WO1995001869A1

WO1995001869A1 - Indentation resistant wood

Info

Publication number: WO1995001869A1
Application number: PCT/US1994/007884
Authority: WO
Inventors: Nicholas A. French; W. Dale Ellis; Roger M. Rowell
Original assignee: Haworth, Inc.; United States Department Of Agriculture
Priority date: 1993-07-09
Filing date: 1994-07-05
Publication date: 1995-01-19

Abstract

A method is provided for treating wood veneer or solid wood to provide a higher and more uniform surface hardness to improve resistance to surface indentation and scratching, especially during use as a writing surface on office and other furniture. The method involves impregnating the wood veneer or solid wood with a liquid impregnant comprising a monomer that penetrates into the wood voids without a carrier liquid and polymerizable to a solid polymeric impregnant that is non-degrading to the wood grain appearance and a thermally activated catalyst for polymerizing said monomer. A coloring agent may be mixed with the monomer and catalyst to impart a desired color to the wood at the time of impregnation. After impregnation, the monomer is polymerized to form in the wood lumens, channels, and other voids the solid polymeric impregnant that imparts increased and more uniform hardness to the wood surface.

Description

INDENTATION RESISTANT WOOD

FIELD OF THE INVENTION The present invention relates to the treatment of wood, such as wood veneer and solid wood, to improve its hardness, especially its resistance to indentation and scratching when in use as office furniture, while retaining the wood grain appearance of untreated wood.

BACKGROUND OF THE INVENTION Wood veneered office furniture is in widespread use in the modern office environment. Such office furniture is advantageous in that the wood veneer provides the aesthetic appearance of solid wood without its high cost. Natural wood veneers currently used in the manufacture of office and other furniture comprise thin, narrow sheets or strips (referred to as fletches) of natural wood laid side-by-side and adhesively bonded together to form larger sized veneer sheets that can be cut to desired size/shape and adhered to a suitable furniture substrate material, such as particle board. An alternative to natural veneer referred to as reconstituted veneer also is formed as a veneer sheet that can be cut to size/shape and adhered to a suitable furniture substrate material. Importantly, natural and reconstituted veneers are amenable to staining and other conventional furniture finishing operations employed to fabricate finished furniture products so that the wood veneer will aesthetically match any solid wood trim of like wood species included on the furniture and any solid wood furniture of like wood species, such as for example, solid wood chairs, that may be encountered in an office environment.

Wood veneered office furniture, such as, for example, a desk, work table, credenza, and the like, includes a flat, horizontal writing surface at which day-to-day office activities are conducted. Unfortunately, wood veneer office furniture writing surfaces have been observed to suffer damage referred to as "read through" when the surfaces are subjected to typical hand writing pressure. This damage comprises permanent indentations and scratches in the wood veneer surface caused by the localized surface pressures exerted during the act of writing using a ball point pen, pencil or other pointed writing instrument. Although the pressure exerted during writing varies with the individual writer, most people are estimated to exert about 0.33 to 2 pounds pressure in the process of writing. If an individual uses a fine point ball point pen with a ball diameter of approximately 0.3 milli¬ meters and applies 2 pounds of writing pressure, an equivalent writing pressure (EWP) of approximately 13,900 pounds per square inch is exerted on the writing surface. If the individual uses a writing instrument having a larger point size and/or lower writing pressure, the EWP exerted on the writing surface will be reduced. For example, for an individual using a lead pencil having an approximate point size of 0.9 millimeters and a writing pressure of 1 pound, the EWP will be about 80 pounds per square inch. Thus, the wood veneer writing surfaces can be subjected in use to a wide range of writing pressures, some of which are unexpectedly high pressures per unit surface area. The inability of wood veneer office furniture writing surfaces to withstand the writing pressures commonly encountered in use is attributable to the inherent softness of wood as well as to the anisotropic nature of wood hardness which is known to vary considerably from one wood species to another and, for the same wood species, in dependence on the ratio of latewood (grown in the summer and the early fall) to summerwood (grown in the spring) , the ratio of heartwood to sapwood, extractives content, mineral content, and other factors. As a result, wood veneer typically exhibits a wide variability in hardness across its surface. For example, an oak veneer writing surface may exhibit a higher surface hardness at regions comprising the more dense latewood, and a lower surface hardness at regions comprising the less dense earlywood. The variability of wood veneer surface hardness is even greater in other species of wood. As a result, it has been noted that even writing pressures as low as 80 pounds per square inch can result in permanent indenta¬ tions in most wood veneer writing surfaces; namely, at the softer regions of the wood where earlywood is present.

Although "read through" indentations do not adversely affect the overall structural integrity of wood veneered office furniture, they are perceived by users of the furniture as detracting from its appearance and indicating a lack of durability of the furniture. In particular, "read through" damage is perceived as the primary shortcoming associated with the use of wood veneered office furniture.

There thus is a need for an improved wood veneer that can overcome this primary shortcoming of the natural and reconstituted wood veneers currently in use while retaining their desirable wood grain appearance and amenability to staining and other conventional finishing operations such that the treated veneer is the general aesthetic equivalent of untreated veneer. In particular, there is a need for a treatment for wood veneer to provide higher and more uniform surface hardness so as to render the treated veneer more resistant to "read through" damage in use as a writing surface on office and other furniture. One treatment in use heretofore to harden wood materials has involved the application of hard, glossy surface coatings (e.g. varnish) onto the wood material. However, when a hard surface coating is employed, the overall hardness of the coated wood material is still controlled or limited by the hardness of the underlying wood substrate. Moreover, when indentation of the coated surface occurs, the indentation may be more visible on the coated surface than an uncoated surface as a result of light refraction by the glossy coating. Another treatment in use heretofore to harden wood flooring materials has involved vacuum impregnation of the wood with a mixture of organic monomers, cross- linking agents, catalysts, and the like followed by radiation or heat-induced polymerization of the monomers in-situ in the wood to form a solid impregnant that imparts higher hardness thereto. However, the hardness requirements for wood flooring applications generally are less rigorous than those for a wood veneer writing surface. For example, a 150 pound woman wearing a stiletto heel shoe having a heel area of only 0.25 square inch exerts a pressure of about 2400 pounds per square inch on flooring as compared to the aforementioned, unxpectedly high equivalent writing pressure (EWP) of approximately 13,900 pound per square inch exerted on a writing surface when an individual writes with 2 pounds of writing pressure using a fine point ball point pen having a ball diameter of approximately 0.3 millimeters. Moreover, the same person wearing a typical high heel shoe (heel area of about 0.5 square inches) or walking shoe (heel area of about 3 square inches) will exert only approximately 600 and 50 pounds per square inch of pressure, respectively, on the flooring.

Generally, the treatments used heretofore in the art to increase wood hardness have been found to suffer from one or more of the following disadvantages: 1) surface hardness is not increased to a high enough level to resist "read through" damage at the writing pressures described hereabove, 2) uniform surface hardness is not achieved, 3) the treated wood does not retain its natural appearance, 4) the treated wood is not amenable to staining, 5) the treated wood allows bleed-through of adhesive used to adhere the wood to a core material, 6) the treatment is too complicated, and 7) the treatment is too costly. There thus continues to be a need for a treatment for wood veneer effective to provide higher and more uniform veneer surface hardness so as to render the veneer more resistant to "read through" damage when in use as a writing surface on office and other furniture while retaining the wood grain appearance and stainability of untreated wood veneer to conventional furniture finishing operations used in the fabrication of office and other furniture.

Moreover, in the manufacture of office and other furniture such as desks having a wood veneer writing surface, a solid wood decorative edge trim or band oftentimes is applied to the exposed side surfaces of the particle board substrate underlying the wood veneer top to hide the substrate side surfaces from view. There is a need for a treatment for such solid wood members to provide higher and more uniform surface hardness so as render the solid wood edge trim or band more resistant to indentations and scratches when in use on office and other furniture, while retaining the wood grain appearance of an untreated solid wood edge trim or band and stainability of untreated wood to conventional furniture finishing operations.

Furthermore, there is a need to produce such improved wood veneer and solid wood members, as well as office and other furniture including same, by methods that involve less processing steps, are less time consuming, and/or are less costly than wood treatment processes used heretofore so that high volume, cost effective production can be achieved.

It is an object of the invention to satisfy these needs.

SUMMARY OF THE INVENTION One aspect of the present invention involves a method of treating wood veneer sheet to provide a surface thereon having improved resistance to "read through" indentations and scratching when the surface is used as a writing surface. The method comprises impregnating a wood veneer sheet proximate a surface thereof with a liquid impregnant comprising a) a monomer that penetrates inwardly into the wood veneer cells, pores, lumens, channels, etc. (i.e. wood voids) without a carrier vehicle, such as a carrier liquid or solvent, and is polymerizable in the wood veneer to a solid polymeric impregnant that improves veneer surface hard¬ ness and is non-degrading to the wood grain appearance of the veneer and b) a thermally activated catalyst for polymerizing the monomer. The impregnated wood veneer sheet is pressed under temperature and pressure con¬ ditions to polymerize the monomer and form in the wood veneer voids the aforementioned solid polymeric impre¬ gnant that imparts to the veneer surface increased hard¬ ness and resistance to writing indentations and scratching as compared to untreated wood veneer, while retaining the wood grain appearance thereof.

In one embodiment of the invention, the wood veneer sheet is impregnated by subjecting the sheet to a relative vacuum and then contacting the sheet with the liquid impregnant. The impregnated wood veneer sheet is pressed between opposing heated press members in a direction perpendicular to the sheet surface and in a manner to retain some surface pores and voids present on the untreated veneer surface, thereby preserving a wood texture on the treated wood veneer surface. Preferably, the wood veneer sheet includes about 55 to about 85 weight % of the solid-polymeric impregnant after the pressing operation.

In the manufacture of furniture in accordance with another aspect of the invention, a wood veneer sheet can be impregnated as described hereabove and pressed at elevated temperature and pressure prior to or after attachment to a suitable furniture substrate material. For example, the wood veneer sheet can be impregnated with the liquid impregnant, pressed between heated pres¬ sing members to polymerize the liquid impregnant to a solid impregnant that imparts increased surface hard¬ ness to the veneer, and then attached (e.g. adhesively bonded) to a suitable furniture substrate material. Alternately, the wood veneer sheet can be impregnated and then positioned on a suitable furniture substrate with a suitable adhesive therebetween. The wood ve¬ neer/furniture substrate assembly is pressed between heated pressing members to form the aforementioned solid polymeric impregnant in the veneer sheet and also to bond the veneer sheet to the substrate material as a laminate. Thus, veneer pressing and veneer-to-substrate bonding can be conducted in one step instead of separate steps. The present invention provides a treated wood veneer surface, as well as furniture (e.g. office furniture) including same, wherein the wood veneer is impregnated proximate a surface thereof with a solid polymeric impregnant that provides a higher and more uniform surface hardness and resistance to surface damage, especially indentations and scratching from writing pressure, as compared to untreated wood veneer heretofore used. The solid polymeric impregnant is non- degrading to the wood grain appearance of the untreated veneer so that the veneer is the general asethetic equivalent of untreated veneer. As mentioned herebelow, the wood veneer can be colored during impregnation or after attachment to a furniture substrate material.

Importantly, treated wood veneer in accordance with the invention is amenable to finishing and coloring (e.g. staining) after bonding to a furniture substrate material using conventional finishing and coloring tech¬ niques so that high volume furniture production can be achieved without the need to alter existing finishing operations.

Alternately, in accordance with another embodiment of the invention, the surface of the wood veneer sheet can be colored at the time when the wood veneer is impregnated with the liquid impregnant so as to avoid the need for a separate coloring operation after attachment of the wood veneer to a furniture substrate material. In this embodiment of the invention, the liquid impregnant introduced into the wood voids comprises a polymerizable liquid monomer, a coloring agent, such as a dye, for coloring the wood, and a thermally activated catalyst for polymerizing the monomer.

Both solid wood as well as wood veneer can be colored in the impregnated condition and then treated to polymerize the monomer to harden the wood in accordance with still another aspect of the present invention.

In practicing a further aspect of the invention to harden a wood member, including wood veneer and solid wood, regardless of its intended use, the liquid impregnant preferably comprises substantially undiluted ethylene glycol dimethylacrylate monomer and a catalyst in an amount effective to polymerize the monomer to harden the wood member. Even more preferably, the liquid impregnant comprises about 0.5 to about 2.0 weight % catalyst and the balance essentially ethylene glycol dimethylacrylate.

The present invention provides a hardened wood member for myriad uses, the wood member being hardened by virtue of the presence therein of a solid polymeric impregnant comprising solely a polymer of ethylene glycol dimethylacrylate.

The invention may be understood better when con¬ sidered in light of the following detailed description of certain specific embodiments thereof which are set forth hereafter in conjunction with the following draw¬ ings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a process flow chart illustrating certain embodiments of the invention for treating individual wood veneer sheets and attaching each treated veneer sheet to a furniture substrate, such as a desk or credenza top made of particle board, to provide a hardened writing surface thereon that is resistant to surface indentations and scratching.

Figure 2 is a perspective view of apparatus useful for impregnating a wood veneer sheet and removing excess liquid impregnant therefrom prior to hot pressing of the impregnated sheet to harden the veneer surface. The liquid impregnant transfer conduits, valves, etc. are shown schematically for convenience. Figure 3A is an elevational view of the treatment container with the container lid in the closed position.

Figure 3B is a fragmentary elevational view of the treatment container illustrating a veneer sheet wiper assembly positioned on the treatment container with the lid open.

Figure 4 is a schematic sectional view of hot press¬ ing apparatus for hot pressing an impregnated wood veneer sheet so as to harden the veneer surface. Figure 5 is a schematic sectional view of hot press¬ ing apparatus for hot pressing an impregnated wood veneer sheet positioned on a furniture substrate material so as to harden the veneer surface and also bond the veneer to the substrate material to form a laminate.

Figure 6 is a partial sectional view of a laminated veneer/substrate/backer board assembly illustrating a decorative edge trim or band for attachment thereon.

Figure 7 is a bar graph illustrating the resistance to surface indentations of untreated natural maple, natural cherry, and obeche wood veneer specimens and of similar veneer specimens treated in accordance with the invention as measured under conditions simulating the actual act of writing using a ballpoint pen.

Figure 8 is a sectional view of a testing device used to measure the indentation resistance of the un¬ treated and treated wood veneer specimens of Figure 7.

Figures 9A, 9B and 9C are photographs of the surface of untreated wood veneer specimens (Fig. 9A-maple, Fig. 9B-cherry, and Fig. 9C-obeche mahogany) finished by con¬ ventional staining and top coating, illustrating the wood grain appearance and surface indentation/scratching observed on the untreated wood veneer.

Figures 10A, 10B and 10C are photographs of the surface of similar wood veneer specimens treated in ac¬ cordance with the invention and finished by the same conventional staining and top coating as the untreated specimens of Figures 9A-9C, illustrating substantial retention of the wood grain appearance of the untreated wood veneer specimens and lack of surface indentation/scratching.

Figures 11A, 11B and lie are photomicrographs at a magnification of 100 X of a cross-section of natural wood veneer specimens in the untreated condition (Fig. HA-maple, Fig. HB-cherry, Fig. HC-obeche mahogany) . Figures 12A, 12B and 12C are photomicrographs at a magnification of 100 X of a cross-section of wood veneer specimens similar to those of Figures 11A, 11B and 11C after treatment in accordance with the invention.

DETAILED DESCRIPTION The present invention will be described herebelow with respect to Figure 1 which is a process flow chart for treating individual wood veneer sheets and attaching each treated veneer sheet to a furniture substrate material, such as a desk or credenza top made of particle board, to provide a hardened writing surface thereon that is resistant to writing indentations and scratching. The process flow chart of Figure 1 is offered for purposes of illustration and not limitation of the invention. For example, although the process flow chart of Figure 1 is directed toward treating individual wood veneer sheets, the invention is not so limited and can be used to treat individual solid wood members of myriad types (e.g. solid wood edge trim or bands referred to hereabove) to improve the surface hardness thereof while retaining the wood grain appearance of untreated wood.

Moreover, wood veneer sheets treated in accordance with the invention can be used for applications other than writing surfaces on office and other furniture. For example, treated wood veneer in accordance with the invention will find use as indentation and scratch resistant work surfaces or decorative surfaces on myriad types of office and residential furniture such as countertops, tables, wooden desks, steel desks with wooden tops, credenzas, corners, bridges, returns, consoles, convergants, filing and other cabinets, and the like.

As mentioned, Figure 1 illustrates a process flow chart for treating individual wood veneer sheets and attaching each treated veneer sheet to a furniture sub- strate to provide a hardened writing surface thereon that is resistant to writing indentations (i.e. "read- through") and scratching. The wood veneer sheets can comprise natural wood veneers and reconstituted wood veneers widely used in the manufacture of office and other furniture. As is well known, natural wood veneers are fabricated from thin, narrow veneer sheets or strips (referred to as fletches) of natural wood laid side-by- side and adhesively bonded together to form a larger sized veneer sheet (e.g. 2 feet in width, 5 feet in length, and 0.030 inch in thickness) that can be cut or trimmed to appropriate size/shape for the underlying furniture substrate to which the veneer will be bonded. As is also well known, reconstituted veneer comprises obeche or like wood adhesively bonded together into a veneer sheet that also can be cut to appropriate size/shape for the furniture substrate to which the veneer will be bonded. Exemplary wood veneer sheets 10 for impregnation in accordance with one embodiment of the invention are shown in Figure 2. Each veneer sheet includes major faces or surfaces 12, 14 on opposite sides thereof.

Preferably, the individual wood veneer sheets 10 exhibit a moisture content below about 20% prior to the vacuum/atmospheric impregnation step. The veneer sheets can be dried, if necessary, prior to impregnation to this end. An illustrative vacuum/atmospheric impregnation apparatus useful for liquid impregnation of relatively large wood veneer sheets 10 of the size that would be used in the manufacture of office furniture, such as desks, is shown in Figure 2. The invention is not limited to the particular vacuum/atmospheric impregna¬ tion apparatus 20 shown in Figure 2 and can be practiced using other impregnation apparatus, such as the apparatus described in the Examples set forth herebe- low.

The vacuum/atmospheric impregnation apparatus 20 shown in Figure 2 comprises a lower shuttle table 22 on which a plurality of untreated wood veneer sheets 10 are stacked (only one sheet 10 shown) prior to impregna¬ tion. To effect impregnation of individual veneer sheets 10, an inner end 15 of each veneer sheet 10 is successively clamped on a vertically movable clamp head 24 and moved from the horizontal position Pl to the vertical position P2 above a treatment container 26 as shown in Figure 2. The treatment container 26 is formed of plate members Pl, P2 joined together by, for example, welding, and reinforced by flanged end beams Bl (one shown) and flanged side beams B2 welded thereto as illustrated in Figures 3A-3B. The end beams Bl and side beams B2 are not shown in Figure 2 for the sake of simplicity.

The clamp head 24 is releasably connected to linkages 25 of a crane 28 that is vertically movable by a suitable motor (not shown) on the upstanding frame 31. The clamp head 24 and veneer sheet 10 clamped thereon are lowered by the crane 28 from the position P2 toward the treatment container 26 to position the veneer sheet 10 within the treatment container 26 with the veneer sides spaced generally equidistantly from the vertical sides of the container 26. The clamp head 24 is received in the upper end 26a of the container 26 when the veneer sheet 10 is properly positioned in the container 26. The crane linkages 25 then are disconnected from the clamp head 24 and raised by the crane 28 to an upper position out of the way of the operator of the impregnation apparatus 20. A container lid 27 is hinged on plate P3 fixed on the treatment container 26 and is closed to seal the upper end 26a of the container 26, Figure 3A. The wood veneer sheet 10 residing in the treatment container 26 is subjected to an impregnation cycle which comprises an initial deaeration stage wherein the container 26 is evacuated by one or more vacuum pumps PV (one schematically shown) communicated to the container 26 by conduit 29 to remove air from the wood veneer (i.e. from the lumens, channels, vessels, and other voids in the wood veneer) , and a subsequent stage wherein liquid impregnant is introduced into the evacuated treatment container 26 to impregnate the wood veneer sheet 10. The liquid impregnant is transferred from a liquid impregnant storage tank T into the con- tainer 26 through conduit 29a by pressure gradients or di ferentials established therebetween. Impregnant transfer valves 33, 35 are actuated as appropriate to achieve evacuation of the container 26 and then transfer of liquid impregnant between tank T and container 26. Once the liquid impregnant is introduced into the treatment container 26, the container is vented to ambient by suitable actuation of a vent valve to provide atmospheric pressure on the liquid impregnant so as to facilitate impregnation of the veneer sheet 10. The liquid impregnants can be transferred from the container

26 back to the tank T through conduit 29b by suitable actuation of valves 33, 35.

The initial vacuum level and evacuation time can be selected as needed to effect desired impregnation of the veneer sheet 10 with the liquid impregnant. Typically, each veneer sheet 10 is impregnated with the liquid impregnant uniformly across the surfaces 12 and 14 and through a substantial portion of its thickness as a result of the small sheet thickness (e.g. 0.030 inch thickness) and high wood veneer porosity. However, impregnation of the wood veneer sheet 10 proximate both surfaces 12, 14 and through its entire thickness is not essential in practicing the invention so long as a sufficient impregnation is achieved to provide a higher and more uniform surface hardness proximate at least surface 12, which will constitute a writing surface when the veneer is attached to substrate. Moreover, there may be some variation in the depth of impregnation within the same veneer sheet 10. Typically, the wood veneer sheet will absorb 50 to 70 % by weight liquid impregnant based on veneer sheet weight gain. Preferably, the wood veneer sheet absorbs from 65 to 70 % by weight impregnant based on sheet weight gain to provide sub¬ stantially improved surface hardness in the final treated veneer sheet. After the veneer sheet 10 is impregnated with the liquid impregnant, the container lid 27 is opened, and the crane 28 is lowered so that the crane linkages 25 can be reconnected to the clamp head 24. A wiper device 30 then is positioned on the upper end 26a of the container 26, Figure 3B, so that excess liquid impregnant is removed from the surfaces 12, 14 of the veneer sheet 10 as it is raised by the crane 28 out of the container 26 to the position P2 shown in Figure 2. The wiper device 30 comprises opposing wiper blades 33 for wiping opposite surfaces 12, 14 of the veneer sheet

10 and a clamping fixture 35 for cooperably positioning the wiper blades relative to the veneer sheet surfaces 12, 14. The wiper device 30 can be slid into the position shown in Figure 3B on plate P3 atop the container 26. The impregnated veneer sheet 10 is raised by crane 28 out of the container 26 to the position P2 shown in Figure 2. The lower end of the impregnated veneer sheet 10 at position P2 is maneuvered onto the upper shuttle table 32 such that lowering of the crane 28 will cause the impregnated veneer sheet 10 to slid onto the shut¬ tle table 32, or onto a stack S of one or more previously impregnated veneer sheets 10 thereon, for temporary storage until each impregnated veneer sheet can be hot pressed in accordance with the invention. The total impregnation cycle time for each wood veneer sheet 10 typically is approximately 5 minutes.

The impregnation cycle described hereabove is repeated for additional untreated veneer sheets 10 temporarily stored on the lower shuttle table 22.

The particular impregnation apparatus 20 described hereabove and shown in Figures 2 and 3A-3B is offered merely for purposes of illustrating, and not limiting, the present invention. The present invention can be practiced using other impregnation apparatus capable of impregnating the wood veneer sheets 10 with liquid impregnant.

As indicated in Figure 1, the untreated wood veneer sheets 10 can be colored (e.g. dyed) during the impreg¬ nation cycle, if desired. To this end, the liquid impr¬ egnant will include a suitable coloring agent, such as a dye, to color the veneer during the impregnation cycle. Alternately, as also indicated in Figure 1, and explained herebelow, the wood veneer sheets 10 in the impregnated and hot pressed condition can be colored

(e.g. stained) after attachment to a furniture substrate using conventional furniture finishing techniques.

In accordance with the present invention, the liquid impregnant introduced into the wood veneer comprises a monomer that is effective to penetrate inwardly into the wood cells, pores, lumens, channels, vessels (wood voids) without the need' for a carrier vehicle, such as a carrier liquid or solvent, and that is polymerizable in- situ in the wood voids. The carrier-free liquid impregnant also includes a thermally activated catalyst in an amount effective to polymerize the particular monomer upon the application of heat to the impregnated veneer sheet. The monomer is selected to be polym¬ erizable in the wood veneer to a solid polymeric impr¬ egnant that not only imparts increased hardness to the veneer surface but also is non-degrading to the veneer wood grain appearance in the treated condition such that the treated wood veneer is the approximate asethetic equivalent of untreated wood veneer from a wood grain appearance standpoint. Within these criteria, the monomer itself is selected to have low molecular weight (e.g. molecular weight less than 200) and resulting low viscosity (e.g. about 5 to about 10 centipoise) , con¬ trollable polymerization reactivity via the heat activated catalyst, chemical stability for process con- trol consistency, and compatibility to the environment and operators of the treatment equipment. In addition, the solid polymer impregnant resulting from polymerization of the monomer is selected to exhibit a suitable high hardness, water white color (i.e. colorless), and refractive index of approximately 1.5.

If the treated wood veneer is to be colored (e.g. stained) after attachment to a furniture substrate, the monomer is selected to produce a solid polymer impregnant that permits conventional wood coloring (e.g. staining) and other conventional furniture finishing techniques without adversely affecting the wood grain appearance of the wood veneer.

The thermally activated catalyst is provided in an amount to provide controlled polymerization of the monomer to a solid thermoset polymer upon application of heat to the impregnated veneer sheet 10. The liquid impregnant desirably is compatible with and capable of treating different wood veneer species, such as cherry, oak, maple, etc. such that there is no need to use different liquid impregnants when different wood veneer species are to be treated on the same apparatus.

A liquid impregnant satisfying the aforementioned criteria preferably comprises a substantially undiluted acrylic resin monomer, a thermally activated catalyst for polymerizing the monomer, and an optional coloring agent if the wood veneer is to be colored at the time of impregnation. By "substantially undiluted" is meant that the monomer is present in an amount of at least about 90 weight %, preferably about 98 weight %, of the liquid impregnant, the balance of the impregnant comprising the catalyst and the optional coloring agent without other monomers being present. No volatile carrier liquid or solvent is used or needed for effective wood impregna¬ tion in accordance with the invention. When the wood veneer sheet is not to be colored at the time of impregnation, the liquid impregnant even more preferably consists essentially of about 0.5 to about 2.0 weight % thermally activated catalyst and the balance substantially undiluted ethylene glycol dimethylacrylate (molecular weight of about 198) . A particularly preferred liquid impregnant solution con¬ sists essentially of 99.5 weight % ethylene glycol dime- thacrylate (EGDMA) monomer and 0.5 weight % 2-2'-azobis (2-methylbutyronitrile) catalyst. This liquid impregnant solution is used at room temperature. The

EGDMA monomer is available from Sartomer Co., Oaklands Corporate Center, 468 Thomas Jones Way, Eaton, PA 19341. The 2-2' azobis catalyst is available under the trademark VAZO 67 from E. I. duPont de Nemours & Co., Chemicals & Pigments Dept. , Wilmington, DE 19898. When the wood veneer sheet is to be colored at the time of impregnation, the liquid impegnant solution described hereabove will include a suitable coloring agent, such as a dye. A dye useful to this end comprises a chromium or cobalt complex dye and is present in the liquid impregnant solution in an amount of about 1 to about 10 weight %, the balance of the solution comprising the monomer and catalyst. This dye is useful for coloring light colored wood species veneer. After impregnation, excess impregnant is removed from each veneer sheet 10 by the wiper blades 33 (or alternately by simply allowing the excess to drip off of the veneer sheet) . Then, the individual liquid impreg¬ nated wood veneer sheets 10 are subjected to a hot pressing treatment to polymerize the liquid monomer in- situ in the wood veneer voids to form therein the afore¬ mentioned solid polymeric impregnant (i.e. the polymer of EGDM) that imparts to the veneer sheet surface 12 higher and more uniform hardness and resistance to writ- ing indentations and scratching as compared to untreated wood veneer, while preserving the wood grain appearance of the untreated wood veneer.

In accordance with the illustrated embodiment of the invention, each liquid impregnated veneer sheet 10 can be hot pressed by the alternative sequences shown in Figure l. In particular, one sequence involves hot pressing each liquid impregnated wood veneer sheet 10 to polymerize the monomer and then attaching the hot pressed veneer sheet 10 to a suitable furniture sub- strate using conventional hot press/bonding techniques.

The other sequence involves initially positioning each liquid impregnated veneer sheet 10 on an adhesively coated furniture substrate and then hot pressing the veneer/adhesive-coated substrate assembly to concur¬ rently polymerize the monomer and bond the veneer sheet to the substrate to form a laminate. In conducting the first-mentioned sequence, each liquid impregnated wood veneer sheet 10 is prepared for hot pressing by positioning thin, thermally deformable polyethylene (PE) films or sheets 40, 42 adjacent the respective opposite surfaces 12, 14 of the veneer sheet 10 as shown, for example, in Figure 4. The PE films 40, 42 function as release films to permit ready removal of the hot pressed veneer sheet from the hot press and also as deformable films that contour to the surface porosity of the veneer sheet surface 12, 14 to displace any liquid impregnant present. Such film deformation thereby retains at least some surface porosity present on the untreated veneer sheet so that a desirable wood texture is preserved on the treated veneer sheet.

The liquid impregnated veneer sheet 10 sandwiched between the PE films 40, 42 is placed between heated upper and lower pressing members 50, 52 of a conven¬ tional hot press 55. As shown in Figure 4, the upper pressing member 52 is driven by a suitable hydraulic cylinder or other pressing device 53 to exert a c- ontrolled pressure on the veneer sheet 10 in a direc¬ tion normal (perpendicular) to the surfaces 12, 14. However, the pressing operation can be conducted using any press construction wherein one or both of the heated pressing members 50, 52 are movable to effect the desired pressing action.

The pressing members 50, 52 are conventionally heated so as to conductively heat the veneer sheet 10 to a controlled temperature to effect polymerization of the monomer by heat activation of the catalyst. The pressing pressure is controlled to provide desired deformation of the PE films 40, 42 into the surface porosity of the veneer sheet 10 to preserve the wood texture of the untreated veneer sheet and to control the veneer surface hardness. During pressing, the pressing members 50, 52 help to block access of ambient oxygen to the impreg- nated veneer sheet 10. This is beneficial for the specific monomer described hereabove since oxygen inhib¬ its its polymerization. The pressed wood veneer preferably includes about 55 to about 85 weight % of the solid polymeric impregnant (i.e. polymer of EDGMA) . After pressing, the upper pressing member 50 is raised to permit removal of the pressed veneer sheet 10 and separation of the films 40, 42 therefrom. The films 40, 42 are simply peeled away from the pressed veneer sheet 10.

For purposes of illustration and not limitation, in hot pressing a wood veneer sheet (0.030 inch in thick¬ ness) impregnated with the aforementioned liquid impreg¬ nant consisting essentially of 99.5 weight % EGDMA monomer and 0.5 weight % 2-2'azobis catalyst, the hot pressing step is conducted at a veneer temperature of 150 degrees C (90 to 180 degrees C being usable) to activate the catalyst to effect polymerization and at a pressure of 100 psi for approximately 1 minute. PE films 40, 42 having a thickness selected in the range from 0.5 to 2.0 mils are used under these pressing conditions for the purposes described hereabove.

The hot pressed veneer sheet 10 is attached to a suitable backed or unbacked furniture substrate, such as, for example, a backed or unbacked particle board having a size/shape suitable, for example, for a desk top, using conventional hot press adhesive bonding tech¬ niques well known in the art. The veneered furniture substrate 100, Figure 6, then can be finished using con- ventional furniture finishing techniques as described herebelow.

In conducting the second-mentioned sequence, each liquid impregnated wood veneer sheet 10 is initially positioned on a suitable furniture substrate 60 backed by an optional backer board 64 as shown in Figure 5. The backer board 64 may comprise an untreated or treated veneer sheet if desired. A suitable thermally activated adhesive (e.g. urea formaldehyde) is provided between the veneer sheet 10 and the substrate 60 and between the substrate 60 and the backer board 64, if present. Then, the veneer/ substrate/optional backer board assembly 70 is placed between the pressing members 50, 52 with a thin, thermally deformable polyethylene (PE) film or sheet 40 between the veneer sheet surface 12 and the pressing member 50 as shown in Figure 5. A similar PE film can be positioned adjacent the surface 65 of the backer board 64, or substrate surface 62 if^' the backer board is not present, in the event adhesive may come in contact with the pressing member 52.

The PE film 40 functions in the manner described hereabove with respect to Figure 4 as a release film to permit ready removal of the hot pressed assembly from the hot press and also as a deformable film that contours to the surface voids of the veneer sheet surface 12 to displace liquid impregnant therefrom and thereby preserve at least some veneer surface porosity.

The pressing members 50, 52 are conventionally heated to conductively heat the assembly 70 to a controlled temperature to effect polymerization of the monomer impregnated in the veneer sheet 10 by heat activation of the catalyst. Application of heat and pressure to the assembly 70 bonds the veneer sheet 10 to the substrate 60 and bonds the substrate to the backer board 64, if present. The pressing pressure is controlled to provide desired deformation of the PE film 40, into the surface porosity of the veneer sheet 10, to control the veneer surface hardness, and to effect veneer sheet/substrate/backer board bonding.

The upper pressing member 50 is driven by the hydraulic cylinder or other pressing device 53 to exert a controlled pressure on the assembly 70 in a direction normal (perpendicular) to the bond interfaces between the veneer sheet 10/ substrate 60/optional backer board 64 to this end.

A veneered, laminated substrate 100, Figure 6, comprising the veneer sheet/furniture substrate/backer board thereby is formed in a one step pressing operation in accordance with this embodiment of the invention. After^' pressing, the upper pressing member 50 is^" raised to permit removal of the veneered substrate 100 and separation of the film 40 therefrom. For purposes of illustration and not limitation, in hot pressing an assembly comprising wood veneer sheet (0.030 inch in thickness) impregnated with the aforemen¬ tioned liquid impregnant consisting essentially of 99.5 weight % EGDMA monomer and 0.5 weight % 2-2'azobis cata¬ lyst, a particle board substrate (1.125 inch in thickness), and a backer board (0.030 inch in thickness) , the hot pressing step is conducted for approximately 5 minutes at a veneer/ substrate/backer broad temperature of 150 degrees C and at a pressure of 100 psi using PE films 40, 42 having thicknesses in the range from 0.5 to 2.0 mils.

The veneered, laminated substrate 100, Figure 6, then can be finished using conventional furniture finishing techniques as described herebelow.

In particular, the veneered, laminated substrate 100 formed by either of the first or second mentioned sequences described hereabove is finished in the manner indicated in Figure 1. For example, the veneered, laminated substrate 100 can be machined by conventional techniques to appropriate end product dimensions, such as to the desired width and length for a desk top. The machined substrate 100 will have an exposed edge 102 around the periphery thereof where the edges of the veneer sheet 10, substrate 60, and backer board 64, if present, are machined and thus visible. As shown in Figure 6, a solid wood edge trim or band member 104 is attachable by adhesive to the exposed edge 102 to hide it from view. The invention envisions in one embodiment impregnating and hot pressing the solid wood edge band 104 in the manner described hereabove to improve its hardness and resistance to indentations and scratching in use as a component of the furniture. To facilitate impregnation and especially hot pressing in the manner described hereabove, the edge band member 104 preferably is impregnated and hot pressed while it has the square or other flat-sided profile shown in sold lines in Figure 5. After attachment to the exposed edge 102, the outer flat side 104a of the treated edge band member 104 can be optionally machined to a rounded pro¬ file, if desired, as shown by phantom lines in Figure 6.

Then, the veneer top surface 12 corresponding to a writing surface and the edge trim or band member 104 are sanded using conventional procedures to desired surface finish. If the wood veneer sheet 10 and edge band member 104 are not previously colored, the sanded veneer top sur¬ face 12 and edge band member 104 can be stained to a de¬ sired decorative color. Some wood species, such as cherry, mahogany, maple, anegre and pine, are normally used in the stained condition and thus can be stained after the sanding operation. Importantly, the solid i- mpregnant (i.e. polymer of EDGMA) formed in-situ in the wood veneer and/or solid wood edge band member does not degrade the response of the wood to staining so that a natural stained wood grain appearance is achieved. Thus, the appearance of the stained veneer top surface 12 and the stained edge band member 104 will closely match one another; i.e. the stained veneer surface 12 will be the aesthetic equivalent of the stained solid wood edge band member 104. Furthermore, the appearance of the stained veneer top surface 12 and the stained edge band member 104 will visually match other furniture of like wood species used in proximity thereto; e.g. other solid wood furniture that might be used in the same office.

Other wood species, such as maple and light oak, are normally not used in the stained condition and thus would not be stained after the aforementioned sanding operation. Importantly, the solid impregnant (i.e. polymer of EDGM) formed in-situ in the wood (wood ve¬ neer and/or solid wood edge band member) is non-de- grading to the natural wood grain appearance such that the treated wood exhibits the same wood grain appearance as untreated wood.

Final finishing of the veneered, laminated substrate 100 involves application to the veneer top surface 12 and edge band member 104 of one or more conventional top coats of nitrocellulose (conversion varnish) or other finish coats as desired. For example, multiple top coats of nitrocellulose can be sprayed on the veneer top surface 12 and edge band member 104 and dried in a heated chamber to finish coat the veneered substrate

100.

Those skilled in the art will appreciate that the veneered, laminated substrate 100 can be finished after assembly to other furniture components; e.g. a veneered desk top substrate can be attached to the desk base and the entire assembly finished (e.g. stained and top coated) in one operation. Alternately, the veneered, laminated substrate 100 can be finished (e.g. stained and top coated) prior to assembly to other furniture components.

The following Examples are offered to illustrate the invention in greater detail without in any way the scope of the invention. Example 1

Natural maple and cherry wood veneer sheets and obeche veneer sheets having thicknesses of 0.030 inch were made into square specimens of 6 inches x 6 inches size. Each veneer specimen was placed in an impregnant container positioned inside of a belljar vacuum chamber. A vacuum level of about 9 millimeters (mm) of Hg was established in the vacuum chamber for a period of 10 or less minutes using a conventional vacuum pump. While maintaining this vacuum level, a degassed, liquid impregnant solution comprising 99.5 weight % EGDMA monomer and 0.5 weight % 2-2' azobis catalyst (VAZO 67) was introduced into the vacuum chamber to immerse the veneer specimen in the container. When the veneer specimen was immersed, the vacuum was released by venting the vacuum chamber to ambient atmosphere, providing atmospheric pressure in the chamber. Each specimen remained immersed in the liquid impregnant for about 15 minutes and then was removed from the container. Each liquid impregnated veneer specimen was hot pressed in a pressing apparatus similar to press 55 shown in Figures- 3 and 4 at about 100 degrees C and a pressure of 200 psi for 3-5 minutes.

The treated wood veneer specimens were laminated to a 1.0 inch thick particle board substrate, sanded, stained, and top coated with a conventional conversion varnish prior to being subjected to testing to determine the resistance to writing indentations. Wood veneer specimens not treated in accordance with the invention but finished in like manner were made for comparison purposes.

The resistance of the treated and untreated wood ve¬ neer specimens to writing indentation was determined using the test device shown in Figure 8. The test de¬ vice comprised a cylindrical housing 200 (diameter, d, of 3 inches and height, h, of about 3 inches) and a frusto-conical plug 210 received in the housing 200. The test device weighed 4.275 pounds. The plug 210 in¬ cluded a rounded point 212 having a radius of 0.015 inch mounted thereon to simulate the ball of a ballpoint pen. The plug 210 was biased downwardly by a spring 214 confined in the housing 200 by a threaded set screw 216 in the manner shown in Figure 8. The set screw 216 pro¬ vided means for adjusting the simulated writing pressure at different values. The indentation resistance test was conducted by manually moving the test device shown in Figure 8 laterally across the finished, upper wood veneer specimen surface. In particular, the test was conducted manually by hand placed atop the device and applying downward pressure to maintain the bottom of the test device even with the veneer specimen while moving the test device a preselected lateral distance; e.g. 4 inches.

The resistance of the wood specimen to indentation by the test point 212 was determined^•by the operator 's passing a finger over the path of movement of the test device in a direction transverse thereto to feel for indentation of the veneer. The first sensed indentation (damage) of the veneer surface and simulated writing pressure where the first sensed indentations occurred is presented in the bar graph of Figure 7. The data set forth in the bar graph represent an average value for hundreds of each type of treated and untreated wood veneer specimens tested. From the bar graph of Figure 7, it is apparent that the treated maple, cherry, and obeche veneer specimens exhibited a dramatic improvement in indentation resis¬ tance to simulated writing pressure as compared to wood veneer specimens which were finished in a like manner but were not treated in accordance with the invention. In particular, for untreated maple veneer specimens, the first sensed surface indentation occurred at an average writing pressure of 2.2 pounds, whereas for maple spec¬ imens treated in accordance with the invention, the first sensed surface indentation occurred at an average writing pressure of 6 pounds.

For untreated cherry veneer specimens, the first sensed surface indentation occurred at an average writing pressure of 1.3 pounds, whereas for cherry specimens treated in accordance with the invention, the first sensed surface indentation occurred at an average writing pressure of 7 pounds.

For untreated obeche veneer specimens, the first sensed surface indentation occurred at an average writing pressure of just below l pound, whereas for obeche specimens treated in accordance with the inven¬ tion, the first sensed surface indentation occurred at an average writing pressure of 5 pounds.

Figures 9A-9C and 10A-10C are photographs of surfaces of respective untreated and treated maple, cherry and obeche (mahogany) veneer specimens after identation testing illustrating visible surface indentation/scratching of the untreated specimens and lack of surface indentation/scratching of treated specimens.

Moreover, the wood grain appearance of the treated maple, cherry, and obeche .veneers was observed to be the approximate aesthetic equivalent of that of the respective untreated veneers. For example, a comparison of Figures 9A-9C and 10A-10C illustrates that the wood grain appearance of the treated specimens is the approximate aesthetic equivalent of that of the untreated specimens.

Figures 11A-11C are photomicrographs of untreated specimens of maple, cherry, and obeche (mahogany) , respectively, and Figures 12A-12C are photographs of similar specimens treated in accordance with the invention. Figures 12A-12C illustrate the substantial degree and uniformity of impregnation of the wood voids achieved in the treated specimens.

Example 2

Natural maple wood veneer sheets having thicknesses of 0.030 inch were made into square specimens of 6 inches x 6 inches size. Each veneer specimen was placed and sealed inside vacuum/atmospheric impregnation con¬ tainer, Figure 6. A vacuum level of 9 mm of Hg was established in the vacuum chamber for a period of 10 or less minutes using a vacuum pump. While maintaining this vacuum level, a liquid impregnant solution comprising either a) 99.5 weight % EGDMA monomer and 0.5 weight % 2-2 ' azobis catalyst (VAZO 67) or b) 99.5 weight % methyl methacrylate (MMA) monomer and 0.5 weight % 2-2' azobis catalyst (VAZO 67) was introduced into the chamber to immerse the veneer specimen. When the veneer specimen was immersed, the vacuum was released by vent¬ ing the chamber to ambient atmosphere, providing atmospheric pressure in the chamber. Each specimen remained immersed in the liquid impregnant for 15-45 minutes and then was removed from the container.

This immersion time was chosen based on preliminary tests to correlate immersion time to weight gain of the specimens, wherein immersion times of 15, 25, 35, and 45 minutes produced specimen percent weight gains of 63.4, 64.2, 68.3, and 68.8 %, respectively, under the conditions disclosed.

Each liquid impregnated veneer specimen was hot pressed in a pressing apparatus similar to press 55 shown in Figures 3 and 4 at 100 degrees C and a pres¬ sure of 200 psi for 10 minutes. The weight gain of the specimens after the impregnation treatment was measured. The treated wood veneer specimens were laminated to a 0.75 inch thick plywood substrate, sanded, stained, and top coated with a conventional conversion varnish prior to being subjected to testing to determine the resistance to writing indentations.

The treated wood veneer specimens and untreated natural maple veneer specimens were subjected to the indentation test described above.

The test results are shown in Table I herebelow.

TABLE I

Indentation

Specimen Weiσht Gain Force (lbs,

Untreated 0 .0.7

MMA 55.8 1.0

EGDM 52.0 2.2

It is apparent that the veneer specimens impregnated with polymerized methyl methacrylate monomer exhibited only a slight improvement in scratch resistance as compared to the untreated veneer specimens. On the other hand, the veneer specimens impregnated with polymerized EDGM monomer exhibited greater than a three-fold improvement in scratch resistance as compared to the untreated veneer specimen. This example indicates that substantially undiluted EGDMA monomer is the preferred liquid impregnant as compared to substantially undiluted methyl methacrylate liquid impregnant.

Example 3

Natural earlywood and latewood maple wood veneer sheets having thicknesses of 0.030 inch were made into square specimens using the procedures and the liquid i- pregnant comprising the EGDMA monomer and VAZO 67 in proportions set forth in Example 2.

The treated earlywood and latewood maple veneer specimens were subjected to the indentation test described hereabove in Example 1.

The test results are shown in Table II herebelow. TABLE II

Indentation Wood Veneer Type Force (lbs

Earlywood 2.1

Latewood 2.3

This example illustrates that the scratch -resistance of treated earlywood veneers and treated latewood veneers was comparable. A more uniform hardness ^"thereby can be achieved in a veneer sheet having earlywood and latewood regions.

Example 4

Natural maple wood veneer sheets having thicknesses of 0.030 inch were made into square specimens using the procedures and the liquid impregnant comprising the EGDMA monomer and VAZO 67 in proportions set forth in Example 2. Treated and untreated specimens were bonded to 1.0 inch thick particle board to form a laminate.

The treated wood veneer laminate. specimens and untreated wood veneer laminate specimens were subjected to a falling dart test to measure the resistance of the laminate specimens to indentation. The falling dart test was conducted at 20 inch-pounds of force pursuant to ASTM test D5178-91. The dart was allowed to fall onto the wood veneer surface of each laminate specimen. The depth of penetration of the falling dart into the lami¬ nate specimen was measured.

The test results are shown in Table III herebelow.

TABLE III Specimen Indentation Untreated .042 inch

MMA .040 inch

EGDM .038 inch

It is apparent that the veneer specimens impregnated with polymerized methyl methacrylate monomer exhibited a lesser indentation resistance than the veneer specimens impregnated with polymerized EDGM monomer. This example also indicates that substantially undiluted EGDM monomer is the preferred liquid impregnant as compared to substantially undiluted methyl methacrylate liquid impr¬ egnant.

Example 5

Natural ash, cherry, mahogany, oak, and pine wood veneer sheets having thicknesses of 0.030 inch were made into square specimens using the procedures and the liquid impregnant comprising the EGDMA monomer and VAZO 67 in proportions set forth in Example 2. The weight gain of the specimens was measured after impregnation. Treated specimens were bonded to 1.0 inch thick particle board to form a laminate.

The treated veneer laminate specimens were subjected to the falling dart test and the indentation test described hereabove in Example 1.

The test results are shown in Table IV herebelow. ^' TABLE IV

Indentation

Specimen Weiαht % Gain Indentation Force

Ash 70 .032 inch 2.4 lbs

Cherry 82 .034 2.2

Mahogany 75 .035 2.1

Oak 65 .028 2.7

Pine 85 .042 2.0

Example 6

Maple and cherry natural wood veneer sheets having thicknesses of 0.030 inch were made into specimens of 6 inches x 6 inches size. Each veneer specimen was placed and sealed inside vacuum/atmospheric impregnation container, Figure 6. A vacuum level of 9 mm of Hg was established in the vacuum chamber for a period of 15 minutes using a vacuum pump. While maintaining this vacuum level, a liquid impregnant solution comprising 93.5 weight % EGDMA monomer, 6 weight % coloring dye (Orasol dye available from Ciba-Geigy, Newport, Delaware), and 0.5 weight % 2-2' azobis catalyst (VAZO 67) was introduced into the chamber to immerse the veneer specimen. When the veneer specimen was immersed, the vacuum was released by venting the chamber to ambi¬ ent atmosphere, providing atmospheric pressure in the chamber. Each specimen remained immersed in the liquid impregnant for 15 minutes and then was removed from the container. Each liquid impregnated veneer specimen was hot pressed in a pressing apparatus similar to press 55 shown in Figures 3 and 4 at 100 degrees C and a pres¬ sure of 200 psi for 10 minutes.

This impregnation/coloring step was effective to dye the wood veneer to the desired color.

The treated wood veneer specimens then were finished and where observed to retain the wood grain appearance of untreated wood veneer in the finished condition. ^{' •}

As is apparent from the detailed discussion of the invention set forth hereabove, a combination of advan¬ tages are achieved by the present invention in the treatment of wood veneer and solid wood; namely, the surface hardness of wood veneer and solid wood can be increased and rendered more uniform to resist indenta¬ tions and scratching, especially "read through" damage at relatively high writing pressures encountered in use as a writing surface, while the treated wood retains its natural appearance. Moreover, the treated wood is amena¬ ble to coloring at the time of impregnation or during conventional furniture finishing operations.

While the invention has been described in terms of specific embodiments thereof, it is not intended limited thereto but rather only to the extent set forth hereafter in the following claims.

Claims

Claims ;The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Method of treating a wood veneer sheet to provide a writing surface thereon having improved resistance to writing indentations, comprising: impregnating the wood veneer sheet proximate a surface thereof with a liquid impregnant comprising a monomer that penetrates into the wood veneer voids and is polymerizable therein to a solid polymeric impregnant that is non-degrading to the veneer wood grain appearance, and a thermally activated catalyst for polymerizing said monomer, and pressing the impregnated wood veneer sheet under temperature and pressure conditions to polymerize said monomer and form in the wood veneer said solid polymeric impregnant that imparts to said surface increased hard¬ ness and resistance to writing indentations as compared to untreated wood veneer sheet while retaining the wood grain appearance thereof.

2. The method of Claim 1 wherein a natural wood veneer sheet or reconstituted wood veneer sheet is im¬ pregnated with said liquid impregnant.

3. The method of Claim 1 wherein the wood veneer sheet is impregnated by subjecting the wood veneer sheet to a relative vacuum and then contacting the liquid impregnant with the wood veneer sheet.

4. The method of Claim 1 wherein after pressing, the wood veneer sheet includes about 55 to about 85 weight % of said polymeric impregnant.

5. The method of Claim 1 wherein said impregnated wood veneer sheet is pressed by a heated press member engaging said surface.

6. The method of Claim 5 wherein said impregnated wood veneer sheet is pressed in a manner to retain some voids present at the surface of the untreated veneer sheet.

7. The method of Claim 6 including disposing a thermally deformable material between said press member and said surface and deforming said material into voids present at said surface.

8. The method of Claim 5 including juxtaposing the impregnated wood veneer sheet and a substrate and pressing said impregnated wood veneer and said substrate together between heated press members to form a laminate thereof.

9. The method of Claim 8 wherein said impregnated veneer sheet is pressed in a manner to retain some voids present at the surface of the untreated veneer sheet.

10. The method of Claim 9 including disposing a thermally deformable material between a said press member and said surface and deforming said material into voids present at said surface.

11. The method of Claim 1 wherein said liquid impregnant comprises substantially undiluted acrylic resin monomer and the catalyst.

12. The method of Claim 11 wherein said monomer comprises ethylene glycol dimethylacrylate.

13. The method of Claim 12 wherein said liquid impregnant comprises about 0.5 to about 2.0 weight % catalyst and the balance essentially ethylene glycol dimethylacrylate.

14. The method of Claim 11 wherein said liquid impregnant includes a coloring agent such that said wood veneer is colored during impregnation.

15. The method of Claim 1 wherein after said wood veneer sheet is pressed, said surface is colored.

16. Method of making furniture having a wood ve¬ neer surface with improved resistance to writing inden¬ tations, comprising: impregnating a wood veneer sheet proximate a sur¬ face thereof with a liquid impregnant comprising a mono¬ mer that penetrates into the wood veneer voids and is polymerizable therein to a solid polymeric impregnant that is non-degrading to the veneer wood grain appearance and a thermally activated catalyst for polymerizing said monomer, pressing the impregnated wood veneer sheet under temperature and pressure conditions to polymerize said monomer and form in the wood veneer said solid polymeric impregnant that imparts to said surface increased hard¬ ness and resistance to indentations as compared to un¬ treated wood veneer sheet while retaining the wood grain appearance thereof, and attaching the pressed wood veneer sheet to a furni¬ ture substrate to provide a writing surface thereon.

17. The method of Claim 16 including surface finishing the wood veneer after attachment to the furni¬ ture substrate.

18. The method of Claim 16 wherein the wood veneer sheet is impregnated with a liquid impregnant comprising a substantially undiluted acrylic resin monomer and the catalyst.

19. The method of Claim 18 wherein said monomer comprises substantially undiluted ethylene glycol dimethylacrylate.

20. The method of Claim 18 wherein said liquid impregnant comprises about 0.5 to about 2.0 weight % catalyst and the balance essentially ethylene glycol dimethylacrylate monomer.

21. Method of making furniture having a wood veneer surface with improved resistance to writing indentations, comprising: impregnating a wood veneer sheet proximate a surface thereof with a liquid impregnant comprising a monomer that penetrates into the wood veneer voids and is polymerizable therein to a solid polymeric impregnant that is non-degrading to the veneer wood grain appearance and a thermally activated catalyst for polymerizing said monomer, positioning the impregnated wood veneer sheet and the substrate in juxtaposition with adhesive therebetween, and pressing the impregnated wood veneer sheet and the substrate under temperature and pressure conditions to polymerize said monomer and form in the wood veneer said solid polymeric impregnant that imparts to said surface increased hardness and resistance to indentations as compared to untreated wood veneer sheet while retaining the wood grain appearance thereof and to bond said wood veneer sheet and said substrate.

22. The method of Claim 21 including surface finishing the wood veneer after bonding to said substrate.

23. The method of Claim 21 wherein the wood veneer sheet is impregnated with a liquid impregnant comprising a substantially undiluted acrylic resin monomer and the catalyst.

24. The method of Claim 23 wherein said monomer comprises substantially undiluted ethylene glycol dimethylacrylate.

25. The method of Claim 23 wherein said liquid impregnant comprises about 0.5 to about 2.0 weight % catalyst and the balance essentially ethylene glycol dimethylacrylate monomer.

26. A method of hardening wood, comprising: impregnating at least a portion of the wood with a liquid impregnant comprising substantially undiluted ethylene glycol dimethylacrylate monomer and a thermally activated catalyst, and polymerizing the monomer in said wood to form a solid polymeric impregnant comprising a polymer of ethylene glycol dimethylacrylate that increases wood hardness and retains the wood grain appearance of untreated wood at a surface thereof.

27. The method of Claim 26 wherein after polymerization, the wood veneer includes about 55 to about 85 weight % of said polymeric impregnant.

28. The method of Claim 26 wherein said monomer is polymerized by pressing the impregnated wood by a heated press member engaging said surface.

29. The method of Claim 28 wherein said impregnat¬ ed wood is pressed in a manner to retain some voids present at the surface of the untreated veneer sheet.

30. The method of Claim 29 including disposing a thermally deformable material between said press member and said surface, and deforming said material into said voids at said surface.

31. A method of coloring and hardening wood, comprising: impregnating at least a portion of the wood with a liquid impregnant comprising a monomer, a coloring agent, and a catalyst, said coloring agent imparting a color to said wood, and polymerizing the monomer in said wood to form a solid polymeric impregnant therein that increases wood hardness.

32. The method of Claim 31 wherein said coloring agent comprises a dye.

33. The method of Claim 31 wherein said monomer comprises ethylene glycol dimethylacrylate.

34. The method of Claim 33 wherein said catalyst comprises a thermally activated catalyst.

35. The method of Claim 31 where polymerization of said monomer is effected by heating the impregnated wood.

36. The method of Claim 35 wherein the impregnated wood is heated by engagement with a heated press member.

37. The method of Claim 31 wherein wood veneer is colored and hardened.

38. The method of Claim 31 wherein solid softwood or hardwood is colored and hardened.

39. A wood veneer writing surface having improved resistance to writing indentations, comprising wood veneer impregnated proximate a surface thereof with a solid polymeric impregnant that provides a higher, more uniform surface hardness and thus higher resistance to writing indentations as compared to untreated wood veneer, said solid polymeric impregnant being non- degrading to the wood grain appearance of said veneer.

40. The writing surface of Claim 39 wherein the polymeric impregnant comprises solely a polymer of ethylene glycol dimethacrylate.

41. The writing surface of Claim 39 wherein the wood veneer surface is colored.

42. The writing surface of Claim 39 wherein the treated wood veneer surface includes voids at said surface.

43. The writing surface of Claim 39 wherein said wood veneer is a pressed wood veneer sheet.

44. Furniture having a wood veneer writing surface resistant to writing indentations, comprising a furniture substrate and a treated wood veneer surface on said substrate, said wood veneer surface comprising wood veneer impregnated proximate a surface thereof with a solid polymeric impregnant that provides a higher, more uniform surface hardness and thus higher resistance to indentations as compared to untreated wood veneer, said solid polymeric impregnant being non-degrading to the wood grain appearance of said veneer.

45. The furniture of Claim 44 wherein the wood veneer surface is colored.

46. The furniture of Claim 44 wherein the treated wood veneer surface includes voids at said surface.

47. The furniture of Claim 44 wherein the polymeric impregnant comprises solely a polymer of ethylene glycol dimethylacrylate.

48. The furniture of Claim 44 comprising office furniture.

49. A treated wood member impregnated with a solid polymeric impregnant comprising solely a polymer of ethylene glycol dimethylacrylate.

50. The wood member of Claim 49 comprising a wood veneer sheet.

51. The wood member of Claim 50 comprising solid softwood or hardwood.

52. The wood member of Claim 49 wherein said wood member is colored in the liquid impregnated condition.