Coating apparatus – With heat exchange – drying – or non-coating gas or vapor... – Plural treatments
Reexamination Certificate
2000-01-14
2001-05-15
Edwards, Laura (Department: 1734)
Coating apparatus
With heat exchange, drying, or non-coating gas or vapor...
Plural treatments
C118S068000, C118S221000, C118S224000, C118S249000, C118S261000
Reexamination Certificate
active
06231670
ABSTRACT:
FIELD OF THE INVENTION
Our present invention relates to a method of and to an apparatus for the impregnation and coating of paper webs and, more particularly, the impregnation and coating of paper which can be used as a cover sheet for a wear-resistant laminate.
In particular, the method and apparatus of the invention produce a cover sheet for laminates, for example, pressed board or laminates of a plurality of layers of paper or cellulosic materials, utilizing a paper web which is displaced along a continuous path and is usually impregnated with a resin (i.e. a synthetic resin) and then is coated on one side with a coating mass or composition comprised of a liquid resin, usually a synthetic resin, and fine grained abrasive material, especially corundum, before the paper web is dried.
BACKGROUND OF THE INVENTION
Swiss Patent 432,818 describes a process and apparatus for the coating of paper webs which impregnates a continuous paper web by passing it through a resin bath. The excess of the impregnating resin is then pressed out of the web in the nip between a pair of squeezing rolls. The coating mass or composition is then applied by a nozzle tube onto one surface, usually an upper surface, of the freshly impregnated still-wet paper web and is smoothed with a doctor strip. The so impregnated and coated paper web can then be carried through a dryer on a transport belt, cut into sheets and laminated as the cover sheet on a stack in a hot press.
In a similar process described in German Patent 195 08 797 C1, the upper web impregnated with the resin is dried to a predetermined original moisture content before it is coated with the composition on one side. After such coating the paper web is dried to a final moisture content. The resulting decorative paper is pressed to a laminate by applying it to a board of a wood composition.
The coating composition or mass may include a resin component which, by comparison with the melamine resin commonly used for lamination, has a significantly higher viscosity and is applied in a relatively thick layer in which the particles of hard material like corundum, can be uniformly distributed. One of the advantages of this process and especially the homogeneous distribution of the hard-material particles is that a smooth surface can be formed which is not interrupted by projecting hard material particles embedded in the composition and from which the hard material particles do not ablate.
This latter patent also notes that hard material particles which may emerge from the surface can cause increased wear of the tools used in processing the laminated products and, in particular, the press parts when hot pressing is used. Nevertheless press wear remains a significant problem when the coating mass or composition contacts the press parts and the earlier process is practiced.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to provide a method of the type described wherein further processing of the coating paper, especially hot pressing, does not lead to rapid wear of the parts or tools of the processing machinery.
Another object of the invention is to provide an improved method of producing paper for use as cover sheets in lamination which can improve laminating economies and provide high quality wear resistant laminated products.
It is also an object of the invention to provide an improved method of and apparatus for the impregnation and coating of paper webs whereby drawbacks of earlier systems are avoided.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are attained, in accordance with the invention in a method of impregnating and coating of paper for use as a cover sheet in a wear-resistant laminate which comprises the steps of:
(a) impregnating a paper web with a synthetic resin;
(b) thereafter applying a coating composition containing a liquid resin and a fine-grain abrasive material to one side of the paper web impregnated with the synthetic resin to produce a coated paper;
(c) thereafter drying the coated paper to form an abrasive layer on the coated paper;
(d) applying over the abrasive layer on the coated paper a coating of a liquid resin free from abrasive particles; and
(e) drying the coating on the coated paper web.
The liquid resin can, in particular, be applied in an amount of 10 to 80 g/m
2
and preferably the liquid resin is applied in this amount to both sides of the paper web, i.e. to the side provided with the abrasive layer and to the opposite side of this web. Advantageously, the web is dried in step (c) to a residual moisture content of 8 to 17% and in step (e) to a residual moisture content of 4 to 9%.
The apparatus for carrying out the method can comprise:
means for forming a path for a paper web;
impregnating means along the path for impregnating the paper web with a synthetic resin;
a first coater along the path downstream of the impregnating means for thereafter applying a coating composition containing a liquid resin and a fine-grain abrasive material to one side of the paper web impregnated with the synthetic resin to produce a coated paper;
a dryer along the path downstream of the first coater for thereafter drying the coated paper to form an abrasive layer on the coated paper;
a second coater along the path downstream of the dryer for applying over the abrasive layer on the coated paper a coating of a liquid resin free from abrasive particles; and
a further dryer along the path downstream of the second coater for drying the coating on the coated paper web.
The second coater can include a screen-coating roller and preferably the second coater can include:
a deflecting roller around which the paper web is looped;
a metering roller parallel to the deflecting roller and defining a gap therewith at driven at least approximately synchronously with the deflecting roller;
a slot nozzle for applying liquid resin to the web on the deflecting roller directly or to the metering roller; and
a doctoring element comprising a rectangular flap of flexible elastomeric material affixed at one side along an edge parallel to the rollers and resting slackly on an upper stretch of the web coming off the deflection roller.
The apparatus can further comprise a retaining bar receiving the edge parallel to the rollers, and a vibrator connected to the bar for vibrating same.
Alternatively, the second coater includes:
a deflecting roller around which the paper web is looped;
a slot nozzle for applying liquid resin to the web on the deflecting roller directly;
a premetering element comprising an elastic strip of limited stiffness and composed of plastic for controlling an amount of liquid resin applied to the web; and
an air brush trained on the web on the deflection roller.
An applicator can be provided between the first coater and the further dryer for applying a liquid resin to the opposite side of the paper web between steps (c) and (e). This applicator may also be a screen coating roller and is preferably provided between the second coater and the dryer.
REFERENCES:
patent: 3034926 (1962-05-01), Carter et al.
patent: 3121642 (1964-02-01), Biskup
patent: 4782753 (1988-11-01), Bolza-Schunemann
patent: 5168806 (1992-12-01), Reder et al.
patent: 5788792 (1998-08-01), Lee
patent: 6054177 (2000-04-01), Endoh et al.
patent: 6060124 (2000-05-01), Ikegawa et al.
patent: 432 818 (1965-03-01), None
patent: 36 109 43 (1987-07-01), None
patent: 195 08 797 (1996-08-01), None
patent: 198 14 212 (1999-09-01), None
patent: 198 25 156 (1999-10-01), None
Erkelenz Willi
Fischer Marina
Fischer Siegfried
Klas Ernst
Krossa Gisbert
Dubno Jerbert
Edwards Laura
Fischer Marina
VITS Maschinenbau GmbH
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