Technical presentation discusses LFI process, challenges and the development of two technologies to achieve high surface quality (Class A) composites

Pittsburgh, PA – February 10, 2009 – Recent advancements in the polyurethane long fiber injection (LFI) process have resulted in a dramatic increase in its commercial interest for producing a wide range of products, including entry door skins, truck bodies and spa panels. However, one major challenge has remained with the technology: producing defect-free, Class A surfaces for LFI composites.

The specifics of the LFI process and two technologies that can be used to achieve Class A surfaces were explored in detail at the recent COMPOSITES+POLYCON 2009. This annual conference, sponsored by the American Composites Manufacturers Association, took place Jan. 15 – 17, 2009, in Tampa, Fla. Usama Younes, principal scientist, polyurethanes, Bayer MaterialScience LLC, presented a technical paper, Development of Class A Polyurethane LFI Composites, during a session on Materials: Resins.

According to the author, because of the entrapment of air bubbles and glass read through, it is difficult to produce high quality, Class A surfaces using the LFI process. Bayer MaterialScience scientists have, however, developed two technologies that make it possible to obtain a Class A surfaces using LFI.

The first is use of an inmold, hybrid polyester gel coat, which acts both as the glossy surface and the barrier layer to the glass read through.

The second is use of an inmold polyurethane paint, followed by a unique polyurethane barrier coat spray designed to resist both thermal and mechanical deformations, and finally, the addition of the long fiber polyurethane material. Use of the polyurethane barrier spray in conjunction with LFI shortens demold time and also improves the surface quality by preventing the glass from showing through the surface. Younes points out that development of the proper barrier coat material is critical, because the barrier coat itself can cause surface defects. The new class of barrier coat developed by Bayer MaterialScience has a high glass transition temperature and a low roughness value, which was determined through atomic force microscopy (AFM).

The paper also discusses LFI technology and gel time, including a test conducted using dissolved carbon dioxide as a blowing agent. Because a poor surface results when a material starts to gel prior to the mold closing during the LFI process, an extended gel time on a hot mold is essential to achieving a defect-free surface. Water is an environmentally friendly blowing agent, but it also decreases gel time, making it problematic in developing Class A surface composites. Dissolved carbon dioxide achieved both a longer gel time and, with careful control, a high-quality surface.

About Bayer MaterialScience
Bayer MaterialScience LLC is one of the leading producers of polymers and high-performance plastics in North America and is part of the global Bayer MaterialScience business with nearly 15,400 employees at 30 sites around the world and 2007 sales of 10.4 billion euros. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction, medical, and sports and leisure industries. Our inorganic basic chemicals unit produces chlorine and related essential products for the chemicals industry. Let us give life to your vision. Bayer MaterialScience – Where VisionWorks.

Bayer Corporation, headquartered in Pittsburgh, is a subsidiary of Bayer AG, an international health care, nutrition and high-tech materials group based in Leverkusen, Germany. In North America, Bayer had 2007 net sales of 8.1 billion euros and employed 16,800 at year end. Bayer’s three subgroups, Bayer HealthCare, Bayer CropScience and Bayer MaterialScience, improve people’s lives through a broad range of essential products that help diagnose, prevent and treat diseases; protect crops and enhance yields; and advance automobile safety and durability.