CROSSLINKING AGENTS FOR POLYMER SYSTEMS

Description

[0001] The present invention relates to a crosslinking agent for polymeric systems comprising elemental sulfur, phenolic resin, thiazole disulfide compounds and metal salts based on thiocarbamates, and to its use in vehicle production.

[0002] Manufacturing an automobile requires a significant amount of technical resources and employees. Vehicles are usually manufactured in line production, with the unfinished vehicle passing through numerous stations, each of which carries out a few simple steps to further complete the car. For example, the body is first assembled from sheet metal using spot welding or adhesive technology to form the body-in-white, which is then painted in a subsequent step. The painting process itself also involves several steps. To achieve the finished painted body, the vehicle usually goes through one or more immersion baths in which the body is first protected against corrosion. A filler is then applied, which allows the top coat to be applied evenly, giving the vehicle the desired color and is finally sealed with a clear coat.In vehicle assembly, the painted body is supplemented with any remaining components. Line production, valued for its efficiency, presents the challenge that the chemical components used in each step must be compatible with the components used in the other steps. For example, the adhesive used in the production of the body-in-white must not react with the paints used in the painting process, while the adhesives used to attach panels must not react with the paints while still adhering to them.

[0003] Due to the coordination of the individual components, any change in the process requires review and, if necessary, readjustment of the individual components. For example, following an improvement in dip coating systems in which conventional tin catalysts were replaced with bismuth catalysts to reduce the curing temperature of the paints, sulfur-curing adhesives applied to the paints no longer performed as expected. This occurred because the bismuth catalysts reacted with the sulfur, resulting in either uncured paints at the adhesive application sites, making these areas highly susceptible to corrosion, or the formation of bismuth sulfide, which caused defects and imperfections in the topcoats and clearcoats.

[0004] WO 2006 / 076958 A1, WO 2011 / 020714 A1 and WO 02 / 48255 A2 disclose rubber damping compounds which may contain a sulfur-based system with accelerators as vulcanizing agent.

[0005] Since industry does not want to forego the advantages associated with the use of bismuth-based catalysts, there is a need for systems, especially adhesive systems, that are compatible with the improved catalysts and modified process flows.

[0006] It is therefore the object of the present invention to provide a system, in particular an adhesive system, which has a high tolerance to bismuth, is compatible with bismuth catalysts and, moreover, can be integrated into the established processes of vehicle production.

[0007] It was surprisingly found that this task is solved by a crosslinking agent which, in addition to elemental sulfur and phenolic resin, contains thiazole disulfide compounds and metal salts based on thiocarbamates.

[0008] Therefore, a first object of the present invention is a crosslinking agent for polymeric systems comprising a) elemental sulfur; b) one or more phenolic resins; c) one or more thiazole disulfide compounds; and d) one or more metal salts based on thiocarbamates.

[0009] The crosslinking agent according to the invention showed good compatibility with the bismuth catalysts used in the dip coating of vehicle bodies and could be applied to correspondingly coated substrates without any reduction in performance.

[0010] Sulfur-containing crosslinking systems often have the disadvantage of high sulfur emission rates. This, in addition to the health risks during use, results in products manufactured using sulfur-containing crosslinking systems, such as rubber products, exhibiting an unpleasant odor, making them unsuitable for applications in enclosed spaces, such as vehicle interiors. In contrast to conventional systems, the crosslinking agent according to the invention exhibited little to no sulfur emission, which not only reduces the health risk but also expands the areas of application for the crosslinking agent according to the invention.

[0011] The crosslinking agent according to the invention can be used, for example, for curing polymeric systems. The degree of crosslinking of the polymer can be controlled not only by the duration of the polymerization but also by the amount of active component. Depending on the application, a high or low degree of crosslinking may be desired. However, the content of sulfur as the active component should not be chosen too high in order to avoid sulfur emissions. It has surprisingly been found that even with a comparatively high sulfur content in the crosslinking agent according to the invention, the sulfur emissions observed in other systems could be largely avoided. In this regard, it has proven advantageous in the context of the present invention if the amount of sulfur in the crosslinking agent does not exceed 5% by weight. Therefore, an embodiment is preferred in which the crosslinking agent according to the invention contains 1 to 5% by weight, preferably 1.5 to 4% by weight.-% of elemental sulfur, based on the total weight of the crosslinking agent.

[0012] The crosslinking agent according to the invention further comprises at least one phenolic resin, which allows, in particular, the consistency of the crosslinking agent to be adapted for the respective application. The phenolic resin content in the crosslinking agent is preferably 0.5 to 4 wt. %, particularly preferably 0.7 to 3 wt. %, based in each case on the total weight of the crosslinking agent. The phenolic resin used in the crosslinking agent according to the invention is preferably one obtained by condensing a mixture comprising formaldehyde and phenol. Particularly preferably, the mixture contains an excess of phenol. In particular, the molar ratio of formaldehyde to phenol in the mixture is less than 1:1.

[0013] The crosslinking agent according to the invention comprises one or more thiazole disulfide compounds. It has surprisingly been found that the addition of these compounds particularly promotes tolerance to bismuth compounds, such as bismuth-based catalyst systems. The proportion of the one or more thiazole disulfide compounds in the crosslinking agent according to the invention is preferably 0.3 to 7 wt. %, more preferably 0.5 to 5 wt. %, based in each case on the total weight of the crosslinking agent. The one or more thiazole disulfide compounds are preferably selected from benzothiazole disulfide (MBTS) and / or zinc benzothiazole disulfide (ZMBT).

[0014] The one or more metal salts based on thiocarbamates contained in the crosslinking agent according to the invention preferably make up 0.2 to 2 wt. %, preferably 0.4 to 1.5 wt. % of the crosslinking agent according to the invention, based in each case on the total weight of the crosslinking agent. It has proven particularly advantageous if at least one of the one or more metal salts based on thiocarbamates comprises at least one zinc salt. Therefore, an embodiment is preferred in which at least one of the one or more metal salts based on thiocarbamates comprises at least one zinc salt, in particular zinc dibenzoylthiocarbamate.

[0015] The crosslinking agent according to the invention may also comprise additional components, such as fillers and additives, which serve in particular to adapt the properties of the crosslinking agent to the respective requirements. In a preferred embodiment, the crosslinking agent according to the invention further comprises fillers, preferably those selected from the group consisting of carbon black, calcium carbonate, coated calcium carbonate, and calcium oxide. The amount of filler is preferably 40 to 70 wt.%, particularly preferably 45 to 65 wt.%, in each case based on the total weight of the crosslinking agent.

[0016] In a particularly preferred embodiment, the crosslinking agent according to the invention comprises the following: a) elemental sulfur in an amount of 1 to 5 wt.%, preferably 1.5 to 4 wt.% b) one or more phenolic resins in an amount of 0.5 to 4 wt.%, preferably 0.7 to 3 wt.%; c) one or more thiazole disulfide compounds in an amount of 0.3 to 7 wt.%, preferably 0.5 to 5 wt.%; and d) one or more metal salts based on thiocarbamates in an amount of 0.2 to 2 wt.%, preferably 0.4 to 1.5 wt.%, wherein the amounts in each case relate to the total weight of the crosslinking agent.

[0017] The crosslinking agent according to the invention may further comprise a polymeric component, preferably in an amount of 15 to 35 wt. %, preferably 20 to 30 wt. %, based in each case on the total weight of the crosslinking agent. The polymeric component is preferably a polymer from the group of polybutadienes, in particular a mixture of a polybutadiene and a polybutadiene-maleic anhydride adduct. The crosslinking agent particularly preferably contains a liquid polymeric component, in particular a liquid polybutadiene, preferably with a weight-average molecular weight Mw of 500 to 10,000 g / mol, in particular 1,000 to 5,000 g / mol (measured by GPC against a polystyrene standard).

[0018] Although the crosslinking agent according to the invention can be used in all possible technical fields, it is particularly suitable for use in vehicle construction. Therefore, a further subject of the present application is the use of the crosslinking agent according to the invention in vehicle production.

[0019] The crosslinking agent according to the invention has proven particularly advantageous as an adhesive in the manufacture of vehicle bodies and interior fittings and demonstrated good compatibility with the electrophoretic dipping processes used in vehicle manufacturing, for example, in the painting of bodies and body parts. In a preferred embodiment, the crosslinking agent according to the invention is therefore used in electrophoretic coating processes and / or in conjunction with "Liquid Applied Sound Deadeners" (LASD). The so-called "Liquid Applied Sound Deadeners" are liquid-applied foam insulation materials that can significantly reduce vibrations and noise in vehicles and can be used to attach additional insulation materials.In a further preferred embodiment, the crosslinking agent according to the invention is used in the presence of bismuth catalysts.

[0020] The present invention is explained in more detail with reference to the following examples, which are in no way to be understood as a limitation of the inventive concept. Examples:

[0021] The compositions summarized in Table 1 were prepared, with the quantities given in weight percentages based on the total weight of the composition. Table 1: component Example 1 Example 2 Example 3 polymer 24 24 24 filler 64,74 63,74 62,74 Phenolic resin 0,9 1,9 2,9 sulfur 2,5 2,5 2,5 Zinc dibenzoylthiocarbamate 1,5 1,5 1,5 Benzothiazole disulfide 5,0 - 5,0 Zinc benzothiazole disulfide - 5,0 - Additive 1,36 1,36 1,36 In total 100,00 100,00 100,00

[0022] The compositions in Table 1 were tested for their compatibility with common electrophoretic coating systems, using the bismuth-containing coating CathoGuard 800 from BASF SE, Germany, as an example. The composition was applied as a droplet to a sample sheet and coated with the coating. The coating was cured and evaluated under the conditions specified in Table 2. Table 2: Condition 10 min;165 °C 15 min;165 °C 20 min;165 °C 5 min;170 °C 10 min;170 °C Result 0 0 0 0 0 Legend: note Evaluation 0 No change in the surface 1 First signs of change 3 Blistering of the paint layer; no detachment 5 Detachment of the paint layer from the surface

[0023] As can be seen from the data provided, the compositions according to the invention exhibit excellent compatibility with common coating systems.

[0024] Sulfur emission tests also demonstrated the low emission tendency of the compositions according to the invention. For this purpose, the compositions were applied to a metal sheet in a 2 mm thick layer by doctor blade coating. The sheet was placed in a 1-liter metal can for curing and sealed with a wet-cataphoretic coating. The test setup was cured in a laboratory oven at 105 °C for 6 minutes and 190 °C for 30 minutes, during which the outgoing emissions reacted with the cataphoretic coating. The sulfur concentration on the contaminated cataphoretic coating surface was subsequently analyzed using XPS. The measurements showed a concentration of sulfur atoms in the range of 0.5 atomic %.

Claims

1. A crosslinking agent for polymeric systems, comprising a) elemental sulfur ; b) one or more phenolic resins ; c) one or more thiazole disulfide compounds ; and d) one or more metal salts based on thiocarbamates.

2. The crosslinking agent according to claim 1, characterized in that the amount of elemental sulfur is 1 to 5 wt.%, preferably 1.5 to 4 wt.%, in each case based on the total weight of the crosslinking agent.

3. The crosslinking agent according to at least one of claims 1 or 2, characterized in that the amount of phenolic resin in the crosslinking agent is 0.5 to 4 wt.%, preferably 0.7 to 3 wt.%, in each case based on the total weight of the crosslinking agent.

4. The crosslinking agent according to one or more of the preceding claims, characterized in that the phenolic resin is obtained by condensation of a mixture comprising formaldehyde and phenol, the mixture having an excess of phenol, and the molar ratio of formaldehyde to phenol in the mixture being preferably less than 1:1.

5. The crosslinking agent according to at least one of the preceding claims, characterized in that the amount of one or more thiazole disulfide compounds is 0.3 to 7 wt.%, preferably 0.5 to 5 wt.%, in each case based on the total weight of the crosslinking agent.

6. The crosslinking agent according to at least one of the preceding claims, characterized in that the one or more thiazole disulfide compounds is selected from benzothiazole disulfide (MBTS) and / or zinc benzothiazole disulfide (ZMBT).

7. The crosslinking agent according to at least one of the preceding claims, characterized in that the one or more metal salts based on thiocarbamates comprise at least zinc dibenzoyldithiocarbamate.

8. The crosslinking agent according to at least one of the preceding claims, characterized in that the amount of the one or more metal salts based on thiocarbamates is 0.2 to 2 wt.%, preferably 0.4 to 1.5 wt.%, in each case based on the total weight of the crosslinking agent.

9. The crosslinking agent according to at least one of the preceding claims, characterized in that the crosslinking agent further comprises fillers, the fillers preferably being selected from the group consisting of carbon black, calcium carbonate and calcium oxide.

10. The crosslinking agent according to at least one of the preceding claims, characterized in that the crosslinking agent comprises the following: a) elemental sulfur in an amount of 1 to 5 wt.%, preferably 1.5 to 4 wt.%; b) one or more phenolic resins in an amount of 0.5 to 4 wt.%, preferably 0.7 to 3 wt.%; c) one or more thiazole disulfide compounds in an amount of 0.3 to 7 wt.%, preferably 0.5 to 5 wt.%; and d) one or more metal salts based on thiocarbamates in an amount of 0.2 to 2 wt. %, preferably 0.4 to 1.5 wt.%, the stated amounts each relating to the total weight of the crosslinking agent.

11. The crosslinking agent according to at least one of the preceding claims, characterized in that the crosslinking agent further comprises a polymeric component, preferably in an amount of 20 to 50 wt.%, preferably 25 to 40 wt.%, in each case based on the total weight of the crosslinking agent.

12. The crosslinking agent according to claim 11, characterized in that the polymeric component is selected from the group of polybutadienes.

13. A use of a crosslinking agent according to at least one of claims 1 to 12 in vehicle manufacture.

14. The use according to claim 13, characterized in that the crosslinking agent is used in electrophoretic coating processes, in particular in electrophoretic dip coating and / or in connection with "liquid applied sound deadener."15. The use according to one or both of claims 13 and 14, characterized in that the crosslinking agent is used in the presence of bismuth catalysts.