Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 BACKGROUND OF THE INVENTION
This invention relates to stencilling apparatus,
and more particularly to screen stencilling, usually for
printing, employing a direct, regulated flow through action
from ahead of the squeegee to behind the flow coater, by
passage over the squeegee into a control reservoir between
the squeegee and the flow coater, and from the reservoir
onto the stencil screen.
Screen stencilling is widely used for selectively
depositing coating materials such as inks, adhesives 9 and
other functional and/or decorative deposits through a screen
stencil onto stock such as paper, polymers, cloth, wood,
laminates, and the like for making posters, decalcomania
coatings, graphic designs, and the like. A typical apparatus
for screen stencilling is set forth in U. S. Patent 2,606,492.
Usually, the process involves the spreading of a layer of
the fluid on a fine mesh screen, followed by forcing a
portion of the fluid layer through the pattern areas of the
screen with a squeegee, onto the stock. The excess ink is
forced to one end of the screen by this squeegee. The
excess ink is subsequently spread back onto the screen by a
flow coater for the next stencilling stroke. A common
tendency of the stencilling fluid is to thicken or even dry
because of solvent or carrier liquid evaporation while the
excess stencilling fluid is repeatedly wiped off the stencil
screen ahead of the squeegee and spread again onto the
stencil screen on the return stroke.
SUMMARY OF THE INVENTION
.
An object of this invention is to provide novel
flow through stencilling apparatus wherein the stencilling
fluid is constantly maintained in a controlled amount on the
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stencil screen both ahead of and behind the squeegee-flow
coater assembly. The stencil screen is not exposed to the
air to allow fluid clinging to the screen strands to dry and
partially or totally plug screen openings. Rather, the
screen is kept constantly covered. This also keeps the
screen openings filled with fluid rather than allowing air
entry therein, thus assuring a complete reproduction of the
` stencil image when the squeegee traverses the screen. A
portion of the stencilling fluid is forced by the squeegee
through the stencil screen in conventional fashion, while
the excess flows directly through special openings in the
squeegee into a control reservoir formed between the squeegee
and the following flow coater, a portion of the fluid then
flowing from the reservoir directly beneath the lower edge
of the flow coater to form a layer or coating of controlled
thickness on the stencil screen for the next stencilling
stroke.
The bottom edge of the flow coater can be straight
since the screen area being flow coated is close to the
screen area between the drum and squeegee so as to be
basically flat rather than sagging as occurs when the screen
is flow coated on the return stroke at which time the screen
is elevated off the impression surface or drum.
The invention is particularly advantageous in the
printing of half tone and/or color process printing where
the screen mesh orifices are very small and prove to plug
from dried ink and/or capture air, either of which prevents
full image reproduction.
These and other features, advantages, and objects
of the invention will be apparent from a study of the
detailed specification in conjunction with the drawings.
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1 BRIEF DESCRIPTION OF THE DRA~INGS
Fig. 1 is a perspective view of a stencil screen
printing press employing this invention;
Fig. 2 is a fragmentary, somewhat enlarged per-
spective view of a portion of the press in Fig. l;
Fig. 3 is an elevational, partially schematic view
of the squeegee assembly of this invention;
Fig. 4 is a perspective view of the fluid pumping
portion of the apparatus;
Fig. 5 is a substantially enlarged plan view of a
portion of the apparatus in Fig. 2;
Fig. 6 is an elevational view of the apparatus in
Fig. 5; and
Fig. 7 is an end, partially sectional view of the
apparatus in Fig. 6. t
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now specifically to the drawings, the
complete press assembly 10 there depicted includes a frame
subassembly 12, a stencil frame subassembly 14, a squeegee
subassembly 16, and a stock infeed subassembly 18. Beneath
the squeegee subassembly 16 is a stock supporting subassembly
20 ~Fig. 7), most frequen~ly a rotational cylinder or drum.
The framework subassembly 12 and stock supporting subassembly
20 may be of conventional construction as in U. S. Patent
2,606,492 or U. S. Patent 3,120,180, for example. Alter-
natively, the stock support can be flat as in U. S. Patent
2,917,997, for example. The stock infeed subassembly 18 and
outfeed subassembly can also be conventional.
The particular stock involved may be either sheet
stock or web stock. If web stock, web handling equipment of
the type set forth in U. S. Patents 3,779,160 or 3,650,207
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1 can be employed. The stencil frame subassembly 14 can also
be of conventional type as, for example, in U. S. Patent
3,359,663 or U. S. Patent 3,273,497.
The squeegee subassembly 16 is located above the
stock support or impression cylinder subassembly 20, while
the stencil frame 26 is therebetween in usual fashion.
Relative motion between the squeegee 32 and stencil 24 is
preferably achieved by not moving the squeegee 32 horizon-
tally, while horizontally reciprocating the stencil 24 with
its frame and advancing the stock support.
The stencil screen 24 extends across the bottom
plane of stencil frame 26 immediately above the surface of
support 20 upon which stock 28 is maintained, so that
resilient blade element 30 of squeegee 32 can force a
portion of the stencilling fluid through the open pattern
areas of the stencil screen onto the stock 28 as the rela-
tive motion between the squeegee and stencil screen occurs.
Relative movement is made to occur between the stencil frame
and the squeegee and flow coater assembly during stencilling,
usually by moving the stencil frame. In this disclosure,
for convenience such relative movement will sometimes be
referred to in terms of advancement of the squeegee and flow
coater. The stencil frame can be reciprocated by suitable
gears engaging racks 25 ~Fig. 6), or the like. Stock 28
advances with the screen, at the same rate and in the same
direction in conventional fashion.
The transversely extending squeegee 32 is supported
along the crown of the drum 20 on a suitable mounting plate
34, the opposite ends of which are secured to a pair of
brackets 36. These brackets in turn are mounted upon
vertically reciprocable columns 38 slidably supported in
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1 framework 12 of the press. Suitable shifting mechanism such
as cams, solenoids, air cylinders, or the like (not shown)
are connected in conventional fashion to reciprocate columns
38 and thus raise and lower the squeegee subassembly 16
relative to the stencil frame 26. Normally, the stencil
frame is also caused to move vertically relative to support
cylinder 20 by shifting the stencil frame vertically up away
from the support cylinder during the nonprint return stroke
of the stencil frame, so as not to smear the freshly coated
liquid on the stock. Alternatively, the cylinder or drum 20
can be lowered away from the stencil screen 24 for this
purpose. Since this forms no part of the present invention
and is very conventional, further description is not necessary.
Spaced behind upstanding squeegee 32, relative to
the squeegee direction of advance in the print stroke, is an
upright, generally vertical flow coater panel 40 which
serves as a flow coater blade, the lower edge of which is
vertically spaced slightly above the horizontal plane of the
lower edge of blade element 30 of squeegee 32. This spacing
thus spaces it slightly above the stencil screen also, and
is preset to a controlled fraction of an inch for obtaining
a predetermined coating thickness of the spreading fluid
flowing from the reservoir 90 beneath the flow coater blade
onto the screen during the printing stroke. This flow
coater 40 also extends transversely of the stencil screen
frame, being parallel to the squeegee.
It has its upper edge mounted to a support member
42 having pivot pins 44 on its opposite ends. These pivot
pins 44 rotate with pivoting of the flow coater, and are
pivotally mounted in a pair of end plates 100 to support the
flow coater.
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1 If the viscosity control aspect of the parent
application hereof is employed, there is also secured on one
of these pivot pins 44, i.e., on one end of the squeegee
subassembly, a first upright lever 50 and a second longi-
tudinally extending lever 52. Lever 50 is pivotally re-
sponsive to pivotal movement of flow coater 40 to actuate
switching mechanism 120 in a manner to be described. Lever
52 is operated by a cam roller 56 to forcefully pivot flow
coater 40 toward and away from the squeegee 32 in a manner
to be described, for closing and opening the bottom of
reservoir 90. Roller 56 engages the free end of canti-
levered lever 52. This roller is on the end of a fulcrumed
lever 58. Lever 58 is pivotally secured intermediate its
ends on a pin 60. Pin 60 is attached to bracket 62 which in
turn is secured to mount 34 by a threaded fastener 64. The
opposite end of lever 58 from wheel 56 is adapted to abut a
stop plate 68. An abutment stud 70 on lever 58 is verti-
cally adjustable to control the engagement with stop plate
68 in a fashion and for a reason to be understood from the
description to follow. Stop plate 68 is laterally slidable
on a fixed plate portion 12' of frame subassembly 12 within
guide 74, to be shiftable to an inactive position out of
engagement with lever 58. The position of stop plate 68
relative to guide 74 can be varied by loosening set screw 76
to allow its shank to shift in slot 74'. Raising and
lowering of mount 34 by columns 38 causes lever 58 to pivot
with engagement and disengagement of stop plate 68 to shift
wheel 56 vertically, thereby shifting lever 52 vertically
which moves flow coater 40 toward and away from squeegee 32.
The space between squeegee 32 and flow coater 40 defines a
fluid reser~oir 90 ~Fig. 7~ generally closed on the ends by
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1 end plates 100. When flow coater 40 is shifted into en-
gagement with the back surface of squeegee 32, this reser-
voir is closed at the bottom, while shifting of flow coater
40 away from the squeegee opens the bottom of this reservoir
to allow liquid to be in contact with stencil screen 24 and
to also flow under the lower edge of the flow coater when
the stencil is advanced. End plates 100 have their forward
edges secured to squeegee 32, and extend back astraddle the
ends of flow coater 40.
The shifting of flow coater 40 by lever 52 is for
the purpose of opening and closing this reservoir during the
print and return strokes, respectively, as will be under-
stood more fully from the description to follow. Thus,
printing ink or other functional stencilling fluid is
dispensed from this reservoir 90 and uniformly coated on the
stencil by flow coater 40, as the squeegee prints ahead of
this flow coater and reservoir.
Any excess ink ahead of the squeegee can flow up
and back through passages 32', i.e., directly through the ~
body of the squeegee, into reservoir 90 behind the squeegee ~ -
and in front of flow coater panel 40. If the excess ink
does not flow over the squeegee, i.e. through the squeegee
body, as sometimes occurs, but rather flows out ahead
thereof, the arrival of the squeegee at the end of the
stencil screen frame will cause the ink to dam up and at
that time flow through the squeegee body~ During the
printing stroke, a controlled portion of the stencilling
fluid in the reservoir also flows out beneath the lower edge
of the flow coater panel onto the screen to recoat it.
Hence there can be a constant flow through operation during
printing, and the stencil screen ahead of the squeegee,
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1 within the squeegee assembly, and behind the flow coater is
constantly kept covered with fluid in a print and flow
function. Thus, the screen is not exposed to air to either
dry the ink on the strands and thereby cause partial or
total plugging of the mesh orifices, or to form an air
pocket preventing total image reproduction with the sub-
sequent printing strokes. Hence faster drying inks can be
effectively used to thereby lessen subsequent drying time
and energy.
If it is desired to employ the solvent additive
feature of this assembly, as the viscosity increases slightly,
the flowing force of the ink or other fluid through the
restricted area of the slot beneath the lower edge of flow
coater 40 and above the upper surface of the screen in-
creases, causing the flow coater to proportionately pivot
counterclockwise (as viewed in Fig. 7) about pivot pins 44. ;
This then applies a rotational shifting force to lever 50,
overcoming the controlled bias on slide plunger 110 (Fig. 7)
which engages lever 50 intermediate its ends and is slidably
mounted in a housing 112. The bias is supplied by a com-
pression coil spring 114 trapped in this housing between the
inner end of pin 110 and an adjustable stud 116. Also
engaging the upper end of lever 50 is the spring-mounted
actuator 118 of a conventional limit switch 120. Mounted
atop this limit switch by a bracket 126 is a bulb socket 122
retaining a lightbu]b 124 therein. Switch 120 is mounted on
support 128 above housing 112 which in turn is secured to
member 34. A predetermined arcuate movement, therefore, of
lever 50 in a counterclockwise direction will ultimately
cause the limit switch to be activated when the viscosity
increases to a certain predetermined value. This elec-
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l trically actuates the bulb 124 but more importantly, sim-
ultaneously activates electrical motor 140 (Fig. 4) which t
operates a pump 46.
This motor has a cam 142 mounted on its drive
shaft, which cam engages with a cam follower 144 forming
part of a liquid pump 146. This can be a simple diaphragm
pump such as a fuel pump from an internal combustion engine
or the like. Rotation of the cam 142 reciprocates cam
follower 144 to cause a pumping action, which preferably is
limited to one rotation of cam 142 by another limit switch
148 activated by the cam as it completes one revolution.
Pump 146 has a supply conduit 150 ~Fig. 3) communicating
with a supply 152 of liquid in a suitable container 154
forming a reservoir. An output 156 from the pump includes a
lS perforated dispensing tube 158 extending over the stencil
frame adjacent squeegee 32. The motor 140, pump 146, and
control switch 148 are preferably enclosed in a housing 149
(Fig. 3).
Liquid dispensing tube 158 can be mounted immedi-
ately ahead of squeegee 32, relative to the direction of
printing motion of the squeegee. This is shown in Fig. 3
and in phantom lines in Fig. 7. This tube can be held in
position by any suitable brackets 170 attached to squeegee
32. An alternative positioning of tube 158 is shown at 158a
in Fig. 7, i.e., behind squeegee 32, between squeegee 32 and
flow coater 40, above the fluid level in reservoir 90.
Again, suitable brackets 170a may be attached to squeegee 32
to support the tube in this position. Each of these two
positions is advantageous for certain types of arrangements
as explained more fu]ly hereinafter. Outlet 156 from the
pump is connected to this conduit dispensing tube 158 as by
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1 a flexible conduit 157 or the like to allow the squeegee
subassembly to be freely vertically reciprocated.
Extensive experimentation with the apparatus
disclosed has shown that the solvent additive feature is not
always necessary. The unique structure and arrangement of
the components themselves in this novel print and flow
system serve to stabilize the condition and operation of the
stencilling fluid.
OPERATION
The operation of the press basically includes a
print stroke and a return stroke. During the print stroke,
the stencil screen frame 26 with screen 24 moves in one
direction between the lowered squeegee subassembly 16 and
the underlying stock on the stock support 28 subassembly 20.
During the return stroke, the stencil screen 24 is returned
while the squeegee subassembly 16 is elevated and the
stencil screen is out of engagement with the departing stock
just printed. During this return stroke, the new stock is
introduced to be subsequently printed.
The operation is started by inserting a stencil
screen 24 with the desired stencil thereon between the
squeegee subassembly 16 and support cylinder 20 and pre-
paring the web or sheet stock 28 to be fed into registry on
the support surface or cylinder 20. Ink or other functional
stencilling fluid is placed in reservoir 90 between squeegee
32 and flow coater 40 while the squeegee subassembly is
elevated by columns 38. In this condition, the flow coater
is preferably in engagement with the back edge of the
squeegee to close off the bottom of reservoir 90.
Excess solvent or carrier liquid for the ink or
other functional liquid may be contained in reservoir 154
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1 and motor 140 is inactive at this time.
During the print stroke, columns 38 are lowered,
thereby lowering the entire squeegee subassembly into
printing relationship relative to the stencil screen. On
the first stroke, the unit will not print unless ink has
been previously applied to the stencil screen, because the
ink is flow coated on the screen immediately behind the
squeegee during the print stroke. Assuming, therefore, that
the second print stroke is about to begin, and the squeegee
subassembly is lowered, this causes the outer end of lever
;; 58 to engage stop plate 68, causing it to pivot about its
- central pin 60 to lower wheel 56 and thereby depress lever
52. This depression rotation of lever 52 about its pivot 44
causes flow coater 40 to tilt away from the squeegee and
open the bottom of reservoir 90.
The shifting of flow coater 40 away from squeegee
- 32 is against the bias of coil spring 114 compressed by pin
; 110 as lever 50 pivots with the flow coater. This initial
pivoting of lever 50 also depresses part way the limit
switch 118 but insufficient to throw the switch. Instead of
this mechanical lever system of opening and closing the
reservoir by shifting the flow coater out of and into
engagement with the squeegee, alternative operating means
could be employed such as an electrical solenoid, a fluid
cylinder, and the like.
As the stencil screen moves beneath the squeegee
and flow coater, squeegee blade 30 in engagement with the
screen forces a portion of the ink ahead of it through
stencil 24 onto stock 28 on support surface 20. Excess ink
ahead of the squeegee blade can flow up and back through
openings 32' in the body of squeegee 32 above blade 32, into
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1 reservoir 90 behind the squeegee, i.e. between the upright
squeegee and the flow coater panel. As the squeegee prints,
the trailing flow coater, by its slight spacing above
stencil 24, allows a controlled thickness of liquid to flow
from reservoir 90, beneath the lower edge of flow coater 40,
and onto stencil 24 for the next print stroke. Thus, during
the print stroke, there is a steady flow of stencilling
fluid through the stencil subassembly, keeping the stencil
covered with fluid, keeping a minimum of excess fluid in
front of the squeegee and a controlled thickness behind the
flow coater, using the reservoir as a variable quantity
control. At the end of the stroke, as the squeegee and the
end panel of the stencil frame are brought into close
proximity, more excess ink tends to be forced back through
the squeegee body into the reservoir.
During the return stroke, after the print stroke
has been completed, the squeegee subassembly is elevated by
columns 38, enabling the stencil screen to be returned to
its initial position without the squeegee forcing ink
through it on the return stroke.
Lifting of the squeegee subassembly enables lever
58 to shift away from stop plate 68, allowing wheel 56 to
rise, allowing lever 52 to rise, and enabling compression
spring 114 to shift lever 50, which thereby rotates the flow
coater 40 into engagement with squeegee 32 to close the
bottom of the liquid reservoir 90. The stencil frame is
also shifted vertically above the print cylinder and stock
during this return stroke.
In some operations, after repeated print strokes
and return strokes, with the ink being repeatedly flow
coated onto the stencil and excess ink being recycled back
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1 into reservoir 90 through openings 32' in squeegee 32,
sufficient evaporation of the solvent or carrier liquid
occurs to increase the viscosity of the ink or other func-
tional liquid being coated. If the viscosity sensing and
solvent supply system is employed, the flow coater 40 senses
the increased viscosity of the liquid flowing through the
restricted slot defined by its lower edge and the stencil.
The increased drag on the flow coater with increased vis-
cosity of the fluid causes the lower edge of the flow coater
to pivotally shift to the rear, shifting lever 50 further
against the bias of compression coil 114 until finally, at a
predetermined viscosity, actuator 118 of limit switch 120 is
shifted a sufficient amount to throw the limit switch. The
amount of viscosity required to do this can be preset by
: 15 adjusting the knob 116 to vary the initial preset compres-
sion on spring 114, and thus, the bias supplied thereto in
opposition to the lever 150 actuating limit switch 120.
When limit switch 120 is activated, it allows electrical
power to flow to electric motor 140 that operates pump 146
through cam 42. This motor cycles through one revolution
(or otherwise as desired) until limit switch 148 is thrown
to deactivate the system, and during which time pump 146
sends a predetermined supply of solvent or carrier liquid
from reservoir 154 through line 150, through the pump,
through line 156-157 and into conduit 158 where the liquid
is dispensed through its series of spaced orifices 158'.
This drops down into the ink or other functional liquid to
lower the viscosity thereof. Lowering this viscosity will,
in succeeding printing strokes, cause the flow coater to
shift a less amount and thereby prevent actuation of the
pump again until the critical viscosity is again reached.
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1 Indicator bulb 124 shows when the pump is in operation.
Various additional features, advantages, and
objects of this invention will occur to those in the art
upon reviewing this disclosure. The particular construc- :
tional details set forth are intended to be illustrative of
the inventive concept, which is to be limited only by the
scope of the appended claims and the reasonably equivalent
structures to those defined therein.
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