Patent EP-1016754-A1 (EP)
Inventor: SCHERB THOMAS THOROEE
IPC: D21F3/02
Filed: 1999-12-23
Abstract: The papermaking machine, especially for tissue or toilet paper, has at least one press gap (12) between a shoe press unit (14) and the drying/tissue cylinder (16). The length (L) of the press gap is ≤ 60 mm, in the direction (l) of web travel. The pressure profile along the length (L) of the press gap (12) has a max. pressure of ≥ 3.3 MPa.  The press gap length (L) is pref. ≤ 50 mm, and the max. pressure is 4.8 MPa within a press gap length stretch of 37 mm. To form a tissue paper web, the angle between the tangent at the end of the press gap (12) at the drying cylinder (16) and the carrier blanket (18) leaving the press gap (12) is ≥ 10 degrees and especially ≥ 18 degrees and pref. ≥ 20 degrees . The press blanket (20) is ridged and/or is fitted with blind drillings. The length (L) of the press gap (12) can be ≥ 80 mm and pref. less than 200 mm and especially a max. of 150 mm. The max. pressure in the pressure profile is ≤ 2 MPa. The max. linear pressure applied in the press gap (12) is 90-110 kN/m and/or the shoe press unit (14) has a press shoe (22) with a number of independent press components (26) across the direction (l) of web travel, to be pressed against the drying cylinder. The drying cylinder (16) is a Yankee cylinder and/or has an asymmetrical pressure profile along the length (L) of the press gap. The max. pressure is applied in the trailing one-half or one-quarter of the press gap length (L), in the direction (l) of web travel. The mean pressure rise gradient from the start of the press gap to the max. pressure zone, with a carrier blanket of a new value, is ≥ 40 kPa/mm and especially ≥ 60 kPa/mm and pref. ≥ 120 kPa/mm and/or the mean pressure drop gradient at the end of the press gap with a new value carrier blanket is ≥ 300 kPa/mm and especially ≥ 500 kPa/mm and pref. ≥ 800 kPa/mm or ≥ 800 kPa/mm or ≥ 960 kPa/mm and/or the water-absorbent blanket (18) in the press gap (12) lies between the impermeable press blanket (20) and the web with the web in contact with the drying cylinder (16) and/or a felt blanket is used for the water-absorbent carrier (18). The water-absorbent carrier blanket (18) has different qualities through its thickness, with a finer structure at the side towards the web than at the other side. The press blanket (20) has a surface which is smooth, ridged and/or with blind drillings and/or at least one additional press gap (12) is formed at the drying cylinder (16) using two shoe press units (14). A further press gap (12) is formed before the drying cylinder (16), in the direction (l) of web travel and/or the carrier blanket (18) and the web pass through at least one preceding suction unit. The suction unit has a suction roller and/or a suction shoe and/or it is a shoe press roller where the press blanket is pref. formed by the press mantle (20) of the shoe press roller (14). The shoe press unit (14) has at least one replaceable press shoe (22) and/or the carrier blanket is structured to give an imprint or patterning. An Independent claim is included for tissue-toilet paper prodn., where the wet fiber web is within the press gap (12) for a time span of max. 3 ms at a pressure of at least 3.3 MPa or at least 3.5 ms at a max. pressure of 2 MPa.