Note: Descriptions are shown in the official language in which they were submitted.
2~g
.
?rocess and Ap?aratus for Ine ~roauclion ol a flexiDle ana
dimensionally stabie lmaqe Carrier for Screen ~rintinq.
T'ne invention relates lo a process and apparatus for the
production of a fle~ible and dimensionaliy stable image carrier
for screen printing. Above all, the dimensional stabiiily is
required in tensiie stress.
Up to now, image car~iers for screen printing have generally
been woven from metal wires or monofilamen~ polymer t..reaas. As
is well known, tne woven meshes are tnicker where warp and wef
wires or threads cross over. ~hiist calendering of the woven
screen can reduce this extra thic~ness on the crossover points,
it cannot completely overcome it. Therefore, it is r.ot possible
to prouce entirely flat or plane meshes or image carr,ers by
weaving. In particular, fine gauzes woven from thin wires or
threads snow this thickening effeci on the crossover points very
markediy. Tne present invention is tnere ore particulzrly aimea
at screen pr~nling ;neshes where tne wire or thread coun~ exceeas
10/cm, and especially w.-.ere it e.xceeds ~JCm.
Additionally, with syn~r.e~ c gauzes, the mesh cannot ~e lixed z~
the crossover poinis, so that the warp anà weft threads can be
disiodged against each other unaer stress. Sucn mesnes ~eco.ne
useful afLd stable for screer prin~ing only when are stretcned
and fixed ~o rigid scree.l p~n~ing frames witn tensions of 2u
N/cm and hiy;ner.
Screen printing i~age carriers are also ~nown where Ihe
disadvan~ages of woven gzuzes are avoided. In ~:nese perforaiea
metal foils tne openings are hexagonal aperiures connec~ed to
each otner by me,zllic walis, e.g. nickel, to achieve Ire
necessary s~ability. As thes~ aperiured metal foiis are often
elec~-oformed, a Aigh rejection rate is unavoidabie ~nd their
manufacture is therefore expensive.
- 2~2~
,
It is an objecl OI -ne presenl invenlion to prouce a image
carrier or screen prin~ ng ~esn free of t;~e above disadvantages
and which can be mar.~factureà relatively cheaply.
This can be achieved in accordance with rhe present invention Dy
the follow~ny s~eps:
- a cliche consisting of a dimensional stable material is
provided on its surfac~e witr. interconnecling grooves, the
inside width of which forms ~ne aperlures of the screen or
image carrier and the thickness OI them forms tne tnick-
ness of the walls or tne screen or image carr~er,
- tne grooves of ~he cliché are at leas~t par~iaiiy rii;ed
with a hardenable resin;
- the resin is, at least partially, solidified in the
grooves and subsequen~ly removed from tne clicné.
In this new process, on ~ tne construcrion of a ihigh precision
cliche, of wnich at leas~ tr.e surrace prererably consists of a
met~l, is r~iativeiy experlsive. Tne grcoves ca preferably _e
p.rovided ~y a laser beam, or may De chemicaliy etched, or
mechanically enqraved. The meial surfzce of the ciicne ,~ay
consis~ o~ brass or copper, whicr. may be surface nardened, e.g.
by nickel or nard chrome plaiing. âuch a ciicne has a goo;1
durabiiity so that many screen printing meshes can De produced
by i~.
In a preferred ernbodlment ~he grooves are formea ir. straignc
lines at right angles to each other. ~lternativel-~, tne grooves
may be arranged sucn as to produce a honeycomb patterned ~creen.
Where the grooves meet a conriuence of liquid resin occurs,
followed by the solidificatio~ of the resin in one plane ~y
thermal, chemical or radiation inducea polymerisation.
The separation OI ihe 50 Iormed mesh or image carrier from the
cliche can be aided by release coating tne grooves of the
cliché, e.g. with a silicone oil, and~or Dy a~idin~ siiicone oii
~o the iiquia resin.
2~2~
The tensile strength of themesh can be improved Dy streng~nening
the mesh, ai le~st in one direction, by incorporating reinfor-
cement filaments - consisting, for example, of polyesler, fiDer
glass or metai ~ which are prefera~ly laid into the grooves
after fiiling them with llquià resin.
The cross~section of the grooves may be V-shaped or U-shapea and
may additionally be enlarged conically. Furthermore, tne grooves
in one ~ireciion may differ in numbersjcm, shape and depth from
those of the other intersecting direclion.
For continuous manufac~ure of screen printing screens in accor-
~ance with tne present invention, a rotataDie cylindricai
cliche, having grooves along the cirumrerence and along the
generating iines, is used.
Reinforcement of the selvage (selvedge) of Ihe gauze can be
obtained by a stepped increase in tne depth of the grooves, at
least on two opposite sides of the cliche. The selv~ge of the
scre~n may be even further strengthened by introducing reinfor-
cement filaments into the stepped selvage grooves befo~e the
resin is haraened. The thic~.ness ol the gauze may aiso be varied
by cnanging ihe soiids coni~ni or tne iiguid resir..
The following explains the working of the invention ~y way of
examples in connection with Ihe drawings:
rig. i snows schematicaliy a flat grooveG ciiché
~ which can bè used for the produc~ion of
individuai screens having the same si~e as
the clicnb;
Fig. 2 shows a rotata~le, cy-lindricai ciiche fo~ he
continuous produciion o, mesnGs in accordance
witn ~he invention~
2~2~
.
-- 4
Fig. 3, shows e~amples or various cross sections of
a - e grooves;
Fig. 4 illuslrates the enlargemen~ of a plan view of
ihe surface of a cliché as shown in rigs. i
and 2;
Fig. 5 is a cross section of the reinforced selvage o
a mesh made in accordance witn tne inveniion;
Fig. ~ is a schematic dispiay of a produc~ion line for
the continuous produc~ion o~ image carriers
for screen printing.
The piane metal surface of the cliche 1 in accordance with Fig.
1 shows longitudinai grooves 2 and those 3 at a righc angle lo
them. The grooves have ~een produced by one of the aDove
mentioned methods, e.g. by etcning. The plate 1 is surrounded Dy
a raised grooveless border 4; the edges 5 in the longtudinal
direction which are free of grooves, have a row of proiusions o.
Their purpose is io create holes in the longitudinal edges of a
image carrier 11 (Fig. ~) so that the finished carrier 11 can be
convenienlly located and fixed to a seif-~ensioning screen
frame, e.g. using the ~creenfix ~andling System or the Platefi~-
System of the PRSS-~aschinen AG of Winterthur, ~witzeriand.
The distance between the grooves 2,3 delermines the aperture _
(Fig. 5) in the gauze or carrier 11. The ma~imum width b (Fig.
5) of the connecting walls 12 is determined by the maximum width
c (Fig. 3c) of the grooves 2,3.
Plane clichés 1 are preferaDly used for the pro~iuction of
scre~ns or carriers 11 wnich need no rein~orcement 9, or of
honeycomb paiterned screens which cannot be reinforced by
filaments.
2~Q~
For a continuous production which will ~e described laler, a
rotatable mandrel 7 (Fig. 2) is used; the longituciinal groo-~es 2
are located along the periphery of the cylinder, the latitu-
dinals, that is to say, those at a rignl angle to the
longitudinals, extend along the generating lines of tne
cylinder. During the rotation of the cylindrical cliché 7
dimensionally stable filaments or reinforcing thin wires 9 may
be laid into the peripherical grooves 2; when the grooves 2 wiii
be fiiled with iiquid resin, the reinforcements 9 will De
embedded into the resin.
The reinforcements 9 serves to the purpo~e oi- increasing the
dimensional stability of the image carrier 11, especially for
increasing its ~ensile sirengtn. Ii is, oi course possible to
reinforce the grooves 3 instead or in adai~ion to the grooves 2.
As may be seen in Fig. 2, the grooves 3 are mereiy ~rovided in
the middle section 8 of the cyiinder jacket wnilst ihe edges 10
are stepped, at least approximaiely to th dept~l of tne grooves.
Reinforcing filaments 9 are distributed on the selvage 10 to
reinforce the edges of the screen or image carrier 11.
. . .
Cross sectiGnal semicircles, as shown in Fig. 3a, or circular
~egments have been proved to be useful for the grooves 2,3,
possibly ~ith rectangular sections added to them (Fig. 3bj. Of
course other cross sections, as shown in Figs. 3c, 3d and ~e,
are also applicable. ~s has already slaied, distance, shape and
depth of the grooves ~ or 3 are ihe same in one direciion, but
may be varied for the other directior..
Fig. 4 snows an eniarged ~,ew of ihe surface ol tne cyiinaer 7
shown in Fig. 2 which cyiinder 7 represents the regative form of
the gau~e or image carrier 11 ol Fig. 5.~Tne peripilerai grooves
2 con~aining the reinforcemer;~ fiiamen~s 9 are ver~icaiiy
aligned, the raised parts 1~ of tne surface whic;n form the
apertures of the screen or image carrier 11 are snown ha~cr.ed in
Fig. 4.
2~201~8
~,
As may be seen from the shape of the wdils 12 of ~he image
carrier 11 in Fig. 5, the peripheral grooves 2 of the cyiinder 7
are circular or U- ~ shaped respeclively and are reinforcea
with filaments 9, as shown in Fig. 3 and may be wider towaras
che surface 15 of the cylinder 7. On the left side or Fig. 5 may
be seen a selvage 16, reinforced by filaments 9 also, producea
by a stepped recess 10 in the surlace of the cylinder 7 (Fig.
2).
Fig. & shows a schematic view of a production arrangemeni for
the continùous production of screens or image carri~rs 11. 21 is
a warp beam with a brake 22, reinforcing filaments 9 are
inserted into the grooves 2 (Fig. 2) of a rotatable cyiinder 7.
Between both cylinders 21 and 7 a reed 23 is provided to
straighten and guide the reinforcing fiiamenis 9.
The arive (noi shown) of the continuous screen production line
or arrangement which bears a slight resemblance to a weaving
machine, is effected by a ~raction beam 24, following the
cylinder 7. The partially hardened screen 11 is pulied over the
traction beam 24 and pressed against it by pressure rollers 25.
The continuous screen production arrangement or machine, shown
by way of example only, has a coating trough 26 which filis at
least pa~ialiy the grooves 2,3 of the cylinder 7 over its wnole
width with a liquid resin, then the reinforcing filaments 9 are
fed ~y the reed 23 and an inlet 27 into the peripherai grooves 2
of the cylinder 7. As has ~een statea ~elore, the thickrAes3 a
~ (Fig. S) of the screen or image carrier il can ~e con~roiieà i~y
the depth of the grooves ar~d/or, to a certain exteni, also Dy
the soiids content ol tne iiquid resin.
Alternativeiy, the coating trough 26 can also ~e placed behind
the inlei 27 for the reinforcing ~ilaments 9.
-- 2~2~ 8
Surplus resin is removed by a aoctor blaàe 28 and can ~e
recycled to the coating trough 26 via a return pipe 29. The
liquid resin having been doctored by the blade 2a into the
grooves 2,3 of the rotating cylinder 7, is then solidi~ied by a
radiator 30 which emits radiation of a wavelengtn suitable for
curing the resin system used. When the screen or image ca~rier
11 parts from the cylinder 7, it is sufficiently hardened to be
transported over the rollers 24 and 25 to the final hardening
into a after-cure chamber 31 which also contains a radiator of
suitable wavelength.
THe finished screen or image carrier 11 is finally rolled via
a deflection roller 32 onto a driven ~eam 33. The drive and
clutch mechanism of thi~ beam lS not shown.
_.~
