Composite veneer or plywood panel
US 2831793 A
Description (OCR text may contain errors)
Apnl 22, 1958 A. ELMENDORF 2,831,793
COMPOSITE VENEER 0R PLYwooD PANEL Filed Nov. 2, 1955 I? vez? 02 ./rmz'i? Wife/M7029@ United States Patent O 2,831,793 COMPOSITE VENEER R PLYWOOD PANEL Armin Elmendorf, Winnetka, lll. Application November 2, 1955, Serial No. 544,575 13 Claims. (Cl. 154-453) This invention relates to a composite wood veneer panel, it being understood that wood veneer is, for convenience, hereinafter called venecn` One purpose of my invention is to provide a veneer panel having a compressed core consisting of bonded ligno-cellulose particles, or fibers.
Another purpose is to provide a veneer board or panel in which veneers containing open defects are used.
The present application is a continuation-in-part of my copending application, Serial No. 393,028, filed November 19, 1953, for Composite Veneer or Plywood Panels, now abandoned, and describes and claims the product of my copending application, Serial No. 538,661l filed October 5, 1955, for Process for Manufacturing Veneer Panels, which is a continuation-impart of my earlier application, Serial No. 366,968, filed July 9, 1953, now abandoned.
The product should be considered initially against the background of the industry.
The prolonged great demand for hardwood plywood for furniture, doors and wall paneling has now drained the forests of all the major countries of the world of most of their virgin timber suitable for conversion into veneer and plywood, and it will be many years before tree farming will again yield logs of the size and quality of those that have been consumed for that purpose. The second growth timber that must now be cut in ever increasing quantity contains many branches that reveal themselves as knots in the veneer, and if the knots are defective they generally fall out, causing open defects. Checks in the log ends, due to drying before the veneers can be cut, cause splits in the veneer, and such splits, when wide, are also revealed as open defects.
In conventional hardwood plywood manufacture, the veneers are dried and open defects are generally clipped out, thereby causing a serious waste, regretted by every plywood manufacturer, but accepted because all current processes of plywood manufacture require their removal. While open defects in the faces are permitted in the lowest grades of plywood, their presence greatly degrades the plywood. Open and exposed defects in the veneer core of 3-ply panels and in the cross-banding of 5-ply panels cannot be tolerated if the panels are given a high polish finish, because they show through.
The present invention seeks to alleviate the industrial situation described above. It aims at the complete utilizalion of the veneers that may contain open defects by plugging the defects of the veneers automatically durng manufacture, and in such a way that defects of any iize, shape or number can be accepted in the surface /eneer used.
Mending of open defects is becoming of increasing mportance on account of the progressive lowering of the luality of the logs available for conversion into veneer. l`he present invention is aimed at improving the situation n the hardwood plywood industry. In the manufacture )f the new plywood or veneered panels ot this invention 2,831,793 Patented Apr. 22, 1958 ICC the plugging of the surface layer openings is done simultaneously with the formation of the board.
It is not necessary to indicate any specific mechanism for making my product, as I employ equipment well known in the field. I illustrate typical products as follows, wherein:
Figure 1 is a perspective view, with parts in section, illustrating my product with an open defect filled by the core material;
Figure 2 illustrates my product in section, on an enlarged scale, illustrating a particle core, and with no defect showing in the veneer;
Figure 3 is a similar section, illustrating an open defect lled with fibrous core material; and
Figure 4 illustrates a 5-ply construction with a defect in the cross-banding, lilled by the core particles.
Like parts are indicated by like symbols throughout the specification and drawings.
Considering, first, the product of Figure 1, I use, in place of the middle veneer ply of conventional plywood, a composite fibrous core which may consist, for example, of ligno-cellulose particles such as hammermilled wood waste shavings, fibers or strands, bonded together with a binder under heat and pressure. The core may have a density comparable with that of the face veneers I usc, although the density may be higher. The core particles l employ may come from wood waste, and cost much less than the currently used veneer cores of the same thickness. The particles are bonded together with any suitable binder such as a protein adhesive or a synthetc resin of any type suitable for bonding wood such as urea or phenolic resins. When using hammermilled particles or strands or shavings I may advantageously employ the fines for the surface in contact with the veneer. These surface fines may be produced by rejecting all particles retained on a l0mesh screen, the larger particles being used in the interior of the core. By this I eliminate telegraphing of coarse particle through the veneer. I nd it advantageous to have iifty percent or more of the core particles in Contact with the veneer of a fineness to pass a ZO-mesh screen.
l have also found that great manufacturing economies result if the very thin veneers required are used green. I have found that satisfactory filling of open defects becomes possible if the face veneers are less than the standard thicknesses used throughout the plywood industry today, namely, 1&4 of an inch and l/g of an inch. My results are best achieved if the face veneers are less than ihn of an inch, herein referred to as very thin veneers. l have found veneers of MM of an inch highly satisfactory. My results are also generally best achieved if the veneers entering the press have a moisture content above the fiber saturation point, that is, above 25%.
ln view of the fact that, in my product, the core veneers are completely eliminated, and the amount of wood used for the two face veneers together is no more than a single ply of veneer in conventional plywood, and since single layers of thin veneer can be used at each face of my board, very substantial economies are achieved, resulting in a significant conservation of the timber supply. If veneer cores are used, in combination with their veneer faces, differences in density of the summer wood and the spring wood of an annual ring of the veneer core are liable to telegraph through the face veneers. In my finished board, the exposed veneer surfaces are smooth and fiat, and therefore require very little sanding so that veneers as thin as 1,4100 of an inch may be used. Where the veneer in contact with the fibrous core is of uneven thickness or density, or is roughly cut, the inequalities are taken up in the core and are not exteriorly apparent.
When the cores are made of line wood fibers or liber bundles bonded together, the best results are obtained if the fibers lie largely in planes generally parallel to the panel faces. When wood particles or shavings are used, I obtain a satisfactory product with phenolic resin or urea resin binders used in conjunction with wood particles that have passed through a l-mesh screen. when the binders used are in a proportion of to 10% of the weight of the wood particles. When resin-coated wood bers are used and the core density is between 0.7 and 1.0, the resin may be only 2% to 3% of the weight of fibers, with the resin coating the fibers.
My product permits good knothole filling, with the material of the core, if the hot plate pressure used compresses the core to a density slightly exceeding the density of the wood used. In practice, in my product, the density of the core always exceeds the density of the natural wood of the core particles, if low density woods are used. For the core I therefore prefer to use woods having a density below about 0.5 in order to obtain some com pression and yet produce a low density panel, that is. a panel having a density of 0.5 to 0.7.
I may use a wide variety of woods for my core material. ln fact, almost any species may bc employed. When making a low density panel I prefer, however, the use, for the core material, of low density woods such as cedar, aspen, Cottonwood, and redwood. By low density woods, l mean woods whose average density at l2% moisture is less than 0.5.
I have found a striking difference in the results obtained when thin green face veneers of angiosperrn species such as birch, elm, ash, maple, gum, and oak are used in place of gymnosperm species such as pine and nr, apparently due to the presence of pores in the former, the so-called hardwoods, whereas the latter contain no pores. The pores in hardwood veneers appear to permit ventilation or steam escape even though they are mainly parallel to the veneer faces, and so prevent blistering and veneer checking. The nonporous Woods are generally unsatisfactory for face veneers because they result in defective panels.
Superior bonding of green veneer to the particle core is obtained when using dry adhesive such as powdered resins applied to the veneer. The steam generated in the hot press causes the resin or binder to flow into the spaces between the particles or fibers near the surface. thereby providing a high density hard surface zone which functions like cross-banding veneer in a 5ply plywood panel. I thereby provide an excess of bonding material in the outer portions of the core, the thin veneer faces being firmly bonded to such outer portions of the core, the inner portion of the core having a smaller ratio of bonding component to the wood particles.
If the veneer contains open defects, as indicated in Figures l and 3, the openings are filled with core material. I nd the use of botanic fibers to be advantageous. with some of the fibers or fiber bundles of the core material extending from the core to the surface of the panel. By botanic fibers l mean the organic fibers of which wood is composed, or bundles of the same.
When green veneers are bonded, by conventional procedure, to conventional low density wood fiber boards of the insulation board type. they frequently check in service, due apparently to insufficient constraint at the inner surface. I have found that thin, green face veneers do not shrink or check during or after pressing and drying under pressure, when such veneers are bonded to the core of my product. Their width remains the same as when green. and there is no subsequent checking of the face veneers under any changes in humidity. Moreover, the steam generated from the veneer during pressing in a hot plate press plasticizes and softens the veneer so that it may be compressed by the hot plate pressure. The plasticizing and compressing of the thin face vencer. in contact with the smooth hot plate surfaces of my process. produces a superior surface for subsequent finishing with lacquers or other finishes.
In the manufacture of my product I subject the assembled components to simultaneous heat and pressure. thereby forcing adhesive between the particles or fibers near the surface to form a hard surface zone, and, at the same time, obtain the bonding together of the particles of the core, the plasticizing and compressing ofthe veneer. the drying of thc veneer, and the bonding of the vencer to the cere. lt should be kept in mind that a very smooth outer surface of the veneer results from the subjection of the vcnccr to pressure at a time when it is directly in contact with n smooth metal plate. With some veneers a pressure of 1.50 p. s. i. is adequate to compress them if they contain moisture in excess of 25%. If open defects are present in the veneer the Filling of the defects also takes place simultaneously, with the above mentioned results. lt will be clear that great savings in manufac turing costs over conventional plywood manufacture are thereby obtained.
The boards may be of various sizes, and may be of substantial width and length. As examples of practical dimensions I may mention boards of 4 feet by 8 feet. In making boards of such size l find it especially important to be able to use the face veneers in one piece. This is practically impossible with the use of veneers of the specified thickness, that are dry, as it is practically impossible to produce enc-piece dry veneers of this size. without splitting them.
In my product, when green vencer is used, and it is subjected to pressure in the course of making the product, the veneer is of the same across-the-grain width as in the green condition. Under many circumstances, and with many woods, it is of substantially' less than its original green thickness. However, the veneers of some porous woods that are heavy and dense, such as birch or maple, compress much less than veneers of some of the softer. porous woods, such as aspen or basswood. In the case of birch. for example, the compression may be only about .003 of an inch in veneers .015 of an inch thick. In the case of soft veneers, where the original thickness may be 0.30 of an inch, the same veneer, subjected to the condition of the manufacture of my product, may be only about .0l7 of an inch thick.
I find it important, in my product, to have a zone in the wood particle core, adjacent the veneer, in which the ratio of the bonding component to the wood particles is substantially higher than in the interior of the core. This result is obtained, in my product, when some of the bonding adhesive used for the veneer is forced into the spaces between the wood bers or particles at or near the surface. This result appears to be facilitated by the steam generated from the moisture of the green veneers, so that a hard foundation layer results, to which the face veneer is bonded. Itis the strength of this zone which prevents the veneer from checking.
Referring to the drawings in somewhat greater detail. 1 indicates a core, in my completed product, of particles or fibers consolidated by the above-described application of heat and pressure. The density of this core ranges, generally, from .5 to 1.0. 2, 2 indicate the zones in which the ratio of bonding component to wood particles is substantially higher than in the interior of the panel. 3, 3 indicate the surface layers of face veneer. In Figure l, 4 indicates an open defect or aperture in one of the face vener surface layers 3. 5 indicates the mass of core material which fills the fault 4, and has a flat outer surface flush with the flat outer surface of the layer 3 in which a fault 4 occurs. If the binder for the veneer is applied to the pre-pressed core mat, the results are as shown in Figures l and 3, and the high resin zone extends into the open defect in the veneer. If, however, the adhesive is applied to the veneer, the high resin zone stops at the edge of the defect and the lower resin oore extends into the defect. In the latter case there is less danger of bonding to the metal plate at the defect.
Figure 2 represents a substantial enlargement of part of the structure of Figure l. In it one of the surface layers of face veneer 3 is illustrated in substantially larger scale than in the more or less diagrammatic showing of Figure l. It will be evident that the outer surface 3a is fiat and plane, whereas the inner surface 3b is not strictly parallel with the outer surface, and is not truly plane. The irregularities may be somewhat exaggerated in the drawing, but what I wish to indicate is that, to the extent that there are irregularities or differences of thickness in the veneer, they are taken up in the interior of my product. Some ring-porous veneers are of uneven densities in the annual ring structure and compress unevenly because of such differences in density. Such compression does not cause any surface unevenness. The fiat metal surface with which the veneer is in contact during the manufacture of the product provides the true, plane, outer surface 3a desired for finishing, and the core follows the uneven inner surface of the veneer.
As to all of the figures, it will be understood that I do not wish to limit myself, or intend to limit myself, to any particular type or range of particles, except so far as I limit myself specifically in my claims. Figure l may be taken diagrammatically, in that I may employ core particles such as are indicated at 6 in Figure 2, or core fibers or strands such as are indicated at 7 in Figure 3. By strands I mean thin, narrow, long shavings with parallel surfaces. I may also use ordinary thin shavings. [n Figure 3, I illustrate, at 8, an open defect in the face veneer 3 into which the fibers or particles extend. While Figure 3 is to be taken as generally diagrammatic, it is ntended to indicate a disposition of the fibers or fiber Jundlcs or strands or shavings in general parallelism with he outer surface 3a of the final product. I indicate, also, n Figures 2 and 3, one of the outer zones of the core in vhich the ratio of the bonding component to the wood articles or fibers is substantially higher than in the ineror of the core. This zone is indicated at 6a in Figlre 2, and at 7a in Figure 3.
In Figure 4, I illustrate substantially the board as hown in Figure l, except that, in the place of single ayers of face veneer, I illustrate at one face of the prodct a cross-banding veneer layer l0, and at the other ace a cross-banding layer 11. It will be noted, also, that show the cross-banding layer of veneer 10 as having an pen defect 12 filled with core material 13, this core ma- :rial being covered by the face veneer 3.
It will be realized that I have described and shown erein a practical, efficient, and useful product. It will e realized, however, that the details of the product and s components are subject to substantial variation with- Jt departing from the spirit of my invention. I therere wish my description and drawings to be taken as in broad sense illustrative and diagrammatic, rather than 1 limiting me to the specific disclosure herein. For
iample, a wide variety of woods may be employed, havg different compressibility. The fibrous wood particles the core may be varied substantially in size and shape. The type of bonding components used may be widely ried, as may the distribution of the bonding component the core. It is important, however, that the outer surces of the board be flat and parallel, even though the ner surfaces of the veneer layers may contact or abut e core with a surface departing substantially from the me. Irregularities of compression of the veneer layers e taken up within the interior of the board. The core bonded together and is bonded to the veneer layers, d, preferably, the ratio of the bonding component to e wood particles is higher adjacent the veneer layers in in the interior of the panel. While I speak generally thin veneers, I prefer to use veneers of less than 7&0 an inch in thickness, and have found veneers of 1,4m of inch in thickness to be practical.
[n the manufacture of panels inch or more in thickis, and where accuracy of thickness is important, I
`fer to bond two panels, each having veneer on one face, back to back thereby producing a 2-ply core with a layer of adhesive between the plies. In that case the thickness of the panel can be controlled by first sanding or planing the back of each half and the thin veneer faces need not be excessively sanded.
l. A composite wood veneer panel including a brous ligno-cellulose particle core consisting of fibrous woody particles bonded together, and a thin porous wood veneer layer bonded to a surface of the core, the veneer layer being dry but having the same across-the-grain width as the width of the same veneer in green condition, the veneer layer having a thickness of the order of M50 to 1/100 of an inch, the core including a surface zone more dense than the interior of the core, at least 50% of the particles in contact with the veneer having a fineness such as to pass a 20-mesh screen, the ratio of bonding component to wood particles in the surface zone being higher than the same ratio in the interior of the core, the veneer layer being bonded to the exterior of said dense surface zone, the outer surface of the veneer layer being plane, the inner surface in contact with the core `being uneven, whereby inequalities in thickness of the veneer layer are taken up by the outer surface of the core.
2. A composite wood veneer panel including a fibrous ligne-cellulose particle core consisting of fibrous woody particles bonded together, and a thin porous angiosperrn wood veneer surface layer bonded to a surface of the core, the veneer layer being dry but having the same across-the-grain width as in the green condition, the veneer layer having a thickness of the order of 1/30 to A00 of an inch, the core including a surface zone more dense than the interior of the core, at least 50% of the particles in contact with the veneer having a fineness such as to pass a 20-mesh screen, the ratio of bonding component to wood particles in the surface zone being higher than the same ratio in the interior of the core, the veneer layer being bonded to the exterior of said dense surface zone, the wood from which the core particles are derived having a density less than 0.5, the core exceeding in density the wood from which the core particles are derived.
3. A composite wood veneer panel including a fibrous ligno-cellulose particle core consisting of fibrous woody particles bonded together, and a thin, porous angiosperm wood veneer surface layer bonded to a surface of the core, the veneer layer being dry but having the same across-the-grain width as in the green condition, the veneer layer having a thickness of the order of l@ to M00 of an inch, the core including a surface zone more dense than the interior of the core, at least 50% of the particles in contact with the veneer having a fineness such as to pass a 20mesh screen, the ratio of bonding cornponent to wood particles in the surface zone being higher than the sume ratio in the interior of the core, the veneer layer Ibeing bonded to the exterior of said dense surface zone, the wood from which the core particles are derived having a density less than 0.5 and the core having a density of 0.5 to 0.7.
4. The product of claim 1, in which the veneer surface layer is compressed to less than its original thickness.
5. The product of claim 1, in which the veneer surface layer has openings into which the core extends, to an outer plane flush with the outer surface of the veneer layer.
6. The product of claim 2, in which the veneer surface layer has openings into which the core extends, to an outer plane ush with the outer surface of the veneer layer.
7. The product of claim l, in which a layer of surface veneer is bonded to each side surface of the core.
8. The product of claim 2, in which a layer of surface veneer is bonded to each side surface of the core.
9. A composite wood veneer panel including a fibrous ligno-cellulose particle core consisting of fibrous Woody particles bonded together, and a thin wood veneer layer of the angiosperm species bonded to a surface of the core, the veneer layer having a thickness of the order of V50 to A00 of an inch, the veneer layer being compressed so as to have a thickness less than its original wood thickness, the veneer layer being dry but having the same across-the-grain width as the width of the same veneer in the green condition, the core including n surface zone more dense than the interior ot' the core, at leaf-,L 50% of the particles in contact with the veneer having a fineness such as to pass a 20-mesh screen, the ratio of bonding component to wood particles in the surface zone being higher than the same ratio in the interior of the core, the veneer layer being bonded to the ext-:rior of said dense surface zone, and having a density of 0.7 to 1.0.
10. A composite wood veneer panel including two cornponents bonded back to back, each component including a fibrous ligne-cellulose particle core consisting of fibrons woody particles bonded together, and a thin potous angiosperm wood veneer layer bonded to a surface of the core, the veneer layer being dry but having the same across-the-grain width as the width of the same veneer in green condition, the veneer layer having a thickness of the order of 1/0 to 1,6m, of an inch. the core including a surface zone more dense than the interior of the core, at least 50% of the particles in contact with the veneer having a fineness such as to pass a 20-mesh screen, the `ratio of bonding component to wood particles in the surface zone being higher than the same ratio in the interior of the core, the veneer layer being bonded to the exterior of said dense surface zone, the Outer surface of the veneer layer being plane, the cores of the two components being bonded together so that the veneer layer of each component is exposed.
11. A composite wood veneer panel as set forth in claim 1, wherein the fibrous woody particles in the interior of the core include wood shavings.
l2. A composite wood veneer panel as set forth in claim I, wherein the fibrous woody particles in the interior of the core include wood fiber bundles bonded together.
13. A composite wood veneer panel as set forth in iaim 1, wherein the fibrous woody particles in the iniuiior of the core include wood strands.
References Cited in the le of this patent UNlTED STATES PATENTS 2,066,734 Loetscher Jan. 5, 1937 2,124,921 Lederer July 26, 1938 2,337,792 Yokell Dec. 28, 1943 2.356,625 Schumann Aug. 22, 1947 2,419,614 Weich Apr. 29, 1947 2,5 4,318 Elmendorf Iuly 4, 1950 2,542,025 Goss Feb. 20, 1951 2,545,603 Beyers et ai Mar. 20, 1951 2,642,371 Fahrni June 16, 1953 2,698,271 Clark Dec. 28, 1954 2,708,296 Soehner May 17, 1955