Automotive trim panel having dual density foam support layer

A trim panel for use in automotive trim applications is made from a laminate of a thermoformable support layer and an A-side layer made of vinyl or cloth or similar material. The laminate is thermoformed to impart permanently the contour of a rigid substrate to which the panel will be attached. The support layer retains the desired contour without the use of other materials. The support layer is made of an intermediate layer and a bottom layer of thermoformable foam. The foam layers have different densities to allow selection of the hand or touch of the A-side layer.

BACKGROUND OF THE INVENTION 
The interior trim appearance of an automobile has been a key area of 
marketing focus. Interiors are often given treatments which provide 
increases in perceived value as well as brand differentiation. Efforts to 
cut costs by removing even small interior trim details have met with 
significant adverse sales impact. 
The current automotive interior styling trend is toward a softer, 
wrap-around styling vision which places special emphasis on the tactile 
feel of the interior, as well as the visual impression. The hard plastic 
substrates and surfaces of car interiors in past years are being replaced 
by the trend toward padded or cushioned surfaces, covered by either vinyl 
or textile materials. Accordingly, parts such as instrument panels, arm 
rests, center consoles, seating, head rests, door skins and body pillar 
trim have increasingly been provided with soft, padded interior trim for 
styling purposes, for noise abatement and for safety concerns. 
The automotive interior surfaces just described typically comprise a 
structural substrate of aluminum, plastic or the like which is relatively 
rigid. A layer of padding and a trim panel may cover the interior surface 
of the substrate. The term "relatively rigid" as used herein refers to the 
fact that the substrate has greater stiffness than the trim panel covering 
it. Obviously some flexibility is found in components such as door panel 
substrates. 
The surface of the trim panel which is exposed to the passenger is referred 
to as an A-side layer. Typical materials for the A-side layer are leather, 
vinyl or textile materials, including cloth or carpet. Vinyl materials 
often have a cotton knit backing and textiles usually have a latex 
backcoating applied by the fabric manufacturers to stabilize the cloth. 
While the materials used as A-side layers serve their cosmetic purposes 
well, none of them by themselves provide the soft, padded or cushioned 
effect desired, nor will they retain a shape. Accordingly, a layer of 
padding and structure must be provided between the substrate and the 
A-side layer. 
A preferred approach for a padded trim panel is to attach the padding to 
the A-side material and pre-form this laminate to the contour of the 
substrate. Such a pre-formed, pre-padded panel can then be attached to the 
substrate in a single step by any method and without the need for 
laborious hand contouring. A trim panel of this type is described and 
claimed in pending U.S. patent application Ser. No. 08/797,643, entitled 
"Automotive Trim Panel and Method of Making Same", invented by Vincent 
H-H. Jones and David L. Simon, and U.S. patent application Ser. No. 
08/797,646, entitled "Method of Thermoforming an Automotive Trim Panel", 
invented by Vincent H-H. Jones, David L. Simon and Scott M. Kloock, both 
filed on Jan. 31, 1997 and assigned to the present assignee. The 
disclosures of these applications are incorporated herein by reference. 
As mentioned above A-side materials by themselves cannot be formed into a 
permanent non-flat contour. The A-side materials on their own lack 
sufficient stiffness to retain any particular contour or shape, i.e., they 
will fold or collapse under their own weight. The referenced applications 
describe an A-side plus foam laminate material which overcomes these 
drawbacks and provides a self-supporting, contoured, padded trim panel 
ready for attachment to a substrate in any desired manner. Process 
controls are provided which allow thermoforming these parts in quantity 
with precise, repeatable accuracy. Thermoforming is defined as the forming 
of a thermoplastic sheet by heating it and then placing it into a mold to 
shape it. Cooling takes place in the mold so when the part comes out it 
will be self-supporting, i.e., it will retain the shape or contour of the 
mold. 
The present invention is a further refinement of the trim panel described 
in the above applications. One of the characteristics of a trim panel 
A-side layer is the feel or tactile reaction to the textural qualities of 
smoothness, flexibility and softness, such as might be obtained when one 
brushes his or her hand across the surface of the A-side layer. This 
characteristic is referred to as the "hand" or "touch" of the material. 
Obviously determination of a desirable hand depends on the preferences of 
individual users and is thus quite subjective. However, objective factors 
can be measured and selected to allow designers to create a hand that 
might vary from a soft touch (sometimes referred to as a loose hand) to a 
somewhat stiffer feel. The former might be appropriate for a luxury 
automobile while the latter might be preferred by owners of sports cars. 
The primary factor in defining a hand is the lateral spring rate of a 
material, i.e., the spring rate in a direction parallel to the surface. 
The perpendicular spring rate defines the amount of cushion a user will 
feel. 
It has been found that the spring rates of thermoformable foams used in the 
making of automotive trim panels are primarily dependent on the density of 
the foam. Given the typical range of thicknesses of foam, a foam density 
of about 2.7 to about 4.0 pounds per cubic foot is required to achieve the 
perpendicular spring rate that produces the desired cushioned feel. But 
the lateral spring rate for foam of this density is too large to allow for 
a feeling of a soft touch or loose hand. 
SUMMARY OF THE INVENTION 
The present invention is directed to a new material for use as an 
automotive trim panel and a method for making a panel that allows 
selection of the hand of the panel. The trim panel has an A-side layer 
laminated to a dual-density thermoformable support layer. 
The support layer is actually two laminated layers of thermoformable foam, 
each layer having a density that is different from the other layer. Thus, 
the trim panel has an A-side layer, an intermediate foam layer next to the 
A-side layer, and a bottom foam layer next to the intermediate foam layer. 
The thermoformable foam could be urethane, polyethylene or polypropylene 
foam. Either the urethane or polyethylene foam may be either closed or 
open cell, and may be thermo or chemically cross-linked. A typical range 
of thickness for the support layer is about 0.080"-0.320", although the 
invention is not limited to this range.

DETAILED DESCRIPTION OF THE INVENTION 
A preferred embodiment of the laminate for the present invention is shown 
generally at 40 in FIG. 1. The laminate comprises an A-side layer 42, an 
intermediate foam layer 44 and a bottom foam layer 46. Together the foam 
layers 44 and 46 define a thermoformable support layer. The A-side layer 
42 is made of vinyl as described above. Vinyl A-side layers have a typical 
thickness of about 0.030" to 0.050". 
The intermediate layer 44 is preferably closed cell urethane foam having an 
initial thickness in the range of 0.040" to 0.160" and a density less than 
1.0 pound per cubic foot. The bottom layer 46 is also a closed cell 
urethane foam having an initial thickness in the range of 0.080" to 0.160" 
and a density of between 2.7 to 4.0 pounds per cubic foot. The three 
layers 42, 44 and 46 are laminated together, such as by flame laminating. 
In a flame laminator a thin portion of a foam layer is liquified which 
will allow the foam layer to be laminated either to the A-side layer or 
the other foam layer. Sintered lamination could be also be used. Sprayed 
adhesives could be used. 
In the described embodiment the intermediate foam layer 44 has a low 
density (less than 1.0 pound per cubic foot) and thus a low lateral spring 
rate. The lateral spring rate is measured in a direction parallel to the 
plane of the A-side layer, as indicated by line A. The bottom foam layer 
46 has a different, higher density of about 2.7 to 4.0 pounds per cubic 
foot. The higher density means the bottom layer has a higher lateral 
spring rate. The lateral spring rate of the bottom layer 46 may be on the 
order of ten times the lateral spring rate of the intermediate layer 44. 
Because the intermediate layer 44 is adjacent the A-side material 42, the 
low lateral spring rate of the intermediate layer is the primary 
contributor to the hand of the panel. The high lateral spring rate of the 
bottom layer 46 does not adversely impact the hand because the bottom 
layer 46 is isolated from the A-side layer 42 by the intermediate layer 
44. Also, while the perpendicular spring rate (in the direction of line B 
in FIG. 1) is somewhat softened by the presence of the low density 
intermediate layer, it is still in an appropriate range because vertical 
forces on the panel involve the spring rates of both the intermediate and 
bottom layers. 
It can be seen that the dual density support layer allows a designer to 
select a hand or touch suitable for his or her particular application. The 
embodiment disclosed above will effect a soft touch or loose hand. 
Alternate thermoformable foams includes polyethylene or polypropylene foam. 
Any of these may be either closed or open cell, and may be thermo or 
chemically cross-linked. Also, it will be understood that the thicknesses 
and densities specified are examples only and the invention is not limited 
to those specifically set forth. For example, the dual density support 
layer of the present invention could advantageously be applied to a trim 
panel having a shirred appearance as disclosed in U.S. patent application 
Ser. No. 08/797,641, filed Jan. 31, 1997 and assigned to the present 
assignee, the disclosure of which is incorporated herein by reference. In 
such an application it may be desirable to create the shirred appearance 
by compressing the material into the grooves of the thermoforming tooling. 
The thickness of the starting material would then be increased to about 2 
to 12 mm for the bottom layer foam. 
An example of a trim panel on which the material of the present invention 
could be used is an upper bolster for the top portion of an interior door 
panel. Such a bolster is shown as part of the complete door panel shown 
generally in FIGS. 2 and 3 at 23. The panel includes a relatively rigid 
substrate 24, which forms no part of the present invention. The substrate 
defines a contour which includes an arm rest 25, an indentation 26 
(forming a door pull) and a door latch opening 27. A rigid substrate 28 
for a map pocket is added to the basic substrate 24. The substrate 24 is 
covered with a skin 29 which is formed in accordance with this invention 
from a thermoformed foam support layer and a vinyl A-side layer. The upper 
bolster 30, typically with a cloth A-side layer is added on the top 
portion of the skin. Similarly, a cloth map pocket insert 31 is applied to 
the map pocket substrate 28. 
An alternate embodiment of the trim panel is shown in FIG. 4. This 
embodiment is the same as FIG. 1 with the addition of a backing layer 48 
of felt attached to the bottom foam layer 46. This has the advantage of 
providing a stiffer part while still having the desired hand. 
While a preferred form of the invention has been shown and described, it 
will be realized that alterations and modifications may be made thereto 
without departing from the scope of the following claims. For example, the 
foam for the intermediate layer may be chosen such that it has a higher 
density, and therefore a higher lateral spring rate, than the bottom 
layer.