Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-01-24
2002-04-02
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S017000, C524S025000
Reexamination Certificate
active
06365650
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention generally relates to adhesives for joining wood products, and more particularly to two-part polyurethane adhesives modified with soy protein which adhesives are both heat and radio frequency (RF) curable.
Glued wood products have been traditionally used in this country in a variety of applications. The adhesives for such bonded or laminated wood products conventionally are based on phenol-formaldehyde, urea-formaldehyde, polyvinyl acetate, resorcinol-formaldehyde, polymeric diphenylmethane diisocyanate (MDI), and hot met adhesives. The glued wood products include plywood, particleboard, oriented strand board (OSB), medium density fiberboard (MDF), laminated veneer lumber (LVL), laminated beams, and a variety of other engineered wood products. Among them, laminated beams, I-beams, LVL, and a variety of engineered wood products are used for structural wood applications. Generally, these engineered wood products require an initial finger jointing of short pieces of wood or parallel laminated veneers (PLV) before they can be constructed into long and/or thick beams or lumbers. Consequently, it is important that the finger-jointed area must have good strength to be used for structural wood applications. For present purposes, all of the foregoing products are known as “laminated wood products.”
At present, phenol-resorcinol-formaldehyde (PRF) is widely used in industry for finger joint applications. When adhesive is applied to the fingers, the finger jointed wood or PLV is crowded together using an end pressure until a “tip gap” of 1-40 mils is achieved. Its is essential that the fingers do not “bottom out.” The finger joints then are moved into a curing zone where hot platens or dielectric plates are used to cure the finger joints under heat or radio frequency and pressure for typically less than 30 seconds and then the joints are removed away from the curing zone. The adhesives must be able to fill the gaps or voids between the fingers when curing is complete in order for the product to exhibit good strength and a smooth appearance.
One the other hand, the speed of curing must be fast under these conditions in order to hold the finger-jointed pieces together for further processing, such as beam lamination and l-joint assembly. This is especially true in a high-speed commercial finger jointing process. Generally, adhesives with high solids and fast curing profiles are regarded as appropriate for such an application.
It should be mentioned also that two-part PRF and melamine-formaldehyde (MF) adhesives generally are used in industry as adhesives in preparation of radio frequency (RF) cured finger joint assemblies. Both of these adhesives are highly polar, which makes them respond well to RF curing. RF curing drives the bondline temperature sufficiently high to permit the MF or PRF to condense quickly. Due to the rigid ring structure of both PRF and MF, these adhesives cure to give a high T
g
, rigid, three-dimensional network in a short time; thus, producing acceptable immediate handling strength (proof-loading).
Soy protein products have been utilized as adhesives for wood bonding since the 1930's. Their use soon declined as a result of the development of petroleum derived adhesives. Economic and ecological pressures in the 1990's renewed interest in the practical use of soy protein products in wood adhesives. Heretofore, soybean protein has been proposed for use with phenolic resin, urea resin, or resorcinol resin, such as is described in JP 06200226, 58034877, 50034632, and 04057881. In JP 50034632 and 04057881, adhesives are proposed that consist of soy protein as the major component and isocyanate as a minor component because the soy protein, like wheat flour, is capable of thickening the mixture by absorbing moisture in the wood to give an adhesive with fast drying capability. In recent years, soybean-based adhesives were developed and used primarily in a “honeymoon” system, such as those described by Scheid, “Finger-Jointing and Other Uses of Environmentally Friendly Soy-Based Adhesives”,
Wood Technology Clinic and Show,
Conference Proceeding, Portland, Oreg., Mar. 25-27, 1998; and Steele, et al., “Finger Jointing Green Southern Yellow Pine With A Soy-Based Adhesive”,
Wood Technology Clinic and Show,
Conference Proceeding, Portland, Oreg., Mar. 25-27, 1998.
BRIEF SUMMARY OF THE INVENTION
An adhesive suitable for bonding wood is both heat curable and radio frequency (RF) curable. This adhesive is composed of an isocyanate-terminated prepolymer and a hydrolyzed soy protein having a pH of at least about 9. The weight ratio of prepolymer to soy protein hydrolyzate ranges from about 70-90 to 30-10. Further increases in the ratio of the soy protein hydrolyzate in the mix would lead to a high viscosity, paste-like material that would not be acceptable for most, if not all, applications contemplated herein, such as, for example, gluing wood, such as, for example finger joints.
DETAILED DESCRIPTION OF THE INVENTION
It is well known that woods are porous materials that contain different moisture contents, depending upon type of wood, storage environment, etc. Moisture contents can vary from as low as 5 wt-% to greater than 30 wt-%. For adhesives to properly bond wood, it is important that the adhesive penetrates deep into the wood and interlock with the cellulose structure upon cross-linking. If the adhesive cures too fast, however, such desirable penetration is not achieved. An adhesive predominating with soy protein hydrolyzate would react and dry very rapidly, thus decreasing the ability of the adhesive to penetrate into the wood's structure to provide a strong bond.
To strike a balance, then an isocyanate-terminated prepolymer becomes the predominant component of the adhesive composition and an aqueous hydrolyzed soy protein a minor component. Such a composition would substantially decrease the rapid thickening action of the soy protein component, thus allowing the adhesive time to penetrate into the wood's structure. Water would react with the prepolymer for cure of the prepolymer in addition to the reaction between the prepolymer and the soy protein hydrolyzate component. Such a balanced cure results in strong bonds by virtue of the wood penetration of the adhesive coupled with the necessary speed of cure required in commercial settings. The examples will amply demonstrate the performance of the inventive adhesive in engineered wood applications.
Information on soy protein can be found in, for example, Kirk-Othmer,
Encyclopedia of Chemical Technology,
Third Edition, Volume 21, pp. 418-422 (1983). Soy protein hydrolyzates generally are prepared by hydrolyzing soy protein powder with an aqueous caustic solution. Treatment of soy protein with soluble caustic is necessary because the caustic breaks the internal hydrogen bonds of the coiled protein molecules and makes most of their complex polar structure available for adhesion to wood. See, for example, Bian, et al., “Adhesive Performance of Modified Soy Protein Polymers”,
Polym. Prep., Am. Chem. Soc. Div., Polym. Chem.,
Volume 39 (1988), pp. 72-73. The major mechanism of protein gluing involves the dispersing and unfolding of the protein molecules in solution so that the unfolded molecules' increased surface area can contact an increased area of the wood. Additionally, the unfolded protein molecules become entangled with each other during the curing process for improving bond strength. The resulting protein hydrolyzate generally has a pH of greater than about 9 and often between about 9.5 and 12. Consequently, the hydrolyzed soy protein molecules are high in polarity, an added benefit for RF curing.
Appropriate caustics for use in hydrolyzing soy protein include, for example, the oxides, hydroxides, and the like, of alkali metals and alkaline earth metals, caustic alcohols, and the like. Representative suitable caustics include, for example, NaOH, CaO, CH
3
ONa, C
2
H
5
ONa, C
3
H
7
ONa
Chen Gang-Fung
Day David E.
Jones David
Ashland Chemical Company
Cain Edward J.
Mueller and Smith LPA
LandOfFree
Heat and radio frequency-curable two-pack soy protein-based... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat and radio frequency-curable two-pack soy protein-based..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat and radio frequency-curable two-pack soy protein-based... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2862281