US3639200A

US3639200A - Textured wood panel

Info

Publication number: US3639200A
Authority: US
Inventors: Armin Elmendorf; Thomas W Vaughan
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-12-19
Filing date: 1969-12-19
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

The invention relates to a ligno-cellulosic building board having a nonrepetitive textured surface on at least one side. This side consists of a layer of ligno-cellulosic particles with elevations and depressions, the specific gravity of the particles of the elevations being substantially the same as the specific gravity of the particles in the depressions. The density of the fibers at the surface has therefore been equalized over the entire area of the board. In one form of the invention a layer of coarse particles is used, the sharpness of the edges of the coarse particles being concealed with fine particles. The product is produced by pressing a layer of binder coated ligno-cellulosic particles on a substrate in a hot plate press with a cushion, preferably of silicone rubber, between the hot platen of the press and the layer of particles.

Description

United States Patent Elmendori et al.

[ 5] Feb.1,1972

[541 TEXTURED WOOD PANEL [22] Filed: Dec. 19,1969

[2]] Appl.No.: 889,842

Related U.S. Application Data [63] Continuation of Ser. No. 403,448, Oct. 9, 1964, abandoned.

[52] U.S.Cl v.161/ll6,144/320, 144/328, 156/62.2,156/154,156/219,156/323,161/151, 161/158, 161/162, 161/164, 161/170, 264/113,

[51] Int. Cl. ..B271 11/00, B32b 5/16, B321) 21/02, B32b 21/12,B32b 21/14 [58] Field ofSearch ..161/56,116,41,60,162,151,

161/158, 168-170, 164, DIG. 3; 264/112, 113, 119, 128, 162; 156/622, 219, 220, 279, 289, 323, 154; 144/320, 328

2,301,951 11/1942 lsman ..264/113 X 2,431,720 12/1947 Willey ..l6l/D1G. 3 2,713,014 7/1955 Johnson ..161/56 X 2,766,162 10/1956 Boehm et al.. .l6l/l70 UX 3,188,367 6/1965 Gottschalk ..264/1 13 X Primary Examiner-William A. Powell Attorney-Townsend and Townsend [57] ABSTRACT The invention relates to a ligno-cellulosic building board having a nonrepetitive textured surface on at least one side. This side consists of a layer of ligno-cellulosic particles with elevations and depressions, the specific gravity of the particles of the elevations being substantially the same as the specific gravity of the particles in the depressions. The density of the fibers at the surface has therefore been equalized over the entire area of the board. In one form of the invention a layer of coarse particles is used, the sharpness of the edges of the coarse particles being concealed with fine particles.

The product is produced by pressing a layer of binder coated ligno-cellulosic particles on a substrate in a hot plate press with a cushion, preferably of silicone rubber, between the hot platen of the press and the layer of particles.

7 Claims, 5 Drawing Figures TEXTURED WOOD PANEL This application is a continuation of application Ser. No. 403,448, filed Oct. 9, 1964, entitled Textured Panel and Method of Making Same, now abandoned. The present invention relates to panels having a textured surface which is composed in part or entirely of ligno-cellulosic fibers. The invention eliminates some of the liabilities inherent in the surfaces of particle boards and plywood when such boards are used on building exteriors. I

The invention includes a body portion or substrate and a surface layer which may be added to the substrate or may be part of the substrate. The density of the fibers at the surface has been equalized over the entire area of the board as will be shown in detail below. Whereas a smooth flat surface is universally sought in the manufacture of particle boards and plywood, the surface of the present invention has a texture with many elevated areas and valleys between the elevations. The surface layer generally consists of wood shavings or other ligno-cellulosic particles such as strands, splinters, or flakes bonded together with a synthetic resin. The surface layer of the invention may be added to a board product such as plywood or gypsum board, or it may be part of the body of a board such as particle board or an embedded fiberboard."

Particle boards are well-known products of manufacture and therefore do not require description. Embedded fiberboard is a type of particle board made of wood shavings or strands bonded with an inorganic binder. Particle boards have a smooth surface and are generally used as a base for veneers or high-pressure lamina in furniture, or as an underlayment under flexible floor coverings in the building industry. The surface of embedded fiber board is generally not as smooth as that of particle board because it is not sanded, and it reveals the strands or shavings of which it is made. Embedded fiberboard is primarily used for building exteriors where it is exposed to the weather because it is more weather resistant than most board products exposed to the weather.

Manufacture of Douglas fir plywood in the Pacific Northwest is a large industry and while some of the plywood produced is used for building exteriors, it has the serious liability that the face veneer checks or cracks in the'weather. Fissures such as these cause paint to crack and the surface to disintegrate.

Most particle boards are made of shavings or splinters. When exposed to the weather the board surface becomes rough, even though painted on account of differences in expansion of adjacent or neighboring surface particles when exposed to the weather. This phenomenon is sometimes referred to as popping. It results in deterioration of the panel surface and has long militated against the use of particle boards for building exteriors.

The present invention has for its primary purpose the elimination of the liabilities described above when particle boards and plywood are used for building exteriors. It has a further purpose in the production'of a texture which has eye appeal. The resultant panel surface no longer resembles flakes or shavings, in the case of particle boards, or veneer, in the case of plywood. The texture more nearly resembles that of a porous stone and, consequently, appeals to builders.

In describing the phenomenon associated with the production of the present invention, it is important to examine the basic structure of wood and the physics of shrinkage and expansion. It requires a clear picture of the changes that take place in the wood fiber of which wood is composed when the fiber is subjected to heat and pressure and when it is subsequently exposed to moisture followed by drying.

The wood fiber varies in size and composition with the species, rate of growth of the tree, and many other factors. It is basically a fine tube with pointed and closed ends, the length of the tube being perhaps 100 times as great as its diameter. The diameter may be about one one-thousandths inch and its length from one-sixteenth to one-tenth inch. It is hollow, the cavity within being known as the lumen. When wood, in its natural state, expands or contracts due to changes in its moisture content this is due to the absorption or loss of moisture in walls of the fiber and not due to free water in the lumen. On the other hand, when particle boards expand in thickness due to wetting, this is generally due partly to the change in thickness of the walls of the fiber or cell but primarily to the straightening out of the fibers that have been crushed or bent in compacting masses of flakes or shavings during manufacture. Upon wetting, the distorted fibers tend to resume their original shape. Hence, the expansion of wood substance in particle boards may greatly exceed the expansion of wood in its natural state. Studies made of the density of particle boards have shown that the specific gravity of the board at or near the surface is greater than that at the board center, leading to the conclusion that the fibers near the surface have been crushed more than those near the mid plane.

The flakes or shavings of which particle board is generally made may range in thickness from about ten-thousandths to twenty-five-thousandths inch. In other words, the thickness of the shaving, which to eye appears to be thin, may be from 10 to 25 times the diameter of the fiber. v

While particle boards are generally made of shavings or flakes of wood, the surface layers of the present invention may also be made of bundles of wood fibers. Particles of the shaving type are preferred but the boards may also be made of flakes, splinters or strands. As in the manufacture of all particle boards, the component flakes are bonded together with an appropriate resin, the bonding being achieved in a hot plate press. The density of the wood substance in the surfaces of particle boards is always higher than the density of the original wood as produced by nature. The specific gravity of a particle board made of wood shavings a specific gravity of 0.40 may be 0.60, and the specific gravity of the surface layers of the same particle boards may be as high as 0.8, or even higher. This indicates that the wood fibers have been crushed. Having been crushed, they expand when moistened. lf some particles have been crushed more than others, they will expand more than others, and at spots where a number of shavings or strands cross there may be a substantial stack of fibers that cross each other, all superimposed in layers and all crushed. Since the surface particles are randomly distributed and are of various sizes, numerous stacks are formed in depositing the flakes or strands, and the expansion that takes place upon wetting results in an uneven surface. Even when oriented into comparative parallelism many strands cross each other and build up such stacks. A surface which was originally flat and smooth takes on a pebbled appearance when it is dampened, and the surface remains pebbled when the board dries. Such uneven expansion and contraction causes paint disintegration.

Particle board surfaces which are smooth are nevertheless composed of particles of varying size and varying degrees of compression. The density of the wood substance at or near the surface, when very small areas are concerned, will vary considerably across the surface of a board. The fibers of particles that have been highly compressed will cause small areas to show a substantially higher specific gravity than neighboring small areas where the fibers were not so highly compressed. The compressive stresses exerted by hot pressplates over small areas where strands or fibers cross are considerably greater than in neighboring small areas only partly filled with wood substance.

By placing a thin release sheet over a smooth substrate such as plywood, then randomly distributing resin-coated particles such as shavings over the release sheet, and thereupon compacting such a layer with hot plate pressure, the plywood surface is indented irregularly over the entire surface. This observation is made upon removing the release sheet with its layer of compacted particles. At some spots the plywood is deeply indented and in other spots not the slightest indentation is to be observed. Where the dents occur the compressive strength of the plywood has been exceeded and the surface fibers of the veneer have been crushed. From this, it must be concluded that fibers of the particles over spots of noticeable indentation have also been crushed since they were of the same wood as the veneer. They were subjected to a specific pressure exceeding the crushing strength of the fiber. By specific pressure we mean pressure per unit area, and in this case, per very small area, say, per square millimeter. Having been subjected to crushing pressure, such particles will, upon subsequent humidification, expand more than the particles in small adjacent areas which were subjected to lower specific pressure due perhaps to the fact that in the neighboring areas the particles were very loosely distributed and possibly smaller. The effect is that the surface of the lamina becomes pebbled and rough.

If as in the present invention a cushion such as a layer of silicone rubber, say, about one-eighth inch thick, is placed over the loosely felted layer of resin-coated particles, which may be about three-eighths inch thick, and hot plate pressure is applied to the rubber, the coarse particles at spots where fibers are stacked in great number can press into the rubber so that the specific pressure on these particles is reduced by the cushion, and more of the total pressure is carried by the neighboring particles, which may have been loosely felted. The specific pressure on the loosely felted particles is increased, and these will, consequently, be compacted more than originally when no rubber cushion was used. If the cushion pressure is maintained until the binder has set, then the surface, upon removal of the pressure, is not flat but has the contour assumed by the indented rubber during pressing.

If a layer of particles and a rubber cushion is placed over a thin flexible release sheet on plywood substrate and the same overall hot plate pressure is applied as in the test in which no cushion was used, we have noted that the plywood is no long indented, leading to the conclusion that the specific pressure, that is, the pressure over small areas (areas smaller than that of the small particles) has been substantially equalized over the entire area. The specific gravity of the wood substance in the large particles that were compressed when smooth plate pressure was applied without a rubber cushion is reduced when a rubber cushion is used, and the specific gravity at the previous low density areas is increased. Consequently, when the fibers at a surface that has been subjected to equalized pressure are humidified the resultant expansion of the large particles per unit of thickness is substantially the same as the expansion in the neighboring areas. The expansion over small areas over the entire surface has been made uniform. In other words, the expansion of the fibers in the wood substance at the bulges wood particles such as fine sawdust is placed on the release sheet as a cushion. The release sheet with its bed of fine particles is and compacted particles is not substantially different from the expansion at the depressions or valleys. The difference in the density of the compacted particles at the elevations and of the particles in the valleys has been greatly reduced from that of the same or similar particles similarly placed and compacted under hot plate pressure without a cushion.

The same result can be obtained if in place of a rubber cushion over the particles we use a thin flexible and stretchable release sheet that can withstand the temperatures of the plates, and a bed of small uncoated bed of fine particles is then simply lifted off after the resin binder has set, leaving the bumpy surface of equalized density.

Panels of the present invention, whether the body of the board is a particle board, embedded fiberboard, or plywood, all have a relief surface with numerous elevations and valleys between the elevations. If they are manufactured so as to obtain an equalized density over the entire surface such a surface differs from that obtained when an embossing plate is used, the plate having a pattern to be imprinted or pressed on to the ligno-cellulosic panel. There are several basic differences between an embossed panel and the panel of the present invention besides the fact that the specific gravity of the particles at the surface of an embossed panel is not uniform over the entire area being higher in the valleys than in the elevations. A further major difference lies in the fact that the pattern obtained with theembossing plate is repeated with each panel produced, whereas the pattern obtained when the surface pressure is equalized as described is never repeated. No

matter how many thousands of panels of the present invention are produced, no two square feet will ever have exactly the same pattern. The situation is analogous to that which exists in the manufacture of plywood panels. The figure or grain of no two pieces of veneer is ever exactly the same. Similarly, the configuration of the surface of equalized density on two boards is never identically the same. We therefore refer to the configuration of the panel surface as nonrepetitive, and since it has elevations and depressions, we refer to the surface as having a relief texture.

A particle board having a surface of equalized density can be so made that the fibers at the surface are bonded together simultaneously with the bonding of the fibers or shavings of the body of the board. The same results may, however, be obtained when a layer of surface shavings of equalized density is formed on a base panel such as plywood or gypsum board or even particle board previously made. The shrinkage of the surface lamina in the plane of the board after leaving the press is very small and, consequently, when such a lamina is produced on a thick plywood panel on only one side, the resultant panel is still commercially flat.

When strands are oriented into parallelism with numerous strands crossing other strands at small angles, shrinkage stresses after leaving the press across the grain of the strands are substantially greater than in the direction of the strands. In applying such an oriented strand lamina on to a plywood panel, it is therefore advisable to place the strands or splinters so that they cross the grain of the outer veneer to which the lamina is bonded.

If the surface of equalized density is obtained in the original pressing of a particle board, it is best to equalize the density of the particles on both the back side and front side simultaneously in the pressing.

Equalizing the pressure on the surface particles by cushion pressure results in another improvement in the surface. It has been found that surface fibers can no longer be scuffed off as readily as in boards pressed with hot plate pressure and without a cushion. Flakes at the surface have been bent straplike, over other flakes thereby restraining the latter in their tendency to expand. They have been well bonded and so cannot be torn off by scuffing, and being well bonded at the edges of flakes that tend to expand they also inhibit the expansion of the latter.

Other features and advantages of the present invention will become more apparent upon a perusal of the following description taken in conjunction with the accompanying drawings wherein similar characters of reference refer to like structure in each of the several views.

FIG. 1 is an elevational sectionalview of an assembly of elements in a press in accordance with the present invention.

FIG. 2 is a view similar to FIG. 1 of an alternative assembly.

FIG." 3 is a view similar to FIG. 1 of still another alternative assembly.

FIG. 4 is an elevational sectional view of a panel produced in accordance with the present invention.

FIG. 5 is a plan view of the structure shown in FIG. 4 with the tops of the surface elevations removed.

FIG. 1 shows an assembly in a hot plate press in which an equalized density pattern is obtained on one surface of a plywood panel. In this figure, I shows the plywood panel, 2 the ligno-cellulosic particles such as shavings or strands coated with a synthetic resin, 3 a rubber cushion, and 4, metal cauls on the top and bottom of the assembly. The drawing shows the assembly under pressure between press platens II and represents a cross section through the assembly illustrating the unevenness of the inner surface of the rubber cushion and the matching. surface, namely, the outer surface of the layer of wood particles.

Tests made to determine the amount of particles in the form of shavings or strands bonded together with a synthetic resin required on a Douglas fir plywood panel sufficient to prevent checking of the plywood show that at least about pounds of such wood particles, namely shavings and strands, must be used per thousand square feet of panel surface in order to prevent checking of the face veneer. Table I below gives the results of certain tests.

The tests were made on three-cighths inch Douglas fir plywood faced with shavings bonded together with melaminefortified urea, compacted to equalized density.

'lesl specimens 6 inch x10 inch were subjected to 10 cycles of soaking in water for 4 hours then oven-drying for 20 hours. Table I gives the surface composition, the amount of surface material and the number of checks in the specimen after the test. Where two lamina compositions are indicated the finer composition covers the exposed surface.

TABLE 1 Weight, pounds Num- Spccimeu per M ber of Number Surface lamina composition sq. it. checks 1, 2, 3 t. No facing 0 1 120 4 Sanding dust... 65 40 Sanding dust- 130 Planet shavings and sanding dust 115 21 Planer shavings and sanding dust 195 0 Coarse and fine shavings 170 0 Router shavings and fine shavings 170 0 Pole splinters and fine shavings 170 0 Planer shavings and fine shavings 150 5 Router shavings. A 105 16 Redwood splinters 65 23 Redwood shaving 105 25 Redwood shavings 130 4 Redwood shavings and sanding dus A 170 0 1 Average.

In place of the silicone rubber cushion the same effect can he obtained by placing a thin synthetic rubber sheet or other stretchable release sheet between the particles and a cushion bed of uncouted wood particles such as fine sawdust. Upon removal from the press after the resin has set. the membrane is easily separated from the textured surface of the consolidated particles. The sawdust and the membrane can be used over again.

FIG. 2 shows an assembly in a hot press in which a mat of resin-coated wood particles 5 is compacted between rubber cushions 6, a cushion being used on each side. If the resin is cured while the particles are under compression the latter are bonded together in the configuration imparted to the surface by the yielding rubber cushion. In place of the rubber cushion the combination of a thin membrane or release sheet 7 of any type which will not bond to the particles and a cushion of fine sawdust or other compressible waste material may be used in place of the silicone rubber illustrated at 6. The same assembly is also applicable to the manufacture of an embedded fiberboard in which the particles are shavings, or strands, and the binder is Portland cement. Pressure must be maintained until the cement has set. This may take from 8 to 12 hours. A stack of such assemblies is built up and held under pressure as by means of retaining clamp, introduced while the stack is under pressure.

FIG. 3 shows the preferred method of producing boards of shavings bonded together with an inorganic binder. It eliminates the need for a metal caul between each pair of mats. In place of a metal caul a thin stretchable release sheet 9 is sued. Since Portland cement does not set rapidly, at large stack of mats of this type can be assembled at one time and all the mats pressed together simultaneously. Pressure is maintained by means of retaining clamps until the cement has set. Upon release of the pressure the surface of the solidified mats has taken on an unevened textured surface of equalized density as described. The outer surfaces of the stack may be provided with a cushion of sawdust. All of the inner surfaces are distorted to the extent required to obtain equalized specific pressure. Many different kinds of release sheets may be used such as vinyl, polyethylene films, or synthetic rubber. When the cement has set the pressure is released and the panels are separated at the release sheets which are used over again. The panel are then dried and trimmed.

FIGS. 4 and 5 illustrate an important variation of the surface of the panels produced in any of the previous assemblies. After the binding resin or cement has set, the tops of the elevations are removed as by sanding. As a result, the elevations all have a fiat surface in one plane. The material above the plane XX has been sanded or planed off. The portion removed is shown at 10. FIG. 5 shows a plan view of a panel having flat facets it) produced by sanding the elevations illustrated in cross section in FIG. 4. It is this texture of random configuration which has the aesthetic appeal found desirable by discriminating builders.

It is well known that when shavings are used on the surface of particle boards conventionally manufactured, the edges of the shavings or flakes are usually sharply delineated. I have found it desirable to eliminate such sharp outlines and to improve the texture thereby. Thls is readily done by distributing a layer of fine wood particles such as small thin flakes or sawdust or other small particles and a binder over the entire surface of the coarse particle layer before pressing. When small particles are bonded together it is necessary to increase the resin content. For that reason a resin content of 10 to 15 percent may be required, when urea adhesive is used as the binder. The amount of fine particles of this kind required to conceal the sharpness of the edges of the particles is substan' tially less than that of the larger particles used. The overall thickness of the layer of particles of equalized density may be about one-sixteenth inch.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity and understanding, it is understood that certain modifications may be practiced within the spirit of the invention as limited only by the scope of the appended claims.

We claim:

I. A building board having a nonrepetitive relief texture on at least one surface comprising: a substrate formed at least in part of ligno-cellulosic fibers and having a layer of con solidated ligno-cellulosic particles randomly distributed on said surface to present a wood substance thereon, the particles being bonded together and to the substrate, the surface having numerous elevations and depressions, the elevations being at areas in which the fibers were stacked in greater number than in adjacent areas in the original unconsolidated state and the depressions being at the areas containing fewer fibers in the original unconsolidated state, the specific gravity of the wood substance at the elevations and that of the wood substance at the adjacent depressions being substantially the same.

2. The ligno-cellulosic building board in accordance with claim 1, wherein the substrate is a plywood panel that checks in the weather when exposed, the layer of particles weighing at least about pounds per 1000 sq. ft. of surface.

3. A building board as set forth in claim ll, wherein said substrate includes a plywood panel that checks in the weather when exposed, said particles including wood shavings weighing at least about I50 pounds per 1,000 square feet of surface.

4. A ligno-cellulosic building board having a nonrepetitive texture on at least one side, said side of the board consisting of consolidated ligno-cellulosic particles presenting a wood substance with elevations and depressions, the elevations being at areas in which the fibers were stacked in greater number than in adjacent areas in the original unconsolidated state, and the depressions being at the areas containing fewer fibers in the original unconsolidated state, the specific gravity of the wood substance at the elevations being substantially the same as the specific gravity of the wood substance at the depressions.

5. A ligno-cellulosic building board in accordance with claim 4, wherein the textured side of said board consists of a layer of coarse ligno-cellulosic particles covered with a thin layer of fine ligno-cellulosic particles, the sharpness of the edges of the coarse particles being concealed with the fine particles.

6. The building board in accordancewith claim 4, wherein each elevation has a flat surface and the flat surfaces of ad jacent elevations lie in the same plane.

7. The building board in accordance with claim 4, wherein the board is formed of ligno-cellulosic particles from said one side to the opposite side thereof.

IOIOZI 045i

Claims

2. The ligno-cellulosic building board in accordance with claim 1, wherein the substrate is a plywood panel that checks in the weather when exposed, the layer of particles weighing at least about 150 pounds per 1000 sq. ft. of surface.
3. A building board as set forth in claim 1, wherein said substrate includes a plywood panel that checks in the weather when exposed, said particles including wood shavings weighing at least about 150 pounds per 1,000 square feet of surface.
4. A ligno-cellulosic building board having a nonrepetitive texture on at least one side, said side of the board consisting of consolidated ligno-cellulosic particles presenting a wood substance with elevations and depressions, the elevations being at areas in which the fibers were stacked in greater number than in adjacent areas in the original unconsolidated state, and the depressions being at the areas containing fewer fibers in the original unconsolidated state, the specific gravity of the wood substance at the elevations being substantially the same as the specific gravity of the wood substance at the depressions.
5. A ligno-cellulosic building board in accordance with claim 4, wherein the textured side of said board consists of a layer of coarse ligno-cellulosic particles covered with a thin layer of fine ligno-cellulosic particles, the sharpness of the edges of the coarse particles being concealed with the fine particles.
6. The building board in accordance with claim 4, wherein each elevation has a flat surface and the flat surfaces of adjacent elevations lie in the same plane.
7. The building board in accordance with claim 4, wherein the board is formed of ligno-cellulosic particles from said one side to the opposite side thereof.