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(11) | EP 0 058 621 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Reducing the deposition of pitch-like resins in the production of paper |
| (57) Pitch-like resin deposits are reduced or prevented during the papermaking process
by adding to the papermaking slurry from 0.5 to 20 parts per million by weight of
a polymer or copolymer of the formula:
where DMDAAXθis a polymer unit resulting from monomeric dimethyldiallylammonium X ⊖ ; X ⊖ is an anion; m is from 100 to 90 weight percent; and n is from 0 to 10 weight percent, said polymer or copolymer having a weight average molecular weight of from about 100,000 to 4 x 106. |
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention concerns compositons and methods for reducing or preventing the deposition of pitch-like resin during the papermaking process.
[0002] Particularly, the present invention concerns the addition of from 0.5 to 20 parts per million by weight of poly(dimethyldiallylammonium chloride), optionally copolymerized with up to 10 mole percent of acrylamide, to the papermaking slurry in order to prevent or reduce pitch-like resin deposits.
2. Brief Description-of the-Prior Art
[0003] Various approaches have been taken in the past to solving the problem of pitch deposition in papermaking. For example, various anionic materials have been employed, especially sodium salts of sulfonated naphthalene-formaldehyde condensates. However, these materials sufffer from the disadvantage of interfering with the performance of various cationic additives which are commonly used in papermaking today. As another example, clay has often been used in an effort to detackify pitch. While clay is cheap, however, it must be used in large amounts to control the pitch, which may result in a weakened paper. Also, the pitch is not dispersed and can cause spotting on the paper. Talc has also been used to control pitch by adsorbing dispersed resin particles on the faces of the talc platelets; but talc creates handling problems and requires expensive automatic feeding systems. Dispersants, or surface active agents have been utilized to stabilize, solubilize, and redisperse resin deposits. However, some dispersants are toxic; and large doses can result in extensive detachment of existing deposits, with severe consequences downstream. Papermaker's alum, usually together with sodium hydroxide or sodium aluminate, has been used to flocculate the dispersed resin particles in papermaking furnishes. However, alum does not completely eliminate pitch deposition problems, and in high concentrations causes a loss of drainage and retention. In addition to the chemical control methods described above, many nonchemical techniques have been utilized to control the deposition of pitch-like resins, including proper seasoning of the wood, good washing of the chemical pulp, avoidance of foam buildup, and systematic cleaning of the stock system.
[0004] Another approach to controlling pitch deposition is through the use of different polymer compositions.
[0005] Mechanisms of pitch deposition in newsprint mills and the control of such depositions with traditional retention aids such as high-molecular-weight cationic polyacrylamides and very high-molecular-weight polyoxyethylene, is described by Allen, L.H., Tappi, 63, 2, pp. 81-87 (Feb. 1980); and Pelton et al., Pulp Pap. Can., 81, 1, pp. T9-T15 (1980).
[0006] The use of various polymer compositions to prevent the deposition of pitch in papermaking is described in the following U.S. patents: 3,081,219 (N-vinyl-2-pyrrolidinone); 3,873,417 (terpolymer); 3,992,249 (anionic polymer containing hydrophobic and hydrophilic linkages); 4,190,491 (linear cationic polymer); and 4,184,912 (surfactant, dispersant, and anionic polymer).
[0007] The search for polymer compositions which will reduce or prevent the deposition of pitch in papermaking has thus met with only a limited degree of success; and the effective polymers discovered thus far have been of various types. The search for polymer compositions to reduce or prevent pitch deposition is, consequently, one which is still ongoing. The polymer compositions of the present invention satisfy this continuing need and are not suggested by the polymers which have been utilized in the past, as described above.
DETAILED DESCRIPTION OF THE INVENTION AND
PREFERRED EMBODIMENTS
[0008] The physical distribution of wood resin in aqueous pulp suspensions or slurries has been found to vary. In newsprint pulps, for example, the resin occurs (1) on the surfaces of fibers and fines, sometimes as a thin, generalized film, but more often as discrete patches or droplets; (2) inside parenchyma cells; and (3) in colloidal form suspended freely among the fibers in the process liquid.
[0009] The mechanisms of deposition of the pitch-like resin on the surfaces of process equipment during papermaking have also been found to vary. For example, resin transfer from and to fibers in a flowing pulp suspension probably exists in a dynamic equilibrium of deposit and removal. In areas of intense hydrodynamic shear, such as between the fourdrinier wire and foils or flat boxes, resin probably is transferred from fiber surfaces; and the cleaning effect of other fibers is minimized by the flow of resin to an area of less shear.
[0010] In the press section, the intense pressure of the nips results in a transfer of a certain amount of resin from the surfaces of the fibers to those of the felts, and some parenchyma cells may also be ruptured. About 10% of the resin in the pulp is transferred to the felt where it can cause plugging .of the pores or deposit subsequently during the felt dewatering process on the Uhle box lips.
[0011] Dispersed or colloidal resin deposits occur when hydrodynamic shear is sufficient to overcome naturally-occurring electrical and steric repulsion between the resin particles and a surface on which they might deposit. Deposition of dispersed resin is also promoted by the different processes of evaporation, creaming and coalescence, and foam formation and collapse.
[0012] In accordance with the present invention, the problems of pitch-like resin deposition during the papermaking process described above are reduced or prevented by incorporating in a pitch-like-resin-containing paper pulp slurry from 0.5 to 20 parts per million by weight of a polymer or copolymer of the formula:
where DMDAAX- is a polymer unit resulting from monomeric dimethyldiallylammonium X ;
X- is an anion;
m is from 100 to 90 weight percent; and
n is from 0 to 10 weight percent;
said polymer or copolymer having a weight average molecular weight of from about 100,000 to 4 X 106.
[0013] Any anion (counterion) compatible with the papermaking process may be employed, and chloride is preferred. Other acceptable anions include acetate, citrate, formate, glycolate, lactate, nitrate, oxalate, propionate, sulfate, and other halides, for example.
[0014] Preferred polymer compositions of Formula I are (1) where n is 0 weight percent, giving a homopolymer of dimethyldiallylammonium chloride (DMDAAC); and (2) where n is 5 weight percent, giving a 95:5 weight ratio copolymer of dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM). A preferred weight average molecular weight for the homopolymer (1) is 115,000, and for the copolymer (2) is 2 X 106.
[0015] Preparation of the pitch deposition control polymer compositions of the present invention is described in U.S. Pat. Nos. 2,884,058; 2,923,701; and 3,288,770.
[0016] The pitch control additives of the present invention may be incorporated into the pulp slurry at any stage of the pulping operation, including prior to or after digestion, during beating, in the stock-chest, or in the headbox of the papermaking machine. The pitch control additives may also be added to the whitewater being recirculated for pulp slurry dilution prior to the headbox. This is the preferred point of addition.
[0017] The amount of pitch control additive incorporated into the pulp slurry to be treated will be between 0.5 and 20 parts per million by weight, based on the total weight of pulp slurry treated. This amount of incorporated additive will correspond approximately to from 0.005 to 0.1% by weight, based - on the weight of pulp solids.
[0018] The polymer additives of the present invention are soluble in water in all proportions, and thus are conveniently metered to a pulp slurry in aqueous solution, preferably at from 0.1 to 1.0% solids, that is, at a 1000:1 to 100:1 water to polymer dilution ratio. Most preferably, the polymer additives are metered at a 1.0% solids concentration. Where the polymer additives are added to the whitewater being recirculated to the headbox through a fan pump, the polymer additives may be added neat, that is, at the percent solids concentration in which they are usually prepared and used: about 5 to 25% solids.
[0019] The present invention is more particularly described in the example which follows, which is intended to illustrate, but not to limit, the present invention.
EXAMPLE
[0020] This example illustrates the effectiveness of the pitch control additives of the present invention in reducing pitch deposits by attaching pitch colloidal particles to wood fibers and fines, measured as a percent count reduction from blank.
[0021] The pulp slurry involved was a combination of pulp from four pulping systems: kraft, groundwood, thermo-mechanical, and cold soda.
[0022] The ability of each polymer to attach pitch colloidal particles to fibers was measured by using a Britt jar. Once the Britt jar propeller was set in motion (200 rpm), headbox stock (500 ml) was added to the jar. Because of pitch count variability, samples were done by buckets. The count for each sample was logged against the count for the blank from the same bucket. A 0.1% solution of each test polymer was made, and polymer treatment in a 1 ppm - 20 ppm dosage range was added in different samples. After mixing for a specific time period (2 minutes), filtrate was withdrawn from the bottom of the jar and filtered through steel wool. The number of colloidal particles per unit volume present in the filtrate was counted by using a microscope and hemacytometer. The particles were counted within ten .05 mm x .05 mm x .1 mm unit volumes. The count was averaged per one unit. The effectiveness of a polymer was evaluated by determining the percent count reduction from the blank.
1. A method of reducing or preventing the deposition of pitch-like resin during the
papermaking process, comprising incorporating into a pitch-like-resin-containing paper
pulp slurry from 0.5 to 20 parts per million by weight, based on total weight of paper
pulp slurry, of a polymer or copolymer of the formula:
where DMDAAX⊖ is a polymer unit resulting from monomeric dimethyldiallylammonium X⊖;
said polymer or copolymer having a weight averag.e molecular weight of from about 100,000 to 4 X 106.
where DMDAAX⊖ is a polymer unit resulting from monomeric dimethyldiallylammonium X⊖;
X⊖ is an anion;
m is from 100 to 90 weight percent; and
n is from 0 to 10 weight percent;
said polymer or copolymer having a weight averag.e molecular weight of from about 100,000 to 4 X 106.
2. The method of Claim 1 wherein n is 0 weight percent, X is chloro, and the polymer
is poly (dimethyldiallylammonium chloride).
3. The method of Claim 2 wherein the weight average molecular weight of the polymer
is 115,000.
4. The method of Claim 1 wherein n is 5 weight percent, X⊖ is chloro, and the copolymer
is 95:5 dimethyldiallylammonium chloride/acrylamide.
5. The method of Claim 4 wherein the weight average molecular weight of the copolymer
is 2 X 106.