Imported: 10 Mar '17 | Published: 27 Nov '08
USPTO - Utility Patents
The invention relates to a method for treating a fibrous web downstream of slitting. In the method, the finishing of a fibrous web for providing desired properties is performed by using one or more finishing units, at least one of which comprises a web processing apparatus provided with a metal belt.
The present invention relates to a method for treating a fibrous web downstream of slitting, said treatment comprising e.g. calendering, coating or various combinations thereof.
A wide variety of paper and board grades exist and can be divided according to basis weight in two classes: papers of a single ply with a basis weight of 25-300 g/m2 and boards produced by multilayer technique with a basis weight of 150-600 g/m2. As noted, the borderline between paper and board is floating, the boards with lowest basis weight being lighter than the heaviest papers.
The following representative descriptions are examples of currently employed values for fibrous webs and substantial deviations from such values are possible. The main source for descriptions is the publication Papermaking Science and Technology, section Papermaking Part 3, finishing, edit. Jokio M., publ. Fapet Oy, Jyvskyl 1999, page 361.
Mechanical pulp based or wood containing printing papers include newsprint, uncoated magazine and coated magazine paper.
Newsprint consists either entirely of mechanical pulp or may contain a small amount of bleached softwood pulp (0-15%), and/or recycled pulp can be used for replacing some of the mechanical pulp. The following values can probably be considered common for newsprint: basis weight 40-48.8 g/m2, ash content (SCAN-P 5:63) 0-20%, PPS s10 roughness (SCAN-P 76-95) 3.0-4.5 m, Bendtsen roughness (SCAN-P21:67) 100-200 ml/min, density 600-750 kg/m3, brightness (ISO 2470:1999) 57-63%, and opacity (ISO 2470:1998) 90-96%.
Uncoated magazine paper (SC=supercalendered) generally comprises mechanical pulp at 50-70%, bleached softwood pulp at 10-25%, and fillers at 15-30%. Typical values for calendered SC paper (including, among others, SC-C, SOB and SC-A/A+) are basis weight of 40-60 g/m2, ash content (SCAN-P 5:63) of 0-35%, Hunter gloss (ISO/DIS8254/1) of 20-50%, PPS s10 roughness (SCAN-P 76:95) of 1.0-2.5 m, density of 700-1250 kg/m3, brightness (ISO 2470:1999) of 62-70%, and opacity (ISO 2470:1998) of 90-95%.
Table 1 presents typical values for mechanical pulp containing, coatable papers. (MFC=machine finished coated, FOO=film coated offset, LWC=light weight coated, MWC=medium weight coated, HWC=heavy weight coated).
Coated magazine paper (LWC=light weight coated) contains mechanical pulp at 40-60%, bleached softwood pulp at 25-40%, and fillers and coating agents at 20-35%.
HWC can be coated even more than twice.
Woodfree printing papers made of chemical pulp or fine grade papers include uncoated- and coated-chemical pulp based printing papers, in which the fraction of mechanical pulp is less than 10%.
Uncoated printing papers based on chemical pulp (WFU) contain bleached birchwood pulp at 55-80%, bleached softwood pulp at 0-30%, and fillers at 10-30%. WFU shows wide fluctuation of values: basis weight 50-90 g/m2 (even up to 240 g/m2), Bendtsen roughness 250-400 ml/min, brightness 86-92%, and opacity 83-98%.
Coated printing papers based on chemical pulp (WFC) have coatings fluctuate over a wide range according to requirements and application. The following are typical values for once and twice coated printing paper based on chemical pulp: once coated basis weight 90 g/m2, Hunter gloss 65-80%, PPS s10 roughness 0.75-2.2 m, brightness 80-88%, and opacity 91-94%, and twice coated basis weight 130 g/m2, Hunter gloss 70-80%, PPS s10 roughness 0.65-0.95 m, brightness 83-90%, and opacity 95-97%.
Other papers include, among others, sackkraft, tissue, and wallpaper.
Board making is performed by using chemical pulp, mechanical pulp and/or recycled pulp. Board grades can be divided e.g. in the following main groups according to applications intended therefor.
Corrugated board including a liner and a fluting.
Boxboards used for making boxes, containers. Boxboards include, among others, liquid packaging boards (FBB=folding boxboard, LPB=liquid packaging board, WLC=white-lined chipboard, SBS=solid bleached sulfite, SUS=solid unbleached sulfite).
Graphic boards used for making e.g. cards, folders, files, cases, covers, etc.
As indicated by the foregoing, there is a huge variety of paper and board grades and machines of several different types are used for making the same.
It is an objective of the present invention to provide a method and apparatus for treating coated and uncoated papers and boards in an optimal manner in a process following the actual manufacturing line downstream of slitting, the webs to be treated being narrow, e.g. 0.15-4.5 m, the size of finishing machines being thus designed respectively to be substantially smaller than the processing equipment normally present in the manufacturing line.
In order to accomplish the objectives of the invention, a method of the invention is characterized by what is set forth in the characterizing clause of claim 1. In the method, the treatment of a fibrous web for providing desired properties is performed e.g. at a printing site, prior to passing the fibrous web to a printing press, by using one or more finishing units, at least one of which is a metal-belt equipped web processing apparatus, e.g. a metal belt calender, a coater, a dryer, a dry coater or the like.
A metal belt calender, which allows for the use of a very extensive pressure range and application time (heat transfer time and/or treating time) in a treatment zone, one and the same apparatus being applicable for the treatment of numerous different coated and uncoated printing papers and boards, has been described in more detail e.g. in earlier applications PCT/FI03/00066, PCT/FI03/00067 and PCT/FI03/00068 of the applicant for present application, and thus it is not described further at this time. In a metal belt calender, the length of a treatment zone is determined by means of the disposition of belt guiding elements and/or the design and/or disposition of counter-elements, and the contact pressure applied to a web within the treatment zone can be made adjustable for example within the range of about 0.01 MPa to about 200 MPa.
The size of a metal belt calender can be made smaller when using it the treatment of rolled-up narrow fibrous webs adapted to the width of a printing press or some other further processing machine. The use of a metal belt calender enables a rapid change of treatment conditions, allowing e.g. for the manufacture of paper and board grades for different applications on the basis of one and the same stock, said stock possibly consisting of a coated or uncoated web of paper or board. Hence, a switch between grades can be implemented readily and quickly, enabling the manufacture of even small batches in a cost effective fashion. In addition, the stock purchase costs of a printing house will be reduced.
Furthermore, metal belt calendering stabilizes the structure of a fibrous web, enabling the minimization of bubbling in a printing press resulting from the use of a water-soluble printing ink.
A method of the invention can also be accompanied by a relatively light treatment of the printed fibrous web with a metal belt calender downstream of the printing press, if such treatment is beneficial for polishing the print.
In association with a metal belt calender can also be provided elements for coating a fibrous web, such as for example a dry coating apparatus or a separate coater, upstream or downstream of the metal belt calender. In association with a printing press can be provided not only metal belt calenders but also other types of calenders for enabling a versatile treatment of the fibrous web prior to passing it to the printing press.
A metal belt calender can also be used for drying a fibrous web, thus enabling the use of a higher rolling-up moisture on the papermaking line.