Paper making and fiber liberation – Processes and products – Plural fiber containing
Reexamination Certificate
1997-10-30
2001-10-02
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Plural fiber containing
C162S142000, C162S149000, C162S109000, C162S111000, C162S112000, C162S113000
Reexamination Certificate
active
06296736
ABSTRACT:
BACKGROUND OF THE INVENTION
In typical papermaking processes, a general correlation exists between fiber coarseness and softness or handfeel of the resulting paper product.
Expensive high quality fibers such as bleached northern softwood kraft fibers are fine, flexible and are used to produce soft, desirable tissue products. In contrast, mechanical pulping of softwoods produces high-yield, coarse, stiff fibers typically used to make newsprint.
Newspapers contain a preponderance of coarse, high yield fibers, typically stone groundwood) (SGW), thermomechanical pulp (TMP), and/or chemithermomechanical pulp (CTMP) fibers. Such coarse newsprint fibers are usually highly refined to cause fractures and fibrillations which aid in imparting strength to the resulting newsprint. Such refining changes the freeness of the coarse fiber from “high” freeness fibers to “low” freeness fibers. If such refined, high-yield, coarse, mechanically pulped fibers were used in a tissue making process the resulting sheet is not soft, and therefore much less desirable as a tissue product.
A recent thorough discussion of the relationship between tissue softness and fiber coarseness is contained in Canadian Patent No. 2,076,615. Attempts to produce soft tissue or towel type sanitary paper products from a majority of high yield, coarse fibers such as CTMP, TMP or SGW pulp have not been successful. Likewise, producing soft tissue and towel products by recycling old newspapers has not been very successful partially because the predominant fiber in newsprint or in old newspapers are low freeness, coarse, high yield fibers as well as the relatively high level of fines found in such newspapers.
Other complicating factors in producing soft tissue and towel products from recycled newspapers are problems with papermachine operation due to poor drainage of low freeness fibers and problems with fines and other substances that accumulate in the papermachine water system (whitewater). These materials make it difficult to crepe the tissue sheet from the Yankee drying cylinder, and therefore necessitate operating the papermachine at conditions which do not promote maximum softness.
There is a long felt and unmet need for a soft paper product made from high-yield, coarse, fibers from recycled newspapers. There is also a need for an economical and practical process of treating high-yield, coarse fibers from recycled newspapers so they are suitable for making soft paper products. This need also extends to a process for treating newspapers
ewsprint fibers so they are suitable for making soft paper products as well as soft paper products containing such treated fibers.
SUMMARY OF THE INVENTION
The present invention addresses the needs described above by providing a method of modifying coarse high-yield type pulp from recycled newspaper into pulps suitable for making soft tissue type products. In accordance with the present invention, coarse, low freeness high yield type pulp found in newsprint (i.e., newspapers can be modified to produce soft tissue products by washing the pulp to reduce the proportion of fines in the pulp and by treating the pulp with a surfactant system as it is introduced into the papermachine.
The method of making sanitary paper products from newspapers includes the steps of: (a) pulping newspapers in water with agitation to produce a pulp slurry, the pulp from the newspapers having an average fines content of greater than about 40% and a Canadian Standard Freeness of less than about 250; (b) washing the pulp, whereby the fines content is reduced to less than about 35% and the Canadian Standard Freeness is increased to more than about 300; (c) introducing the treated pulp at a papermaking consistency into the headbox of a paper making machine; (d) adding from about 0.01% to about 1.5% of a surfactant system to the treated pulp; and (e) utilizing the treated pulp in a paper making process to produce sanitary paper products.
The surfactant system may be composed of a mixture of nonionic and cationic surfactants. The surfactant system may be added to the treated pulp in an amount from about 0.01% to about 1.5% based on the weight of dry fiber. For example, the surfactant system may be added to the treated pulp in an amount of from about 0.025% to about 0.75% based on the weight of dry fiber. The treated pulp may be introduced into the paper making machine at a papermaking consistency ranging from about 1.0% to about 0.01%.
The present invention encompasses the method described above wherein the sanitary paper product made using the treated pulp is a tissue paper made at a basis weight between 7 and 35 pounds per ream. The sanitary paper product may also be a paper napkin made at a basis weight between 7 and 35 pounds per ream. The sanitary paper product may also be a paper towel made at a basis weight between 12 and 40 pounds per ream.
Generally speaking, the recycled newspaper pulp may be composed of cellulosic fibers at least 80% of which are coarse fibers having a Kajaani coarseness greater than 17 milligrams per 100 meters. For example, the pulp may be composed of cellulosic fibers at least 80% of which are coarse fibers having a Kajaani coarseness greater than 20 milligrams per 100 meters.
The recycled newspaper pulp may have an average fines content of greater than about 45% prior to treatment. For example, the pulp from recycled newspapers may have an average fines content of greater than about 46% prior to treatment. As another example, the pulp from recycled newspapers may have an average fines content of greater than about 48% prior to treatment.
The recycled newspaper pulp may have a Canadian Standard Freeness of less than about 200 prior to treatment. For example, the pulp from recycled newspapers may have a Canadian Standard Freeness of less than about 170 prior to treatment. As another example, the pulp from recycled newspapers may have a Canadian Standard Freeness of less than about 150 prior to treatment.
According to the invention, the recycled newspaper pulp is washed so that the fines content is reduced to less than about 35%. For example, the pulp from recycled newspapers is washed so that the fines content is reduced to less than about 30%. As another example, the pulp from recycled newspapers is washed so that the fines content is reduced to less than about 29%.
In an aspect of the invention, the recycled newspaper pulp is washed so that the Canadian Standard Freeness is increased to more than about 350. For example, the pulp from recycled newspapers is washed so that the Canadian Standard Freeness is increased to more than about 360. As another example, the pulp from recycled newspapers is washed so that the Canadian Standard Freeness is increased to more than about 370.
The present invention also encompasses a method of modifying pulp from recycled newspapers to improve its tissue and towel making properties. The method of modifying pulp from recycled newspapers includes the steps of: (a) pulping newspapers in water with agitation to produce a pulp slurry, the pulp from the newspapers having an average fines content of greater than about 40% and a Canadian Standard Freeness of less than about 250; (b) washing the pulp, whereby the fines content is reduced to less than about 35% and the Canadian Standard Freeness is increased to more than about 300; (c) introducing the treated pulp at a papermaking consistency into the headbox of a paper making machine; and (d) adding from about 0.01% to about 1.5% of a surfactant system to the treated pulp, so that the treated pulp may be utilized in a paper making process to produce sanitary paper products.
The surfactant system may be composed of a mixture of nonionic and cationic surfactants. The surfactant system may be added to the treated pulp in an amount from about 0.01% to about 1.5% based on the weight of dry fiber. For example, the surfactant system may be added to the treated pulp in an amount of from about 0.05% to about 0.75% based on the weight of dry fiber. The treated pulp may be introduced into the paper making machine at a papermak
Hsu Jay Chiehlung
Lakhani Nauman Noorali
Chin Peter
Dority & Manning P.A.
Kimberly--Clark Worldwide, Inc.
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