Coating apparatus – Control means responsive to a randomly occurring sensed... – Responsive to attribute – absence or presence of work
Reexamination Certificate
2000-08-14
2002-10-01
Edwards, Laura (Department: 1734)
Coating apparatus
Control means responsive to a randomly occurring sensed...
Responsive to attribute, absence or presence of work
C118S301000, C118S310000, C118S315000, C101S119000, C101S120000, C101S123000, C347S021000, C347S043000
Reexamination Certificate
active
06458211
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and to a method for applying a medium in liquid, powder or paste form to a substrate, to a system having a plurality of such devices, as well as to a use of such device, method and system.
BACKGROUND OF THE INVENTION
The substrate in question is preferably a textile substrate, although large area substrates may also quite generally be used, for example a substrate made of foil, nonwoven fabric, metal, carpet, plastic, paper, wallpaper, wood, glass, porcelain, ceramic or a similar material. The substrate may also be a printing support, for example a printing plate or a printing roll, to which it is necessary to apply printing ink as a medium prior to printing on a substrate made of paper, wallpaper etc. The advantage is that the medium can be applied at specific points on the printing support. With the medium a pattern is to be applied to such a substrate with the sharpest possible contours and a high resolution.
Corresponding to the large number of different substrates indicated above, many methods and devices for patterning surfaces of such substrates are also known. If they are to function with a printing speed which is high enough for mass production, these methods and devices basically require stencils which are per se expensive to produce. An example which may be mentioned in relation to this is that of the textile printing industry: for the screen printing preferably employed in this case, millions of printing stencils are made year after year just for rotary and flatbed printing. A large number of gravure cylinders are also produced for printing on films.
For rotary screen printing, a distinction is essentially made between two ways of producing the stencils: these are directly patterned DEP stencils (DEP=Direct Electrolytic Patterning) and resined stencils. The DEP stencils have the pattern electrolytically applied directly to them and can thus be used without further etching. With DEP stencils, the pattern and the colour separation are therefore already incorporated into the relevant dies.
Conversely, for the production of resin stencils, cylindrical screens are firstly produced electrolytically in a relatively complicated way. Various etching resists are then applied, according to the etching technique which is being used. All the openings existing in the stencils are closed with the etching resist during this. The desired printing pattern is then created by controlled release of openings for the respective colour separated beforehand from the model. This procedure can be carried out either using photographic development and wet chemical washing of the resist, or by direct digital transfer of the information using a laser device which “burns off” the etching resist using a laser beam.
Resin stencils have the advantage over DEP stencils that, by removing and re-applying the resist, they can be reused many times for different designs, whereas the DEP stencils can be used only for one design.
In short, the production of printing stencils, whether rolls or plates for typographic or gravure printing on paper and film, or screen stencils for rotary printing or flatbed printing on textile or carpet, is elaborate. The same is also true as regards the resin stencils which can be used repeatedly, since with these, for repeated use, the resist firstly needs to be removed, after which resist is again applied, dried etc. and this is followed by etching.
The production of such stencils finally only leads to economically viable products, for example printed textile, if the stencils are produced in large numbers and can be employed over an extended period of time for printing on large numbers of articles.
Now, especially in textile printing the problem arises that the time for which printing patterns are regarded as fashionable is becoming ever shorter, and at the same time the variety of patterns is increasing continually. Always producing new stencils therefore leads, every time fashion changes, to new rises in costs for every shorter “yardages”. This means that, especially in printing businesses in Europe and the USA, there are commonly large stocks of out-of-date stencils, the number of which may amount to several tens of thousands of stencils.
It should also be pointed out that stencil production as a whole, as well as stencil recycling, are very environmentally unfriendly and involve a large consumption of energy.
In view of this situation, consideration has already been given, for printing on textiles, to abandon the screen printing method and, for example, employ a digital inkjet printing method, successfully used in the paper industry, in order to transfer a pattern to textiles. In a method described in U.S. Pat. No. 4,324,117, liquid droplets are sprayed from very fine nozzles onto well-defined points on a substrate. The color mixing is in this case carried out with up to eight colors per point. Each of the eight colors can be applied in 256 levels. In spite of this variety of colors, the color space which can be obtained is limited in comparison with the color space of the screen printing method.
Thus, inkjet printing methods do indeed have the advantage that it is possible to avoid the elaborate production of stencils, that they furthermore make it possible to print without regard to register, and that it is unnecessary to premix color pastes. However, industrially usable production systems which make it possible to produce large yardages have not yet successfully been made. Individual systems have to date operated in the field of patterning with a printing speed of at most 1 m/min., while the average printing speed of a rotary printing machine is about 40 to 120 m/min.
It should moreover be taken into account that, with the inkjet printing methods, the droplets are formed within very fine nozzles having diameters in the micrometer range, for example 10 &mgr;m. These fine nozzles therefore unavoidably give rise to the problem of their clogging. With such nozzles, it is therefore only possible to use particular categories of color in highly pure form for printing, in order to minimize the risk of the nozzles clogging. The color space is accordingly also limited, and the use of, for example, metallic colors which are needed in fashion to obtain an iridescent effect, is out of the question.
A replacement for screen printing with stencils, which is suitable for mass production, has thus not yet been successfully found.
From the abundant prior art, only a few documents will be dealt with below by way of example:
DE 31 37 794 C2 describes a device for continuously delivering a minimal amount of liquid to a web of material. This device has a fine-meshed screen and a blowing device directed against the screen. The screen rests in this case as a textile mesh belt without pressure on the web of material, or is guided or laid over it, and the blowing device is arranged above the mesh belt section carrying the ink.
As a supplement to this, DE 31 46 828 C2 proposes using a bath as a liquid delivery device, and arranging the blowing device behind and at a higher level than the delivery device in the running direction of the endless screen belt. Such a device could per se be used for patterning/printing if etching is carried out beforehand.
DE 40 01 452 A1 describes a device for continuously delivering a liquid to a web of material, having a moving screen, means for filling the openings in the screen and a blowing device for transferring the liquid held in the openings in the screen onto the web of material. The device for filling the openings in the screen consists of chambers which are arranged opposite one another on both sides of the screen and bear on the screen, one chamber being designed as a feed chamber and being connected to a liquid feed, while the other chamber is designed as a discharge chamber and is connected to a liquid drain.
Furthermore, DE 42 28 177 A1 discloses a device for continuously delivering a liquid to a web of material having a moving screen, having filling chambers which are arranged o
Juffinger Josef
Wefers Lothar
Edwards Laura
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Stork Textile Printing Group B.V.
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