Drying and gas or vapor contact with solids – Apparatus – With fluid current conveying of treated material
Reexamination Certificate
2001-09-28
2003-10-21
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
With fluid current conveying of treated material
C034S084000, C034S638000, C034S639000, C034S643000
Reexamination Certificate
active
06634120
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an apparatus for coating one or both sides of a moving fiber web, in particular a paper web or a carton (i.e., cardboard) web, with a liquid or pastous coating material, the apparatus including a coating station for applying a coating onto the web and a non-contact turning apparatus following, viewed in the web's moving direction, the coating station.
2. Description of the Related Art
From WO 98/32921 an apparatus for coating a paper web on one side which includes a coating station and a non-contact turning station is known. After the coating station, in which a coating material is applied onto the moving paper web with the moving paper web being supported by a backing roll, the paper web moves on to a turning roll. From there it travels to a non-contact turning and drying apparatus and moves therethrough. After leaving the non-contact turning and drying apparatus, it is then led to calender-like cylinders which contact and thereby dry the paper web completely. The paper web is then moved on to further processing. In WO 98/32921, for example, an arrangement of four such coating apparatuses in successive sequence is shown, wherein, onto each side of the paper web, a coating material is applied twice. One disadvantage of this prior art coating apparatus is, on the one hand, that the coating is negatively influenced by turning the humid paper web before it has at least partially dried. This disadvantage tends to be even more pronounced since, due to the construction space available, turning rolls with small roll diameters are usually used which leads to a sharp bending of the paper web at the turning point.
In addition, the use of such a turning roll makes it impossible to convert a coating apparatus to an apparatus with which double-coating can be realized since, in this case, the turning roll would be in direct contact with the humid coating which would intolerably influence the coating's quality.
The combination of a non-contact turning apparatus and a non-contact air dryer shown in WO 98/32921, in connection with the non-contact turning and drying apparatus, is, for example, already known from DE 295 11 089 U1. From EP 0 770 731 A1, it is further known to locate a turning apparatus and a drying apparatus under one common housing in order to prevent humid exhaust gas and/or humid exhaust air from escaping into the machine hall.
What is needed in the art therefore is a coating apparatus which at least reduces, if not even eliminates, the risk of quality losses of the coated web.
SUMMARY OF THE INVENTION
This reduction is achieved according to the invention by a coating apparatus in which the web leaves the coating station and enters the non-contact turning apparatus while changing direction in one plane only. This means that the web moves in free motion without applying an external force from the point of leaving the coating station to the point of entering the non-contact turning apparatus, thereby guaranteeing that the coating layer applied onto the web in the coating station can be fixed in the turning apparatus while maintaining the quality obtained in the coating station.
Here, “leaving the coating station” refers to the point at which the web separates from the web guiding element, serving the purpose of directly applying a coating onto the web. Such a guiding element can be, for example, an applicator roll, a support roll or a band endlessly running around a shoe or similar devices. Decisive is that the web's coating condition is changed at the guiding element concerned and, with the exception of some desired drying effects, remains unchanged from the point of separation from it.
When referring to the web entering the non-contact turning apparatus, the point at which the turning apparatus influences the web noticeably, i.e. the point at which gas jets from the turning apparatus or infra-red rays hit the web in such a way that the web's temperature is changed, is referred to.
In the present invention the length of the web's free motion, i.e. the length of the path of the web between two guiding elements which are in contact with the web, is extended compared with the coating apparatuses known from prior art. This is even more extraordinary since many experts are of the opinion that, with an increase in the length of the free motion, the instability of the web's path also increases and that therefore the expert should be urged to reduce the length of free motions. Surprisingly, the advantageous effects of the present invention can be achieved without taking additional measures or installing further components for increasing the stability of the web's path when moving through the coating apparatus.
In addition to the fact that quality impairing effects on the web during turning are avoided, a further advantage can be achieved by the coating apparatus of the present invention: in contrast to the coating apparatus known from prior art, it is now possible to apply at a coating station a coating material onto both sides of the web because of the planar and externally unaffected path of the web after leaving the coating station. Thus, the space, especially the longitudinal dimension required by the coating apparatuses in which a web is to be double-coated once or several times, can be considerably reduced. This means that valuable construction space can be saved.
The coated web's quality can be further improved by having the web leave the coating station in an upward direction, preferably in an essentially vertical direction. It is often the case that when the web separates, for example, from the applicator roll or a similar coating element used for indirectly applying a coating material onto the web, an effect called “misting” occurs, i.e., a vapour of small coating beads or droplets is formed in the wedge between the web and the surface of the coating element. If the web is, however, leaving the coating station in an upward direction, preferably in an essentially vertical direction, the probability that the small beads fall on the coated web decreases with the increasing pitch angle. The beads are rather more likely to fall back on the coating element instead.
It is, however, also conceivable that the web could leave the coating station in a downward direction. This can be especially helpful in cases where already existing coating apparatuses and/or devices with non-contact turning apparatuses are to be converted in such a way that the web is traveling in one plane only without changing direction between leaving the coating station and entering the non-contact turning apparatus.
As has already been mentioned, the free motion of the web after the coating station serves the purpose of extracting humidity from the web. If the web is leaving the coating station in an upward or downward direction, there is a sufficient path for the web to dry without having to increase the length of the coating apparatus and, with it, its need of space since, in this case, the turning apparatus can be located either essentially above or underneath the coating station.
The non-contact turning apparatus can turn the web by approximately 90°. This is advantageous if web processing units of great length, e.g. a calender, follow the turning apparatus. The web can, for example, leave the coating station in a vertically upward direction, be turned by the turning apparatus by 90 ° to a machine running direction and then be led back to the height level of the coating station by a vertically arranged calender. In doing so, the available construction space can be used optimally by arranging the web processing units in a compact way. The machine running direction is the direction the web travels, starting with unwinding the web supply to be coated to reeling in the coated web.
In case no further web processing units are to follow the non-contact turning apparatuses, a sufficient drying length can also be obtained by having the web turned by approximately 180° by non-contact turning appa
Bowden Edwin V.
Helmer Knut
Lazarus Ira S.
Ragonese Andrea M.
Taylor & Aust P.C.
Voith Paper Patent GmbH
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