Method for producing a three-dimensional composite article

Abstract

Method for producing a three-dimensional composite article (21a, 21b, 21c), in particular a sporting article, comprising the steps: a. Providing a movable mold (11); b. filling a first material (14) into the casting mold (11) in a first process step (P1); c. heating the casting mold (11) and the first material (14) in a second process step (P2) and maintaining the temperature; d. cooling the casting mold (11) and the first material (14) in a third process step (P3); e. filling a second material (15) comprising fibers into the mold (11) in a fourth process step (P4), wherein at least one of the materials (14, 15) is a polymer material; f. moving the casting mold (11) at an approximately constant first rotational speed in the first to fourth process steps; g. Heating the casting mold (11) and the first (14) and second (15) materials, increasing the rotational speed in a fifth process step (P5) and maintaining the temperature; h. Cooling the casting mold and the resulting composite article made of the first (14) and the second (15) material in a sixth process step (P6); and i. Reduce the speed to zero.

Description

I. Technical area

[0001] The present invention relates to a method for producing a three-dimensional composite article. II. State of the art

[0002] The production of three-dimensional objects through rotational molding is well known. Rotational molding is an established process in plastics engineering, primarily used to manufacture large, hollow components with complex geometries. Typical applications include tanks or housings for devices and systems. In this process, a hollow mold filled with plastic powder is usually rotated biaxially and heated. Typically, thermoplastic base powder melts successively in the mold and adheres upon contact to the mold wall, which is heated above the melting temperature of the thermoplastic material being processed. This process creates a melt film on the mold wall. The rotation is adjusted so that every area of ​​the mold wall comes into contact with unmelted powder, which primarily collects in the lower area of ​​the cavity, in order to achieve a uniform wall thickness.As the mold cools while it is still rotating, the melt solidifies. The component, cooled to demolding temperature, is then removed from the mold.

[0003] For example, US Pat. No. 4,093,219 A relates to sports balls. To produce the bladder, a polyester elastomer is centrifugally molded by rotating a hollow mold containing a specific amount of this elastomer in fine powder form. The mold is simultaneously rotated about two mutually perpendicular axes, while the compression mold is moved through zones containing heating units (250°C) and cooling units. The mold is then moved without rotation to a demolding station.

[0004] US 8 210 973 B2 proposes rotational molding as an alternative to the production of a bladder for a sports ball by blow molding.

[0005] US 2009 / 0266823 A1 relates to a method for producing a sealing bladder made of a thermosetting polymer for a tank containing liquid under pressure. The method includes the steps of (a) providing a polymerization mixture containing the precursor components of the thermosetting polymer and optionally at least one polymerization catalyst, (b) polymerizing the mixture to obtain the thermosetting polymer in a rotating mold to form the bladder, and (c) removing the resulting thermosetting polymer bladder from the mold.

[0006] US Pat. No. 5,433,438 A relates to a ball for play, therapy, and sports training. The ball is manufactured by distributing a foamy polyurethane mixture in a mold and rotating the mold a predetermined number of revolutions. The mold is rotated to completely cover the inner surface of the mold with foam material.

[0007] DE 27 23 625 A1 relates to a ball made of thermoplastic material and a method for its production. Centrifugal casting technology is used to produce the ball. In this process, a spherical mold made of two complementary parts performs a planetary motion, during which the thermoplastic materials of the various layers of the ball are fused, from the outer layer to the inner layer. The production method is characterized in that the material for the inner layer is added after opening the mold at a temperature at which the fusion of the material forming the preceding layer(s) is not yet complete, so that this layer(s) can tear at the level of the connection between the two complementary parts of the mold.

[0008] US 4,258,917 A relates to a rotational molding process for producing rubber-reinforced articles. The process involves forming two preformed and preshrunk half-shells of nonwoven fabric, which are then inserted into the upper and lower halves of a rotational mold to line their inner surfaces. The nonwovens are cut to cover the flange area between the two halves of the mold or so that one half-shell overlaps the other. A circular strip of film formed from a terminal amine liquid polymer is then inserted between the layers of nonwovens in the flange area or between the overlapping portions of the nonwovens, and a carboxyl-containing polymer mixture is added to the lower half of the mold.The mold is tightly closed and the materials are rotationally molded at a temperature sufficient to seal and impregnate the nonwoven half-shells and encapsulate them with the liquid carboxyl-containing polymer mixture to produce a dimensionally stable bladder or ball.

[0009] EP 0 365 488 A1 relates to a method for producing hollow elastic bodies, in particular balls and similar objects, as well as balls produced in this way. A ball is produced by centrifugal molding, according to which, in a mold consisting of two separable, complementary halves, which is imparted with planetary motion, plastics materials for forming the ball-forming layers are poured one after the other, namely starting from the outer layer to the innermost layer. The material for forming one of the inner layers is introduced after opening the mold at a temperature such that the material forming the preceding layer(s) has not been completely melted, thus allowing the layer(s) to break at the level of the junction between the two molded parts.

[0010] DE 2 049 907 A relates to a thin-walled inflatable hollow body, in particular a game ball, made of an elastic, thermoplastic material, and a process for its production. A vinyl plastisol filling with a measured amount of fine hair-like fibers uniformly distributed throughout the plastisol is first introduced into a lower shell of a mold. The mold is closed and set in rotation about several axes while the mold is heated from the outside in a heating chamber. The heating time is such that the flake-containing charge is increasingly evenly distributed over the inner surface of the hollow mold.

[0011] DE 2 403 982 A1 relates to a method for producing plastic containers, in which the plastic is introduced in the plastic state into the interior of a centrifugal mold and the mold is rotated about an axis.

[0012] US 2003 / 0227103 A1 relates to a multi-element movable vacuum chamber for rotational modeling, which includes a rotational mold having a predefined shape and a rotation axis, as well as a box containing molding material.

[0013] GB 1 254 090 A relates to a process for rotational modelling of thermoplastic synthetic resins.

[0014] DE 689 11 647 T2 relates to a method for producing elastic hollow bodies, in particular balls and similar objects, as well as to a ball produced in this way.

[0015] GB 1533 897 A relates to shaped fiber-reinforced plastic articles and processes for their manufacture.

[0016] US 4 104 357 A relates to low-speed rotational molding of thermosetting plastics to produce an article with relatively thin walls.

[0017] DE 22 08 299 A relates to a process for molding hollow articles made of synthetic resin, and in particular to a process for molding hollow articles made of glass fiber laminate produced by mixing glass fibers in unsaturated polyester resin.

[0018] EP 0 022 165 A1 relates to a substantially uniform layer of a fiber-reinforced plastic material produced in a rotational molding process by pretreating the fibers by at least partially coating them with a thermoplastic resin which is compatible with the layer-forming plastic material, has a melting point substantially no higher than that of the layer-forming plastic material, and is sinterable therewith to produce discrete reinforcing fibers having the required integrity, length and strength for rotational molding, and subjecting a substantially homogeneous mixture of the pretreated fibers and the layer-forming plastic material to a rotational molding process, whereby a layer of fiber-reinforced plastic material having a substantially uniform distribution of the fibers over the entire thickness of the layer is produced.

[0019] A disadvantage of existing rotational molding processes has been that they do not produce satisfactory results in the production of three-dimensional composite objects. This is due to the inability to achieve sufficient homogeneity of the components forming the composite material in the rotational mold. The reason for this is suspected to be the different size, shape, and density of the components, which cause them to separate in the mold. Furthermore, some components tend to form agglomerates in the mold.

[0020] The present invention is therefore based on the object of providing a method for producing a three-dimensional composite object that overcomes or at least mitigates the disadvantages of the prior art. In particular, the method according to the invention should enable homogeneous mixing and / or a targeted and defined distribution of the various materials in a rotational mold. Furthermore, the method according to the invention should enable the targeted introduction of specific functions or functionalities into the composite object to be produced.

[0021] This object is achieved by a method according to claim 1. The dependent claims contain advantageous developments. III. Summary of the invention

[0022] The claimed subject matter is defined by independent claim 1.

[0023] The method according to the invention for producing a three-dimensional composite article, in particular a sporting article, comprises the steps: a. Providing a movable mold (11); b. filling a first material (14) into the casting mold (11) in a first process step (P1); c. heating the casting mold (11) and the first material (14) in a second process step (P2) and maintaining the temperature; d. cooling the casting mold (11) and the first material (14) in a third process step (P3); e. filling a second material (15) comprising fibers into the mold (11) in a fourth process step (P4), wherein at least one of the materials (14, 15) is a polymer material; f. moving the casting mold (11) at an approximately constant first rotational speed in the first to fourth process steps; g. Heating the casting mold (11) and the first (14) and second (15) materials, increasing the rotational speed in a fifth process step (P5) and maintaining the temperature; h. Cooling the casting mold and the resulting composite article made of the first (14) and the second (15) material in a sixth process step (P6); and i. Reduce the speed to zero.

[0024] According to the invention, two materials are poured into the rotational mold, at least one of which is a polymer material. The polymer materials used according to the invention can be thermoplastic materials and / or cross-linking materials.

[0025] If the filled polymer material is a thermoplastic material, it is preferably heated and / or cooled. This material melts upon heating and thus forms the carrier or matrix material. The second material can be, for example, fibers that are embedded in the first carrier material after rotational molding or adhere flatly to its surface.

[0026] When using thermosetting materials, a binder can be added to aid in mixing the materials. Alternatively, the thermosetting materials can bond together based on their inherent properties alone. Alternatively, catalysts can also be used.

[0027] In the context of the present invention, moving the casting mold is understood to mean, for example, rotating the casting mold, pivoting the casting mold (e.g. about an axis), moving back and forth, moving up and down, etc.

[0028] To achieve a homogeneous distribution of the second material in the manufactured composite article, at least one process parameter is adjusted during the execution of one or more of the preceding steps. A homogeneous distribution of the embedded material is important for the resulting composite material to exhibit the desired stability.

[0029] In the context of the present invention, a distribution of the second material is considered homogeneous if the second material mixes well with the first material. In particular, a homogeneous distribution exists if, when viewed macroscopically, the component in a representative surface element shows the second material to be evenly distributed over the surface. The surface of the second material is predominantly wetted with the first material. The size of the representative surface element depends on the size of the three-dimensional composite article to be produced by rotational molding. In particular, a homogeneous distribution does not exist if the second material forms so-called agglomerates. However, a distribution is considered homogeneous which is subject to density fluctuations or has a density gradient, as long as the second material is present throughout the first material.The first material can form microscopic islands in which no second material can be found.

[0030] If, in the example of the fibers, they were not mixed or only insufficiently mixed with the first polymeric carrier material and were bonded force-fit, the fibers would have virtually no effect on the strength of the composite material. It is well known that fiber composites acquire advantageous properties through the mutual interactions of their two components, which is only ensured with sufficient mixing.

[0031] The inventors have recognized that a homogeneous and / or targeted and defined mixing of the first polymeric material (the embedding "matrix") with the second material can be achieved by adjusting at least one process parameter during the execution of one or more of the preceding steps of the process. Examples of process parameters are given below, the adjustment of which leads to a homogeneous distribution of the second material in the produced composite article.

[0032] Depending on the materials used, these process parameters are the rotational speed of the mold, the speed at which the mold is moved, the deflection of the mold in the case of a pivoting movement, the heating time of at least one of the materials, the cooling time of at least one of the materials, the viscosity of the first material and the angle of the rotational axes of the mold, the ratio of the rotational speeds around the rotational axes of the mold, the holding times of the first and / or second material in the mold, the filling times of the first and / or second material and combinations of these parameters.

[0033] One process parameter identified by the inventors as relevant is the rotation speed of the casting mold. If the rotation speed is selected according to at least one of the materials in the process according to the invention, this leads to a homogeneous distribution of the materials. For example, when using two materials according to the claim, the rotation speed can be lower or higher than the rotation speed when using only a single material. The latter rotation speed is defined by the fact that it enables a uniform distribution of the first material in the casting mold.

[0034] Another process parameter identified by the inventors as relevant is the speed at which the mold is moved. If this speed is selected according to at least one of the materials in the process according to the invention, this leads to a homogeneous and / or targeted and defined distribution of the materials.

[0035] Another process parameter identified by the inventors as relevant is the deflection of the mold during a pivoting movement. Deflection is defined as the maximum angle by which the mold is pivoted relative to its rest position during the pivoting movement. If this angle is selected according to at least one of the materials, a homogeneous and / or targeted and defined distribution of the materials can be ensured.

[0036] Another process parameter identified by the inventors as relevant is the heating time of the materials, for example, by heating the mold, particularly when using thermoplastic materials. A homogeneous distribution of the second material in the produced composite article is achieved if the heating time is shorter than the heating times typically used in rotational molding. Therefore, if two materials are used according to the claim, at least one of which is a thermoplastic carrier material, the heating time must be shorter to achieve a homogeneous distribution of the second material than if only the first material were used.

[0037] Another process parameter identified by the inventors as relevant is the time until at least one of the materials solidifies, for example, by cooling the mold. A homogeneous distribution of the second material in the produced composite article is achieved when the time until the first material solidifies is shorter than the solidification times typically used in rotational molding. Therefore, if two materials are used according to the claim, at least one of which is a polymeric carrier material, the time until solidification must be shorter to achieve a homogeneous distribution of the second material than if only the first material were used.

[0038] Another process parameter identified by the inventors as relevant is the angle of the mold's rotation axes. If the mold has two rotation axes, these must be essentially perpendicular to each other to achieve a homogeneous distribution of the second material. "Essentially perpendicular" means an angle of 90° within the scope of normal manufacturing fluctuations. In the context of the present invention, the term "rotation axis" refers to both rotation axes and pivot axes. For example, it is possible for the mold to have a single axis in the form of a pivot axis.

[0039] Another process parameter identified by the inventors as relevant is the time of filling the second material. The inventors have recognized that the most homogeneous distribution of the second material is achieved if the second material is poured into the mold on the side facing away from the tool before the first material has completely softened.

[0040] If the second material comprises fibers in the process according to the invention, the inventors have identified the fiber length as a further relevant process parameter. The fiber length is advantageously significantly greater than the critical fiber length, which can be calculated as a function of fiber strength, fiber diameter, and fiber-plastic bond strength. The critical fiber length indicates the fiber length at which reinforcement of the composite article by means of the fibers occurs. Longer fiber lengths increase the tensile strength of the composite article and, in particular, also its toughness under impact loading.

[0041] In summary, the inventors have recognized that the adjustment of certain process parameters is essential to achieve a homogeneous distribution of the second material in the composite article. Examples of such process parameters and how they are to be adjusted have been provided and will be explained in more detail in the description of preferred embodiments.

[0042] It should be emphasized at this point that several of the mentioned process parameters can be adjusted simultaneously to achieve a homogeneous distribution of the second material. For example, the rotation speed and heating time can be adjusted simultaneously as described herein.

[0043] Likewise, the heating and cooling times, or the rotation speed and fiber length, can be adjusted simultaneously. Any combination of the process parameters mentioned herein, which are essential for a homogeneous distribution of the second material, is possible.

[0044] The fibers can be, for example, aramid fibers. Aramid fibers have a very low thermal expansion coefficient. In combination with a generally higher thermal expansion coefficient of the polymeric first material, a highly dimensionally stable composite article can be obtained. Other organic fibers, e.g., organic fibers (polymer fibers, natural fibers, etc.) or inorganic fibers can also be used. Furthermore, it is also possible to use fibers made of the same material as the matrix (self-material fibers). In this case, the fibers advantageously have greater strength than the matrix.

[0045] The fibers as the second material can be coated with a polymer material, e.g., the first material. This results in better mixing of the first and second materials, since the surface structure of the coated fibers is compatible with the surface structure of the first material, e.g., adhesion-compatible.

[0046] The first and / or second material may be a reactive material. For example, it may be a reactive plastic.

[0047] The first material can be a thermoplastic polyurethane (TPU). TPU is relatively easy to process. Furthermore, TPU is an elastomer that is dimensionally stable, deforming under tensile and compressive stress, but largely returning to its original shape when stress-free. This makes TPU very well suited for producing pressurized three-dimensional objects, such as ball bladders. TPU is also suitable for three-dimensional objects that are regularly exposed to impact, such as shin guards for soccer players.

[0048] The first material can be provided in liquid and / or granular form. This allows for metered filling of the material into the mold, e.g., using a flow meter. The filling of the first material can thus also be automated.

[0049] The rotatable mold can rotate about at least two axes. This makes it particularly suitable for producing spherical objects, as rotation about the two axes ensures even distribution of the first and second materials in the mold.

[0050] The first axis can be a rotary axis and the second axis can be a swivel axis.

[0051] The rotatable mold can rotate around three axes. This enables the production of complex geometries, which may include undercuts.

[0052] The method steps according to the invention can be performed at least twice without removing the cooled materials from the mold in between, in order to obtain a multilayer composite article. In this way, a multilayer three-dimensional article can be obtained. The intermixed first and second materials are deposited layer by layer on the previous layer. Since the individual layers are thinner than the total wall thickness of the composite article, segregation of the first and second materials is prevented or at least reduced, since the two materials are more likely to segregate in thicker layers than in thinner layers.

[0053] A further aspect of the present invention relates to a three-dimensional composite article, in particular a sporting article, which was produced according to the described method.

[0054] The three-dimensional composite object can be a hollow body. This can be, in particular, a bladder for a ball. The ball can be a soccer ball.

[0055] Alternatively, the three-dimensional composite article may be a shin guard or a shoe.

[0056] Yet another aspect of the present invention relates to a rotatable casting mold suitable for carrying out the described method.

[0057] The casting mold can advantageously have at least one sensor which records at least one process parameter during the implementation of the method according to the invention. The process parameter can be the temperature, the rotational speed of the casting mold, the speed at which the casting mold is moved, the deflection of the casting mold in the case of a pivoting movement, an acceleration acting on the casting mold and / or on the materials filled into the casting mold, the thickness of at least one material layer, or the distribution of the first and / or second material. The data recorded by the sensor can be evaluated during the implementation of the method in order to adapt at least one process parameter. The sensor can be a temperature sensor, a tachometer, an acceleration sensor, an optical sensor or an acoustic sensor.The use of sensors enables targeted process control, allowing specific functions or functionalities to be incorporated into the composite object to be manufactured. IV. Brief description of the drawings

[0058] Aspects of the present invention are explained in more detail below with reference to the accompanying figures. These figures show: Fig. 1A to 1D: a schematic illustration of the method according to the invention; Fig. 2: optional post-processing steps within the scope of the method according to the invention; and Fig. 3: a schematic illustration of the method according to the invention for producing a multilayer composite article; Fig. 4A: a schematic illustration of the method according to the invention; Fig. 4B: Course of speed and temperature during the implementation of the method according to the invention; Fig. 5: a comparison of a conventional rotational molding process with an embodiment of a process according to the invention; and Fig. 6A and Fig. 6B: Results of measurements performed on a sample reinforced with coated fibers according to the present invention. V. Detailed description of preferred embodiments

[0059] In the following, embodiments and modifications of the present invention are described in more detail.

[0060] An embodiment of a method according to the invention for producing a three-dimensional composite article, in particular a sporting article, is described below with reference to Fig. 1A to 1D.

[0061] The method comprises the first step of providing a rotatable mold 11. In the Fig. Figures 1A to 1D show a round mold 11, which is suitable, for example, for producing a bladder for a soccer ball. However, the mold can also have other geometric shapes, such as a cylinder or a complex three-dimensional geometry.

[0062] In the embodiment of the Fig. 1A to 1D, the casting mold 11 has two axes of rotation, a vertical axis of rotation 12 and a horizontal axis of rotation 13. In principle, however, the casting mold 11 can also have a different number of axes of rotation. For example, if the casting mold is cylindrical, it generally has only one axis of rotation. If the casting mold has a complex three-dimensional geometry, the casting mold can have more than two axes, for example, three axes. The axes of rotation can be cardanically mounted, i.e., in the case of two axes, by two bearings with axes of rotation intersecting at right angles to each other.

[0063] The method further comprises the step of filling a first material 14 into the mold 11. The Fig. Figure 1A shows the state after the first 14 and the second material 15 have been filled into the mold 11. In the embodiment of the method according to the invention according to Fig. 1A to 1D, the first material 14 and a second material 15 were already mixed with one another before the materials were poured into the mold 11. Furthermore, it is possible for the first material 14 and the second material 15 to be poured into the mold 11 at the same time, in particular at the beginning of the process. The first material 14 is a polymer material such as thermoplastic urethane (TPU). In principle, an ester-based TPU or an ether-based TPU can be used. The first material 14 can be poured into the mold 11 in granular and / or liquid form or mixed with the second material 15. Since a flow meter can be used in this case, the filling can also take place fully automatically. Another example of the first material 14 is Elastollan® SP 9305, which is manufactured, for example, by BASF SE.This is a powdery material in its unprocessed state with a low-viscosity melt.

[0064] The method further comprises the step of filling the second material 15 into the mold 11, as already explained, the Fig. 1A shows the state after the first material 14 and the second material 15 have been poured into the mold 11. The second material 15 can be, for example, fibers such as aramid fibers. In this way, a three-dimensional composite fiber article can be obtained that has excellent strength and stability.

[0065] An exemplary second material 15 is a 2500 dtex hybrid yarn, such as the Twaron® 1111 core yarn. This has a core made of 420 dtex aramid yarn twisted at 100 rpm. The sheath material is TPU Elastollan® SP 9305. The fiber content of the hybrid yarn is approximately 13.2 vol.%.

[0066] The first material 14 and / or second material 15 may also be polyamide.

[0067] To facilitate thorough mixing of the first material 14 and the second material 15 in the mold 11, the fibers can be coated with the first material 14, for example, TPU. Due to the similar surface structure of the first material 14 and the second material 15, this prevents or at least reduces the separation of the two materials in the mold 11.

[0068] The second material 15 can also be a polymeric material, e.g., a reactive material. Thus, according to the invention, it is possible, for example, for the first and second materials to each be 2K PU materials or 2K resins. It is also possible for the first material to be a 2K PU material and the second material to be a 2K resin, or vice versa. It is also possible for the first material to be PU while the second material is TPU, or vice versa. Likewise, the first material 14 and / or second material 15 can be polyamide.

[0069] The first material, like the second material, can also be a mixture. For example, the first material can be a mixture of two components and / or the second material can be a mixture of two components. For example, the first material can comprise a base material (also referred to as a matrix). The base material can be mixed with at least one further component. The further components can be, for example, prefabricated components and / or semi-finished products. For example, electronic elements or light-emitting elements could be mixed with the base material. Examples of such elements are lighting elements (LEDs, OLEDs, etc.), sensors, chips or weights. Furthermore, it is possible for such elements to serve purely decorative purposes.

[0070] The second material 15 can also be filled into the mold 11 in granular and / or liquid form. Since a flow meter can be used in this case, the filling process can also be fully automated.

[0071] The method further comprises the step of rotating the mold 11 as shown in the Fig. 1A and Fig. 1B. The mold is rotated about the rotation axes 12 and 13, for example, by means of motors. The first material 14 and the second material 15 are distributed and mixed in the mold 11.

[0072] The exemplary procedure according to Fig. 1 further comprises the step of heating the materials 14, 15, for example by heating the mold 11, as in the Fig. 1B. The casting mold 11 is continuously rotated about its rotational axes 12 and 13. When the casting mold 11 reaches the melting temperature of the first polymeric material 14, it melts and the second material 15 is incorporated into the melt. Due to the rotation of the casting mold 11, the melt is deposited on the inner wall of the casting mold 11. The process step according to Fig. 1B is preferably used when using a thermoplastic polymer.

[0073] In the Fig. 1B shows that the materials 14, 15 are heated externally by means of the casting mold 11. For example, the casting mold 11 can be placed in a furnace for this purpose. Alternatively, the casting mold 11 can also be heated internally and, for example, have bores through which a hot liquid is pumped. Electrically operated heating elements arranged on or in the casting mold 11 are also conceivable. For example, it is also possible for one or more heating lances to be inserted through one or more bores in the casting mold 11.

[0074] The exemplary procedure according to Fig. 1 further comprises the step of cooling the materials, for example by cooling the mold 11, as in the Fig. 1C. The casting mold 11 is continuously rotated about its rotational axes 12 and 13. When the casting mold 11 falls below the melting temperature of the first polymeric material 14, the latter solidifies and the second material 15 is enclosed therein. Due to the rotation of the casting mold 11, the solidified first material 14, with the second material 15 enclosed therein, is deposited on the inner wall of the casting mold 11, as shown in the Fig. 1C. The process step according to Fig. 1C is preferably used when using a thermoplastic polymer.

[0075] In the Fig. 1C shows that the casting mold 11 is cooled from the outside. For example, the casting mold 11 can be placed in a cooling chamber for this purpose. Alternatively, the casting mold 11 can also be cooled from the inside and, for example, have bores through which a cold liquid is pumped. Electrically operated cooling elements (e.g., Peltier elements) arranged on or in the casting mold 11 are also conceivable. For example, it is also possible for one or more cooling lances to be inserted through one or more bores in the casting mold 11.

[0076] Both the heating and cooling lances mentioned can be designed such that they are arranged so that they can be displaced relative to the mold along their longitudinal axes. For example, different areas inside the mold can be cooled or heated differently. This is particularly important for the production of multi-layer composite articles, since different layers can be cooled or heated successively.

[0077] It is possible for the method according to the invention to carry out the previously explained method steps b. to f. at least twice without removing the cooled materials 14 and 15 from the casting mold 11, in order to thus obtain a multi-layer composite article. The first material 14 and second material 15, which are mixed by the rotation of the casting mold 11, are deposited layer by layer on the previous composite layer. Since the individual layers are thinner than the total thickness of the material, demixing of the first material 14 and second material 15 is prevented. In particular, the second material 15 is prevented from settling on the first material 14.

[0078] The method further comprises the step of adjusting at least one process parameter during the performance of one or more of the preceding steps so that a homogeneous distribution of the second material 15 is achieved in the produced composite article. To achieve a homogeneous distribution of the second material 15 in the produced composite article, at least one process parameter is adjusted during the performance of one or more of the preceding steps. A homogeneous distribution of the embedded material 15 is important so that the resulting composite material has the desired stability.

[0079] According to the invention, homogeneous mixing of the first polymeric material 14 (the embedding "matrix") with the second material 15 can be achieved by adjusting at least one process parameter during the implementation of one or more of the preceding steps of the process. Examples of process parameters are given below, the adjustment of which leads to a homogeneous distribution of the second material 15 in the produced composite article.

[0080] Depending on the materials used, these process parameters are the rotational speed of the mold, the speed at which the mold is moved, the deflection of the mold in the case of a pivoting movement, the heating time of at least one of the materials, the cooling time of at least one of the materials, the viscosity of the first material and the angle of the rotational axes of the mold, the ratio of the rotational speeds around the rotational axes of the mold, the holding times of the first and / or second material in the mold, the filling times of the first and / or second material and combinations of these parameters.

[0081] One process parameter recognized as relevant by the inventors is the rotational speed of the casting mold 11. If, in the process according to the invention, the rotational speed is selected according to at least one of the materials 14, 15, this leads to a homogeneous distribution of the materials 14, 15. For example, when using two materials 14, 15 according to the claims, the rotational speed can be lower or higher than the rotational speed when using only a single material. Another relevant process parameter when using a thermoplastic first material and / or a thermoplastic second material is the heating time of the casting mold 11. A homogeneous distribution of the second material 15 in the produced composite article is achieved if the heating time is shorter than the heating times usually used in rotational casting.Therefore, if two materials 14 and 15 are used according to the claim, one of which is a thermoplastic polymeric carrier material, in order to achieve a homogeneous distribution of the second material 15, the heating time must be shorter than if only the first material 14 were used.

[0082] Yet another relevant process parameter when using a thermoplastic first material and / or a thermoplastic second material is the cooling time of the mold 11. A homogeneous distribution of the second material 15 in the produced composite article is achieved when the cooling time is shorter than the cooling times typically used in rotational molding. Therefore, if two materials 14 and 15 are used, one of which is a thermoplastic polymeric carrier material, in order to achieve a homogeneous distribution of the second material 15, the cooling time must be shorter than if only the first material 14 were used.

[0083] Another relevant process parameter is the angle of the rotation axes 12 and 13 of the casting mold 11. If the casting mold 11 has two rotation axes, these must be essentially perpendicular to each other to achieve a homogeneous distribution of the second material 15. "Essentially perpendicular" means an angle of 90° within the scope of normal manufacturing variations.

[0084] Another relevant process parameter is the time of filling the second material. The most homogeneous distribution of the second material 15 in the composite article can be achieved if the second material is filled into the mold before the first material softens. If the first material 14 is a thermoplastic material, the second material 15 can be filled into the mold 11, for example, no later than 200 seconds after the first material 14.

[0085] If, in the context of the inventive method, the second material comprises 15 fibers, the fiber length is another relevant process parameter. The fiber length is advantageously significantly greater than the critical fiber length, which can be calculated based on fiber strength, fiber diameter, and fiber-plastic bond strength. The critical fiber length indicates the fiber length at which reinforcement of the composite article by means of the fibers occurs. Depending on the composite article to be produced, the fiber length can be, for example, between 30 and 120 mm. Longer fiber lengths increase the tensile strength of the composite article.

[0086] The Fig. Finally, Figure 1D shows that the finished three-dimensional composite article comprising the first 14 and second material 15 is removed from the mold 11.

[0087] The method according to the invention can optionally comprise a series of preprocessing steps. For example, the inside of the mold 11 can be temporarily or permanently coated (e.g., by spraying or evaporating) to prevent, or at least reduce, adhesion of the molded three-dimensional composite article. Likewise, the method according to the invention can comprise a series of optional processing steps following rotational molding. For example, the three-dimensional composite article can be printed or coated. Mechanical post-processing is also conceivable. For example, if it is a bladder for a ball, a valve can be attached to it.

[0088] The Fig. Figure 2 shows optional post-processing steps for three different geometries of the three-dimensional composite object. The left column of the Fig. Figure 2 shows a cylindrical composite article 21a and, below, a schematic cross-sectional view of the outer wall 22a of the composite article 21a obtained by rotational molding in the context of the present process. Accordingly, the outer wall 22a comprises a first polymeric material and homogeneously embedded fibers for reinforcement. A foam 23a is then applied to the outer wall 22a, followed by an insert or decorative element 24a. Finally, the outer wall 22a is coated with a thin layer 25a.

[0089] The middle column of the Fig. Figure 2 shows a spherical composite article 21b and, below, a schematic cross-sectional view of the outer wall 22b of the composite article 21b obtained by rotational molding within the scope of the present method. Accordingly, the outer wall 22b comprises a first polymeric material and homogeneously embedded fibers for reinforcement. A foam 23b is then applied to the outer wall 22b, followed by an insert or decorative element 24b. Finally, the outer wall 22b is coated with a thin layer 25b.

[0090] The right column of the Fig. Figure 2 shows a composite article 21c with a complex geometry and, below, a schematic cross-sectional view of the outer wall 22c of the composite article 21c obtained by rotational molding within the present process. Accordingly, the outer wall 22c comprises a first polymeric material and homogeneously embedded fibers for reinforcement. A foam 23c is then applied to the outer wall 22c, followed by an insert or decorative element 24c. Finally, the outer wall 22c is coated with a thin layer 25c.

[0091] The Fig. Figure 3 shows exemplary processes for producing a multilayer composite article within the scope of the present invention. Analogous to Fig. 2, shows the left column of the Fig. 3 the production of a cylindrical composite object, the middle column the production of a spherical composite object and the right column the production of a composite object with a complex geometry.

[0092] First, in a first group of process steps "A", a first layer 31 of the composite article is produced in a rotatable casting mold 11. If this first layer 31 is a composite layer, i.e. a layer comprising a first polymeric material and a second material (e.g., a fiber material), the group of process steps "A" comprises the process steps already explained in detail. If the first layer 31 is not a composite layer, the group of process steps "A" does not necessarily comprise all process steps (a.) to (g.). For example, in this case, the layer 31 could comprise only a single material, and therefore the process step (c.) of filling in a second material could be omitted. Alternatively, it is also possible for the first layer 31 to be inserted into recesses or depressions 34 of the mold 11.Thus, the layer 31 could have been prefabricated from one or more materials outside the mold 11. Furthermore, the first layer 31 could also have been formed directly in the aforementioned recesses or depressions 34, for example, by a suitable injection molding process.

[0093] The first layer 31 can also be components, for example, prefabricated components and / or semi-finished products. For example, electronic elements or light-emitting elements could be inserted into the aforementioned recesses or depressions 34 of the mold 11. Examples of such elements are lighting elements (LEDs, OLEDs, etc.), sensors, chips, or weights. Furthermore, it is possible for such elements to serve purely decorative purposes.

[0094] As an alternative to providing recesses or depressions 34, the first layer 31 or the components forming the first layer could be held to the mold 11 in another way, for example, by magnetic attraction or by vacuum. For example, instead of recesses 34, vacuum holes could be provided in the mold 11, through which the first layer 31 can be sucked.

[0095] It is also possible that the mold 11 instead of the one shown in Fig. 3 has protrusions 34 shown in the recesses. The protrusions could be used to create grooves in the outer surface of the first layer 31.

[0096] Next, in a second group of process steps "B", a second layer 32 of the composite article is created in the rotatable casting mold 11. This layer 32 is deposited onto the first layer 31 and forms a bond with it. If this second layer 32 is a composite layer, i.e. a layer comprising a first polymeric material and a second material (e.g., a fiber material), the group of process steps "B" includes the process steps already explained in detail. If the second layer 32 is not a composite layer, the group of process steps "B" does not necessarily include all process steps. For example, in this case, the layer 32 could only comprise a single material, and therefore the process step (c.) of filling in a second material could be omitted.

[0097] Finally, in a third group of process steps “C”, a third layer 33 of the composite article is produced in the rotatable casting mold 11. This layer 33 is deposited onto the second layer 32 and forms a bond with it. If this third layer 33 is a composite layer, i.e. a layer which comprises a first polymeric material and a second material (e.g. a fiber material), the group of process steps “C” comprises the process steps already explained in detail. If the third layer 33 is not a composite layer, the group of process steps “C” does not necessarily comprise all process steps. For example, in this case the layer 33 could only comprise a single material and therefore the process step of filling in a second material could be omitted.

[0098] In any case, at least one of the three layers 31, 32 and 33 is a layer which is produced according to the process steps already explained in detail. The number of layers in the Fig. 3 is merely an example. Instead of three layers, the composite article could also have two or more layers. In any case, at least one of these layers is a layer produced according to the process steps already explained in detail. The process according to the invention enables the homogeneous production of various layers or plies.

[0099] Based on the Fig. 4A and Fig. 4B, the method according to the invention is explained below, especially with regard to the speeds and temperatures used for the casting mold 11. Fig. 4A a cylindrical casting mold 11 during the individual process steps and the Fig. 4B shows the temperature 43 and speed 44 during the process. Instead of a cylindrical mold 11, a mold of any shape can be used, e.g., a spherical mold. As shown in the Fig. 4A, in a first process step "P1," the mold 11 (also referred to as tool) is filled with a first thermoplastic material 14 (also referred to as matrix). Subsequently, in a process step "P2," the mold 11 and the first material 14 contained therein are heated to a first temperature, which is then maintained as shown in Fig. 4B. The heating can be carried out, for example, by means of an infrared radiator 41. The casting mold 11 and the first material 14 located therein are cooled in a process step "P3", e.g., by means of a compressed air cooling system 42. Subsequently, in a process step "P4", the casting mold 11 is filled with the second material 15, which in the example of the Fig. 4A fibers. The rotational speed of the mold 11 is at an almost constant, relatively low level during the process steps “P1”, “P2”, “P3” and “P4”, as shown in Fig. 4B shown.

[0100] In a process step "P5," the casting mold and the first material 14 and second material 15 contained therein are heated to a relatively high temperature, e.g., by means of the infrared radiator 41. Once this temperature is reached, the rotational speed of the casting mold 11 is increased. The temperature remains at a constant high level for a period of time referred to as the holding time 45. In a final process step "P6," the casting mold 11 and the resulting composite article made of first material 14 and second material 15 are cooled. The rotational speed of the casting mold 11 is then reduced to zero, and the composite article is demolded. Cooling can be effected, for example, by means of the compressed air cooling system 42.

[0101] The following are particularly advantageous combinations of speed and temperature in process step “P5”, which lead to easily processable composite articles: 30 rpm (revolutions of the mold 11 per minute) at 220-240°C, 100 rpm at 230-240°C, 200 rpm at 200-220°C and 300 rpm at 160-220°C.

[0102] Within the scope of the method according to the invention, composite materials can also be used as starting materials for rotational molding in order to achieve a homogeneous distribution of the second material 15 in the three-dimensional composite article. For example, it is possible to use fiber bundles or yarns coated with a polymeric material, for example a thermoplastic first material 14 (composite fibers). In the left half of the Fig. Figure 5 schematically shows a conventional rotational molding process in which composite fibers are not used, nor is at least one process parameter adjusted during the process to achieve a homogeneous distribution of the second material 15 in the produced composite article. Accordingly, the polymeric carrier or matrix material 14 and the fibers 15 separate.

[0103] In the right half of the Fig. Figure 5 schematically shows a method according to the present invention in which composite fibers are additionally used. The fibers of the second material 15 are coated with the first polymeric material 14. The resulting three-dimensional composite article exhibits an extremely homogeneous distribution of the fibers 15 within the first matrix material 14.

[0104] The Fig. 6A and Fig. 6B show the results of measurements performed on a rotationally molded TPU sample with coated fibers according to the present invention. A total of four tests were conducted per measurement setting. The fibers are aramid fibers coated with TPU. Fig. Figure 6A shows the influence of the fiber filler content on the tensile strength of the sample. The tensile strength was measured at an angle of 0° to the aramid fibers embedded in the sample. An unreinforced sample (0% filler content) has a tensile strength of 20 N / mm 2 Even with a filler content of 3.8% of the aramid fiber, the tensile strength increases to almost 40 N / mm 2 , almost double.

[0105] The diagram of the Fig.Figure 6B shows the influence of the fiber filler content on the stress required to produce 1% strain in the sample. The stress was applied at an angle of 0° to the aramid fibers embedded in the sample. Without aramid fibers (0% filler content), a stress of only about 1 N / mm is achieved. 2 necessary to stretch the sample by 1%. At just 3.8% aramid fiber filler content, the required tension increases to a good 15 N / mm 2 A further improvement to over 20 N / mm 2 is achieved with a filler content of 5.3%.

[0106] The casting mold 11 used within the scope of the present invention can have at least one sensor which detects at least one process parameter during the implementation of the method according to the invention. The process parameter can be the temperature, the rotation speed of the casting mold, an acceleration acting on the casting mold and / or on the materials filled into the casting mold, the thickness of at least one material layer, or the distribution of the first and / or second material. The data detected by the sensor can be evaluated during the implementation of the method in order to adjust at least one process parameter. For this purpose, the sensor can send the detected data in real time, e.g. wirelessly (via Bluetooth, WLAN, etc.) to a computer, which evaluates the data and, if necessary, initiates a corresponding adjustment of a process parameter. The sensor can be, for example,It could be a temperature sensor, a tachometer, an acceleration sensor, an optical sensor or an acoustic sensor.

[0107] The casting mold 11 used in the present invention can have a patterned surface with depressions and / or elevations on its inside. In this way, the outer surface of the composite article to be produced by the method according to the invention can be provided with a structure. For example, the surface of the casting mold 11 could be designed, for example by means of elevations in the form of webs, so that the outer surface of the composite article has grooves. Such grooves are used, for example, in soccer balls to improve aerodynamic properties. Another example are the dimples found on golf balls, which can also be produced using a casting mold 11 with a patterned surface.

[0108] Possible three-dimensional composite objects that can be obtained using the method according to the invention are, for example, sports balls or bladders or bladder-carcass combinations (composite bladders) for sports balls. For example, in a composite bladder, an additional carcass can be dispensed with if reinforcing fibers 15 are homogeneously distributed directly in the polymeric carrier material 14 using the method according to the invention. The composite bladder then has the necessary stability and tear resistance without an additional carcass. In this way, a whole series of manufacturing steps for the separate carcass are eliminated. In addition, material consumption is minimized and adhesive for fixing the carcass to the bladder can be dispensed with. The ball thus obtained with the composite bladder is largely isotropic.

[0109] Other three-dimensional composite articles that can be produced using the method according to the invention are shin guards. These can be obtained by forming a cylindrical shape. In an optional post-processing step, the resulting composite article can be cut in half to produce two shin guards.

[0110] Finally, shoes or shoe parts can also be manufactured using the method according to the invention. One advantage of manufacturing shoes using the described method is that production is possible entirely without lasts. Last-free shoe production according to the method according to the invention is more flexible and saves time and money. List of reference symbols 11 Casting mold 12 vertical axis of rotation 13 horizontal axis of rotation 14 first material 15 second material 21a, 21b, 21c three-dimensional composite body 22a, 22b, 22c Wall of a three-dimensional composite body 23a, 23b, 23c foam 24a, 25b, 24c insert or decorative element 25a, 25b, 25c thin layer 31 first layer 32 second layer 33 third layer 34 Deepening 41 infrared heaters 42 Compressed air cooling 43 Temperature curve 44 Speed ​​curve 45 holding time

Claims

[1] Method for producing a three-dimensional composite article (21a, 21b, 21c), in particular a sporting article, comprising the steps: a. Providing a movable mold (11); b. filling a first material (14) into the casting mold (11) in a first process step (P1); c. heating the casting mold (11) and the first material (14) in a second process step (P2) and maintaining the temperature; d. cooling the casting mold (11) and the first material (14) in a third process step (P3); e. filling a second material (15) comprising fibers into the mold (11) in a fourth process step (P4), wherein at least one of the materials (14, 15) is a polymer material; f. moving the casting mold (11) at an approximately constant first rotational speed in the first to fourth process steps; g. Heating the casting mold (11) and the first (14) and second (15) materials, increasing the rotational speed in a fifth process step (P5) and maintaining the temperature; h. Cooling the casting mold and the resulting composite article made of the first (14) and the second (15) material in a sixth process step (P6); and i. Reduce the speed to zero. [2] Method according to the preceding claim, wherein the fibers are aramid fibers, polymer fibers and / or natural fibers. [3] A method according to any one of claims 1 or 2, wherein the fibers are coated with the first material. [4] Method according to one of claims 1 to 3, wherein the first and / or second material is a reactive material. [5] Method according to one of the preceding claims, wherein the first and / or second material is a thermoplastic material, in particular a polyurethane, TPU. [6] Method according to one of the preceding claims, wherein the first and / or second material is a thermosetting material. [7] A method according to any one of the preceding claims, wherein the first material is provided in liquid and / or granular form. [8] Method according to one of the preceding claims, wherein the movable mold is rotatable about at least two axes. [9] Method according to one of the preceding claims, wherein the movable mold is rotatable about three axes.

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