Coating apparatus – Solid applicator contacting work – Movably mounted applicator
Reexamination Certificate
1998-10-14
2001-02-27
Edwards, Laura (Department: 1734)
Coating apparatus
Solid applicator contacting work
Movably mounted applicator
C118S211000, C118S212000, C118S249000, C118S413000
Reexamination Certificate
active
06193799
ABSTRACT:
The present invention relates to a device for the application of a coating composition on a travelling web, particularly a paper web. The device is of the type comprising a transfer roll, a support roll cooperating therewith, the web travelling in a nip between said rolls. The device further comprises a gravure roll intended for the application of an adapted quantity of the coating composition on the transfer roll for further transfer to the travelling web.
A traditional so called flexo coater has for a function to transfer onto a travelling paper web a predetermined layer defined by a gravure roll. This gravure roll is via a dosage roll supplied with an excess of a composition which is pressed into the valleys of the gravure roll, and with a blade or a doctor
5
the excess composition on the gravure roll is removed so that after this doctoring step only the valleys of the gravure roll are filled with composition. From the gravure roll the material is transferred onto a transfer roll which in turn moves the material over to the surface of the paper web. In the prior art the composition is contained in a van, wherein the dosage roll is dipped into the composition and transferred therefrom to the dosage nip between the dosage roll and the gravure roll. In the traditionally designed flexo coaters the blade or doctor is of a so called pushing type which is mainly used in all applications where the function is to scrape a travelling surface, for example a roll surface. In the present case the surface of the gravure roll is to be scraped clean so that the present composition only is found in the valleys of the gravure roll.
An important area of use for flexo coaters is the application of microcapsules in the manufacture of so called NCR-paper.
An example of a modified form of flexo coaters is found in EP-A1 0 037 682 where, as is clear from figure
An example of a modified form of flexo coaters is found in EP-A1 0 037 682 where, as is clear from
FIG. 1
, the gravure roll is dipped into the coating composition, the excess composition being removed by means of a pushing doctor in a conventional manner.
The present invention has for its object to improve the function of the flexo coater in several respects.
One object of the present invention is to improve the function of the doctor with regard to wear of the gravure roll.
Another object is to provide reduced wear of the doctor blade.
Yet another object is to provide better filling of the valleys of the gravure roll.
Yet an object of the invention is to provide reduced deposition onto the doctor blade and thereby reduced risk for scratches in the coating composition subject to dosage.
Another object of the invention is to eliminate the problem of sedimentation in the fountain tray.
For these and other objects which will be clear from the following disclosure the present invention provides for a device for the application of a coating composition on a travelling web, particularly a paper web. The device comprises a transfer roll, a support roll cooperating with the transfer roll, and the travelling web is fed in a nip between said rolls. The device further comprises a gravure roll intended for the transfer of an adapted quantity of the coating composition onto the transfer roll for further conveyance to the travelling web. In addition, the device according to the invention comprises means for passing of the web through said nip.
The device according to the invention is characterized by blade means for the removal of excess of coating composition from the gravure roll, said blade means being arranged in trailing position in relation to the moving surface of the gravure roll.
In a preferred embodiment of the invention said blade means is arranged under an angle in relation to the moving surface of the gravure roll of less than about 45°. A preferred angle is from about 10 to about 30°.
The device according to the invention is suitably provided with application means for the application of the coating composition on the moving surface of the gravure roll upstream of said blade means. This applicatin means comprises in one embodiment a tube extending across the full width of the travelling web and being provided with a slit or a row of nozzles extending along said tube. On the other hand the application means can comprise a dosage roll cooperating with the gravure roll to the formation of a pool of coating composition upstream of said blade means.
The device according to the present invention is suitably provided with a fountain tray for the recovery of excess coating composition. It is furthermore suitable that the movable surfaces of the rolls move pair-wise in the same direction.
The invention is particularly applicable to the coating of paper webs. It is furthermore particularly preferred to use said device according to the invention for the application of coating compositions containing microcapsules used in carbon-free copying paper.
REFERENCES:
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patent: 2199228 (1940-04-01), Obenshaw et al.
patent: 2271801 (1942-02-01), Morrison et al.
patent: 3018757 (1962-01-01), Loppnow
patent: 3952700 (1976-04-01), Little, Jr. et al.
patent: 4675208 (1987-06-01), Kageyana et al.
patent: 4821672 (1989-04-01), Bruno
patent: 4844002 (1989-07-01), Yasui et al.
patent: 1079058 (1980-06-01), None
patent: 0037682A1 (1981-10-01), None
patent: 0557635A1 (1993-09-01), None
BTG Kalle Inventing AB
Burns Doane Swecker & Mathis L.L.P.
Edwards Laura
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