METHOD FOR PRODUCING A RUBBER-PLASTIC COMPOSITE

Description

[0001] The present invention relates to a method for producing a rubber-plastic composite, comprising the steps (a) of molding an unvulcanized elastomer, (b) of partially vulcanizing the molded elastomer at a temperature of at least 140°C to a degree of vulcanization in the range of 10 to 40%, (c) of cooling the partially vulcanized elastomer to a temperature of less than 100°C within less than 20 minutes, (d) of overmolding the partially vulcanized elastomer with a plastic, and (e) of heat-treating the partially vulcanized elastomer overmolded with a plastic at a temperature in the range of 100°C to 170°C for a duration of 5 minutes to 5 hours to complete the vulcanization and form a rubber-plastic composite.

[0002] Elastomers are used in numerous applications, for example, as seals, damping elements, covers, or membranes. When rubber parts need to be permanently bonded, composite parts made of such elastomers with a hard component have proven effective. In automotive engineering, for example, the hard component has traditionally been made of metal. However, to significantly reduce weight, i.e., to achieve lightweight construction, plastic components are increasingly used as the hard component today. These are lightweight, do not corrode, and can be injection-molded into complex parts. A bond between a rubber and a plastic component is usually created using an adhesion promoter or an adhesive. However, the use of adhesion promoters or adhesives requires a multi-stage, complex, and often environmentally damaging process. Furthermore, the adhesive strength is not always sufficient.

[0003] To solve this problem, the so-called plastic-rubber composite process (also known as the K&K process) was proposed. Certain rubber / plastic combinations, such as SBR / PPE or XNBR / PA, can be directly bonded together using this process without the need for adhesion promoters or adhesives. The rubber component is applied to the plastic and then vulcanized in the presence of the plastic, resulting in adhesion of the rubber component to the plastic. This process can be carried out in one or two stages. The two-stage injection molding process is similar to the two-stage production of two-color injection-molded parts. First, the rigid molded part is produced, for example, by injection molding, extrusion, embossing, or pressing. In a second step, it is coated with the rubber component, which may be pre-molded, and exposed to the vulcanization conditions of the rubber.Applying the rubber to the rigid molded part can be done by pressing, embossing, injection molding, or extrusion. The single-stage injection molding process is analogous to the single-stage two-color injection molding process. In this case, one injection molding machine is equipped for processing thermoplastics, the other for processing rubber. The mold or cavity for the rubber compound is heated to the specified vulcanizing temperature, which should be below the solidification temperature of the plastic compound. The K&K process is described, for example, in JP 2010022582 A.

[0004] WO 2011 / 138300 A1 and in " High-Performance Polymers in Plastic-Rubber Composites" by Evonik Industries (see https: / / www.vestamid.com / sites / lists / RE / DocumentsHP / Plastic-rubbercomposites-EN.pdf).

[0005] However, the plastic components suitable for the K&K process must be extremely stiff, hard, and thermally stable to withstand the vulcanization process. This makes these plastic-rubber composite parts unsuitable for certain applications, such as in sports shoes. Furthermore, the injection molds required for the K&K process are generally very expensive.

[0006] The present invention therefore aims to provide a method for producing a rubber-plastic composite that does not have the disadvantages described above. In particular, a method is to be provided that enables a bond between rubber and plastic without the use of adhesion promoters, that is not only suitable for producing rubber-plastic composites with a rigid plastic component, and that can be carried out with simpler or more economical tools.

[0007] This problem is solved by the embodiments characterized in the claims.

[0008] In particular, according to the invention, a method for producing a rubber-plastic composite is provided, comprising the steps (a) of molding an unvulcanized elastomer, (b) of partially vulcanizing the molded elastomer at a temperature of at least 140°C to a degree of vulcanization in the range of 10 to 40%, (c) of cooling the partially vulcanized elastomer to a temperature of less than 100°C within less than 20 minutes, (d) of overmolding the partially vulcanized elastomer with a plastic, and (e) of heat-treating the partially vulcanized elastomer overmolded with a plastic at a temperature in the range of 100°C to 170°C for a duration of 5 minutes to 5 hours to complete the vulcanization and form a rubber-plastic composite.

[0009] The present invention is based on the consideration that the disadvantages of the adhesive bonding process and the K&K process could be avoided if the vulcanized rubber component could be overmolded with the plastic, i.e., if the K&K process could be carried out in reverse. However, the rubber component is no longer active after vulcanization and therefore no longer forms a stable bond with the plastic. It has now been surprisingly discovered that this problem can be solved according to the invention by first only partially vulcanizing the rubber component and then overmolding it with plastic. Since the rubber component is not yet fully heated, the stable bond with the plastic can be formed during the injection molding process or during post-heat treatment. This allows the rubber component to reach the optimal degree of vulcanization, and the bond between the rubber and plastic is strengthened or completed.

[0010] In step (a) of the process according to the invention, an unvulcanized elastomer is first formed. An elastomer is understood to be a dimensionally stable but elastically deformable plastic whose glass transition temperature is below room or operating temperature. Any unvulcanized elastomer suitable for the intended application can be used for the process according to the invention. Preferably, the unvulcanized elastomer is selected from the group consisting of polyacrylate rubber (ACM), ethylene acrylate rubber (AEM / EAM), ethylene propylene diene copolymer (EPDM), ethylene propylene copolymer (EPM), fluororubber (FKM), (partially) hydrogenated nitrile rubber (HNBR), carboxyl group-containing nitrile rubber (XNBR), nitrile butadiene rubber (NBR), natural rubber (NR), styrene butadiene rubber (SBR), methyl vinyl silicon rubber (VMQ), polybutadiene rubber (BR), polyisoprene rubber (IR) and combinations thereof.Particularly preferred is (partially) hydrogenated nitrile rubber (HNBR) as the unvulcanized elastomer. The unvulcanized elastomer can be used unblended or blended with at least one other rubber component, in particular with one of the aforementioned rubber types, for example in the form of an EPM / EPDM or SBR / BR blend. EPM or EPDM, or an EPM / EPDM blend, is of particular importance.

[0011] The unvulcanized elastomer can be used together with suitable compounding ingredients, which, for example, include at least one crosslinker or a crosslinking system (crosslinking agent and accelerator). Peroxides are preferably used as crosslinkers due to their improved resistance to heat aging. Other compounding ingredients include, for example, fillers, vulcanization activators, oils, processing aids, plasticizers and / or antioxidants, as well as optionally further additives such as fibers and color pigments. In this regard, reference is made to the general state of the art in elastomer compounding technology. According to a preferred embodiment of the present invention, the elastomer contains additives selected from the group consisting of vulcanizing agents, vulcanization activators, oils, and fillers.

[0012] The unvulcanized elastomer is shaped, i.e., brought into the intended form. This can be done by any suitable method known in rubber technology, for example, by pressing, embossing, injection molding, or extrusion. According to a preferred embodiment of the present invention, step (a) of the inventive process is carried out in a vulcanization press. This has the advantage that the next step (b) of vulcanization can be carried out simultaneously or directly thereafter.

[0013] In step (b) of the process according to the invention, the molded elastomer is vulcanized at a temperature of at least 140°C to a degree of vulcanization in the range of 10 to 40%. The vulcanization step can be carried out in the usual manner. Preferably, the vulcanization is performed in a vulcanization press. The optimal vulcanization conditions depend on the selected rubber compound and, in particular, on the vulcanization system used, as well as the selected shape of the molded elastomer. Suitable vulcanization temperatures are, for example, in the range of 140°C to 250°C, preferably in the range of 170°C to 200°C. Besides the elastomer compound, the vulcanization times depend on the vulcanization temperatures and the geometry of the parts. They generally range between 30 seconds and 15 minutes; lower temperatures and thicker rubber parts require longer times.Vulcanization preferably takes place under increased pressure, in particular under a pressure in the range of 10 to 200 bar.

[0014] According to the invention, vulcanization is not carried out completely, but only to a degree of vulcanization in the range of 10 to 40%. Preferably, vulcanization is carried out to a degree of vulcanization of 10 to 30%, and even more preferably to a degree of vulcanization of 10 to 20%. The degree of vulcanization can be determined by any suitable method known to those skilled in the art. For example, it can be determined from a rheometer curve measured according to DIN 53529. A degree of vulcanization of 0% is defined for the lowest value of the tensile stress over time, and a degree of vulcanization of 100% for the highest value of the tensile stress over time. According to a preferred embodiment of the present invention, vulcanization is carried out at least until the dimensional stability of the molded elastomer is reached, i.e., until the so-called "curing point." This can also be obtained from a rheometer curve.This has the advantage that the shape of the elastomer does not change in the subsequent process steps.

[0015] According to a preferred embodiment of the present invention, steps a) and b) are carried out simultaneously in a vulcanization press. In this way, the manufacturing process can be significantly simplified.

[0016] In step (c) of the process according to the invention, the partially vulcanized elastomer is cooled to a temperature of less than 100°C within less than 20 minutes. This step serves to minimize or completely prevent further vulcanization of the partially vulcanized elastomer due to residual heat. According to a preferred embodiment of the process according to the invention, the cooling takes place in less than 10 minutes, and even more preferably in less than 5 minutes. It is further preferred that the partially vulcanized elastomer is cooled to a temperature of less than 80°C, and even more preferably to less than 60°C. According to a particularly preferred embodiment of the present invention, the partially vulcanized elastomer is cooled to a temperature of less than 80°C within less than 5 minutes.

[0017] In step (d) of the process according to the invention, the partially vulcanized elastomer is overmolded with a plastic. The plastic can be any plastic suitable for the intended application. Preferably, the plastic is selected from the group consisting of polyamide (PA), polyphenylene ether (PPE), polyphthalamide (PPA), polyurethane (PU), polyether block amide (PEBA), and combinations thereof.According to a particularly preferred embodiment, this plastic is in the form of a thermoplastic elastomer (TPE) or as a thermoplastic elastomer alloy with a rubber selected from the group consisting of polyacrylate rubber (ACM), ethylene acrylate rubber (AEM / EAM), ethylene propylene diene copolymer (EPDM), ethylene propylene copolymer (EPM), fluorocarbon rubber (FKM), (partially) hydrogenated nitrile rubber (HNBR), carboxyl group-containing nitrile rubber (XNBR), nitrile butadiene rubber (NBR), natural rubber (NR), styrene butadiene rubber (SBR), methyl vinyl silicon rubber (VMQ), polybutadiene rubber (BR), polyisoprene rubber (IR), and Combinations of these exist in the form of thermoplastic vulcanizates (TPE-V or TPV).

[0018] Depending on the intended application, all suitable combinations of plastic and elastomer can be used for the process according to the invention. According to a preferred embodiment of the present invention, one of the following plastic / elastomer combinations is used: ACM with PA; AEM / EAM with PA; AEM / EAM with PPA; EPDM with PPE; EPDM with PA; FKM with PA; FKM with PPA; HNBR with PA; HNBR with PPA; NR / SBR with PPE; SBR with PPE; SBR / EPDM with PPE; SBR / NBR with PPE; VMQ with PA; VMQ with PPA; XNBR with PA. Polyamide (PA) is particularly preferred as the plastic and (partially) hydrogenated nitrile rubber (HNBR) as the elastomer. In principle, any polyamide can be used, for example PA6, PA66, PA610, PA88, PA612, PA810, PA108, PA9, PA613, PA614, PA812, PA128, PA1010, PA10, PA814, PA148, PA1012, PA11, PA1014, PA1212 and PA12. Among these, PA12 and PA612 are particularly preferred.

[0019] The plastic may contain other suitable additives. However, according to a preferred embodiment of the present invention, the plastic contains no reinforcing agents or fillers, in particular no glass fibers or graphite.

[0020] The step of overmolding the partially vulcanized elastomer with the plastic can be carried out in any manner known to those skilled in the art. According to a preferred embodiment of the present invention, the partially vulcanized elastomer is placed in an injection mold after step (c) and step (d) is carried out therein. It has been found within the scope of the present invention that the usual temperatures and pressures during the injection process, as well as its usual duration, are sufficient to allow the vulcanization of the rubber component to continue.

[0021] In step (e) of the process according to the invention, the partially vulcanized elastomer, overmolded with a plastic, is heat-treated at a temperature in the range of 100°C to 170°C for a duration of 5 minutes to 5 hours to complete the vulcanization and form a rubber-plastic composite. According to a preferred embodiment, the heat treatment is carried out at a temperature of at least 100°C and less than 140°C, and more preferably at a temperature of at least 120°C and less than 140°C. According to a further preferred embodiment, the heat treatment is carried out for a duration of 1 to 3 hours. It is particularly preferred to carry out the heat treatment at a temperature of at least 120°C and less than 140°C for a duration of 1 to 3 hours. The heat treatment can, in particular, be carried out at a temperature of 130°C for a duration of approximately 2 hours.In contrast to vulcanization, the heat treatment is preferably carried out under a pressure in the range of 0.5 to 5 bar, particularly preferably under normal pressure.

[0022] The inventive method has the advantage over conventional methods that the use of adhesion promoters or adhesives for bonding rubber and plastic can be dispensed with. Preferably, the inventive method therefore does not include the use of an adhesion promoter. Furthermore, this method can be carried out with tools commonly used in plastics technology and does not require the special tools necessary for the K&K process. Finally, it is also unnecessary to reinforce the plastic component with reinforcing agents or fillers, for example, glass fibers or graphite, since the plastic component is only subjected to heat treatment, but not vulcanization.

[0023] The present invention further relates to a rubber-plastic composite obtainable by the method according to the invention.

[0024] The rubber-plastic composite according to the invention can be used in numerous applications, for example in complex components, assemblies, or composites for automotive engineering. The rubber-plastic composite according to the invention can also be used, for example, in shoes. Accordingly, the present invention further relates to a shoe comprising the rubber-plastic composite according to the invention. Preferably, this is a soccer shoe, wherein the sole of the soccer shoe represents the plastic component of the rubber-plastic composite and the studs represent the rubber component of the rubber-plastic composite.

[0025] The invention will now be explained in more detail using examples. Examples

[0026] Rubber-plastic composites were produced using the inventive method, employing an HNBR rubber and a PA612 plastic. Vulcanization was carried out at a temperature of 140°C until a degree of vulcanization of 20% was achieved. The composite was then cooled to 40°C within 20 minutes. Subsequently, it was overmolded with the plastic and subjected to heat treatment at 130°C for 2 hours.

[0027] The resulting rubber-plastic composites were subjected to a separation test to determine the force required to separate (i.e., until complete separation or until separation to the point of tearing) the rubber and plastic. The results are shown in Table 1 below. Four samples were produced and measured for each example, with the average value for the four samples and the standard deviation in parentheses given in the table below. Table 1: Sample width [mm] Force [N] Separation resistance [N / mm] Cohesive fraction [%] Example 1 (n=4) 14,08 (0,81) 89,1 (8,1) 6,3 (0,4) 96 (3) Example 2 (reference) (n=4) 14,36 (0,08) 59,7 (9,5) 4,2 (0,7) 5(4)

[0028] Example 1 describes the measurement results for a rubber-plastic composite produced by the inventive method, while the final heat treatment step was omitted in the method for producing the rubber-plastic composite according to Example 2. It is evident that the composite produced by the inventive method requires a significantly greater force to separate the two components and thus exhibits a significantly higher separation resistance. This confirms that a stable rubber-plastic composite can be produced using the inventive method.

Claims

1. Method for producing a rubber-plastic composite, comprising the following steps: a) shaping an unvulcanized elastomer, b) partially vulcanizing the shaped elastomer at a temperature of at least 140°C up to a degree of vulcanization in the range from 10% to 40%, c) cooling the partially vulcanized elastomer to a temperature of less than 100°C within less than 20 minutes, d) overmoulding the partially vulcanized elastomer with a plastic, and e) heat treating the partially vulcanized elastomer overmoulded with a plastic at a temperature in the range from 100°C to 170°C for a duration of from 5 minutes to 5 hours to complete the vulcanization and form a rubber-plastic composite.

2. Method according to Claim 1, wherein the unvulcanized elastomer is selected from the group consisting of polyacrylate rubber (ACM), ethylene-acrylate rubber (AEM / EAM), ethylene-propylene-diene copolymer (EPDM), ethylene-propylene copolymer (EPM), fluoro rubber (FKM), (partially) hydrogenated nitrile rubber (HNBR), carboxylated nitrile rubber (XNBR), nitrile-butadiene rubber (NBR), natural rubber (NR), styrene-butadiene rubber (SBR), methyl-vinyl-silicone rubber (VMQ), polybutadiene rubber (BR), polyisoprene rubber (IR), and combinations thereof.

3. Method according to Claim 1 or 2, wherein the plastic is selected from the group consisting of polyamide (PA), polyphenylene ether (PPE), polyphthalamide (PPA), polyurethane (PU), polyether block amide (PEBA), and combinations thereof.

4. Method according to Claim 3, wherein the plastic is present in the form of a thermoplastic elastomer (TPE) or as a thermoplastic elastomer alloy with a rubber selected from the group consisting of polyacrylate rubber (ACM), ethylene-acrylate rubber (AEM / EAM), ethylene-propylene-diene copolymer (EPDM), ethylene-propylene copolymer (EPM), fluoro rubber (FKM), (partially) hydrogenated nitrile rubber (HNBR), carboxylated nitrile rubber (XNBR), nitrile-butadiene rubber (NBR), natural rubber (NR), styrene-butadiene rubber (SBR), methyl-vinyl-silicone rubber (VMQ), polybutadiene rubber (BR), polyisoprene rubber (IR), and combinations thereof.

5. Method according to any of Claims 1 to 4, wherein a plastic / elastomer combination selected from the group consisting of ACM with PA; AEM / EAM with PA or PPA; EPDM with PPE or PA; FKM with PA or PPA; HNBR with PA or PPA; NR / SBR, SBR, SBR / EPDM or SBR / NBR with PPE; VMQ with PA or PPA; and XNBR with PA, is used.

6. Method according to Claim 5, wherein the plastic used is polyamide (PA) and the elastomer used is (partially) hydrogenated nitrile rubber (HNBR).

7. Method according to any of Claims 1 to 6, wherein in step b) the vulcanization is conducted up to a degree of vulcanization in the range from 10% to 20%.

8. Method according to any of Claims 1 to 7, wherein the partially vulcanized elastomer in step c) is cooled to a temperature of less than 80°C within less than 5 minutes.

9. Method according to any of Claims 1 to 8, wherein the heat treatment in step e) is conducted at a temperature of at least 120°C and less than 140°C for a duration of from 1 to 3 hours.

10. Method according to any of Claims 1 to 9, wherein the plastic contains no reinforcers or fillers, preferably selected from glass fibers and graphite.

11. Method according to any of Claims 1 to 10, wherein the method does not include the use of an adhesion promoter.

12. Method according to any of Claims 1 to 11, wherein steps a) and b) are conducted simultaneously in a vulcanizing press.

13. Method according to any of Claims 1 to 12, wherein the partially vulcanized elastomer after step c) is placed into an injection mould and step d) is conducted in said mould.