Calendering system using hard and soft nips

Details Calendering system using hard and soft nips Calendering system using hard and soft nips

1999-03-12

2001-02-06

Silverman, Stanley S. (Department: 1731)

Paper making and fiber liberation

Apparatus

Running or indefinite length product forming and/or treating...

C162S360200, C162S206000, C162S358100, C162S360200, C162S360300, C162S161000, C427S366000, C427S361000, C100S16200R, C100S331000

Reexamination Certificate

active

06183603

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to calendering systems. Such structures of this type, generally, employ the use of hard or soft nips to provide excellent smoothness without gloss mottle.
2. Description of the Related Art
It is well known in calendering systems, particularly heated soft roll calendering systems, to employ a soft roll at high pressures. Exemplary of such prior art is U.S. Pat. No. 4,624,744 ('744) to J. H. Vreeland, entitled “Method of Finishing Paper Utilizing Substrata Thermal Molding”. While the '744 patent does achieve calendering, the use of the high nip pressures, namely, pressures above 2000 psi, reduce the bulk of the paper. Consequently, such use of a calendering device is, typically, employed when calendering fine papers. Consequently, a more advantageous calendering system, then, would be employed if calendering could be done at lower nip pressures in order to reduce bulk loss.
It is apparent from the above that there exists a need in the art for a calendering system which is able to calender as well as the known calendering systems, while providing excellent smoothness without gloss mottle (an uneven pattern of gloss or reflectance), but at the same time is able to calender at lower nip pressures.
It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.
SUMMARY OF THE INVENTION
Generally speaking, this invention fulfills these needs by providing a substantially gloss mottle-free calendered paper with significantly increased smoothness consisting of a coated paper produced by a method comprising, passing the coated paper through a first nip formed between a substantially harder calendering roll and a heated roll means, passing the coated paper through a second nip formed between a substantially softer calendering roll and the heated roll means to produce a substantially gloss mottle-free calendered paper having significantly increased smoothness and operating the method at nip pressures between the first and second nip of substantially less than 2000 psi.
In certain preferred embodiments, the harder calendering roll has a surface hardness of greater than 80 shore D. The heated roll is a polished metallic roll. The softer calendering roll has a surface hardness of less than or equal to 80 shore D. Also, calcium carbonate (CaCO
3
) is added to the coating placed upon the paper. The coating is applied at a coat weight of approximately 8-24 lbs/3900 ft
2
. The coating contains at least 40% solids and at least 30% CaCO
3
.
In another further preferred embodiment, the use of the harder-softer roll combination allows one to produce a paper which is substantially gloss mottle-free and has a significantly increased smoothness.
The preferred calendering system, according to this invention, offers the following advantages: good stability; good durability; substantially reduced gloss mottle; significantly increased smoothness; reduced operating nip pressures; increased operating capacity; reduced converting problems; and excellent economy. In fact, in many preferred embodiments, these factors of improved gloss mottle, improved smoothness, reduced nip pressures, increased capacity, and reduced converting problems are optimized to an extent that is considerably higher than heretofore achieved in prior, known calendering systems.


REFERENCES:
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patent: 2395992 (1946-01-01), Clark
patent: 3124480 (1964-03-01), Mahoney et al.
patent: 3124481 (1964-03-01), Mahoney
patent: 3268354 (1966-08-01), Hain
patent: 3338735 (1967-08-01), Hain
patent: 3617445 (1971-11-01), Brafford
patent: 3982056 (1976-09-01), Holder, Jr.
patent: 4492612 (1985-01-01), Matarainen
patent: 4534829 (1985-08-01), Ahrweiler et al.
patent: 4624744 (1986-11-01), Vreeland
patent: 4670102 (1987-06-01), Maurer et al.
patent: 4915026 (1990-04-01), Halme
patent: 5237915 (1993-08-01), Rounsley
H. L. Schmidlin, Raybestos-Manhattan, Inc., “Rubber roll hardness-another look,” Pulp & Paper,Mar. 18, 1968.

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