Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
1998-12-04
2001-01-09
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S005000, C162S008000
Reexamination Certificate
active
06171440
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for repulping wet strength paper and more particularly it relates to such a process incorporating in the paper a cationic thermosetting resin.
2. Description of the Prior Art
Wet strength resins are often added to paper including paperboard at the time of manufacture. In the absence of wet strength resins, paper normally retains only 3% to 5% of its strength after being wetted with water. However, paper made with wet strength resin generally retains at least 10%-50% of its strength when wet. Wet strength is useful in a wide variety of paper applications, some examples of which are toweling, milk and juice cartons, paper bags, and liner board for corrugated containers.
As stated in Handbook for Pulp and Paper Technologists, Gary A. Smook, Angus Wilde Publications, 1992: “Paper has traditionally been defined as a felted sheet formed on a fine screen from a water suspension of fibers. Current paper products generally conform to this definition except that most products also contain non-fibrous additives. Dry forming methods are now utilized for the manufacture of a few specialty paper products. Pulp is the fibrous raw material for papermaking. Pulp fibers are usually of vegetable origin, but animal, mineral, or synthetic fibers may be used for special applications. The distinction between paper and paperboard is based on product thickness. Nominally, all sheets above 0.3 mm thickness are classed as paperboard; but enough exceptions are applied to make the distinction somewhat hazy.”
Because of increased commercial emphasis on developing paper products based on recovered cellulose, there is growing interest in developing paper which is readily repulpable. Paper and paperboard waste materials are difficult to repulp in aqueous systems without special chemical treatment when they contain wet strength resins.
Improving the repulpability of paper containing wet strength resins has generally been achieved by modifying the repulping conditions.
In U.S. Pat. No. 2,872,313, House et al. teach the use of hypochlorite salts to repulp paper containing polyaminoamide/epichlorohydrin wet strength resins. Miller, in U.S. Pat. No. 3,427,217, teaches the use of oxidizing salts such as sodium hypochlorite, ammonium persulfate and others, to repulp wet strength paper containing resins such as polyaminoamide/epichlohydrin resins, urea-formaldehyde and melamine-formaldehyde resins, etc. Although the hypochlorite salts effectively repulp wet strength paper, they are also chlorinating agents under some conditions and can form environmentally undesirable chlorine-containing degradation products in the process effluents.
Schmalz, in TAPPI, 44, no. 4, pp 275-280, April 1961, teaches the repulping of polyaminoamide/epichlorohydrin resin-containing paper with hypochlorite, or with strong alkali. Although the alkali method will not chlorinate organic byproducts, it is a relatively slow process.
Espy, in European Patent Application Publication No. 585,955-A, discloses a composition for repulping paper containing polyaminoamide/epichlorohydrin wet strength resins in an aqueous slurry, which comprises treatment with a non-chlorinated oxidizing agent and an alkali that is a water-soluble buffering salt capable of maintaining a pH of 7-12 in the aqueous reaction mixture.
Caropreso et al., in PCT International Publication No. WO 94/20682 disclose a composition containing a persulfate and a carbonate, bicarbonate or sesquicarbonate, which composition is suitable for oxidizing wet strength resin used in wet strength paper. The combination is stated to decrease the time required to repulp wet strength paper.
In U.S. Pat. No. 5,330,619, Henry et al. teach a method for treating fibrous sheet materials, such as paper or paperboard containing wet strength resin, which comprises reacting the fibrous materials with an enzyme to hydrolyze the resin and thereby improve repulping of the fibrous materials.
Copending application filed Jun. 3, 1996 (Hercules' Docket No. Dasgupta Case 12 “Process of Repulping Wet Strength Paper” Sunil P. Dasgupta) discloses a process for repulping paper by providing paper comprising at least one coacervate complex made from at least one cationic polymer and at least one anionic polymer and repulping the paper to obtain recycled pulp fibers.
Since many of the repulping processes used for wet strength paper result in formation of environmentally undesirable chlorine-containing degradation products, involve strong oxidizing agents, or proceed slowly, there is a need for improved methods for making wet strength paper that will be readily repulpable without significantly lowering the wet and dry strength properties of the paper.
SUMMARY OF THE INVENTION
According to the present invention there is provided a process for repulping paper comprising:
(a) providing paper comprising at least one cationic thermosetting resin comprising the reaction product of
(i) at least one polyamide having secondary amine groups made from reactants comprising (&agr;) at least one polyalkylene polyamine, (&bgr;) at least one of succinic acid or its ester or anhydride and (&ggr;) optionally at least one dicarboxylic acid (other than succinic acid) or its ester or anhydride, and (ii) epihalohydrin; and
(b) repulping the paper to obtain recycled pulp fibers.
Further according to the present invention there are provided recycled pulp fibers made by the process for repulping paper, paper made from such recycled pulp fibers and repulpable, wet strength paper made with cationic wet strength resin.
DETAILED DESCRIPTION OF THE INVENTION
Cationic thermosetting resins suitable for use in the present invention comprise the reaction product of polyamides having secondary amine groups and epihalohydrin. The polyamides are made from polyalkylene polyamines, succinic acid or its ester or anhydride and optionally dicarboxylic acid (other than succinic acid) or its ester or anhydride.
The dicarboxylic acids contemplated for use in the present invention are saturated aliphatic dicarboxylic acids, preferably containing from 3 to 8 carbon atoms, such as: malonic, glutaric, adipic, and so on. Of these the saturated aliphatic acids having from 4 to 6 carbon atoms in the molecule, such as glutaric and adipic are most preferred. Blends of two or more of these dicarboxylic acids may also be used, as well as blends of one or more of these with higher saturated aliphatic dicarboxylic acids, such as azelaic, sebacic, as long as the resulting long chain polyamide is water-soluble.
A variety of polyalkylene polyamines including polyethylene polyamines, polypropylene polyamines, polybutylene polyamines and so on may be employed herein of which the polyethylene polyamines represent an economically preferred class. More specifically, the polyalkylene polyamines of this invention are polyamines containing two primary amine groups and at least one secondary amine group in which the nitrogen atoms are linked together by groups of the formula —C
n
H
2n
— where n is a small integer greater than unity and the number of such groups in the molecule ranges from two up to about eight and preferably up to about four. The nitrogen atoms may be attached to adjacent carbon atoms in the group —C
n
H
2n
— or to carbon atoms farther apart, but not to the same carbon atom. This invention contemplates not only the use of such polyamines as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenetriamine, and the like, which can be obtained in reasonably pure form, but also mixtures and various crude polyamine materials. For example, the mixture of polyethylene polyamines obtained by the reaction of ammonia and ethylene dichloride, refined only to the extent of removal of chlorides, water, excess ammonia, and ethylenediamine, is a very satisfactory starting material. Most preferred are the polyethylene polyamines containing from two to four ethylene groups, two primary amine groups, and from one to three secondary amine groups, e.g. diethylenetriamine (DETA).
T
Hercules Incorporated
Nguyen Dean T.
Sloan Martin F.
Szanto Ivan G.
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