Patent Application
20100258973
The present invention relates to the manufacture of grained panels for interior trim wherein the grain or texture on the outer surface of the soft skin may be created during the molding process, wherein the panels include a fiber backing.
Decorative trim panels for the interior of vehicles often comprise hard injection molded plastic having a textured surface. For more luxurious vehicles, a softer feel and appearance may be desired. This may be accomplished by calendaring or casting a separate relatively softer textured skin which may then be backed with a foam layer and a reinforcing substrate. To provide soft trim panels for applications such as seat backs, console bases, or door panels, the manufacturing process may generally involve three separate processes, 1) forming a textured skin, 2) forming a substrate layer and 3) placing the skin and substrate into a third mold and pouring urethane foam precursors between them to integrate the skin and substrate into a molded panel. This may involve numerous molds and a substantial amount of labor.
A relatively new area of consideration in which automobile manufacturers may attempt to please consumers is an area called haptic technology. Haptics may generally be defined as the science of applying touch (tactile) sensation and control to interaction with computer applications. In automotive applications, the term relates to the sense of touch when contacting the surface of an interior trim panel and whether the surface of the panel feels warm or cool, soft or hard and textured or smooth. Panels which are sensed to be warm, soft and textured are believed to provide a more positive response from the consumer than panels which may be hard, cold and smooth surfaced.
In a first aspect, the present disclosure is directed at a method for forming a textured trim panel in a single molding step, comprising providing a compression mold having a textured or grained cavity, providing an untextured polymeric skin, and providing a web of natural and synthetic fibers. This may be followed by heating the web of natural and synthetic fibers to a temperature between the glass transition temperature and the melt temperature of the synthetic fibers and placing the untextured polymeric skin into the textured cavity surface of the compression mold. This may be followed by placing the heated web onto the polymeric skin, closing the compression mold and compressing the web and the skin to a thickness in the range of about 1.0 mm to 5.0 mm. This may then be followed by demolding a trim panel having a textured or grained skin and a fibrous substrate layer.
In another aspect, the present disclosure is directed at a trim panel molded by the above-described process.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain principles of the invention.
The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The present disclosure is directed at a compression molding process for forming a grained trim panel having a soft warm textured feel. The textured panel may include a fiber backing which provides improved mechanical strength, wherein the fibers are applied to the panel in a compression molding operation, where the fibers may be preheated.
The process is described in block form in
Aliphatic thermoplastic polyurethanes may be preferred as they provide a rather warm natural feel rather than a cold “plastic” feel. This may be because the TPU skin removes less heat upon contact with the skin than other plastic materials due to its heat capacity. The skin is provided without a grain or texture as one or more textures or grains may be imparted to the surface of the skin by the surface of the compression mold during the molding process. Other polymers which may find use in the process described herein, but having somewhat different haptics, may include, but not be limited to, polyolefin (TPO), polyvinylchloride (PVC) and blends of aliphatic and aromatic thermoplastic polyurethane (TPU).
In addition, the skin may comprise two layers of TPU, with a thin layer of aliphatic polyurethane covering a base layer of aromatic polyurethane, the aliphatic provide the weathering resistance required and the aromatic providing heat resistance. Reference to aliphatic herein, therefore to an aliphatic diisocyanate, is reference to a diisocyanate that contains, for example, only hydrocarbon functionality, for example, the use of an isocyanate such as hexamethylene diisocyanate or (HMDI). The aliphatic TPU is therefore one that may be formulated specifically to optimize weatherability, and as a consequence, it may preferably employ aliphatic functionality. The overall level of aliphatic functionality may therefore be greater than 75% (wt.) and fall within the range of 75-100% (wt). A completely (100% wt.) aliphatic polyurethane would therefore include a polyurethane that relies upon an aliphatic diisocyanate, an aliphatic polyol (e.g., aliphatic polyether or polyester) and an aliphatic chain extender. The aliphatic polyurethane so prepared may also be prepared in the presence of a urethane catalyst.
Accordingly, any suitable aliphatic organic diisocyanate, or mixture of diisocyanates, may be used in the skin forming process of the present invention. Representative examples of suitable organic diisocyanates may include, isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hydrogenated MDI, hydrogenated XDI, cyclohexane diisocyanate, mixtures and derivatives thereof and the like. The aliphatic diisocyanates can be present in amounts ranging from about 20% to about 50% but are preferably present in amounts in the range of approximately 25% to 40% (by wt.).
Accordingly, the base layer may comprise a base polyol component similar to that used in the formulation for the outer layer together with a relatively lower cost aromatic isocyanate such as diphenylmethane diisocyanate. A cycloaliphatic (secondary) amine may be added to provide urea linkages and improve the retention of physical properties after heat aging.
At Block 200, a web of fibers may be provided to be used as the substrate in the trim panel. The web may be sourced from either natural or synthetic fibers. The web of fibers may be, for instance, a needle-punched or hydroentangled blend of natural and synthetic fibers in a nonwoven configuration. The natural fibers may comprise, for instance, cellulose, lignocellulose, hemp, sisal, etc. The synthetic fibers may comprise, for instance, polypropylene, polyester (for instance, PET), polyethylene or combinations thereof. Generally, the web of fibers will comprise weight ratios of fibers in the range from about 20% polypropylene to about 80% polypropylene. The web may have a basis weight in the range from about 1400 to about 2000 grams per square meter and have a thickness of about 10-15 mm. before compression. The fibers (synthetic and/or natural) may act as a binder in the molding process to adhere the web of fibers together, as well as to adhere the skin to the formed substrate of molded fibers.
At Block 300, a compression mold may be provided for forming the trim panel, the mold being of metal construction and, more particularly steel, vapor deposited nickel or electroformed nickel. The surface of the cavity of the compression mold may have one or more textures or grains or other decorative patterns formed thereon which may be imparted to the aliphatic thermoplastic polyurethane skin in the compression molding process. The mold may be operated in the range of about 40° C. to about 60° C. The surface of the mold may further include one or more vent holes.
By mold texture, it is understood to mean the visual or tactile surface characteristics and appearance of the mold surface, generally in a regular or repeating pattern. By grain, it is understood to mean that the mold surface may be a reproduction of the treated surface of an animal skin.
At Block 400, the ungrained or untextured skin may be placed face down into the compression mold. This may be followed by (Block 500) heating the web of natural and synthetic fibers to a temperature between the glass transition temperature (Tg) and the melting temperature (Tm) of the fibers. In the case of polypropylene, the Tm may be in the range of about 170° C. to about 220° C. The skin may also be heated to a temperature to assist in transferring the texture from the mold surface into the skin surface.
It may be appreciated that by heating at a temperature at or above Tg, and below Tm, one may provide that the fibers may ultimately adhere to each other. As noted, above, this then provides that the fibers may act as a binder with the panel layer, in the sense that the fibers and polymeric skin layer become bonded together, i.e. the fibers to one another and the fibers to the skin material.
At Block 600, the heated web may be transferred to the compression mold, placed onto the backside of the ungrained skin and the mold closed. The heat from the web and the pressure of the closed mold may then cause the grain or texture(s) from the mold surface to be imparted to the surface of the skin. The web may be compressed by the mold under a pressure in the range of about 100-300 N/square centimeter to thin the web from the 10-15 mm original thickness to a final thickness in the range of about 1.0 mm. to about 5.0 mm., preferably about 1.8 mm to about 2.5 mm. The heated polypropylene fibers may then cool and act as a binder for the web and the skin.
Following a short mold residence time, in the order of 75 seconds or so, a grained trim panel having a warm feel and an aesthetically pleasing texture may be demolded.
Such panels as described herein may find particular use in automotive applications where physical contact with a person may be possible and the surface characteristics may be appreciated by such person. This may include, for instance, door panels, close-out panels, seat back panels, glove box doors, console bases and console lids.
Such panels may include fasteners such as clips or hook (touch) fasteners molded into the construction during the compression molding process, or they may be assembled into the vehicle via vibration or ultrasonic welding.
The description and drawings illustratively set forth the presently preferred invention embodiments. The description and drawings are intended to describe these embodiments and not to limit the scope of the invention. Those skilled in the art will appreciate that still other modifications and variations of the present invention are possible in light of the above teaching while remaining within the scope of the following claims. Therefore, within the scope of the claims, one may practice the invention otherwise than as the description and drawings specifically show and describe.
