METHOD FOR MANUFACTURING COMPONENTS

Description

[0001] The present invention relates to a method according to the preamble of claim 1.

[0002] In the prior art, it is known to produce components from a thermoplastic elastomer using an injection molding machine, whereby gas is introduced into the melt in the extruder tube via an injector, so that the final manufactured component exhibits a certain degree of porosity. Such injection molding technologies are used, for example, to reduce the amount of material consumed per component due to the porosity created by the gas.

[0003] Furthermore, it is known in the art to use foamed plastics such as polyurethane for vibration isolation in machinery, buildings, roads, and the like. However, the foamed polyurethanes are not produced by injection molding but by a foaming process that is known per se.

[0004] AT 009 383 U1 discloses a method according to the preamble of claim 1.

[0005] The object of the invention is to improve a method of the above-mentioned type in such a way that components made of a thermoplastic elastomer can be produced by injection molding and then used specifically for vibration isolation.

[0006] To solve this problem, a method according to claim 1 is proposed.

[0007] The core principle of this process is to inject the gas-enriched melt in the extruder tube into the mold cavity and then increase the volume of the gas-enriched melt by foaming it within the mold cavity. This foaming process in the injection mold allows for the targeted production of a component, resulting in a degree of foaming in the interior of the finished component ranging from 30% to 70%, preferably from 50% to 60%. The degree of foaming is a measure of the porosity created in the component by the foaming process. The degree of foaming, expressed as a percentage, is calculated by multiplying the ratio of the density of the final product to the density of the raw material by 100%. The final product is the corresponding interior area of ​​the component. The raw material is the thermoplastic elastomer, which is then processed in the extruder tube of the injection molding machine.

[0008] It has been shown that components produced using the inventive method exhibit elastic properties due to their high degree of foaming, which qualify these components for use in vibration isolation in machines, roadways, buildings, and the like. The inventive production of such components from thermoplastic elastomer using injection molding opens up a wide variety of shapes in a cost-effective process.

[0009] The pressure in the melt within the extruder tube is advantageously in the range of 250 bar to 400 bar, preferably 300 bar to 350 bar, during the gas enrichment process, where 1 bar, as is generally known, corresponds to 10⁵ Pascals in SI units. To enrich the melt with gas, the gas is advantageously introduced via the injector at a pressure that is preferably 20 bar to 50 bar higher than the pressure in the melt within the extruder tube. It is advantageously provided that, during the gas enrichment process, the gas is partly dissolved in the melt and partly incorporated into the melt in the form of gas bubbles. These gas bubbles in the melt then serve as nucleation sites during the foaming process in the injection mold, in order to achieve the finest and most uniform porosity or pore distribution possible, at least in the interior of the component produced in this way.This in turn is advantageous for equipping the component with vibration isolation properties that are as uniform and defined as possible.

[0010] Advantageously, it is provided that a large proportion of the gas is dissolved in the melt during gas enrichment, and only a small portion is incorporated into the melt in the form of gas bubbles. Accordingly, preferred methods according to the invention provide that, during gas enrichment in the melt in the extruder tube, more than 90% by weight and less than 100% by weight of the gas is dissolved in the melt. The gas bubbles incorporated into the melt in the extruder tube are advantageously very small. Preferably, the gas bubbles incorporated into the melt have a diameter of less than 0.3 µm.

[0011] The methods according to the invention can be carried out in various configurations. For this purpose, injection molding machines known in the prior art, equipped with a suitable injector on the extruder tube, can be used. The thermoplastic elastomers from which the vibration isolation components are manufactured using the methods according to the invention are elastomers that behave like classic elastomers at room temperature but become deformable when heated. These are usually copolymers consisting of a softer elastomeric component and a harder thermoplastic component. Examples of thermoplastic elastomers include urethane-based thermoplastic elastomers (TPU), thermoplastic polyamide elastomers (TPA), thermoplastic copolyester elastomers (TPC), and thermoplastic vulcanizates (TPV).As is generally known, these thermoplastic elastomers can be melted and shaped in the described injection molding process, retaining this shape after cooling. However, these thermoplastic elastomers can also be melted again by renewed exposure to heat and / or shear forces. In the processes according to the invention for manufacturing components according to the invention, which are described in more detail below, thermoplastic elastomers in the form of TPC or TPV, particularly preferably in the form of TPA or TPU, are preferably used as the starting material.

[0012] A first embodiment of the inventive process provides that the mold cavity of the closed injection mold is only partially filled with the gas-enriched melt during the injection process, and that the mold cavity is then completely filled by pressure relief of the gas-enriched melt through foaming of the melt, while maintaining a constant volume. In this embodiment of the inventive process, the mold cavity of the closed mold is thus only partially filled during the injection process. During and after the injection process, pressure relief occurs in the melt, since the pressure in the mold cavity of the closed injection mold is significantly lower than the injection pressure during the injection process and also lower than the holding pressure in the extruder tube after completion of the injection process.This pressure relief allows the desired porosity to form during foaming in the melt. The gas previously dissolved in the melt forms corresponding porosity or gas bubbles in the still-soft melt at the gas bubbles embedded within the melt, which act as nucleation sites. This foaming process increases the volume of the gas-enriched melt in the mold cavity, so that after the foaming process is complete, the mold cavity is entirely filled with the melt. Gases or air displaced from the mold cavity during this foaming process can escape from the injection mold via vent edges and channels known in the prior art. The foaming process in the mold cavity thus advantageously occurs without back pressure, or in other words, free from back pressure. In this context, it is advantageous to use nitrogen as the gas.Furthermore, it is advantageous if the gas-enriched melt is injected into the mold cavity via a hot runner system. In this context, it is particularly beneficial if a surface of the injection mold bounding the mold cavity has a mean roughness value (Ra) in the range of 0.6 µm to 3.6 µm, preferably from 1.6 µm to 2.2 µm. The mean roughness value (Ra) can be determined according to DIN EN ISO 4287 / 2010.

[0013] Another way of implementing the inventive process involves completely filling the mold cavity of the closed injection mold with the gas-enriched melt during the injection process and then enlarging the mold cavity to foam the melt. In this process as well, gas or air displaced from the mold cavity can escape via corresponding vent edges and / or channels, as are known in the prior art. This process can therefore also be carried out without back pressure. It is particularly preferred in such processes that, to enlarge the mold cavity, at least one wall region of the closed injection mold, which defines the mold cavity, is moved relative to at least one other wall region of the injection mold, which also defines the mold cavity.Enlarging the cavity of an injection mold is known in itself and is implemented in the prior art, for example, in the form of a so-called core pull, whereby the pulled core is then the wall area of ​​the closed injection mold, which is moved relative to the other wall area of ​​the injection mold.

[0014] In these variants of the invention, the relative increase in volume of the mold cavity, expressed as a percentage, essentially corresponds to the desired degree of foaming in the interior of the component. For example, if a degree of foaming of 55% is to be achieved in the interior of the component produced according to the invention, the mold cavity of the closed injection mold is increased by 55% during the foaming of the melt in these variants of the inventive process. Here, too, nitrogen is advantageously used as the gas. It is equally advantageous if the surface of the injection mold bounding the mold cavity has a mean roughness value Ra in the range of 0.6 µm to 3.6 µm, preferably from 1.6 µm to 2.6 µm. Furthermore, it is also preferred in this variant of the process that the gas-enriched melt is injected into the mold cavity via a hot runner.

[0015] The injection molds used in the processes according to the invention can be designed as in the prior art. As a rule, the injection mold consists of at least two parts which, when the mold is closed, are connected to each other in such a way that the molten metal can be injected into the mold cavity. After the foaming process and the hardening of the molten metal, the injection mold is opened so that the finished component can be removed or ejected. This does not require further explanation, as this is known in the prior art of injection molding processes.

[0016] A vibration isolation component made of a thermoplastic elastomer can have a pore space with a plurality of, preferably closed, pores, wherein the component exhibits a degree of foaming in the range of 30% to 70%, preferably 50% to 60%, at least in an internal region. Such components can be manufactured, in particular, using methods according to the invention. In such components, the thermoplastic elastomer forms a kind of matrix in which the pores created by the foaming process are embedded. The pores are thus advantageously filled with nitrogen. The degree of foaming is a measure of the porosity created in the finished component. The pore diameter of the pores in the finished component is preferably on the order of 20 µm (micrometers) to 800 µm, preferably between 40 µm and 400 µm, in the aforementioned internal region.

[0017] It is particularly preferred that the component is surrounded on its surface, preferably completely, by an outer skin which has a lower degree of foaming than the inner area of ​​the component surrounded by the outer skin. This outer skin advantageously forms during the cooling process on the surface of the component, i.e., at the contact surface of the melt with the wall regions of the injection mold surrounding the mold cavity. The outer skin is advantageously relatively thin.

[0018] It preferably has a thickness in the range of 0.2 mm to 5 mm, more preferably from 0.5 mm to 2 mm. Particularly preferably, the outer skin has a thickness in the range of 0.1 mm to 1 mm, more preferably from 0.2 mm to 0.7 mm. In the interior area of ​​the component surrounded by the outer skin, the component advantageously exhibits the aforementioned degree of foaming throughout.

[0019] The components mentioned are preferably relatively small. In this respect, it is advantageously provided that the component has a weight in the range of 0.1 g to 1000 g, preferably from 0.5 g to 500 g, and particularly preferably from 2 g to 100 g.

[0020] In preferred embodiments, it is further advantageously provided that the component has a dynamic modulus of elasticity which is 1.2 to 3.5 times, preferably 1.4 to 2.5 times, and particularly preferably 1.5 to 2 times, of the component's static modulus of elasticity. The static modulus of elasticity is advantageously determined according to ISO 3386-2:1997-06. The dynamic modulus of elasticity is advantageously evaluated according to DIN 53513 1990-03. The same load conditions should be applied when determining the static modulus of elasticity as when determining the dynamic modulus of elasticity.

[0021] The following description of the figures provides further details of preferred embodiments of the invention as examples. They show: Fig. 1 shows a schematic longitudinal section through an injection molding machine which can be used for the process according to the invention; Figs. 2 to 4 show a schematic representation of the injection mold to illustrate a first embodiment of the process; Figs. 5 to 7 show a schematic representation of the injection mold to illustrate a second embodiment of the process according to the invention; and Fig. 8 shows a schematic longitudinal section through a component.

[0022] Fig. 1Figure 1 shows a longitudinal section through a schematically represented injection molding machine 3, which is known per se. The thermoplastic elastomer to be processed enters the extruder tube 2 of the injection molding machine 3 via the feed hopper 17. The thermoplastic elastomer material is typically in the feed hopper 17 in the form of granules. The extruder screw 4 is located in the extruder tube 2 and can be rotated about its longitudinal axis and moved along its longitudinal axis, particularly for carrying out the injection process, by means of the screw drive 21. Heating elements 18 are located on the outside of the extruder tube 2, which can be used to heat the extruder tube 2 and thus also its interior, in which the extruder screw 4 and the material to be processed are located.

[0023] The plastic material in the feed hopper 17, in this case the thermoplastic elastomer, is melted to a melt 5 by rotating the extruder screw 4 and heating it by means of the heating elements 18, as is known per se. The melt 5 passes through the non-return valve 19 in the extruder tube 2 and is thus conveyed by the extruder screw 4 into the area of ​​the injector 6. Gas is supplied to the melt 5 in the extruder tube 2 by means of the injector 6. The mixer 20, which is known per se, helps to enrich the gas in the melt 5. The gas is supplied to the injector 6 from a pressurized gas source 16, which is shown here only schematically. Nitrogen is preferably used as the gas in the processes according to the invention.

[0024] Once a sufficiently large quantity of melt 5 has been produced and enriched with a sufficient quantity of gas, the injection process takes place, as is known per se, by opening the valve 22, which here is designed in the form of a needle valve, and moving the extruder screw 4 under correspondingly high pressure towards the injection nozzle 23 of the extruder tube 2. This causes the gas-enriched melt 5 to be injected from the extruder tube 2 into the Fig. 1 The injection material is injected into the injection mold 8 (not shown) or into its mold cavity 7. Such injection molding machines 3, as well as the process steps described so far, are known per se and do not require further explanation.

[0025] In the process according to the invention, the melt 5 in the extruder tube 2 is advantageously located at a pressure of 250 bar to 400 bar, preferably 300 bar to 350 bar, during gas injection. The gas is advantageously injected into the melt 5 at a relative overpressure of 20 bar to 50 bar. The amount of gas required per unit volume of the melt 5 can be calculated depending on the desired degree of foaming. The injection pressures during the injection process are advantageously in the range of 600 bar to 1500 bar, preferably 800 bar to 1300 bar. Immediately after the injection process, a holding pressure in the range of 50 bar to 300 bar, preferably 100 bar to 200 bar, is advantageously maintained in the extruder tube 2 by means of the extruder screw 4 until the valve 22, i.e., in this case in Fig. 1 The needle valve closes the injector nozzle 23 again.

[0026] As explained at the outset, it is advantageously intended that the gas, when enriched in the melt 5 in the extruder tube 2, is largely dissolved in the melt 5. However, a small portion of the gas should ideally be stored as very small gas bubbles in the melt 5. These bubbles will then serve as nucleation sites for pore formation after the injection process in the mold cavity 7 of the injection mold 8. This nucleation process involves the outgassing of the dissolved portion of the gas from the melt 5. These nucleation sites ensure that a very fine-celled pore space is created in the final product, i.e., in the ultimately manufactured component 1. For the preferred size of the gas bubbles in the melt 5 in the extruder tube 2, as well as the ratio of dissolved gas to gas stored in the melt 5, please refer to the explanations above.

[0027] Based on the Figs. 2 to 4A first variant of the inventive method is now described, in which the volume of the gas-enriched melt 5, injected into the injection mold 8, is increased by foaming in the mold cavity 7 of the injection mold 8 until, at the end of the foaming process, a degree of foaming in the range of 30% to 70%, preferably 50% to 60%, is achieved at least in an internal region 9 of the component 1. As mentioned, the degree of foaming is a measure of the porosity achieved in the final product, i.e., in the component 1.

[0028] The Figs. 2 to 4 Each figure shows a schematic longitudinal section through the closed injection mold 8 and the mold cavity 7 located within it, into which the gas-enriched melt 5 is injected. The following can be seen in the Figs. 2 to 4 This also includes valve 22, even though it is not shown here as a needle valve. It is shown in the Figs. 2 to 4The front end of the extruder tube 2, which is docked to the injection channel 25 of the closed injection mold 8 with its injection nozzle 23, is also visible. The extruder screw 4 located in the extruder tube 2 is also visible. In this first, based on the Figs. 2 to 4 In the described variant of the inventive process, the volume of the mold cavity 7 remains constant throughout the entire process, as long as the injection mold 8 remains closed. The injection nozzle 23 and the injection channel 25 advantageously form a so-called hot runner. This ensures that the gas-enriched melt 5 is injected into the mold cavity 7 via the hot runner without cooling down unnecessarily.

[0029] Fig. 2Figure 1 shows the state in which the gas-enriched melt 5 is injected with valve 22 open. Before injection, the mold cavity 7 is generally completely filled with air. The air displaced from the mold cavity 7 during the injection process can escape to the outside through vent edges and channels of the injection mold 8, which are known per se but not shown here. In the first embodiment of a method according to the invention, the mold cavity 7 of the closed injection mold 8 is only partially filled with the gas-enriched melt 5 during the injection process. This results in a pressure release in the mold cavity 7, causing the melt 5 to foam up within the mold cavity 7.

[0030] In Fig. 3The diagram schematically illustrates that even after the injection process is complete, the melt 5 only fills a portion of the mold cavity 7, and the remaining volumes, labeled 24, remain free of melt 5 during the injection process. Through the foaming process in the mold cavity 7, the entire cavity is gradually filled with melt 5. During foaming, the air from the remaining volume 24 is forced out of the mold cavity 7 through the venting edges and channels in the injection mold 8. The foaming process of the melt 5 in the mold cavity 7 occurs without back pressure, or in other words, without back pressure, since the displaced air can escape from the mold cavity 7 to the outside through the known venting edges and channels of the injection mold 8. In this context, it is also advantageous if the surface of the injection mold 8, which defines the mold cavity 7, has the aforementioned average roughness values ​​Ra.Simultaneously, the foaming process creates a pore space in the melt 5 with a multitude of, preferably closed, pores 13 in the interior 9 of the component 1 produced in the mold cavity 7. During the foaming process, the valve 22 advantageously remains closed, as is the case in . Figs. 3 and 4 as shown. In the extruder tube 2, with valve 22 closed, the gas-enriched melt 5 can then be prepared in parallel for the next injection process in the manner described.

[0031] Fig. 4 The figure schematically shows the final state after complete foaming, when the melt 5 has filled the entire mold cavity 7 and the melt 5 contains the material in Fig. 4The pores 13 shown only schematically are formed. As the melt 5 cools against the wall regions of the injection mold 8 that define the mold cavity 7, the melt 5 hardens, resulting in the formation of the component 1 produced according to the invention with the corresponding degree of foaming in its interior region 9. During this cooling process, an outer skin 15 advantageously forms on the surface 14, with which the melt 5, or the component 1, rests against the wall regions of the injection mold 8. This outer skin 15 advantageously has a lower degree of foaming than the interior region 9 of the component 1 it surrounds. Once the component has completely cooled, the injection mold is opened in a manner known per se (not shown here), and the produced component 1 is ejected. After reclosing the injection mold 8, the described process can then be repeated to produce a new component 1.

[0032] If the injection channel 25, through which the gas-enriched melt 5 is injected into the mold cavity 7, is appropriately designed, the valve 22 may be omitted. This is particularly the case if the melt 5 hardens sufficiently quickly in the injection channel 25 and thus closes the injection channel 25 during the foaming process in the mold cavity 7 in the direction of the extruder tube 2.

[0033] Based on the Figs. 5 to 7A second variant of the method according to the invention is described below. In this variant, the mold cavity 7 of the closed injection mold 8 is completely filled with the gas-enriched melt 5 during the injection process, and subsequently, the mold cavity 7 of the closed injection mold 8 is enlarged to foam the melt 5. In this example, this is also achieved by moving the wall region 11 of the closed injection mold 8, which delimits the mold cavity 7, relative to the wall regions 12 of the injection mold 8. This enlargement of the mold cavity 7 of the closed injection mold 8 is known in the prior art and is, for example, referred to as core pulling. According to the invention, however, this is now used to initiate the foaming process in the mold cavity 7 in the melt 5.The relative increase in volume in the mold cavity 7 can ultimately correspond to the desired degree of foaming.

[0034] In the Figs. 5 to 7 Sections through the injection mold 8 and the mold cavity 7 are again shown. Also shown is the extruder tube 2 connected to the closed injection mold 8, with the extruder screw 4 located therein. In this example, a valve 22 is also provided, with which the injection channel 25 between the extruder tube 2 and the injection mold 8 can be closed.

[0035] Fig. 5Figure 1 shows the position in which, in this variant of the inventive method, the gas-enriched melt 5 is injected into the mold cavity 7 with the valve 22 open. The mold cavity 7 is thereby completely filled with melt 5. The air previously present in the mold cavity 7 is then discharged through vent edges and channels present in the injection mold 8, which are not shown here.

[0036] Once the mold cavity 7 is completely filled with gas-enriched melt 5 at the end of the injection process, as described in Fig. 6 shown, valve 22 is closed. Subsequently, relative movements of wall areas 11 and 12 to each other, as shown in Fig. 7The volume of the mold cavity 7 is shown to be increased. Arrow 10 indicates the direction in which the wall section 11 is moved. This increase in the volume of the mold cavity 7 leads to a pressure release in the gas-enriched melt 5 within the mold cavity 7, causing the melt 5 to foam. Here, too, the portion of the gas present in the melt in the form of gas bubbles acts as nucleation sites, resulting in a pore space structure that is as fine as possible. However, as described in the other process variant, the majority of the gas forming the pores 13 is already present in dissolved form in the melt. The enlargement of the mold cavity 7 is stopped when it reaches the desired size of the component 1 to be produced.Here too, during the cooling process, an outer skin 15 preferentially forms on the surface 14 of component 1 facing the wall regions 11 and 12 of the injection mold 8. This outer skin has a lower degree of foaming than the inner region 9 of component 13. Once the melt 5, and thus component 1, has cooled sufficiently, the injection mold 8 can be opened in a known manner and component 1 ejected. The injection mold 8 is then available again for a new injection process.

[0037] In this variant, it would also be conceivable in principle to omit the valve 22 if the injection channel 25 of the injection mold 8 is closed off correspondingly quickly by the melt 5 cooling sufficiently rapidly.

[0038] Fig. 8Figure 1 now schematically shows a cross-section through a completed component 1. A correspondingly high number of pores 13 have formed in the inner region 9 of component 1, which is surrounded by the outer skin 15. Advantageously, this is a closed porosity. According to the invention, a degree of foaming in the range of 30% to 70%, preferably 50% to 60%, has formed within the pore space. The densities of component 1, i.e., the end product of the process according to the invention, are advantageously in the range between 300 g / dm³ and 850 g / dm³, particularly preferably in the range of 450 g / dm³ to 650 g / dm³. The pores 13 are preferably filled with nitrogen. The components 1 are preferably relatively small components, preferably with a component weight in the range of 0.1 g to 1000 g, preferably from 0.5 g to 500 g, and particularly preferably from 2 g to 100 g. legend Regarding the reference numbers

[0039] 1 Component 2 Extruder tube 3 Injection molding machine 4 Extruder screw 5 Melt 6 Injector 7 Mold cavity 8 Injection mold 9 Interior 10 Pull direction 11 Wall area 12 Wall area 13 Pore 14 Surface 15 Outer skin 16 Compressed gas source 17 Hopper 18 Heating element 19 Non-return valve 20 Mixer 21 Screw drive 22 Valve 23 Injection nozzle 24 Residual volume 25 Injection channel

Claims

1. Method for producing components (1) from a thermoplastic elastomer material, wherein the thermoplastic elastomer material is molten in an extruder pipe (2) of an injection-molding machine (3) with the supply of heat and action of an extruder screw (4) of the injection-molding machine (3) to form a melt (5) and gas is supplied to the melt (5) in the extruder pipe (2) via an injector of the injection-molding machine (3) and the melt (5) is enriched with the gas in the extruder pipe (2) and the melt (5) which is enriched with the gas is subsequently injected in an injection operation from the extruder pipe (2) into a mold cavity (7) of a closed injection mold (8) of the injection-molding machine (3), wherein the volume of the melt (5) which is enriched with the gas and injected into the injection mold (8) is increased by foaming in the injection mold (8) and consequently at the end of the foaming operation at least in an inner region (9) of the component (1) a degree of foaming in the value range from 30 % to 70 %, preferably from 50 % to 60 %, is achieved, characterized in that in the extruder pipe (2), when the gas is enriched in the melt (5), the gas is partially dissolved in the melt (5) and is partially dispersed in the melt (5) in the form of gas bubbles.

2. Method according to claim 1, characterized in that in the extruder pipe (2), when the gas is enriched in the melt (5), more than 90 % by weight of the gas and less than 100 % by weight of the gas is dissolved in the melt (5).

3. Method according to claim 1 or 2, characterized in that the gas bubbles which are dispersed in the melt (5) have a diameter of less than 0.3 µm.

4. Method according to any one of claims 1 to 3, characterized in that the mold cavity (7) of the closed injection mold (8) is filled only partially during the injection operation with the melt (5) enriched with the gas and the mold cavity (7) of the closed injection mold (8) with a constant volume of the mold cavity (7) is then completely filled by means of pressure relief of the melt (5) enriched with the gas by foaming of the melt (5).

5. Method according to any one of claims 1 to 3, characterized in that the mold cavity (7) of the closed injection mold (8) is filled completely during the injection operation with the melt (5) which is enriched with the gas and subsequently the mold cavity (7) of the closed injection mold (8) is increased in order to foam the melt (5).

6. Method according to claim 5, characterized in that in order to increase the mold cavity (7) at least one wall region (11), which delimits the mold cavity (7), of the closed injection mold (8) is moved relative to at least one other wall region (12), which delimits the mold cavity (7), of the injection mold (8).

7. Method according to any one of claims 1 to 6, characterized in that nitrogen is used as the gas.

8. Method according to any one of claims 1 to 7, characterized in that the melt (5) which is enriched with the gas is injected into the mold cavity (7) by means of a hot channel.

9. Method according to any one of claims 1 to 8, characterized in that a surface, which delimits the mold cavity (7), of the injection mold (8) has an average roughness value Ra in the range from 0.6 µm to 3.6 µm, preferably from 1.6 µm to 2.2 µm.