Foam-backed, hollow articles made by cold rotational molding
View Patent ↗Systems and cold rotational molding methods are provided for making hollow, foam-backed polymeric molded articles. The molded articles can be manikins or manikin parts, or other articles, such as frames (e.g. for mirrors and pictures), urns, fixtures, furniture, display props, and garden furniture, made of a thermosetting elastomeric material. The articles are more structurally rigid than previous molded articles utilizing the same amount of polymer material, lighter in weight than previous molded articles having the same structural rigidity, and more resistant to deformation under temperatures up to 180 to 185° F. The process of making a molded manikin part, from the first injection of polymer into the mold until demolding of the finished part, can be completed in as short a time as 18 minutes without the necessity for cradling of the demolded part, even when the part requires one or more flat surfaces.
1. A method for making a hollow molded article that is resistant to heat and impact distortion, said method comprising:
a. introducing a first polymer mix containing uncured thermosetting polymer components for a rigid, hollow polymer shell into a mold in an amount sufficient to form a shell coating of said first polymer mix on the inside surface of the mold;
b. rocking and rotating the mold in multiple directions in a cold rotational molding process to form said shell coating until at least the inner surface of said coating has become tacky;
c. introducing said second polymer mix into the mold in an amount sufficient to form a foam coating on said shell coating;
d. rocking and rotating the mold at room temperature to about 115° F. in multiple directions to form said foam coating bonded to said shell coating and allow said shell coating to cure sufficiently that a molded hollow article made by the foregoing method can be removed from the mold; and
e. removing the molded article consisting essentially of an outer shell layer bonded to an inner foam backing layer from the mold.
2. The method of claim 1 wherein said first polymer mix, for said rigid shell, is introduced into said mold in an amount at least sufficient to form a coating about ⅛ inch to about ¼ inch thick on the inner surface of said mold.
3. The method of claim 1 wherein said second polymer mix, for said foam coating, is introduced into said mold in an amount at least sufficient to form a coating about ⅜ inch to about ¾ inch thick on the inner surface of said shell.
4. The method of claim 1 performed at a temperature within the mold sufficient to maintain the first and second polymer mixes at viscosities low enough to form said coatings.
5. The method of claim 1 which is completed in at most about 18 minutes.
6. The method of claim 1 wherein the first and second uncured polymer mixes comprise polyol or polyester resin, isocyanate, and a curing catalyst.
7. The method of claim 6 wherein first mix, for the polymer shell, has an isocyanate to polyol ratio of about 77:100.
8. The method of claim 6 wherein the second mix, for the rigid polymer foam coating, has an isocyanate to polyol ratio of between about 100:82 and about 100:92.
9. The method of claim 6 wherein the second mix, for the rigid polymer foam coating, has an isocyanate to polyol ratio of about 100:87.
10. The method of claim 6 wherein the uncured polymer components for the shell coating also comprise a pigment or dye effective to produce a desired color of said shell.
11. The method of claim 6 wherein the uncured polymer components for the foam coating also comprise a pigment or dye effective to produce a desired color of said foam backing.
12. The method of claim 1 wherein the mold comprises complex curved surfaces.
13. The method of claim 12 wherein the mold also comprises a flat surface.
14. The method of claim 13 wherein said method also comprises attaching a magnetic component to a flat surface of a molded article made by said method.
15. The method of claim 1 wherein the mold comprises one or more foam buildup-inducing components.
16. The method of claim 15 wherein the foam backing of the molded article comprises areas having greater than average thickness produced by the turbulence induced by the foam buildup-inducing component(s).
17. The method of claim 1 also comprising providing a vent hole in the molded article.
18. The method of claim 1 wherein the mold does not contain an internal armature.
19. The method of claim 1 wherein the mold is a mold for a manikin or a manikin part.
20. The method of claim 1 wherein the mold is sized and shaped to produce a molded article having the size and shape of a normal human body or body part.
21. The method of claim 1 wherein said first and second polymer mixes are polyurethane polymer mixes.