CA1193430A

CA1193430A - Device for applying a medium to a workpiece

Info

Publication number: CA1193430A
Application number: CA000385918A
Authority: CA
Inventors: Mathias Mitter
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-16
Filing date: 1981-09-15
Publication date: 1985-09-17
Also published as: DE3034807A1; DE3176300D1; DE3034807C2; EP0047907A1; BR8105901A; JPS57110363A; EP0047907B1; ATE28221T1

Abstract

ABSTRACT OF THE DISCLOSURE
A device for applying a treating medium to a workpiece has a screen and, above the same, walls defining a space into which the treating medium is supplied and which is open to the screen at its bottom. The space may be of uniform width from top to bottom, or it may become narrower towards the bottom.

Description

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"Device for Applying a Medium to a Workpiece"

BACKGROUND OF lH~ INNENTION
The present invention relates to the applicatlon of a treating medium to a workpiece.
More especially, ~he invention relates to a device for applying a treating medium to a workpiece.
Still more particularly, the invention relates to a device for applying a treating medium ~o a workpiece via a screen.
Devices of this type are already known from the screen-printing ~0 ar~, for example as disclosed in German Allowed Application 2,300,290. How-ever, they are in need of further improvement for reasons known to those skilled in the art.
In particular, such devices can be used to print on textile work-pieces, including carpeting and the like. The medium used may be liquid or paste ink, but it has also been proposed to use the medium in foamed condi-tion.
Various types of screen can be used, e.g. an endless belt-type screen trained aTound rollers, a rotary drum-type screen or even a flat screen. The former two types of screen travel in an endless path; the flat type is usually sta~ionary and the medium applicator device (generally a squeegee) reciprocates over the screen to s~uee~e the medium through the screen openings. Other media may also be applied in this manner, for example mothproofing liquid, fire-proofing liquid or the like. The screen may have all its openings unobstructed ~no pattern being printed) or selected openings may be blocked (so that a pattern is printed). In screen printing machines it is common to have two or more sequentially arranged printing sta~ions each having a screen printing a difEerent color.

If devices of the aforementioned type are used to apply a treating medium in foamed condition, a problem arises with maintaining an adequate supply of Eoam on the screen, given the fact that the machine uses up the ~3~3~

foam at a considerable rate. In particular, it is important that the first-applied foam is also used up first, since foam bubbles have a tendency to burst and to liberate the entrained liquid treating medium. If this occurs under uncontrolled conditions, it can be disadvantageous, especially if it is not assured that there is a uniform flow of foam from the supply device to the screen in operation of the machine.
SU~RY OF T~IE INVENTION
It is therefore an object of the invention to overcome the dis-advantages of the prior art.
A more particular object of the invention is to provide an im-proved device for applying a treating medium to a workpiece which is not pos-sessed of the aforementioned disadvantages.
Still another object is to provlde a device of the type in ques-tion which assures that the inflow (supply) of foamed medium per unit time corresponds exactly or substantially exactly to the amount of medium used up per unit time.
A concomitant object is to provide a clevice of the type under dis-cussion in which undesirably high flow speeds of the foamed medium are avoided.
Still a further object is to provide such a device in which it is assured that the supplied foamed medium travels uniformly towards the screen.
In keeping with the above objects, and with still others which will become apparent as the description proceeds, one aspect of the inven-tion resides in a device for applying a medium to a workpiece, comprising a screen adapted to be superjacent to a workpiece; means delimiting above the screen an enclosed space adapted to receive a medium to be applied to the workpiece; applicator means for applying the medium through the screen and to the workpiece~ the space having a first portion of greater width and a second portion adjacent the applicator means and being of lesser width;
means for discharging printing medium into the first portion of the space;
and means for varying the width of the second portion of the space.

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llaving the foam-receiving space connected with the upper screen sur~ace and with the area of the applica~or device, by a narrowed channel whose width is preferably adjustable, accomplishes the objects of the inven-tion in the desired manner. It assures that the amount of foam in the nar-rowed channel corresponds to the amount of foam used per unit time (e.g.
squeegeed through the screen by the applicator device). Moreover, the foam travels through the narrowed channel with relatively low flow speed. The using-up of foam leaving the channel automatically draws new foam into the top of the channel and downwardly in the same. However, it is also possible for the foam admission space to have a uniform cross-section from top ~where foam is admitted) to bottom ~where foam is used up).
In any case, the invention makes it possible to so supply the treating medium ~preferably, but not necessarily in foamed state) in depen-dence upon the workpiece to be treated that the workpiece receives an ade-quate quantity of the treating medium. For example, napped workpieces ~e.g.
carpeting) can in this manner be supplied with sufficient treating medium to assure that the medium covers the entire nap and penetrates to the bottom (base) of the nap. On the other hand, if a smooth (non-napped) textile is to be treated, then the amount oE medium supplied per unit time must be cor-respondingly small since only the workpiece surEace needs to be wetted.
Exemplary embodiments of the invention are illustrated in the appended drawings. ~lowever, it is to be understood that these are for the purpose of explanation only and that the authoritative definition of the invention is contained only in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectioned, somewhat diagrammatic side view of a print-ing station embodying the invention;
FIG. 2 is a top plan view of FIG. l;
FIG. 3 is a view similar to FIG. 1 but of a different embodiment;
FIG. 4 is a view similar to FIG. 3 but again o a different embodi-ment;

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FIG. 5 is a view similar to FIG. 4 but of yet another embodiment of the invention;
~IG. 6 is a diagrammatic view, illustrating a foam generator which can be used with any of the preceding embodiments; and FIG. 7 is a diagrammatic view of still another embodiment of the invention.
FIG. ~ is a diagrammatic view o~ still another embodiment of the invention.
DESC~IPTION OF PREFE~RED EMBODIMENTS
FIGS. 1 and 2 il]ustrate a screen printing machine 1 having at least one printing station 10. This printing station has an endless belt-type printing screen 2 but could have a drum-type screen (see e.g. FIG. 5) or a flat screen.
Mounted within the confines of screen 2, which is trained around rollers 11, 12 and 13, is a medium applicator device 3 (here in form of a roller squeegee) which squeezes the treating medium (e.g. printing ;nk in foamed and unfoamed state) through the openings of the screen and onto the subjacent workpiece W. In lieu of (or in addition to) the device 3 there may be a suction hox 30 underneath the (gas permeable) printing blanket B on which the wor]cpiece W rests. Suction box ~0 has a suction slot 130 and com-municates via pipe or hose 31 with a suction source 32, e.g. a vacuum pump.
Above the screen 2 and extending over the entire working width thereof (i.e. in direction normal to the plane of FIG. 1) there are walls which define a medium-receiving space 4. IJI this embodiment the space 4 has an upper portion 40 into which medium is admitted by the supply device 5, and a narrow lower portion or channel 41 which extends alongside the appli-cator device 3 and the width of which is adjustable.
In the illustrated embodiment the space 4 is essentially box-shaped, being delimited by an upstream ~as considered in the direction of movement of screen 2) sidewall 42 and a downstream sidewall 43, as well as front and rear endwalls (not shown). The lower end of sidewall 43 carries a glide shoe which embraces a portion of ~he periphery of roller squeegee 3 and makes a seal therewith via a sealing element 45 of e.g. rubber or syn-thetic plastic material. Thus, roller 3 which can be driven can turn but no medium can escape above it.
The suction box 30, known from French Patent No. 984,151, has its slot 130 extend over the entire working width of the screen 2.
An important aspect of this embodiment is that the wid~h of the narrowed channel 41 can be varied. This can be accomplished in a variety of ways. For example, the lower part L42 of wall ~2 may be removable so that it can be replaced with a differently shaped part, as indicated by ~he broken lines in FIG. 1, or to change its position by inserting a filler strip (to move it to the broken-line position). Then again, part 142 can be mounted so that its position can be continuously varied.
The wider upper part 40 of the space ~ can be made so wide that swfficient replacement medium can be present in it at all times. ~or example, iE the medium is in foamed state, the wall portion 2~2 in the cen-tral part of the lea~ing wall 42 may be inclined as shown, to form a chute on which the foam can slide downwardly. The lower part 142 may be shaped to accommodate itself to the form of the device 3 (i.e. here be arcuate to con-form to the roller squeegee). Its lower end preferably extends normal to screen 2 and may have the illustrated bent-over lip which sealingly slides on the screen 2. In all other respects the printing station 10 may corres-pond to the one disclosed in German Patent No. 2,258,892. Roller 11 and/or 12 may be driven; roller 13 may be movable as indicated by arrow 13a to ten-sion the screen 2.
Printing medium foamed or otherwise, is supplied by the supply de-vice 5 which is located above the upper end of space 4; it may be a pipe or tube having a plurality of outlet nipples 50. One or more such pipes 5 may be provided, and each may be made wholly or partly reciprocable over the X

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width of the screen 2, to assure ~miform filling of the space 40 with the medium.
FIG. 2 shows the printing station 10 supported on the frame of the printing machine. It also shows the printing blanket B which travels in the direc~ion indicated by the arrow ~pTeferably endlessly)~ i.e. in the same direction as screen 2. Also shown are two la~eral bearing heads 14 in which the rollers 11, 12 and 13 (the latter is omitted for clarity) are journalled. Heads 14 may also be connected to one another by not-illustrated traverse members. Mounts 46 may connect the leading wall 42 (and any and all walls bounding space 4) to a traverse member 15 which is one of the ones connecting the heads 14.
FIG. 3 shows an embodiment analogous to FIG. 1 and like reference numerals identify like elements therein. There, however, the upper region 40 of the space 4 has part of its leading wall 42 connected with a mounting strip or brace 140, so that the lower part 142 of the wall 42 can be adjust-ably connected to strip 140, thus facilitating~variation of the width oE
channel 41. The endwalls 47 ~one shown) may be plate-shaped. The trailing wall 43 here extends almost to the screen 2 and carries at its lower edge a flexible strip 43a which slides on screen 2 and has the dual purpose of mak-ing a seal therewith and of acting as a doctor-blade type of squeegee. 0-f course, the lower edge of wall 43 could extend directly to the screen and perform these functions.
FIG. 4 is also similar to FIG. 1 and hence like reference numerals designate like elements. In FIG. 4 the squeegee is a doctor-blade type of squeegee 3a having a holder 33 by means of which it is mounted on a shaft 33a with limited freedom of angular displacement (shaft 33a may be secured in bearing heads 14 similar to those of FIG. 2). Trailing wall 43 has a shoe-shaped lower integral portion 44a which engages holder 33 via sealing element 45a.
Lowcr part 142 of leading wall 42 may be replaced with a differ-~ -7-~3~3~

ently shaped part, so that the width a of channel 41 (see FIG. 3) can be varied. Also, by changing the angular inclination of holder 33 on shaft 33a (the holder can be fixed in the selected position by means of e.g. a set screw), the width a can be further adjusted.
The supply of medium is here effected via a pipe or hose 5 having one or more outlet nipples 50, and pipe 5 can be slidably mounted via holder 51 on a traverse secured in bearing heads 14 (FIG. 2~, and be reciprocable via a not-illustrated drive; this assures uniform filling of upper space 40 with the medium which then flows into channel 41.
FIG. 5 shows an embodiment in which the screen 2a is a rotary drum-type screen. The applicator device is again a roller squeegee 3 located in the interior of the screen 2. Wall 42 is analogous to the wall 42 in FIG.
4; changing the position of lower part 142 relative to upper part 42 varies the width of channel 41. A flexible lip 48 at the lower end of part 142 makes a wiping seal with screen 2a. All other elements correspond to simi-larly numbered ones from preceding embodi.ments.
FIG. 6 shows an embodiment of a foam generator suitable for use with all preceding embodiments. Such a foam generator is known per se from German published application OS 2,513,062. The screen 2a is here shown --by way of example-- as a drum-type similar to the one in FIG. 5, having screen-stabilizing end rings 20.
The foam generator 7 has a reservoir 73 containing water, the water-soluble treating liquid (e.g. ink) and a known-per-se foaming agent.
Liquid from reservoir 73 is withdrawn via conduit 72 by gear pump 71 driven by gear motor 70, and is pumped via conduit 172 and flow meter 74 into the mixing container 175 of a mixing head 75. Container 175 may accommodate glass spheres, granulate or some similar material which promotes the forma-tion of foam in the presence of liquid and compressed air.
The compressed air is supplied by a compressor 76 via a conduit 272 in which a shut-off valve 77, a pressure regulator 78 and a flow meter 3~

79 are interposed, and enters in the mixing head 75 an annular space 275 sur-rounding the container 175. From there it enters the container at the bot-tom via openings 375 and converts the liquicl to foam. It is known, of course, that the higher the proportion vf air to liquid, the drier the foam, and vice versa.
It is advantageous in all ernbodiments (in order to make adjustment of the width a simple~ to provide the adjusting mechanisms at or near the axial ends of the space 4, e.g. in FIG. 6 in the region of the end rings 20 where they are readily accessible to an operator.
FIG. 7, finally, is very similar to FIG. 1 and like reference numerals again identify like elements. This Figure shows, however, that the lower wall part 1~2a need not be constricted ~or inclined in direction to-wards the device 3), but can be straight. In fact, although it is shown to be releasable and adjustable or replaceable, it is possible to make it integral with and an extension of the wall part 42. In all other respects this embodiment corresponds to the one in FIG. 1.
The wall 142a and the doctor-blade type of squeegee 3a form alone an uniform channel 41 ending on the sieve or screen 2.
The parts 142a and 3a stand parellel to another. By the channel 41 between them is assured that the supplied foamed medium travels abso-lutely uniformly towards the sieve or screen.
FIG. 8 is also similar to FIG. 1 and like reference numerals again identify like elements in this figure is shown that the wall 142a is curved in the same way as the roller 3 so that the channel is absolutely uniform.
The invention has hereinbefore been described with reference to exemplary embodiments. However, various modifications and changes will offer themselves to those skilled in the art and all such changes are in-tended to be encompassed within the scope of protection of the appended claims.
To summarize the basic considerations behind the invention:

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It is exceedingly difficult and just about impossible to evenly distribute small quantities of treating medium (especially liquid) over the surface of a workpiece web. This is possible only by foaming the mediumO
Foaming alone, however, is still not sufficient to achieve the intended pur-pose: uniform distxibution of small quantities of treating liquid over the workpiece surface is possible only if the foam is reconverted to liquid state --and this is possible with the desired uniformity only if a screen is interposed between the foam and the workpiece surface, so that the medium is applied to the workpiece through the screen.
The foam is pressed (e.g. via a squeegee) or sucked (e.g. via a suction box) through the screen. In so doing the main constituent component of each foam bubble, i.e. the treating liquid, is reconverted to liquid state and the quantity of liquid thus liberated is uniformly distributed over or in the workpiece, over the entire working width of the screen.
The foam bubbles may either be totally destroyed at ~r near the foarn/screen interface, in which case the thereby liberated liquid reaches the workpiece. Alternatively, the foam may only be partly destroyed; in that case, some liquid will bc liberated for application to the workpiece.
The remaining, non-destroyed bubbles of ~oam will pass through the screen and be carried along by the workpiece surface to either burst (and liberate their entrapped liquid) or to become dried in collapsed but non-burst state due to the influence of air, drying, heating cr the like, depending upon what equipment acts upon the workpiece downstream of the location of foam application. Another possibility is for most or all of the foam bubbles to pass through the screen in non-burst state and then to burst either on the workpiece surface or to collapse and become dried as mentioned before.
The foam itself may have many different consistencies, since the types of treating liquid used may vary, the degree of foaming may vary, and the like. Furthermore, the manner in which the foam is made to pass through the screen can be varied. The screen speed, workpiece speed and physical X

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influences acting upon the foam can be varicd. An important role is also played by the type of screen structure in respect of the size and shape of its openings, the thickness of the screen and its frictional resistance at the foamjscreen interface, all of which can be varied by using different screens. Finally, the type, surface struc~ure, previous surface treatrnent and absorption capability of the workpiece itself are parameters which influ-ence the application of the medium. All of the aforementioned parameters are, in fact, freely selectable by a user.
The workpiece may be of paper~ glass, synthetic plastic material or fibrous material (such as textile, napped material such as carpeting).
The treating medium may be of many different kinds. For example, a suitable synthetic plastic resin may be foamed in the presence of an appropriate sol-vent and may be applied through the screen to a glass workpiece, to a paper workpiece or the like. ~halk may be foamed and applied to a paper workpiece as a coating. If synthetic plastic is applied in foamed state to paper, especially absorbent paper, then it can be applied in suEficient quantity to penetrate into the paper. Latex can also be foallled and applied in the :inven-tive manner to e.g. a textile workpiece as a coating; in this instance it may be advantageous to maintain the ~oam bubbles in unburst state to the maximum extent possible and to let them become dried or polymerized on the workpiece surface. Evidently, it is possible to coat, print or cover only portions of the workpiece surface, rather than the entire surface, irrespec-tive of the type of medium used~
The screen or sieve is preferably supported by the surface o-f the workpiece.
FIG. 7, finally, is very similar to FIG. 1 and like reference numerals again identify like elemsnts. This Figure shows, however, that the lower wall part 142a need not be constricted or inclined (in direction to-wards the device 3), but can be straight. In fact, although it is shown to be releasable and adjustable or replaceable, it is possible to make it integral with and an extension of the wall part 42a. In all other respects this embodiment corresponds to the one in FIG. 1.
The invention has hereinbefore been described with reference to exemplary embodiments. However, various moclifications and changes will offer themselves to those skilled in the art and all such changes are in-tended to be encompassed within the scope of protection of the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Device for applying a medium to a workpiece, comprising a screen adapted to be superjacent to a workpiece;
means delimiting above said screen an enclosed space adapted to receive a medium to be applied to the workpiece;
applicator means for applying the medium through the screen and to the workpiece, said space having a first portion of greater width and a second portion adjacent said applicator means and being of lesser width;
means for discharging printing medium into said first portion of said space; and means for varying the width of said second portion of said space.

2. Device as defined in claim 1, said delimiting means comprising a plurality of walls, and said varying means comprising means for replacing portions of at least one of said walls with differently shaped portions.

3. Device as defined in claim 1, said delimiting means comprising a plurality of walls, and said varying means comprising means for changing the position of at least a portion of at least one of said walls and arresting said portion in said changed position.

4. Device as defined in claim 1, said applicator means comprising a squeegee roller, and said delimiting means comprising a wall having an edge portion in sealing but sliding contact with the circumference of said squeegee roller.

5. Device as defined in claim 4, said screen being movable in a pre-determined direction and said wall being a trailing wall as considered in said direction; said delimiting means further comprising a leading wall com-posed of an upper portion defining with said trailing wall said first por-tion of said space, and a lower portion defining with said squeegee roller said second portion of said space.

6. Device as defined in claim 1, said screen being movable in a pre-determined direction, and said delimiting means including a leading wall as considered in said direction, said leading wall having an upper portion; and further comprising means on said lower portion in sealing but sliding con-tact with said screen.

7. Device as defined in claim 6, wherein the last-mentioned means com-prises a lower margin of said lower portion which is bent parallel to said screen counter to said predetermined direction.

8. Device as defined in claim 1, said screen being movable in direc-tion towards said applicator device, and said space being box-shaped and located ahead of said applicator device as considered in the direction of movement of said screen.

9. Device as defined in claim 1; and further comprising suction means having a suction inlet located underneath said screen and said second por-tion of said space.

10. Device as defined in claim 1, said applicator device being an angularly adjustable doctor blade.

11. Device as defined in claim 1, said screen being movable in a pre-determined direction, and delimiting means having a plurality of walls in-cluding an upstream wall and a downstream wall as considered in the direc-tion of movement of said screen, said downstream wall extending to said screen and having a lower portion engaging the screen and acting as a doctor blade.

12. Device as defined in claim 1, said screen being movable in a pre-determined, and said delimiting means including an upstream wall as con-sidered in the direction of movement of said screen, said upstream wall hav-ing an upper portion and a lower portion and a mounting strip connecting said upper and lower wall portions and allowing limited freedom of displace-ment of the lower wall portion in and counter to said predetermined direc-tion.

13. Device as defined in claim 1; further comprising a pair of lateral bearing heads at opposite lateral sides of said screen; a traverse member connecting said bearing heads; and wherein said delimiting means comprises a plurality of walls mounted on said traverse member.

14. Device as defined in claim 1, said discharging means comprising an elongated pipe having at least one outlet nipple and being mounted for reciprocation in direction of its elongation and transversely of said screen.

15. Device as defined in claim 1, said varying means comprising means for continuously varying the width of said second portion.

16. Device as defined in claim 1, said screen being movable in a pre-determined direction, and said delimiting means comprising a plurality of walls including an upstream wall as considered in said direction, said screen having lateral side walls and said upstream wall having end portions adjacent said lateral sides, said lateral wall having an upper wall portion and a lower wall portion which is adjustable relative to said upper wall por-tion to thereby vary the width of said second portion of said space; and said varying means comprising actuating elements accessible at said lateral sides for continuously adjusting and then arresting their lower wall portion.

17. Device as defined in claim 1, said screen being movable in a pre-determined direction, and said delimiting means including an upstream wall as considered in said direction and composed of an upper wall portion and a lower wall portion adjustable relative to said upper wall portion, said lower wall portion having a shape accommodated to that of said applicator means.

18. Device as defined in claim 17, said lower wall portion extending parallel to said applicator means.

19. Device as defined in claim 17, said applicator means including a squeegee roller, and said lower wall portion being arcuately curved in accom-modation to the curvature of said roller.

20. Device as defined in claim 17, said lower wall portion extending normal to said screen.

21. Device for applying a medium to a workpiece, comprising a screen adapted to be superjacent to a workpiece;
means delimiting above said screen a channel space adapted to receive a medium to be applied to a workpiece;
applicator means for applying the medium through the screen and to the workpiece, said channel having an upper portion spaced from and a lower portion adjacent to said screen and to said applicator means, and said channel having a uniform width throughout said upper and said lower portions; and means for discharging printing medium into said upper portion.