Wood laminates

Details Wood laminates Wood laminates

1998-07-20

2001-10-16

Weisberger, R C (Department: 2164)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including grain, strips, or filamentary elements in...

C428S096000, C428S114000, C428S294400, C428S902000, C428S107000, C428S109000, C428S113000, C428S326000, C428S479600, C156S060000, C156S061000, C156S276000

Reexamination Certificate

active

06303207

ABSTRACT:

The present invention involves mats having particular use in bonding to wood and in making improved wood products and the method of making such mats. The mats produced according to this invention are useful as reinforcement and dimensional stabilizers for making a large number of products such as wood laminates of all types, hard faced wood products such as plywood for making concrete forms, and many other similar uses. The mats are also useful as stabilizing and reinforcing substrates for various other products.
BACKGROUND
It is known to make reinforcing mats from glass fibers and to use these mats as substrates in the manufacture of a large number of roofing products. Any known method of making nonwoven mats can be used, such as the conventional wet laid processes described in U.S. Pat. Nos. 4,112,174, 4,681,802 and 4,810,576, the disclosures of which are incorporated herein by reference. In these processes a slurry of glass fiber is made by adding glass fiber to a typical white water in a pulper to disperse the fiber in the white water forming a slurry having a fiber concentration of about 0.2-1.0 weight %, metering the slurry into a flow of white water to dilute the fiber concentration to 0.1 or below, and depositing this mixture on to a moving screen forming wire to dewater and form a wet nonwoven fibrous mat.
This wet nonwoven mat of glass fiber is then transferred to a second moving screen and run through a binder application saturating station where an aqueous binder mixture, such as an aqueous urea formaldehyde (UF) resin based binder mixture, is applied to the mat in any one of several known ways. The binder saturated mat is then run over a suction section while still on the moving screen to remove excess binder. The wet mat is then transferred to a wire mesh moving belt and run through an oven to dry the wet mat and to cure (polymerize) the UF based resin binder which bonds the fibers together in the mat. Preferably, the aqueous binder solution is applied using a curtain coater or a dip and squeeze applicator, but other methods of application such as spraying will also work.
In the drying and curing oven the mat is subjected to temperatures up to 450 or 500 degrees F. for periods usually not exceeding 1-2 minutes and as little as a few seconds. Alternative forming methods include the use of well known processes of cylinder forming, continuous strand mat forming which lays continuous strands of glass fibers in overlapping swirls, and “dry laying” using carding or random fiber distribution.
UF resins, usually modified with one or more of acrylic, styrene butadiene, or vinyl acetate resins, are most commonly used as a binder for fiber glass mats because of their suitability for the applications and their relatively low cost. Melamine formaldehyde resins are sometimes used for higher temperature and/or chemical resistant applications. To improve the toughness of the mats, a combination of higher mat tear strength and mat flexibility, which is needed to permit higher processing speeds on roofing product manufacturing lines and for maximum roofing product performance on the roofs and in other applications, it is common to modify or plasticize the UF resins as described above.
Mats made in the above described manner perform well in many applications, but do not provide the bonding strength desired for bonding to wood products.
SUMMARY OF THE INVENTION
In the conventional processes of making a nonwoven fiber mat by the processes described above, a slurry of fiber, preferably glass fiber, is metered into a stream of whitewater, preferably cationic to nonionic, and formed into a wet nonwoven mat on a moving, permeable surface and the mat is thereafter bounded with an aqueous urea formaldehyde (UF) binder, preferably an aqueous UF binder in water and modified by mixing in polyvinyl acetate and/or acrylic tripolymer, dried and cured. The present invention uses this general process to make mats, but includes the improvement of using a different binder resin, an aqueous furfuryl alcohol based resin, phenol formaldehyde, melamine formaldehyde, mixtures of these resins in aqueous solution and other similar resins, to produce mats in which the resin binder is dried and “B” staged, i. e. only partially cured. In a “B” staged condition the resin binder provides adequate strength to handle and further process the mat, but retains the ability to bond to wood and to “flow” (plastic deformation) under heat and pressure prior to finally curing, much like a thermoplastic resin, permitting densification of the fiber glass mat without damaging the fibers before becoming fully cured, i. e. thermoset.
The mats of the present invention comprise glass fibers bonded together with a resin binder wherein the resin binder is only partially cured to a “B” stage condition. The mats of the present invention have lower physical properties initially like tensile strength, hot wet strength and tear strength than conventionally cured mats, but the mats of the present invention surprisingly produce substantially higher bonding strength with wood. These mats are then used in the manufacture of wood products wherein one or more layers of the inventive mat are bonded to one or two layers of wood and the resulting laminate are then subjected to high pressure and sufficient heat to finish curing the “B” staged resin in the mat, and any additional resin that might be used to bond the mat to the wood. Wood products made using the mats of the present invention have surprisingly good rigidity and strengths, and when the inventive mats are bonded to the surface of a wood product, the wood product has a surprisingly tough surface. The “B” staged resin, which must be compatible with the thermosetting laminating glues used in the wood composite industry, include urea formaldehyde, phenol formaldehyde, melamine formaldehyde and hot melts as a substantial portion of the binder.
The mats of the present invention can also contain pigments, dyes, flame retardants, and other additives so long as they do not significantly reduce the ability of the mat to bond to a wood surface. The pigments or other additives can be included in the fiber slurry, the binder slurry or can be sprayed or otherwise coated onto the mat later using known techniques.


REFERENCES:
patent: 1299747 (1919-04-01), McClain
patent: 1960176 (1934-05-01), Weber et al.
patent: 3413188 (1963-06-01), Allen
patent: 3669727 (1972-06-01), Raymond
patent: 4337290 (1982-06-01), Kelly et al.
patent: 4615163 (1986-10-01), Curtis et al.
patent: 4954304 (1990-09-01), Ohtake et al.
patent: 5641553 (1997-06-01), Tingley
patent: 55-114561 (1980-09-01), None
Published Patent Application WO 98/49248 Published Nov. 5, 1998.
Proceedings of 1988 International Conference on Timber Engineering, vol. 1, pp. 39-57 from Wood and Fiber Science, vol. 18(1), Jan. 1986.

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