Method of making a sandwich-type, compression-molded, composite component having a cellulose-based core and improved surface appearance

Abstract

A method of making a sandwich-type, compression-molded, composite component having improved surface appearance is provided. Reinforced thermoplastic skins, first and second sheets of thermoplastic adhesive and a cellulose-based core of a blank or stack of sandwich materials are heated to a softening temperature of the thermoplastics. The heated blank or stack is allowed to cool in the mold cavity until inner surfaces of the skins are bonded to top and bottom surfaces of the core by the sheets to seal core cavities. Air in the sealed cavities urges softened portions of the sheets and portions of the core inwardly towards the cavities of the core as the air in the cavities cools to inhibit debossing and improve surface appearance of a first outer surface of the blank or stack.

Claims

1. A method of making a sandwich-type, compression-molded, composite component having improved surface appearance, the method comprising: heating a blank or stack of sandwich material including first and second reinforced thermoplastic skins, first and second sheets of thermoplastic adhesive and a cellulose-based core positioned between the skins and between the sheets and having a plurality of cavities, the skins, the sheets and the core being heated to a softening temperature of the thermoplastics; providing a compression mold including component-forming, upper and lower dies with opposing molding surfaces cooperating to define a mold cavity having a shape substantially corresponding to a desired shape of the component; placing the blank or stack on the lower die in an open position of the mold; moving the dies toward each other until the mold is in a closed position; and allowing the heated blank or stack to cool in the mold cavity in the closed position until inner surfaces of the skins are bonded to top and bottom surfaces of the core by the sheets to seal the core cavities, air in the sealed cavities urging softened portions of the sheets and portions of the core inwardly towards the cavities of the core as the air in the cavities cools; and applying a vacuum at the first outer surface of the blank or stack in the mold cavity sufficient to prevent debossing and improve appearance of the first outer surface during the step of allowing.

2. The method as claimed in claim 1, wherein the first outer surface is an A-surface.

3. The method as claimed in claim 1, further comprising sealing the mold cavity from the surrounding atmosphere during the step of applying.

4. The method as claimed in claim 1, further comprising applying a vacuum at a second outer surface of the stack or blank in the mold cavity to prevent debossing and improve appearance of the second outer surface during the step of allowing.

5. The method as claimed in claim 1, wherein the core is a cellular core.

6. The method as claimed in claim 5, wherein the cellular core is a honeycomb core.

7. The method as claimed in claim 1, wherein each of the skins is fiber reinforced.

8. The method as claimed in claim 1, wherein the thermoplastic of the skins is polypropylene.

9. The method as claimed in claim 1, wherein the component has a thickness in the range of 5 to 25 mm.

10. The method as claimed in claim 1, wherein at least one of the skins is a woven skin.

11. The method as claimed in claim 1, wherein the step of heating is performed outside the mold.

12. A method of making a sandwich-type, compression-molded, composite component having improved surface appearance and for use in a vehicle, the method comprising: heating a blank or stack of sandwich material including first and second reinforced thermoplastic skins, first and second sheets of thermoplastic adhesive and a cellulose-based core positioned between the skins and between the sheets and having a plurality of cavities, the skins, the sheets and the core being heated to a softening temperature of the thermoplastics; providing a compression mold including component-forming, upper and lower dies with opposing molding surfaces cooperating to define a mold cavity having a shape substantially corresponding to a desired shape of the component; placing the blank or stack on the lower die in an open position of the mold; moving the dies toward each other until the mold is in a closed position; and allowing the heated blank or stack to cool in the mold cavity in the closed position until inner surfaces of the skins are bonded to top and bottom surfaces of the core by the sheets to seal the core cavities, air in the sealed cavities urging softened portions of the sheets and portions of the core inwardly towards the cavities of the core as the air in the cavities cools; and applying a vacuum at the first outer surface of the stack or blank in the mold cavity sufficient to prevent debossing and improve appearance of the first outer surface during the step of allowing.

13. The method as claimed in claim 12, wherein the first outer surface is an A-surface.

14. The method as claimed in claim 12, further comprising sealing the mold cavity from the surrounding atmosphere during the step of applying.

15. The method as claimed in claim 12, further comprising applying a vacuum at a second outer surface of the stack or blank in the mold cavity to prevent debossing and improve appearance of the second outer surface during the step of allowing.

16. A method of making a sandwich-type, compression-molded, composite component having improved surface appearance for use in the interior of a vehicle, the method comprising: heating a blank or stack of sandwich material including first and second reinforced thermoplastic skins, first and second sheets of thermoplastic adhesive and a cellulose-based core positioned between the skins and between the sheets and having a plurality of cavities, the skins, the sheets and the core being heated to a softening temperature of the thermoplastics; providing a compression mold including component-forming, upper and lower dies with opposing molding surfaces cooperating to define a mold cavity having a shape substantially corresponding to a desired shape of the component; placing the blank or stack on the lower die in an open position of the mold; moving the dies toward each other until the mold is in a closed position; and allowing the heated blank or stack to cool in the mold cavity in the closed position until inner surfaces of the skins are bonded to top and bottom surfaces of the core by the sheets to seal the core cavities, air in the sealed cavities urging softened portions of the sheets and portions of the core inwardly towards the cavities of the core as the air in the cavities cools; and applying a vacuum at the first outer surface of the stack or blank in the mold cavity sufficient to prevent debossing and improve appearance of the first outer surface during the step of allowing.

17. The method as claimed in claim 16, further comprising applying a vacuum at a second outer surface of the stack or blank in the mold cavity to prevent debossing and improve appearance of the second outer surface during the step of allowing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side sectional view showing various separate layers of a prior art stack or blank of thermoplastic-based layers of material;

(2) FIG. 2 is a top perspective sectional view of the stack of FIG. 1 but without outer carpet layers after low-pressure, cold compression molding of the prior art;

(3) FIG. 3 is a view, similar to the view of FIG. 2, of an edge portion of the molded component;

(4) FIG. 4 is a view, partially broken away and in cross section, of the component of FIG. 3 during compression molding in accordance with the prior art;

(5) FIG. 5 is a view, similar to the view of FIG. 4, but showing a vacuum-assisted compression mold useful in at least one method embodiment of the present invention to improve the surface appearance of the resulting component;

(6) FIG. 6 is a side sectional view showing a stack of various separate sheets or layers of thermoplastic-based and cellulose-based material prior to being compression molded into a composite component having a sandwich structure;

(7) FIG. 7 is a top perspective view, partially broken away and in cross section, of the composite component of FIG. 6 after molding;

(8) FIG. 8 is a view similar to the view of FIG. 7 but providing a bottom perspective view;

(9) FIG. 9 is a top plan view, partially broken away, of a reinforced thermoplastic skin having substantially parallel, visible fibers; and

(10) FIG. 10 is a view similar to the view of FIG. 9 but with substantially randomly oriented visible fibers.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(11) As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

(12) FIG. 5 shows a compression-molded, composite component, generally indicated at 30, which may be used in a vehicle load floor assembly, positioned or supported at the rear of an automotive vehicle. The composite component 30 has a sandwich structure. The composite component 30 includes a load-bearing, first outer skin or layer 14 having an A-surface 28, a second outer skin or layer 18 having a surface 32, and a core 16 positioned between and bonded to the outer layers 14 and 18. The core 16 has a large number of cavities and is preferably a thermoplastic core 16. The outer layers 14 and 18 are bonded to the core 16 by press molding in a mold 20 typically after pre-heating the outer layers 14 and 18 and the core 16 outside the mold 20. The outer layers 14 and 18 are preferably fiber-reinforced thermoplastic layers. The thermoplastic of the layers 14 and 18 and the core 16 may be a polyolefin such as polypropylene. The thermoplastic may alternatively be polyurethane. The fiber-reinforcement may be a glass mat, a natural fiber mat, or a woven or non-woven mat.

(13) The core 16 may be a cellular core having a honeycomb structure. The core 16 may also be made of polypropylene honeycomb, aluminum honeycomb, balsa and polyurethane foam. The resulting composite component or panel 30 typically includes a lightweight, low density core such as the core 16 together with fiber-reinforced thermoplastic skins or layers such as the skins 14 and 18. The resulting component 30 is not debossed and has an improved, overall appearance unlike the components 10 and 10 of FIGS. 2 and 3, respectively.

(14) The composite component 30 may be compression or press molded using a variety of technologies which use a low temperature, compression-molding apparatus but preferably uses the molding apparatus of FIG. 5. The core 16 and the skins 14 and 18 are preferably generally of the type shown in U.S. Pat. Nos. 6,537,413; 6,050,630; and 2005/0189674.

(15) Each resulting panel or component 30 may have a thickness in the range of 5 to 25 mm.

(16) In one example method of making the component 30, a stack of material is pressed in the low pressure, cold-forming mold 20 which has upper and lower forming dies 24 and 26, respectively. The mold 20 is shown in its closed position in FIG. 5 but it is to be understood that the blank or stack of materials is placed on the lower die 26 in the open position of the mold 20 prior to cold pressing.

(17) The stack is made up of the first layer or skin 14, the cellular core 16 and the second layer or skin 18. The stack is pressed at a pressure lying in the range of 1010.sup.5 Pa. to 3010.sup.5 Pa. The first and second skins 14 and 18, respectively, are preferably pre-heated to make them malleable and stretchable. Advantageously, in order to soften the first and second skins 14 and 18, respectively, heat is applied to a pre-assembly constituted by the stack made up of at least the first skin 14, of the cellular core 16, and the second skin 18 so that, while the component 30 is being formed in the mold 20, the first and second skins 14 and 18 have a forming temperature lying approximately in the range of 160 C. to 200 C., and, in this example, about 180 C.

(18) The heated blank or stack is allowed to cool in the mold cavity of FIG. 5 in the closed position of the mold 20 until inner surfaces of the skins 14 and 18 are bonded to top and bottom surfaces of the core 16 to seal the cavities of the core 16. The air in the sealed cavities normally urges softened portions of the skins 14 and 18 inwardly into and towards the cavities of the core 16 as the air in the cavities cools. A vacuum is applied at the first outer surface 28 of the blank or stack by an upper vacuum source through holes or passageways 34 formed through the upper die 24 of the mold 20 sufficient to prevent debossing (as shown in FIGS. 2 and 3) during the cooling and improve appearance of the first outer surface 28. Vacuum is applied by the upper vacuum source under control of a controller.

(19) In like fashion, a vacuum is applied at the second outer surface 32 of the stack or blank by a lower vacuum source through holes or passageways 34 formed through the lower die 26 of the mold 20 to prevent debossing during the cooling and improve appearance of the second outer surface 32. Vacuum is applied by the lower vacuum source under control of the controller.

(20) The mold cavity of the mold 20 is preferably sealed from the atmosphere surrounding the mold 20 during the application of the vacuum at the upper and lower surfaces 28 and 32, respectively, by one or both of the skins 14 and 18 or by a separate, conventional seal (not shown) between the dies 24 and 26 of the mold 20.

(21) Referring now to the FIGS. 7 and 8, a second embodiment of a compression-molded, sandwich-type composite component, generally indicated at 110, is shown. FIG. 6 shows a stack of thermoplastic-based and cellulose-based sheets or layers of material prior to the stack being compression molded into the composite panel or component 110. It is to be understood that one or more of such panels or components constructed in accordance with at least one embodiment of the present invention may be used in a wide variety of environments including an automotive vehicle environment. For example, the panel or component 110 may be a load-bearing vehicle component as shown or an interior trim component.

(22) The component 110 is typically manufactured via a thermo-compression process by providing the stack of material located or positioned within a low pressure, thermo-compression mold either generally of the type shown at 20 in FIG. 4 (without vacuum) or generally of the type shown at 20 in FIG. 5 (with vacuum). As shown in FIG. 6, the stack includes first and second reinforced thermoplastic skins or outer layers 112 and 114, respectively, a cellulose-based core having a large number of cavities such as a paper or cardboard cellular core 116 disposed between and bonded to plys or films or sheets of hot-melt adhesive (i.e. thermoplastic adhesive) 118 and 120 which, in turn, are disposed between and bonded to the skins 112 and 114 by the press or compression molding. The sheets 118 and 120 may be bonded to their respective skins 112 and 114 prior to the press molding or are preferably bonded during the press molding. The thermoplastic of the sheets 118 and 120 is typically compatible with the thermoplastic of the skins 112 and 114 so that a strong bond is formed therebetween. One or more other resins may also be included within the adhesive of the sheets 118 and 120 to optimize the resulting adhesive system. The adhesive system is not a solvent-based adhesive system.

(23) The skins 112 and 114 and their respective sheets or film layers 118 and 120 (with the core 116 in between the layers 118 and 120) are heated typically outside of the mold (i.e. in an oven) to a softening temperature wherein the hot-melt adhesive becomes sticky or tacky. The mold is preferably a low-pressure, compression mold which performs a thermo-compression process on the stack of materials.

(24) The step of applying the pressure compacts and reduces the thickness of the cellular core 116 and top and bottom surface portions of the cellular core 116 penetrate and extend into the film layers 118 and 120 without penetrating into and possibly encountering any fibers located at the outer surfaces of the skins 112 and 114 thereby weakening the resulting bond. Often times the fibers in the skins 112 and 114 are located on or at the surfaces of the skins as shown by skins 112 and 112 in FIGS. 9 and 10, respectively, wherein the fibers are substantially parallel and randomly oriented, respectively.

(25) The cellulose-based, cellular core 116 may be a honeycomb core. In this example, the cellular core has an open-celled structure of the type made up of a tubular honeycomb, and it is made mainly of cellulose and preferably of paper or cardboard. The sticky or tacky hot-melt adhesive extends a small amount into the open cells during the thermo-compression process. It is also possible to use a cellular structure having closed cells, a material, such as a wooden part, to which the top and bottom film layers 118 and 120, respectively, are bonded. The skins 112 and 114 are bonded to the top and bottom surfaces of the core 116 by the sheets 118 and 120 to seal the cavities of the core 116. Air in the sealed cavities urges softened portions of the sheets 118 and 120 and portions of the core 116 inwardly towards the cavities of the core 116 as the air cools to inhibit debossing and improve surface appearance of a first outer surface of the stack. A mold such as the mold 20 of FIG. 5 (with vacuum) may be used to prevent debossing and improve surface appearance at the first outer surface.

(26) Each of the skins 112 and 114 may be fiber reinforced. The thermoplastic of the sheets or film layers 118 and 120, and the skins 112 and 114 may be polypropylene. Alternatively, the thermoplastic may be polycarbonate, polyimide, acrylonitrile-butadiene-styrene as well as polyethylene, polyethylene terphthalate, polybutylene terphthalate, thermoplastic polyurethanes, polyacetal, polyphenyl sulphide, cyclo-olefin copolymers, thermotropic polyesters and blends thereof. At least one of the skins 112 or 114 may be woven skin, such as polypropylene skin. Each of the skins 112 and 114 may be reinforced with fibers, e.g., glass fibers, carbon fibers, aramid and/or natural fibers. At least one of the skins 112 and 114 can advantageously be made up of woven glass fiber fabric and of a thermoplastics material.

(27) The resulting panel 110 may have a thickness in the range of 5 to 25 mm.

(28) In one example method of making the panel 110, a stack of material may be pressed in a low pressure, cold-forming mold (not shown). The stack is made up of the first skin 112, the first film layer 118, the paper cellular core 116, the second film layer 120 and the second skin 114, and is pressed at a pressure lying in the range of 1010.sup.5 Pa. to 3010.sup.5 Pa. The first and second skins 112 and 114, and the first and second film layers 118 and 120 are preferably pre-heated to make them malleable and stretchable. Advantageously, in order to soften the first and second skins 112 and 114, and their respective film layers 118 and 120, respectively, heat is applied to a pre-assembly made up of at least the first skin 112, the first film layer 118, the paper cellular core 116, the second skin 114 and the second film layer 120 so that, while the panel 110 is being formed in the mold, the first and second skins 112 and 114 and the film layers 118 and 120 have a forming temperature lying approximately in the range of 160 C. to 200 C., and, in this example, about 180 C.

(29) While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.