Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
A6-A4-,00 13:48 TUD DEZ.S SG 5.1 ID= +49 351 4637170 S.02
1
Wood component and ~a method for the production and application of the
same
Description
The invention relates to a w ~ od component in which the wood has altered
properties in geo-
metrically defined areas. Th~ invention also relates to a method for producing
such compo-
nents and to the application ~f said component. 1'he ixivention can be
employed in the wood-
working and wood processi ~ industries, in the building arid construction
industries, and in
the craft and trade.
In woodworking, lasers are sed for, in addition to surveying processes,
cutting and piercing
processes. A novel applicati n field is the removal of material using laser
irradiation. Selt
man, J.: Freilegen der Holzs durch UV-Bestrahlung (Laying bare of the wood
structure
by UV-irradiation), I-Iolz al~ Roh- and Werkstoff, Springer-Verlag, 53(1995),
pp. 225-228;
and Panzncr, M. et al.: Experimental Investigation of the Laser Ablation
Process on Wood
Surfaces, Fourth Inteniatio Conference on Lascr Ablation COLA, Monterey,
California,
1997 describe different s' ibilities arid methods for the removal of the wood
layer spoiled
9
by mechanical removing prq~cesses using electromagnetic beams of different
wavelengths.
From DE 94 02 G8I.5 U1, ~ device is known for the processing of glass,
plastics, semicon-
ductors, wood or ceramics, hick uses laser radiation from a laser radiation
source that emits
laser radiation in form of a l~ser beam, focussing this laser radiation
through a focussing opti-
w w
This device is designed to a able an effective removing mechanism which is
designed to heat
the ,material to be processed ery heavily in the range of wavelengths of 1.4
Ltm to 3.0 pm so
that so-called micro-explosi ns occur. The heated material is removed. This
process is used
cal system onto a glass, pl ' tic, semiconductor, wood or ceramic material
component. 'Ibis
device is characterized in tlialt the laser radiation used has a wavelen h of
l .4 m to 3.0 m.
for marking components o~ generating mechanical stresses in glass tubes to
subsequently
break them in a melting zonel,.
In DE 40 33 2SS A1 a mcth~d is described that is designed to upgrade wood
veneers for vis-
ual effect by emphasizing t a grain. This is reached by pyrolytic browning of
the wood sur-
face using IR-radiation. The alterations following the laser cutting of wood
and wood materi-
als were investigated, amo others, by Parameswaraa, N.: Feinstrukturelle
Veriinderungen
an durch Laserstratil getr~nnten Schnittfl~.chen von Holz and Holzwerkstoffen
(Fine-
CA 02306630 2000-04-14
A6-A4-90 13:48 TUD DEZ.S SC 5.1 ID= +49 351 4637170 S~A3
2
structural alterations of laser-cut surfaces of wood and wood materials), Holz
als Roh- and
Werkstoff, Berlin 40(1982) 1, pp. 421-X28, who found the following: The brown
to black
colour of the cutting surfac Ids is due to the mainly thermal cutting process
and typical of a
pyrolysis in the cellular ar I of separating. A surface largely melted down is
produced which
very much reduces the diam tens of the cell lamina. The high temperatures in
the cutting kerf
(approx. 700 °C, Arai et al. 1979) lead to a gradual.transformation of
the wall components
into a glassy body. Back, E.Z.,.: Cellulose bci hohen Temperaturen:
Selbs~tvernetzung ... (Cel-
lulose at high temperatures: self cross-linking ...), Das Papier, 27(1973),
pp. 475-483, theo-
retically detcnnined the mel~ng temperature of cellulose of approx. 450
°C based on the glass
temperature. Further, he foul~d that melting without pyrolytic side effects
will only be possi-
ble if heating and cooling occur in a sufiflciently short period of time.
The above-mentioned melting processes when processing wood are considered to
be adverse
side effects. To date, no alterations of specific wood properties has been
created.
In addition to the typical p~rolytical degradation processes when wood is
laser-processed,
melting is also known as a s ndary transformation process. As a rule, melted
areas are con-
sidered negative concerning a quality of the wood surface processed.
Additionally, the py-
rolytical degradation produ~ generated in processing are held and solidified
in the melt.
Known methods, such as las~~ r dividing, confine theirselves to evaporating
wood substance by
thermal or photochemical ~pling of the laser during processing. Thereby, the
alteration of
the wood structure in the are ~ adjacent to the processing zone is arbitrary.
Degradation .proc-
esses are not controllable, c hardly be avoided, and lead to a reduced quality
of the wood
processed in this way. Diffe nt methods, such as plasma processing (DE 41 35
697 A1), re-
quire much effort to prepare the wood and complicated jigs, which prevents the
industrial-
scale applicarion.
It is the objective tion
of this inv to
describe
a
wood
component
as
well
as
a
method
for
the
production and applicationsaid
o component,
in
which,
in
geometrically
defined
areas,
the
wood has altered loch
properties that
chemically
and
physically,
systematically
altered
prop-
erties of the wood low. This is to avoid any treatment of
surface fo the wood surface other-
wise necessary, and numlxr
to open of
new
possible
uses
and
fields
of
application
of
wood.
According to the invention, a problem is solved using a wood component having
the prop-
erties listed in Claim 1. A eat number of component versions follow from the
dependent
claims. Further, the problem is solved using a process having the properties
listed in Claim
11. Versions of the process fqllow from the dependent claims. Applications of
the component
follow from the Claims 22 to I28.
CA 02306630 2000-04-14
06-04-9A 13:49 TUD DEZ~5 SG 5.1 ID= +49 351 4637170 S.A4
3
The wood component has alt~red properties in geometrically defined areas.
According to the
invention, the geometrically efined areas have exclusively the properties of
solidified wood
melts. In the context of the ependent Claims 2 to 10 it follows that said
areas are single or
several wood cells or single or several cell walls. From the melting together,
alterations of
properties of physical and chemical nature as well as tailored alterations of
the deformation
behaviour follow.
According to the Claims 22 ~0 28, the melt can be used for the production of
joints of wood
com vents and/or wood p ~ 'cles, or, respectively, reinforcements can be
incorporated into
po
the melt.
The main constituents of wo ~ d, cellulose, lignin and hemicelluloses, similar
to other polymers
have no melting point but th;era is a wide transition interval in phase
transformation. In con-
trast to plastics, wood has ~ o homogeneous structure and, hence, no softening
point but a
softening temperature range In wood, thermal degradation processes already
start at tem-
peratures lower than 100 °C~. However, the critical factor for the
beginning and progress of
pyrolysis is the dtuation of heat influence, since pyrolysis is a continuous
course of successive
degradation processes. Soft~ning starts at temperatures about 100 °C,
progressing with a
quickly decreasing degree o~ polymerization of the chains and beginning
plasticization. Mol-
ten wood is characterized in that it has a low degree of polymerization,
increased proportion
of amorphous substance, los fibrillar structure of the cellulose and typical
cell structure, ho-
mogenization axed increased ~ elting temperature when repeatedly heated.
a oduction of wood com vents is established
Accordingly, the method to ,CIaIm I 1 for th pr po
such that the geometrically defined areas are melted by contact-free, short-
time, preferably
within less than or equal 50 s, high energy input, so that the degree of
polymerization of the
chains decreases quickly an~plasticization begins, and the melt solidifies
within this period of
time.
Advantageously, laser light is used as the electromagnetic radiation. The
scope of the interac-
tion zone, the interaction pe I'od and the intensity are realized by a
combination of the relative
movement between beam d workpiece as well as through methods of dynamic beam
form-
ing. Processing is in a gas atmosphere defined by composition, pressure and
temperature.
1-leating can be in an inert las atmosphere as well as in free atmosphere. The
process of the
invention can be combinedith other methods of woodworking, e.g. mechanical
processing.
Melting can be used within ~ defined time regime shortly before, during, or
shortly after proc-
essing using another
CA 02306630 2000-04-14
06-04-00 13:49 TUD DEZ.S SG 5.1 ID= +49 351 4637170 S.05
' 4
From the invention, the foil wing advantages result. Melting makes possible to
change the
structure of wood. Closing tl~e wood cells directly leads to a decrease of the
specific surface
and the capillary take-up of Z~umidity is reduced, or prevented, respectively.
Wood and wood
particles can be joined with ei ch other by welding without any, or using
solely wood-inherent
(e.g. lignin) fihing materials. By melting, wood can be joined with other
materials, especially
transparent polymers or fibr us materials. Melting is possible in a locally
limited space or on
a complete surface, whereb the proportion of melted volume has a geometrically
defined
magnitude on or below the ~urface, thus also defining the degree of alteration
of physical
and/or chemical properties. .$y melting, tailored physical and/or chemical
alterations arc pro
duced in the wood. To reap I a this, also extraneous substances can be melted
into the wood.
Said extraneous substances an be particles and/or pigments. Before the melting
process they
are applied into or onto the ood through, for example, impregnating,
immersing, coating, or
during the melting process,~or example, by means of a gas or powder beam. The
diffusion
properties of the wood to ambient media are changed. The diffusion properties
in the main
cutting directions of the wood are essentially homogeneous in melted areas.
Melting leads to
I
hydrophobing of the wood urface. Due to the tailored physical and/or chemical
alterations,
melted wood has an improv d resistance to wood pest. Hardness and abrasion
resistance of
the wood surface can be ad usted. The optical properties (absorptivity,
reflectivity and dif
fusing power) of the wood surface are deliberately altered. The lustre of
melted wood is
clearly different from that of unmelted wood. Softening of wood substance in
the range of
glass temperature offers nov~l possibilities for the deformation of wood.
In the following, the inventiøn is further explained by examples of
embodiment.
In order to protect the end o~ an 8 cm x 10 cm cross-sectioned wood beam from
capillary wa-
ter absorption, a closed su~ace of melted wood with a maximum thickness of 0.5
mm was
produced in the range of thGl cross-cut grain. To produce this melted area the
laser beam of a
continuous C02-laser with power of 2500 W and a laser spot diameter of 6 mm
was mean-
dered over the cross-cut s ace to be processed of the beam end using a double-
mirror scan-
ner, with a track overlap of 0 percent and a velocity of 6 m/s.
In order to produce a hom 'geneous, closed melted zone with a thickness of
more than 0.4
mm, the cell structure withi the geometrically defined area must be abolished.
Therefore, the
wavelength and duration of a laser action were chosen such that the solid wood
constituents
were melted to a depth of a rox. 0.8 mm.
CA 02306630 2000-04-14
06-04-.0A 13:50 TUD DEZ.5 SG 5.1 ID= +49 351 4637170 5.06
The decreased capillary wa' absorption was evaluated by wetting with a defined
water vol-
ume and measurement of th~time until the complete penetration of the water.
The investi
ga_
tion of the melted wood s ce showed a penetration time prolonged by the factor
7.1.
Two spruce veneers 3 were elded together by melting of the lignin contained in
the wood.
To this end, the veneers 3, Irst, were smoothed by ironing and fixed in a
suitable ftxture so
that they lie close together ithout any clearance over the whole weld length.
To produce a weld S the laser beam 2 of a continuous COz-laser with a power of
2SU0 W, a
spot diameter of 13 mm and a velocity of 12 m/s was linearly moved over the
prepared weld
area.
In order to produce a homogeneous closed weld S of a thiclmess of, at least,
O.S mm, the cell
i
structure within the geometrically defined area must be abolished. Therefore,
the wawclcngth
and duration of the laser b iam 2 were chosen such that the solid wood
constituents were
melted to a depth of approx. ~ mm.
After processing, both venee#s 3 arc joined with each other by the weld 5.
After separating the
two veneers from each othe I;, the microscope clearly shows a fracture edge
over the whole
weld length. Below the fract~e edge a homogeneous melt layer is observed. The
cell struc-
ture is abolished down to a deb ptb of 0.4 mtn.
,, . . . . .
CA 02306630 2000-04-14
A6-A4-9A 13:50 TUD DEZ.S SG 5.1 ID= +49 351 4637170 S.07
6
Nomenclature
1 Beam guiding
2 Laser beard
3 V eueer
4 Processing direction
Weld
6 Melt
CA 02306630 2000-04-14
