Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Autogenously or by activation of dry coated particles
Reexamination Certificate
2001-05-02
2003-10-21
Lechert, Jr., Stephen J. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Autogenously or by activation of dry coated particles
C264S119000, C264S293000
Reexamination Certificate
active
06635208
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to the revolutionary wood flake molding technology invented by wood scientists at Michigan Technological University during the latter part of the 1970s.
B. Background of the Art
Wood flake molding, also referred to as wood strand molding, is a technique for molding three-dimensionally configured objects out of binder coated wood flakes having an average length of about 1¼ to about 6 inches, preferably about 2 to about 3 inches; an average thickness of about 0.005 to about 0.075 inches, preferably about 0.015 to about 0.030 inches; and an average width of 3 inches or less, most typically 0.25 to 1.0 inches, and never greater than the average length of the flakes. These flakes are sometimes referred to in the art as “wood strands.” This technology is not to be confused with oriented strand board technology (see e.g., U.S. Pat. No. 3,164,511 to Elmendorf) wherein binder coated flakes or strands of wood are pressed into planar objects. In wood flake or wood strand molding, the flakes are molded into three-dimensional, i.e., non-planar, configurations.
In wood flake molding, flakes of wood having the dimensions outlined above are coated with MDI or similar binder and deposited onto a metal tray having one open side, in a loosely felted mat, to a thickness eight or nine times the desired thickness of the final part. The loosely felted mat is then covered with another metal tray, and the covered metal tray is used to carry the mat to a mold. (The terms “mold” and “die”, as well as “mold die”, are sometimes used interchangeably herein, reflecting the fact that “dies” are usually associated with stamping, and “molds” are associated with plastic molding, and molding of wood strands does not fit into either category.) The top metal tray is removed, and the bottom metal tray is then slid out from underneath the mat, to leave the loosely felted mat in position on the bottom half of the mold. The top half of the mold is then used to press the mat into the bottom half of the mold at a pressure of approximately 600 psi, and at an elevated temperature, to “set” (polymerize) the MDI binder, and to compress and adhere the compressed wood flakes into a final three-dimensional molded part. The excess perimeter of the loosely felted mat, that is, the portion extending beyond the mold cavity perimeter, is pinched off where the part defining the perimeter of the upper mold engages the part defining perimeter of the lower mold cavity. This is sometimes referred to as the pinch trim edge.
U.S. Pat. No. 4,440,708 and U.S. Pat. No. 4,469,216 disclose this technology. The drawings in U.S. Pat. No. 4,469,216 best illustrate the manner in which the wood flakes are deposited to form a loosely felted mat, though the metal trays are not shown. By loosely felted, it is meant that the wood flakes are simply lying one on top of the other in overlapping and interleaving fashion, without being bound together in any way. The binder coating is quite dry to the touch, such that there is no stickiness or adherence which hold them together in the loosely felted mat. The drawings of U.S. Pat. No. 4,440,708 best illustrate the manner in which a loosely felted mat is compressed by the mold halves into a three-dimensionally configured article (see
FIGS. 2-7
, for example).
This is a very unusual molding process as compared to a molding process one typically thinks of, in which some type of molten, semi-molten or other liquid material flows into and around mold parts. Wood flakes are not molten, are not contained in any type of molten or liquid carrier, and do not “flow” in any ordinary sense of the word. Hence, those of ordinary skill in the art do not equate wood flake or wood strand molding with conventional molding techniques.
One problem with this technology is the difficulty of molding parts having relatively narrow channels projecting from the part. It is difficult to force the wood flakes down into the narrow channels. Hence, parts having relatively narrow reinforcing ribs projecting from one side could not heretofore be made using this technology.
SUMMARY OF THE INVENTION
In the present invention, it has been surprisingly discovered that relatively narrow, channel shaped projections from a surface of a molded wood strand product can be formed effectively and efficiently during the molding process by placing at least one binder coated implant having sufficient length, width, and height, within a projection defining void in the mold cavity, followed by compressing the loosely felted wood flake mat into the mold cavity and curing the resulting composite part.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification and claims. A more detailed description of the present invention shall be discussed further below.
REFERENCES:
patent: 3164511 (1965-01-01), Elmendorf
patent: 3238281 (1966-03-01), Kato
patent: 4131705 (1978-12-01), Kubinsky
patent: 4213928 (1980-07-01), Casselbrant
patent: 4241133 (1980-12-01), Lund et al.
patent: 4246310 (1981-01-01), Hunt et al.
patent: 4248163 (1981-02-01), Caughey et al.
patent: 4248820 (1981-02-01), Haataja
patent: 4337710 (1982-07-01), Haataja et al.
patent: 4384019 (1983-05-01), Haataja
patent: 4408544 (1983-10-01), Haataja
patent: 4440708 (1984-04-01), Haataja et al.
patent: 4469216 (1984-09-01), Haataja et al.
patent: 4790966 (1988-12-01), Sandberg et al.
patent: 4960553 (1990-10-01), DeBruine et al.
patent: 5002713 (1991-03-01), Palardy et al.
Lechert Jr. Stephen J.
Price Heneveld Cooper DeWitt & Litton
Strandwood Molding, Inc.
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