Methods for manufacturing fiber composite components and using transmission and / or turbidity measurement

Abstract

Processes for the production of fiber composite components comprising the following steps: - Introducing a fiber material into a cavity of a tool with an upper and a lower tool half, - Introducing a resin material into the cavity and impregnating the fiber material with the resin material, wherein the resin material contains a release agent for demolding the fiber composite component from the tool, - Hardening of the resin material, - Demolding of the fiber composite component, - Performing a transmission measurement and / or a turbidity measurement on a pure resin area of ​​the fiber composite component and - Adjusting the release agent depending on the determined transmission value and / or turbidity value.

Description

[0001] The present invention relates to a method for manufacturing fiber composite components with improved optical properties. Furthermore, the present invention also relates to the use of transmission measurement and / or turbidity measurement for the manufacture of fiber composite components.

[0002] When fiber-reinforced composite components are manufactured using processes such as resin infusion or vacuum infusion, a fiber material, for example in the form of a fiber preform, is placed into a cavity of a mold. After closing the mold, which usually consists of an upper and a lower mold half, a resin is introduced into the cavity, saturating the fiber material. This is followed by a curing step of the resin. The finished fiber-reinforced composite component can then be removed from the mold cavity after the mold is opened. To prevent the fiber-reinforced composite component from sticking to the mold and to improve demoldability, thereby also preventing damage to the component, a release agent is added to the resin in small quantities.Since the release agent is inert to both the resin and the fiber material, it very often leads to significant visual defects in the fiber composite component, particularly clouding or a milky appearance. Therefore, the aim is to achieve the lowest possible concentration of release agent in the resin material; however, excessively low amounts can impair demolding. Thus, it is crucial to select a suitable release agent and precisely determine the required quantity. Because the release agent is usually added to the resin material shortly before infusion, determining its quantity is only possible in the finished component. This is achieved using LC / MS or HPLC-MS methods, i.e., chemical analysis techniques. However, these methods are time-consuming and expensive, and require trained personnel. Furthermore, the measurement inaccuracy of these methods is very high.

[0003] Based on this prior art, the object of the present invention is to provide a method for producing a fiber composite component with good demoldability and improved optical properties, wherein the method is reproducible with consistently high precision, easy to apply, cost-effective, and fast. Furthermore, the object of the invention is to provide a use for transmission measurements and / or turbidity measurements.

[0004] The object of the invention is achieved by a method for producing fiber composite components, comprising the following steps. In a first step, a fiber material is introduced into a cavity of a tool with an upper and a lower tool half. The specific fiber material is not limited. It can, for example, be individual fibers or fiber bundles, or fiber semi-finished products such as fiber mats, fiber fabrics, fiber knits, fiber woven fabrics, and the like. The shape of the cavity formed by the tool halves preferably corresponds to the negative shape of the fiber composite component to be produced.

[0005] After the fiber material is placed into the cavity, the tool is typically closed. A resin material is then introduced into the cavity. The specific resin material is not limited and can be thermoplastic, thermosetting, or elastomeric. If the resin material requires a hardener to cure or crosslink, this may also be included, along with other functional compounds such as plasticizers, wetting agents, colorants, and the like.

[0006] As another important component, the resin material contains at least one release agent that enables or facilitates the demolding of the fiber composite component from the mold. The specific type of release agent is not limited. Conventional release agents, i.e., organic release agents such as fats, oils, silicones, and the like, and preferably water-based release agents, can be used. These compounds are inert to both the resin material and the fiber material, meaning they do not react with it. To prevent reactions with the other components of the resin material, the release agent is preferably mixed with it immediately before the resin material is injected into the cavity.

[0007] By introducing the resin material into the cavity, the fiber material is impregnated with the resin. The resin then hardens. The curing process depends on the nature of the resin material and can be selected accordingly.

[0008] Once the resin has cured, the finished fiber composite component can be demolded from the mold. This is usually done by opening the mold to release the cavity.

[0009] The fiber composite component exhibits so-called pure resin areas at its edges. These are formed during the impregnation of the fiber material with resin. Typically, to achieve complete impregnation of the fiber material with resin, an excess of resin is used. This allows air bubbles to be expelled from the fiber material, resulting in pure resin areas at the edges of the fiber composite component that contain no fiber material whatsoever. A transmission measurement and / or a turbidity measurement is then performed on these pure resin areas. The transmission and turbidity measurements are carried out according to ASTM D1003-13. The higher the measured transmission value, or the lower the measured turbidity value, the lower the proportion of release agent. Conversely, the lower the measured transmission value, or the higher the measured turbidity value, the higher the proportion of release agent.Transmission measurement, turbidity measurement, or a combination of these two methods can be used to test the suitability of a release agent for use with a specific resin. By comparing the transmission and turbidity values ​​of different release agents, the agent that results in particularly low turbidity or high transmission can be identified. Furthermore, by comparing the measured turbidity or transmission values ​​with standard values ​​for a specific release agent / resin combination, a predetermined amount of release agent used can be verified, and if necessary, the amount of release agent to be added can be adjusted.The process must be adjusted, and on the other hand, an optimal amount of release agent must be determined that allows for easy demolding of the fiber composite component from the tool while minimizing optical impairment.

[0010] This is achieved by adjusting the amount of the separating agent depending on the determined transmission value and / or turbidity value.

[0011] For example, a fiber composite component can first be manufactured with a defined amount of release agent. The transmission value or turbidity value of a pure resin area of ​​the component, determined in this process, can then be compared with a specified transmission and / or turbidity value for the amount of release agent used, or with a corresponding range of values ​​(also called a tolerance range) that ensures good demoldability and minimizes the turbidity of the pure resin area of ​​the fiber composite component and / or maximizes the transmission of the pure resin area. If the currently determined value is within the specified value / range, no adjustments are necessary.If the transmission value and / or the turbidity value is outside the specified value / range, the corresponding release agent content is either below the amount required for demoldability (the determined transmission value is therefore above the specified transmission value / range, or the determined turbidity value is below the specified turbidity value / range) or above the amount of release agent desired for good optics (the determined transmission value is therefore below the specified transmission value / range, or the determined turbidity value is above the specified turbidity value / range) and can be increased or decreased accordingly so that the subsequent production produces fiber composite components with very good qualitative and optical properties.

[0012] Since transmission and turbidity measurements can be performed quickly without requiring complex equipment or significant costs, the method according to the invention is very well suited for in-process control. Process deviations and parameter deviations can be addressed very quickly. This allows for the precise production of fiber composite components with good demoldability and improved optical properties while maintaining consistently high quality. Furthermore, since the method does not require chemical analysis, it can be easily performed non-destructively by untrained personnel without extensive sample preparation. In addition, the measurement inaccuracy for transmission and turbidity measurements is significantly lower than for, for example, liquid chromatography-mass spectrometry (LC / MS or HPLC / MS) methods and is typically below ± 5%, so that the release agent content can be adjusted to approximately ± 0.1 wt.-%, based on the total resin content, can be precisely adjusted.

[0013] The dependent claims contain advantageous embodiments and further developments of the invention.

[0014] According to an advantageous embodiment of the inventive method, the amount of release agent is reduced when the determined transmission value falls below 70% and, in particular, below 50%. Transmission values ​​of less than 50% already lead to a significant impairment of the optical appearance of fiber composite components, which manifests itself as cloudiness or a milky appearance. In this case, the release agent content is too high and can be adjusted to a lower level.

[0015] The amount of release agent is further advantageously increased if the determined transmission value exceeds 90%. At transmission values ​​above 90%, defects occur on the surface of the fiber composite component, caused by the component adhering to the mold and thus by incomplete demolding and poor demoldability. Even if surface defects are not yet visible to the naked eye, their probability is high at transmission values ​​above 90%. In this case, the release agent content is too low and can be adjusted to a higher value.

[0016] The inventive method can be carried out in a more time-efficient and cost-effective manner, provided in particular that no adjustment is made to the amount of separating agent if the determined transmission value T satisfies the following equation: 50% < T < 90%.

[0017] Another advantageous improvement provides that the amount of separating agent is reduced if the measured turbidity exceeds 85%.

[0018] Turbidity values ​​above 85% indicate an excessively high concentration of release agent. This significantly impairs the appearance of the fiber composite component.

[0019] It is further advantageous to increase the amount of release agent if the measured turbidity falls below 60%. A turbidity below 60% indicates a very low release agent content, which manifests itself in poor demolding. This can be prevented by increasing the amount of release agent added to the resin material.

[0020] As already described above for transmission values ​​T between 50% and 90%, it is advantageous in light of the time-saving of the process according to the invention and also with regard to the process costs if no adjustment of the amount of separating agent is made, provided that the determined haze H satisfies the following equation: 60% < H < 90%, where “H” stands for the English term “haze”.

[0021] The advantageous further development of manufacturing the fiber composite component by means of wet pressing or injection pressing or by means of a vacuum infusion process or resin injection process allows fiber composite components with consistently good and, in particular, visually appealing properties to be produced with precision and at high cycle rates.

[0022] The invention also describes the use of transmission and / or turbidity measurements to determine the optimal amount of release agent in the production of a fiber composite component. The transmission and / or turbidity measurements are performed according to ASTM D1003-13. An optimal amount of release agent is achieved when the demoldability of the fiber composite component is good and the optical properties are minimally affected by the release agent. These characteristics are reflected in the transmission and turbidity values.

[0023] The advantages, beneficial effects and further developments described for the method according to the invention also apply to the use according to the invention.

[0024] Further details, features and advantages of the invention will become apparent from the following description and the figures. These show: Fig. 1. Illustrations showing the turbidity of pure resin areas of fiber composite components with different levels of release agent, Fig. 2. A graphic illustrating the turbidity of pure resin areas of fiber composite components depending on the content of release agent and Fig. 3 A graphic illustrating the transmission of pure resin areas of fiber composite components depending on the content of release agent.

[0025] In detail, it shows Fig. 1 Seven images of pure resin areas of fiber-reinforced composite components, produced with varying concentrations of release agent, illustrate the influence of the release agent on the turbidity of the pure resin areas, which is also reflected in the finished fiber-reinforced composite component. The images show pure resin areas with increasing concentrations of release agent from 0.5 wt.% to 1.8 wt.%, each based on the total weight of resin material. The resin material contained an epoxy resin (Huntsman Epoxy Resin XB3585) and an amine-based hardener (Huntsman XB3458). An oil (EWOmold 3202) was used as an example of a release agent. The ratio of epoxy resin to hardener was 100 parts by weight epoxy resin to 20 parts by weight hardener.

[0026] The fiber composite component was manufactured using a resin infusion process (RTM process). A carbon fiber fleece was used as the fiber material. After the resin material had cured, the resulting pure resin layer was separated, and the samples shown were extracted from it. The samples were photographed against a black background to better assess the turbidity. It can be seen that the milky appearance increases with increasing concentration of release agent. A tolerable turbidity is approximately 1.6 wt% release agent and should not exceed 1.8 wt%, based on the total weight of resin material.

[0027] Fig. Figure 2 is a graphic illustrating the turbidity of pure resin areas in fiber-reinforced composite components as a function of the release agent content. For this purpose, fiber-reinforced composite components as described above were used for the samples. Fig. As explained in section 1, the components were manufactured using an RTM process. The pure resin areas were separated and examined. The average thickness of these pure resin areas was 1 mm, measured using a micrometer. This thickness is determined by the cavity of the mold used and is consistent for a series of fiber-reinforced composite components.

[0028] The pure resin section for curve A contained an epoxy resin (Huntsman Epoxy Resin XB3585) and an amine-based hardener (Huntsman XB3458). An oil (EWOmold 3202) was used as a release agent. The ratio of epoxy resin to hardener was 100 parts by weight epoxy resin to 19 parts by weight hardener.

[0029] The pure resin section for curve B contained an epoxy resin based on bisphenol-A-epichlorohydrin and bisphenol-F-epichlorohydrin (Hexion EPIKOTE™ Resin 06000) and an amine-based hardener (Hexion EPIKURE™ Curing Agent 06130). An oil (PAT657 BW) was used as a release agent. The ratio of epoxy resin to hardener was 100 parts by weight epoxy resin to 17 parts by weight hardener.

[0030] The pure resin section for curve C contained an epoxy resin based on bisphenol-A-epichlorohydrin and bisphenol-F-epichlorohydrin (Hexion EPIKOTE™ Resin 06000) and an amine-based hardener (Hexion EPIKURE™ Curing Agent 06130). An oil (PAT657-1 BW) was used as a release agent. The ratio of epoxy resin to hardener was 100 parts by weight epoxy resin to 17 parts by weight hardener.

[0031] The samples (pure resin areas of the manufactured fiber composite components) were subjected to transmission measurements (see Fig. 3) or turbidity measurements (see Fig. 2) subjected to. The measurements were performed according to ASTM D1003-13.

[0032] A qualitative comparison of curves A, B, and C shows that curve B exhibits the lowest turbidity values ​​depending on the release agent concentration. Therefore, of the three release agents tested, PAT657 BW is the most suitable in the specified resin / hardener combination.

[0033] Curve A shows a higher scatter of values ​​than curves B and C. Therefore, the release agent EWOmold 3202 is less suitable for the production of fiber-reinforced composite components in the specified resin / hardener combination. Checking the release agent concentration of this agent is difficult.

[0034] Curve C shows that the release agent PAT657 BW-1, in the resin / hardener combination, leads to higher turbidity than the release agent PAT657. Therefore, it is somewhat less suitable in combination with the specified resin / hardener system.

[0035] Overall, release agent concentrations up to 1.8 wt% resulted in very low turbidity. Release agent concentrations below 0.7 wt% led to poorer demoldability of the fiber composite component from the RTM tool. Demoldability was optimal at 1.6 wt% release agent.

[0036] Fig. Figure 3 is a graph illustrating the transmission of pure resin areas in fiber-reinforced composite components as a function of the release agent content. The measured samples that resulted in curves A to C were the same ones used for the turbidity investigation (see Figure 3). Fig. 2) were used. This allowed for a very good comparison between the respective turbidity and transmission values.

[0037] In detail, Fig. Figure 3 shows that the transmission of the pure resin layer decreases with increasing release agent concentration. The highest transmission values ​​were achieved with curve B, i.e., for the release agent PAT657 BW. The variation in transmission values ​​was not as pronounced in curve A. Nevertheless, the best results were obtained for the release agent PAT 657 BW. For release agent concentrations between 0.5 wt% and 1.8 wt%, transmission values ​​were obtained that showed minimal optical impairment of the pure resin layer and thus also of the fiber composite component, while simultaneously ensuring good demoldability from the mold. Demoldability was optimal at 1.6 wt% release agent.

[0038] The determined transmission and turbidity characteristic curves (standard curves) for the respective release agents can be used as comparative values ​​to compare the release agent concentrations in series production or to compare different release agents with each other. With a release agent concentration of 1.6 wt%, a comparable transmission and turbidity value should result for the series production of a fiber composite component, as can be read from the corresponding "standard curves".

[0039] The preceding description of the present invention serves only for illustrative purposes and not to limit the invention. Various changes and modifications are possible within the scope of the invention without departing from the scope of the invention and its equivalents.

Claims

[1] Method for the production of fiber composite components comprising the steps: - Introducing a fiber material into a cavity of a tool with an upper and a lower tool half, - Introducing a resin material into the cavity and impregnating the fiber material with the resin material, wherein the resin material contains a release agent for demolding the fiber composite component from the tool, - Hardening of the resin material, - Demolding of the fiber composite component, - Performing a transmission measurement and / or a turbidity measurement on a pure resin area of ​​the fiber composite component and - Adjusting the release agent depending on the determined transmission value and / or turbidity value. [2] Method according to claim 1, characterized by , that the amount of release agent is reduced if the determined transmission value falls below 50%. [3] Method according to claim 1 or 2, characterized by, that the amount of separating agent is increased if the determined transmission value exceeds 90%. [4] Method according to any one of the preceding claims, characterized by , that no adjustment of the amount of release agent is made if the determined transmission value T satisfies the following equation: 50% <T<90%. [5] Method according to claim 1, characterized by , that the amount of separating agent is reduced if the measured turbidity exceeds 85%. [6] Method according to claim 1 or 5, characterized by , that the amount of separating agent is increased if the measured turbidity falls below 60%. [7] Method according to any one of the preceding claims, characterized by , that no adjustment of the amount of separating agent is made if the determined turbidity H satisfies the following equation: 60% <H<90%. [8] Method according to any one of the preceding claims, characterized bythat the fiber composite component is manufactured by means of wet pressing or injection pressing or by means of a vacuum infusion process or resin injection process. [9] Use of transmission measurement and / or turbidity measurement to determine an optimal amount of release agent in the manufacture of a fiber composite component.

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