US3542641A

US3542641A - Method of making water laid,stained wood sheet

Info

Publication number: US3542641A
Application number: US687282A
Authority: US
Inventors: Merle J Showalter; Richard J Hohenwarter
Original assignee: Armstrong Cork Co
Current assignee: Armstrong World Industries Inc
Priority date: 1967-12-01
Filing date: 1967-12-01
Publication date: 1970-11-24
Anticipated expiration: 1987-11-24

Description

Nqv. 24', 1970 M. J/SHOWAL'I'ER T L METHOD OF MAKING WATER LAID, STAINED WOOD SHEET med Dec 1; 1967 means 'INVENTORS MERLE J- SHOWALTER mcrmao J- nonznwmraa PRODUCT .M Mr R S; D A m W L G Y R J l MR U B m m m 5 W N an Y1. .l m m a S 5 MM D w .W m R N E I T T m as Ew 1 m GRAIN PATTERN .EMPHASIZED BY DIFFERENT COLORING,

sues? :OF WATER-LAID wooo FIBERS ATTORNEY United States Patent O 3,542,641 METHOD OF MAKING WATER LAID, STAINED WOOD SHEET Merle J. Showalter and Richard J. Hohenwarter, Lancaster, Pa., assignors to Armstrong Cork C0., Lancaster, Pa., a corporation of Pennsylvania Filed Dec. 1, 1967, Ser. No. 687,282 Int. Cl. D21f 11/00 U.S. Cl. 162-134 3 Claims ABSTRACT OF THE DISCLOSURE Method, and product, of making a patterned wood sheet by forming a sheet of wood fibers from an aqueous slurry and impressing a pattern into one face of the sheet by embossing with a die having lands and valleys to produce the desired pattern. The patterning step produces regions of increased density in the sheet. There is then applied over the entire surface of the sheet a liquid stain adapted to be absorbed to a different extent in the regions of reduced density as opposed to the regions of higher density. A color differential is thus produced. If necessary, excess stain is removed from the surface of the sheet. The resulting patterned and stained sheet is then subjected to pressure to flatten the stained surface to the desired extent.

BACKGROUND OF THE INVENTION Field of the invention The invention relates generally to the formation of such products as artificial wood veneer and patterned boards and planks having the desired pattern embedded in the surface thereof in the form of varying concentrations of a suitable stain.

Description of the prior art Prior processes and methods for forming artificial veneers or patterned boards and the like have involved embossing a wood surface followed by filling the embossed embossed regions with plastic compositions or similar filling materials. This process is exemplified by U.S. 1,947,-

459, Casto. Other processes have involved putting a resist or stencil on a thin wood surface and spraying or otherwise applying a coloring material through the resist, as shown by U.S. 1,936,182, Beiger.

The present invention operates on a theory different from those of these prior patents and enables one to produce an excellent artificial wood veneer, and other products, in an inexpensive manner. Natural wood veneer is growing scarcer as the supply of suitable trees diminishes, and accordingly, the present invention steps into the gap caused by the diminishing supply of the natural product.

SUMMARY OF THE INVENTION This invention relates to the method of making a patterned wood sheet comprising forming a slurry of wood fibers in water followed by the addition of any desirable materials such as binders or Water repellants. A sheet is formed from the resultant slurry and a pattern is impressed in the surface of the resulting sheet by means of a suitable die platen or other convenient means for compressing some portions of the fibrous surface of the sheet to a greater extent than adjacent portions. This patterning results in relatively hard and soft spots throughout the sheet to form the pattern. The sheet maybe dried to any desirable extent. There is then applied to the patterned face of the sheet a liquid stain adapted to be absorbed into the face of the sheet, the absorption taking place to a different extent in the less dense areas than in the increased dense areas resulting from the patterning step. Since in the preferred method more of the liquid stain is absorbed in the regions 3,542,641 Patented Nov. 24, 1970 ice BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified flow diagram of the method of the present invention, and

FIG. 2 is a perspective view of the product of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The fibrous slurry from which the wood fiber sheet is to be made will be prepared in accordance with known methods. Wood fibers which may come from steamcooked wood pulp, Puget Sound sulphite, kraft fibers, or wood fibers from any source suitable for making a wetlaid sheet may be used as a starting material. The fibers are slurried in the water and any mechanical refining desired may then be carried out. The consistency of the slurry will generally range from about 0.2%-3%. If an artificial wood veneer is to be made, it is normally desirable to add 1%-10% by weight of a binder to the aqueous slurry of wood fibers in order to enhance the strength of the resulting thin sheet. The preferred binder will be a phenol-formaldehyde resin, normally in the B stage so as to be curable on the fibers upon the application of heat to the sheet. The resin may be deposited onto the fibers by any of the known processes, including the variety of beater saturation processes available. Although elastomeric binders such as the synthetic rubbers may be added to the aqueous slurry in the form of their latices in order to bind the fibers of the fibrous sheet, such is not preferred in the present method due to the subsequent need for the penetration of a liquid stain into the sheet itself. The liquid stain will penetrate rubber-bonded sheets as will be explained below, but greater sheet rigidity and clarity of pattern will be achieved by use of the phenolformaldehyde resin, or one of the other thermosetting resins in the amounts stated.

It is preferred that water repellants be added to the slurry to be picked up by the fibers prior to sheet formation. These water repellants may be any of the known water repellants normally used in the sheet-making processes. It is preferred to use tall oil acids, or any of the long-chain fatty acids possessing 12 carbon atoms or more in the molecule in order that the final product will repel moisture and will not be subjected to undue moisture growth in use. The tall oil acids or other fatty acids or other water repellants are simply added to the aqueous slurry prior to sheet formation. They are added in an amount of about 2%-S% based on the weight of the wood fibers.

Sheet formation proceeds normally. If an artificial wood veneer is to be formed, the sheet will normally be thinner in the range of 0.015"0.030", while if a wallboard or plank is to be made, the sheet will normally have a thickness in the range of As- /2. Normal board and sheet-making processes are used in the formation of the sheet. Water may be removed in the usual manner by allowing it to drain through a mold or through a sheetmaking wire or cylinder.

As the next step, the formed sheet will normally have a pattern impressed in its surface while it is still wet, although some drying may take place first. To achieve the requisite compression of the fibers it is preferred that at least about 30% by weight water remain in the sheet, although much larger amounts of water up to about 100% by weight may remain in the sheet if the patterning step is applied with care. The preferred way to accomplish impressing a pattern into one face of the sheet is to simply press into that face a platen which has in it the reverse of the desired pattern. If an artificial wood veneer is to be made, then the pattern to be impressed into the surface of the sheet will simulate the grain of a suitable wood. A piece of natural wood may be used as the embossing platen. For example, a piece of Douglas fir has regions of hard and soft spots which may be emphasized by sandblasting the surface of the natural wood with a relatively soft sandblasting material such as ground walnut shells. The resulting die may be pressed into the surface of the sheet made as described above to form in the sheet the grain pattern of the Douglas fir. A similar sequence of steps may be used to impress into the surface of the sheet the grained pattern of walnut, oak, cherry, Philippine mahogany which is really a species known as lauan, or any other desired wood pattern. It will be appreciated that metal plates having geometrical designs, human figures, or any desired pattern or design may also be prepared and used to impress a pattern into the surface of the sheet.

The resulting sheet will have in it regions of varying density due to the compression of the fibers by the elevated portions of the pattern pressed into the surface of the sheet. A wide variety of density variations may be achieved across the surface of the sheet depending on the pattern pressed into the surface of the sheet. A simple pattern or an exceedingly complex pattern may thus be achieved by establishing varying degrees of compression of the fibers in one region as contrasted with the fibers in another region of the face of the sheet.

After the pattern has been impressed in the sheet, and the sheet preferably dried, a liquid stain is coated or sprayed across the entire surface of the sheet. Normally it is preferred that the liquid stain be applied to the surface of a sheet which contains less than about by weight water based on the weight of the fibers. This reduced Water content will ensure better pickup of the liquid stain by the sheet. It is preferred that the water content of the sheet be in the range of about 2%7% by weight based on the weight of the fibers before the liquid stain is applied.

Since some areas of the patterned sheet are more dense than others, the liquid stain will be absorbed to a greater extent in the less dense areas than in the areas having a higher density. In this manner, color differentials will become apparent on the surface of the sheet according to the density of the fibers in any particular region. The liquid stain may comprise any of the usual wood stains normally used to impart walnut, mahogany, oak, cherry, or any other of the wood stain colors normally used. Since the sheet is made of wood fibers, these wood stains may be coated over the surface of the patterned sheet in any convenient manner as by use of a doctor blade, roll coater, reverse roll coater, spray coating, curtain coating, and the like. Simple wiping on of the liquid stain may suffice. Depending on the density of the portions of the sheet which are to show a color different from the balance of the sheet, the liquid stain may be left on the surface of the sheet for a fraction of a second or for several minutes or more. On a continuous production line it is convenient to apply the exact amount of stain needed to produce the desired color differentials, and no excess will remain to be removed. The point is, if any excess of liquid stain exists, it should be removed. Another method of producing a color differential is to apply a bleaching solution that runs off the elevated, less dense regions and gathers and exerts a more pronounced bleaching effect in the more dense regions.

Pigmented solutions or slurries, bleaching solutions,

dye solutions, and other similar coloring solutions may be used instead of the normal liquid wood stains of commerce. It is necessary only that the liquid stain, whatever it is, penetrate the surface of the sheet more in some areas than in others and impart to some regions a color different from that of another region of the same face of the sheet.

After the removal of the excess liquid stain, if any, the sheet will be pressed to flatten to the desired extent the stained surface of the sheet. This pressing step serves to close the pores between the wood fibers, and the pressing step may serve to consolidate and strengthen the entire sheet and, if heat is applied, to cure any thermosetting binder used on the fibers in the original aqueous slurry. Since the visual pattern effect is achieved by a coloring differential, the pattern surface of the stained sheet may be pressed completely flat and smooth while still preserving and, in fact, enhancing the pattern appearance. The pressing step will normally entail some degree of heating in order to remove any residual moisture or solvents from the sheet. The pressing step may be followed by any lacqnering or clear-coating steps normally used on natural wood veneer to preserve and protect the wood, and to bring out the grain or otherwise enhance the color differential. The lacquers or coatings may be glossy or flat as desired, but they will all be sufiiciently transparent that the differential coloring effect may be seen through the coating.

If the present method is used to prepare an artificial wood veneer, the resulting product is a sheet which very closely resembles a natural wood veneer but which has far greater strength, flexibility and is much more crackresistant than natural wood veneer. Additionally, due to the presence of any desirable additives, the artificial wood veneer made by the present method will have greater dimensional stability, will be more moisture and fungus resistant, and may more efficiently be used in the manufacture of furniture and the like.

The following example illustrates an embodiment of the invention. All parts are by weight unless otherwise stated.

EXAMPLE A sheet was made having the following formula: Ingredients Parts Wood pulp, cooked 30 Wood flour 10 Phenol-formaldehyde resin, B stage 2 Papermakers alum 1 Tall oil fatty acids l The pulp and wood flour were slurried in 3,750 parts of water followed by one pass through a beater. The resin and tall oil fatty acids were then added followed by the addition of the alum. The resulting slurry was poured into a mold and a sheet having a thickness of 0.060" was prepared.

A sandblasted block of Douglas fir was placed on top of the wet sheet. The resulting embossed sheet was dried to a water content of 2%7% The dried sheet was flooded with a walnut wood stain, and the excess stain was wiped off. The regions of higher density-the depressed regionsdid not absorb as much stain as the lower density regions; the lower density regions were appreciably darker in appearance. The stained sheet was hot pressed at 200 F. for three minutes at a pressure of 500 pounds per square inch. On spraying the cooled sheet with lacquer, a strong attractive flexible wood veneer sheet resulted.

We claim:

1. The method of making a smooth surfaced wood sheet having a simulated wood grain pattern embedded in one surface thereof in the form of varying concentrations of wood stain comprising (a) forming in Water a slurry of wood fibers,

(b) forming a sheet from said slurry and removing up to 70% of the water therefrom,

(c) impressing a three-dimensional wood grain pattern into one face of said sheet by compressing the fibers in the pattern to a variable density greater than the density of the fibers in other regions of said face,

(d) drying the sheet to a water content of from 2% to 7% by weight, based on the weight of the fibers,

(e) applying to said patterned face a uniform coating of a liquid wood stain whereby the stain is absorbed to a different extent in the less dense regions than in the more dense regions of the sheet thereby producing a variable color differential between said regions,

(f) removing any excess liquid stain from said patterned face, and then,

(g) pressing the patterned face to flatten the stained surface.

2. The method according to claim 1 in which said liquid stain is applied to the surface of said sheet in an References Cited UNITED STATES PATENTS 1,867,575 7/1932 Loetscher 162-117 X 1,956,866 5/1934 Keller 162-165 X 2,216,803 10/1940 Benda 117-11 X 2,402,966 7/1946 Linzell 162-117 S. LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner US. Cl. X.R.