Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-08-13
2002-06-18
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S407000, C156S922000, C156S284000
Reexamination Certificate
active
06406786
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the manufacture of industrially usable bodies, such as boards, panels and molded products of plant composite materials, more especially fiberboard, particleboard and the like made of bonded straw, wood pieces or particles or the like. More particularly, the present invention relates to the bonding of solid organic materials including wood particles, wood fibers, straw and the like, sometimes hereinafter broadly referred to as “lignocellulosic” materials
1
, and especially in the manufacture of composite or bonded products from such lignocellulosic materials, particularly composite straw or the like products or composite wood products such as plywood and reconstituted wood, e.g. fiberboard, chipboard, particleboard, and the like.
1
Although wheat straw and other bodies of annual plants contain some lignin, they are not usually referred to as lignocellulosic materials. However, for purposes of the present invention, these are included within the term “lignocellulosic materials”.
BACKGROUND OF THE INVENTION
Although substantial strides have been made in recent years in the bonding of wood particles such as shown in the Stofko U.S. Pat. No. 4,944,823, which relates to the use of isocyanate based adhesives, wood particles are still mostly bonded by liquid adhesives produced by the condensation of formaldehyde with urea, melamine or mixtures thereof, or with phenol, resorcinol or mixtures thereof.
Procedures have also been developed to convert liquid phenolic resins to water-soluble solid powders by spray drying. Such spray-dried phenol-formaldehyde resins in powdered form are more economical than liquid phenol-formaldehyde resins in the manufacture of some composite wood products. Thus, such powdered phenol-formaldehyde resins are being manufactured and used in the oriented strand board industry. Spray drying, however, is not suitable for producing powdered resins from other liquid resins, such as urea-formaldehyde or other aldehyde condensation products.
As was the case in 1985 when the application which matured into Stofko '823 was filed, there is still a continuous incentive to reduce the costs involved in the manufacture of bonded wood products. Moreover, it would still be desirable to avoid the use of formaldehyde condensation products in view of the fact that such condensates can release formaldehyde which is at least an eye and mucosa irritant, which is carcinogenic, and which certainly has an undesirable odor. Many attempts have been made to solve these problems. One approach is disclosed in an earlier Stofko patent, namely U.S. Pat. No. 4,183,997, which discloses a binder for wood based on carbohydrates and catalyst.
The use of liquid isocyanate adhesives such as 4,4-diphenylmethane diisocyanate (hereinafter MDI) has remained difficult for the reasons set forth in the aforementioned Stofko U.S. Pat. No. '823. The above-mentioned spray drying which can be used to produce powdered phenol-formaldehyde resins is also not suitable for producing powdered resins from MDI. Thus, a main problem of the use of MDI as a bonding resin is that it is too concentrated; as a result it is very difficult to distribute small quantities of MDI over a large surface of lignocellulose materials to be bonded. New liquid spraying techniques have improved but not solved the problem of resin distribution over the bonding surface. Most attempts to extend MDI, such as by emulsification and incorporation of water, have failed.
So far, the only practical means of extending MDI is that disclosed in Stofko U.S. Pat. No. '823 wherein the MDI is extended by a suitably active particulate material, exemplified therein as preferably carbohydrates, especially sugars and starches, by intermixing and pre-reacting the liquid MDI with such an active solid particulate material or pasty material. The reaction produces a more fully activated powdery adhesive, e.g. a carbohydrate powder, which can be more easily distributed than liquid MDI and which provides excellent composite wood products such as plywood, particleboard, fiberboard, chipboard and the like.
Whereas excellent composite products can be formed according to the exemplified embodiments of Stofko U.S. Pat. No. '823, the preferred active materials disclosed in that patent, namely sugars and starches, have the significant disadvantage of being soluble or gellable in water, and the inorganic active materials do not work as well. Moreover, the bulk densities of the MDI-reacted sugars and starches of U.S. Pat. No. '823 are undesirably high so that a much greater amount of powdered binder is needed for effective bonding of lignocellulosic materials than is desirable; for example, sucrose has a specific volume of 1.8 cm
3
/g and wheat flour has a specific volume of 1.48 cm
3
/g.
As indicated above, the preferred active carriers for the MDI in Stofko U.S. Pat. No. '823, i.e. starches and sugars, are relatively heavy. To obtain an easily spreadable powdery binder using starch or sugar according to Stofko U.S. Pat. No. '823, it is necessary to have a starch:MDI ratio of at least 4:1, or a sucrose:MDI ratio of at least 9:1; otherwise the binder is either pasty or even a high viscosity liquid due to the inevitable presence of moisture and the fact that sugar crystals are water soluble and starch particles are gellable in water. Thus, another problem according to the examples of Stofko '823, if insufficient starch or sugar is present, i.e. less than the aforementioned ratios, is that the binder is in a form which is difficult to use, namely the undesirable pasty or high viscosity liquid form which is difficult to use.
At the present time, there are only two industrially viable methods for distributing polymeric MDI-based adhesives, namely by spraying liquid adhesives or by high shear blending of powdered adhesives, and an easily spreadable powder consistency cannot be made according to the starch and sugar examples of Stofko U.S. Pat. No. '823 using lower ratios of starch or sugar to MDI than those indicated above, as would be desirable.
Thus, the need still exists for improvements in bonding materials for lignocellulosic materials such as wood chips, wood fibers and other organic materials including straw, organic fibers, etc., or even for woodboard in the manufacture of plywood. In particular, a suitable way to increase the efficiency of MDI distribution to a better level than what is disclosed in Stofko '823 has heretofore not been found.
SUMMARY OF INVENTION
It is therefore an object of the present invention to overcome deficiencies in the prior art, such as indicated above. It is another object to provide improvements in the bonding of solid lignocellulosic materials. It is a further object to provide for improved wood bonding using an improved particulate isocyanate-based adhesive.
In general, the present invention relates to an improved process for producing an isocyanate-based adhesive in lightweight powder form which is reactive with lignocellulosic materials to bond such materials, and preferably one which not only bonds such lignocellulosic materials but also does not adhere to metals, as well as the resultant novel composition and its use. The process contemplates subjecting fine powders of crude cellulose polysaccharides to a modification step using an isocyanate, most preferably MDI, and preferably also in the presence of a suitable mold release agent e.g. a high melting point wax such as montan wax or zinc stearate, the modification including contacting the crude cellulose polysaccharide particles with the selected isocyanate in an amount sufficient to effectively produce the subject powder-form reactive cellulose polysaccharide/isocyanate adhesive binder, with or without the optional mold release agent being present. As a result, the isocyanate-activated cellulose polysaccharide particles provide for a large and significant extension of the isocyanate which in turn facilitates improved distribution of the resultant adhesive. If suitable lubricant is pr
Browdy and Neimark , P.L.L.C.
Carbocol Systems Inc.
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