StyLight: Next-Gen Aesthetic Composites Based on Styrenic Co-Polymers

StyLight product portfolio

Launched in October 2016, Stylight,a new generation of thermoplastic composites from INEOS Styrolution, remains a relatively young material, but INEOS Styrolution already developed and proposes a commercial product portfolio to fulfil the requirements of the targeted applications. This portfolio is divided into two categories, on the one hand, products optimised for aesthetic semi-structural applications named “StyLight Aesthetic S” and on the other hand products optimised for structural, non-visible applications, called “StyLightStructural S”.

In this portfolio, INEOS Styrolution proposes products based on Glass woven fabrics, Glass Non-crimp fabrics (NCF) as well as one woven Carbon Fibre grade for aesthetic semi-structural applications. These different textile types offer a diversity of mechanical properties, surface qualities and capabilities. Stylight sheets are available in any thickness from 0.25 mm up to 5 mm and in black or natural colour. The “Aesthetic S” product range is available with or without a fleece and an extra thermoplastic layer can be applied on demand on the visible side of the application. Until now all these Stylight products are based on one single type of matrix ie. a modified SAN matrix (stands for the “S” in the product name), it is nevertheless not excluded that new styrenic based thermoplastic matrices will be launched in the future to enhance the Stylight offering depending on market demand.

The thermoformed composite sheet is in most cases only one component of the application, a back injection moulded reinforcement is typically needed for three-dimensional parts used in automotive, electronic or sports applications. For that purpose, INEOS Styrolution developed and validated different high flow injection moulding materials with optimising adhesion on the Stylight sheet.

Consequently, the performance of the finished part will be determined by the combination of both components, the composite Skylight “skin” and the back injected moulded material.  Adhesion between both components has been measured on simple rib test tools to find the optimum material properties offering strength, surface quality adhesion and high flow to fill thin ribbing design, resulting in a portfolio of short glass fibre reinforced ABS/PA blends (Terblend® N) and ABS (Novodur®), they are identified with the suffix “SL”.

Finally, above and beyond the static mechanical performance of Stylight, INEOS Styrolution performed fatigue tests to evaluate the long-term resistance of this new type of styrenic composite in comparison to alternative thermoplastics-based composites, as well as epoxy-based composites. The results are showing the good performances of Stylight carrying a flexural load of 250 MPa after more than 2 Million cycles (tests performed by IVW, Kaiserslautern). 

Surface aesthetics

Although Stylight shows a higher stiffness and a good stability versus other currently available thermoplastic composites on the market, these advantages alone would not justify the investment to develop and launch a new composite thermoplastic type on the market.

But the Stylight composite is adding another significant advantage: Its surface properties. Outstanding surface quality inherent to a styrenic matrix makes it possible to extend the application scope of composite thermoplastic to visible aesthetic parts at a competitive price level.

The lower shrinkage during the consolidation step of our amorphous styrenic copolymer matrix based on a modified SAN reduces the surface roughness (“waviness”) significantly, offering a superior surface quality compared to most existing standard thermoplastic composites.

Beside the surface “flatness” advantage, the low shrinkage of the styrenic copolymer matrix is enhancing the dimensional stability of the finished parts and reduces the risk of warpage. Combined with its low water absorption the Stylight part dimension remains stable after manufacturing making it suitable for applications in the vehicle interior or high tech applications requiring a good fit and finish. In combination with its good chemical resistance (environmental stress crack resistance, “ESCR”), Stylight is a robust and versatile composite solution suitable for aesthetic semi-structural high performance applications.

Demonstrator

In order to validate these promising laboratory results and to validate the manufacturing behaviour of Stylight, INEOS Styrolution decided to invest in a real size prototype mould made of steel, combining different features.

The concept of a door panel design was selected as it combines different construction, manufacturing challenges and complex shapes to demonstrate the performance of Stylight. Different surface aesthetics and a semi-structural reinforcement have been integrated into the demonstrator design.

A thermoplastic composite sheet with a thickness of 1,2 mm was chosen to provide the best compromise between weight saving, good surface quality combined with a high mechanical strength while allowing the draping of a complex shape design.

Surface decoration

One of the major challenges of the demonstrator was to take advantage of the Stylight surface property and demonstrate the feasibility to achieve a decorated surface in one single manufacturing step. We focused on two critical areas of the demonstrator: the lower part where the composite sheet is directly visible and the central part where the composite is covered and decorated directly in the mould with an insert developed by the company LEONHARD KURZ Stiftung & Co KG (Furth). 

Different surface structures have been applied on the demonstrator: a high gloss surface finish around the loud speaker circle, a fine grain in the lower part, and a leather type grain in the upper part.

Industry applications for the new material

The development and launch of this new material is mostly driven by the growing demand of light weight solution in the automotive industry to contribute to fuel efficiency. So far, the applications of composite thermoplastics in automotive have been focussing on the substitution of heavy structural parts typically made of steel but without any particular aesthetical value. INEOS Styrolution is convinced that there is more potential for thermoplastic composites to reduce weight in a whole new range of applications with partially visible surface.

Price remains one of the main obstacles slowing down the penetration of thermoplastic composites in the industry. The high price of the semi-finished sheet, inherent to its manufacturing and raw material cost, added to the significant upfront investment required by the part supplier to develop expertise and to acquire new tooling and handling equipment makes this innovation affordable only to a relatively small market potential.

One of the solutions to reduce system costs is to integrate structural and aesthetic functions, reducing the number of components for a given application, taking advantage of Stylightproperties. For this purpose INEOS Styrolution partners with KTM, a creative engineering office to develop and propose innovative design concepts for a selected number of applications.

These selected automotive applications are offering the highest integration potential from INEOS Styrolution’s and KTM’s perspective:

Automotive door module:  Typically a door module comprises of three functions, an externally visible surface, typically a sheet of painted metal, a non-visible semi-structural part, typically supporting all electronic and mechatronics of the door module and insulating the cockpit from the water, and an interior visible surface. Here Styrolution is developing a concept to integrate the non-visible semi-structural function with the interior visible.

Automotive central console: This application is also very demanding with a directly visible surface, supporting electronic equipment and providing local structural stiffness. Moreover, the space available inside a console is very tight. It should allow space for the wire tree and storage space. Here again a thin wall providing structural stiffness and offering a high surface quality is offering potential for the integration of multiple functions.

Automotive lift gate: There are many lift gate designs available depending on vehicle shape and design. Different composite solutions from long glass fibre reinforced PP to SMC have been used for quite some time. Until now the interior visible surface is covering the structural frame. Attempts were made to overmold a thermoplastic composite retainer with injected molded GF PP but this is adding cost and weight. Here Stylight is offering a potential integration solution.

Body panel for trucks or tractors: A massive weight reduction is possible with the replacement of thick SMC panel currently being used in this field. But this application is more demanding than initially expected. Dimensional stability, class A surface quality, wind resistance, resistance to powerful vibrations are among the long list of specifications. Some of these panels also integrate functions like front light or bonnet. Here, Stylight may again have a good value proposition to reduce weight.

For each of these different applications, alternative design solutions will be proposed, enhancing function integration, reducing the overall number of parts, striving for cost and weight reductions. These concepts will be available to INEOS Styrolution customers as of mid-2017 to inspire engineers and designers thinking “out of the box”.