Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1999-07-23
2003-07-08
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C264S124000, C264S128000, C428S506000, C428S514000, C428S529000, C428S537100, C524S014000
Reexamination Certificate
active
06589660
ABSTRACT:
TECHNOLOGICAL FIELD
The present invention pertains to weatherable building materials prepared from lignocellulosic fibers. More particularly, the subject invention pertains to door systems capable of withstanding conditions to which outside entry doors are exposed.
BACKGROUND
In former times, entry doors were constructed of seasoned or kiln dried wood. Wooden doors are strong and relatively durable. However, their manufacture is relatively expensive due to numerous manual operations as well as the time required to allow adhesives to harden and/or cure during construction. Moreover, as wood is a natural product and susceptible to wide variation in makeup, grain patterns, density and the like, doors often exhibit warping, twisting, or bowing. Exterior wood products exposed to moisture exhibit a tendency to rot. With respect to insulation value, wood leaves much to be desired. Finally, high quality lumber suitable for manufacturing doors, jambs, thresholds, and other entry door system components, is becoming increasingly scarce and expensive. Finger-jointed door jambs and the like have become common for this reason. However, while such components are suitable for painting, the finger joints make them unsuitable for staining and/or varnishing.
Some of the previously identified drawbacks were overcome by the introduction of metal doors of sandwich construction. Such doors generally have a surrounding frame of wood or compressed wood product, and an insulating foam core onto which are joined metal skins. Such doors are less expensive to manufacture, are better insulators, and are highly rot resistant. Unfortunately, the difference in temperature between the inner and outer skins in cold weather coupled with a relatively high coefficient of thermal expansion of the metal can produce a temporary bowing rendering the door difficult to close. More importantly, such doors are susceptible to denting and rusting. Aesthetics of metal doors, even when painted, are less than desirable.
Interior door systems have been made of a variety of compressed wood products. Such doors often have outer skins of compression molded wood fibers or flours with or without interior foam insulation, and structural members of wood or particle board. Wood fibers, chips, and similar starting materials are inexpensive and easily processed on a large scale. Phenol/formaldehyde resol resins or similar resins of urea/formaldehyde, melamine/formaldehyde, and the like are generally used as binders in these systems. However, such doors are incapable of withstanding exterior conditions, and often are unsuitable even for interior locations where humidity extremes are encountered, i.e. basements, bathrooms, and the like.
Manufacture of weatherable building materials from compression molded wood products has not met with a great deal of success. Such products can absorb large amounts of water, plasticizing the fibers and decreasing strength and modulus. When heated by the sun, the water contained in such materials may cause both the product interior as well as surface layers and/or coatings to blister, peel, or delaminate. Coating such components with water impermeable coatings such as coatings of melamine resins, decreases water penetration. However, water may still enter through coating imperfections, cracks, scratches, or through openings necessary for mounting of hardware, i.e. lock sets, door knobs, deadbolts, hinges, and the like. No commercial products in this category have met the accelerated ageing test as more fully defined hereafter.
A recent high density fiberboard exterior door product is believed to employ three layers of coatings, including: a 12 weight percent phenol/formaldehyde partial resin prepress coating applied at approximately 175° C., a melamine-fortified urea/formaldehyde prepress sealer coating, and a post-press primer paint coating on the exterior surface. This door system has had poor acceptance in the market because it has experienced repeated warping due to moisture intrusion and unacceptably large deformations where the sun has disrupted the moisture equilibrium within the exterior skin. The manufacturer of this exterior door advises consumers to avoid use of a storm door, where heat may build-up above 54° C., again because of drying effects on the dimensional stability of the product. The manufacturer specifies that up to a year may be needed before a warped door caused by moisture variations can correct itself. Many discerning customers in the building trade have found these deficiencies too severe to warrant use of the doors.
The use of phenol/formaldehyde, urea/formaldehyde and other resins provides a binder system which is adequate for interior products slated for use in dry areas. However, the resins are relatively expensive, and must be used in fairly large quantities when products exhibiting high tensile strength and modulus are desired. Thus, European published patent applications EP-A-0 161 766 and EP-A-0 492 016 as well as related U.S. Pat. No. 5,017,319 to Shen teach the avoidance of synthetic adhesives by digesting lignocellulosic materials to the stage where liberated saccharides and oligosaccharides are produced, a portion of these dehydrating to produce furfural and other condensable products which then may react and crosslink, serving as a binder resin. The digestion proceeds in situ and the resulting partially digested fiber/adhesive mixture molded under heat and pressure, or the resinous adhesive may be isolated and applied to lignocellulosic or other substrates in place of more expensive synthetic adhesives.
While the molded products taught by the various Shen patents and publications may be economically produced, they suffer from a deficiency in physical properties such as tensile strength and modulus. Moreover, although the Shen adhesive is described as being waterproof, the latter is a relative term. While products produced according to Shen are suitable for interior use, these products fail both the accelerated ageing test and thickness swelling test, and thus cannot be made into commercially acceptable weatherable, exterior products.
It would be desirable to provide building materials and door systems capable for use in exterior locations which exhibit only low degrees of swelling when exposed to water; which do not exhibit blistering, peeling, or delamination, yet which can be prepared from inexpensive and easily processed lignocellulosic materials. It would be further desirable to produce entry doors and door system components which exhibit high flexural strength and modulus and further exhibit substantial retention of these properties in accelerated ageing tests. It would be still further desirable to provide door systems which can be aesthetically stained and varnished as well as capable of being painted.
SUMMARY OF THE INVENTION
The present invention pertains to weatherable building materials of compression molded lignocellulosic fibers which have been partially digested under conditions such that partial breakdown of hemicellulosic and other components takes place; contacting the fibers with a thermosettable novolac resin, optionally in conjunction with other resins, compression molding in the presence of a methylene source, and applying a prepress and/or post press impregnant which provides a water repellant but water vapor transmissive exterior.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The weatherproof construction materials of the present invention employ a unique combination of binders and coatings to produce building materials which are strong and which maintain their strength and modulus properties under extreme conditions. The subject invention materials exhibit little swelling upon exposure to moisture, even after water immersion. Moreover, the unique ability of the subject invention materials to release moisture without delamination, blistering, or other moisture-induced artifacts, allows use of the subject materials in exposed locations such as exterior doors, door jambs, thresholds, trim, etc., as well as in other weatherable building materials such a
Minke Ronald C.
Porter Cem A.
Templeton G. Daniel
West Kenneth J.
Brooks & Kushman P.C.
Nakarani D. S.
TT Technologies, Inc.
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