Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With chemical or physical modification of liberated fiber
Reexamination Certificate
2001-02-27
2003-09-30
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With chemical or physical modification of liberated fiber
C162S023000, C162S026000, C162S065000, C162S076000, C162S078000, C162S080000, C162S082000, C162S083000, C162S090000
Reexamination Certificate
active
06627041
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to papermaking fibers and more specifically to a method of bleaching and providing durable curl to fiber by way of high temperature and pressure, low mechanical energy processing.
BACKGROUND
Refining and bleaching cellulosic fibers for papermaking is well-known. Various systems and processes are used for preparing pulps, including chemical pulping processes such as the Kraft process, mechanical processes, chemi-mechanical processes, thermo-mechanical processes and so forth. The art is appreciated by reference to the following patents and patent applications.
U.S. Pat. No. 2,008,892 to Asplund discloses an apparatus for refining wood chips into mechanical pulp provided with a grinding portion including a stationary disk, and a rotating disk.
There is disclosed in U.S. Pat. No. 2,516,384 to Hill et al. a process for mechanically curling cellulose fibers. The method of the '384 patent includes forming the pulp in the presence of a limited amount of aqueous liquid into small, discreet nodules of fibers and causing the nodulated pulp to form into rotatable units and travel roll wise under compression, thereby subjecting the nodules to mechanical pressure with continuous reorientation of the nodules relative to the direction of applied pressure and thus imparting kinks, bends, and twists to the pulp fibers or fiber bundles. See Col. 4, lines 73 and following, through Col. 5, lines 1-20.
U.S. Pat. No. 3,023,140 to Textor discloses adding hydrogen peroxide and wood chips to a refiner for the purpose of simultaneously bleaching and refining the chips. (See FIGS. 2 and 3).
U.S. Pat. No. 3,382,140 to Henderson et al. is directed to a process for fibrillating cellulosic fibers. Cellulosic high consistency papermaking pulp in the form of a semi-solid, nonflowable and nonpumpable lumping mass composed of defibered fibers is continuously refined by passage through a refining space comprising opposed disk like working surfaces relatively rotatable about a common axis wherein the pulp is continuously maintained packed under high compression to cause defibrillation by interfiber friction along the surfaces of the individual separated fibers without substantially fracturing the fibers. In general, fibrous material is defibered and then dewatered to increase its consistency to a level where it forms a semisolid, nonflowable, moist mass adapted for high consistency refining. Pulp consistency in the range of between about 10% and about 60% with the fibers in intimate contact; preferably between about 20 and 35% is satisfactory. If the consistency is much below 10% (according to the patent) the amount of water present may act as a lubricant preventing the desired refining by inter-fiber friction. If much greater than 60%, the pulp will be too dry which may result in burning under the inter fiber friction. Examples of the '140 patent teach mechanical power input of from about 5 to about 40 HP day/ton of pulp produced.
There is disclosed in U.S. Pat. No. 3,773,610 to Shouvlin et al. a pressurized system for pulp refining including pressurized double disk treatment. According to the '610 patent, all fibrous materials are passed through a series of treatments under a steam pressurized atmosphere of from 10 to 150 psig and a temperature of between 115° C. and 200° C. in the absence of accompanying liquid. The raw fibrous materials are initially passed through a tube in which they conditioned by either the steam atmosphere, or by liquid chemicals under steam pressure, and then are passed between simultaneously rotating disks of a double disk refiner which is also under steam pressure. Subsequent to treatment with the disks the fibrous materials are passed to another conditioning tube, such as a digester or a bleach tower where they are further conditioned by liquid chemicals under the same steam pressurized conditions. The fibrous materials may thereafter be washed, cooled and/or pressed.
U.S. Pat. No. 3,808,090 to Logan et al. relates to a method of making wood pulp involving the mechanical abrasion of wood particles in the presence of water in an inert gaseous atmosphere. According to the process, wood particles are fed into a substantially closed chamber where they are mechanically abraided in the presence of water in an inert gaseous atmosphere (steam) at an environmental pressure of 10-60 psig, a temperature of 160°-300° F. and under a power consumption of 50-150 HP day/ton. In the '090 patent the Aspland process is characterized as suitable only for low quality pulp. It is noted that the conditions of the Aspland process are selected to provide mechanical reduction of the wood into fibers with the least possible energy input. To this end, high pressures of the order of 115-150 psig and relatively low energy input of the order of 7-12 HP day/ton are employed to obtain the best results. See Col. 1, lines 51-65.
U.S. Pat. No. 3,873,412 to Charters et al. relates to a method of mechanically refining a mixture of Kraft and semichemical pulp. The method is used for producing pulp for use in the manufacture of Kraft type products such as liner board and bag grade paper comprising the steps of steaming small segments of fibrous material, defiberizing the same in a pressurized atmosphere at an elevated temperature and, while the resultant fiber products are still hot, mixing them with hot Kraft pulp and then refining the mixture so obtained.
U.S. Pat. No. 3,948,449 to Logan et al. is directed to an apparatus for the treatment of lignocellulosic material. The '449 patent also relates to the production of a mechanical pulp of improved strength properties. The lignocellulosic material is fed into a substantially closed chamber where it is mechanically abraided under a power input of 15 or more HP day/ton. During the abraiding step the material is maintained in an inert gaseous atmosphere at a pressure of 10-80 psig, preferably 20-40 psig. It is noted in the '449 patent that the Asplund process is well known in the industry for the manufacture of low grade pulps for employment in the manufacture of roofing and flooring felts. The system involves generally presteaming wood chips followed by refining under high pressure. The products are not suitable for high quality or high strength papermaking because of their inherent low strength and other poor papermaking qualities.
U.S. Pat. No. 4,036,679 to Back et al. is directed to a process for producing convoluted and fiberized cellulose fibers and sheet products. The process includes the application of contortive forces to a pulp mass under controlled operating conditions, wherein the feed rate, work space gap and relative rate of movement of the working elements applying the contortive forces are correlated to maintain the work space filled with fibers under sufficient compression.
U.S. Pat. No. 4,187,141 to Ahrel et al. relates to the production of bleached wood pulp from wood chips using a disk refiner. In this patent it is disclosed to impregnate wood chips with an alkaline bleaching liquid prior to defibrating the chips in the refiner.
U.S. Pat. No. 4,409,065 to Kasser discloses a method of making an improved bag from Kraft pulp including a curlation step before web formation. The curlation step is preferably carried out promptly before the web is formed.
U.S. Pat. No. 4,431,479 to Barbe et al. is directed to a method for treating pulp fibers that have already been curled. The method includes subjecting the pulp to a heat treatment while the pulp is at a high consistency, thereby rendering the curl permanent to subsequent mechanical action. The permanent curl has advantages for paper machine runnability and for increasing the toughness of the finished product. During the process of papermaking most of the curl in both high consistency refined mechanical and high yield sulfite pulp is lost in the subsequent steps of handling at low consistency and high temperatures. See Col. 3, lines 20-29. In the '479 patent the method of curling takes place at medium to high consistency (1
Alvo Steve
Ferrell Michael W.
Georgia-Pacific Corporation
LandOfFree
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