A system for reducing interroller and/or interweb contamination

Abstract: A web handling system to prevent a web drive system to become contaminated by insufficiently dried portions of the web whereby a web (1) passes over a support (21) and where the obverse surface (5) of the web (1) is brushed at least during the period the nonuniformly coated portions pass roller (21), thereby to, at least partially, remove the nonuniformly coated portions.

Description: Field of the invention This invention relates to a web handling method to prevent a web drive system from becoming contaminated by insufficiently dried portions of the web. Description of the prior art In the manufacture of numerous products liquid compositions are coated on a continuous web. The coated surface of the support is then subjected to controlled temperatures and humidities to effect setting and drying. Depending on the particular path that the web must follow during processing, it may be necessary or expeditious for the web's coated surface to contact rollers which guide the web along a given path. In such processes, it is important that the web be completely dried prior to contacting a roller or windup to prevent interroller and/or interweb contamination. If there are portions of the web that have not completely dried, the rollers will be contaminated and will in turn contaminate subsequent sections of the web as they pass over them. If portions of not fully dried web surface are wound up, they can stick to the backside of the web that lies on top. In this way large portions may become unacceptably contaminated. This contamination is a particular problem in the manufacture of photographic materials where coating compositions are applied to various supports such as paper or film. In order to obtain the high coating speeds needed in today's competitive environment it is essential that the coating operation be a continuous uninterrupted process. This is obtained by the use of complex equipment which splices the trailing edge of a web to the leading edge of another without stopping the web and its transport system. It is possible that the coating procedure is disrupted when a splice passes the coating station. In general when a coating process starts or is disturbed the coated surface is nonuniform, but covered with thicker layers. Since dryers are designed with a capacity adequate to dry the normal coating to the desired dryness, heavier or thicker web coatings due to the start or disturbances of the process often are insufficiently dried. Some known methods to alleviate this problem are the use of a suction device adjacent the coating apparatus which acts as a vacuum cleaner on demand to suction off excess fluid from the web surface. This, however, requires cleaning of the suction tube after each operation to assure that there are no lingering specs of coating material which may dry out and impede the suctioning system. In EP 0 254 306 a multi-roll web support arrangement is described to evacuate the excess fluid from the web surface. This arrangement has some major disadvantages. When the set of rollers is rotated the path of the web changes and lengthens slightly. In order to deal with these variations in pathlength and tension on the web, the web handling device has to be made more complex. The outer surface of the blotting rollers has to be cleaned or changed after each or at least after some operations. These disadvantages make the arrangement described not desirable in a modern and automatic production plant. In the alternative, the drying capacity of the dryer could be increased to handle the excess material on the web. However, this is inefficient and can lead to excessive drying of the normal coating. SUMMARY OF THE INVENTION Objects of the invention It is an object of the present invention to provide an improved web handling method that prevents the web drive system from being contaminated by insufficiently dried portions of the web. It is a further object to provide a system for carrying out such method that is simple of construction and easy to maintain. Statement of the invention In accordance with the present invention, a method of reducing contamination of rollers in coated web handling systems in which a coated web has incompletely dried layer portions, comprises the steps of : advancing the coated web through a brushing station containing web brushing means, and when a heavier coated portion of said web that will result in incompletely dried layer portions occurs, temporarily displacing said web brushing means in said web brushing station from an inoperative position separated from the coated web surface to an operative one where the web brushing means makes contact with the coated surface, whereby the web brushing means in said operative position at least partially removes said heavier coated regions from said web. In the act of brushing there is a relative velocity difference between the brushing means and the coating to be brushed. The brushing of the web can be done in the countercurrent direction relative to the web movement. The nonuniformly coated portions which are brushed off of the web may be continuously evacuated. In implementating the above method, an installation may be used comprising : support means for supporting the backside of a moving web, means for detecting when a heavier coated portion of a coated web that will result in an incompletely dried layer passes over said suport means, and brushing means which at least partially brushes off said heavier coated portion from said web during its passage over said support means. The brushing in said system may be done in countercurrent direction relative to the web movement. The removed nonuniformly coated portions may be continuously removed by evacuating means. The brushing means may be a cylindrical brush which extends over the total width of said web and which may rotate in the countercurrent direction relative to the webmovement. In order to remove the nonuniformly coated portions evacuated from said web and sticking to said brush a knife may be positioned in contact with the hairs of said brush. Said removed nonuniformly coated portions may be evacuated continuously. Finally, in order to automate the operation of the installation, means may be provided for generating a signal indicative of the passage of incompletely dried coating portions of the web past a support means and for placing the brushing means in contact with the web. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described hereinafter by way of an example with reference to the accompanying drawings, wherein : fig. 1 is a diagrammatic illustration of a web handling system, fig. 2 is a diagrammatic illustration of a preferred embodiment of a brushing arrangement of said web handling system in operative position, and fig. 3 is a diagrammatic illustration of a preferred embodiment of a brushing arrangement of said web handling system in non-operative position. Detailed description of the invention Referring to figure 1 there is shown in greatly simplified form a web handling arrangement. As may be seen a web 1 is unwound from a supply roll 2 and driven through a known web handling arrangement represented by block 3. This arrangement 3 contains the driving forces, arrangements to guide and to direct the web 1, to control the lateral web position and the web tension. This arrangement 3 also contains known arrangements (not illustrated) to splice the trailing edge of a web to the leading edge of another one without stopping the web and its transport system. The web 1 is driven through a coating and chilling station of conventional design generally represented by block 4. The web 1 has an obverse surface 5 and a reverse surface 6. During its passage through the coating section 4 a liquid layer (or layers) is coated on the obverse surface 5. This obverse surface 5 is normally coated with a layer or layers of uniform thickness, however, at the start and the end of the process, when splices pass, in general when any disturbance occurs, the coating is nonuniform and the surface 5 is locally covered with heavier or thicker layers. These nonuniformities will result in incompletely dried coated portions of web 1 and are detected by a controller 7 which is linked with a system represented by block 20 which removes, at least partially, the nonuniformly coated portions of the web 1. The web 1 is then driven through conventional drying and conditioning arrangements represented by block 8, again some web handling arrangements 9 which have the same function as arrangement 3, and finally is wounded around a wound up roll 10. Web handling system 9 allows again changing of wound up roll without stopping the web or its transport system. Figure 2 is a detail view of brushing arrangement 20. Suppose a start of a coating procedure, the deposited layer being nonuniformly coated on the obverse surface 5 of web 1. Controller 7, which is the process computer of the whole system detects the start of the coating procedure. Knowing the webspeed and the weblength between brushing arrangement 20 and coating arrangement 4, controller 7 calculates the time the nonuniformities of the coated material reach support roller 21. Controller 7 gives order to start the rotation of brush 22 which is a cylindrical brush extending over the total width of the web. Brush 22 is rotating in countercurrent direction relative to the web movement and placed in a position where no contact with web 1 is made as in figure 3. At the same time the air inside box 24 is evacuated with a known ventilation device 25. Some seconds before the nonuniformly coated portions would reach roller 21, controller 7 gives order to displace rotating brush 22 towards roller 21. Brush 22 is then placed so that web 1 pushes in the hairs of the brush for 1 to 4 mm. When the nonuniformly coated portions reach roller 21 these portions are now being brushed off in such a way that the heavier or thicker portions are removed from web 1. If any nonuniformly coated portions stick to the web unless the brushing handling, the thickness of these portions is reduced to a magnitude that can be sufficiently dried by drying arrangement 8. A metallic knife blade 23 is positioned in the hairs of the brush for a depth not more than 2 mm. This knife blade has to remove the not fully dried coated portions which stick to the hairs of brush 22. Brush 22 and knife blade 23 are placed inside a box 24 which isolates the brush and the knife blade from the rest of the system. Inside this box 24 the air is loaded with particles which formed the nonuniformly coating on the obverse surface of the web 5. This air is continuously sucked off with a usual air evacuation means 25. Box 24 and air evacuating means 25 are constructed so that no particles leave the area between box 24 and web 1 on support 21, except those that are evacuated through the air evacuation means. Some time, eg. ten seconds, after brush 22 made contact with web 1 controller 7 gives order to withdraw the brush 22 from the web 1 in a position where no contact with web 1 is made. Brush 22 stops rotating and 5 seconds later the evacuation of air ends. During the normal coating procedure the brush is withdrawn from the web as shown in figure 3. The following data illustrate the described arrangement : total diameter of the brush 130 mm, smooth nylon hairs with a diameter between 0.15 to 1.5 mm and a length of 22 mm, brush density approximate 450 hairs/square centimeter, measured on the clamped end of the hairs, speed of brush 900 rev/min, speed of web 100 m/min. The invention is not limited to the embodiment described hereinbefore. It is also possible to place the brushing arrrangement 20 further downstream in the web handling system. For instance, the brushing arrangement 20 can be placed in the drying and conditioning arrangement 8, but before the coated obverse surface of the web 5 contacts any roller or is windup. It is even possible to place the brushing arrangement 20 after the drying and conditioning arrangement 8, so that only the not completely dried portions are to be removed. The brushing means can also be brushlike rollers covered with hairs made of other materials than plastics. The rollers can be covered with a foam structure, plush material or any other material that is capable of evacuating the nonuniformly coated portions from the web. It is a major advantage if these materials can be continously cleaned by any means.

Claims: A method of reducing contamination of rollers in coated web handling systems in which a coated web has incompletely dried layer portions, comprising the steps of : advancing the coated web (1) through a brushing station (20) containing web brushing means (22), and when a heavier coated portion of said web that will result in incompletely dried layer portions occurs, temporarily displacing said web brushing means (22) in said web brushing station (20) from an inoperative position separated from the coated web surface to an operative one where the web brushing means makes contact with the coated web surface, whereby the web brushing means in said operative position at least partially removes said heavier coated regions from said web. A method according to claim 1, wherein said brushing is done in countercurrent to the web movement. An installation for reducing contamination of rollers in coated web handling systems, comprising : support means (21) for supporting the backside (6) of a moving web (1), means (7) for detecting when a heavier coated portion of a coated web that will result in an incompletely dried layer passes over said support means, and brushing means (22) which at least partially brushes off said heavier coated portion from said web during its passage over said support means. An installation according to claim 4, wherein said brushing means is formed by at least one brush roller (22) rotatable in countercurrent relative to the web movement, and bodily displaceable with respect to the web. An installation according to claim 3 or 4, comprising a blade (23) for removing said brushed off heavier coated portions from said brushing means. An installation according to claims 3 to 5, wherein said support means is in the form of a backing roller (21), and said brush roller (22) and blade (23) are mounted within a housing (24) which engages an angular portion of said backing roller (21). An installation according to claim 6, which has blower means (25) for evacuating the air from said housing (24).

Inventors: GEERTS HENDRIK JOZEF, MUEES WILLEM, GEERTS, HENDRIK JOZEF, MUEES, WILLEM, Mües, Willem
Applicants: AGFA GEVAERT NV, AGFA-GEVAERT NAAMLOZE VENNOOTSCHAP
Application year: 1991
Main classification: G03C1
IPC codes: G03C1, B65G45, B05C11, B65H20