WO2004035856A1

WO2004035856A1 - Process for metal-coating wood

Info

Publication number: WO2004035856A1
Application number: PCT/GB2003/004157
Authority: WO
Inventors: Stephen Anthony Noble
Original assignee: Stephen Anthony Noble
Priority date: 2002-10-19
Filing date: 2003-09-26
Publication date: 2004-04-29
Also published as: GB0224351D0; AU2003267641A1

Abstract

A process for applying a metal coating to a wood substrate (10) involves an initial step of abrading a surface (11) of the substrate (10), so as to produce an enhances three-dimensional grain profile defined by a series of peaks (17) and troughs (18) on said surface (11). A base coating (21) including a first metal is then applied to the abraded surface (16), following which a further coating (22) including a second metal is applied on top of the base coating (21). Finally, the coated substrate (40) is subjected to a finishing process in which some of the further coating (22) is removed to expose some of the base coating (21) therebeneath.

Description

Process for Meta l-Coati ng Wood

This invention relates in a first aspect to a process for applying a metal coating to a wood substrate In a second aspect, the invention also relates to a wooden article having a metal coating thereon

A wide variety of decorative and protective surface coatings and treatments for wood are known In fact, the number of available

treatments is almost as vast as the possible end-uses of wood itself

Each different treatment is designed to give a different effect to the

finished wood product, whether that effect be purely decorative, purely

protective or a combination of the two Commonly used coatings

include paints, varnishes, waxes, oils, lacquers, resins, creosote and the like Commonly used non-coating techniques include weathering

and bleaching amongst others

The demand for individuality and originality in wood products is ever-increasing, particularly in the fields of furniture and home interior

design, with designers constantly looking for fresh and innovative

aesthetic effects

The present invention seeks to provide a process by which a

unique and imaginative aesthetic effect can be applied to wood either

before or after it has been worked into a finished product, and which

also imparts certain protective properties to the finished wood product This is achieved by the adaptation of existing technology from the field

of metal coating

According to a first aspect of the present invention there is provided a process for applying a metal coating to a wood substrate comprising the successive steps of

(a) abrading a surface of the wood substrate,

(b) applying a base coating including a first metal to the

abraded surface,

(c) applying a further coating including a second metal, and

(d) subjecting the coated substrate to a finishing process

The term "abrading" as used herein , refers to any process by

which material is removed from the surface of the wood substrate by

being worn away Thus, the term includes for example the use of high

pressure liquids as well as particulate and abrasive solids The term

"metal" as used herein includes metal ions, and compounds and alloys

of metals, as well as metals in their elemental form

The aesthetic effect produced by the process is most effective

when the wood substrate used has a readily-visible grain pattern The wood substrate is therefore preferably selected from pine, ash, beech, maple, birch, oak, cherry, spruce, cedar, elm, walnut or eucalyptus

Most preferably, the wood substrate is pine

The abrading process in step (a) preferably includes a

procedure whereby the relatively soft wood material between

successive grains is removed, down to a pre-determmed depth from

the surface of the substrate The depth to which the surface is

abraded will vary according to user preference, but will typically be in the range of from 1 to 2 mm This produces an enhanced three- dimensional grain profile defined by a series of peaks and troughs on the surface of the substrate This may be achieved by a variety of different techniques, however it is currently preferred to employ a grit-blasting procedure, utilising a particulate abrasive selected from aluminium oxide, chilled iron, garnet, copper slag, mineral grit or plastic blast media. Most preferably, the abrasive is aluminium oxide. Possible alternative methods include the use of carbon dioxide pellets, or even vegetable material such as crushed nut shells and the like.

The enhanced three-dimensional grain profile contributes to one of the unique aesthetic properties of wood which has been subjected to the process of the present invention. When the wood substrate emerging from step (a) is subsequently coated with metal in steps (b) and (c), each metal coating follows the contours of the surface, adhering both to the peaks and the troughs. By subsequently removing, during step (d), an upper layer of the coating from the peaks only, down to a pre-determined depth, a distinctive pattern is obtained in the finished product, wherein the metal coating on the peaks is visibly different from the metal coating in the troughs.

The finishing process in step (d) therefore preferably includes a procedure in which the further coating that has been applied in step (c) is removed from above the grain peaks, thereby exposing the underlying base coating, but is retained in the grain troughs. In certain embodiments of the present invention, step (c) is repeated one or more times so as to provide multiple coatings. In such embodiments, the corresponding procedure in step (d) involves removing all such further coatings from the areas above the grain peaks, thereby exposing all previously-applied coatings

It has been found that of all available metal coatings, zinc displays the best adherence to the abraded wood substrate It is therefore preferred that the base coating in step (b) includes zinc, and most preferably is a tin-zinc alloy The base coating is preferably

applied to a thickness in the range of from 25 to 100 μm, and most

preferably is at least 75 μm

The metal employed in the further coatιng(s) applied in step (c) may in theory be any metal or alloy which is capable of being formed into a wire or ground into a powder Preferably, the metal is selected from copper, zinc, tin, or iron, and in particular may be an alloy selected from brass, bronze or stainless steel

The metal coatings in steps (b) and (c) are preferably applied by a thermal spraying process Such processes are well known from the field of metal spraying, and therefore will not be described here in detail The particular process used may be selected from a flame spraying process, a plasma spraying process, a high velocity oxygen fuel (HVOF) spraying process or an electric arc spraying process Most preferably, an electric arc spraying process is used A single application of the further coating in step (c) will produce the desired aesthetic effect in the finished product However, in an alternative embodiment of the process, step (c) is repeated one or more times thereby to apply one or more further coatings Each repetition of step (c) preferably utilises a coating including a different metal to that of the previous coating As has already been discussed, the finishing process in step (d)

preferably includes a procedure in which the or each further coating is removed from above the grain peaks. Alternatively, step (d) may

include a step of polishing only the grain peaks thereby imparting a sheen to the peaks in contrast to the troughs which will remain dull.

The two procedures may of course be combined for any one substrate,

so that some of the peaks have an underlying coating exposed , whilst

others are merely polished . Most preferably, step (d) includes one or

more of the following procedures, namely grinding, sanding , brushing,

burnishing, and polishing. Step (d) preferably also includes an

additional procedure of lacquer sealing the coated substrate to prevent

oxidation of the metal coatings.

The scope of the present invention also extends to include a wooden article having a metal coating thereon which has been applied

by a process as described above.

Therefore, according to a second aspect of the present

invention, there is provided a wooden article having a metal coating

thereon, said wooden article further having an enhanced three- dimensional grain profile defined by a series of peaks and troughs, and

wherein the metal coating on the peaks is visibly different to the metal

coating in the troughs.

The provision of metal coatings on the wooden article, gives rise to further benefits of a protective, rather than a decorative nature. The wood is protected by being isolated from the atmosphere, whilst also being made substantially impervious to liquids, and substantially fire- retardant. However, despite the presence of the metal coatings, it has been found that metal-coated wooden articles produced according to the present invention, can still easily be cut and worked as one would

do with untreated wood.

The present invention will now be described in detail, though only by way of example, with reference to the accompanying drawings,

in which:

Figure 1 is a perspective view of a wood substrate, prior to being

processed according to the present invention;

Figure 2 is a cross-sectional view of the substrate of Figure 1 ;

Figure 3 is a cross-sectional view of the substrate of Figures 1 and 2, after having been abraded in step (a) of the process of the

present invention;

Figure 4 is a cross-sectional view of the substrate of Figure 3, after a base coating has been applied in step (b) of the process;

Figure 5 is a cross-sectional view of the substrate of Figure 4,

after a further coating has been applied in step (c); and

Figure 6 is a cross-sectional view of the substrate of Figure 5, after having been subjected to the finishing process of step (d).

Referring first to Figure 1 , there is shown a wood substrate,

generally indicated 10, represented here as a generally orthogonal block having a flat upper surface 1 1 , bound by sides 12 and ends 1 3. The substrate 1 0 has a clearly visible natural grain pattern, consisting of a plurality of grain lines 14 extending through the substrate 1 0 in a direction approximately parallel to the sides 12. Visible gram lines 14 on the surface of a substrate are exposed by the action of cutting through natural tree rings in the raw timber,

when forming the substrate Evidence of this can be seen on the ends

1 3 of the substrate 1 0, where the gram lines 14 are curved, as appears best from Figure 2 The wood material 1 5 in the areas between the

grain lines 14, is somewhat softer than that at and immediately

adjacent the grain lines 14

One embodiment of the process of the present invention will now

be described The untreated wood substrate 10, as shown in Figure 2

is abraded in step (a) of the process, by grit-blasting with aluminium

oxide particles having a diameter of between 1 05 and 21 0 μm, using a

pressure blast system operating at around 100 psi (689 kPa) This removes the soft material 15 between the gram lines 14 down to a

depth of around 1 to 2 mm As can be seen best from Figure 3, the abraded substrate 20 emerging from step (a) thus has a contoured surface 16 consisting of a

series of peaks 17 and troughs 1 8 Each peak 17 is associated with a

gram line 14, whilst each trough 1 8 is associated with an area between

the gram lines 14 from which the soft material 1 5 has been removed in

step (a)

Note that Figure 3 (and subsequent Figures) have been

elongated in the vertical direction, so as to exaggerate the contours of the surface 16 and subsequent coatings applied thereto, in order to make the Figures clearer Additionally, the thickness of the coatings in Figu res 4 to 6 is exaggerated, and not to scale The abraded substrate 20, is coated with zinc in step (b) of the

process This is applied by an electric arc spray gun, operating at a

voltage of 22 V and an amperage of 1 00 A, from a 2 3 mm (1 1 gauge)

zinc wire The pressures of the primary and secondary air supplies are each set at 90 psi (620 kPa), and the spray gun is arranged at a

distance of between 1 50 to 200 mm (6 to 8 in) from the contoured

surface 16 of the substrate 20 As is shown in Figure 4, the base- coated substrate 30 emerging from step (b) thus has a layer of zinc

base coating 21 adhered to the contoured surface 16 The base

coating 21 is typically applied to a depth of around 75 μm

In step (c) of the process, the base-coated substrate 30 is spray-

coated with a second metal, such as copper, again by an electric arc

spray process The process is essentially the same as that described above for step (b), except that the operating voltage of the spray gun

may vary between 22 and 33 V, depending on the metal used

As is shown in Figure 5, the further-coated substrate 40 emerging from step (c) thus has a layer of copper top coating 22

adhered to the base coating 21 Although represented in Figure 5 as

being of approximately the same thickness as the base coating 21 , the

top coating 22 may in practice be up to around 1000 μm in thickness

If desired , step (c) may be repeated one or more times with different coatings in order to build up a multi-layer coating

Finally, in step (d) of the process, the coated substrate 40 is

subjected to a finishing process, in which those areas of the top coating 22 which overlie the peaks 1 7 of the contoured surface 16 , are removed down to a pre-determmed depth, which will be set according

to user preference This is achieved by grinding or sanding the coated substrate 40, followed if desired by an additional step of polishing in

order to impart a sheen to the exposed metal coatings 21 , 22 As is shown in Figure 6, the finished article 50 emerging from

step (d) thus has a discontinuous level surface consisting of a series

of platforms 23 corresponding to the position of the peaks 17 in the

contoured surface 16 The size of the platforms 23 will be determined

by the depth down to which the top coating 22 is removed At each

such platform 23, the base coating 21 visibly protrudes through the

gaps in the top coating 22 created in step (d), whilst between the

platforms 23, in the areas corresponding to the troughs 18 in the contoured surface 16, the top coating 22 remains

The grain lines 14 are thus highlighted or "picked out" in one metal (/ e the base coating 21 ), whilst the remainder of the surface of

the article 50 is coated with another metal (/ e the top coating 22)

This provides a unique and striking aesthetic effect

It will be appreciated that where step (c) has been repeated one

or more times with further coatings, the visual effect will vary in that the base coating 21 will be visible at the peaks 1 7, a first-applied

further coating will be visible in the areas immediately adjacent the

peaks, and a subsequently-applied further coating will remain elsewhere on the article 50 The possible variations achievable by using further coatings, and by varying the depth to which the finishing process is applied, are virtually unlimited Further steps of applying conventional coatings, such as paint, to the coated substrate prior to step (d) may also be used, in order to

provide a still further variation to the unique aesthetic qualities of wooden articles produced by the process of the present invention

Claims

1 A process for applying a metal coating to a wood substrate, comprising the successive steps of

(a) abrading a surface of the wood substrate, (b) applying a base coating including a first metal to the

abraded surface,

(e) applying a further coating including a second metal, and

(f) subjecting the coated substrate to a finishing process

2 A process as claimed in claim 1 , wherein the wood substrate is

selected from a wood naturally having a readily-visible grain pattern

3 A process as claimed in claim 1 or claim 2, wherein the wood substrate is selected from pine, ash, beech, maple, birch, oak, cherry,

spruce, cedar, elm, walnut or eucalyptus

4 A process as claimed in any of the preceding claims wherein the

wood substrate is pine

5 A process as claimed in any of claims 2 to 4, wherein step (a)

includes a procedure whereby relatively soft wood material between successive grains is removed, thereby producing an enhanced three-

dimensional grain pattern defined by a series of peaks and troughs on

the surface of the substrate

6 A process as claimed in any claim 5, wherein step (a) includes a

grit-blasting procedure

7 A process as claimed in claim 6, wherein the grit-blasting utilises a particulate abrasive selected from aluminium oxide, chilled iron, garnet, copper slag , mineral grit or plastic blast media

8. A process as claimed in claim 7, wherein the abrasive is

aluminium oxide.

9. A process as claimed in any of claims 5 to 8, wherein the finishing process in step (d) includes a procedure in which a further

coating applied in step (c) is removed from the grain peaks, thereby

exposing an underlying coating , but is retained in the grain troughs.

10. A process as claimed in any of the preceding claims, wherein

the base coating applied in step (b) includes zinc.

1 1 . A process as claimed in any of the preceding claims, wherein the base coating applied in step (b) is a tin-zinc alloy.

12. A process as claimed in any of the preceding claims, wherein

the base coating in step (b) is applied to a thickness of at least 75 μm.

1 3. A process as claimed in any of the preceding claims, wherein

the further coating applied in step (c) includes a metal selected from

copper, zinc, tin, or iron.

14. A process as claimed in any of the preceding claims, wherein the further coating applied in step (c) includes an alloy selected from

brass, bronze or stainless steel.

1 5. A process as claimed in any of the preceding claims, wherein in

steps (b) and (c) the metal coatings are applied by a thermal spraying

process.

16. A process as claimed in any of the preceding claims, wherein in steps (b) and (c) the metal coatings are applied by a process selected

from a flame spraying process, a plasma spraying process, a high velocity oxygen fuel (HVOF) spraying process or an electric arc spraying process.

17. A process as claimed in any of the preceding claims, wherein in steps (b) and (c) the metal coatings are applied by an electric arc spraying process.

18. A process as claimed in any of the preceding claims, wherein step (c) is repeated one or more times thereby to apply two or more further coatings.

19. A process as claimed in claim 18, wherein each repetition of step (c) utilises a further coating including a different metal to the previous coating.

20. A process as claimed in any of the preceding claims, wherein the finishing process in step (d) including one or more of the following procedures, namely burnishing, grinding, sanding, brushing and/or polishing.

21 . A process as claimed in any of the preceding claims, wherein step (d) also includes a procedure of lacquer-sealing the coated substrate, thereby to prevent oxidation of the metal coatings.

22. A wooden article having a metal coating thereon, said metal coating having been applied by a process as claimed in any of claims 1 to 21.

23. A wooden article having a metal coating thereon, said wooden article further having an enhanced three-dimensional grain pattern defined by a series of peaks and troughs, and wherein the metal coating on the peaks is visibly different to the metal coating in the troughs.