Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-08-08
2001-09-11
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S275500, C156S275700, C156S299000, C156S300000, C156S302000, C156S312000
Reexamination Certificate
active
06287410
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a continuous process for producing a pressed-wood composite product from a prepared pre-assembly mat which includes selected wood components along with intercomponent, heat-curable adhesive. In particular, it relates to such a method, and also to an apparatus for implementing this method, which utilizes time-spaced stages of both pressure application and heat introduction as an approach for achieving the final integrated pressed product. Such an approach yields a superior compressed-wood product, does so with equipment which is compactly and efficiently organized, and accomplishes processing in steps which offer significant control over end-product results.
A typical end product resulting from practice of the present invention might, for example be plywood, or laminated veneer lumber (LVL), which, after production can be cut for use, or otherwise employed, in various ways as wood-based building components. The starter material, so-to-speak, which can be effectively treated by the process and the machinery of this invention, insofar as the relevant wood componentry is involved, would typically be, in addition to a suitable heat-curable adhesive, (a) thin sheet veneers of solid wood, (b) oriented strands (or other fibrous make-ups) of smaller wood components, (c) solid wood lumber of various sizes, (d) already pre-made expanses of plywood which themselves are made up of thinner layers of wood plys, or (e) other wood elements.
Describing for a moment conventional LVL fabrication processing, LVL is typically made of glued, thin, veneer sheets of natural wood, utilizing adhesives that are mostly formed of Phenol Formaldehyde formulations which require heat to complete a curing process or reaction. In the state of the art today, there are several well-known and widely practiced methods of manufacturing and processing to create LVL. The most common pressing technology involves a platen press, and a method utilizing such a press is described in U.S. Pat. No. 4,638,843. Pressing and heating is typically accomplished by placing precursor LVL between suitable heavy metal platens. These platens, and their facially “jacketed” wood-component charges, are then placed under pressure, and are heated with hot oil or steam to implement the fabrication process. Heat from the platens is slowly transferred through the wood composite product, the product shrinks and compresses under pressure to the desired final thickness, and the adhesive cures after an appropriate span of pressure/heating time. This process is relatively slow, often taking, with conventional equipment of the type generally just described, about 19-minutes or so (per unit area) to compress and cure a finished product having a final thickness of about 1.5-inches.
Recognized today in the art is the fact that the addition of suitable radiofrequency (RF) energy to the environment within (i.e., in between) opposing press platens can accelerate the heating and curing process. Accordingly, the use of this augmentive RF approach to heating can shorten fabrication times. However, there are occasions involving problems with arcing due to high voltage that is in existence with respect to such RF energy employment. Such arcing is typically exacerbated by the presence of uncured and moist adhesive which squeezes out to regions of exposure on the sides of the material being pressed. U.S. Pat. No. 5,628,860 describes an environment where this kind of situation can occur.
Another conventional process employed for the preparation of LVL is described in U.S. Pat. No. 5,895,546. This patent discusses the use of microwave energy to preheat loose LVL lay-up materials, which are then finished in a process employing a hot-oil-heated, continuous-belt press. This process avoids the RF arcing problem just mentioned above by the fact that it typically employs a significantly lower-voltage and a higher-frequency heating energy than that which is employed in an RF environment of the traditional approach. However, this type of processing still requires conventional hot-oil energy in the final pressing stage of activities. For example, a press time for the production of a final 1.5-inches product is typically here around 11- or 12-minutes (per unit area). For a much thicker product, for example, for a final LVL product with a thickness of about 3.5-inches, production time can be three or four times this length. Further, a problem often specifically associated with microwave pre-heating is that such pre-heating is carried out on what can be referred to as loose lay-up (pre-assembly) materials, and any line stoppage can cause adhesive to dry out and become unusable for completing product production. Further, in any situation wherein a belt press is employed, such a press is a very expensive piece of equipment, much more expensive than a platen press, and consequently, not always the most desirable machinery-route (economically) to use.
U.S. Pat. Nos. 4,456,498 and 5,228,947 disclose processes utilizing microwave energy during the adhesive curing and compression process. Such energy is applied through ceramic-covered wave-guides that are positioned in openings between continuous-belt press sections in formation machinery. This approach to production is typically limited to the production of relatively large beam materials, and thus does not have a very wide-ranging applicability. Additionally, it typically requires a higher than often desirable spread of glue, and a significant wood densification—matters which are not always particularly wanted.
In this setting, a general object of the present invention is to provide a unique, continuous-flow process, and a system for implementing the same, which offers a wide degree of versatility with respect to the fabrication of a pressed-wood composite product, utilizing extremely efficient machinery which is relatively inexpensive in comparison with prior art machinery, and which can accomplish complete fabrication and adhesive curing with a relatively low expenditure of energy, in a relatively short period of time, and with substantial adjustable control afforded over processing parameters (pressure, temperature, time) in any given “processing window” for each region in processed material. The term “processing window” is here employed to refer to the overall time during which each region in the material that is being processed is subject to the different, required processing activities. By establishing, selectively, the physical space occupied (in the system of this invention) by each processing component, continuous-flow processing is enabled in a setting where greater or lesser processing times for exposure to the specified activities furnished by any given component can be varied simply by charging/adjusting/designing the physical size of that component, as measured in the direction of material travel in the system. In addition, and very significantly, the process and system of the present invention can, in most instances, produce a resulting product which is superior to its prior art counterparts in terms of economy of manufacture, stability in final form, and ease of confident usability either as an end product, or as a precursor to yet another, future end product.
According to a preferred manner of practicing the invention, a prepared mat of preassembled wood components, and intercomponent distributions of an appropriate heat-curable adhesive, are fed in a continuous-flow manner through a processing zone wherein the mat is subjected to time-spaced intervals of compression pressure, along with time-spaced intervals of microwave-introduced heat. While, within the context of the generally unique concept of this invention involving employing such “time-spaced” activities, the specific organization of pressure and heating intervals is a matter of wide and free choice, one approach which has been found to be extremely successful in the making of, for example, LVL, is an approach which utilizes a “cyclic” application of pressure, i.e., cycles alternating betwe
Kolisch Hartwell Dickinson & McCormack & Heuser
Yao Sam Chuan
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