Static structures (e.g. – buildings) – Composite prefabricated panel including adjunctive means – Sandwich or hollow with sheet-like facing members
Reexamination Certificate
1999-08-02
2001-05-08
Kent, Christopher T. (Department: 3635)
Static structures (e.g., buildings)
Composite prefabricated panel including adjunctive means
Sandwich or hollow with sheet-like facing members
C052S309900, C052S313000, C052S316000, C052S455000, C052S456000, C052S784150
Reexamination Certificate
active
06226958
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to insulated door assemblies having compression molded skins which exhibit minimal thermal deflection. More particularly, the subject invention pertains to insulated door assemblies having skins of compression molded, moderately dark colored, fiber-reinforced sheet molding compound which exhibit reduced thermal expansion and contraction, which retain the ability to receive pigmented stains in a uniform manner, and to improved processes for their preparation.
BACKGROUND ART
Entry door system containing fiber reinforced compression molded door skins are becoming increasingly popular. An example of the latter is the Classic-Craft™ door available from Therma-Tru Corporation. Such entry door systems contain front and back skins which are generally both prepared from fiber reinforced sheet molding compound which has been compression molded to provide a wood grain pattern on the door skin. These door skins are mounted onto stiles and rails and contain highly efficient thermal insulation between the skins. Examples of such door assemblies may be found in U.S. Pat. Nos. 4,550,540 and 5,537,789. Such door entry systems are much more thermally efficient than solid wood doors or insulated metal doors, as well as being more aesthetically pleasing than the latter.
However, the increased thermal efficiency of such doors is a mixed blessing, often being so effective in reducing thermal transmission from the exterior to the interior that temperature differentials of 55-60° C. may be created between the exterior and interior skins. In such cases, the skin exposed to the higher temperature will expand to a greater degree than the skin exposed to the lower temperature environment. A portion of this expansive force may be resisted by the adhesive which adheres the skin to the frame; by the frame itself; and by the insulating core. However, stresses on these door components increase dramatically as the temperature differential between opposing skins increases. The stresses can be so great as to temporarily warp the door assembly in a phenomenon known in the industry as “thermal deflection”. Consumers, as can be imagined, are generally distraught when they observe this behavior. In addition, the warping or bowing which the door experiences may be of such magnitude that contact between the weatherstripping and door assembly may be lost, thus allowing considerable air infiltration and associated thermal loss.
When thermal deflection occurs, discerning consumers find the products unacceptable in insulated entry door assemblies of even typical residential height, for example, those of about 2 m (6 feet) in height. These doors have lock edges termed “lock stiles” of which the section above the lock may be viewed simplistically as a cantilevered beam approximately 1.1 m in length. Attempts to minimize thermal deflection have been centered on structural changes to the door support members. For example, structural modifications on typical residential insulated door assemblies may use laminated beams in the lock edge or lock stile to reduce thermal deflection. However, the use of such laminated beams results in significant increase in raw material cost. Moreover, such efforts have not been entirely satisfactory, and thermal deflection continues to be a design issue in such products.
While thermal deflection has been a considerable problem in entry doors of normal height, when taller doors are used as dictated by recent trends in building products, the problem becomes even more severe. In such taller doors, the lock position remains at a relatively stationary height, i.e., a height convenient for grasping with the hand of the hypothetical “normal” individual. However, the increased height thus requires a considerably longer portion of the door to be located above the lock set. Thus, the combination of increased skin surface area generating greater force, and a longer cantilevered length, results in a magnitude of thermal deflection which is unacceptable for such doors, even those containing laminated beams in the lock stile.
Numerous materials exist which could be substituted for the fiber reinforced sheet molding compound used to make fiber reinforced door skins. Unfortunately, however, the materials of which the door skin is constructed must meet numerous criteria other than merely minimal thermal expansion. For example, the skins must be relatively strong and yet must have appreciable resiliency in order that they may survive the destructive forces generated upon thermal expansion. Further, and more importantly from a commercial aspect, the door skins must be capable of receiving a pigmented stain in a uniform manner, and should also be capable of being economically pigmented to produce a medium dark to dark surface prior to staining and finishing.
For example, early “fiberglass” doors were colored white. The white substrate was visible through the thin films of solid color stains used to achieve an appearance of wood. Discerning customers found the substrate color to be unacceptable. Moreover, at locations of the door experiencing wear, the underlying white surfaces are easily exposed, rendering the door aesthetically displeasing. Since about 1984, most manufacturers have pigmented the molding compounds used to compression mold the skins with dark or medium darkness pigments. Thus, the materials of skin construction must be capable of receiving such pigments and also of receiving a stain coating in a uniform manner. Furthermore, the materials of construction must be relatively economical in order that the door systems may be made available at a reasonable price. For these reasons, fiberglass sheet molding compound, consisting predominately of curable unsaturated polyester resins generally incorporating one or more co-curable unsaturated monomers, continue to be used to manufacture textured, compression molded door skins.
In the preparation of molded articles by the compression molding of unsaturated polyester/co-curable unsaturated monomer compositions, considerable shrinkage results during the molding process due to a volume decrease in the curable ingredients as these react and crosslink. In non-textured articles, the result may be a cured product which no longer has the dimensions of the mold. In textured articles, the decrease in volume may produce articles with insufficient or indistinct texture. Addition of shrink reducing adjuvants have been found to lower the propensity of the curing polymer system to shrink, thus allowing for full definition of textured surfaces. The efficacy of shrinkage control adjuvants may be assessed by visually observing surface texture, or by measuring the dimensions of cured articles and comparing them to mold dimensions. As the dimensional coefficient of thermal expansion is generally not a linear function of temperature, the expansion and contraction of a cured, finished product over the temperature ranges expected of exterior doors cannot be predicted from measurements made based on compression molding temperatures. Furthermore, those skilled in the art of sheet molding compounds have not been concerned with the thermal expansion of cured, finished products per se, only with changes in volume which are the result of curing during the molding process.
Use of sheet molding compound containing low profile additives was disclosed in low linear thermal coefficient expansion moldable materials in Assignee's U.S. Pat. No. 5,537,789. However, the low profile additive was deemed important to minimize shrinkage of the hot and partially cured skin during molding. There is no recognition apparent from the '789 patent that the low profile additive had any effect on either the linear thermal coefficient of expansion itself or the ability of a door made from compression molded sheet molding compound to resist thermal deflection.
It has been discovered that reduction of the thermal expansion of compression molded door skins prepared from unsaturated polyester sheet molding compounds over the temperature extremes expected during
Davis, III Eugene R.
Scheffel Greg W.
Templeton G. Daniel
West Kenneth J.
Brooks & Kushman P.C.
Kent Christopher T.
Therma-Tru Corporation
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