Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-03-09
2003-06-17
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S168100, C162S168200, C162S168300, C162S164500, C162S183000
Reexamination Certificate
active
06579417
ABSTRACT:
The present invention relates to the field of synthetic polymers obtained from water-soluble monomers, or from mixtures of such monomers, and their specific application to the manufacture of a sheet of paper, paperboard or the like.
These polymers were introduced as flocculating agents some forty years ago, with molecular weights which at that time were relatively low. U.S. Pat. No. 3,325,490 (Goren) describes various gel polymers.
It is possible to use some of the Goren polymers as coagulating agents, particularly for coagulating very fine solid matter in suspension.
Modern flocculating agents have been researched in industry for at least two decades, for example those for the flocculation of solid matter in suspension in the field of water treatment, and especially in municipal sewage treatment, which are linear polymers of very high molecular weight. U.S. Pat. No. 3,557,061 may be cited as an example in this field.
European patent 0 201 237 describes a flocculation process in which a polymer material is added to water to form an aqueous composition, and is used to flocculate the solid matter in suspension in an aqueous suspension, this polymer comprising a polymer of high molecular weight that is subjected to a shearing, this shearing being carried out before or during the flocculation and the polymer being required to have certain intrinsic properties, which are indicated in this patent.
According to this document, the polymer is a polymer of high molecular weight, formed from water-soluble monomers or from a mixture of such monomers, and the polymer is subjected to shearing. The process described in this patent is characterized in that it is possible to carry out the shearing before or during the flocculation. European patent 0 201 237 further indicates that the polymer used comprises a cross-linked water-swellable polymer which it is possible to shear to an intrinsic viscosity of at least 4 dl/g. It is also indicated that the aqueous composition containing the polymer material can be a stable and homogenous composition, the shearing in this case causing an increase in the intrinsic viscosity of at least 1 dl/g.
In this document, “stable and homogenous” designates a polymer composition that is stable when the polymer is at full equilibrium with the water, i.e., when it has reached its ultimate degree of solubility or swelling. The composition is also homogeneous in the sense that the polymer remains uniformly dispersed throughout the composition, without having a tendency to precipitate after several days.
This document specifically describes a number of applications for water treatment, which is clearly precisely the main application intended, and coal ore treatment.
This patent also mentions, very briefly and without providing an exemplary embodiment or even any precise instructions for implementation, an application to paper or paperboard manufacturing; it merely indicates that the polymer can be added at an early stage of the pulp (fibrous mass) circulation line with a shearing along the flow line of the suspension, near the drainage stage or another water removal stage. The patent indicates that the shearing is carried out by pumping, hence by means of the “fan pump” or mixing pump effectively disposed in line in paper machines.
For the other applications, and especially for water treatment, the document also indicates that it is possible to carry out the shearing on the production line, as the suspension to be flocculated approaches a centrifuge, a filter press or a belt press, or another water removal stage. It is also indicated that the shearing can be carried out during a water removal stage that is conducted under a certain shear, preferably in a centrifuge or even in a filter press or a belt press.
Hence, this document only teaches a shearing of the flocs in the mixing pump or “fan pump” for the papermaking application. Moreover, it teaches that very low shear rates can be appropriate in the other applications, since filter presses and belt presses induce very low shear.
The present invention relates to a considerable improvement of this process and of the corresponding flocculating agents, with unexpected advantages in the application specific to the manufacture of a sheet of paper, paperboard or the like when operating under specific conditions, which are described below.
According to the present invention, the only flocculating agent used, which is intended to markedly improve the retention, formation, drainage and other properties of the paper or paperboard sheet thus obtained, is a cross-linked polymer or copolymer formed from suitable water-soluble monomers or mixtures of such monomers.
The process according to the invention is characterized in that the cross-linked polymer is sheared before introduction or injection into the suspension to be flocculated.
Therefore, there is no shearing of the suspension containing the polymer.
The monomers can be nonionic, but generally at least some of the monomers used to form the polymer are ionic. The monomers are usually monomers with monoethylenic unsaturation, sometimes allylic monomers, but generally vinyl monomers. These are generally acrylic or metacrylic monomers.
Suitable nonionic monomers are acrylamide, metacrylamide, N-vinyl methyl acetamide or N-vinylformamide, vinyl acetate, vinylpyrrolidone, methyl methacrylate or other methacrylates of acrylic esters, or of other esters with ethylenic unsaturation, or of other vinyl monomers that are insoluble in water such as styrene or acrylonitrile.
Suitable anionic monomers are for example sodium acrylate, sodium methacrylate, sodium itaconate, 2-acrylamido-2-methylpropane sulfonate (AMPS), the sulfopropylacrylates or sulfopropylmethacrylates, or other water-soluble forms of these polymerizable sulfonic or carboxylic acids. It is possible to use a sodium vinylsulfonate or an allylsulfonate, or a sulfomethyl acrylamide.
Suitable cationic monomers are the dialkylaminoalkyl acrylates and methacrylates, particularly dialkylaminoethyl acrylate, as well as their salts acidified or quaternized by means known to one skilled in the art, such as benzyl chloride, methyl chloride, aryl chloride, alkyl chloride, dimethyl sulfate, and even the dialkylaminoalkylalkylacrylamides or -methacrylamides, as well as their salts acidified or quaternized in a known way, for example methacrylamidopropyltrimethylammonium chloride (MAPTAC) and the Mannich products such as the quaternized dialkylaminomethylacrylamides. The alkyl groups in question are generally C
1
-C
4
alkyl groups.
The monomers can contain hydrophobic groups, for example as described in European patent 0 172 723, and in certain cases allylic ether monomers could be preferred.
The cross-linking can be carried out during or after the polymerization, for example by reaction of two soluble polymers having counter-ions, or by reaction on formaldehyde or a polyvalent metal compound. Often the cross-linking is carried out during the polymerization by addition of a cross-linking agent, arid this method is clearly preferred according to the invention. These processes for polymerization with cross-linking are known.
The cross-linking agents that can be incorporated include ionic cross-linking agents such as polyvalent metal salts, formaldehyde, glyoxal, or preferably, covalent cross-linking agents that will copolymerize with the monomers, preferably monomers with diethylenic unsaturation (like the family of diacrylate esters such as the diacrylates of polyethylene glycol PEG) or polyethylenic unsaturation, of the type classically used for the cross-linking of water-soluble polymers, and particularly methylenebisacrylamide (MBA), or any of the other known acrylic cross-linking agents.
The quantity of cross-linking agents, and particularly of methylenebisacrylamide (MBA), that can be incorporated according to the invention is generally on the order of 5 to 100 ppm, preferably 5 to 40 ppm, and according to the best method, around 20 ppm of cross-linking agent/active material (polymer).
For details of the above, please refer to the con
Hund Rene
Jehn-Rendu Christian
Bacon & Thomas
SNF S.A.
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