs to normal or standard conditions, a gas release or desorption process takes place in the respective plastic material pre-expanded particles filled with blowing agent and usually softened by heat. The gas releasing or desorption process of the blowing agent represents an essential prerequisite for the bubble growth process required for the production of plastic foam particles and, if applicable, for the bubble formation process within the respective plastic material particle. In the third step of the process, more specifically, the plastic foam particles produced according to this process are formed from the typically heat-softened pre-foamed particles of plastic material present after the second step of the process, filled with blowing agent, by a corresponding outgassing or desorption treatment. As described below, by controlling the cell formation and cell growth processes associated with the corresponding gas release or desorption, it is possible in some cases to achieve cell structures with locally different cell properties and thus graded plastic foam particles.

[0093] The combination of nucleation and targeted softening properties has a significant effect on the desorption of the blowing agent. More specifically, new small cells can be formed through individual nucleation points, resulting in a fine cell structure within each plastic foam particle. The corresponding fine cell structure is more specifically characterized by small cells and their approximately uniform distribution within each plastic foam particle.

[0094] It is true that in general, this method makes it possible to produce plastic foam particles, more specifically having bubble sizes in the range of 0.5 to 250 μm. The actual cell size (of course, here we generally refer to the average) can therefore be set over a very wide range and can be adjusted process-wise depending on the selected process conditions. The same applies to the cell size distribution within the respective plastic foam particles.

[0095] More specifically, it is true that this method can be used to form plastic foam particles having (average) bubble sizes of less than 100 μm, more specifically less than 75 μm, even more specifically less than 50 μm, even more specifically less than 25 μm.

[0096] The third step S3 of the method can optionally be at least partially automatable or can be performed in a partially automated manner by an expansion device 4. The expansion device 4 is provided for radiation-based expansion of a blowing agent to produce plastic foam particles at least under the influence of temperature and performs a corresponding radiation-based expansion process. The corresponding expansion device 4 is therefore typically designed as or comprises a heating device based on radiation, ie generally a temperature control device 4.1. Temperature control device 4.1 includes a temperature control or processing space, the temperature of which is controllable or at least controlled based on radiation. The corresponding temperature control device 4.1 may also have a conveyor device 4.3, which is configured to transport the expanding plastic material particles along a conveyor line through the corresponding temperature control or treatment space. The corresponding expansion device 4 may in every case have a control and / or adjustment unit 4.2 implemented in hardware and / or software that is set up for control and / or adjustment, i.e. in general for setting certain dynamic and / or static transport and / or temperature parameters in the corresponding temperature control or treatment space.

[0097] The density of the plastic foam particles produced in the third step S3 of the method is usually significantly lower than the initial density of the plastic material pre-expanded particles provided in the first step S1. This results in the cellular properties of the plastic particles producible or produced according to the method. The bulk density of the plastic foam particles produced in the third step S3 of the method is therefore significantly lower than the bulk density of the plastic material pre-expanded particles provided in the first step S1 of the method.

[0098] The plastic foam particles produced in the third step S3 of the method can be (further) expandable, as described above, which can represent an essential property for the above-mentioned, more particularly steam-based or non-steam-based, further processing of the plastic foam particles for the production of particle foam moulded articles.

[0099] As mentioned above, the filling of the plastics material pre-expanded particles with the blowing agent can take place under the influence of pressure and temperature. Thus, the initial pressure and temperature conditions in the second stage S2 of the method are predominant, parameters which can be varied more specifically depending on the material in order to fill the plastic material pre-expanded particles with blowing agent and subsequently target specific properties of the plastic foamed particles produced or to be produced. Of course, time is also important, i.e., more specifically, the course and duration of the pressure and temperature conditions in the second stage of the method are important parameters influencing the filling of the plastics material pre-expanded particles with the blowing agent, i.e., more specifically, the absorption and concentration of the blowing agent in the plastics material pre-expanded particles.

[0100] The filling of the plastics material pre-expanded particles with the blowing agent can be carried out under a pressure, for example, in the range of 1 to 200 bar, more specifically depending on the chemical composition of the plastics material pre-expanded particles and / or the blowing agent, where pressure more specifically refers to the pressure of the corresponding filling device 3 or the pressure in the treatment space when the second stage S2 of the method is carried out.

[0101] The filling of the plastics material pre-expanded particles with the blowing agent can be carried out, for example, more specifically at a temperature in the range of 0 to 250° C. depending on the chemical composition of the plastics material pre-expanded particles and / or the blowing agent. Temperature more specifically refers to the pressure or the temperature in the process space of the corresponding filling device when the second stage S2 of the method is carried out.

[0102] Filling the plastic material pre-expanded particles with the blowing agent can be carried out, for example, for a time in the range of 0.1 to 1000 hours, depending, for example, on the chemical composition of the plastic material pre-expanded particles and / or the blowing agent. As mentioned above, the periods given as examples above are, more specifically, the periods during which the plastic material particles are exposed to pressure or temperature within the pressure or processing space of the corresponding filling device 2 when the second stage S2 of the method is carried out.

[0103] The expansion of the blowing agent-filled plastic material particles to produce plastic foam particles under the influence of temperature, more specifically depending on the chemical composition of the blowing agent-filled plastic particle material and / or the blowing agent, is carried out, for example, at normal pressure, i.e. at an ambient pressure of about 1 bar. A certain pressure level, for example a positive or negative pressure level, can thus fundamentally simplify the foaming process of expanding the blowing agent-filled plastic material pre-expanded particles to produce plastic foam particles, but is not absolutely necessary.

[0104] The expansion of the foamed plastic material particles under the influence of temperature to produce the foamed plastic particles can be carried out, for example, at a temperature in the range of 0 to 300° C., depending, more specifically, on the chemical composition of the foamed plastic particle material and / or the foaming agent. The aforementioned temperatures may more specifically refer to the inlet temperature when the plastic material pre-expanded particles filled with the blowing agent enter the corresponding expansion device 4, and / or the outlet temperature when the plastic foam particles exit the corresponding expansion device 4. The corresponding inlet and outlet temperatures may be the same, similar, or different. In case the corresponding expansion device 4 has a conveying device 4.3 configured to convey the plastic material particles filled with the blowing agent along the corresponding temperature control device 4.1, the aforementioned temperature can refer to the temperature when the pre-expanded plastic particle material filled with the blowing agent enters the corresponding expansion device or temperature control device 4.1, i.e. in the initial region of the corresponding conveying device 4.3 (entrance temperature) and / or the outlet temperature when the plastic particles leave the corresponding expansion device or temperature control device 4, i.e. in the terminal region of the corresponding conveying device (outlet temperature). Usually, the entrance temperature will be lower than the outlet temperature.

[0105] The expansion of the blowing agent-filled plastic material pre-expanded particles under the influence of temperature can be achieved by irradiating the blowing agent-filled pre-expanded plastic particle material with high-energy thermal radiation, more specifically infrared radiation. The temperature control, i.e. more specifically the heating of the plastic material pre-expanded particles filled with a blowing agent, can be carried out in a targeted manner, more specifically depending on the material, by selecting and / or setting the high energy radiation characteristics, more specifically its wavelength, resulting in a melting or fusion-free process. In the case of softening with heating of the plastic material pre-expanded particles filled with a blowing agent, melting or fusion, i.e. an insufficient stability of the softened plastic material particles, is undesirable for the foaming process of the plastic material particles filled with a blowing agent. Research has shown that infrared radiation is particularly suitable in this case, since in combination with a conveying device it allows a targeted and very easily controllable volumetric heating of the plastic material pre-expanded particles filled with foaming agent, a controllable softening process and a controllable expansion process, which is therefore essential for setting the properties of the plastic foam particles produced.

[0106] More specifically, the expansion of the plastic material particles filled with the blowing agent can be carried out under the influence of temperature by irradiating the plastic material pre-expanded particles filled with the blowing agent with high-energy thermal radiation, more specifically infrared radiation. More specifically, the plastic material particles filled with the blowing agent are continuously conveyed on at least one conveyor line defined by a conveying device 4.3 along at least one radiation generating device 4.4 which generates corresponding high-energy radiation, more specifically infrared radiation. The corresponding radiation generating device 4.4 can be more specifically designed as or include an infrared oven, more specifically an infrared continuous oven. The corresponding infrared oven can include one or more infrared emitters arranged or formed along the corresponding conveyor line. The corresponding infrared emitters can have a variable radiation power, for example, optionally in the range of 1 to 500 kW. The aforementioned output may more specifically refer to area output per square meter. More specifically, 5 to 100 kW / m 2 The area output of can be used. Variable radiator or variable radiator (area) output can be used to create different temperature zones, which also provide parameters to influence the expansion process.

[0107] According to this method, plastic material particles filled with a foaming agent are expanded under the influence of temperature (more specifically, at a lower temperature compared to the expansion process previously carried out) to produce plastic foam particles, after which the produced plastic foam particles can be cooled, as described above. Cooling, which is expediently rapid, makes it possible to "freeze" the cell structure of the plastic foam particles present after the expansion process. In this way, further global or merely localized expansion of the plastic particles, which may be undesirable after the expansion process, can be specifically prevented, while the cell structure of the plastic particles, which may be desirable after the expansion process, can be maintained. Cooling can occur, more specifically, from a processing temperature above a reference temperature, more specifically, above room temperature, which can be used as the reference temperature, to a cooling temperature below the processing temperature or reference temperature, more specifically, room temperature. Therefore, a separate temperature control device for cooling the plastic particles is not necessarily required, but it is sufficient to cool the plastic particles to room temperature or store them at room temperature after the foaming process.

[0108] According to this method, as also indicated above, a plastic pre-expanded particle material can be provided or used which comprises at least one, more particularly functional, additive or auxiliary material, such as a fiber or fiber material and / or a dye or color material and / or a nucleating substance or nucleating material and / or a substance or materials, in order to targetably influence or control the softening properties of the plastic material particles filled with the blowing agent. Thus, according to this method, the compounded plastic material pre-expanded particles can also be filled with a blowing agent and expanded, which results in plastic foam particles with special properties. More specifically, through the selection of the target and the corresponding concentration of additives or auxiliary materials, tailor-made plastic particles can be produced for a specific application or area of ​​use. The additives or auxiliary materials may have been introduced into the plastic material pre-expanded particles as part of their production.

[0109] More specifically, for the further processing to achieve special material properties of the plastic foam particles producible according to the present method or of the expanded bead moldings produced from the plastic foam particles producible according to the present method, fibers or fiber materials (which in principle may be organic or inorganic fibers or fiber materials, for example aramid, glass, carbon or natural fibers) can be used. The corresponding plastic foam particles or the foamed bead moldings produced therefrom are characterized on the one hand by a special density due to their cellular structure, and on the other hand, more specifically due to the processing, by the mechanical bonding of adjacent cells within each plastic foam particle and / or between each adjacent plastic foam particle due to special mechanical properties. During the subsequent processing into the particle foam moldings, these special mechanical properties can be utilized or even modified locally or integrally. In principle, the same applies to additives or auxiliary materials in non-fibrous or non-fibrous form, such as, for example, organic and / or inorganic additives or auxiliary materials in the form of spheres, globules, platelets or the like, regardless of their chemical composition.

[0110] In addition to influencing the mechanical properties of the plastic particles in a targeted manner, corresponding additives or auxiliary materials can be used to influence the electrical and / or thermal properties of the plastic particles in a targeted manner. Thus, plastic particles with special electrical and / or thermal conductivity can be produced by means of electrical and / or thermally conductive additives or auxiliary materials, such as, for example, metal and / or carbon black particles.

[0111] The concentrations of the corresponding additives or auxiliary materials can in principle be freely chosen but usually vary from material to material. It is therefore mentioned merely by way of example that plastic material pre-expanded particles can be provided or used which contain one (or more) additives or auxiliary materials (respectively) in a concentration between 0.01% by weight (this applies more particularly to chemically active additives) and 60% by weight (this applies in particular to fibrous additives). As noted above, the concentration will generally depend on the particular chemical and / or physical properties of the additive.

[0112] According to this method, in principle any polyolefin-based plastic material can be provided or used as starting material. For example, according to the method, plastic material particles selected from the group consisting of polypropylene, polypropylene blends, polyethylene, polyethylene blends, polyethylene-polypropylene blends, copolymers of ethylene and at least one other olefin monomer, copolymers of propylene and at least one other olefin monomer and / or mixtures thereof can be provided or used.

[0113] When polyolefin-based blends are used which comprise at least two (poly)olefin components differing in at least one chemical and / or physical parameter and / or parameter relating to molecular structure, these blends can in principle be present in any proportional composition whose respective proportions add up to 100%. Thus, the first component can be present in any weight percent between 1 and 99% and the second component can be present in any weight percent between 99 and 1%, the respective percentages adding up to 100 weight percent. Of course, percentages less than 1% and greater than 99% are also contemplated.

[0114] This method makes it possible, depending on the process conditions selected, for example, to produce foamed plastic particles having a uniformly or non-uniformly distributed cell structure. As a result, the properties, in particular the distribution of the cell structure within each plastic foam particle, can be influenced by the pressure, temperature, time during loading or expansion, transport times or conditions between the individual method steps S1-S3 in addition to material-specific parameters.

[0115] When plastic foam particles with a non-uniformly distributed cell structure are produced according to the present method, each plastic foam particle may have different cell numbers and / or shapes and / or sizes in the core and edge regions. Thus, graded plastic foam particles with a special range of properties can be produced by different distributions of cell numbers, cell shapes and / or cell sizes. As a result, graded plastic foam particles may have different cell properties in the (outer) edge region and the (inner) core region, e.g., core-shell particles.

[0116] In general, more specifically depending on the degree of expansion and, optionally, the filler content, plastic foam particles having a bulk density ranging between 5 and 1000 g / l can be produced according to this method. The actual bulk density (which of course also in this context usually refers to the average) can therefore be set over a very wide range and can therefore be adjusted depending on the selected process conditions.

[0117] 2 includes the above-mentioned feeding device 2, filling device 3, and expansion device 4. The filling device 3 can generally be referred to as the first device and is set up for filling the pre-expanded thermoplastic with a blowing agent under the influence of pressure. The expansion device 4 can be generally referred to as the second device and is set to expand the blowing agent for producing plastic foam particles under the influence of temperature.

[0118] The supply device 2 may include suitable handling devices for handling the plastics material pre-expanded particles in order to supply them. In a similar manner, the device 1 may include a handling device 5 downstream of the expansion device 4 for removing the plastic foam particles produced, not shown. As mentioned above, the corresponding handling device can be designed as or include a transport device. More specifically, conveying devices suitable for conveying loose particulate material are considered, for example pneumatic conveying devices configured to form a conveying flow.

[0119] As mentioned, the second device may include a transport device, more specifically, a combination conveyor and temperature control device. The corresponding combined conveyor and temperature control device can, for example, be designed as a continuous oven or at least include a continuous oven, more specifically as an infrared continuous oven including one or more infrared emitters.

[0120] Furthermore, the second device may be associated with a relaxation apparatus (not shown), e.g. a relaxation space in which the generated plastic foam particles are stored under defined chemical and / or physical conditions, more specifically, at predetermined temperature conditions and for a predetermined time. A corresponding relaxation device can, for example, be designed as or include a vacuum device.

[0121] In all exemplary embodiments, it is conceivable that the device 1 comprises a conveying device, by means of which the plastic material pre-expanded particles, or subsequently the plastic expanded particles, are conveyed continuously or discontinuously through the individual devices 2-4.

[0122] FIG. 3 shows a schematic cross-sectional view of a plastic foam bead produced according to a method according to an exemplary embodiment. Specifically, this is a portion of a microscope image of foam beads made from plastic foam particles made from pre-expanded polypropylene (EPP) produced according to the present method, having an initial bulk density of about 75 g / l, which has been reduced to a bulk density of about 17 g / l.

[0123] FIG. 4 shows a schematic diagram of a plastic foam bead produced according to a method according to an exemplary embodiment. The schematic diagram shows a cellular plastic particle with locally different cellular properties, i.e. a graded cellular plastic particle. Specifically, the plastic foam particles have a non-uniformly distributed cell structure in that the plastic particles have different, i.e. more, cells in the edge regions R than in the core regions K. The inner dashed line indicates that the transition between the edge region R and the core region K may be continuous. The edge region R may optionally be locally more or less distinct.

Claims

1. Providing a plastic material in the form of pre-expanded particles of a polyolefin-based resin; A step of filling the polyolefin resin pre-expanded particles with a foaming agent; and A step of expanding the polyolefin resin pre-expanded particles filled with a foaming agent. Including, The expansion of the polyolefin-based resin pre-expanded particles filled with the foaming agent is carried out by irradiating the polyolefin-based resin pre-expanded particles filled with the foaming agent with high energy.

2. A method for producing expanded polyolefin resin particles comprising the steps of:

2. The method for producing polyolefin-based resin foamed particles described in claim 1, characterized in that the process of expanding the polyolefin-based resin pre-foamed particles filled with the foaming agent is carried out by irradiating infrared rays onto the polyolefin-based resin pre-foamed particles filled with the foaming agent.

3. The method for producing polyolefin-based resin expanded particles described in claim 1, characterized in that the step of filling the polyolefin-based resin pre-expanded particles with a foaming agent is carried out at a pressure in the range of 1 to 200 bar.

4. The step of filling the polyolefin-based resin pre-expanded resin particles with a foaming agent is carried out at a temperature in the range of 0 to 250° C. The method for producing expanded polyolefin resin particles according to claim 2 .

5. The method for producing expanded polyolefin resin beads according to claim 1, wherein the step of expanding the plastic material beads filled with the foaming agent is carried out at a temperature in the range of 20 to 300°C.

6. The step of expanding the polyolefin-based resin pre-expanded particles filled with a foaming agent is carried out by irradiating the polyolefin-based resin pre-expanded particles filled with a foaming agent with high-energy radiation, The polyolefin resin pre-expanded particles filled with a foaming agent are transported on at least one conveyor line, and infrared rays are irradiated by an infrared emitter of a radiation generating device that generates high-energy radiation and is arranged or formed along the conveyor line. A method for producing the expanded polyolefin resin particles according to claim 1.

7. The polyolefin resin foamed particles are cooled from a processing temperature in a step of expanding polyolefin resin pre-expanded particles filled with a foaming agent to a cooling temperature lower than the processing temperature. A method for producing the expanded polyolefin resin particles according to claim 1.

8. A polyolefin-based resin pre-expanded particle containing at least one additive or auxiliary material in a concentration of 0.01% by weight to 60% by weight is used. A method for producing the expanded polyolefin resin particles according to claim 1.

9. The polyolefin resin pre-expanded particles are selected from the group consisting of polypropylene, polypropylene blends, polyethylene, polyethylene blends, polyethylene-polypropylene blends, copolymers of ethylene and at least one other olefin monomer, copolymers of propylene and at least one other olefin monomer, and / or mixtures thereof; A method for producing the expanded polyolefin resin particles according to claim 1.

10. The polyolefin resin foamed particles are characterized in that the number and / or size and / or shape of bubbles are different between the core region and the edge region. A method for producing the expanded polyolefin resin particles according to claim 1.

11. The foaming agent is Flammable or non-flammable organic gases, or Inert gas, or At least one selected from nitrogen, carbon dioxide, or air, or a mixture thereof; A method for producing the expanded polyolefin resin particles according to claim 1.

12. 2. The method for producing expanded polyolefin resin beads according to claim 1, wherein the expanded polyolefin resin beads are produced with a bubble size in the range of 1 to 250 μm.

13. 2. The method for producing expanded polyolefin resin beads according to claim 1, wherein the expanded polyolefin resin beads are produced to have a bulk density in the range of 5 to 1000 g / l.

14. An apparatus for producing expanded polyolefin resin beads, comprising: a first device installed for filling the polyolefin resin pre-expanded particles with a blowing agent, the first device including a pressure vessel device; and A second device installed for expanding a blowing agent for producing polyolefin resin expanded particles, the second device including a radiation generating device for generating high-energy radiation. An apparatus for producing expanded polyolefin resin particles comprising:

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