Method for manufacturing a foam component

Abstract

Method for manufacturing a foam component free from additional blowing agents, comprising the steps: a. Providing a particulate non-porous starting material (110, 111, 112) in a mold (230); b. Softening of the starting material (110, 111, 112); c. Inducing a pressure change within the mold to cause a foaming process in at least part of the softened starting material (113) without the use of an additional blowing agent; and d. Solidification of the foamed starting material (116).

Description

I. Technical Field

[0001] The present invention relates to a method for manufacturing a foam component. II. State of the art

[0002] The production of foam components using blowing agents is a well-established process. Foaming polymers with blowing agents can occur, for example, through physical or chemical means. Furthermore, low-viscosity polymers can also be mechanically processed into foam structures, for example, by spraying. In known physical foaming processes, the blowing agent is injected into a melt under high pressure and is thus dissolved within it. Typical blowing agents used are hydrocarbons, especially butanes and pentanes, as well as the inert gases carbon dioxide and nitrogen. In known chemical processes, chemical substances are introduced into the melt, which, under the influence of heat, form gaseous products in a chemical reaction. Typical chemical blowing agents used include isocyanate, azodicarbonamide, hydrazine, zinc carbonate, and sodium bicarbonate.Common processes employing physical or chemical foaming include injection molding, extrusion, and autoclaving. In these processes, cell formation or nucleation of the dissolved gas occurs due to a pressure drop, such as when the melt exits the nozzle in foam extrusion. Cell growth and the resulting foam cells are primarily determined by the pressure drop, the blowing agent content, and the blowing agent distribution within the material. Cell stabilization is achieved through cooling and solidification of the plastic.

[0003] For example, WO 2015 / 182721 A1 refers to the manufacture of a foam-molded article.

[0004] CN 105 451 956 B relates to a process for manufacturing a foamed object with low density.

[0005] EP 2 139 658 B1 relates to a process for manufacturing foamed plastic parts with a solid outer skin and a foamed core.

[0006] DE 17 29 011 A relates to a method and a device for producing a foamed cell molded body.

[0007] DE 10 2016 223 980 A1 relates to a method for manufacturing a plastic component, in particular a damping element for sportswear, a plastic component manufactured using such a method, for example a sole or part of a sole for a shoe, and a shoe with such a sole.

[0008] Furthermore, Vetter et al., in “Influence of vacuum on the morphology and mechanical properties in rotational molding” published in the International Journal of Polymer Science, refer to the fact that rotational molding is suitable for the production of seamless hollow bodies with a high degree of design flexibility.

[0009] A disadvantage of known foaming processes has been found to be that a large proportion of known blowing agents can have a negative impact on the environment. Furthermore, there is a risk that some of the blowing agent remains in the produced foam component, which, in addition to the aforementioned environmental pollution, can also negatively affect the health of living beings in the vicinity of these foam components, such as components of sporting goods, insulation materials in vehicles, etc. Moreover, the use of blowing agents in the production of foam components incurs additional costs, which reduces the efficiency of these processes.

[0010] The present invention is therefore based on the objective of providing a method for manufacturing a foam component which overcomes, or at least reduces, the disadvantages of the prior art. In particular, the method according to the invention should enable the efficient production of foam components without the additional addition of blowing agents.

[0011] This problem is solved by a method according to claim 1. The dependent claims contain advantageous further developments. III. Summary of the invention

[0012] The inventive method for producing a foam component, free from additional blowing agents, comprises the steps of: (a.) providing a particulate non-porous starting material in a mold; (b.) softening the starting material; (c.) inducing a pressure change within the mold to cause a foaming process in at least part of the softened starting material without the use of a blowing agent; and (d.) solidifying the foamed starting material.

[0013] The inventors have recognized that by inducing a pressure change within the mold, it is possible to trigger a foaming process in at least a portion of the softened starting material. The softening of the starting material can initially lead to local sintering of the particles. The foaming process according to the invention does not require the use of an additional blowing agent besides the process atmosphere. In the context of this invention, "additional blowing agents" refers to conventional blowing agents, which are already known, for example, from chemical or physical foaming processes in the prior art. The foaming process according to the invention can therefore be categorized as a physical foaming process without an additional blowing agent.Thus, the present invention not only represents an efficient and more cost-effective way to manufacture a foam component compared to conventional methods based on additional blowing agents. Furthermore, the elimination of an additional blowing agent improves the environmental footprint, enabling more sustainable production of foam components.

[0014] In some embodiments, the starting material can comprise particles with a size of 0.01 to 3 mm, preferably 0.02 to 1.5 mm, and particularly preferably 0.05 to 0.7 mm. The inventors have found that the choice of particle size significantly affects the quality of the resulting foam component, with the specified particle size range proving particularly advantageous. In particular, the final cell size in the manufactured foam component can be specifically influenced by the particle size. Furthermore, the particle size can affect the cell distribution, allowing it to be adapted depending on the intended use of the foam component.

[0015] The starting material used according to the invention can be a thermoplastic and / or crosslinking polymer material. Crosslinking polymer materials can, for example, include thermosetting materials. In this way, the present invention presents a method for a variety of different starting materials.

[0016] In some embodiments of the present invention, the softened starting material can have a viscosity in the range of 10 1 up to 10 5 Pa·s, preferably 10 2 up to 10 4The inventors have recognized that the specified viscosity of the softened starting material is particularly advantageous for inducing the foaming process. For example, sufficient flowability and / or deformability of the starting material is a prerequisite for the expansion of inclusions within the starting material upon induced pressure drop. If the viscosity of the softened starting material is too low, the gas inclusions cannot be stabilized within the softened starting material before or during an expansion process. In this case, the gas inclusions can diffuse to the surface. Conversely, if the viscosity is too high, a significant pressure differential may be necessary to initiate an expansion process at all. Likewise, the choice of viscosity of the softened starting material can influence the nature of the gas inclusions, in particular the thickness of the cell walls of the expanded gas inclusions.

[0017] In some embodiments of the present invention, the softening in step (b.) can include the inclusion of at least one gas, in particular air or nitrogen, in the softened starting material. The inventors have found that viscous particle surface layers can form during the softening of the starting material, a process commonly referred to as "sintering." During these sintering processes, the process gas or process gas mixture present between the particulate starting material, in particular air or nitrogen, is trapped within the softened starting material. This eliminates the need for chemical blowing agents or the additional introduction of gases into the mold, thus contributing to environmental protection. Furthermore, the use of gases or gas mixtures already present in the mold, such as air, can reduce the cost of the process.Furthermore, to prevent thermo-oxidative degradation processes in the softened starting material, a protective gas such as nitrogen can be used as a process gas. Similar to using air as a process gas mixture, this would also be environmentally friendly and / or cost-effective. In addition, the use of a protective gas can be gentler on the material than using air.

[0018] Additionally, the foaming process can be induced by the expansion of at least one gas trapped in the softened starting material. In this way, the present invention represents a particularly advantageous method for generating gas inclusions in a softened material and causing these to expand, and thus foam, by changing the pressure within the mold.

[0019] In some embodiments of the present invention, the softening process in step (b.) may include heating the starting material. Softening the starting material by heating is a process step that can be controlled very precisely using current control technology. This is an important factor for the production of a high-quality foam component according to the present invention. For example, heating makes it possible to adjust the viscosity of the softened material very precisely, which in turn can influence foam formation.

[0020] Furthermore, heating the starting material can include heating by direct heat input into the starting material or heat input via the mold. Additionally or alternatively, heating can occur through conduction or convection.

[0021] If direct heat input into the starting material is involved, this can be achieved, for example, by electromagnetic radiation, particularly in the range of 1 to 300 GHz. Thermal radiation, especially in the infrared range, can also be used. In both cases, it is possible to direct the radiation directly into the mold or to position the radiation emitter within the mold. In this way, the present invention enables the starting material to be heated within the mold without having to heat the mold itself. This improves the energy efficiency and thus also the cost efficiency of the present method compared to conventional methods from the prior art.

[0022] If heat is introduced into the starting material via the mold, a decreasing temperature gradient can exist from the mold wall to the interior of the mold within the softened starting material. In this way, for example, the particulate starting material in contact with the inner wall of the mold softens first. This can cause this initially softened layer of the starting material to adhere to the mold wall. Particles located further inside can subsequently sinter through contact with the already plasticized particles. Thus, the particulate starting material can melt layer by layer until the entire material is in a molten state. This leads to an advantageous gas inclusion in the softened starting material according to the present invention.

[0023] In some embodiments of the present invention, the number of gas inclusions in the softened starting material can be adjusted via a temperature profile during heating. The inventors have discovered that, with extensive heat input, depending on the solubility of the gas or gas mixture present, such as air or nitrogen, in the softened starting material, diffusion of the gas molecules can occur, particularly into the polymer melt. This allows the number of gas inclusions in different layers or regions to be selectively adjusted depending on the temperature profile of the softened starting material. For example, it is possible to reduce the number of gas inclusions by applying heat.

[0024] In particular, an outer layer of the starting material in contact with the mold may have fewer gas inclusions than other areas of the starting material. If heat is applied via the mold, the starting material is heated from the outside in. Gas inclusions in the areas of the softened material in contact with the mold wall can be reduced or dissolved first. This makes it possible, for example, to produce integral foam structures with adjustable outer layer thickness through targeted temperature control. In the context of the present invention, the term "integral foam structure" refers to foam structures that have an internal core of foam cells and a substantially cell-free outer layer. The term "substantially cell-free outer layer" includes production-related variations and inaccuracies.

[0025] In this case, the edge layer can have a thickness of 0.1 to 2.0 mm, preferably 0.3 to 1.7 mm, and particularly preferably 0.5 to 1.5 mm. In this way, the present invention presents a method for producing integral foam structures with a preferred edge layer thickness of a few micrometers. This allows for a particularly high flexural strength of the foam component. Furthermore, a low density of the foam component can be achieved. A low density has a positive effect, for example, on the weight of the foam component. In addition, this can reduce material costs in the production of the foam component.

[0026] In some embodiments of the present invention, the processing temperature of the starting material can be above its melting point. In this way, for example, the density of gas inclusions in the softened material can be controlled. Thus, the structure of the foam component, and in particular the foam density or degree of foaming, can be advantageously adapted to the respective application.

[0027] In some embodiments of the present invention, the temperature within the mold can differ in at least two areas. Furthermore, the properties of the foam component, such as density, cell size, cell distribution, etc., can be influenced by selecting the temperature at which the pressure change is induced. In this way, a local foaming process or a locally differentiated foaming process can be induced under inhomogeneous thermal conditions, which can be selectively set, for example, by locally temperature-controlling different areas within the mold. Likewise, it is possible to generate graded properties via a locally varying temperature profile within the mold.

[0028] In some embodiments of the present invention, the pressure change can include a reduction in pressure. The inventors have found that by reducing the pressure within the mold, any gas inclusions that may be present or intentionally induced within the softened starting material adapt to this pressure reduction, in particular by expansion. Thus, the pressure reduction can be advantageously used to initiate a foaming process. A prerequisite for the expansion of the gas inclusions due to the induced pressure reduction is sufficient flowability or deformability of the softened starting material surrounding the expanding gas inclusions. If gas expansion is possible based on the external factors, the foaming process can take place at least until the pressure present in the gas inclusions corresponds to the pressure set in the mold by the pressure reduction.In this way, pressure reduction can include a parameter for adjusting the increase in the size of the gas inclusions, in particular the resulting foam bubble size.

[0029] In some embodiments of the present invention, the pressure change can be 0.05 to 5.0 bar, preferably 0.1 to 2.0 bar, and particularly preferably 0.2 to 1.0 bar. The inventors have recognized that, in contrast to established methods from the prior art, a few hundred millibars may be sufficient for a method according to the invention for manufacturing a foam component. This makes it suitable for the method according to the invention to produce molds that are more cost-effective and can be designed for only small pressure differences. This can lead to a significant cost reduction of the claimed method. In particular, when manufacturing large foam components, such as tanks, housings for devices and systems, etc., which are mostly produced by rotational molding, considerable cost savings in mold production can be achieved due to the only small pressure differences required.In addition, lower pressure differences are achieved more quickly within the mold compared to established methods. This can shorten the manufacturing time of individual foam components, making the inventive method more efficient than established, longer-lasting methods. Furthermore, the inventive method can offer a way to make physical foaming possible even in processes where physical foaming is largely excluded, since more expensive mold technology would be necessary to adapt the molds used to high pressures.

[0030] In some embodiments of the present invention, the initial pressure in the mold before softening can correspond to atmospheric pressure or overpressure. The inventors have found that one of the parameters for inducing foaming in the softened starting material is the magnitude of the pressure change after the starting material has softened. Thus, with an initial pressure of one atmosphere, the foaming process can be induced by creating a vacuum in the mold. On the other hand, with an initial pressure above one atmosphere, i.e., with overpressure in the mold, the foaming process can be induced by reducing the overpressure, in particular to atmospheric pressure. The method according to the invention is therefore flexible with respect to the internal pressure of the mold. This can be advantageous, for example, with regard to the mold to be used, in particular its suitability for overpressure or overpressure.Negative pressure plays an important role in further manufacturing steps after inducing the pressure change, especially during or after the solidification of the foamed starting material, and / or in other parameters.

[0031] Furthermore, the inventors have determined that by generating overpressure at a time when only a portion of the starting material, particularly an outermost layer or area, is in a softened state, gas inclusions in this softened part can be reduced. Gas inclusions may still occur in parts, layers, or areas that only soften after the overpressure is generated. By subsequently reducing the pressure, these gas inclusions, which remain in the parts softened after the overpressure was generated, can be caused to expand. By precisely controlling the timing of the application of overpressure or underpressure in the mold, the layer thickness, degree of foaming, material density, or other parameters of the foam component, either for individual layers or for the entire foam component, can be specifically adjusted.

[0032] Furthermore, the overpressure can comprise compressed air. In this way, the costly and / or environmentally harmful use of additional gases can be avoided in the production of foam components according to the invention. Alternatively, the overpressure can comprise compressed nitrogen. Compared to air, this also provides a cost-effective and / or environmentally friendly method for the production of foam components. In addition, the use of nitrogen can prevent thermo-oxidative degradation processes in the softened starting material.

[0033] In some embodiments of the present invention, inducing the pressure change can include inducing the pressure change at or above the melting temperature of at least a portion of the starting material. The inventors have recognized that the viscosity of the starting material changes depending on the temperature. Furthermore, they have found that the foaming process according to the invention develops differently depending on the viscosity of the softened material with respect to the aforementioned parameters of the foam, such as density, cell size, cell number, etc. Thus, the possibility of inducing the pressure change at different temperatures relative to the melting temperature of the starting material represents a means of adjusting the parameters of the foam component.

[0034] In some embodiments of the present invention, the magnitude of the pressure change within the mold can differ in at least two regions of the mold. Since the magnitude of the pressure change is a key parameter for the size of individual cells in the foamed starting material, varying cell sizes in the foam component can be achieved by using at least two different pressure change regions.

[0035] In some embodiments of the present invention, the foaming process can be individually adjusted in each of at least two areas within the mold by means of a temperature and / or pressure difference. Thus, the method according to the invention offers the possibility of individually adapting individual areas of the foam component to the intended use. For example, in areas with increased stability requirements, the cell size within the foam component can be deliberately kept small. Furthermore, for example, in another part where low weight is advantageous, the cell size can be increased and / or the density of the starting material reduced.

[0036] In some embodiments of the present invention, the foaming process cannot be induced in at least one region of the mold. In this way, the present invention provides a means of creating foamed and non-foamed areas within a single manufacturing process in a foam component. Therefore, the additional joining of foamed and non-foamed areas can be avoided.

[0037] In some embodiments of the present invention, the solidification process can include solidification after the pressure change has been induced. The inventors have recognized that stabilization or solidification of the resulting foam structure occurs as soon as the flowability or deformability, due to a selected pressure change, no longer permits further expansion of the gas inclusions. Therefore, it is advantageous to wait to solidify until after the induced pressure change, particularly after the foaming process has been initiated. In the case of crosslinking starting materials, such as thermosetting materials, a crosslinking reaction, for example, can lead to the solidification or stabilization of the foam structure.

[0038] In some embodiments of the present invention, solidification can include cooling the foamed starting material. In the case of thermoplastic starting materials, for example, solidification can be achieved by the softening of the starting material during a cooling process. Thus, a cooling process of the foamed starting material, in particular by cooling the mold, can represent an advantageous and well-controlled solidification process.

[0039] In some embodiments of the present invention, the density of the foam component can be adjusted, at least partially, by varying the magnitude of the pressure change. The inventors have recognized that the increase in size of individual gas inclusions in the softened starting material can be adjusted by varying the magnitude of the pressure change. Since an increase in the size of the gas inclusions in the foam component reduces its density, the density of the foam component can thus be efficiently adjusted by varying the magnitude of the pressure change.

[0040] In some embodiments of the present invention, the structure of the foam component can be influenced at least partially by at least one of the following properties of the starting material: particle material, particle shape, particle size and particle size distribution.

[0041] The inventors have determined that, in addition to controlling the density via pressure, the inventive method for manufacturing foam components offers further process-related possibilities for influencing the properties of the resulting foam components. For example, the choice of the starting material represents a key control parameter. Furthermore, the initial diameter of the starting material in its softened state and before the expansion of any existing gas inclusions is crucial for the final cell size and distribution in the foamed starting material. Thus, the resulting foam structure can be advantageously influenced by the particle shape, particle size, and particle size distribution. Likewise, the foam structure can be adjusted or adapted locally or in parts of the foam component by using different particle sizes, which can be arranged separately from one another, for example, side by side.The varying bubble diameters of the resulting gas inclusions can lead to different degrees of foaming in the corresponding areas or parts after foaming, even with a uniform pressure drop in the mold. The invention also allows for the use of multiple materials or polymer blends, representing a further parameter for influencing or adapting the foam component. For example, the particles of the starting material can have a so-called "core-mantle structure," whereby a particle core and a particle mantle can exhibit different properties, such as softening or hardening behavior, or similar characteristics. In this way, the processing and / or application properties of a foam component according to the invention can be specifically optimized. Furthermore, it is possible to coat a thermoplastic particle core with a thermoset or elastomer.This can, for example, result in improved compression set behavior of the softened starting material. Likewise, elastomeric particle cores, for example recycled material, e.g., from old car tires or used sporting goods, with a thermoplastic particle coating can be used for the production of foam components according to the invention.

[0042] In some embodiments of the present invention, the method may further include introducing a second material into the mold. In this way, the method provides a means of producing a foam component that can be adapted to a variety of applications.

[0043] In some embodiments of the present invention, the second material can comprise a filler or a reinforcing element. Thus, for example, in addition to an advantageously low density of the foam component, particularly high stability of the foam component can be achieved. Likewise, a variety of properties of other materials, in particular fillers or reinforcing elements, can be integrated into the foam component using the method according to the invention.

[0044] In some embodiments of the present invention, no foaming process can occur in the second material. In this way, the fundamental properties of the second material can be retained despite a foaming process in at least part of the starting material. Furthermore, this makes it possible to combine the properties of both materials.

[0045] In another aspect, the present invention relates to a foam component which was manufactured according to a method according to one of the preceding embodiments.

[0046] The numerous advantages of the present invention, which have already been explained above in relation to exemplary embodiments of a method for manufacturing a foam component, are equally applicable to exemplary embodiments of a foam component and a mold for manufacturing a foam component.

[0047] In some embodiments of the present invention, the foam component can comprise a hollow body. In this way, the method according to the invention, particularly by rotational molding, represents an efficient way to produce high-quality hollow bodies from foamed material without the use of chemical blowing agents.

[0048] In some embodiments of the present invention, the foam component may comprise a non-foamed outer layer.

[0049] In some embodiments of the present invention, the surface layer can have a thickness of 0.1 to 2.0 mm, preferably 0.3 to 1.7 mm, and particularly preferably 0.5 to 1.5 mm.

[0050] In some embodiments of the present invention, the foam component can comprise open-cell, mixed-cell, or closed-cell gas inclusions. In this way, different properties can be achieved in the manufactured foam component, such as the absorption of liquids in the case of open-cell gas inclusions or, conversely, the repellency of liquids in the case of closed-cell gas inclusions. In the case of closed-cell gas inclusions, a foam component according to the present invention is advantageously suited, for example, as a buoyancy aid in floating devices, particularly boats, swimming aids, or surfboards, due to its adjustable density.

[0051] In some embodiments of the present invention, the foam component may comprise an integral foam structure.

[0052] In some embodiments of the present invention, the foam component can be designed as an insulating material. Since the expansion of the gas inclusions in foam components according to the invention is adjustable, and since air as well as a variety of polymer materials exhibit poor thermal conductivity, the foam components according to the invention can be particularly well suited as insulating material.

[0053] In some embodiments of the present invention, the foam component can comprise a damping material, particularly for sporting goods. As already explained above, the inventive method allows the number and size of gas inclusions in a foam component to be adjusted. Furthermore, this method allows the use of starting materials with rubber-elastic properties, such as thermoplastic elastomers, for the production of foam components. In this way, damping materials with excellent mechanical damping properties and comfort characteristics, such as those advantageous for shoe soles, can be produced particularly efficiently. In particular, different elements of a shoe sole, including outsoles, midsoles, or similar components, for which it is advantageous to have different properties, such as thermal insulation, damping, cushioning, etc., can be produced with particular efficiency.The components can be produced in a single process step according to the invention. This eliminates the need for time-consuming and costly joining or gluing of the individual elements.

[0054] In some embodiments of the present invention, the foam component can comprise a part of a sporting goods article, in particular a ball or protective gear. A part of a ball can, for example, comprise a layer of a panel or a plurality of different layers of a panel. The different layers can include, among other things, an outer cover layer, a middle foam layer, and a support layer, each having different properties. According to the invention, the plurality of different layers can be produced separately and then joined together. Alternatively, the plurality of different layers, in particular including an inner bladder of the ball, can also be advantageously produced in a single process. In this way, the present invention provides a particularly sustainable method for manufacturing balls in which the bonding of the individual panel layers can be dispensed with.In addition, the amount of residual material is significantly reduced in the production of individual layers in a single process step compared to conventional methods already known from the prior art. It should be noted that the production of different layers in a process according to the invention is not limited to the manufacture of balls, but is suitable for a variety of foam components. If the component of a sporting goods article is a protector, this could include, for example, helmets, shin guards, chest protectors, joint protectors, etc. Such protectors can be adapted for attachment to sportswear. Furthermore, the component of a sporting goods article could comprise at least part of a backpack, a bag, a stick, in particular a hockey stick, or similar item.

[0055] In another aspect, the present invention relates to a mold suitable for carrying out a method for producing a foam component according to the present invention and comprising a device for control, in particular for reducing the pressure in the mold.

[0056] In some embodiments of the present invention, the mold can be designed for a maximum pressure of up to 50 bar, preferably 25 bar, particularly preferably 10 bar, and most preferably atmospheric pressure.

[0057] In some embodiments of the present invention, the mold can be designed for a minimum pressure of up to 0.8 bar, preferably 0.5 bar, more preferably 0.2 bar, and particularly preferably 0.1 bar.

[0058] In some embodiments of the present invention, the pressure and / or temperature can be individually adjustable in at least two areas within the mold.

[0059] In some embodiments of the present invention, the mold can be designed to be movable. In this way, the mold according to the invention is suitable for a variety of molding processes, in particular for rotational molding or motion molding. IV. Brief description of the drawings

[0060] In the following, aspects of the present invention will be explained in more detail with reference to the accompanying figures. These figures show: Fig. : a schematic illustration of the method according to the invention; Fig. : a schematic illustration of a mold for manufacturing a foam component; Fig. : Exemplary progression of pressure or temperature as a function of time during the execution of the method according to the invention; Fig. : Density profile of a foam component as a function of an induced pressure reduction; Fig. : a schematic illustration of a foam component after indexing different pressure reductions; and Fig. : a schematic illustration of different foam components. V. Detailed description of some exemplary embodiments

[0061] Exemplary embodiments of the present invention relating to a foam component are explained in more detail below. While specific combinations of features are described with respect to the exemplary embodiments of the present invention, it should be understood that the disclosure is not limited to such embodiments. In particular, not all features need to be present to realize the invention, and the embodiments can be modified by combining certain features of one embodiment with one or more features of another embodiment.

[0062] An embodiment of a method 100 according to the invention for producing a foam component is described below with reference to the Fig. described.

[0063] The first step of process 100 involves providing a particulate starting material, such as powder, pellets, microgranules, or similar, in a mold. The particle size, defined by the longest dimension of a particle, can range from 0.01 to 3 mm. It should be noted that in the Fig. For the sake of clarity, a depiction of a closed form has been omitted. Instead, the contact surface of the particles represents a side wall 131 of a form according to the invention, on which in Fig. a first layer of a particulate starting material 110 is provided.

[0064] Procedure 100 further includes the step of softening the starting material. In the Fig. The softening process is achieved by heating the particulate starting material 110. This process can be carried out at a constant initial pressure p0, where p0 can be atmospheric pressure or gauge pressure according to the invention. The heating 120 is achieved by heat input via the mold, which can be accomplished, for example, by irradiating the mold wall 131, particularly with infrared radiation (IR radiation), or by using a variothermally temperature-controlled mold wall 131. Alternatively, the heating can also be achieved by direct heat input into the starting material, for example, by electromagnetic radiation or IR radiation. In this case, a radiation emitter can be arranged inside the mold. A preferred range for the electromagnetic radiation lies between 1 and 300 GHz.

[0065] Due to the heating 120 of the mold wall 131, the first layer of the particulate starting material 110 begins to soften over time and adhere to the mold wall 131, which in Fig. The process is schematically illustrated for the first layer 110. Further particles in a second 111, third 112, and subsequent layers begin to sinter with already softened and plasticized particles. In this way, the particulate starting material melts layer by layer until the entire starting material is in a softened, particularly molten, state 113. This process is described in the Fig. It should be noted that, for the sake of clarity, the individual layers are shown in the Fig. The material can be added gradually. However, it is preferred that at least part of the particulate starting material is provided in one step and then softened layer by layer, as shown.

[0066] During melting, gas inclusions 114 are trapped between the individual particles in the developing melt phase due to the sintering processes that occur. The trapped gas or gas mixture 114 can be, for example, air or nitrogen. Further gas inclusions 114 can also arise, for example, from the use of starting materials with porous particles. The particle size, shape, and particle size distribution can significantly define the dimensions, number, and distribution of the gas inclusions 114 in the melt 113 and thus the initial conditions for the foaming process. The polymer materials used can be thermoplastic materials and / or crosslinking materials. Another prerequisite for the foaming process is that the softened material is in the viscous phase, with a viscosity in the range of 10 1 up to 10 5 Pa·s, preferably 10 2 up to 10 4Pa·s is advantageous for a foaming process. In this viscosity range, the viscous melt, due to its flowability, can provide space for the expanding gas inclusions 115, thus enabling the expansion. Furthermore, the melt in this viscosity range is viscous enough to bind the expanded gas inclusions 115 within it. This binding can, firstly, at least partially prevent the expanded gas inclusions 115 from rising in the melt due to their lower density compared to the softened starting material 113. Secondly, the binding can prevent cell collapse or rupture of the cell walls of the expanded gas inclusions 115 within the melt. In this way, the viscosity of the softened starting material, along with the magnitude of the induced pressure change, can represent a parameter for the formation of different cell structures, e.g., open-cell, mixed-cell, closed-cell, or similar.

[0067] In a further step, method 100 comprises inducing a pressure change within the mold to induce a foaming process in at least a portion of the softened starting material 113 without the use of an additional blowing agent besides the process atmosphere. The foaming process is based on the expansion of the enclosed gases 114 within the melt 113. This expansion can be induced by a pressure drop within the mold, where p0 is the mold pressure at the start of the process and p1 is the pressure applied to initiate the foaming process. A preferred pressure change can be in the range of 0.05 to 5.0 bar, although a pressure change in the range of 0.2 to 1.0 bar may be sufficient for expansion. The reduction of the initial pressure can be achieved using an external pump.On the other hand, it is also possible to increase the hermetically sealed volume of the mold, for example by moving at least part of a mold wall. 131 , to induce a pressure reduction. The foaming process can be considered complete when the pressure inside the gas inclusions 115, based on the expansion, has adjusted to the reduced pressure p1 within the mold.

[0068] In a final step of process 100, the foamed starting material 116, together with the expanded gas inclusions 115, must be solidified or stabilized. The stabilization of the expanded gas inclusions 115, which subsequently form the foam cells of the foam component, can be achieved by solidifying the foamed starting material 116 through a cooling process 123. Alternatively, in the case of crosslinking polymer materials as starting material, a crosslinking reaction can be induced to stabilize the foam cells 115.

[0069] An exemplary embodiment of mold 230 for manufacturing a foam component is described below with reference to the Fig. described.

[0070] The assembly 200 comprises a mold 230, which is rotatably mounted on a shaft 234. By rotating the mold smoothly, a foam component with a substantially constant thickness can be produced, with the phrase "substantially" encompassing minor production-related thickness variations on the order of 1–5%. The mold 230 has a cylindrical outer wall 231, which can be hermetically sealed via a lower flange 232 and an upper flange 233. The mold 230 is suitable, for example, for the production of hollow bodies. Furthermore, the mold 230 is suitable for both negative and positive pressure in a range from 1 mbar to 50 bar, whereby pressure differences of just a few hundred millibars after softening of the starting material can be sufficient for foam formation.The outer wall 231 can be heated via an IR emitter 235, thereby heating the starting material located in the form 230 (not shown in . Fig. ) can be heated via the outer wall 231. For process control, a pyrometer 236 is located inside the mold 230, which can determine the temperature of the softened starting material and / or the melt. Other temperature sensors, such as a thermocouple or a quartz crystal oscillator, can be used instead of or in conjunction with the pyrometer 236. To allow the internal pressure of the mold 230 to be varied, a connection 237 is provided on the lower flange 232 via a rotary feedthrough 238. This connection 237 can be connected to a vacuum pump for pressure reduction or to a compressor or a device with compressed gas to generate overpressure. The mold 230 can be divided into individual segments (not shown in Fig. ), in which the internal pressure can be individually adjusted. Similarly, individual sections of the mold can be heated or cooled separately. By dividing the mold, a graded or sectionally differentiated foam component can be produced.

[0071] In Fig. Figure 340 shows an exemplary curve 300 of an internal pressure as a solid line and a temperature of the starting material as a dotted line 341 as a function of the process duration during the execution of an embodiment of a method according to the invention. At the beginning, the starting material is at room temperature 320 or slightly above it, i.e., 10–15 °C, due to residual heat from the mold from previous manufacturing processes or the waste heat from the entire setup. The internal pressure 325 of the filled and sealed mold is atmospheric pressure at the beginning of the process. By means of a constant temperature ramp 321, the starting material is heated to its melting temperature or above and held at this temperature for a certain, preferably isothermal, holding time 322.By holding the melt for a period of time 322 above the melting temperature, it can be ensured that the entire starting material is in a softened or molten state, or at least that surface softening of the particles enables sintering. Furthermore, holding the melt above the melting temperature reduces the number of dissolved gas inclusions in the melt. When heat is introduced into the material via the mold, this occurs preferentially first in the layer in contact with the mold wall and spreads from there further into the interior of the melt. Thus, a targeted holding time 322 can, for example, achieve a foam-free outer layer and / or an integral foam structure in the manufactured foam component. After the isothermal holding time 322 has elapsed, the cooling process 323 begins. During the cooling process 323, a pressure reduction 326 takes place.The timing of the pressure reduction 326, and thus the vacuum application temperature within the cooling process 323, can be made dependent on the viscosity of the melt, which increases during the cooling process 323. Due to the pressure reduction 326, the undissolved gas inclusions in the softened starting material, i.e., the melt, expand, thereby inducing the foaming process. Once the internal pressure of the gas inclusions has adjusted to the reduced internal pressure of the mold, the foaming process is complete. The holding time 327, during which the vacuum is maintained, can depend on the viscosity, the amount of pressure reduction, and other parameters of the foaming process.Once the foamed material has solidified again due to the cooling process 323 and the foam has thereby stabilized, the internal pressure can be increased again 328 until atmospheric pressure 329 is reached, the mold can be opened, and the at least partially finished foam component can be removed. In addition to the exemplary process 300, other processes, with in particular different times and magnitudes of at least one temperature change and at least one pressure change, are also possible within the scope of the present invention.

[0072] In Fig. Figure 400 shows an experimentally determined density curve of a manufactured foam component as a function of the induced pressure change. To generate the curve, at least eight foam components were manufactured under different induced pressure changes, their densities determined according to DIN EN ISO 845, and interpolated between the resulting measurement points. Since the density reduction in this case is based on the expanded gas inclusions, this can be considered a measure of the foaming process or the degree of foaming. Thus, curve 402 clearly demonstrates that for the inventive method of manufacturing a foam component, even a few hundred millibars can be sufficient to induce the foaming process.With a pressure difference of only one bar, for example, the density of a foam component according to the invention can be reduced to more than one-third without the use of additional blowing agents. Thus, the method according to the invention is particularly suitable, for example, for lightweight construction, for the production of buoyancy aids, such as for boats, swimming aids or surfboards, or other areas of application.

[0073] In Fig. are photographs 500 and in Fig. Computed tomography images 501 schematically depict foam components of the invention with different degrees of foaming or different densities. High-density polyethylene (HDPE) was used in the manufacture of the foam components, although other starting materials, in particular thermoplastic or cross-linking polymer materials, can also be used within the scope of the present invention. If no pressure difference is induced in a manufacturing process according to the invention, i.e., Δp vAt a pressure of Δp = 0, gas inclusions 514 may occur in the solidified starting material 516 due to the particulate nature of the initial material; however, these inclusions are not expanded. No expanded gas inclusions are present in the outer layer 517, which was in contact with the mold wall. Therefore, this is an area of ​​a foam component that existed in a part of a mold during manufacturing, where the foaming process was not induced. This behavior changes even with an induced pressure reduction of Δp. y =400 mbar, whereby the existing gas inclusions 515 in the solidified starting material 516 are already expanded. In Fig. It is particularly evident that the majority of the expanded gas inclusions 515 are closed-cell.

[0074] If the induced pressure difference is increased to Δp v =950 mbar or Δp v =999 mbar, as in Fig. As also shown, the size of the expanded gas inclusions 515 in the solidified starting material 516 continues to increase. In the case of a pressure change of Δp v At Δp = 950 mbar, the gas inclusions are essentially mixed-cell, i.e., with few exceptions. This changes with a further increase in the pressure difference to Δp. v = 999 mbar, in which case the gas inclusions 515 are essentially open-cell. It should be noted that the surface layer 517 always has fewer gas inclusions than the remaining residue of the solidified starting material 516. The thickness of this surface layer 517 can be between 0.1 mm and 2.0 mm, but preferably between 0.5 mm and 1.5 mm.

[0075] Overall, based on the Fig. It will be shown that the density of a foam component according to the invention can be adjusted at least partially by the magnitude of the pressure change.

[0076] In Fig. A foam component 600 according to the invention and a part 601 of a foam component according to the invention, in which no foaming process has been induced, are shown side by side for direct comparison. Both foam components 600, 601 consist of solidified starting material 616, with expanded gas inclusions 615 being clearly visible only in the foam component 600. The gas inclusions cause a significant increase in the volume, in particular the thickness, of the foam component 600. In this way, the present invention enables the production of foam components 600 with a lower density compared to the unfoamed starting material, without the use of additional blowing agents.

[0077] In Fig. Figure 1 shows a schematic close-up cross-section of another foam component 610, which, for example, was made of thermoplastic polyurethane (TPU). The foam component 610 has expanded gas inclusions 615 in the solidified starting material 616. In addition, an outer layer 617, which, for example, was in contact with the mold wall during production, is free of gas inclusions. In this way, the method according to the invention can be used particularly efficiently for the production of integral foam structures without the use of blowing agents.

[0078] In Fig. Figure 620 schematically illustrates another foam component 620 according to the invention. Similar to foam component 610, foam component 620 also has a gas inclusion-free outer layer 617 and expanded gas inclusions 615 in the solidified starting material 616. In this case, however, a further outer layer 618, which also has no gas inclusions, was applied to the foam component 620. The second outer layer 618 can also consist of the solidified starting material 616 or of a different material. A possible manufacturing process for the foam component 620, if it is manufactured from a starting material, can comprise the following steps: providing a particulate starting material in a mold; closing the mold and inducing a vacuum in the mold; softening a first part of the starting material, in particular the part corresponding to the outer layer 617;Providing atmospheric pressure in the mold; softening a second part of the starting material, in particular the part in which gas inclusions are provided, wherein the softening of the second part is carried out at atmospheric pressure; inducing a vacuum to cause a foaming process in the second part; softening a third part at vacuum, in particular the part corresponding to the outer layer 618;Solidification of the foamed and unfoamed starting material, application of atmospheric pressure after solidification, and subsequent opening of the mold. In this way, the foaming process can be individually controlled in each of at least two areas within the mold by means of a temperature and pressure profile. Thus, the present invention is particularly suitable for producing individual layers with different degrees of foaming and thereby different properties of a foam component within a single manufacturing process, eliminating the need for subsequent bonding of the individual layers. It should be noted that the method according to the invention is not limited to three layers. More than three layers and / or the use of different materials in the individual layers can also be produced by a method of the present invention.

[0079] In Fig. Figure 630 schematically illustrates another foam component 630 according to the invention. Similar to foam components 610 and 620, foam component 630 also has a gas-inclusion-free outer layer 617 and expanded gas inclusions 615 in the solidified starting material 616. In this case, however, a further outer layer 619, which also has gas inclusions, has been applied to the foam component 630. The outer layer 619 consists of a different starting material than the solidified starting material 616, but can also consist of the same material. Likewise, the second material can comprise a filler, for example fibers, or a reinforcing element in which the foaming process is not induced. The second material can be at least partially surrounded by or enclosed within the solidified material.

[0080] In Fig. Figure 640 schematically illustrates another foam component 640 according to the invention. Similar to foam components 610, 620, and 630, foam component 640 also has expanded gas inclusions 615 in the solidified starting material 616. In this case, the outer layer 617 is significantly thinner than in the previous embodiments 610, 620, and 630, similar to foam component 600. Another difference lies in the graduated increase in the thickness of the foam component 640, from a minimum thickness 652 to a maximum thickness 651. A substantially trapezoidal structure of the foam component 640 can be selectively achieved, for example, by using a mold wall that is not oriented perpendicular to gravity. The mold wall contains the particulate starting material, which is softened and then solidified again after pressure reduction.Similarly, the essentially trapezoidal structure of the foam component 640 can be produced by an induced pressure change with a graduated temperature profile along the mold. This graduated temperature profile can lead to a graduated viscosity of the softened starting material, which can affect, for example, the degree of foaming or the size of the expanded gas inclusions 615. Other shapes of foam components can be achieved in the same way by adjusting the orientation and shape of the mold. On the other hand, a trapezoidal shape of the foam component, similar to foam component 640, can also be achieved through a graduated foaming process. This can be accomplished, for example, by holding times at graduated temperatures within the mold, thereby controlling the number or density of the gas inclusions.Alternatively, a graded pressure difference can be induced along the softened starting material. In these cases, however, the degree of foaming, density, cell size, or other parameters of the generated foam would also be graded along the solidified starting material (in ). Fig. (not shown).

[0081] Possible foam components that are free of additional blowing agents and can be obtained using the inventive method are, for example, insulating materials. Due to the expanded gas inclusions and the typically poor conductivity of these gases, especially their poor thermal conductivity, these materials can be advantageously used for insulation, particularly for thermal insulation.

[0082] Other foam components that are free of additional blowing agents and can be produced using the inventive method include, for example, cushioning materials, particularly for sporting goods. One advantage of manufacturing shoes using the described method is, for example, that production is possible entirely without lasts. Last-free shoe production according to the inventive method is more flexible and saves time and money. Furthermore, the inventive method is advantageously applicable to the production of multi-layered elements, such as those required for shoe soles or protectors, in a single manufacturing process, since subsequent bonding of the different layers or elements is unnecessary.In addition, the manufactured sporting goods, especially sportswear, are better suited for direct contact with the skin than comparable state-of-the-art sporting goods due to the absence of additional propellants.

[0083] Furthermore, sporting goods such as balls, protectors, helmets, shin guards, bags, backpacks, rackets, etc., can be partially or completely manufactured using the method according to the invention. In the case of protectors, these can be obtained, depending on the body part to be protected, for example, by a substantially cylindrical shape adapted to the body part to be protected. In an optional post-processing step, the resulting foam component can be cut into two halves to allow, for example, a chest protector to be worn. The protectors can also be adapted for attachment to sportswear.

[0084] Finally, buoyancy aids, such as floats, boats, swimming aids, surfboards, or other items, can also be manufactured using the inventive method. Due to the adjustable foaming process, the density, and thus the buoyancy, can be set directly during the manufacturing process. This eliminates the need for complex processes involving the combination and joining of several different buoyancy aids.

Claims

[1] Method for producing a foam component free from additional blowing agents, comprising the steps: a. Providing a particulate non-porous starting material (110, 111, 112) in a mold (230); b. Softening of the starting material (110, 111, 112); c. Inducing a pressure change within the mold to cause a foaming process in at least part of the softened starting material (113) without the use of an additional blowing agent; and d. Solidification of the foamed starting material (116). [2] Method according to claim 1, wherein the starting material (110, 111, 112) comprises particles of a size of 0.01 to 3 mm, preferably of 0.02 to 1.5 mm, particularly preferably of 0.05 to 0.7 mm. [3] Method according to claim 1 or 2, wherein the starting material (110, 111, 112) comprises a thermoplastic and / or crosslinking polymer material. [4] Method according to any one of claims 1-3, wherein the softened starting material (113) has a viscosity in the range of 10 1 up to 10 5 Pa·s, preferably 10 2 up to 10 4 Pa·s exhibits. [5] Method according to any one of claims 1-4, wherein the softening comprises the inclusion of at least one gas (114), in particular air or nitrogen, in the softened starting material (113). [6] Method according to claim 5, wherein the foaming process is caused by expansion of the at least one gas (114) enclosed in the softened starting material (113). [7] Method according to any one of claims 1-6, wherein the softening comprises heating (120) of the starting material (110, 111, 112). [8] Method according to claim 7, wherein the heating (120) of the starting material (110, 111, 112) comprises heating (120) by direct heat input into the starting material (110, 111, 112) or heat input via the mold (230). [9] Method according to one of claims 7-8, wherein a number of gas inclusions (114) in the softened starting material (113) is adjustable via a temperature profile of heating. [10] Method according to any one of claims 1-9, wherein the processing temperature of the starting material (110, 111, 112) is above its melting temperature. [11] Method according to one of claims 1-10, wherein a temperature within the mold (230) is different in at least two areas of the mold (230). [12] Method according to any one of claims 1-11, wherein the pressure change is 0.05 to 5.0 bar, preferably 0.1 to 2.0 bar, particularly preferably 0.2 to 1.0 bar. [13] Method according to any one of claims 1-12, wherein an initial pressure (325) in the mold (230) before softening corresponds to atmospheric pressure or overpressure. [14] Method according to claim 13, wherein the overpressure comprises compressed air or nitrogen. [15] Method according to any one of claims 1-14, wherein the amount of pressure change within the mold (230) is different in at least two areas of the mold (230). [16] Method according to one of claims 11-15, wherein the foaming process can be individually adjusted in each of the areas within the mold (230) by means of a temperature and / or pressure difference in at least two areas. [17] Method according to any one of claims 1-16, wherein the foaming process is not caused in at least one area of ​​the mold (230). [18] Method according to any one of claims 1-17, wherein the solidification comprises solidification after inducing the pressure change. [19] Method according to any one of claims 1-18, wherein the solidification comprises cooling (123, 323) of the foamed starting material (116). [20] Method according to one of claims 1-19, wherein a structure of the foam component is influenced at least partially by at least one of the following properties of the starting material (110, 111, 112): material of the particles, particle shape, particle size and particle size distribution. [21] Method according to any one of claims 1-20 further comprising introducing a second material into the mold (230). [22] Method according to claim 21, wherein the second material comprises a filler or a reinforcing element. [23] Method according to claim 21 or 22, wherein no foaming process occurs in the second material.

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