Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-01-14
2001-11-06
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S219000, C156S245000, C156S307300, C264S119000, C264S322000
Reexamination Certificate
active
06312540
ABSTRACT:
The disclosed invention is to a method for manufacturing a molded door skin from a solid flat wood composite material, as well as the resulting skin and a hollow core door produced therefrom. More particularly, the disclosed invention is to a method for manufacturing a molded door skin in which a flat or planar solid blank of wood composite material is pre-heated, moisturized, and heated in a press to a temperature sufficient to soften the blank and during which the press platen(s) are pressure actuated to close, with the closing pressure thereafter increased continuously to a preset limit in order to deform the blank into a molded configuration suitable for a door skin and ultimately for being assembled into a hollow core door.
Hollow core doors are used in both interior and exterior applications. Many hollow care doors are made from door skins formed from wood composite materials. These wood composite materials may include particle board, flake board, hard board, and medium density fiberboard (“MDF”). The wood composites often utilize a resin binder, which frequently is a thermal setting resin, in order to maintain the wood fibers forming the composite in solid form.
A hollow core door may be of the “flush” type, that is one that is flat or planar on both major surfaces (i.e. both door skins are flat and do not include panels molded therein). Alternatively, a hollow core door may be of the “molded” type, that is one having a series of three-dimensional panels or the like formed or molded into the skins as they are being manufactured.
Standard molded door skins are formed from a relatively thick non-solid mat or bat of material, which is thereafter compressed in a press to a relatively thin, final thickness. The mat can be produced from either dry or wet fibers. If the mat has a very high water content, with the result that water is squeezed out during the pressing operation. The press may be a multiple platen press, having a series of skin forming pockets. Because the mat is in a flexible state prior to the pressing operation, then the resulting solid skin has sharply defined features acceptable to consumers because the wood fibers can flow in order to conform to the mold. Due in part to the high captial costs involved to build plants to make molded skins, manufacturers frequently require that individual orders be for a large number of skins in order to permit maximum operating efficiencies. Smaller orders become cost prohibitive.
Flush door skins on the other hand may be made in a similar manner as moulded skins, except that the original mat or bat of wood fibers is pressed flat, and is not three-dimensionally molded to form panels or the like. Alternatively, a continuous belt press may be used for flat skins. Thus, a flush door skin originates from a relatively thick non-solid mat or bat of wood-like fibers, which is pressed into a planar or flat shape to define the flush solid skin. This means that standard medium density fiberboard, or hardboard may be used.
Standard molded door skins are relatively expensive, because the capital cost is quite high due to the need for dies, presses, and the like. The flat or planar skins used for flush doors, on the other hand, are relatively inexpensive, but do not provide the aesthetic features often desired by consumers.
Because of the cost differential between a wood composite “flush” or “flat” skin and a wood composite “molded” skin, attempts have been made to transform flush skins into molded skins in an effort to more inexpensively produced molded door products. Such prior efforts have not resulted in commercially acceptable door skins, principally because the appearance of the surface has typically not been satisfactory. Prior efforts to transform flush skins into molded skins have generally resulted in the final molded skin having a cracked, marred, or otherwise aesthetically displeasing configuration and/or appearance.
It is apparent from the above that there exists a need in the art for a method of manufacturing a molded door skin from a flat wood composite blank which permits a standard flush or flat skin blank to be used as the base material, and which results in a molded door skin having features and surface characteristics acceptable to consumers. Yet a further need in the art is a molded door manufactured from flat wood composite door skins, which has suitable resistance to moisture, so that the door may be used for exterior applications.
It is a purppose of this invention to fulfill the above-described needs in the art. In commonly owned U.K. Application No. 9707318.3), there is disclosed a method of making a hollow core door by reforming flush or flat door skins into molded skins via a press, wherein pressure applied to platens of the press is increased in a series of steps. It has been found that the method of the prior application can be improved upon, as set forth below, to enable more efficient flat skin shaping, and improved strength to the end product door.
The disclosed invention meets these and other needs in the art. It is a purpose of this invention to fulfill the above-described needs in the art.
A primary object of the disclosed invention is a method of manufacturing a molded door skin from a flush wood composite blank through applying continuously increasing pressure to a moistened and softened flat blank, so that the resulting skin has molded features and surface characteristics acceptable to consumers.
A further object of this invention is a molded door skin that is impervious to moisture, with the result that the door will not distort and therefore will be suitable for exterior applications.
A method of manufacturing a door skin, according to one aspect of the invention, comprises the steps of providing a solid wood composite flat blank (i.e. one that has already been compressed from its thick, loose, moisture-containing state). The blank is pre-heated and moisturized, coated with a sealer, and placed between platens of a heated press. The platen(s) are heated to a temperature sufficient to soften the resin in the blank and thus to soften the blank, sufficient pressure is applied to close the platens, and the pressure is continuously increased for thereby causing the blank to be deformed into a molded shape determined by the configuration of the platens. The rate of closure of the press is determined by, and is a function of a number of characteristics including, the hardness, density, density profile, depth of molding, and percentage binder or resin content of the flush skin blank being reformed. The molded and now reformed blank is then removed from between the press platens.
A door skin, according to another aspect of the invention, comprises a molded medium density fiberboard three-dimensional blank. The blank has a first portion with a first preselected thickness. The blank has a second portion with a second preselected thickness. The second thickness is less than the first thickness.
A door skin, according to a further aspect of the invention, comprises, after reforming in the press, a molded medium denisty fiber board three dimensional blank having a density of from about 550 to about 1,200 kg/m
3
, which density is substantially uniform throughout the thickness of the skin (i.e. plus/minus about 75 kg per cubic meter throughout the skin's thickness, preferably within about plus/minus 25 kg per cubic meter).
A door, according to a still further aspect of the invention, comprises a peripheral frame having oppositely disposed sides. At least a first molded skin is provided. The skin has first and second sides. The first or exterior side of the skin has a moisture impervious barrier applied wholly there about. The door skin second or interior side is secured to one of the frame sides. A second door skin is secured to the opposite side of the frame.
It is also an object of this invention to provide a door skin, that after reforming into a molded skin, is stronger than a standard flush or flat skin blank and a molded skin. In certain embodiments, the reformed molded skin has a bond strength of at
Ball Michael W.
Liniak, Berenato, Longacre & White LLC
MDF Inc.
Piazza Gladys
LandOfFree
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