METHOD FOR THE PRODUCTION OF CELLULAR POLYOLEFIN-BASED PLASTIC PARTICLES

Description

[0001] The invention relates to a method for producing cellular polyolefin-based plastic particles.

[0002] Methods for producing cellular polyolefin-based plastic particles, which are further processed, in particular for the production of particle foam molded parts, are known in principle from the prior art.

[0003] Known methods for producing cellular polyolefin-based plastic particles are based on a two-stage process, which in a first stage involves melting a thermoplastic polyolefin-based plastic material in an extruder and loading the thermoplastic polyolefin-based plastic material melt thus generated within the extruder with a blowing agent, and in a second stage involves granulating or comminuting the strand-like thermoplastic polyolefin-based plastic material emerging from the extruder and expanding or expanding due to the blowing agent.

[0004] In the first stage of this process, the blowing agent dissolves in the thermoplastic polymer melt due to the pressure and temperature conditions prevailing in the extruder. After the blowing agent-laden thermoplastic polyolefin-based polymer material exits the extruder, the pressure drop causes the polyolefin-based polymer material to expand as a result of the blowing agent transitioning into the gas phase.

[0005] In the second stage of a corresponding process, e.g. by means of a cutting device, the granulation or comminution of the polyolefin-based plastic material emerging in strand form from the extruder and, as described, immediately expanding due to blowing agent after exiting the extruder, results in cellular polyolefin-based plastic particles which can be further processed into a particle foam molded part in a separate processing process.

[0006] Known processes are comparatively complex in terms of both plant and process engineering. Furthermore, the cellular polyolefin-based plastic particles that can be produced using known processes are in need of improvement with regard to properties such as size, morphology, and cell distribution; the possibilities for influencing these properties of the cellular polyolefin-based plastic particles through plant or process engineering are significantly limited with known processes.

[0007] Furthermore, it is not possible to produce cellular polyolefin-based plastic particles from a pre-expanded polyolefin-based plastic material using known methods. This is particularly true because the described extrusion-based process damages or destroys the structure of the pre-expanded polyolefin-based plastic material particles, especially due to the mechanical and thermal energy input.

[0008] This applies particularly to the fundamentally well-known autoclave processes in which pre-expanded polyolefin-based plastic material particles are expanded batchwise and thus discontinuously into foam beads in an autoclave unit (so-called post-expansion / post-expansion unit) using superheated steam. Areas for improvement include, among others, energy inefficiency, the infrastructural requirements for steam generation and supply, the risk of deterioration in the morphology of the produced foam beads across their entire volume, high variability due to differing thermal conditions in the various areas of the autoclave unit, and the subsequent drying processes required to remove the moisture from the superheated steam.

[0009] US 2010 / 024085 A1 discloses a process for producing pre-expanded polypropylene particles.

[0010] US 2005 / 0059747 A1 discloses a method for processing expandable polymer particles.

[0011] Based on this, the present invention aims to provide an improved method for producing cellular polyolefin-based plastic particles, which also enables the production of cellular polyolefin-based plastic particles, particularly with specifically adjustable properties for subsequent processing into particle foam molded parts and their application or usage properties, starting from pre-expanded polyolefin-based plastic material particles.

[0012] The problem is solved by a method according to claim 1. The dependent claims relate to possible embodiments of the method.

[0013] A first aspect of the invention relates to a method for producing cellular polyolefin-based plastic particles; the method described herein is therefore generally used for producing cellular polyolefin-based plastic particles. The polyolefin-based plastic particles that can be produced or are produced according to the method are therefore polyolefin-based plastic particles that have a cellular structure, at least partially, typically completely. The cellular polyolefin-based plastic particles can also exhibit a certain (further) expansiveness, particularly due to a specific blowing agent content—whether a residue from the described method or one introduced subsequently in a separate process step. The polyolefin-based plastic particles that can be produced or are produced according to the method are therefore polyolefin-based plastic particles that have a cellular structure, at least partially, and typically completely.The cellular polyolefin-based plastic particles produced by this process can therefore be expandable and / or (mechanically) compressible due to their cellular structure. The cellular polyolefin-based plastic particles produced by this process can in all cases be described as "foam particles" or "foamed beads." As will be shown below, the process can also be described as a method for radiation-based modification, i.e., in particular for the post-expansion or further expansion, of pre-expanded polyolefin-based plastic particles. The radiation-based modification serves in particular to selectively influence the cellular properties and thus the cellular structure of corresponding pre-expanded polyolefin-based plastic particles using radiation, which, as mentioned, specifically refers to post-expansion or further expansion.

[0014] The cellular polyolefin-based plastic particles, hereinafter also referred to as "plastic particles" or "cellular plastic particles," can be further processed into a molded particle foam part in one or more independent subsequent processes. This further processing of the cellular plastic particles into a molded particle foam part can be carried out using steam or superheated steam (steam-based) or without steam or superheated steam (non-steam-based or dry).

[0015] The steps of the process for producing cellular plastic particles will be explained in more detail below.

[0016] In the first step of the process, a plastic material is provided in the form of pre-expanded polyolefin-based plastic particles. These pre-expanded polyolefin-based plastic particles, hereinafter referred to simply as "pre-expanded plastic particles," can also be called "pre-expanded plastic particles." The plastic material, which is a polyolefin-based particle foam material and thus already a cellular polyolefin-based plastic material, is provided in the first step of the process in the form of pre-expanded plastic particles. The provided pre-expanded plastic material is therefore particulate, i.e., in bulk form.In the first step, at least one measure is generally carried out to provide a particulate, i.e., in particular bulk-like or -shaped, pre-expanded plastic material in the form of corresponding pre-expanded plastic material particles. Depending on the material composition or modification, the density of the pre-expanded plastic material particles provided in the first step of the process is typically below 1 g / cm³ due to the cellular structure, particularly in a range between 0.05 and 1.5 g / cm³, from which the pre-expanded properties of the provided pre-expanded plastic material particles result; the matrix of the provided pre-expanded plastic material particles thus exhibits a porous or cellular structure.

[0017] Despite their cellular structure, the matrix of pre-expanded plastic material particles may contain at least one additive or material, such as elongated, spherical, or platelet-shaped fillers. Particularly for pre-expanded plastic material particles containing additives or materials, the density may, depending on the concentration, exceed 1 g / cm³. These additives or materials may themselves be cellular in nature and / or have cellular properties.

[0018] The first step of the process can be carried out, optionally at least partially or fully automatically, by means of a supply device designed for the continuous or discontinuous supply of a suitable plastic material in the form of pre-expanded plastic material particles. Such a supply device can, for example, be a conveying device by means of which the pre-expanded plastic material particles to be processed into the corresponding cellular plastic particles can be conveyed to a loading device for the second step of the process. Such a conveying device can, for example, be designed as a belt conveyor or a flow conveyor, or include such a conveyor. The conveying of the pre-expanded plastic material particles to a loading device is carried out by means of a conveyor system.The loading device(s) performing the second step of the process can therefore include receiving the pre-expanded plastic material particles into a conveying flow; the pre-expanded plastic material particles can therefore be conveyed by means of a conveying flow to or into a loading device performing the second step of the process.

[0019] In a second step of the process, the pre-expanded plastic material particles are loaded with a blowing agent, at least under the influence of pressure. In this second step, the pre-expanded plastic material particles are thus loaded with a blowing agent, at least under the influence of pressure—depending on the material, a specific (elevated) temperature may also be applied. Therefore, in the second step, at least one measure is generally carried out to load the pre-expanded plastic material particles with a blowing agent, at least under the influence of pressure. Phenomenologically, the second step of the process typically results in an enrichment of the blowing agent within the respective pre-expanded plastic material particles.The accumulation of the blowing agent in the respective pre-expanded plastic material particles can result, depending in particular on the chemical configuration of the pre-expanded plastic material particles, the blowing agent, and any additives or materials contained therein, as well as on the pressure and / or temperature conditions, which, as mentioned, are typically also material-dependent, for example, from or through absorption and / or dissolution processes of the blowing agent in the respective pre-expanded plastic material particles. Due to the cellular structure of the pre-expanded plastic material particles, accumulation or dissolution can occur.The propellant can also accumulate within the cell spaces defined by the cellular structure; therefore, the internal volume of a pre-expanded plastic material defined by the cell spaces can be used as a receiving space for the absorption of propellant in the second step of the process.

[0020] The pressure level in the second step of the process is typically chosen, depending on the material, such that the cellular structure of the pre-expanded plastic material particles is not damaged; in particular, the pressure level in the second step of the process is chosen such that the cellular structure of the pre-expanded plastic material particles is not undesirably damaged by the pressure, i.e., does not plastically deform or even completely collapse. In this context, the effective difference between the external loading pressure and the intracellular pressure is of particular importance.

[0021] The same applies in particular to the pressure rise rate, i.e., the rate at which the external pressure is increased from a starting level to a target level in the second step. Typically, the pressure rise rate lies in a range between 0.001 bar per minute and 1000 bar per minute.In particular between 0.01 bar per minute and 1000 bar per minute, further in particular between 0.1 bar and 1000 bar per minute, further in particular between 1 bar and 1000 bar per minute, further in particular between 2, 3, 4, 5, 6, 7, 8, 9 or 10 bar and 1000 bar per minute, further in particular between 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 89, 85, 90, 95 or 100 bar per minute and 1000 bar per minute, further in particular between 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 per minute and 1000 bar per minute. All intermediate values ​​not explicitly listed here are also conceivable.

[0022] Gases such as carbon dioxide or a mixture containing carbon dioxide and / or nitrogen, such as air, can be used as blowing agents. In general, any flammable or non-flammable organic gases, i.e., in particular butane or pentane; or inert gases, such as noble gases, i.e., in particular helium, neon, argon; or nitrogen, or mixtures thereof, can be used. The term "blowing agent" can therefore also include a mixture of chemically and / or physically different blowing agents. The selection of the blowing agent is typically made taking into account its incorporation capacity in the pre-expanded plastic material particles, and thus taking into account the chemical and / or physical configuration or composition of the pre-expanded plastic material particles. If the pre-expanded plastic material particles contain additives or materials, their properties, such as...The chemical and / or physical configuration of the additives or materials must also be taken into account when selecting the propellant.

[0023] The second step of the process can be carried out, optionally at least partially or fully automatically, by means of a loading device designed to load the pre-expanded plastic material particles with a blowing agent, at least under pressure, or to perform a corresponding loading process. Such a loading device can, for example, be designed as an autoclave, i.e., generally as a pressure vessel comprising a pressure or process chamber, which may be temperature-controlled. Furthermore, such a loading device can include a temperature control unit designed to maintain the temperature of the corresponding pressure or process chamber.In all cases, a corresponding loading device may include a hardware- and / or software-implemented control and / or regulation unit, which is designed to control and / or regulate, i.e., generally to adjust, certain dynamic and / or static pressure and / or temperature parameters within a corresponding pressure or process space.

[0024] In a third step of the process, the pre-expanded plastic material particles loaded with blowing agent are expanded to produce cellular plastic particles under the influence of temperature, i.e., in particular, elevated temperature. In this third step, the blowing agent-loaded pre-expanded plastic material particles are thus typically exposed to elevated temperature, i.e., generally thermal energy, which leads to outgassing and / or expansion of the blowing agent contained within the pre-expanded plastic material particles. This typically occurs in a dry environment, i.e., without the external influence of fluids such as steam or water. In particular, the outgassing of the blowing agent in the cells and matrix regions of the thermally softened pre-expanded plastic material particles causes a further expansion of the plastic material particles, which occurs after cooling."Freezing" leads to the formation of plastic particles with a permanent cellular structure, possibly altered compared to the starting material, for example with regard to cell number and / or shape and / or size, and thus to the formation of the cellular plastic particles to be produced. In the third step of the process, at least one measure is generally carried out to outgas or expand the blowing agent contained in the cells and matrix regions of the pre-expanded plastic material particles, which are softened or softened at least by the influence of temperature and thus at least thermally, in order to produce cellular plastic particles. Phenomenologically, in the third step of the process, particularly due to the outgassing or desorption of the blowing agent from the cells and matrix regions of the softening or softened particles, the following occur:Softened pre-expanded plastic material particles undergo further cell growth, and potentially renewed cell formation with subsequent cell growth within the pre-expanded plastic material particles, leading to the production of cellular plastic particles that exhibit a lower density, potentially significantly so, compared to the pre-expanded plastic particles. Cell formation, if it occurs, is typically based on the aforementioned desorption of the blowing agent at nucleation points in the plastic material particles that soften due to temperature influence, while cell growth is typically based on overpressure-induced expansion of the blowing agent in already formed or existing cells. As also mentioned, the cellular structure thus formed, or the further expansion state achieved with it, is determined by the respective...a temperature reduction of the cellular plastic particles produced in this way, i.e., by cooling them, e.g., in the environment, permanently "frozen" or fixed them.

[0025] In principle, it follows that after the pressurization process in the second step of the procedure, i.e., upon pressure drop, particularly to normal or standard conditions, outgassing and desorption processes occur within the respective pre-expanded plastic material particles loaded with blowing agent and typically softened by thermal deposition. The outgassing and desorption processes of the blowing agent are essential prerequisites for the cell growth processes and, where applicable, cell formation processes within the respective plastic material particles required for the production of cellular plastic particles. From the pre-expanded plastic material particles present after the second step of the procedure, loaded with blowing agent and typically softened by thermal deposition, the following processes occur in the third step of the procedure, particularly due to corresponding outgassing and desorption.Desorption processes formed the cellular plastic particles produced according to the procedure.

[0026] As mentioned, the cellular plastic particles produced according to the process have a lower density than the pre-expanded plastic particles, so that the process, as also mentioned, serves to produce cellular plastic particles of lower density and can therefore also be described or considered as a process for radiation-based modification, i.e. in particular for radiation-based post-expansion or further expansion, of pre-expanded plastic particles.

[0027] As will be explained below, by controlling appropriate outgassing or desorption-induced cell formation and cell growth processes, it may be possible to realize cellular structures with locally different cell properties and thus graded cellular plastic particles.

[0028] In general, the process allows for the production of cellular polymer particles with a cell size ranging from 0.5 to 250 µm. The actual cell size—typically an average, of course—can therefore be tailored over a very wide range depending on the chosen process conditions. The same applies to any distribution of cell sizes within the individual cellular polymer particles.

[0029] In particular, the method described herein is suitable for producing cellular plastic particles with a (mean) cell size below 250 µm, especially below 240 µm, further especially below 230 µm, further especially below 220 µm, further especially below 210 µm, further especially below 200 µm, further especially below 190 µm, further especially below 180 µm, further especially below 170 µm, further especially below 160 µm, further especially below 150 µm, further especially below 140 µm, further especially below 130 µm, further especially below 120 µm, further especially below 110 µm, further especially below 100 µm, further especially below 90 µm, further especially below 80 µm, further especially below 70 µm, further especially below 60 µm, further especially below 50 µm, further especially below 45 µm, further especially below 40 µm,further, in particular below 35 µm, further, in particular below 30 µm, further, in particular below 25 µm, further, in particular below 24 µm, further, in particular below 23 µm, further, in particular below 22 µm, further, in particular below 21 µm, further, in particular below 20 µm, further, in particular below 19 µm, further, in particular below 18 µm, further, in particular below 17 µm, further, in particular below 16 µm, further, in particular below 15 µm, further, in particular below 14 µm, further, in particular below 13 µm, further, in particular below 12 µm, further, in particular below 11 µm, further, in particular below 10 µm, or even smaller. All intermediate values ​​not explicitly listed here are also conceivable.

[0030] The third step of the process can be carried out, optionally at least partially or fully automatically, by means of an expansion device designed for the radiation-based expansion of the blowing agent to produce cellular plastic particles, at least under the influence of temperature, to perform a corresponding radiation-based expansion process. Such an expansion device is typically designed as a radiation-based heating device, i.e., generally as a temperature control unit comprising a temperature-controlled or process chamber that is at least radiation-controlled. Such a temperature control unit may also include a conveying device designed for conveying the plastic material particles to be expanded along a conveying path through a corresponding temperature control or process chamber.In all cases, a corresponding expansion device may include a hardware- and / or software-implemented control and / or regulation unit, which is designed to control and / or regulate, i.e., generally to adjust, certain dynamic and / or static conveying and / or temperature and / or radiation parameters within a corresponding temperature control or process room.

[0031] In particular, the third step of the process can optionally be carried out continuously, which is advantageous compared to the batch-wise autoclave-based processes mentioned at the beginning.

[0032] The density of the cellular polymer particles produced in the third step of the process is typically significantly lower than the initial density of the pre-expanded polymer particles provided in the first step, thus determining the cellular properties of the polymer particles produced by the process. The bulk density of the cellular polymer particles produced in the third step of the process is correspondingly significantly lower than the bulk density of the pre-expanded polymer particles provided in the first step of the process.

[0033] The cellular plastic particles produced in the third step of the process are, as mentioned above, typically expandable; this can be an essential property for the described further processing of the cellular plastic particles for the production of particle foam molded parts, in particular steam-based or non-vapor-based processing.

[0034] This process is distinguished from known methods by its unique dynamic process control, which requires the softening necessary for expansion, but unlike an extrusion process, does not require the complete melting of a pre-expanded plastic material loaded with blowing agent. Therefore, it does not require the pressure- and temperature-intensive loading of a plastic material melt with a blowing agent. The dynamic process control, and in particular the resulting rapid (volume) heating – in contrast to convective and conductive energy transport in steam-based post-foaming – is also important for good energy efficiency and the significantly finer cell morphology mentioned below (due to the lack of time for cell aggregation).The process therefore involves a (significantly) simplified effort in terms of both plant and process engineering, as pre-expanded plastic material particles are loaded with a blowing agent, and corresponding blowing agent-loaded plastic material particles can be converted into cellular plastic particles, at least under the influence of temperature, in particular under the influence of temperature and pressure.

[0035] Furthermore, the properties of the cellular plastic particles produced or manufactured according to the process are improved, particularly with regard to the number, size, shape and distribution of the cells, which results from the easily adjustable and very well controllable process conditions during the loading in the second step of the process and during the expansion in the third step of the process.

[0036] In contrast to the autoclave-based expansion processes described at the beginning, this method enables a continuous expansion process of corresponding pre-expanded plastic particles loaded with blowing agent, which, due to the lack of use of hot steam, does not require subsequent drying.

[0037] The process thus enables a significantly expanded process window that can be precisely adjusted or controlled for each plastic material, making it possible in principle to produce cellular plastic particles with desired properties from any (thermoplastic) pre-expanded plastic material particles.

[0038] As indicated, the loading of pre-expanded plastic material particles with a blowing agent can be carried out under the influence of pressure and temperature. The parameters that can be varied for loading the pre-expanded plastic material particles with blowing agent, and subsequently for the targeted adjustment of certain properties of the cellular plastic particles to be produced or produced, particularly depending on the material, are therefore, firstly, the pressure and temperature conditions prevailing in the second step of the process. Naturally, time, i.e., in particular the progression and duration of the pressure and temperature conditions, in the second step of the process, is also a parameter that influences the loading of the pre-expanded plastic material particles with blowing agent, i.e., in particular, the absorption of the blowing agent into the pre-expanded plastic material particles.

[0039] Specific parameters for carrying out the second step of the process are given below as examples: The loading of the pre-expanded plastic material particles with the blowing agent(s) can, for example, depending particularly on the chemical composition of the pre-expanded plastic material particles and / or the blowing agent, take place at a pressure in a range between 1 and 200 bar, in particular in a range between 1 and 190 bar, further in particular in a range between 1 and 180 bar, further in particular in a range between 1 and 170 bar, further in particular in a range between 1 and 160 bar, further in particular in a range between 1 and 150 bar, further in particular in a range between 1 and 140 bar, further in particular in a range between 1 and 130 bar, further in particular in a range between 1 and 120 bar, further in particular in a range between 1 and 110 bar.further, in particular, in a range between 1 and 100 bar, further, in particular, in a range between 1 and 90 bar, further, in particular, in a range between 1 and 80 bar, further, in particular, in a range between 1 and 70 bar, further, in particular, in a range between 1 and 60 bar, further, in particular, in a range between 1 and 50 bar, further, in particular, in a range between 1 and 40 bar, further, in particular, in a range between 1 and 30 bar, further, in particular, in a range between 1 and 20 bar, further, in particular, in a range between 1 and 10 bar. As a lower limit, instead of 1 bar, 2, 3, 4, 5, 6, 7, 8, 9, or 10 bar may also be used. The above, as mentioned,The pressures mentioned as examples refer specifically to pressures within a pressure or process chamber of a corresponding loading device during the execution of the second step of the process. All intermediate values ​​not explicitly listed here are equally conceivable.

[0040] As mentioned, the pressure level and, in particular, the rate of pressure increase in the second step of the process is typically chosen, depending on the material, such that the cellular structure of the pre-expanded plastic material particles is not damaged; in particular, the pressure level and, in particular, the rate of pressure increase in the second step of the process are chosen such that the cellular structure of the pre-expanded plastic material particles does not deform plastically due to pressure (effective difference between external loading and intracellular pressure) and may even collapse.

[0041] The loading of the pre-expanded plastic material particles with the blowing agent(s) can be carried out, for example, depending particularly on the chemical composition of the pre-expanded plastic material particles and / or the blowing agent, at a temperature in the range between 0 and 250°C, further particularly in the range between 0 and 240°C, further particularly in the range between 0 and 230°C, further particularly in the range between 0 and 220°C, further particularly in the range between 0 and 210°C, further particularly in the range between 0 and 200°C, further particularly in the range between 0 and 190°C, further particularly in the range between 0 and 180°C, further particularly in the range between 0 and 170°C, further particularly in the range between 0 and 160°C, further particularly in the range between 0 and 150°C, further particularly in the range between 0 and 140°C.further, in particular, in a range between 0 and 130°C, further, in particular, in a range between 0 and 120°C, further, in particular, in a range between 0 and 110°C, further, in particular, in a range between 0 and 100°C, further, in particular, in a range between 0 and 90°C, further, in particular, in a range between 0 and 80°C, further, in particular, in a range between 0 and 70°C, further, in particular, in a range between 0 and 60°C, further, in particular, in a range between 0 and 50°C, further, in particular, in a range between 0 and 40°C, further, in particular, in a range between 0 and 30°C, further, in particular, in a range between 0 and 20°C. The above, as mentioned,The temperatures mentioned as examples refer specifically to temperatures within a pressure or process chamber of a corresponding loading device during the execution of the second step of the process. All intermediate values ​​not explicitly listed here are equally conceivable.

[0042] Loading the pre-expanded plastic material particles with the propellant or a blowing agent can, for example, B., in particular depending on the chemical composition of the pre-expanded plastic material particles and / or the blowing agent, for a period of time in a range between 0.1 and 1000 h, in particular in a range between 0.1 and 950 h, further in particular in a range between 0.1 and 900 h, further in particular in a range between 0.1 and 850 h, further in particular in a range between 0.1 and 800 h, further in particular in a range between 0.1 and 750 h, further in particular in a range between 0.1 and 700 h, further in particular in a range between 0.1 and 650 h, further in particular in a range between 0.1 and 600 h, further in particular in a range between 0.1 and 550 h, further in particular in a range between 0.1 and 500 h, further in particular in a range between 0.1 and 450 h,further, in particular, in a range between 0.1 and 400 h, further, in particular, in a range between 0.1 and 350 h, further, in particular, in a range between 0.1 and 300 h, further, in particular, in a range between 0.1 and 250 h, further, in particular, in a range between 0.1 and 200 h, further, in particular, in a range between 0.1 and 150 h, further, in particular, in a range between 0.1 and 100 h, in particular, in a range between 0.1 and 90 h, in particular, in a range between 0.1 and 80 h, in particular, in a range between 0.1 and 70 h, in particular, in a range between 0.1 and 60 h, in particular, in a range between 0.1 and 50 h, in particular, in a range between 0.1 and 40 h, in particular, in a range between 0.1 and 30 h, in particular, in a range between 0.1 and 20 h, in particular, in a range between The tests will be conducted at 0, 1, and 10 hours. As mentioned above,The exemplary time durations mentioned refer in particular to the pressure or temperature exposure of the plastic material particles within a pressure or process chamber of a corresponding loading device during the execution of the second step of the process. All intermediate values ​​not explicitly listed here are equally conceivable.

[0043] Specific parameters for carrying out the third step of the process are given below as examples: The expansion of the blowing agent-loaded plastic material particles to produce the cellular plastic particles under the influence of temperature, particularly depending on the chemical composition of the blowing agent-loaded plastic particle material and / or the blowing agent itself, can be carried out, for example, at normal pressure, i.e., an ambient pressure of approximately 1 bar. A specific pressure level, such as overpressure or underpressure, is therefore possible for expanding the blowing agent-loaded pre-expanded plastic material particles to produce the cellular plastic particles, but is not absolutely necessary, which generally simplifies the expansion process.

[0044] The expansion of blowing agent-loaded plastic material particles to produce cellular plastic particles under the influence of temperature can, for example, depending on the chemical composition of the blowing agent-loaded plastic particle material and / or the blowing agent, occur at temperatures in a range between 20 and 300°C, particularly in a range between 20 and 290°C, further particularly in a range between 20 and 280°C, further particularly in a range between 20 and 270°C, further particularly in a range between 20 and 260°C, further particularly in a range between 20 and 250°C, further particularly in a range between 20 and 240°C, further particularly in a range between 20 and 230°C, further particularly in a range between 20 and 220°C, further particularly in a range between 20 and 210°C, further particularly in a range between 20 and 200°C.further, in particular, in a range between 20 and 190°C, further, in particular, in a range between 20 and 180°C, further, in particular, in a range between 20 and 170°C, further, in particular, in a range between 20 and 160°C, further, in particular, in a range between 20 and 150°C, further, in particular, in a range between 20 and 140°C, further, in particular, in a range between 20 and 130°C, further, in particular, in a range between 20 and 120°C, further, in particular, in a range between 20 and 110°C, further, in particular, in a range between 20 and 100°C, further, in particular, in a range between 20 and 90°C, further, in particular, in a range between 20 and 80°C, further, in particular, in a range between 20 and 70°C, further, in particular, in a range between 20 and 60°C, further, in particular, in a range between 20 and 50°C, particularly in a range between 20 and 40°C,Further testing should be carried out, particularly in a range between 20 and 30°C. All intermediate values ​​not explicitly listed here are also conceivable.

[0045] The aforementioned temperatures may refer in particular to an inlet temperature at the entry of the blowing agent-loaded pre-expanded plastic material particles into a corresponding expansion device and / or to an outlet temperature at the exit of the cellular plastic particles from a corresponding expansion device. Corresponding inlet and outlet temperatures may be the same, similar, or different. If a corresponding expansion device includes a conveying system configured to transport the blowing agent-loaded plastic material particles along corresponding temperature control devices, the aforementioned temperatures may refer to a temperature at the entry of the blowing agent-loaded pre-expanded plastic material into a corresponding expansion or...The temperature control unit (inlet temperature), thus referring to the initial section of a corresponding conveying system, and / or the outlet temperature at the exit of the plastic particles from a corresponding expansion or temperature control unit (outlet temperature), thus referring to the final section of a corresponding conveying system. Typically, the inlet temperature is lower than the outlet temperature.

[0046] The expansion of pre-expanded plastic material particles loaded with blowing agent under the influence of temperature is achieved by irradiating the pre-expanded plastic material with infrared radiation. Infrared radiation with wavelengths in the range between 1 and 15 µm, particularly between 1.4 and 8 µm, and especially between 1.4 and 3 µm, is particularly suitable. The wavelengths of the infrared radiation are typically selected depending on the material. The temperature control, i.e., the heating, of the pre-expanded plastic material particles loaded with blowing agent can be achieved, particularly depending on the material, by selecting and / or adjusting the properties of the high-energy radiation used.In particular, their wavelength can be precisely controlled without risking undesirable melting or complete melting of the pre-expanded plastic particles during heating, which would result in insufficient stability of the softened particles. Infrared radiation proved particularly suitable in studies, as it enables targeted and, in conjunction with a conveying system, highly controllable volume heating of the pre-expanded plastic particles, a controllable softening process, and thus—essential for adjusting the properties of the cellular plastic particles to be produced—a controllable expansion process.

[0047] The expansion of the blowing agent-loaded plastic material particles occurs under the influence of temperature by irradiating the pre-expanded plastic material particles loaded with a blowing agent with high-energy thermal radiation, namely infrared radiation. The blowing agent-loaded plastic material particles are conveyed along at least one conveying path defined by a conveying device, in particular continuously, along at least one radiation-generating device that produces corresponding high-energy radiation, i.e., infrared radiation. Such a radiation-generating device can be, in particular, configured as or comprise an infrared oven, especially a continuous infrared oven. Such an infrared oven can comprise one or more infrared emitters arranged or configured along a corresponding conveying path.Corresponding infrared emitters can, for example, have a (possibly variable) radiant power in a range between 1 and 500 kW, further specifically in a range between 1 and 450 kW, further specifically in a range between 1 and 400 kW, further specifically in a range between 1 and 350 kW, further specifically in a range between 1 and 250 kW, further specifically in a range between 1 and 200 kW, further specifically in a range between 1 and 150 kW, further specifically in a range between 1 and 100 kW, and further specifically in a range between 1 and 50 kW. The lower limit can also be 2, 3, 4, 5, 6, 7, 8, 9, or 10 kW instead of 1 kW. All intermediate values ​​not explicitly listed here are also conceivable.

[0048] The aforementioned performance figures refer in particular to area output per m². Studies have shown that area outputs between 5 and 100 kW / m² yielded particularly good results. Different temperature zones can be created using variable radiators or variable radiator (area) outputs, thus providing a parameter for influencing the expansion process.

[0049] According to the procedure, after the expansion of the blowing agent-loaded plastic material particles to produce the cellular plastic particles, the resulting cellular plastic particles can be cooled under the influence of a temperature (particularly lower than that of the preceding expansion process), as indicated above. This cooling, which should be expediently rapid, effectively "freezes" the cellular structure of the plastic particles present after the expansion process. In this way, any further, integral or even local expansion of the plastic particles, which may be undesirable after the expansion process, can be specifically prevented, for example, to maintain a desired cellular structure of the plastic particles after the expansion process.Cooling can be achieved, in particular, from a process temperature above a reference temperature (room temperature can be used as the reference temperature) to a cooling temperature below the process or reference temperature (room temperature). Therefore, separate temperature control devices for cooling the plastic particles are not strictly necessary; it may suffice if the plastic particles are cooled to room temperature after the expansion process or stored at room temperature.

[0050] As indicated above, the process involves providing or using pre-expanded plastic particle material containing at least one, in particular functional, additive, such as a fibrous material and / or a dye and / or a nucleating agent and / or a substance or material, such as additives for adjusting melt viscosity (e.g., chain extenders) or for increasing the absorption coefficient (e.g., graphite, carbon black), to selectively influence or control the softening behavior of the blowing agent-loaded plastic particle material. Alternatively or additionally, pre-expanded plastic particle material containing at least one additive from the group consisting of antioxidants, UV stabilizers, antistatic additives, flow or non-stick additives, flame retardants, pigments, dyes, and mixtures thereof, may be provided or used.an antioxidant may, for example, constitute a proportion in the range of 0 to 2.5 wt.%, in particular between 0 and 1 wt.%; a UV stabilizer, such as amine- or nickel-based UV stabilizers, may, for example, constitute a proportion between 0 and 5 wt.%, in particular between 0 and 2.5 wt.% (for amine- or nickel-based UV stabilizers, in particular a proportion between 0 and 5 wt.%, and further, in particular between 0 and 2.5 wt.%); an antistatic additive a proportion between 0 and 5 wt.%, in particular between 0 and 1 wt.-2.5 wt.%; a flow or non-stick additive a proportion between 0 and 5 wt.%, in particular between 0 and 2.5 wt.%; an antiblocking additive a proportion between 0 and 5 wt.%, in particular between 0 and 2.5 wt.%; a nucleating additive in a proportion between 0 and 5 wt.%, in particular between 0 and 2.5 wt.%, and a flame retardant additive in a proportion between 0 and 65 wt.%, in particular between 0 and 20 wt.%.-%, furthermore, in particular, between 0 and 5 wt.%, furthermore, in particular, between 0 and 2.5 wt.%. Pigments or dyes, such as carbon black, can (each) have a proportion between 0 and 15 wt.%.

[0051] Therefore, compounded and pre-expanded plastic material particles can also be loaded with blowing agents and expanded using this process, resulting in cellular plastic particles with specific properties. In particular, tailored plastic particles can be produced for specific applications or areas of use through the targeted selection and concentration of appropriate additives or materials. These additives or materials may have been incorporated into the pre-expanded plastic material particles during their production.

[0052] In particular, fibrous materials – which can be organic or inorganic, such as aramid, glass, carbon or natural fibers – allow for the realization of specific material properties of the cellular plastic particles produced or manufactured according to the process, or of a particle foam molded part produced from the cellular plastic particles produced or manufactured according to the process, with regard to further processing.Corresponding cellular plastic particles, or particle foam molded parts produced from them, can be characterized by a particular density due to their cellular structure and, in particular, by special mechanical properties resulting from the mechanical connections between adjacent cells within and / or between adjacent cellular plastic particles that arise during processing. During subsequent processing into particle foam molded parts, these special mechanical properties can be utilized locally or integrally, or further modified. The same applies—in principle, regardless of their chemical composition—to non-fibrous or non-fiber-like additives or materials, such as spherical or platelet-like organic and / or inorganic additives or materials.

[0053] In addition to selectively influencing the mechanical properties of plastic particles, the electrical and / or thermal properties of the plastic particles can also be specifically influenced by appropriate additives or materials. Thus, plastic particles with specific electrical and / or thermal conductivity can be produced, for example, by using electrically and / or thermally conductive additives or materials, such as metal and / or carbon black particles, etc.

[0054] The concentration of corresponding additives or materials can generally be freely chosen, although typically depending on the material. Therefore, it is merely stated as an example that pre-expanded plastic material particles can be supplied or used with one (or more) additive(s) or materials in a concentration between 0.01 wt% (this applies particularly to chemically active additives) and 60 wt% (this applies particularly to fibrous additives). As indicated, the concentration typically depends on the specific chemical and / or physical properties of the additives or materials, or their combination.

[0055] It was mentioned that, in principle, any thermoplastic polymer material can be provided or used as a starting material according to the procedure. By way of example only, this means that pre-expanded polyolefin-based polymer material particles from the following groups are provided or used according to the procedure: polypropylene, polypropylene blend, polyethylene, polyethylene blend, polyethylene-polypropylene blends, copolymers of ethylene and at least one other olefinic monomer, copolymer of propylene and at least one other olefinic monomer, and / or mixtures of the aforementioned. Blends or mixtures of different thermoplastic polyolefin-based polymer materials can therefore also be used; modified polyolefin (mPO) is mentioned here as just one example.

[0056] If polyolefin-based blends are used that contain at least two (po-Iy)olefinic components differing in at least one chemical and / or physical parameter and / or molecular configuration parameter, these components can, in principle, be present in any proportion, with the respective proportions adding up to 100%. Accordingly, a first component can have any weight percentage between 1 and 99 wt%, and a second component any weight percentage between 99 and 1 wt%, with the respective proportions adding up to 100 wt%. Of course, proportions below 1 wt% and above 99 wt% are also conceivable.

[0057] For example, a copolymer of propylene and at least one other olefinic component can be used, wherein the proportion of the at least one olefinic monomer is in a range between 0.5 and 50 wt.%, in particular between 1 and 10 wt.%. The corresponding olefinic monomer can be, besides ethylene / propylene, also butene, hexene, octene, etc. The same applies to a copolymer of ethylene and at least one other olefinic component.

[0058] Corresponding copolymers can have a melting temperature in a range between 100 and 140°C, particularly between 120 and 140°C, and especially above 140°C.

[0059] Likewise, mixtures of at least two different copolymers can be used. By way of example only, reference is made to a mixture of a first copolymer of propylene and at least one olefinic component with a melting point above 140°C (copolymer A) and another copolymer of propylene and at least one olefinic component with a melting point between 120 and 140°C (copolymer B). The proportion of copolymer B, relative to the total mixture, can be in a range between 0.1 and 50 wt%, in particular in a range between 0.1 and 25 wt%. The proportion of copolymer A is correspondingly high, so that the proportions add up to 100 wt%.

[0060] As mentioned, all plastic materials used may contain one or more additives, such as fibers. All plastic materials used may be recycled or contain a proportion of recycled materials.

[0061] It was mentioned that the properties of the lower density cellular plastic particles that can be produced or manufactured according to the process are particularly influenced by the process conditions during the loading and expansion processes.

[0062] Depending on the chosen process conditions, cellular plastic particles with a uniformly or unevenly distributed cellular structure can be produced using this method. The properties, i.e., in particular the distribution of the cellular structure, within the respective cellular plastic particles can therefore be influenced not only by material-specific parameters but also by pressure, temperature, and time during loading or expansion, as well as by the conveying or residence times and conditions between the individual process steps.

[0063] If cellular polymeric particles with an unevenly distributed cellular structure are produced according to the process, the individual cellular polymeric particles can exhibit a different number, shape, and / or size of cells in a peripheral region than in a core region. Thus, graded cellular polymeric particles can be produced which, due to the different distribution of cell number, cell shape, and / or cell size, possess a special range of properties. Graded cellular polymeric particles can therefore, for example, similar to core-shell particles, exhibit different cellular properties in an (outer) peripheral region than in an (inner) core region.

[0064] Appropriately configured cellular plastic particles can be achieved, in particular, by loading the compact starting material with blowing agent for too short a time, which then only adheres near the edges, so that subsequent expansion occurs primarily at the edges. Conversely, an excessively long storage time between blowing agent loading and expansion can lead to cellular plastic particles in which the "core" is predominantly foamed.

[0065] In general, the process allows for the production of cellular polymer particles with a cell size ranging from 0.5 to 250 µm. The actual cell size—typically an average, of course—can therefore be tailored over a very wide range depending on the chosen process conditions. The same applies to any distribution of cell size within the individual cellular polymer particles.

[0066] Furthermore, it is generally true that, depending particularly on the degree of expansion and any filler content, cellular plastic particles with a bulk density in the range of 5 to 1000 g / l can be produced using this process. The actual bulk density – naturally, this is typically an average – can therefore be adjusted over a very wide range, and thus tailored to the specific requirements, depending on the chosen process conditions.

[0067] The following is a purely exemplary description of a pre-expanded plastic material particle that can be processed or has already been processed within the framework of the procedure, along with the associated parameters for carrying out the second and third steps of the procedure: In the first step of the procedure, a pre-expanded expandable polypropylene plastic material, i.e., polypropylene plastic material particles, with a bulk density of approximately 75 g / l, was provided. In the second step of the procedure, the pre-expanded plastic material particles were loaded with air as a blowing agent in a pressure vessel at a pressure of approximately 8 bar for a period of 100 hours, without any separate temperature control. The pressure increase rate was approximately 0.2 bar per hour.In the third step of the process, the blowing agent-loaded plastic material particles were expanded by, in particular, continuous or discontinuous, conveying the pre-expanded plastic material particles loaded with blowing agent through an infrared continuous furnace comprising several infrared emitters. This involved conveying the plastic material particles along a conveying / temperature section approximately 5 m long, formed by a plurality of temperature control elements in the form of infrared emitters with a total emitter output of approximately 20 kW. The temperature of the conveyor belt at the inlet of the conveying section was approximately 85°C, and the temperature of the conveyor belt at the outlet of the conveying / temperature section was approximately 160°C. The conveying speed was approximately 450 mm / s. The cellular plastic particles produced in this way had a bulk density of approximately 35 g / l.

[0068] A second aspect of the disclosure relates to a process for processing a plastic particle material formed by, or containing or comprising, cellular plastic particles produced according to the process of the first aspect, for the production of a particle foam molded part.

[0069] A third aspect of the invention relates to a device for producing cellular plastic particles according to a method according to the first aspect, comprising: a first device which is configured for loading the pre-expanded thermoplastic material with a blowing agent under the influence of pressure, wherein the device in particular comprises a loading device, e.g. in the form of a pressure vessel device; and a second device which is configured for expanding the blowing agent to produce cellular plastic particles under the influence of temperature, wherein the second device comprises a radiation generating device for generating infrared radiation, wherein the radiation generating device is configured as an infrared continuous furnace.

[0070] The second device may include a conveying device, in particular a combined conveying and temperature control device. Such a combined conveying and temperature control device is designed as, or includes, an infrared continuous furnace comprising one or more infrared emitters.

[0071] The second unit may also include a relaxation unit, such as a relaxation chamber, in which the manufactured cellular polymer particles are stored (relaxed) for a defined period of time under defined chemical and / or physical conditions, i.e., in particular, a defined temperature ratio. Such a relaxation unit may, for example, be designed as or comprise a decompression unit.

[0072] It is conceivable that the device further comprises the or a conveying device by means of which the manufactured cellular plastic particles are conveyed continuously or discontinuously through a corresponding relaxation space.

[0073] The device may further include suitable handling equipment for handling the pre-expanded plastic material particles for their provision and / or for the removal of the produced cellular plastic particles. Such handling equipment may also be designed as or include conveying equipment. In particular, conveying equipment suitable for conveying bulk materials, such as pneumatic conveying equipment designed to create a conveying flow, is suitable.

[0074] The device can generally include a conveying device by means of which the pre-expanded plastic material particles or, subsequently, the cellular plastic particles can be conveyed continuously or discontinuously through the individual components of the device.

[0075] All statements relating to the procedure according to the first aspect apply analogously to the procedure according to the second aspect and the device according to the third aspect.

[0076] The invention is further explained below by way of example embodiments with reference to the figures. These show: Fig. 1 a flowchart to illustrate a process according to an exemplary embodiment; Fig. 2 a schematic representation of a device for carrying out a method according to an exemplary embodiment; and Fig. 3 , 4 Each is a schematic representation of a cellular plastic particle produced according to a specific embodiment.

[0077] Fig. 1 shows a flowchart to illustrate a process according to an exemplary embodiment.

[0078] The process is a method for producing cellular plastic particles; the process thus serves to produce cellular plastic particles. The plastic particles produced according to the process, which have a lower density compared to the starting material, are therefore plastic particles that exhibit a cellular structure, at least partially, and possibly completely. Furthermore, the plastic particles can exhibit a certain (additional) expandability, particularly due to a specific blowing agent content—whether a residue from the described process or introduced subsequently in a separate process step. The cellular plastic particles produced according to the process can therefore be expandable and / or (mechanically) compressible.

[0079] The lower-density cellular plastic particles produced according to the process can be further processed into a molded particle foam part in one or more independent subsequent processes. This further processing of the plastic particles into a molded particle foam part can be carried out using steam or superheated steam (steam-based) or without steam or superheated steam (non-steam-based or dry).

[0080] The steps of the process for producing cellular plastic particle density are described below with reference to the Fig. 1 and 2 explained in more detail.

[0081] In the first step S1 of the process, a plastic material is provided in the form of pre-expanded plastic material particles. These pre-expanded plastic material particles can also be referred to as "pre-expanded plastic particles." The pre-expanded plastic material particles, which are typically thermoplastic plastic particles and thus considered the starting material, are provided in the first step of the process. The provided starting material is therefore particulate, i.e., in particular, bulk-like or in bulk form. In the first step, at least one measure is generally carried out to provide a particulate, i.e., in particular bulk-like or in bulk form, (thermoplastic) plastic material in the form of corresponding pre-expanded plastic material particles.Depending on the material composition or modification, the density of the pre-expanded plastic material particles provided in the first step of the process is typically below 1 g / cm³ due to the cellular structure, particularly in a range between 0.05 and 1.5 g / cm³, from which the pre-expanded properties of the provided pre-expanded plastic material particles result; the matrix of the provided pre-expanded plastic material particles therefore has a porous or cellular structure.

[0082] Despite their cellular structure, the matrix of pre-expanded plastic material particles may contain at least one additive or material, such as elongated, spherical, or platelet-shaped fillers. Particularly for pre-expanded plastic material particles containing additives or materials, the density may, depending on the concentration, exceed 1 g / cm³. These additives or materials may themselves be cellular in nature and / or have cellular properties.

[0083] The first step S1 of the procedure can be carried out, possibly at least partially or partially automatically, by means of a Fig. 2 The supply device 2, shown purely schematically, is designed for the continuous or discontinuous supply of corresponding pre-expanded plastic material particles. Such a supply device 2 can, for example, be a conveying device by means of which the pre-expanded plastic material particles to be processed into corresponding cellular plastic particles can be conveyed to a loading device 3 that performs the second step of the process. Such a conveying device can, for example, be designed as a belt conveyor or a flow conveyor, or comprise one such device. The conveying of the pre-expanded plastic material particles to a loading device 3 is carried out by means of a conveyor or a flow conveyor.The loading device 3, which performs the second step of the process, can therefore include receiving the pre-expanded plastic material particles into a conveying flow; the pre-expanded plastic material particles can therefore be conveyed by means of a conveying flow to or into a loading device 3, which performs the second step of the process.

[0084] In a second step S2 of the process, the pre-expanded plastic material particles are loaded with a blowing agent, at least under the influence of pressure. In this second step, the pre-expanded plastic material particles are thus loaded with a blowing agent, at least under the influence of pressure—depending on the material, a specific (elevated) temperature may also be applied in addition to a specific pressure. Therefore, in the second step, at least one measure is generally carried out to load the pre-expanded plastic material particles with a blowing agent, at least under the influence of pressure. Phenomenologically, the second step of the process typically results in an enrichment of the blowing agent within the respective pre-expanded plastic material particles.The accumulation of the blowing agent in the respective pre-expanded plastic material particles can result, depending in particular on the chemical configuration of the pre-expanded plastic material particles, the blowing agent, and any additives or materials contained therein, as well as on the pressure and / or temperature conditions, which, as mentioned, are typically also material-dependent, for example, from or through absorption and / or dissolution processes of the blowing agent in the respective pre-expanded plastic material particles. Due to the cellular structure of the pre-expanded plastic material particles, accumulation or dissolution can occur.The propellant can also accumulate within the cell spaces defined by the cellular structure; therefore, the internal volume of a pre-expanded plastic material defined by the cell spaces can be used as a receiving space for the absorption of propellant in the second step of the process.

[0085] The pressure level and the rate of pressure increase in the second step of the process are typically chosen, depending on the material, such that the cellular structure of the pre-expanded plastic material particles is not damaged; in particular, the pressure level and the rate of pressure increase in the second step of the process are chosen such that the cellular structure of the pre-expanded plastic material particles does not plastically deform and even collapse due to pressure (effective difference between external loading and intracellular pressure).

[0086] Gases such as carbon dioxide or a mixture containing carbon dioxide and / or nitrogen, such as air, can be used as blowing agents. In general, any flammable or non-flammable organic gases, i.e., in particular butane or pentane; or inert gases, such as noble gases, i.e., in particular helium, neon, argon; or nitrogen, or mixtures thereof, can be used. The term "blowing agent" can therefore also include a mixture of chemically and / or physically different blowing agents. The selection of the blowing agent is typically made taking into account its incorporation capacity in the pre-expanded plastic material particles, and thus taking into account the chemical and / or physical configuration or composition of the pre-expanded plastic material particles. If the pre-expanded plastic material particles contain additives or materials, their properties, such as...The chemical and / or physical configuration of the additives or materials must also be taken into account when selecting the propellant.

[0087] The second step S2 of the procedure can, if necessary at least partially or partially automatically, be carried out by means of a Fig. 2 The loading device 3, shown purely schematically, is designed for loading the pre-expanded plastic material particles with a blowing agent, at least under pressure, or for carrying out a corresponding loading process. Such a loading device 3 can, for example, be designed as an autoclave, i.e., generally as a pressure vessel 3.1 comprising a pressure or process chamber. Such a loading device 3 can also include a temperature control device 3.2, which is designed for temperature control of a corresponding pressure or process chamber. In all cases, such a loading device can include a hardware- and / or software-implemented control and / or regulation unit 3.3, which is used for control and / or regulation.generally set up for adjusting certain dynamic and / or static pressure and / or temperature parameters within the pressure or process space.

[0088] In a third step of the process, the pre-expanded plastic material particles loaded with blowing agent are expanded to produce cellular plastic particles under the influence of temperature, i.e., in particular, elevated temperature. In this third step, the blowing agent-loaded pre-expanded plastic material particles are thus typically exposed to elevated temperature, i.e., generally thermal energy, which leads to outgassing and / or expansion of the blowing agent contained within the pre-expanded plastic material particles. Specifically, the outgassing of the blowing agent in the cells and matrix regions of the thermally softened pre-expanded plastic material particles causes a further expansion of the plastic material particles, which occurs after cooling."Freezing" leads to the formation of plastic particles with a permanent cellular structure, possibly altered compared to the starting material, for example with regard to cell number, cell shape, and / or cell size, and thus to the formation of the cellular plastic particles to be produced. In the third step of the process, at least one measure is generally carried out to outgas or expand the blowing agent contained in the pre-expanded plastic material particles, which are softened or softened at least by the influence of temperature and thus at least thermally, in order to produce cellular plastic particles. Phenomenologically, in the third step of the process, particularly due to the outgassing or desorption of the blowing agent from the cells and the matrix regions of the softening or softening particles, the following occur:Softened pre-expanded plastic material particles undergo cell growth, possibly further cell growth, and potentially renewed cell formation with subsequent cell growth within the pre-expanded plastic material particles, leading to the production of the cellular plastic particles. Cell formation, if it occurs, is typically based on the aforementioned desorption of the blowing agent at nucleation points in the plastic material particles that have softened due to temperature influence, while cell growth is typically based on overpressure-induced expansion of the blowing agent in already formed or existing cells. As also mentioned, the cellular structure thus formed, or the further expansion state achieved with it, is permanently "frozen" or fixed by a temperature drop of the cellular plastic particles produced in this way, i.e., by their cooling, e.g., at ambient temperature.

[0089] In principle, it follows that after the pressurization process in the second step of the procedure, i.e., upon pressure drop, particularly to normal or standard conditions, outgassing and desorption processes occur within the respective pre-expanded plastic material particles loaded with blowing agent and typically softened by thermal deposition. The outgassing and desorption processes of the blowing agent are essential prerequisites for the cell growth processes and, where applicable, cell formation processes within the respective plastic material particles required for the production of cellular plastic particles. From the pre-expanded plastic material particles present after the second step of the procedure, loaded with blowing agent and typically softened by thermal deposition, the following processes occur in the third step of the procedure, particularly due to corresponding outgassing and desorption.Desorption processes form the cellular plastic particles produced according to the procedure. As will be explained further, by controlling appropriate outgassing or desorption-induced cell formation and cell growth processes, cellular structures with locally differing cell properties, and thus graded cellular plastic particles, can potentially be realized.

[0090] Nucleation, in conjunction with targeted adjustment of the softening behavior, has a decisive influence on the desorption of the blowing agent. In particular, a large number of individual nucleation points allows for the formation of numerous new small cells, resulting in a fine cell structure within the respective cellular polymer particles. This fine cell structure is characterized by small cells and a largely homogeneous distribution of these cells within the respective cellular polymer particles. Generally, the process can be used to produce cellular polymer particles with a cell size ranging from 0.5 to 250 µm. The actual cell size—of course, this typically refers to an average—can therefore be precisely tailored to the specific requirements of the process, depending on the chosen process conditions.The same applies to any distribution of cell sizes within the respective cellular plastic particles.

[0091] In particular, the process can be used to form cellular plastic particles with a (mean) cell size below 100 µm, especially below 75 µm, further especially below 50 µm, further especially below 25 µm.

[0092] The third step S3 of the process can be carried out, optionally at least partially or fully automatically, by means of an expansion device 4, which is configured for radiation-based expansion of the blowing agent for the production of cellular plastic particles, at least under the influence of temperature, to perform a corresponding radiation-based expansion process. Such an expansion device 4 is therefore typically designed as a radiation-based heating device, i.e., generally as a temperature control device 4.1 comprising a temperature control or process chamber that is at least radiation-controlled or temperature-controlled. Such a temperature control device 4.1 can further comprise a conveying device 4.3, which is configured for conveying the plastic material particles to be expanded along a conveying path through a corresponding temperature control or process chamber.In all cases, a corresponding expansion device 4 can have a hardware- and / or software-implemented control and / or regulation unit 4.2, which is designed for controlling and / or regulating, i.e., generally for setting, certain dynamic and / or static conveying and / or temperature parameters within a corresponding temperature control or process chamber.

[0093] The density of the cellular polymer particles produced in the third step S3 of the process is typically significantly lower than the initial density of the pre-expanded polymer particles provided in the first step S1, thus determining the cellular properties of the polymer particles produced by the process. The bulk density of the cellular polymer particles produced in the third step S3 of the process is correspondingly significantly lower than the bulk density of the pre-expanded polymer particles provided in the first step S1 of the process.

[0094] The cellular plastic particles produced in the third step S3 of the process can, as mentioned above, be (further) expandable; this can be an essential property for the described further processing of the cellular plastic particles for the production of particle foam molded parts, in particular steam-based or non-vapor-based processing.

[0095] As indicated, the loading of the pre-expanded plastic material particles with a blowing agent can be carried out under the influence of pressure and temperature. The parameters that can be varied for loading the pre-expanded plastic material particles with blowing agent, and subsequently for the targeted adjustment of certain properties of the cellular plastic particles to be produced or produced, particularly depending on the material, are therefore, firstly, the pressure and temperature conditions prevailing in the second step S2 of the process. Naturally, time, i.e., in particular the course and duration of the pressure and temperature conditions in the second step of the process, is also a parameter that influences the loading of the pre-expanded plastic material particles with blowing agent, i.e., in particular the absorption or accumulation of the blowing agent in the pre-expanded plastic material particles.

[0096] The loading of the pre-expanded plastic material particles with the blowing agent(s) can be carried out, for example, at a pressure in the range of 1 to 200 bar, depending in particular on the chemical composition of the pre-expanded plastic material particles and / or the blowing agent. The pressure refers in particular to the pressure within a pressure or process chamber of a corresponding loading device 3 during the execution of the second step S2 of the process.

[0097] The loading of the pre-expanded plastic material particles with the blowing agent(s) can be carried out, for example, at a temperature in a range between 0 and 250°C, depending particularly on the chemical composition of the pre-expanded plastic material particles and / or the blowing agent. These temperatures refer specifically to the temperatures within a pressure or process chamber of a corresponding loading device during the execution of the second step S2 of the process.

[0098] The loading of the pre-expanded plastic material particles with the blowing agent(s) can be carried out, for example, for a period of time ranging from 0.1 to 1000 h, depending particularly on the chemical composition of the pre-expanded plastic material particles and / or the blowing agent. The aforementioned durations, which are examples, refer specifically to the pressure or temperature exposure of the plastic material particles within a pressure or process chamber of a corresponding loading device 2 during the execution of the second step S2 of the process.

[0099] The expansion of blowing agent-loaded plastic material particles to produce cellular plastic particles under the influence of temperature, particularly depending on the chemical composition of the blowing agent-loaded plastic particle material and / or the blowing agent itself, can be carried out, for example, at normal pressure, i.e., an ambient pressure of approximately 1 bar. A specific pressure level, such as overpressure or underpressure, is therefore possible for expanding the blowing agent-loaded pre-expanded plastic material particles to produce cellular plastic particles, but not absolutely necessary, which generally simplifies the expansion process.

[0100] The expansion of the blowing agent-loaded plastic material particles to produce the cellular plastic particles under the influence of temperature can be carried out, for example, at a temperature in a range between 0 and 300°C, particularly depending on the chemical composition of the blowing agent-loaded plastic particle material and / or the blowing agent itself. The aforementioned temperatures can refer, in particular, to an inlet temperature when the blowing agent-loaded pre-expanded plastic material particles enter a corresponding expansion device 4 and / or to an outlet temperature when the cellular plastic particles exit a corresponding expansion device 4. Corresponding inlet and outlet temperatures can be the same, similar, or different. If a corresponding expansion device 4 is a conveying device 4...31, which is configured to convey the blowing agent-loaded plastic material particles along corresponding temperature control devices 4.1, the aforementioned temperatures can refer to a temperature at the inlet of the blowing agent-loaded pre-expanded plastic particle material into a corresponding expansion or temperature control device 4.1 (inlet temperature), i.e., to an initial section of a corresponding conveying device 4.3, and / or to an outlet temperature at the outlet of the plastic particles from a corresponding expansion or temperature control device 4.3 (outlet temperature), i.e., to an end section of a corresponding conveying device. Typically, the inlet temperature is lower than the outlet temperature.

[0101] The expansion of the pre-expanded plastic material particles loaded with blowing agent under the influence of temperature is achieved by irradiating the pre-expanded plastic particle material loaded with blowing agent with infrared radiation.

[0102] The temperature control, i.e., in particular the heating, of the pre-expanded plastic material particles loaded with blowing agent can, depending on the material, be carried out in a targeted manner by selecting and / or adjusting the properties of high-energy radiation, i.e., in particular its wavelength, without risking undesirable melting or perforation of the softened plastic material particles during the expansion process, i.e., insufficient stability of the softened plastic material particles, due to the softening that accompanies heating the pre-expanded plastic material particles.In these investigations, infrared radiation proved to be particularly suitable, as it enables targeted and, in conjunction with a conveying device, very well-controlled volume heating of the pre-expanded plastic material particles loaded with blowing agent, a controllable softening process and thus – this is essential for adjusting the properties of the cellular plastic particles to be produced – a controllable expansion process.

[0103] The expansion of the blowing agent-loaded plastic material particles occurs under the influence of temperature by irradiating the pre-expanded plastic material particles loaded with a blowing agent with high-energy thermal radiation, namely infrared radiation. The blowing agent-loaded plastic material particles are conveyed along at least one conveying path defined by a conveying device 4.3, in particular continuously, along at least one radiation-generating device 4.4 that produces corresponding high-energy radiation, i.e., infrared radiation. A corresponding radiation-generating device 4.4 can, in particular, be configured as or comprise an infrared oven, especially a continuous infrared oven. A corresponding infrared oven can comprise one or more infrared emitters arranged or configured along a corresponding conveying path.Corresponding infrared emitters can, for example, have a radiant power, possibly variable, in a range between 1 and 500 kW. The aforementioned power ratings can refer in particular to area power per m². In particular, area powers between 5 and 100 kW / m² can be used. Different temperature zones can be created by using variable emitters or variable emitter (area) powers, thus also providing a parameter for influencing the expansion process.

[0104] According to the procedure, after the expansion of the blowing agent-loaded plastic material particles to produce the cellular plastic particles, the resulting cellular plastic particles can be cooled under the influence of a temperature (particularly lower than that observed during the expansion process), as indicated above. This cooling, which should be rapid, effectively "freezes" the cellular structure of the plastic particles present after the expansion process. In this way, any further, integral or local expansion of the plastic particles, which may be undesirable after the expansion process, can be specifically prevented, for example, to maintain a desired cellular structure of the plastic particles after the expansion process.Cooling can be achieved, in particular, from a process temperature above a reference temperature (room temperature can be used as the reference temperature) to a cooling temperature below the process or reference temperature (room temperature). Therefore, separate temperature control devices for cooling the plastic particles are not strictly necessary; it may suffice if the plastic particles are cooled to room temperature after the expansion process or stored at room temperature.

[0105] As indicated above, the process allows for the provision or use of at least one additive or material, particularly a functional one, such as a fiber or material, a dye or material, a nucleating agent or material, or a substance or material for the targeted influencing or control of the softening behavior of the blowing agent-loaded plastic particles. This pre-expanded plastic particle material can contain, for example, a fiber or material, a dye or material, a nucleating agent or material, or a substance or material for the targeted influencing or control of the softening behavior of the blowing agent-loaded plastic particles. Thus, compounded pre-expanded plastic particles can also be loaded with blowing agent and expanded using this process, resulting in cellular plastic particles with specific properties. In particular, by selectively choosing and concentrating appropriate additives or materials, tailor-made plastic particles can be produced for specific applications or areas of use.-materials may have been introduced into the pre-expanded plastic material particles during their production.

[0106] In particular, fibrous materials – which can be organic or inorganic, such as aramid, glass, carbon or natural fibers – allow for the realization of specific material properties of the cellular plastic particles produced or manufactured according to the process, or of a particle foam molded part produced from the cellular plastic particles produced or manufactured according to the process, with regard to further processing.Corresponding cellular plastic particles, or particle foam molded parts produced from them, can be characterized by a particular density due to their cellular structure and, in particular, by special mechanical properties resulting from the mechanical connections between adjacent cells within and / or between adjacent cellular plastic particles that arise during processing. During subsequent processing into particle foam molded parts, these special mechanical properties can be utilized locally or integrally, or further modified. The same applies—in principle, regardless of their chemical composition—to non-fibrous or non-fiber-like additives or materials, such as spherical or platelet-like organic and / or inorganic additives or materials.

[0107] In addition to selectively influencing the mechanical properties of plastic particles, the electrical and / or thermal properties of the plastic particles can also be specifically influenced by appropriate additives or materials. Thus, plastic particles with specific electrical and / or thermal conductivity can be produced, for example, by using electrically and / or thermally conductive additives or materials, such as metal and / or carbon black particles, etc.

[0108] The concentration of corresponding additives or materials can generally be freely chosen, although typically depending on the material. Therefore, it is merely stated as an example that pre-expanded plastic material particles can be supplied or used with one (or more) additive(s) or material(s) in a concentration between 0.01 wt% (this applies particularly to chemically active additives) and 60 wt% (this applies particularly to fibrous additives). As indicated, the concentration typically depends on the specific chemical and / or physical properties of the additives.

[0109] In principle, any polyolefin-based plastic material can be provided or used as a starting material according to the procedure. For example, plastic material particles from the following groups can be provided or used according to the procedure: polypropylene, polypropylene blends, polyethylene, polyethylene blends, polyethylene-polypropylene blends, copolymers of ethylene and at least one other olefinic monomer, copolymers of propylene and at least one other olefinic monomer, and / or mixtures of the aforementioned.

[0110] If polyolefin-based blends are used that contain at least two (po-Iy)olefinic components differing in at least one chemical and / or physical parameter and / or molecular configuration parameter, these components can, in principle, be present in any proportion, with the respective proportions adding up to 100%. Accordingly, a first component can have any weight percentage between 1 and 99 wt%, and a second component any weight percentage between 99 and 1 wt%, with the respective proportions adding up to 100 wt%. Of course, proportions below 1 wt% and above 99 wt% are also conceivable.

[0111] Depending on the chosen process conditions, cellular plastic particles with a uniformly or unevenly distributed cellular structure can be produced using this method. The properties, i.e., in particular the distribution of the cellular structure, within the respective cellular plastic particles can therefore be influenced not only by material-specific parameters but also by pressure, temperature, and time during loading or expansion, as well as by the conveying times or conditions between the individual process steps S1-S3.

[0112] If cellular polymeric particles with an unevenly distributed cellular structure are produced according to the process, the individual cellular polymeric particles can exhibit a different number, shape, and / or size of cells in a peripheral region than in a core region. Thus, graded cellular polymeric particles can be produced which, due to the different distribution of cell number, cell shape, and / or cell size, possess a special range of properties. Graded cellular polymeric particles can therefore, for example, similar to core-shell particles, exhibit different cellular properties in an (outer) peripheral region than in an (inner) core region.

[0113] Furthermore, it is generally true that, depending particularly on the degree of expansion and any filler content, cellular plastic particles with a bulk density in the range of 5 to 1000 g / l can be produced using this process. The actual bulk density – naturally, this is typically an average – can therefore be adjusted over a very wide range, and thus tailored to the specific requirements, depending on the chosen process conditions.

[0114] The in Fig. 2 The illustrated embodiment of a device 1 for carrying out the method comprises the aforementioned provisioning device 2, the loading device 3, which is generally designated as the first device, which is set up for loading the pre-expanded thermoplastic material with a blowing agent under the influence of pressure, and the expansion device 4, which is generally designated as the second device, which is set up for expanding the blowing agent to produce cellular plastic particles under the influence of temperature.

[0115] The supply device 2 can include a suitable handling device for handling the pre-expanded plastic material particles for their supply. Similarly, the device 1, although not shown, can include a handling device 5 downstream of the expansion device 4 for removing the produced cellular plastic particles. As mentioned, such handling devices can be designed as or include conveying devices. In particular, conveying devices suitable for conveying bulk materials, such as pneumatic conveying devices designed to create a conveying flow, are suitable.

[0116] The second device, as mentioned, can comprise a conveying device, in particular a combined conveying and temperature control device. Such a combined conveying and temperature control device can, for example, be designed as a continuous furnace, in particular as an infrared continuous furnace comprising one or more infrared emitters, or at least include one such infrared emitter.

[0117] The second unit may also include a relaxation unit (not shown), such as a relaxation chamber, in which the manufactured cellular polymer particles are stored for a defined period of time under defined chemical and / or physical conditions, i.e., in particular, a defined temperature ratio. Such a relaxation unit may, for example, be designed as or comprise a decompression unit.

[0118] In all embodiments, it is conceivable that the device 1 comprises a conveying device by means of which the pre-expanded plastic material particles or, subsequently, the cellular plastic particles are conveyed continuously or discontinuously through the individual devices 2 - 4.

[0119] Fig. 3 Figure 1 shows a schematic representation of a cellular plastic particle produced according to a process, based on an exemplary embodiment, in a sectional view. Specifically, this is a section of a microscopic image of a foam bead made of pre-expanded polypropylene (EPP) with an initial bulk density of approximately 75 g / l and a cellular plastic particle produced according to the process with a reduced bulk density of approximately 17 g / l.

[0120] Fig. 4Figure 1 shows a schematic representation of a cellular polymer particle produced according to a specific embodiment. The schematic representation depicts a cellular polymer particle with locally varying cell properties, thus representing a graded cellular polymer particle. Specifically, the cellular polymer particle exhibits a non-uniformly distributed cellular structure, as the particle has a different, namely higher, number of cells in a peripheral region R than in a core region K. The dashed inner line indicates that the transitions between the peripheral region R and the core region K can be continuous. The peripheral region R may, if necessary, have varying degrees of cellularity locally.

Claims

1. A method for producing cellular plastic particles, comprising: providing a plastic material in the form of pre-expanded polyolefin-based plastic material particles, loading the pre-expanded polyolefin-based plastic material particles with a blowing agent under the influence of pressure, and expanding the pre-expanded polyolefin-based plastic material particles loaded with the blowing agent in order to produce cellular polyolefin-based plastic particles, under the influence of temperature, wherein the expanding of the polyolefin-based plastic material particles loaded with the blowing agent is carried out under the influence of temperature by irradiation of the polyolefin-based plastic material particles loaded with the blowing agent infrared radiation, wherein the polyolefin-based plastic material particles loaded with the blowing agent are conveyed on at least one conveyor line along at least one corresponding radiation generating device generating respective infrared radiation.

2. The method according to claim 1, wherein the loading of the pre-expanded polyolefin-based plastic material particles with the blowing agent, more particularly, depending on the chemical and / or physical composition of the polyolefin-based plastic material particles, is carried out at a pressure in a range between 1 and 200 bar.

3. The method according to claim 1 or 2, wherein the loading of the pre-expanded polyolefin-based plastic material particles with the blowing agent, more particularly, depending on the chemical and / or physical composition of the polyolefin-based plastic material particles, is carried out at a temperature in a range between 0 and 250° C; and / or the loading of the pre-expanded polyolefin-based plastic material particles with the blowing agent, more particularly, depending on the chemical composition of the polyolefin-based plastic material particles, is carried out for a period of time in a range between 0.1 and 1000 h.

4. The method according to any one of the preceding claims, wherein the expanding of the plastic material particles loaded with the blowing agent is carried out under the influence of temperature, more particularly, depending on the chemical composition of the polyolefin-based plastic material particles loaded with blowing agent, at a temperature in a range between 20 and 300° C.

5. The method according to any one of the preceding claims, wherein, after expanding the polyolefin-based plastic material particles loaded with the blowing agent, in order to produce the cellular polyolefin-based plastic particles under the influence of temperature, the cellular polyolefin-based plastic particles are cooled from a process temperature to a cooling temperature below the process temperature.

6. The method according to any one of the preceding claims, wherein the pre-expanded polyolefin-based plastic material particles are provided or used, which contain at least one, more particularly, functional, additive or auxiliary material, more particularly, a fiber or fibrous material and / or a dye or color material and / or nucleation agents and / or additives for specifically influencing the softening characteristics, and / or at least one additive from the group: antioxidant, UV stabilizer, antistatic additive, flow or non-stick additive, flame retardant additive, anti-blocking additive, nucleation additive, pigment, dye and mixtures of the aforementioned, wherein, more particularly, pre-expanded polyolefin-based plastic material particles with at least one additive or auxiliary material in a concentration between 0.01% by weight and 60% by weight are provided or used.

7. The method according to any one of the preceding claims, wherein pre-expanded polyolefin-based plastic material particles are provided or used from the group: polypropylene, polypropylene blend, polyethylene, polyethylene blend, polyethylene-polypropylene blends, copolymers of ethylene and at least one other olefinic monomer, copolymer of propylene and at least one other olefinic monomer and / or mixtures of the aforementioned.

8. The method according to any one of the preceding claims, wherein cellular polyolefin-based plastic particles with a uniformly or non-uniformly distributed cellular structure are produced, wherein, more particularly, cellular polyolefin-based plastic particles with a non-uniformly distributed cellular structure can be produced within respective cellular polyolefin-based plastic particles, wherein respective cellular plastic particles have a different number and / or size and / or shape of cells in an edge region than in a core region.

9. The method according to any one of the preceding claims, wherein a combustible or non-combustible organic gas; or an inert gas comprising noble gases; or nitrogen, carbon dioxide, or a mixture comprising, e.g. air, is used as the blowing agent.

10. The method according to any one of the preceding claims, wherein cellular polyolefin-based plastic particles are produced with a cell size in a range between 1 and 250 µm, more particularly, a cell size below 25 µm.

11. The method according to any one of the preceding claims, characterized in that cellular polyolefin-based plastic particles are produced with a bulk density in a range between 5 and 1000 g / l.

12. An apparatus (1) for producing cellular polyolefin-based plastic particles according to a method according to any one of claims 1 - 11, comprising: - a first device which is set up for loading pre-expanded polyolefin-based plastic material particles with a blowing agent under the influence of pressure, the device, more particularly, comprising a pressure container device; and - a second device which is set up for expanding the blowing agent for producing cellular polyolefin-based plastic particles under the influence of temperature, the second device comprising a radiation generating device for generating infrared radiation, wherein the radiation generating device is configured as an infrared continuous oven.