Coating apparatus – Solid member or material acting on coating after application – Web or belt member
Patent
1995-12-11
1997-08-26
Edwards, Laura
Coating apparatus
Solid member or material acting on coating after application
Web or belt member
118118, 118126, 118257, 118262, 118413, B05C 100
Patent
active
056606311
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a coating device for one- or two-sided coating of a travelling web, preferably a paper web. The invention comprises both the techniques of so called transfer coating using a transfer roller and a direct coating where the metering means works directly on the travelling web.
Even if the invention is not restricted hereto it will in the following be illustrated mainly in connection with so called transfer coating.
Transfer coating means a process where the coating agent, i.e. a coating paste, coating liquid or size, is metered onto a conveyor roller, so called transfer roller, whereby on engagement of the roller on the travelling web the coating agent is applied to same. For using these techniques several devices are known which essentially operate according to three different metering principles.
According to the first principle the metering takes place volumetrically, i.e. the metering means is provided on the surface thereof with parallel grooves or splines. The highest points of the metering means are thus in direct contact with the transfer roller, and thereby volumetric metering takes place by the presence of the coating agent in the interstices between the contact surfaces. On its way to and at the contact transfer site the metered material flows together and forms a fully covering layer of even thickness on the travelling web. An example of techniques based on this principle are described in Swedish patent 8803403-8. The process results in a uniformly metered quantity with small variations of applied amount seen in longitudinal as well as cross-wise of the paper web. However, the techniques are associated with two essential drawbacks.
One drawback resides in the fact that the groove pattern will be gradually worn down, which results in gradual change of the metered amount of coating agent, and in addition replacement of metering means, in this case a roller, involves large expenditures by interrupted production and in connection with recreation of the roller surface for reestablishment of the correct dosage.
The other drawback occurs when applying small quantities of coating agent of high viscosity and at high speed. In view of the fact this prior art uses a metering means in the form of a self-supporting roller the diameter of the roller is considerable in view of the requirement for bending resistance. For volumetric metering of small quantities it is also required to have a very delicate pattern on the surface of the metering roller. At high web speeds this design of the metering roller results in an effect that can be similar to aqua planing. In spite of a high engagement pressure with the metering roller there is risk that the contact between the highest points of the metering roller and the transfer roller is lost which results in uncontrolled dosing.
In the other metering principle the dosing means is constituted by a rotary rod of a small diameter. Differently from the principle first described this rod is not self-supporting but is journalled in a journal fixture extending across the travelling web. An example of this principle is found in DE OS A1 3735889. Also these techniques are associated with drawbacks. One drawback is that the rod by its small diameter is worn down quite quickly. Furthermore, the elongate mounting of the rod is worn down which, in addition to costs for lost production, also results in a risk for admixture of lubricating liquid in the coating agent in view of the fact that the mount has longitudinal channels for lubricating the rod with for example water.
In the third principle for metered coating there is used instead of volumetric metering so called hydrodynamic metering. The device for applying this principle is designed in the same manner as devices used in the previously described principles but the grooved rod is replaced by a smooth rod or a flexible steel blade. The wear problems may largely be eliminated by using this principle in view of the fact that a smooth rod can be easily supplied with a surface layer resistant to wear. F
REFERENCES:
patent: 3182632 (1965-05-01), Vazdikis
patent: 4869933 (1989-09-01), Sollinger et al.
patent: 4880672 (1989-11-01), Eriksson
patent: 5031569 (1991-07-01), Eriksson
patent: 5048453 (1991-09-01), Eriksson
patent: 5133281 (1992-07-01), Eriksson
patent: 5264035 (1993-11-01), Beisswanger et al.
BTG Kalle Inventing AB
Edwards Laura
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