Note: Descriptions are shown in the official language in which they were submitted.
CA 02229174 1998-02-10
A ~VO 9~05963 r~~ .6/01003
TITLE:
Method i~or powder coating and powder for UBe in said method.
T~ ~'AL FIELD:
The present invention r~lat~s to a method for powder
~oating and a plant for carrying out the method~
STATE 0~ TE3E ART:
Powder coating i~ a well known method for coati~g of
o~ject~. T~e starting ~te~ial is a powdered co~tingr which
~ electrically charged and ~y ~y~ a~ainst the ~urraces of
the ob~ect, and which mQ~erial is finally adhered and
~o~_ Led to a so~id state by heating ~o it~ melting point.
Since the ~OI~ ro~s;~t~ of ~ pla~tic which i~ cured by
heating~ thiC mu~t be brough~ ~o a ~ atively high
te~er~L4~e, in the orde~ cf 200 ~.
The coating method may well be pe~ .' on objects h~ving
good heat re~istance ~nd a ~onductive ~urface. If the
sur~ace i~ non-~o~n~tiYe, i~plying that the object cannot
be earthed or ~upplied ~ith a c~arge o~ ~n opposite
polarity to the ~harge o~ ~he powder, di~iculties arise in
getting t~e powder to adhere during ~he time period be~ween
t~e ~ ying and the heatin~ to the melting t~p~rat~re.
~ 30
~hen non-c~n~u~tive ~urfaces ar~ conce~ned, the
di~~icultie~ of obt~;n;ng a pol~rity difference ~etween the
powde~ and the ob~ect ha~ in ce~tain p~oces~es been solved
by e~ther ~oat~g the obje-t ~_th ~ oo~ t-iYe Y~rnigh~ or
~ubjecting it to ~ater of such a ~tate th~t a conductive
~oisture layer i9 ~o~med on the surface~ ~hese methods
ha~e, however, att~;~e~ only limited use ~ca~qe o~
disadYrntage~ ~uch ~g the ~act that the conting involve~ an
additional operation and ~n additional m~teri~l addition~
4Q and may also gi~e in~erior adhesion than powder coating on
CA 02229174 1998-02-10
' W097/05Y63 PCTISE96/01003
the clean s~rface and ~ur~he-m~re, when clear varni~hes are
ro~a~n~, di~coloration.
The addition of water may i ~ the adhe~i~n of the powder
coating and damage the object by confining the applied
water under the coating.
A further method o~ getting the powder to adhere to ths
surf a~e of t~e non-~n~l~ctive object is di~clo6ed in DE,
A1, 3 211 282 ~August Alb~rs). In said dG~I L the object
ha~ing good h~at re~istance and mentione~ to be a glass
o~ject, is heated to a temper8t~re of 400-900 ~C. This
entails ~hat the powder gr~n~ which hi~ the o~je~t ~elt
and are stuek to t~ surface, makin~ it possible to ~ring
the curing process f or the ~ i~n to a h- ,el~OU5~
~olid state, to an en~. Object6 which al~eady at ~ lower
te~ ature run a ri~k of deformation or a change in any
other way cannot ~e treated at the high t~.,.L-~ ~ture
reguired by ~hi~ method. Thus, the method in gue~ion
~o cannot ~e appli~d to e.g. object~ made o~ ~ood or plastic~
Stl~M~ OF T~E lN Y ~'~. ~ lUN:
The o~ject of the in~ention i~ to ~ohieve a m~thod ~hich
may ~e applied to ~e~er coating o~ objects ~hich are not
ZS ~uitable fo~ heating to a high t~ re, which may be
l;~;ted to ~ ~. 100 ~C and al~o ~e~ow. When o~jects
ha~ing a non-co~ otive ~urface are ~ ed, the method
may be carried out without the need ~o~ any ~arnishing with
a conductive Yarnish or any addition of ~oisture The
3a m~thQd i~ there~ore suitable when coating wooden o~jects r
such a~ ~urniture, and objects made of a plas~ic which, fcr
~rl~ ~or re~on~ of ten~city or cost, is chosen from a
type providing the fini~hed object with a s~r~ace having a
d~f~erent look than the one possible with the con~truction
pla~tic itsel~. When wood~n objects are co~cerned, the
CA 02229174 1998-02-10
- W097~U5963 PCT~E96/01003
coating may ~e a clear varnish whiçh allow~ the ~tructure
of the wood to stand out.
According to the invention th~ method compri~es the
~ollowing main step~:
I.
Preparing a powder for the coating, said po~der h~ving a
low m~lting point, ~p,~im~tely 60-100 ~C and consisting
o~ a polymer being cura~le by electromagnetic radiation,
and in p~rticular radiation by ~ltraviolet liyht.
II.
Prepa~ing the object in ~uch a way that ~he powder may be
~5 ret~1n~ on the ~ur~ace of the same until a pormAnent
adherence has been achieved ~h~n~ tO the melting and the
~uring o~ the powder. Thi~ may ~e achieve~ in di~ferent
ways, individual or by in~eraction, and depe~- nt on the
mat~;~l and the design of the obje~t, for ~nst~nce:
a) ~eatlng th~ obj~ct to the melting temperature of ~he
powder ~o that the powder granule~ ~dhere to the surface
durin~ melting. Thi6 may be carried out irre6~e~i~e of the
object ha~ing a conductive sur~ace or not, and making use
~5 o~ the herein dis~lo~e~ powder c., ~Di~ion at a low
temper~ture.
b) S~Laying the ~ r in an ~L,.,v~here he~ted to ~uch an
extent that it attains i~ meltin~ L~-~ a~ure and, in a
st~te melted to at le~t a sticky ~ate, s~ick~ to the
surface of the object.
c) ReL~..Lion of the powder by el~:~Lr~,Ai atic L~.l~e~, thu~ by
g~ing the p~wder an electric potential and the ob~ect a
potential of an opposite polarity. Thi~ may be achieved
when objeet~ having a condn~tive surface are concerned.
CA 02229174 1998-02-10
WO97/Q5963 PC~SE96/010~3
When ob~ect~ having a non-conductive ~urf~ce are concerned,
the ~ur~ace may, as discLosed ~y way of introduction~ be
made ~o~ cti~e by a conductive varnish or by moistening.
Also other methods o~ giving the objeet an opposite
polarit~ a~e conceivable, -.
I~I
Application of the po~der, prefe~ably ~y ~praying while the -~
powder particles are eleatrostatically charged in ~uch a
way that they achieve a good di~tribution in the room.
~u',~v~L, this do~s not exclude applic~tion ~hrough other
method~, ~or in~tance immersion in a fluidised powder.bed
ma~ occur.
lS rv.
~eating to c2use the powde~ partic}e~ to melt to a levelled
layer a~d adhere to the ~urface~ of the o~ject. ~s i~
e~ident from (IIa and b) above, the at~chm~nt of the
powder to the 6urface-o~ the object m7y be done ~y heating
the object or the surr~7n~1; ng atmosphere, 50 that the
Arp1io~tion of the powder and the heating take place in ~he
s2me ~p_~&Lion, whereby ~r~ l heating a~ter the
application of the powder i~ ~n~ssary
V.
Exposing ~he ob;ect to, prefe~ably, ultraviolet radiation, :~
thus initiating the curing process~
From this it i~ evident that the method may be carried out
without creating any oppo~ite polarity ~eL~cen
electro~tat~ ly charged po~der and the object. Such a
polarity di~~erence may, ho~7eve~, occur and is va~uable in
order to ~et the powder dist7~ibuted to all cur~aces of the
object, espec~ y when of a complicated conf iguration .
~5 Thu~, the me~hod does not require, though doe~ no~ exclude,
~ny form of charging or neutralisation of the ob~ect, for
CA 02229174 1998-02-10
W047/OSY63 PCT~E96/~lU03
i~stance when objects made o~ non-con~l~ct~ve ma~erial are
concerned, through the addition o~ ~ny method disclo~ed ~
way of introduç~ion, cQating with a co~ducti~e ~ni Rh or
mois~ning~ QOver~ an electro~tatic charge i~ Rtt~;ne~
in certain material~ when they are heated, a fact which may
be utilised in ~ertain Cil~u~ C~S.
The invention also ~ e~ ~ powder for use in the
method~
DESCRIPTION O~ T~ DRAW~NGSs
In the at ~h~ drawlng~ there is shown, in a fi~ure, a
schematic ,~l~ent~tion o~ a plant for ca~ying out the
me~hod according to the in~ention.
rk~i~k~ EMB~
A brief de~cription o~ ~he method according to the
in~e~tion has been di~clo6ed in ~he i.-L~uc~ion to the
de3cription According to this the method compri~e~ a
number of main steps. These will now ~e de~cribed in
grea~er detail ~or a certain ~ho~; ~.L In said
~;~t, the main steps ha~e been - _ lf - ted by
~t~m~er o~ sub-steps in or~er to adapt the method to the
special requi~ ,Ls of the ~ '~';ment.
Step I : Pr~par~;~ o~ ~Qwder
The powder ~s ~ L~ o~ a polymer and may be pigmented
ror a colo~red coating or non-pigmented for a clear coating
which rende~ the underlying ~ur~ace ~sible. This is
something whiah is often aimed at when wooden object~ are
concerned~ A prin~1rAl ~r~elLy is that the powder should
have a melting point wh~ch is lower than the t,~ _ rature to
which the objects, which are to be coated ~ith the powder,
should be heated. This ~ _ ature limit is partly decided
by the properties of the material of the object, ~ince the
stru~ture o~ certain materials changQ~ at a t~mr~ature,
CA 02229174 1998-02-10
WO g1/05963 PC~/SE~lolno
which may ~e fairly low, already belo~ 100 ~C when certain
~h~r~plastics are con~erned. ~aid tQ~r~ature limit is
al~:o partly d<~c~ by the 5en5itivil:y of the object in
question to deformation when hea~ed. Thi~ sensiti~ity
~eren~ on the const~uction of the object, an ob~ect havin~
a ~o~r~ct form iE; not as ea~ily del~ormed as disc-~ormed or
long ~l a~r objec~s - ~nd al~o ~ç~s on how h~ ,~nou~
the mater~ al in the object is; certain wood species are
very sensitive to deformation when heated. As a pr~n~
region ~or the melt~ng point or the softening poin~ of the
po~der, 60-lO0 ~C may ~e specified.
A~ wil~ be understood by t~e following de~cription, it i~
not nec~ssary ~or the object to be through-heated to the
melting t~r~rat~re of the powder, bu~ only its surface,
~ V~l to s~ch a dep~h that the te~re~ature i~ fairly
uni~ormly di~tributed in ~he obj~ct, and in ~uch a way that
the ~\L-e.a~u~ ret~ un~il the powder is applied o~
its surface. It is not inten~ by the e~ression ~the
2~ melting t~ a~re of the powder" that the powder m~terial
~as to have ~ fluicl, but in many ca~;es it i8
su~ icient that it ha~; r-a~c~e~3 such ~ deg:ree o~ 90~en; n~
that it stickg to the surface inte~ to be coated.
Z5 The fact that only the surface ha~ to be heated and that
the t~ aLu~e m~y be kept low is ndvantageou~ when powde~
coating o~jects which can certainly re~i~t a highe~
t. y~ra~ure, but ~hic~ anyway are di~advantageou~ to heat
to a higher ~ _ ~L~re. ~his is the ca~e ~or instance with
o~jeets of a large weight, where heating to a higher
L ~. rature reyuire~ a high energy consumption. ~his is
pa~ticularly the case wh~n object~ of ~ conducti~e materi71
~re conoer~e~, where the heat r~pidly spreads inwards. One
example is solid c~ iro~ objectsO ~hese reguire a
considerable heating time ~ith hiyh energy cons~ption if
other methods than the present are applied.
CA 02229174 1998-02-10
W097/OS963 ~CT~E~6101003
Another principal property which ~he powder material should
posse~s is that its curing can b~ lnitiated by
electromagnetic radia~ion. Accordin~ to the pre~ent ~t~te
of the artr especially when indust~ial prod~ction i~
S concerned, it has ~een ~hown to ~e most ~d~antayeo~ ~o ~se
ultraviolet ~uV~ radiation and to adapt the po}ymer powder
to this~ In the continue~3 de~;cription of the ~mh~ n~nt W
radlation is th~re~o~e a~ ~d. ~his, however, does not
exclude the use of other ele~tromagnetic radia~ion for the
invention. In addi~ion ccmbinations o~ different type~ of
radia~io~ may be u6eful~
Good le~e~ at a lo~ melting ~mp~rature may be ~t~n~
since the po~der iB at lea~t partiQlly ~ ed of polymers
such as poly~ster in addition to levelling agent~.
~tri~ ~y ~ltraviolet radiation within the ~avelength range
350-400 nm may be att~; n~ if polymer~ in a kn~wn way are
~mive~ with initiator~t ar in another manner are provided
ZO with a curinq ~y~em which m~y be acti~ated by radiation.
These are only exa~les of how said ~o~a~Lies m~y be
att~i~e~ and there are also other powder ~ ition~ whi~h
m~y provide the wan~ed ~ ~er Lies. Without pigmentation o~
o~her dyeing, a clear layer ig ob~;nD~ after curing from
a polymer ~ which does not ~o~ the underlying
sur~ace. If a non-transparent laye~ is wished, such as
op~que, ~hite, black or coloured, pigment~ or other
dyestuffs are added.
~here is also a pos~i~ilit~ ~o control the gloes of the
coated eur~4ce ~y means o~ additi~es~ If the additi~es
produ~e changes in the men~;o~, nece~ary p~o~e~ies, low
melting point and possibility for W curing, thi~ must be
taken into accv~nL when ~ ~ ~ing the po~der and possibly
also when ~iq~ the m~thod.
-
CA 02229174 1998-02-10
WO97/OSs63 PCT/s~96/010
Pre erred compo~:ition o~ the polymer po~der ~or the her~in
described method:
The main ~ nt of the powder is 50-cl~o~ of an
un~aturatedr amorp~ous or cry~tA~ e, polye~ter.
F~ho-m~re a curing agent i~ preferably included in order
to obtain an inc~eased çrossli~ki ng during the ~ou~se of
the curin~. This curing agen~ may to 15-50% be an aromatic
urethane ~iacrylate oligomer, a triacrylate o~
trih~l~G~Lhyl-isocyanurate, a vinyl ester, an oligomer
a~ylo-urethane or the like. Addition of a photoinitiator
i~ required in order to initiate ~he curing ~eguence~ This
addit~on may vary be~ween 1-3~. ~o~ a clear varnish it i~
good to u~e l-hydroxy-cy~lohexyl-ketone as a photoinitiator
and for white pi., 'e' sy~tems Z,4,6-trimethylben~oyl-
diphenylphosfo~ineQxide may be used~ This i~, ho~e~e~, onlyspo~;f~F~ a~ an 7~ and completely differe~t
photo~nitia~or~ may be nee~e~ for ~poci~ purposes~
Additio~ of ~ leYelling agent i~ al~o as~umed. 1-3% of this
i~ recom~n~e~ Acrylate~ for example may be used a~ a
~evelling agent~ Al~o a great ,~ e, o~ other ~dditi~e~ may
be added, for in~tance in order to ~latten the varni~h, to
a~oid problem~ with rume~, o~ the li~e, from the object
which is to be coatçd.
~a6ic recipe ~or a compo~it~on which is preferred ~or
~oating of ~ood (clear varnish) and which proVi~es a good
levell; ng-out a~ter mçlting at low temperatures and good
resi~tance to sol~ents:
Unsatur~ted polyester 70-85
Curing agent 15-30
Photoiniti~tor 1-3%
~evelling agent 1-3%
The melting t~.,.~-~ture of the powder sho~ld ~t the most be
80-90 ~C in order to ensure that a wooden c~ ent is not
CA 02229174 1998-02-10
- W097/05963 PCT/SE96/01003
damaged during the melting phase~ The melting should be
done by means o~ IR he~Lt or with a combination of IR and
conve~tion heating. This implies that ~he melting phase, at
such comp~atively high t~mr~rature~ a~ thi6, doe~ not h~
to ta~e place during a p~rticularly long time sin~e IR
rapidly heat~ the W~IL ~.,~v..ent~ to the wante~
t. ~ ture. A ~ew minutes may be a~umed ~o be what i~
~e~P~, ~ut this i~ ~ery de~ ent on the material which is
to be coated~ Certain wood materials are very sensitive to
a rapid ~eating and may ~Yh~t strong dega~ng. This may
lmply that a slow~r and mDre careful heating method ha~ to
be u~ed.
After melting foll~ws the curing pr~r~ e, ~ee Step v. It
~hould take place at di~eLe~ W -~ave~ength~ dep~n~ing on
how the varnish i8 pigmented and on the photoinitiato~
which ha~ been added. An W spectrum in the lower region,
200-350 ~mr is .,c,..~,el.ientt ~hereby it i~; a~;~med that a
photoin~tiator which ab~or~s in this region is used. In
white pigmented var~h~, rutile titanium dioxide is used
which absorb~ at these wavelengths Consequently, another
photoinitiator, w~ch react~ to wavelengths that are no~
absorbed ~y the pigm~nt, ~ust be ~6ed. This requires the
uoe of another lamp. There are lamps ~hich have a mA~i
at 350-400 nm and at 400-450 nm and there are also
photoinitiators which ~h-----h at these two high ~avelengths.
One mAy also plqment an W c~ring powder coating in many
other ways In each separa~e ca~e the pigments must ~e
adapted to the right photoinitiator and lamp.
~igh intensity lamps may i~ply that it is easie~ t~ cure
thick layers with these and that the curing rate may be
raised. The _ ~r~nt which is to be cured does not have to
be in focu~, but the intensity at a certain distance may ~e
~l~ff~ nt. ~hi~ i~ espec~ y noticeable when clear
CA 02229174 1998-02-10
- W0971059~3 P~ 6/olo
~arn;~ are coneerned; for pigmented systems it is more
im~?orta~t that the intene;ity be as high as possible.
33asic recipe for a ~v,~-osition which i~ }~etter ~;uited ~or
5 coating of metal ~ clear varni~h), and which ~h;h;ts good
~lexibility and ~h~;on to ~et~l~ Should not be used at
~oo low a pro~ess t~ ture.
Unsatura~ed polye~ter 80-ClO0
Curing ~gent 0-20
Photoinitiatorfi 1-3
Lev~llin~ agen~ 1~
AlSo this fQ~ tion may be pigmented~ ~he photoinitiator
sho~ld ~e adapted accordingly.
Wha~ has been said earlier regarding radiation and
radiation data is in principal ~l~o valid ~or ~he last
given recipe. It should al~o ~e men~;one~ that, ~hen
cer~ain evll~osition~ are co~erned, photoinitiators ~y be
replAc~ by othe~ radiation susceptible initiator ~ystem~
The gi~e~ r~c; r~ are only mention~ ~y way of exsmple and
mAy be varied within wide 1 mits, as has been disclosed,
and in ~uch a wsy that they may be u~ed in the de~cribed
method~ ThuS, rcw'~ ~ tion~ for application in the
inventi~n may start ~rom main ~-nL- ~nts other than
polyester, ~}uch a~ epoxy-, acrylates, ureth~nf~Y, l;~m; r~e~
and other~. Also, mixtures of ~vÇ~ ~1 different polymers
3 a may ~e u~çd
~teP TT: Pree~ tiOn C~ ~he o~iect in orcler to retain th~
powder on it~ ~3urface
In the ~hoAi -r L IIa is applied: ~ating the o~ject whi~h
35 i6 to be coated. The obje~t which is to be coa~ed is
assumed to have ~ limited heat re~i~tance; typical o~ 5Uch
CA 02229174 1998-02-10
~V0971o~s63 PC~ISE~6/OlU~3
are wooden obje¢ts, prefi~ed o~jects such ~s w~od~ibre-bo~rd
or pla~tic ~bjec~. This includes objects made ~f
~ rein~orced pl~sti~s and~or o~jects having ~ high addition
of filler. The fact th~t a n~aterial has 1 ~ hea~
~e~i-tance, as when wood and a majority of pla~tic~ are
co~c~rned, generally al~o implie~ that it is non-
~n~ ti~e. Materials of high heat re~i~tance are typic~lly
con~truc~ion metals which are ~o~ ctive. Cv~ve~L; OnA~
po~der ~Pating gen~rally pre~ume~ obj~cts with a conductive
sur~ace, howe~rer t:he present in~entlon ~ not lim;ted to
~ch o~ject~ ~ut may ad~antageously be ~pplled al~o when
non-co~ tiYe sur~aces are cQ~rned, and no pre~reaL.~r~
~n order to achieve conducti~e properties has to occur~
~hi~ m~ke~ the m~thod par~icularly valua~le. Eoweuer, the
m~thod ~ay ~1BO~ as earlier men~ion~, advantageou~ly ~e
applied to solid object~, e.g. ca~t i on ho~ , in order
to redu~e ~he energy con~umption for heating. The heating
may occur in dif~erent wa~: through ~..~cLion ~y mean~ o~
heat ai~ flow, through in~rared radiation, or in
e~e~Lional case~, when for ins~ance plates which are to be
coa~ed only o~ one side are conce~ned, through heat~ng by
co~tion from heated ~urfaces. Particularly useful i~ a
method in ~hich si~ult~ne~ heating occ~rs ~ mean~ o~
c~n~cLion by air flow and by means of IR radiation. The I~
radiation provides a ~apid and ~ ti~ely deep heating
of sur~aces which are hit and the ai~ f low re~ults in the
tc LF-~L~e being ~ery uni~ormly di~tributed over the
surf~ces of the object. This e~en applies for ob~ect~
ha~ing a very co~pl~ted outer shape and also when the IR
radiation doe~ no~ rea~h all surface sectors ~he heating
is presumed to occur in a ~h~hP~, set up for the purpose,
in a plant ~her~ the objects which are ~o be ¢oated may be
transported Le~en di~erent work station~ inte~ for
carrying out the method steps~ See the description of the
plant.
CA 02229174 1998-02-10
wos7/oss63 ~cT/sEs6loloo
St.ep III: Powder s~ra~inn
~,8 ~;oon ~s the heating has been peri~ormed, th~ pe~ive
o~jeots ~re transported to a loca~ion at which the po~der
may be ~p~ayed on. This is convc-liently ~c~om~ hed by
mean~ o~ spray guns arranged in s~ch ~ way that the
sur~aces whi~h are to be coated may be impacted ~y the
powder ln ~nn~tion with thiL, it i~ ~GI,~enient i~ the
guns are arra~ged to charge the powder with an
elect~ostatic chargl3. It i8 previously known to use a high
voltage d~iven charging device, or that the powder, d~ring
its journey ~hro~gh the ~ r ~ying eq~ip~nt~ i~ charged by
~rictio~ again~t walls made of a material adapted to the
~ e. The charge make~ the ~..l~- qr~n~l~C repel each
other, where~y clouds of part;çl~ are formed which
encompa~s the object.
When the particle~ impact the obje~t they willr when
~ ,. in~ the afo~ o~ adaption LeL~_e1. the heat~ng
t. _ a~ure o~ the obje~t~ and the m~l~ng ~er -latu~e o~
the powder, arri~e in a ~ticky state and be deposi~d on
the ~ur~ace of the oh~e~ In this manner the re~pecti~e
ob~ects receive a cove~ing, ~ut uncured layer o~ the
polymer-ba~ed coating material.
2~ Stçp TV: ~e~tinq t~ the ~elting t ~ ~tu~e of the powder
AS already evident, such heating i~ per~ in t-~n~ction
~ith the application of the powder.
Com~l ~m~n~ry ~tep: Interm~ te t~mr~ing
~uring with W radi~ion now rc--i n~ in order to o~tain a
finished coating~ ~owe~ert it ~ay, at least in ce~tain
ca~e~, be con~enient to regulate the condition of t~e
applied, sticky coating layer. Such a ~hange o~ the layer
occurs ~y means o~ a emr~-ature change, either c~oling or
3~ heating.
CA 02229174 1998-02-10
W0~7~596~ PCT~6/01003
In certain case5 there mlght be ~ risk that the layer, in
its partly dissolved, tacky state and particularly through
the continued heating by mean~ o~ conduction from the
heated obje~t, r~q~ such a i~luent state that there i5 a
risk of running and d:cop-- for~ing at protruding edges. In
o~der to ~ve~.L this, cooling ~ay ~e undertaken, thus
lowering the t~ atùre which was necessary ~or m~lting
the powder particles to a t~ r~aLure at which the ~o
layer obtain~ a more ~olid ~tate.
Alter~atively, in ca~e it is not ~un~r~ient to heat the
object to the temp~ UL~ which the utili~ed powder
require6 ~or the desired melting r heating after the
spraying ~ay instead 4e val~able in order to lower the
visco~ity. In ~hi~ way, ~he inr~rletely melted powder
gr~n~7~ can ke made to run toge~er in order to ~orm an
uni~orm la~er. I~ the tem~el~-ure on the object has ~een
k~3p~ low h~ e it should not be exposed l;o a ~i ~hc~-
~ _ aL~re, this su~sequent heating must be performed in
s~ch a way tha~, i n the main, only the applied layer is
heated but not the underlyin~ object. Thus, the heating may
be undertaken by means o~ a ~apid proce~s involving I~
radiation, co~lve~liently in combination wi~h ~ heated air
flow in a shor~ proces~.
- In FHny ca~es there is on the whole no nee~ ~or such an
int~ te t~ ins. In that case this step is omitted.
S~ U:~.i nq
As ~ention~ earlier~ the pol~erization of the powder
material G~ by h~ating, a~3 a rule in ~ v~cLion oven,
when ~o,,ve~.L~nA7 powder co~t~ng i~ ~rned hcco~dingly
the heatlng at f~rst leads to a ~usion of the material
while the powde~ granules are inlti lly ret~; n~ by means
of elec~rostat~c forces. Thereafter the curing, which i~
initiated by the heating, ~u~s
CA 02229174 1998-02-10
W097J05963 P~T/S~96/01003
14
The precent method i~ a~ud at carrying out the process at
~uch a low t~ -~ature th~t no c~ing ~an be att~i n~ by
means of the heating, or that in any ~ase would ~equire
~uch a :Long t:Lme after init;iation, thal: it would render it
unfea~ible in an industrial proces~. -
Accordingly, the curing muE;t ~e accornE~ hs~ in another
~ay~ by initiation o~ the curing proce~s ~y me~ns Of
ultraviblet radiation. ~nder Step I it has been descri~ed
how the powder material i~ prepared for such a c~ring.
The W curing takes pl~ ce in a sp~c i ~ 1 1 y adapted cl~mh~
into which the object~ a~e ~rou~ht after the powder
~ ing ~nd the p~s~ible interme~; Ate t , ing~ In the
rh~m~r'~ a ' ~ o~ W radiators are arranged, ~rom which
the radiation ~':h~ reach all coated surf aces of the
o~jec~ When ce~ain o~jects having a ~nmrli~ted ~hape and
n coating on many di~ferent sîdes are e~on~rned, ~~ ial
arran~Ls might be neces~ary Thu3, it m;3y be nece~:~;ary
2 0 to ar~ange a lar~e n~l~e~ o~ ~3v radiators dire~ted in
dif f erent ways and they may ~lso be ~:upplemented with
mirrorQ, re-directing the present r2~diation at new angles.
I1~Y~ ~ L of th~ W rays arouncl the respe~ive objects coulcl ~ -
al~30 be arranged. Altl3rnatively, the objects may be rotated
or moved in another way in front o:E the radiat~on sources.
F
When t:he radiation im~acts the coating layerr the ini~iator
systcm of the m~erial will start thc polymerization. It i~-
there}~y po~sible to co~ ct t~is very rapidly - times down
to 2 ~eco-l~s are possible. The short proces~inq time in
relation to the t~me for heat curing gives ; , ~nt
~dv~.Lages ~hen industri~l production i~ eoneerned. On the
one hand, a ~aster flo~-through of work pieces and, on the
other hand, a possi~ility to reduce the length of the pl~nt
in rel~ion to what i~ required for a cu~ing oven are
att~ i ne~3 .
CA 02229174 1998-02-10
W 097105963 PCT~E96101003
The earlier men~ioned in~erm~;Ate t~r~in~, particulariy
coolingr may ~ke place slmultaneously with the W
r~diation. By means Qf ~n adapted cooling i~ may be
p ~v~ ed that the t~ L,~,~ture during the curing reaches
di~adv~nt~geously hig~ ~alues because of the energy
~ lb~tion frPm the ~low of heated ob~ects and be~au~e of
the W radia~on.
A~ter Step v, the method has been completed and the object~
have ob~ine~ ~ cured ~oati~g. Accordingly, all advantages
~hich are a~ociated with powder coating, name~y the
po~c;~ ty o~ o~t~i~;ng g~eatEr l~yer tbir~ne~e and
higher ~h~n;~al resi tance as ~rA ed to wet vArni~h;ng,
ha~e been att~ . The mcthod is al50 ~ery environmentally
~riendl~ This is ~e~ e no sol~en~s need to be ~e~, and
po~der which in the spraying ~tep did not impact the
o~ject, may ~e collected in the ~praying chamber in order
to be reused.
A plant in which the different method ~tep~ may he carried
out in a ~a~ional, indu~trial proces~ i~ depicted in the
at~h~ drawing.
The pla~t ~hown in the drawing is in ~he ~orm o~ a ~unnel
1 through which the objects 2 which are to ~e treated may
be passed by means of a ~u~r~n~oA ~ r~ 3, the
transporting' po~tion of wh~oh is trav~ll1 n~ ln a dire~tion
~rom t~e le~t to the right in the drawing In the d~awing,
the tl~n~el is shown in an opened-up s~ate along a
~ongit~AinAl section. Ac~ordingly it 1~ e~ident that it is
divided into four ch~.~L~r~, each being adapted for the
realization o~ one o~ the Step~ V - Preparation o~ the
powder, Step I i~ not included in the plant - the powder i~
pre~umed to be added in a state o~ p~eparation, ready ~or
use in the plant~
CA 02229174 1998-02-10
W097/0~963 PCT/SE96/01003
16
Initially there is a ¢hamber 5 for Step II, the heating.
~his ch~mher ~hih~ts both r~diators 6 f~ infrared light
a~ well as inlet openin~s 7 for heat~d air ~rom a com~ined
heating and blower set.
Therea~te~, a ~hA~r g follow~ ~or the spraying process.
Inside ~his a ntlm~r o~ ~pray guns 10 are in~erted, which
via hose~ 12 are ~o~n~rted to a powder container 13~ As is
sho~n, ~he ~pr~y guns m~y be pro~i~ed with several ~pray
noz~les 15. Th~ough a pre~urized air-dri~en system ~hich
is not ~hown in greater detail, the powder may be ~ucked
~rom the cont~in~r 13 up through the hose lZ to the
rçBpecti~e gun 10 in order to be sL~eL~d out via the
nozzles 15. In thi6 context it i~ as~ned that inside the
~pray guns there are ~h~nnels ~ade of a material, ~or
instance polytet~al~luoroethylene, which by means of
fricl;ion ~etween the walls and the po ~ er lend~; the latter
an elec~rostatic charge. Alternati~e}y, or additi~n~l ~y,
the guns m~y be pro~ided with c~arging ~urfaces w~ich are
supplied with a high voltage electrical current~
The next ~h~m~er 16 i~ arranged for the occaoi~n~lly
occurring p~st-t~ .~r~ng. It i~ provided with inlet
openin7s 17 for either heated or cooJ~ air and may a~so be
supplied ~ith IR r~diators f~r _ _l~m~ntary heating. This
,h; ~ m~y ~e omitt~:d if, in the ~t~L~ ~e~:3e~ cc~ e--ned, no
pQ~;t--t~ ~ring is ~,~_~ned.
A r~ inin~ ch~ r 18 ~: adapted for step V, the cu~ing
step. A ~ of r~di~tors 19 for W radiation are placed
in the chambe-. A~ earlier men~io~P~, mirrors for re-
directing o~ radiation may al~o be pre~ent ~nd the wall~ o~
the cha~be~ may ~l.v~niently be re~lective.
In order to enable the te~..~aLure to be kept con~tant or
to even achieve cooling in this ~h: 'cr, it is p~ovided
CA 02229174 1998-02-10
Y~O97/O~g63 PC~/SE96/01003
~ith inlet openings 22 for air. This air may be collected
partly fro~ a ~et~rn line 23 ~rom the chamber ~nd partly
from an inlet 24 from .a source of air with a t~r~ature
corre~pon~ing to or lower than the lowes~ t~ ~ature which
i5 ~ ;umed to }:e re~uired ~rom the cooling air through ~he
r~r~n; ngs 22. Thi:~ source may be the z~mbient atmo~phere i~
the ~ nt t~ rature is suf f iciently l~w, or air ~rom a
refrigerating ~a~h;n~, ~ur~h~ re, there is an outlet 25
~or air ~rom the outlet opening 26 in the chamber, in case
the di~charged air is not completely going in L~ and in
through the opening~ 22, but is ~ompletely or partially
rerl~ by air fro~ ~he inlet 2~. The ~-~olLion ~L..__n
~L~ ~1 ai~ s~pplied through the op~ings 22 and ~re~h air
from the inlet 25 is controlled by a ~hpr~tat-cont~olled
thro~tle 27 in order to keep the t~ _ ~ature in~ide the
~h~be~ c~n~tant at the temperature mo5t suitable ~o~ the
~ v~ S ~
As a rule, it cannot be a~oided ~hat ~ea~ i~ ac~ ted
during a continuou~ coating p~oce~, gi~in~ ri~e to a heat
increa~e which has to be controlled, ~ince the heat~d
ob~ects which are brought in pro~ide a cont;nu~ heat
contribution, ~imultaneously a~ it ~annot be a~oide~ ~hat
the radiators 19 emit a cer~ain waste energy and the W
radiation itself give~ an ene~gy ~ontribution. This can
: ~n~ _~ently be done by means o~ the described cooling
~ystem.
When carrying out the method in the des~ribed plant, the
objects are in tu~n ~u~r~n~ on the transporting portion
of the ~on~o~ 3. Initially the objects are brouy~t into
the ch~ 5 in turn. The conveyor moves with a speed
~dapted to the length of time required ~or the treatment
step in order to obt~in a ~U~f iciçnt retention t~me in the
respecti~e ~hEmbe~s. In the chamber S the object~ are
~urrounded by heated air, blown through the opening~ 6 in
CA 02229174 1998-02-10
W Og7/05g63 PC~/SE96/01003
a smooth ~low, and are exposed to IR radiation from the
rays 7. T~is lead~ to a heating, ~ell di~tributed over the
~urface of the objec~s, ~hich is driven far enough to make
it po~ible to retain the heat ~equired ~o~ the next ~tep.
n the ~h~mhc-r 9 the next step i~ p~rforme!d, the po~der
spraying~ It ~hould be e~ident from ~he preceding
de~cription ~h~ow this i~ per:Eormed with the aid of the ~;pray
guns 10. The~e generally have to ~e adapted to the object
in ~ues~ion in terms of their positions and o~ten also to
their design, 4Or instance the ~ of nozzle~;. In
certain ca~es, it might ~e nececsary to suspend the ~pray
guns in a ~ vable w~y, mak~ng them perl~or~ a ~ u~ L
pattern during the spraying.
I~ req~ired, a complem~ntary hea~ treaL~ L is performed in
the c}~mhe- 16, either cooling in order to ~t~ e the
layer on the heated objects, or heating in o~der to a~hieve
a better levelling-out o4 the layer sticking onto the
obiect~.
Finally, ~he curing is initiated in the chr ' _ 18 by
radia~ion ~rom the VV radiator~ 19. A~tç~ .the irradiation
o~ in co~ Lion to it, a certain cur~ng time may be
~S required, ~nd the ~h~ '~ 18 i~ cG~ ien~ly ext~n~ in
such a way that the layer i~ ~t~hi 1; Q~ whe~ the object~
leave ~he chamber. Accord~ngly, the radiati'on e~uipment may
be d~ferentiated along the extensi~n o~ the cha~hsr, for
in~tance with a more inten~ive radiation at the inlet end
of the c~hi.~r ~han at the ou1:let end.
The herein described method and plant are de~cribed as a
preferred embo~imen~. Ho~.eve~, other em~od~ment~ may be
$ncluded within the scope o~ ~he apr~ claim~. Ry way of
introduction it has been qnt~ned tha~ the retention o~
the powder applie~ on the surî~ce of the objec~ may be
CA 02229174 1998-02-10
W097~5963 PCT/SE96/01003
~ccomplished in other known ~ay~ than by me~ns of a
preheating of the objects. In those ca~es where objects
having a c~n~--cti~e ~urface a~e co~c~?rned, ~he sticking o~
the powder on~o the objects ~ay ~ery conveniently be done
by mean of electrostatic force~, while th~ melting o~ the
po~der which il3 necessary for the ~lO~~~S, in that caf;e il3
done by mean~ of a post-heating without the need ~or the
objects ~o be preheated. Such an ~mh~rl; m~nt of the method
t~ereb~ ¢ompletely follows the speci~ied main step~: Step
IIc, elec~ro~tatic chargi~g or neutralisation of the
o~ject; Step III, application of the powder; Step IV,
heating to the ~elting t~rrerature of the powder; and Step
V, curing.~
Several dif~ L ~thods }~ave alE;o been i n~; c~e~ :Eor the
application o~ the powder, o~ which spraying of the powder
is the mo~t useful method snd has therefore been cho~en in
the pre~r~ed emk~; L.
Consequently, the method a~ well as the ~o.~e~ compo~ition
may ~e adapted ln a mul~itude o~ different ways to the
actual requil~,..~l,-s and types of objects which are ~o be
treated, and to the material thereof. ~ ~.. to all
,S ~ nt~ ib, however, t~at mel~ing o~ a powder which is
2S fusible at a low t~ eL~LIlre is Appl ~ thus brinyin~
about the form~tio~ o~ a polymer layer on the ~ur~ace o~
the re~pecti~e o~ject~ which are to be coated~ whereafter
the curing ta~es place ~y ~ean~ of radiation wi~ho~t any
Ru~tantial te~l dture increase. Througho~t the p~ocess a
t~m~ature is thu~ main~;nP~ which i~ ~onsidera~1~ lower
than that which has p~e~iously been practised within t~e
f ield.
