Coating apparatus – Immersion or work-confined pool type – Work-confined pool
Patent
1983-05-26
1986-01-21
McIntosh, John P.
Coating apparatus
Immersion or work-confined pool type
Work-confined pool
118414, B05C 3132
Patent
active
045651558
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a size press, which comprises three coating rolls, which form two press nips as pairs with each other, the paper web to be treated being passed through the said press nips so that both sides of the web are treated in the said nips.
Most of the production of fine papers is surface-sized or coated. Surface-sizing is a relatively simple and inexpensive quality-improvement method of paper. The surface-sizing is usually performed in an on-machine size press placed in the paper machine. Surface-sizing of fine-paper qualities that contain mechanical pulp is becoming more common especially for offset printing purposes. Besides these, kraft liners, boards, and various base papers are surface-sized or precoated in a size press. The fields of application of size presses mentioned above can be divided into four groups.
In a way known from prior art, the paper web is run through a roll nip of a size press. The size is fed in the press onto the paper by forming a pool in front of the nip, in which pool the web becomes wet and adsorbs size. Between the rolls of the size press, size is pressed into the paper web owing to the hydrodynamic pressure. At the same time, owing to the hydrodynamic pressure, a size film is formed between the paper and the roll, which film is split at the outlet of the roll and allows a film of size to remain on the paper. The quantity of size remaining on the paper depends on the viscosity of the size, on the machine speed, on the diameter of the roll, on the surface properties of the roll, on the line pressure, as well as on factors attributable to deformation of the roll.
The oldest one among the prior-art size presses is the so-called vertical size press, wherein the rolls are placed one above the other and the paper passes horizontally between the rolls. In the prior-art horizontal press, the rolls are placed on the same horizontal level and the paper passes vertically between the rolls. A third prior-art size press is the so-called diagonal press, wherein the rolls are placed one above the other at an angle of about 45.degree.. This is the best prior-art solution in view of the passing of the web at high running speeds.
The roll diameters of the size press are important from the point of view of the running properties. For the nip rolls of prior-art size presses, diameters of the order of 800 to 1500 mm have been chosen at running speeds of 10 to 17 m/s. As is well known, by increasing the roll diameter when the speed is increased, attempts are made to prevent splashing in the pool gap, because such splashing disturbs uniform moistening of the paper web.
Mostly rubber has been used as the covering material of the rolls in the size press. Presses are also known in which the hard roll is of metal and the soft roll of rubber. Thus, softer and harder pressing zones are used. At higher speeds, rolls of a larger diameter are used than at lower speeds.
Besides a sufficient wetting time, good penetration of the size into the surface also requires high compression, 20 to 50 kN/m.
In respect of the prior-art technology related to the present invention, reference is made to the Finnish Pat. No. 28,686 (Class 55 f 15/20, published on Mar. 15, 1957, Combined Locks Paper Co, U.S.A.). From this Finnish patent, such a paper coating machine is known in prior art as comprises a hard centre roll and, in connection with it, two nips through which the paper web to be coated is passed. The size or any other coating agent is first brought from a trough via several applicator rolls onto the said hard-faced roll, from which it is pressed onto the web in the first nip. The other side of the web is coated by, from the trough, bringing the coating agent via several applicator rolls onto the latter nip roll, from which it is pressed onto the other face of the web in the latter nip formed in connection with the hard centre roll. According to the said Finnish patent, the nip rolls form nips with the lower hard centre roll so that these nips are placed in connection with the centre r
REFERENCES:
patent: 2257113 (1941-09-01), George
patent: 4108110 (1978-08-01), Berry
patent: 4177304 (1979-12-01), Berry
patent: 4259921 (1981-04-01), Wallsten
patent: 4325784 (1982-04-01), Dreher
McIntosh John P.
Valmet Oy
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