Use of copolymers of 2-acrylamido-2-methylpropane sulfonic acid for improving retention and dewatering in the manufacture of paper

Abstract

 A process for improving retention of fillers and pulp fines and increasing rate of dewatering of furnish in the manufacture of paper, by addition thereto of a water-soluble copolymer containing from about 2.5 to about 35 mole percent repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid and a water-soluble polymer selected from the group consisting of polyacrylamide and acrylamide copolymers.

Description

Background of the Invention

Field of the Invention

[0001] This invention relates to a process for improving retention of fillers and pulp fines and increasing rate of dewatering of furnish in the manufacture of paper, as well as to paper products of such process.

Description of the Prior Art

[0002] In the general practice of papermaking, an aqueous pulp suspension, or "furnish", of cellulosic fibers resulting from pulping of the feed wood stock is hydraulically and mechanically conveyed onto a wire grid or screen which is in motion to produce a wet web of cellulosic fibers. The wet fiber web is dewatered on the screen, by drainage of liquid therefrom, following which the wet web may be further treated, dried, calendared, and subjected to additional treatments as desired.

[0003] In general practice, a number of additives are contained in the furnish which is passed to the wire substrate wet web forming means. These additives may include processing aids for improving operation of the papermaking machinery, as well as paper chemicals for improvement of the properties of the finished paper product. Suitable processing aids may include retention aids for the retention of filler additives in and on the resultingly formed web and reduction of loss of paper pulp fines from the furnish during the dewatering step and drainage aids for improving the rate of dewatering of the furnish on the wire forming means. Other additives may include formation aids, flocculants, defoamers, wet-web-strength additives, pitch control agents, slimicides, creping aids, and the like, as is well known to those skilled in the art.

[0004] Functional additives may include fillers as mentioned, sizing aids and the like. The fillers may include optical brighteners, opacifiers, and pigments. Sizing agents are employed to provide the paper product with resistance to wetting by liquids, such as ink, water and the like, and rosin or waxes are typically employed for such purpose.

[0005] Based on considerations of efficiency and ease of processing, it is desirable to add retention aids to the furnish prior to the wet web formation step, to neutralize or reduce negatives surface charges inherently present on cellulosic fibers and fines and to cause coflocculation of fillers, fibers and fines so that they cohere, in addition to being bonded by the retention agent.

[0006] A number of retention aids have been employed in prior art, generally containing amine or quarternary ammonium groups, such as diethylenetriamine-adipic acid polyamide treated with epichlorohydrin, polymers of ethylenimine and di- methyldiallylammonium chloride, and aminoethyl acrylates copolymers. Also employed in the prior art is hydrated aluminum sulfate, i.e., alum, used both singly and in combination with other retention aids. Also heretofore employed are various polymers and copolymers of acrylamide, of ionic and nonionic types. In particular, polyacrylamides of cationic and anionic type have been employed in combination with alum. Although combinations of retention aids have been employed to provide high levels of filler retention, such as by addition of a low molecular weight cationic polymer to the furnish followed by a high molecular weight anionic polymer, such combinations can deleteriously affect web formation by promoting excessive flocculation of the cellulosic fibers, which must be compensated for by agitative treatment of the furnish upstream of the wet web formation step in the papermaking process.

[0007] Similarly, numerous drainage aids have been employed in papermaking to provide increased capacity for processing rate in the papermaking process in systems where dewatering or liquid drainage is the rate-limiting step in the process.

[0008] Although it is generally desirable to maximize retention and drainage rates in the papermaking system, the additives which heretofore have been employed for such purpose frequently deleteriously co-act with one another to reduce their effectiveness, due to the opposed character of the operations of drainage and enhancement of retention. Further, many drainage and retention aids heretofore employed are characterized by low levels of activity at lower pH.

[0009] Accordingly, it is an object of the present invention to provide an improved process and composition for enhancing retention and rate of dewatering of furnish in the manufacture of paper.

SUMMARY OF THE INVENTION

[0010] In one aspect, this invention relates to an additive composition for improving retention of fillers and pulp fines and increasing rate of dewatering of furnish in the manufacture of paper, comprising (a) a water-soluble copolymer containing from about 2.5 to about 35 mole percent repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid, and (b) a water-soluble polymer selected from the group consisting of polyacrylamide, and copolymers containing from. about 70 to about 100 mole percent of repeating units derived from acrylamide wherein the weight ratio of (a) to (b) is from about 8:1 to about 0.125:1.

[0011] In another aspect of the invention, there is provided an improved process for enhancing retention of fillers and pulp fines and increasing rate of dewatering of furnish in the manufacture of paper, comprising adding to said furnish prior to the dewatering thereof (a) from about 0.1 to about 3.0 pounds per ton of said furnish of a water-soluble copolymer containing from about 2.5 to about 35 mole percent repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid, and (b) from about 0.1 to about 5.0 pounds per ton of said furnish of a water-soluble polymer selected from the group consisting of polyacrylamide, and copolymers containing from about 70 to about 100 mole percent of repeating units derived from acrylamide.

[0012] The invention also relates to a paper product of the process as described in the preceding paragraph.

DETAILED DESCRIPTION OF THE INVENTION

[0013] In connection with the present invention, it has surprisingly and unexpectedly been discovered that the use in combination of a water-soluble copolymer containing from about 2.5 to about 35 mole percent of repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid (hereinafter denoted as AMPS) and a water-soluble polymer selected from the group consisting of polyacrylamide, and copolymers containing from about 70 to about 100 mole percent of repeating units derived from acrylamide react synergistically in providing higher levels of retention and rate of dewatering (drainage rate) than is achievable with either component when used alone. Furthermore, in contrast to prior art combination drainage/retention aid additives, the composition of the present invention is relatively insensitive to pH and is highly effective in both acid and alkaline systems. Although AMPS polymers and copolymers have been taught as drainage and retention aids in the prior art, e.g., German Offenlegung- sschrift 2,248,752, there has been no recognition that such additives could be used in combination with acrylamide polymers or copolymers in the manner of the present invention, to achieve the enhanced drainage and retention performance levels economically achieved by the composition of the instant invention.

[0014] The composition and process of the present invention may be applied with advantage to furnishes of diverse papermaking stock, such as groundwood, thermal mechanical processing (TMP) pulps, kraft feedstocks and the like, and is particularly efficacious in application to newsprint furnishes containing at least 40 percent by weight of groundwood pulp.

[0015] The AMPS copolymer employed in the present invention contains from about 2.5 to about 35, preferably 5-20 and most preferably from 7-15 mole percent repeating units derived from AMPS. As used herein, AMPS is,intended broadly to refer to 2-acrylamido-2-methylpropanesulfonic acid as well as and any suitable salts thereof. Suitable AMPS copolymers include those containing for example from about 65 to about 97.5 mole percent of repeating units derived from acrylamide, and from about 3 to about 15 mole percent of repeating units derived from acrylic acid. Preferably, the AMPS copolymer has a molecular weight of from about 2 million to about 20 million. Particularly preferred copolymers may for example have a Standard Brookfield viscosity, measured in a 0.20% solution at 25⁰C in 0.33 M NaCl with a #1 spindle rotating at 60 rpm, of 2-10 centipoises.

[0016] The polymeric co-additive employed with the AMPS copolymer is a water-soluble polymer selected from the group consisting of polyacrylamide, and copolymers containing from about 70 to about 100 mole percent of repeating units derived from acrylamide. This polymer may be nonionic or ionic in character and is most preferably cationic. Suitably, this polymer may be a cationic emulsion copolymer containing a 95 mole percent repeating units derived from acrylamide and 5 mole percent repeating units derived from dimethylaminoethyl methacrylate which is quaternized with dimethyl sulfate, the copolymer being emulsified with sorbitan monooleate and containing a suitable emulsin breaker. Alternatively, this polymer may be a cationic copolymer of acrylamide and diallyldimethylammonium chloride containing 75 to 99 mole percent repeating units derived from acrylamide and having a molecular weight of less than about 25,000. Other suitable polymers include aminomethylated polyacrylamide and methacrylamidopropyl trimethylammonium chloride/acryamide copolymers.

[0017] In the process of the invention, from about 0.1 to about 3.0 pounds per ton of the furnish of the AMPS copolymer is added, together with from about 0.1 to about 5.0 pounds per ton of the acrylamide polymer or copolymer, preferably from about 0.5 to about 2.0 pounds per ton of the AMPS copolymer and from about 0.5 to about 2.0 pounds of the acrylamide polymer or copolymer. Advantageously, the weight ratio of the AMPS copolymer to the acrylamide polymer or copolymer added to the furnish is in the range of from about 0.125:1 to about 8:1.

[0018] Although, as mentioned, the invention has broad utility in acidic and alkaline furnish media, the composition of the invention is particularly effective at a pH in the range of from about 4.0 to about 5.5. The composition of the invention may be used, for example, in a furnish containing a rosin size and alum at pH levels below about 5. Further, the composition of the instant claimed invention may be employed with conventional retention and drainage aid promoter compounds, such as diallyldimethylammonium chloride polymers or copolymers and polyethyleneimine.

[0019] The following specific examples illustrate specific aspects of the present invention. These examples are set forth by way of illustration only and are not to be construed as limiting on the scope of the present invention except as set forth in the appended claims. In all examples set forth hereinafter parts and percentages are by weight unless otherwise specified.

EXAMPLE I

[0020] The tests described hereinafter were conducted on newsprint furnishes having the compositions shown in Table I below.

[0021] The tabulated values for consistency were measured by filtering a weighed stock sample, then drying the retained fiber and weighing same. Mobility was measured in units of

at the stationary layer in a micro- electrophoresis cell. The values set forth for "CD" represent the cationic demand for the furnish, measured as the dosage, in lbs./ton of furnish, of poly(dimethylamino/epi- chlorohydrin) necessary to reduce the mobility of the furnish sample to zero. Headbox samples of the newsprint furnish described in Table I were obtained from a twin wire papermaking machi.ne, which normally has low first pass retention (FPR). The first pass retention. for the machine is defined as follows:
FPR

x 100%
and thus is a measure of the efficiency of the forming section of the papermaking machine in removing suspended material in the headbox furnish (i.e., fibers, fines and fillers) from the stock. High first pass retention correlates with low recirculation rates of fines and fillers in the papermaking system and better operation of the wet end of the process.

[0022] A Britt jar was used in the following tests to measure the effect of various additives on first pass retention. Conditions of operation (speed of agitation and serum size) were selected so that the FPR obtained with the Britt jar was the same as the FPR measured on the papermaking machine. The furnish for which the Britt jar was calibrated then was treated with the selected amount of furnish additive and FPR measured again in the Britt jar.

[0023] Drainage measurements were.made in a drainage tube, based on the amount (volume) of filtrate collected in a period of 5 seconds.

[0024] In the following Table, samples denoted as "Blank" contained no polymeric additives for enhancement of retention and/or drainage. The remaining samples contained specified amounts of "Polymer M" and/or "Copolymer A." Polymer M is a cationic emulsion copolymer containing 95 mole percent repeating units derived from acrylamide and 5 mole percent repeating units derived from dimethylaminoethyl methacrylate which is quaternized with dimethylsulfate, the copolymer being emulsified with sorbitan monooleate (Arlacel 80, Atlas Division of ICI Americas, Inc.) and Alfonic 1412-60 (Conoco Chemicals Company) emulsion breaker. Copolymer A is a copolymer according to the present invention containing twenty mole percent repeating units derived from AMPS and eighty mole percent repeating units derived from acrylamide.

[0025] Britt jar first pass retention values and drainage tube drainage measurements are set forth in Table II below.

[0026] The results shown in Table II indicate that copolymer A was superior to Polymer M in the provision of high retention and drainage rates and that the combination of Polymer M and Copolymer A provided a surprising and marked improvement in retention and drainage relative to either additive alone, when considered on the basis of equivalent total additive weight. For example, the combination of 1.9 pounds per ton of Polymer M with 1.1 pounds per ton of Copolymer A gave a retention value of 63.4 percent, while three pounds per ton of Polymer M provided a retention value of only 42.2 percent; likewise, the use of four pounds per ton of Polymer M in combination with 2.2 pounds per ton of Copolymer A provided a retention level of 81.2 percent, as contrasted to 6.8 pounds per ton of Polymer M, which yielded a first pass retention value of 62 percent. Concerning the retention data, the combination of Polymer M, at 2.1 pounds per ton, with Copolymer A, at 1.14 pounds per ton, yielded a drainage rate of 16 milliliters for the five second drainage period, while 3.2 pounds per ton of Polymer M gave a drainage rate of only 9 millimeters for the five second period. Relative to Copolymer A alone, which had a concentration of 1.7 pounds per ton yielded a drainage rate of 10 milliliters, an equivalent weight of_Polymer M (1.1 pounds per ton) and Copolymer A (0.57 pounds per ton) gave a drainage rate of 12 milliliters per five second drainage period, an improvement of 20 percent.

EXAMPLE 2

[0027] The tests described below were carried out to determine retention values for various furnishes, including combinations of Copolymer A with various co-additive polymers in varying molar ratios. Copolymer A and Polymer M were again each run separately against a control furnish containing no additives, along with furnishes of the following compositions: Copolymer A in combination with Polymer M, at weight ratios of M/A of 2/1 and 1.24/1; Copolymer A in combination with a cationic polyacrylamide which has been Manniched to a 70% level by reaction with formaldehyde and dimethylamine, hereinafter referred to as Polymer N, at a weight ratio of N/A of 10/1; Copolymer A in combination with an anionic, acrylamide and acrylic acid copolymer containing Alfonic 1412-60, hereinafter referred to as Polymer 0, in a · weight ratio of 0/A of 1.24/1; Copolymer A in combination with a cationic copolymer of acrylamide and diallyldimethylammonium chloride containing 75-99 mole percent repeating units derived from acrylamide with a molecular weight of less than about 25,000, containing 25% glyoxal for cross-linking of the polymer resin, hereinafter referred to as Polymer P, at a weight ratio of P/A of 1.24/1; and Copolymer A in combination with a nonionic polyacrylamide containing three percent Alfonic 1412-60, hereinafter denoted as Polymer Q, at a weight ratio of Q/A of 1.82/1.

[0028] The furnish employed in this series of tests was a newsprint furnish having the following composition: 45 weight % bleached kraft and 55 weight percent groundwood. First pass retention was measured with a Britt jar for the additive compositions shown in Table III below, wherein the retention percentage values are tabulated. The twin wire papermaking machine for which the Britt jar was calibrated had a measured FPR value of 47.5%, which is high for newsprint due to the high amount of kraft in this furnish.

As shown in the Table, the blank control had a first pass retention level of 47.5 percent and retention levels of 80-85% were achieved using Polymer M and Copolymer A separately. Nonetheless, the use of Copolymer A in combination with Polymers M, N, 0, P and Q, in the manner of the present invention, permitted achievement of retention levels as high as 90-95% at comparatively low additive levels, with the compositions of the present invention exemplifying the same marked increase in retention level relative to the separate additives Copolymer A and Polymer M, as previously discussed in Example I above. For example, two pounds per ton of Polymer M alone provided a first pass retention level of 69.4 percent, whereas a combination of 1.14 pounds per ton of Polymer M and 0.91 pounds per ton of Polymer A, representing approximately the same additive total weight, provided a retention level of 90.1 and 90.4. Likewise, two pounds per ton of Copolymer A yielded a retention level'of 80.5 percent, while a combination of 1.14 pounds Polymer 0 per ton and 0.91 pounds Copolymer A per ton, gave a retention level of 88.4 percent, representing an increase of 10% for the 0/A combination relative to Copolymer A alone. The date also show that for Copolymer A alone, an increase in concentration of Copolymer A over about 1.2 pounds per ton is detrimental and results in decreasing retention level with increased concentrations of such copolymer.

EXAMPLE III

[0029] In this example, the effect of ionic charge on the AMPS copolymer employed in the composition of the present invention was investigated using samples of dry polymer. In the evaluation, copolymers of AMPS and acrylamide were employed with varying concentrations of AMPS, in furnishes employing the copolymer alone and in combination with Polymer M as previously described, in the manner of the present invention. The furnish employed in these tests was the same as that employed in Example II, and first pass retention was evaluated by Britt jar test.

[0030] Referring to Table IV below,

Copolymer 1 contains 5 mole percent AMPS and 95 mole percent acrylamide units; Copolymer 2 contains 10 percent AMPS and 90 percent acrylamide units; Copolymer 3 contains 15 percent AMPS and 85 percent acrylamide units; Copolymer A is as described in Example I, containing 20 pecent AMPS and 80% acrylamide units; and Copolymer 4 contains 25% AMPS and 75% acrylamide units. The percent charge on the copolymer, due to the AMPS repeating units therein, are tabulated in Table IV, together with first pass retention values for dosages of the respective copolymers at .4 pounds per ton, .8 pounds per ton and 1.2 pounds per ton, respectively. In addition, the respective copolymers were employed in combination with Polymer M, as previously described in Example I, at weight ratios of M/Copolymer of 0.6/0.5 and 1.1/0.9.

[0031] The retention values shown in Table IV clearly show the marked enhancement when the copolymer is used in combination with Polymer M, relative to the use of the copolymer alone. The data further show that there is an optimum with respect to percentage charge on the copolymer, at approximately 10-20 percent charge, corresponding compositionally to 10-20 percent AMPS in the copolymer. It is to be noted that above about 20 percent charge (twenty percent AMPS), there is a decreasing level of retention with increased charge levels, both for the copolymer alone and for the copolymer in combination with Polymer M.

EXAMPLE IV

[0032] The same copolymers tested in Example III were tested for drainage, alone and in combination with Polymer M. Performance data are shown in Table V below,

wherein the same furnish compositions as Example III were employed. The 5-second drainage volume for the control sample containing no drainage/retention additives was 22 milliliters. Each of the copolymer additives produced substantial increases in drainage, which was further increased by combination with Polymer M in the manner of the present invention. As shown, Polymer M alone produced only a small negative effect on the drainage rate relative to the control sample containing no additives.

EXAMPLE V

[0033] Retention studies were made on a furnish from the same papermaking machine as in Example II, samples of which incorporated various additives, denoted by the same designations as in the preceding examples. Additionally, the additive combinations included a 70:30 acrylamide:acrylic acid copolymer containing Alfonic 1412-60, denoted herein as Polymer R; a 16 weight percent aqueous solution of poly(dialkyldimethyl ammonium chloride), herein designated as Polymer S. The results are shown in Table VI below.

wherein the tabulated retention values illustrate the substantial improvement achieved by Polymer M in combination with Copolymer A in the manner of the present invention, which provided retention levels for the newsprint furnish of 96-99 percent. As also shown by the tabulated data, a combination of cationic polyacrylamide with a copolymer of acrylamide and acrylic acid (Polymer M/Polymer R) resulted in substantially lower retention than the combination of Polymer M with Copolymer A, even at substantially increased levels of Polymer R in the combination with Polymer M relative to the amount of Copolymer A employed in combination with Polymer M.

EXAMPLE VII

[0034] Drainage studies were conducted on wood fiber building board furnish stock, comprising refiner-processed pine chips. This furnish contained hydrated aluminum sulfate (alum) and a pitch rosin size, at a pH of 4-4.5. Samples of this furnish were tested with various additives, as shown in Table VII

wherein the various additives are identified by their designations as employed in the preceding examples. As shown, the combinations of Copolymer A with Polymer S and Copolymer A with Polymer T produced very large increases in drainage rate over Polymer M or Copolymer A used alone. In contrast, the combination of Polymer T with Polymer R resulted in a decrease in drainage rate, relative to the sample containing no drainage/retention additives.

Claims

1. A process for improving retention of fillers and pulp fines and increasing rate of dewatering of furnish in the manufacture of paper, comprising adding to said furnish prior to said dewatering thereof (a) from about 0.1 to about 3.0 pounds per ton of said furnish of a water soluble copolymer containing from about 2.5 to about 35 mole percent repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid, and (b) from about 0.1 to about 5.0 pounds per ton of said furnish of a water-soluble polymer selected from the group consisting of polyacrylamide, and copolymers containing from about 70 to about 100 mole percent of repeating units derived from acrylamide.

2. A process according to Claim 1, wherein from about 0.5 to about 2.0 pounds of said water-soluble copolymer (a) per ton of said furnish are added to said furnish.

3. A process according to Claim 1, wherein from about 0.5 to about 3.0 pounds of said water-soluble polymer (b) per ton of said furnish is added to said furnish.

4. A process according to Claim 1, wherein the weight ratio of copolymer (a) to polymer (b) added to said furnish is in the range of from about 8:1 to about 0.125:1.

5. A process according to Claim 1, wherein copolymer (a) further contains from about 65 to about 97.5 mole percent of repeating units derived from acrylamide, and from about 3 to about 15 mole percent of repeating units derived from acrylic acid.

6. A process according to Claim 5 wherein copolymer (a),has a molecular weight of from about 2 million to about 20 million.

7. A process according to Claim 5 wherein copolymer (a) has a Standard Brookfield viscosity of from about 2 to about 10 centipoises.

8. A process according to Claim 1, wherein polymer (b) is a cationic copolymer of acrylamide and diallyldimethylammonium chloride containing 75 to 99 mole percent repeating units derived from acrylamide and having a molecular weight of less than about 25,000.

9. A process according to Claim 1, wherein the pH of said furnish from the addition of copolymer (a) and polymer (b) thereto through said dewatering is maintained in the range of from about 4.0 to about 5.5.

10. A paper product of the process of Claim 1.

11. An additive composition for improving retention of fillers and pulp fines and increasing rate of dewatering of furnish in the manufacture of paper, comprising (a) a water-soluble copolymer containing from about 2.5 to about 35 mole percent repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid, and (b) a water-soluble polymer selected from the group consisting of polyacrylamide, and copolymers containing from about 70 to about 100 mole percent of repeating units derived from acrylamide wherein the molar ratio of (a) to (b) is from about 0.125:1 to about 8:1.