Plastic molded part and process for its manufacture

Abstract

Method for producing a molded part (1), in particular a container, from plastic by rotational molding, wherein a plastic precursor of the plastic intended for the plastic molded part (1) is introduced into a rotational melting mold (9), wherein the plastic precursor is present as a melt in the rotational melting mold (9) and polymerizes under rotation of the rotational melting mold (9) while simultaneously shaping, wherein the method comprises the following steps: a) Inserting at least one insert element (18) made of an absorbent and / or impregnatable material into the rotational mold (9); b) Inserting the plastic precursor into the rotational mold (9); c) Setting the rotary melting mold (9) into rotation so that part of the melt is taken up by the at least one insert element (18), characterized in that the insert element (18) is placed in the area of ​​the inside of the rotary melting mold in which the wall thickness of the finished molded part is to be locally increased and / or in which a certain contour feature is to be formed on the later molded part and rests against the inside of the rotary melting mold (9).

Description

[0001] The invention relates to a method for producing a molded part, in particular a container, from plastic by rotational molding, wherein a plastic precursor of the plastic intended for the plastic molded part is introduced into a rotational mold, wherein the plastic precursor is present as a melt in the rotational mold and polymerizes under rotation of the rotational mold while simultaneously shaping, according to the preamble of claim 1. The invention further relates to a correspondingly produced plastic molded part.

[0002] Plastic molded parts are used in many areas. As hollow bodies, they are used, for example, in automotive engineering as fuel tanks or as reservoirs for other liquids. Due to their relatively simple design, low weight, and corrosion resistance, plastic containers are a preferred means of storing liquids. They are required to be mechanically stable, lightweight, and to meet the increasingly stringent requirements for efficient packaging in vehicle manufacturing.

[0003] Plastic containers are typically manufactured using a rotational molding process. A common method involves placing a weighed quantity of plastic material, in the form of powder, pellets, micropellets, or similar, into a hollow mold whose inner surface defines the outer surface of the plastic container. The mold is then rotated around two axes, usually perpendicular to each other. Heat is applied to the rotating mold. The rotational speeds of the molds are low, so centrifugal forces have a minimal influence compared to gravity. The plastic material begins to melt and adheres to the inside of the mold, giving the plastic container its final shape. For this very widespread variation of the rotational molding process, processing temperatures above the melting point are not required.Softening temperature of the plastic material is required.

[0004] Some materials, especially thermoplastics with high melting or softening temperatures, or thermosets, are therefore preferably processed in rotational molding in a manner also known per se, such that a chemical precursor of the material intended for the molded part, the so-called polymer precursor, is introduced as a liquid melt into the rotational mold and chemically reacts there under rotation and simultaneous shaping to form the final plastic material, in particular polymerization. This process is advantageously used, for example, for the production of molded parts from polyamide 6 (PA6), polyamide 12 (PA12), or their copolymers, wherein the corresponding lactams, e.g., caprolactam and / or laurinlactam, are used as polymer precursors. These are in solid form at room temperature under normal conditions, but in the rotational molding process they are melts with a very low viscosity (on the order of 10 mPas, i.e., 10⁻⁶ mPas).They are processed (approximately like water). The process temperature is preferably kept below the melting point of the finished plastic.

[0005] The polymerization reactions of dicyclopentadiene (DCPD) to polydicyclopentadiene (PDCPD, e.g., Telene® from Rimtec Corp.) or of cyclic butylene terephthalate (e.g., CBT® from Cyclics) to polybutylene terephthalate (PBT) are also utilized in rotational molding processes. Furthermore, it is known to produce molded polyurethane (PU) parts using rotational molding processes by reacting di- and / or polyisocyanates with di- and / or polyols as polymer precursors.

[0006] All of the aforementioned material systems have in common that the manufactured molded part consists of a plastic material that is only formed during the molding process in the rotary tool from a plastic precursor, which is initially in liquid form in the rotary tool.

[0007] From DE 10 2011 009 748 A1, a process for producing a two-layer plastic is known in which a mixture containing a polyamide precursor compound, at least one activator, and a catalyst is introduced into a preheated mold. Immediately before the mixture is introduced into the preheated mold, the components are mixed and introduced as a single preparation. After the first mixture has at least partially polymerized, a second mixture is introduced into the mold. Following a further polymerization reaction to form another polyamide layer, the mold is cooled so that the plastic product can be demolded.

[0008] US Patent 2009 / 0266823 A1 discloses a process for manufacturing a polyurethane plastic bladder suitable as a liner for fiber-reinforced pressure vessels. The bladder is produced using a rotational molding process from a reactive mixture containing Gyrothane® 900 or 909 (essentially a polyether polyol) and Raigidur® FPG (essentially a diisocyanate) as plastic precursors.

[0009] GB 712 939 A describes a process for manufacturing rotationally symmetrical plastic parts. A curable resin or plastic compound is applied to the inner wall of a rotating mold and distributed within the mold by centrifugal force. The mold is heated to harden the resin, thus forming a hollow plastic part. The resin may contain fillers such as stone, quartz, or porcelain powder, talc, metal powder, or glass fibers. Alternatively, fillers and resin may be applied alternately to the mold to create a multi-layered structure.

[0010] US 4,258,917 A describes a process for manufacturing reinforced rubber-like sports and play balls by rotational molding. Pre-shaped nonwoven half-shells are placed into the halves of a rotational mold. The half-shells are shaped so that they overlap in the flange area of ​​the mold halves. A polymer is injected into the overlapping area of ​​the half-shells. Another polymer is then injected into one half of the rotational mold. The mold is then closed and rotated. The polymer hardens under the influence of heat.

[0011] WO 95 / 00310 A1 describes a process for producing hollow cylindrical, flat castings. For this process, the mold is heated to a temperature above the gelling temperature of the casting material before it is introduced. A mesh screen is then placed in the mold. The casting material can then be introduced, and the mold is set into rotation. The mold rotates until the casting material has solidified and is ready for removal.

[0012] US Patent 3610457 A1 discloses a rotational molding process in which a cotton ball capable of absorbing the melt is attached to an insert. This insert, with the cotton ball attached, is placed in the rotational mold. The cotton ball lies between the inner wall of the rotational mold and the insert, but has no contact with the inside of the rotational mold.

[0013] A fundamental problem in container manufacturing is that the rotary melt mold only defines the outer contour of the molded part, not its inner shape. While a theoretical average wall thickness of the molded part can be achieved by appropriately adjusting the amount of material added to the size of the mold's inner surface area, it cannot be guaranteed that the container will have a constant wall thickness. This thickness is always subject to a certain distribution. Particularly in the area of ​​inner radii, i.e., areas where the mold wall of the rotary melt mold projects into the mold's interior, wall thicknesses are sometimes significantly lower than the average wall thickness. The smaller this inner radius, the greater the extent of this reduction in wall thickness. Conversely, in the area of ​​outer radii, i.e.,Material always accumulates at the outer edge of a plastic container, causing the wall thickness in these areas to exceed the average wall thickness. The extent of this increase in wall thickness increases with decreasing outer radius. While outer radii simply result in an increase in wall thickness, the stability of thin-walled areas around inner radii can be significantly compromised, reducing the load-bearing capacity and durability of the molded part.

[0014] Particular challenges arise with complex shapes, such as integrally formed tabs or similar features. Especially in confined areas, for example, where outer walls run parallel to each other at close intervals, bridging can occur during polymerization, promoting the formation of voids between the walls. The contour feature is then incompletely formed.

[0015] Especially given the increasing demands on vehicle packaging, complex and intricate installation spaces on the vehicle or machine often need to be optimally utilized, resulting in complex container designs. It is therefore desirable to be able to selectively influence the material distribution, even in intricately shaped molded parts. In this context, it is advantageous if the wall thickness can be locally increased at specific locations within the finished plastic container. Simply increasing the amount of material used is only a very limited solution, as the additional material essentially only leads to a further increase in wall thickness in the area of ​​the outer radii, while the wall thickness in the thinner areas is only marginally improved.This measure ultimately only leads to an increase in material consumption and part weight, which in the case of containers and tanks reduces the available usable volume.

[0016] It is known to influence wall thickness distribution by appropriately selecting rotational speeds, speed ratios, temperature profiles within the mold, and other measures. US 3,417,097 A, for example, describes a process in which caprolactam in liquid form is introduced into a rotary mold, conforms to the inner contour of the die as the mold rotates, and polymerizes into a molded part. To improve wall thickness uniformity, it is proposed to divide the material quantity into at least two dosing operations and to follow a predetermined temperature and rotation profile.

[0017] Since, in rotational molding, similar to blow molding and unlike injection molding, only the outer surface of the molded part is limited by the tooling, there are fundamental limitations to the results achievable for a given part geometry. These effects are particularly pronounced when processing monomers that are introduced into the rotary tool as a low-viscosity melt and polymerized under rotation. The more the part geometry deviates from a spherical shape, the wider the distribution of wall thicknesses becomes.

[0018] For rotational molding with plastic powders or pellets based on a thermoplastic sintering process, US Patent 6,852,788 B2 describes a composition of carrier and binder components as well as a plastic powder. This composition is applied as a molding compound to those areas of the rotary tool where the wall thickness of the molded part is to be increased, e.g., in the area of ​​ribs and screw bosses. Among other things, very low-density polyethylene, petrolatum, paraffins, and beeswax are suggested as carrier and binder components. Alternatively, thermoplastics with a low melt index, matched to the base polymer of the molded part, can be used.

[0019] However, this process is not suitable if a polymer precursor is introduced as a melt into the rotational mold and the polymerization of the precursor is carried out and activated below the melting temperature of the finished polymer. Because the process temperatures are kept below the melting temperature of the finished polymer, the powdered polymer material added with the composition would not sinter together with itself or with the newly formed material created by polymerization. Furthermore, the production of the molding compound is comparatively complex.

[0020] It is therefore an object of the invention to propose a simplified way to selectively influence the wall thickness of a plastic molded part, in particular one produced on the basis of a plastic precursor melt, so that the wall thickness of the finished plastic molded part can be selectively increased and strengthened locally.

[0021] This problem is solved according to the invention with the features of claim 1.

[0022] According to the invention, the insert element is placed and, if necessary, fixed, for example glued, in those areas of the rotary tool where the wall thickness of the finished plastic molded part is to be increased or where a specific contour feature is to be formed on the later molded part.

[0023] The rotary melting mold can be preheated for the process.

[0024] The plastic precursor can be introduced into the mold, for example, as a liquid of moderate viscosity. In this case, the plastic precursor is introduced into the rotary melt mold as a liquid melt. However, it can also be added in solid form (e.g., as powder, pellets, flakes, or the like) and melted only in the mold, so that a portion of the resulting melt is absorbed by the insert. In both cases, it is possible to introduce heat into the rotary melt mold during step c). Generally, however, it proves advantageous to perform step c) at a process temperature where the plastic precursor is in liquid form. The insert then becomes saturated with the molten plastic precursor when the rotary melt mold is preferably rotating biaxially.By holding the melt in a clearly defined position, the insert element promotes the build-up of wall thickness in the area of ​​the rotary tool equipped with the insert element, because this area experiences increased material accumulation compared to other areas of the tool due to the suction and impregnation effect.

[0025] However, heating the rotary melting mold during the process is not strictly necessary. Suitable material systems, such as polyurethanes (PU), can also be processed at room temperature. The plastic precursor simply needs to be introduced into the rotary melting mold in liquid form as a melt, where it polymerizes under subsequent rotation of the mold.

[0026] The production of the molded part in the rotary melting mold takes place under minimal pressure, typically below 2000 mbar. Preferably, however, the rotary melting mold is vented, so that the process essentially runs without pressure, i.e., at atmospheric pressure (e.g., 1013 mbar).

[0027] Especially in manufacturing processes where the plastic precursor is introduced into the rotational mold as a melt, i.e., in liquid form, the use of an absorbent and / or impregnatable material proves advantageous, since the rotation of the mold leads directly to the penetration of the melt into the insert element. Preferably, the melt is a low-viscosity melt, particularly a monomer melt, as this exhibits increased absorption and impregnation properties. Polyamide 6 (PA6), polyamide 12 (PA12), and their copolymers are preferred materials for the production of the plastic molded parts according to the invention. In this case, the corresponding lactams, such as caprolactam and / or laurinlactam, are preferably used as the monomeric starting material for the plastic precursor.

[0028] Other suitable materials for manufacturing the molded plastic parts according to the invention are polydicyclopentadiene (DCPD) and polybutylene terephthalate (PBT). In these cases, dicyclopentadiene (DCPD; e.g., Telene® from Rimtec Corp.) or cyclic oligobutylene terephthalate (e.g., CBT® from Cyclics) with the corresponding catalysts or additives are preferably used as the monomeric or oligomeric starting material. Polyurethanes (PU) are also suitable, for whose production mixtures of di- and / or polyisocyanates and di- and / or polyols are used as precursors. One or both of these precursor components can also be oligomers or prepolymers, i.e., polymers with a relatively low molecular weight.

[0029] Plastic precursors within the meaning of the present invention are, in general, monomers, oligomers, prepolymers, and the like, including mixtures of two or more substances of these categories. The plastic precursors according to the invention are present in rotational melt form as a liquid melt and react, optionally under the influence of added catalysts, activators, or other additives, to form a plastic. The reaction may involve radical, cationic, or anionic polymerization, polyaddition, polycondensation, metathesis polymerization, or the like. The resulting plastic may be a thermoplastic or a thermoset.

[0030] It has been found that by selectively using an absorbent and / or impregnatable material in rotational molding based on low-viscosity melts of polymer precursors, sharply defined and stable local increases in wall thickness can be achieved in the relevant areas of the rotary tool where the insert element is located. The insert element absorbs the liquid melt by being saturated with it and / or becoming saturated with it. The absorbent and / or impregnatable material is particularly suitable for processes in which the polymer precursor has a low initial viscosity as a melt. Preferably, the polymerization of the polymer precursor is carried out below the melting temperature of the finished polymer. The prepared melt can, for example, be introduced into the rotational mold via an injection device, preferably one that can be heated.

[0031] In principle, one or more insert elements can be used in the production of a plastic molded part and effectively reinforce the relevant areas.

[0032] In addition to selectively increasing wall thickness and / or improving the definition of certain contour features, the absorbent or impregnable material can also fulfill other functions. For example, it can simultaneously reinforce the corresponding areas of the finished molded part. The absorbent and / or impregnable material can be selected from, or contain, preforms containing, for example, glass fibers, carbon fibers, suitable plastic fibers, or such fibers. Similarly, the insert can incorporate or fix reinforcing elements in the form of inserts, such as a tube element, a support ring, or the like, within the rotary tool, further increasing the stability of the relevant areas in the finished plastic molded part. Preferably, these reinforcing elements are at least partially embedded in the plastic through polymerization.

[0033] Textiles and / or textile composites can be used as absorbent and / or impregnatable materials for the insert element. Woven fabrics, nonwovens, knitted fabrics, and similar materials are particularly suitable. Due to their deformability, these textiles can also be positioned in hard-to-reach areas or internal contour sections of rotational molds. Therefore, these materials are especially suitable for forming a flap on a plastic container. In the case of sheet-like materials, the absorbent or impregnatable material can be folded or rolled regularly or irregularly and stuffed into the designated area of ​​the mold without separate fixing agents, or optionally fixed there with suitable fixing agents such as an adhesive or similar.

[0034] According to another embodiment, the insert element comprises or consists of a preferably open-pored foam and / or a sponge. In this case, the absorbent and / or impregnatable material can be optimally adapted to the contour area of ​​the tool in which it is to be placed. For example, the insert element can be ring-shaped or tube-shaped and thus be used in the area of ​​a container's nozzle. Since this area is subject to frequent stresses, local material reinforcements prove advantageous here. The adaptation of the insert element to the inner contour of the rotary melt mold can be ensured by various measures. For example, the insert element can be manufactured from semi-finished products by casting, injection molding, or machining. It is also possible to spray or pour the insert element directly into the rotary melt mold.

[0035] It has proven advantageous if the insert element is designed to dissolve during the polymerization of the plastic precursor, resulting in it being no longer readily recognizable in the finished molded part. The insert element can dissolve in the reaction mixture of the plastic precursor with which it is impregnated during the manufacturing process. The kinetics of the polymerization, on which the viscosity profile of the reaction mixture depends, and the rate of dissolution can be coordinated such that the absorbent and / or impregnatable material only dissolves when the viscosity of the reaction mixture is sufficiently high to ensure that the reaction mixture remains within the mold area and cannot flow out again.

[0036] According to another embodiment, the insert element is not only embedded in the plastic material during the polymerization process, but also chemically bonded to it.

[0037] To improve the absorption of the melt into the insert element, a further embodiment provides that the rotation of the rotary melting mold is interrupted, at least temporarily, in at least one axis of rotation. By controlling and halting the rotation of the rotary tool at suitable times during the process, at least in one axis, the melt can settle in the area of ​​the insert element and penetrate it more effectively. According to a further advantageous embodiment, the rotation of the rotary melting mold is interrupted in such a way that the insert element comes to rest at a lowest point of the rotary melting mold and / or below the level of the liquid melt. This measure can be carried out at least once or, if necessary, repeated for different areas in which insert elements are arranged and / or for one and the same area of ​​the tool.The timing, frequency and duration of these rotation interruptions, as well as the tool position during the standstill, can be selected to achieve the desired result.

[0038] Another embodiment of the invention provides that in a further step d), the rotational mold is stopped, filled with another plastic precursor or plastic material, and set back into rotation so that an inner second plastic layer is formed. The additional plastic precursor can be introduced into the rotational mold after the reaction of the first plastic precursor has completed or at least progressed to the point where the first layer is sufficiently stable when rotation is stopped. In this way, plastic containers with a multilayer wall structure and optimal wall thickness can be produced. Depending on the material used, heat can be introduced into the rotational mold for the polymerization of the additional plastic precursor. However, the temperature reached during the production of the first layer, in conjunction with the heat input of a second polymerization, is often sufficient.Therefore, in material systems whose polymerization is exothermic, such as caprolactam, the introduction of heat can be omitted.

[0039] Further advantages, features, and embodiments of the invention will become apparent from the following description of embodiments and the drawings. All features described and / or illustrated, individually or in any combination, constitute the subject matter of the invention, even independently of their compilation in the claims or their cross-references.

[0040] They show: Fig. 1 a plastic container in a sectional view; Fig. 2. An open rotary melting mold in a perspective view; Fig. 3 in a perspective view an opened rotary melting mold with inserted insert elements according to three embodiments of the invention; Fig. 4 the insert element in section A from Fig. 3; Fig. 5 the insert element in section B from Fig. 3; Fig. 6 the insert element in section C from Fig. 3, Fig. 7 a section through the fastening tab of the molded part produced according to the invention and Fig. 7 a section through the fastening tab of a molded part manufactured according to the state of the art.

[0041] The in Fig. Figure 1, an example of a plastic molded part according to the invention, has a hollow interior 2 defined by the side walls 3 of the liquid container 1. A filling spout 4 is integrally formed with the side wall 3 in the upper region of the liquid container 1, through which the liquid container 1 can be filled. An outwardly projecting nozzle or dome 6 is formed in the bottom region 5 of the liquid container 1. Such a nozzle can, for example, serve to support or anchor the liquid container 1. The nozzle 6 must therefore be able to withstand the load. A tab 8 is formed in the lower region of the lateral outer wall 7 of the liquid container 1, which narrows considerably from the interior 2 of the liquid container 1.

[0042] To manufacture the liquid container 1 from Fig. 1 is a rotary tool, or a rotary melting mold 9, as used in Fig. The device shown in Figure 2 is used. It consists of two halves or mold shells 10, 11, whose edges or flanges 12 are placed together to close them. The inside of the mold shells has a contour 13 that defines the outer shape of the liquid container 1. Fig. 1 is defined when the shells 10 and 11 are placed next to each other. To produce the plastic container, the rotational mold 9 is heated. In its closed state, it is then filled with the chemical precursor of the material intended for the molded part in the form of a low-viscosity monomer melt (not shown) via a filling opening 14 and set into biaxial rotation about the X-axis and the Y-axis. During polymerization, the monomer melt forms the final plastic of the container. During the process, the temperature in the rotational mold 9 is kept below the melting temperature of the finished polymer. During rotation, the melt conforms to the contour 13 and polymerizes. While maintaining rotation, the rotational mold is cooled, opened, and the formed liquid container is removed.

[0043] Especially in areas with a small inner radius, such as in the transition area 15 ( Fig. 1) Between the filling nozzle 4 and the side wall 3, or in the transition area 16 between the bottom area 5 and the nozzle 6, the problem arises that these sections have only a small wall thickness. The section around the tab 8 is also problematic, as it has a rather complex design and two parallel walls 17a, 17b that run close together.

[0044] As in Fig. As shown in Figure 3, the rotary melting mold 9 is fitted with an insert element 18 in each of the critical regions A (tab), B (dome / nozzle) and C (filling nozzle) before being filled with the melt. This insert element is attached to the corresponding contours 13 of the mold shells 10, 11. This is shown in the Fig. Figure 3 shows the first mold shell 10.

[0045] The insert elements 18 each consist of an impregnable or absorbent material capable of absorbing and binding or retaining melt. This results in a local accumulation of material in areas A, B, and C, ensuring that more material is retained and polymerized in these critical areas. Wall thicknesses can be precisely adjusted using the insert element 18.

[0046] In area A ( Fig. 4) The contour 13 of the flap of a liquid container is formed in the mold 10. When the rotational mold is closed, a constriction forms in the direction of arrow 19. If bridging occurs too early during polymerization, closing the constriction, the molding is incomplete. An insert element 18 made of a textile, such as nonwoven, woven, knitted, or the like, is inserted into the constriction 19. The flexibility of this material ensures that even complex shapes can be achieved with the insert element.

[0047] In area B ( Fig. 5) A voluminous insert element 18 in the form of a plug 20 is inserted into the contour 13 of the mold shell 10, which is intended to form the nozzle of a liquid container. This plug 20 can consist, for example, of an open-pore foam or a sponge. Since the plug 20 becomes saturated with the melt, a considerable amount of formed plastic accumulates during polymerization, and the plastic container exhibits a particular wall thickness and strength in this area.

[0048] In area C ( Fig. 6) An insert element 18 in the form of a ring 21 is inserted into the contour 13 of the mold shell 10, which is intended to form the filling spout of a liquid container. The ring 21 rests against the contour 13. A grid-like tube element 22 rests against the inside of the ring 21. During rotational molding, the tube element 22 is embedded in the polymerized plastic and integrally anchored in the wall of the plastic container. The ring 21 also consists of an absorbent or impregnable material, preferably an open-pore foam, which increases the wall thickness in the area of ​​the filling spout.

[0049] As the Fig. Figure 6 shows that the insert elements 18 can be used effectively to anchor insert parts, such as the pipe element 22, in the container wall, so that they are more effectively fused into the container wall, which significantly reduces the risk of leakage in such components. Example (A)

[0050] According to a preferred embodiment for manufacturing a fuel tank, premixes of ε-caprolactam with 0.6 wt% sodium caprolactamate as a catalyst and ε-caprolactam with 0.9 wt% hexamethylene-1,6-bis-carbamido-caprolactam as an activator, respectively, are melted in two separate containers and maintained at 100 °C. The containers with the two premixes are connected via lines to a mixing head, from which another line extends, equipped at its end with an injection device. The mixing head, the lines between the containers with the premixes and the mixing head, and the line from the mixing head to the injection device are heated and maintained at 100 °C.

[0051] A rotary tool, which can be shaped like a motorcycle fuel tank, is lined in the area of ​​a mounting tab of the future motorcycle tank with an absorbent or impregnatable material in the form of a polyamide 6.6 fabric. This is achieved by first rolling the fabric and then stuffing it into the part of the tool responsible for forming the mounting tab. The rotary tool is equipped with a venting device that maintains atmospheric pressure within the tool. The rotary tool is preheated to 160 °C in an oven. The two premixes are combined in equal weight proportions in the mixing head to form a reaction mixture and thoroughly mixed. An initial portion (2200 g) of the reaction mixture is fed into the rotary tool within 20 seconds.The rotary tool is slowly rotated biaxially in an oven maintained at 205 °C, ensuring that the reaction mixture comes into contact with and is deposited on every part of the tool's inner surface. After 200 seconds, the rotation is stopped to add a second portion (2200 g) of the reaction mixture to the tool. The tool is then slowly rotated biaxially for 180 seconds while still heated, before being cooled to 70 °C in a cooling chamber while maintaining rotation. The rotary tool is then opened, and the resulting motorcycle tank-shaped part is removed.

[0052] The motorcycle tank is cut open in the area of ​​the mounting tab, and the wall thickness is measured. Values ​​between 3.5 mm and 5.9 mm are found. Fig. Figure 7 shows a section through the fastening tab of the molded part produced according to the invention. Comparative example (B)

[0053] A second motorcycle tank is manufactured using conventional methods. The procedure follows the process described for example (A), except that the rotary tool is not coated with an absorbent or impregnatable material in the area of ​​a mounting tab for the future motorcycle tank.

[0054] After being removed from the tool, the motorcycle tank is cut open in the area of ​​the mounting tab, and the wall thickness is measured. Values ​​between 0.8 mm and 2.0 mm are obtained. Fig. Figure 8 shows a section through the fastening tab of the molded part manufactured according to the state of the art. Reference symbol list 1 plastic container 2 Interior 3 side walls 4 filling ports 5 Floor area 6 nozzles / dome 7 side exterior wall 8 tab 9 Rotational melting mold 10 mold tray 11 Molding tray 12 Edge / Tool flange 13 Contour 14 Filling opening 15 Transition area 16 Transition area 17a,b parallel side walls 18 insert element 19 bottleneck 20 plugs 21 Ring 22 pipe element

Claims

[1] Method for producing a molded part (1), in particular a container, from plastic by rotational molding, wherein a plastic precursor of the plastic intended for the plastic molded part (1) is introduced into a rotational mold (9), wherein the plastic precursor is present as a melt in the rotational mold (9) and polymerizes under rotation of the rotational mold (9) while simultaneously being shaped, wherein the method comprises the following steps: a) Inserting at least one insert element (18) made of an absorbent and / or impregnatable material into the rotational mold (9); b) Inserting the plastic precursor into the rotational mold (9); c) Setting the rotational melting mold (9) into rotation so that part of the melt is taken up by the at least one insert element (18), characterized by, that the insert element (18) is placed in the area of ​​the inside of the rotary melting mold in which the wall thickness of the finished molded part is to be locally increased and / or in which a specific contour feature is to be formed on the later molded part, and is in contact with the inside of the rotary melting mold (9). [2] Method according to claim 1, characterized by , that the plastic precursor is introduced as a liquid melt into the rotational mold (9). [3] Method according to claim 2, characterized by that the melt is a monomer, oligomer and / or prepolymer melt. [4] Method according to claim 1, characterized by , that the plastic precursor in solid form is introduced into the rotational melting mold (9) and melted in the rotational melting mold (9) by introducing heat. [5] Method according to any one of the preceding claims, characterized by , that in step c) heat is introduced into the rotational melting mold (9). [6] Method according to any one of the preceding claims, characterized by , that the polymerization of the plastic precursor is carried out below the melting temperature of the finished plastic. [7] Method according to any one of the preceding claims, characterized by that the insert element comprises textiles and / or textile compositions. [8] Method according to claim 7, characterized by that the insert element comprises a woven fabric, non-woven fabric, knitted fabric or fleece. [9] Method according to any one of the preceding claims, characterized by that the insert element preferably comprises an open-pored foam and / or a sponge. [10] Method according to any one of the preceding claims, characterized by , that the insert element is designed in such a way that it dissolves during the polymerization of the plastic. [11] Method according to any one of the preceding claims, characterized by, that the rotation of the rotofusion mold (9) is interrupted at least temporarily in at least one axis of rotation. [12] Method according to claim 11, characterized by , that the rotation of the rotary melting mold (9) is interrupted in such a way that the insert element comes to rest at a lowest point of the rotary melting mold (9) and / or below a level of the melt. [13] Method according to any one of the preceding claims, characterized by , that in step d) the rotational melting mold (9) is stopped, filled with another plastic precursor or another plastic material and set back into rotation. [14] Plastic molded part, manufactured according to a method according to any of the preceding claims. [15] Molded part according to claim 14, characterized by that the molded part is a hollow plastic body, in particular a container and / or a tank.

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