Coating processes – Application to opposite sides of sheet – web – or strip – Roller applicator utilized
Reexamination Certificate
1997-03-12
2001-02-20
Meeks, Timothy (Department: 1762)
Coating processes
Application to opposite sides of sheet, web, or strip
Roller applicator utilized
C427S361000, C427S365000, C427S366000, C427S382000
Reexamination Certificate
active
06190729
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for two-side coating of a thin printing paper web containing mechanical pulp, e.g., a paper web made of recycled fiber.
The invention further relates to an apparatus suited to two-side coating of a thin printing paper web made of mechanical pulp.
BACKGROUND OF THE INVENTION
Thin printing paper webs containing mechanical pulp are conventionally coated on subsequent coating stations equipped with short-dwell coaters as the coater units. A combination of two subsequent coater stations is necessary as low base paper weight and high content of groundwood make single-run coating on both sides impossible. Two-side coating with conventional methods would excessively wet the web and thus impair its runnability. Furthermore, the measurement of coat weight in a two-side coating operation is difficult.
Despite their multiple benefits, short-dwell coaters also have several drawbacks. Air entrapped in the coat paste easily causes mottling. Because of the small linear application pressure and short application distance, wetting of the base web and subsequent fiber swelling occurs even after the web has passed the doctor blades, thereby impairing the smoothness of the coat being applied. As a rule, doctor blade coating methods become critical with thin webs and particularly with light coat weights.
Paper grades containing a high proportion of mechanical pulp and a high percentage of coat fillers such as, e.g., SC paper (wood containing high filler content super-calendered printing paper) make doctor blade coating impossible because of the fragility of the base paper web.
Web defects leading to brittleness result in low production yield and inferior runnability.
Base paper grades containing recycled fiber have posed unexpected problems in doctor blade coaters; specifically, the coat is easily marked during coating by streaks caused by defective doctor blades.
The darker color of recycled-fiber containing base paper grades make the opacifying power of the coat mix more critical. Because of the way in which doctor blade coating is accomplished, a smooth coat is formed, not a coat of uniform coat weight. As the base paper is not necessarily smooth, the opacifying power obtained in doctor blade coating is insufficient, resulting in mottling of the coated web.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the disadvantages of the above-described prior-art technology and to achieve an entirely novel method and apparatus for two-side coating of a thin printing paper web containing mechanical pulp such as, for example, a paper web grade made of recycled fiber.
The present invention is based on performing the coating operation using a two-step compressive film-lamination technique.
The present invention relates a method and apparatus in which a coating is applied onto both sides of a light base weight printing paper web containing mechanical pulp or recycled fiber in which one side of the web is coated in a first coating station and then dried, at least partially, in a first dryer unit, and then the second side of the web is coated in a second coating station and then dried, at least partially, in a second dryer unit. Both of the two coating layers are formed by applying the required amount of a coating mix onto the perimeter of respective soft film-coating rolls which rotate with a peripheral speed approximately equally to the speed of the paper web. The coating mix is subsequently transferred to the paper web in a nip formed between a respective backing roll and the respective soft film-coating roll.
The invention provides significant benefits.
The present invention cuts in half the amount that a web is wetted in comparison with single-run two-side coating. Thus, the present invention provides good runnability. Further, good coat quality is attained at light coat weights. Particular benefit is achieved with base paper grades containing recycled fibers because the formation of streaks associated with doctor blade coating can be avoided. Since the compressive film-lamination technique forms a coat of uniform weight on the web, the coat has a high opacifying power. For the same reason, a higher burst index relative to doctor blade coating is attained. Moreover, the measurement of coat weight by means of rupturing testers is easy. The present invention imposes minimal mechanical stress on the web. While two-side single-run coating requires a long path of unsupported pulling of the web prior to the web support roll to give the coat a possibility of drying prior to touching the support roll, according to the present invention, the uncoated side can be supported by a roll immediately after the coating of the other side, thus achieving a significant reduction in coater unit size.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are intended solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.
REFERENCES:
patent: 1536479 (1925-05-01), Cumfer
patent: 3034926 (1962-05-01), Carter et al.
patent: 3242583 (1966-03-01), Calkins
patent: 3811821 (1974-05-01), Ariyama et al.
patent: 3874331 (1975-04-01), Kirsen
patent: 3889018 (1975-06-01), Quint
patent: 3895603 (1975-07-01), Barouth et al.
patent: 3897576 (1975-07-01), Qualtrough et al.
patent: 3982056 (1976-09-01), Holder, Jr.
patent: 4012543 (1977-03-01), Ranger et al.
patent: 4112192 (1978-09-01), Vreeland
patent: 4122218 (1978-10-01), Bostrum et al.
patent: 4177304 (1979-12-01), Berry
patent: 4277524 (1981-07-01), Nakajima et al.
patent: 4288473 (1981-09-01), Wallsten
patent: 4391833 (1983-07-01), Self et al.
patent: 4407867 (1983-10-01), Brück et al.
patent: 4478887 (1984-10-01), Sommer et al.
patent: 4839201 (1989-06-01), Rantanen et al.
patent: 4961964 (1990-10-01), Dahlgren
patent: 4965920 (1990-10-01), Smith
patent: 4973441 (1990-11-01), Keller
patent: 5003915 (1991-04-01), D'Amato et al.
patent: 5033373 (1991-07-01), Brendel et al.
patent: 5133279 (1992-07-01), Dudde et al.
patent: 5302249 (1994-04-01), Malhotra et al.
patent: 5310573 (1994-05-01), Tanokuchi et al.
patent: 5407702 (1995-04-01), Smith et al.
patent: 5458913 (1995-10-01), Tsunoda et al.
patent: 5607553 (1997-03-01), Chadha
patent: 552427 (1958-01-01), None
patent: 58179 (1987-09-01), None
patent: 57143 (1990-01-01), None
Bei&bgr;wanger, R., “Neuentwicklung auf dem Gebiet des Leimens, Pigmentierens und Streichens”,Wochenblatt Für Papierfabrikation, 13:1987, pp. 563-570.
Gavelin, Gunnar, “Bestrykning med IR-torkning”,Svensk papperstidning5.1992, pp. 24-26.
Rantanen Rauno
Vikman Kai
Chen Bret
Cohen & Pontani, Lieberman & Pavane
Meeks Timothy
Valmet Corporation
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