Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
1998-04-16
2001-06-12
Lamb, Brenda A. (Department: 1734)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S004000
Reexamination Certificate
active
06245195
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of decontaminating waste paper (secondary fiber). More particularly, this invention relates to cleaning, for the purpose of recycling, secondary fibers contaminated with non-impact inks and/or stickies by introducing a densifying agent and an agglomerating agent into a slurry of the waste paper fibers, followed by passing the slurry through a centrifugal cleaner.
2. Description of Related Art (Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98)
Waste paper, also known as secondary fiber, has long served as a source of raw fiber material in papermaking. Waste paper materials invariably contain one or more contaminants including inks, dye colors, fluorescent whitening agents, and “stickies” (sticky or tacky contaminants including adhesives, binders, plastic films, coatings, waxes, and the like). Sorted waste paper has had most of these contaminated papers removed and represents a higher, more expensive grade of waste paper. The growing utilization of secondary fibers in many types of paper products has made it necessary for paper manufacturers to process lower grades of waste paper (i.e., unsorted waste paper). While various methods have been employed to remove the contaminants to permit incorporation of the secondary fibers with virgin pulp in papermaking, such lower grade furnish is more heterogeneous and typically contains significantly more contaminants than a higher quality waste paper. Conventional treatment methods may not be adequate to permit incorporation of a significant percentage of unsorted waste papers.
Current approaches to processing recycled fibers can be classified as repulping (slushing of fibers and partial detachment of ink/contaminants from fibers), coarse and fine screening (separation of fibers from contaminants by size and shape), centrifugal cleaning (separation based on density differences relative to fibers), flotation (separation by preferential adsorption of detached ink/contaminants onto air bubbles), washing (separation of small entrained particles from fibers by relative flow of water passing by fibers), and dispersion (reduction in size of ink/contaminants by mechanical action). There is an optimum particle size range for separation of particles from fibers in each of these processes. Depending upon the specific cleanliness requirements for the deinked pulp, it takes a combination of most or all of these processes to cover the size range of particles that one typically encounters. Both the washing and flotation processes depend on the proper use of surfactants. Depending on the relative strength and size of the hydrophillic versus hydrophobic portion of the surfactant molecule, the surfactant will cluster around ink and other contaminant particles, rendering the particles hydrophylic for washing purposes or more hydrophobic for flotation. The opposing natures of washing surfactants and flotation surfactants can cause problems in combination flotation/washing systems.
Certain specific removal approaches have been disclosed for specific waste paper contaminants:
U.S. Pat. No. 5,211,809 discloses removing color from dyes from secondary pulps with non-chlorine based bleaching agents in treating sequences using oxygen with combinations of peroxide, ozone, and/or hydrosulfite at controlled pH conditions.
U.S. Pat. No. 5,213,661 teaches using oxygen to reduce the tackiness of stickies in secondary pulps and, optionally, using oxygen with alkali and/or detackification agents for optimum stickies control. U.S. Pat. No. 5,080,759 teaches introducing a water-soluble organotitanium compound into the water system of a papermaking process containing the secondary fiber to reduce the tackiness and adhesive properties of the stickies contaminants.
Also, published Japanese Patent Application No. HEI 3[1991]-199477 teaches a method of recycling used paper containing either fluorescent white paper or colored paper or both by introducing ozone into a dispersed slurry of said used paper.
The effectiveness of contaminant (ink/stickies) removal strategies usually is determined by a combination of TAPPI dirt counts (to quantify larger specks), brightness readings, and image analysis. Image analysis involves the imaging of the surface of a handsheet or piece of paper, followed by digitization of this image by a computer. The resolution is set by specifying the minimum number of pixels that a particle must cover to be represented accurately. The output from the analysis is the total area of contaminant particles above a resolvable size on the surface of the paper sample. The limit of visibility for particles is about 40 micrometers. The standard limit for writing printing grades is less than 5 ppm.
While waste paper contaminants such as dyes, whiteners, and stickies present real problems in recycling, the most common removal problem is with inks. Printing inks have been classified broadly as impact and nonimpact inks.
Impact inks are used in conventional printing processes such as letterpress, flexography, and lithography. These inks are pressed or laid onto the paper but do not fuse with it. They generally consist of a pigment suspended in an oil-based alkaline aqueous medium. The paper industry has been successfully deinking papers containing impact inks for years using washing and/or flotation type systems.
Also, U.S. Pat. No. 4,381,969 teaches bleaching waste paper containing encapsulated constituents such as inks by repulping the waste paper in the presence of an aqueous alkaline solution which contains a peroxide compound such as hydrogen peroxide.
Other patents disclosing deinking methods include:
U.S. Pat. No. 4,013,505, “Method of Deinking Printed Wastepapers”;
U.S. Pat. No. 4,076,578, “Ink Removal From Waste Paper”;
U.S. Pat. No. 4,147,616, “Apparatus for Deinking Printed Wastepaper”;
U.S. Pat. No. 4,780,179, “Method for Producing Pulp from Printed Unselected Waste Paper”;
U.S. Pat. No. 5,151,155, “Process for Deinking Wastepaper with Organically Modified Smectite Clay”;
U.S. Pat. No. 5,221,433, “Deinking Wastepaper Using Alkoxylation Product of Carboxylic Acid Containing an OH Group and Alkylene Oxide”;
U.S. Pat. No. 5,225,046, “Wastepaper Deinking Process”;
U.S. Pat. No. 5,227,019, “Wastepaper Deiitling Process”;
U.S. Pat. No. 5,228,953, “Deinking Waste Paper Using a Polyglycol and a Phosphoric Ester Mixture”; and
U.S. Pat. No. 5,238,538, “Method for Deinking Recycled Fiber by Applying Direct Current Electric Field.”
Increasing amounts of secondary fiber, however, are generated from papers subjected to reprographic printing processes such as electro-photographic copying (e.g., xerography) and laser printing. These printing methods employ nonimpact inks. Nonimpact inks are comprised of a pigment and a thermoplastic resin. The resin is a bonding agent which fuses the pigment to the sheet and to other pigment particles. The pigments employed in nonimpact inks can be categorized as either iron-based or non-iron based (e.g., carbon based). The resin polymers become cross-linked and resistant to chemical and mechanical action, making nonimpact printed papers difficult to deink by conventional deinking processes. Once detached from the fibers the toner ink particles tend toward a size which is larger than that which can be efficiently handled by flotation or washing and too small to be removed by cleaners and screens. Various approaches have been disclosed specifically to remove reprographic type inks:
U.S. Pat. No. 4,276,118, “Deinking Waste Electrophotography Copy Paper”;
U.S. Pat. No. 4,561,933, “Xerographics Deirking”;
U.S. Pat. No. 5,141,598, “Process and Composition for Deinking Dry Toner Electrostatic Printed Wastepaper”; and
U.S. Pat. No. 5,217,573, “Removal of Laser Printer and Xerographic Ink from Recycle Paper.”
Conventional deinking processes require high energy input and employ additives or solvents to assist the removal of reprographic (nonimpact) type inks. Significant fiber loss normally results along with the ink removal. To emp
Lamb Brenda A.
McDaniel Terry B.
Reece IV Daniel B.
Schmalz Richard L.
Westvaco Corporation
LandOfFree
Decontamination of waste papers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Decontamination of waste papers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Decontamination of waste papers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522795