Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Reexamination Certificate
2000-05-08
2002-09-03
Bareford, Katherine A. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
C427S356000, C118S123000, C118S125000, C118S126000, C118S410000, C118S413000, C118S411000
Reexamination Certificate
active
06444269
ABSTRACT:
TECHNICAL FIELD
This invention relates to the continuous coating of sheet or strip articles, such as aluminum or other metal strip, hereinafter generically termed “strip articles.” In an important sense, it is directed to coating heads especially suitable for applying low solvent or reduced solvent coatings or solvent free coatings, e.g. molten polymers, and to coating lines and methods employing such heads.
BACKGROUND ART
More particularly, the present invention is directed to improvements in the types of strip-coating apparatus and methods described in U.S. Pat. No. 4,675,230 and in International (PCT) Application No. PCT/CA94/00291 published Dec. 8, 1994, under International Publication No. WO 94/27739.
U.S. Pat. No. 4,675,230 describes apparatus and procedure for applying a paint or like coating to an elongated strip article using a coating head with a die that has a slit to which coating material is supplied under pressure and a strip-facing extended surface or metering land immediately downstream of the slit, and a support such as a roll around which the strip is advanced past the head for receiving from the slit a layer of paint metered between the die and the strip, wherein a load is continuously exerted on the die during operation for urging the land against the applied paint layer on the strip so as to maintain a uniform metering gap between the land and the coated strip surface. The load may be exerted by devices such as air cylinders acting on the die and capable of adjustment to vary the magnitude of the load for different coating operations. In this way, a coating of superior uniformity can readily be applied to a surface of an article such as sheet metal strip, notwithstanding that the strip characteristically exhibits some variation in thickness along its length; the maintenance of a load on the coating head die facilitates accuracy and ease of setup, and also enables the die to conform positionally to variations in strip thickness, for maintaining a constant metering orifice aperture. U.S. Pat. No. 5,147,462 describes apparatus for automatic film thickness control in coating procedures and apparatus of the same general type.
The methods and apparatus of U.S. Pat. No. 4,675,230 are shown as arranged for applying a coating to one major surface of a strip article (one-sided coating). The aforementioned PCT publication describes modifications or arrangements of methods and apparatus of this type enabling simultaneous application of coatings to both major surfaces of a moving strip or sheet (two-sided coating). The apparatus arrangements thus described for two-sided coating comprise two coating heads of the general type described in U.S. Pat. No. 4,675,320, mounted face-to-face with the strip passing between them.
In particular, the aforementioned PCT publication discloses apparatus for continuous two-sided coating of a strip article, including means for defining a path of continuous longitudinal advance of an elongated strip article having opposed major surfaces to be coated, the path including a rectilinear portion in which the opposed surfaces of the strip article are substantially planar; two coating heads each including a die defining an elongated open-sided slit and having a land portion with an extended land surface immediately adjacent the exit side of the slit, for respectively depositing layers. of liquid coating material on the opposed major surfaces of a strip article advancing in the path; and means for supplying liquid coating material under pressure to the slit of each head. The apparatus thus disclosed also includes means for supporting the dies of the two heads in facing relation to each other on opposite sides of the rectilinear portion of the strip article path while permitting individual translational movement of at least the land portion of at least one of the dies relative to the supporting means in a direction perpendicular to the major surfaces of a strip article advancing in the path. This supporting means positions the heads such that their die slits respectively open toward the opposed major surfaces of an advancing strip article in the rectilinear path portion with their long dimensions extending transversely of the path; their die land surfaces are disposed, substantially in register with each other, beyond the slits in the direction of strip article advance, respectively facing the opposed major surfaces of an advancing strip article and converging toward each other and toward the path in the direction of article advance; and, during operation with the article advancing past the slits and liquid coating material supplied to both slits as aforesaid, the article major surfaces respectively drag layers of coating material from the slits, the layers being thereby deposited on the article major surfaces. In combination with the foregoing features, the disclosed apparatus further includes means for continuously exerting a load on at least the land portion of the aforementioned one die during operation as aforesaid such that the layers of coating material deposited on the strip major surfaces are pressed between the land surfaces of the dies of the heads to maintain the deposited coating layers at predetermined constant thicknesses while the coating layers alone hold the dies entirely away from contact with the strip article major surfaces.
In some embodiments of the described apparatus, the aforementioned one die comprises a land portion as defined above and a portion that is stationary during operation, the land portion being movable relative to the stationary portion and cooperating therewith to define the slit. The load-exerting means, in these embodiments, acts between the supporting means and the movable land portion of the die. In other embodiments, the aforementioned one die is formed integrally and the load-exerting means acts between the supporting means and the entire die, which is supported on a bearing so as to be capable of moving as a unit relative to the supporting means during operation. The other die (including its land portion) can be held entirely stationary during the coating operation, or, alternatively, the dies of both heads (or their land portions) can be movable relative to the supporting means during operation and can both be acted on by load-exerting means.
In the heads of the aforementioned U.S. Pat. No. 4,675,230 and PCT publication, the load-exerting means for the (or each) die conveniently comprises at least one air cylinder acting thereon. Preferably, the load-exerting means comprises a plurality of air cylinders acting at points spaced along the length of the die, and the die is made sufficiently flexible to conform to variations of strip thickness across the width of the strip, for enhanced coating uniformity.
Heretofore, coating heads for use in the apparatus and methods described in the aforementioned patents and publication have been designed with a relatively small cross-section so that the complete die (including land portion) of the head could be flexed by modest applied forces. To achieve the required degree of flexibility for conforming to strip thickness variations as just described, the overall cross-sectional dimensions of the die should not exceed about four inches (10 cm) and should preferably be less than two inches (5 cm). Slot dies for solvent-borne coatings can readily be designed to meet this requirement. However, for solvent free coatings (solvent free molten polymer coatings), the dies must incorporate heating elements and must have specially designed, polished channels to ensure uniform distribution of the coating. For these reasons, typical polymer extrusion dies have overall cross-sectional dimensions in excess of six inches (15 cm). It would not be possible to control the flexing of a die with these dimensions, without resorting to very high loading forces.
DISCLOSURE OF THE INVENTION
The present invention, in a first aspect, broadly contemplates the provision, in apparatus for continuously coating a major surface of a strip article while the article is advancing longitudinally along
Hallam David G.
Innes Robert A.
Alcan International Limited
Bareford Katherine A.
Cooper & Dunham LLP
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