Coating apparatus – Solid applicator contacting work – With work-handling or work-supporting
Reexamination Certificate
2001-04-02
2003-04-29
Edwards, Laura (Department: 1734)
Coating apparatus
Solid applicator contacting work
With work-handling or work-supporting
C118S212000, C118S411000, C118S412000, C118S413000, C118S414000, C118S419000
Reexamination Certificate
active
06554900
ABSTRACT:
The invention relates to an apparatus and a process for the application of a flowable medium from a stock chamber to a surface moved along the apparatus, where the stock chamber partly covers the surface with formation of a sealing gap and an exit gap. The invention furthermore relates to the use of an apparatus of said type.
Apparatuses of said type are widely employed, for example, in the production of labels for coating paper or film webs with adhesives. A common process for this purpose is the engraved roll application process, in which the flowable adhesive is located in an open stock chamber whose opening is in contact with a rotating roll. The roll contains a multiplicity of engraved grooves. During rotation of the roll, the initially empty grooves enter the opening region of the stock chamber from the outside and are filled with adhesive therein. On exit of the roll from the opening region of the stock chamber, excess adhesive is wiped off the surface of the roll by means of a doctor blade which extends over the width of the roll and limits the opening region of the stock chamber. During further rotation of the roll, the latter is brought into contact with the paper or film web to be coated, causing at least some of the adhesive in and on the grooves to be transferred to the web.
The amount of adhesive transferred from the stock chamber to the roll can be varied within narrow limits through the position or contact pressure of the doctor blade at the exit of the roll from the opening region of the stock chamber, i.e. ultimately through the height of the exit gap formed by the doctor blade and the roll surface.
A further doctor blade is generally installed in the region of the entry of the roll into the opening region of the stock container, this further doctor blade taking on the function of a seal between the stock container and the roll surface. In order to prevent excess outflow of the adhesive at this point, the sealing gap formed between this doctor blade and the roll surface must have the smallest possible height.
The contact pressure of the doctor blade at the sealing gap and the height of the exit gap can be adjusted in this known process by changing the position and situation of the application apparatus relative to the rotating roll.
In particular at high roll rotation speeds, complete filling of the roll grooves is no longer guaranteed in this known process, which results in the amount of adhesive taken up during a rotation and thus ultimately the application weight of the adhesive to the web to be coated dropping in an undesired manner. Furthermore, air is increasingly introduced into the stock container through the roll grooves at higher rotation speeds, resulting in undesired foaming in the stock container. The presence of foam in the stock container in turn means that the grooves of the engraved roll are not completely filled with adhesive, but instead partly with air in the form of bubbles, which means that fine bubbles form on the web to be coated, resulting in undesired clouding of the adhesive layer.
In order to prevent said difficulties, it has been proposed to pressurize the adhesive in the stock chamber using suitable means (J. Türk, H. Fietzek, H. Hesser and I. Voges, Perspektiven für die Verarbeitung von Dispersionshaftklebstoffen, reprint TI/ED 1654d, BASF Ludwigshafen, August 1993). This ensures complete filling of the engraved grooves, even at high roll rotation speeds. Depending on the set pressure, a different amount of adhesive is also conveyed out of the application apparatus on the surface of the roll outside the engraved grooves at the exit gap. In this way, the amount of adhesive applied to the roll and thus ultimately the application weight of the adhesive on the web to be coated can be set within a broader range than without the use of pressure. Due to the higher pressure in the stock chamber, it is furthermore achieved that only a greatly reduced amount of air is introduced into the stock container at the sealing gap; in this way, excess foaming is prevented.
However, the higher the roll rotation speed, the higher the pressure in the stock chamber has to be selected in order to prevent the introduction of air into the adhesive. The maximum achievable rotation speed is limited by the fact that, on a further increase in pressure, the adhesive is forced out of the stock container in an uncontrolled manner firstly through the sealing gap and secondly through the exit gap. Exit of adhesive through the sealing gap results in undesired presentation of adhesive in front of this gap, which can result in soiling of the environment of the application apparatus and in operational interruptions. Uncontrolled exit of adhesive through the exit gap in turn results in uneven application of composition to the web to be coated.
In the article “Rasterwalzenauftragsverfahren mit Druckkammerrakel—ein Beschichtungswerkzeug auch für strahlenchemisch härtende Systeme”, IPW 1/97, pp. 1 to 8, it was proposed to construct an application apparatus in such a way that the adhesive flows constantly through the stock chamber in the opposite direction to the direction of movement of the roll. In this way, air introduced into the stock container is constantly transported away by the rotating roll with the flowing adhesive. It was also proposed in this article to incorporate a throttle element into the stock chamber in such a way that a narrow throttle gap with a length of a few centimeters forms between the throttle element and the roll surface, through which gap the adhesive flows in the opposite direction to the direction of movement of the roll surface. In this way, the engravings are filled better with adhesive, and any air present in the engraved grooves is forced out of them, at least partly, and removed from the roll surface with the flowing-off adhesive. In practice, however, precise adjustment of the throttle element independently of the operating parameters, for example roll rotation speed, viscosity and pressure of the adhesive, proves to be difficult and not easily reproducible. In addition, an apparatus of this type cannot reliably prevent the introduction of air into the stock chamber and the formation of bubbles in the adhesive film.
It is an object of the present invention to provide an apparatus for the application of a flowable medium to a surface moved along the apparatus which works reliably even at high surface speeds, in which formation of air bubbles in the medium is reliably prevented, which is of simple construction, and which can be set simply and reproducibly for given operating conditions.
We have found that this object is achieved by an apparatus for the application of a flowable medium from a stock chamber to a surface being moved along the apparatus, where the application chamber at least partly covers the surface. In accordance with the invention, the stock chamber is divided into a pre-chamber and a main chamber, between which is arranged a dividing element which, together with the surface, limits a dividing gap.
The dividing element arranged between the pre-chamber and the main chamber reliably prevents air which has entered the pre-chamber from being transported into the main chamber and resulting in undesired foaming therein. The actual coating of the surface with the desired amount of the flowable medium then takes place free from air bubbles in the main chamber. The pre-chamber and the main chamber advantageously have independent feeds for the medium, so that, for example, the pressure conditions in the pre-chamber and in the main chamber can be selected independently of one another.
Particular advantages arise if the dividing element is arranged in such a way that it touches the surface. This achieves complete separation of the pre-chamber and the main chamber.
In practice, complete touching or contact of the dividing element with the surface can often only be achieved if the surface is stationary. In actual operation, i.e. in the case of a moving surface, unavoidable variations in the guidance of the surface mean that a certain
Aydin Oral
Dragon Andree
Reinhard Frank
Edwards Laura
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pagendarm Technologie GmbH
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