WO1994026972A1

WO1994026972A1 - Paper making processes

Info

Publication number: WO1994026972A1
Application number: PCT/US1994/005350
Authority: WO
Inventors: Roger Y. Leung; Lawrence L. Kuo
Original assignee: W.R. Grace & Co.-Conn.
Priority date: 1993-05-10
Filing date: 1994-05-09
Publication date: 1994-11-24
Also published as: DE4493351T1; BR9406395A; AU6912394A

Abstract

Paper or paperboard are produced from an aqueous pulp suspension which contains, in an amount effective to enhance the retention and drainage of the pulp suspension, a novel drainage/retention aid which includes: a) microparticles; and b) a polymer derived from a homopolymer of N-vinylamide having recurring units of general formula (I) wherein each R is independently selected from H or C1 to C3 alkyl and wherein n is an integer such that the absolute molecular weight of the polymer is at least 10,000 and which, prior to its addition to the pulp suspension, said polymer has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g.

Description

PAPER MAKING PROCESSES

Cross Reference to Related Applications

This application is a Continuation-in-Part of U.S. Serial No. 08/059,691 filed May 10, 1993.

Field of the Invention

This invention relates to a method of making paper or paperboard and more particularly to a novel retention and drainage aid for use in papermaking systems.

Background of the Invention

The manufacture of paper or paperboard involves the processing of an aqueous pulp fiber suspension, often referred to as the "furnish" to produce a uniform dry paper sheet. Numerous additives are used to treat the furnish which effect the final properties of the finished paper. For example, pigments, sizing agents, fillers, and the like are commonly added to the furnish to improve brightness, opacity, softness, smoothness and/or ink receptivity. Common additives include starches, polymers, siliceous particles, kaolin, china clay, calcium carbonate, titanium dioxide, zinc salts, and the like. Retention is a term used in papermaking to denote the extent to which the pulp fibers and other additives which are added to the furnish are retained in the finished paper. The retention of pulp fibers, sizing agents, fillers and other additives in the paper sheet during its formation in a paper making machine is an important requirement to paper makers. A retention aid generally acts by increasing the flocculating tendency of the pulp fibers and additives to inhibit their loss during drainage through the paper machine wires or screens. Numerous factors affect the efficiency of retention aids including 1) variables in the furnish such as pH, consistency, temperature, type of pulp fiber (e.g., fiber length, degree of refining, etc.), and white water recirculation (e.g. degree of system closure) , 2) conditions of the wire or screens such as wire mesh size, machine speed, etc. and 3) factors relating to the additives such as the dosage amount of additives, order of additives, form, shape and density of particles and ionic balance.

Another papermaking requirement that often conflicts with retention is the need for rapid drainage of the aqueous pulp suspension in the sheet forming areas of a paper machine. Aqueous pulp suspensions contain more than 99% water. To convert an aqueous pulp suspension to a finished paper sheet requires a rapid reduction in water content to a level of about 6%. Drainage rates are dependant upon numerous factors including the arrangement of the drainage elements in the paper making machine, (e.g., arrangement of free drainage areas vis-a-vis vacuum assistance area) , characteristics of the wires, screens or fabric, furnish characteristics (e.g. freeness, additives, etc.), furnish thickness, temperature, furnish consistency and wire speed. Suitable retention/drainage aids must not only inhibit the undue loss of fibers and additives, but they must also promote rapid drainage of water from the pulp suspension. Numerous retention/drainage aids are known and are available to paper makers. For example, EP 235,893 describes the use of a combination of organic, substantially linear synthetic polymers and bentonite to improve drainage/retention. Suitable organic polymers are those which provide a bridging mechanism for flocculation. Suitable polymers in this reference require charge densities from 0.35 to 2.5 mEq/g, and molecular weights above 500,000, preferably above 1 million and often above 5 million, most preferably in the range 10 to 30 million or more. However, these high molecular weight polymers are provided to paper makers in the form of a solid material or in emulsion form. The solid form of polymers are generally slow to dissolve in aqueous systems. In addition, these high molecular weight polymers are very shear-sensitive, which present significant handling and quality control problems. For example, since the polymers must be pre-dissolved in an aqueous solution, which requires extensive mixing to assure complete dissolution. However, since these polymers are sensitive to shearing, these mixing procedures often destroy the desirable high molecular weight characteristics as well as overall uniformity of the final polymeric dispersion. In consideration of these problems, investigations into the use of lower molecular weight polymers for use as flocculating agents have been made, however, current low molecular weight polymers e.g., below 500,000 molecular weight, are relatively ineffective flocculating agents.

While many factors influence the performance of polymeric flocculants, the molecular weight of the polymer is the most important factor for effective bridging flocculation. Polymer molecules, when dissolved in aqueous solution, exist as random coils. The radius of gyration of these random coils is dependent on the molecular weight of the polymers, ionic strength of the solution as well as many other factors. The potential for bridging flocculation is increased when the radius of gyration of a polymer is increased. This explains why a lower molecular weight polymer is generally inferior to high molecular weight polymer for bridging flocculation. Thus, a primary focus for research in this area has been directed to increasing the "absolute" molecular weight of the polymer. The absolute molecular weight of polymers is generally determined by methods such as light scattering or colligative property measurements.

However, the absolute molecular weight is not always representative of the size of the polymer molecules. Methods such as intrinsic viscosity measurements or size exclusion chromatography are used to determine the "apparent" molecular weight of polymers because their results are dependent on both the absolute molecular weight and the size of the polymers.

The importance of using high molecular weight polymers for retention/drainage aids is further disclosed in U.S. 4,749,444 which discloses a process for production of paper and cardboard by adding to the paper stock a three component mixture of an activated bentonite, a cationic polyelectrolyte and a high molecular weight acrylamide or methacrylamide polymer having an average molecular weight from 1 to 20 million. The cationic polyelectrolytes must have a charge density not less than 4 mEq/g. This reference discloses that if only bentonite and cationic polyelectrolyte are used, the drainage of the paper stock is poor and if only bentonite and high molecular weight polymer are used, the paper stock flocculates to such an extent that satisfactory sheet formation is not ensured. Thus, in accordance with this reference effective flocculation for drainage/ retention purposes, requires the presence of bentonite, a high molecular weight (meth) acrylamide polymer and a high charge density cationic polyelectrolyte wherein the function of the high charge density cationic polyelectrolyte is to moderate the flocculation to ensure good sheet formation and to reduce the anionicity of the paper stock.

Further in Linhart and Auhorn. in Das Papier, No. 10A, 1992, pp. V38-V45, the use of polyvinylamines as a new class of polymers for paper production is discussed. Polyvinylamines are substantially linear polymers obtained by hydrolyzing N-vinylamide polymers. Since the vinylamine units are cationic, these polymers have a positive charge in solution. By controlling the degree of hydrolysis of the N-vinylamide polymers one can control the charge density of the polymers in solution. This reference discloses that the use of high molecular weight, 100 percent hydrolyzed polyvinylamines as retention aids was hardly better than those of polyethyleneimine, which was a prevailing class of high charge density non-linear cationic polymer. It was further disclosed that "when the molecular weight of polyvinylamines is sufficiently large and charge density reduced, excellent retention and drainage aids are obtained."

U.S. 5,098,521 describes a process for paper and board production which uses a paper stock which contains anionically charged foreign substances by adding to the paper stock N-vinylamide/vinylamine copolymers having less than 10% vinylamine units and having K values of not less than 130 (as determined according to H. Fikentscher) .

Summary of the Invention It is an object of this invention to provide a novel method for preparing paper and paperboard.

It is another object of this invention to provide a novel paper or paperboard product. It is another object of this invention to provide a novel drainage/retention aid for use in papermaking systems.

It is another object of this invention to provide a drainage/retention aid that is readily soluble in aqueous pulp suspensions and does not present handling problems for paper makers.

It is another object of this invention to provide a relatively low molecular weight drainage/retention aid which performs better than conventional very high molecular weight drainage/retention aids.

It is another object of this invention to provide a drainage/retention aid that is less shear sensitive as compared to conventional very high molecular weight acrylamide-derived polymers.

It is another object of this invention to provide a drainage/retention aid with relatively higher charge density and lower polymer dosage, but which provides enhanced performance on drainage/retention as compared to current drainage/retention systems.

It is another object of this invention to provide a novel drainage/retention aid that may be added to the aqueous pulp suspension at any point in the paper making process prior to sheet formation. In accordance with the present invention, there has been provided a method for the production of paper or paperboard from an aqueous pulp suspension which comprises adding to the pulp suspension a drainage/ retention aid which further comprises; a) microparticles; and b) a polymer derived from a homopolymer of N- vinyla ide having recurring units of the general formula: - (- CH₂ - CH -) -_n N - R

I C = O

I

R

wherein each R is independently selected from H or C_α to C₃ alkyl and wherein n is an integer such that absolute molecular weight of at least 10,000 and which, prior to its addition to the pulp suspension, has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g in an amount effective to enhance the retention and drainage of the pulp suspension.

Also in accordance with the present invention, there has been provided a paper or paperboard product containing a drainage/retention aid comprising; a) microparticles; and b) a polymer derived from a homopolymer of N- vinylamide having recurring units of the general formula:

wherein each R is independently selected from H or Cγ to C₃ alkyl and wherein n is an integer such that molecular weight of at least 10,000 and which, prior to its addition to the pulp suspension, has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g. Also in accordance with the present invention, there has been provided a drainage/retention aid comprising; a) microparticles; and b) a polymer derived from a homopolymer of N- vinyla ide having a recurring units of the general formula:

wherein each R is independently selected from H or C_x to C₃ alkyl and wherein n is an integer such that molecular weight of at least 10,000 and which, prior to its addition to the pulp suspension, has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g.

Detailed Description

The present invention is directed to a novel drainage/retention aid and to a method of preparing paper or paperboard which utilizes the drainage/retention aids of this invention. The drainage/retention aids of this invention comprise a combination of a microparticle and a polymer derived from a homopolymer of N-vinylamide having an absolute molecular weight of at least 10,000 and which has been hydrolyzed to provide a charge density between 5 and 24 mEq/g. The drainage/retention aids of the present invention provide effective results when the homopolymer and microparticle are added as the sole active drainage/ retention aid, and thus do not include, or are not used in combination with high molecular weight acrylamide or methacrylamide based polymers, i.e., the present drainage/retention aids are substantially free of high molecular weight acrylamide or methacrylamide polymers. These high molecular weight polymers are more fully disclosed in U.S. Patent 4,749,444. The combination of a high molecular weight polymeric flocculating agent together with microparticles is often referred to as a "microparticle" system. The compositions of the present invention are directed to novel microparticle systems which provide not only enhanced drainage/retention over prior known drainage/ retention aids, but also provide drainage/retention aids which do not have the handling problems of the prior art high molecular weight materials.

Suitable microparticles for use in this invention generally include organic polymeric particles and/or inorganic colloidal particles having positively or negatively charged surfaces. As used herein, the terminology "charged surface" refers to a cationic, anionic or amphoteric surface charge. The charge density of this surface charge is not, per se, critical to the invention, provided of course that the microparticles interact with either the cationic polymers of the invention or the anionic components which are present in the aqueous pulp suspension. It is preferred to use anionic (negatively charged) microparticles for use in combination with the polymers of the invention.

Suitable organic polymeric microparticles for use in the invention include organic polymeric microparticles which are either water dispersible or water soluble, and have a charged surface. Organic polymeric microparticles having the above properties include, but are not limited to, various high molecular weight, cross-linked polymer particles. An example of suitable organic polymeric microparticles are those commercially available from Cytec Industries under the trademark name of POLYFLEX™. These organic polymeric microparticles are more fully disclosed in U.S. Patent Nos. 5,171,808 and 5,274,055 which are incorporated herein in their entirety. Suitable inorganic particles for use in this invention are generally inorganic colloidal materials having positively or negatively charged surfaces and include, but are not limited to particulate siliceous materials, china clay, alumina, titanium, zirconium, tin, borium, calcium carbonate (ground, precipitated or natural) compounds, and the like, and mixtures thereof. The particulate siliceous materials can be selected from water swellable clay materials, colloidal silica solutions, or water dispersible siliceous materials. The water swellable clay materials are primarily smectite or ver iculite type, and are preferably the bentonite type materials. The term "bentonite" generally embraces the sheet silicates that are swellable in water. These are primarily the clay mineral montmorillonite and similar clay minerals, e.g. he orite, nontronite, saponite, volkonskoite, sauconite, beidellite, allevardite, illite, halloysite, attapulgite and sepiolite. If water swellability is not a natural property of the mineral, it may be activated before being used, i.e., -converted to its water-swellable sodium, potassium, lithium, ammonium or hydroxonium form.

Suitable inorganic particles for use in this invention also include "modified" inorganic particles wherein the ionicity of the inorganic particles is modified by contacting the particles with low molecular weight (e.g. below 100,000), high charge density (e.g. at least 4 mEq/g) cationic or anionic polymers. This technique is more fully disclosed in U.S. Patent No. 5,015,334 to Derick which is incorporated herein in its entirety. A preferred modified inorganic particle for use in this invention is a modified bentonite material which was modified with an acrylic or methacrylic polymer. The particle size of the microparticles of this invention is not, per se, critical to the invention provided of course that these particles can disperse or be readily dispersed into an aqueous pulp suspension in a paper making process and which do not negatively affect the surface characteristics of the final paper product. These particles, in general, will have an average dry particle size less than 50 microns, typically in the range l nm to 10 microns, and more typically from 2 nm to 2 microns. Suitable N-vinylamide polymers for use in this invention have recurring units of the general formula:

-(- CH₂ ) ^—n

wherein each R is independently H or C_x to C₃ alkyl and n is an integer such that the absolute molecular weight of the polymer is at least 10,000. A preferred N-vinylamide polymer for use in this invention is N-vinylformamide, i.e., where each R is H.

Methods for the preparation of N-vinylamide polymers are well known to those skilled in the art and include bulk polymerization, precipitation polymerization, solution polymerization or emulsion polymerization techniques. Aqueous solution polymerization in the presence of a free-radical initiator is preferred. The monomer concentration is generally in the range of 5 to 60% by weight, and is preferably between 10 to 30% by weight.

Suitable free-radical initiators include, but are not limited to, azo initiator, peroxide initiator, persulfate initiators and free-radical redox systems. Especially preferred are water-soluble azo initiators such as 2,2'-azobis(N,N'-dimethyleneisobutyramidine)- dihydrochloride, 2,2'-azobis(2-amidinopropane)- dihydrochloride, 4,4'-azobis-(4-cyanopentanoic acid), 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2- hydroxyethyl]propionamide}, and 2,2'-azobis[2-methy1-N- (2-hydroxyethyl)propionamide] . The radical initiator is usually used in an amount of 0.01 to 1 wt% based on N- vinylamide weight. The polymerization reaction is usually carried out under an inert gas atmosphere at 30° to 100°C, preferably between 45° to 70°C.

The absolute molecular weight of N-vinylamide polymer can be controlled by various factors including the particular method of polymerization, the polymerization temperature, the type and amount of initiator, the concentration of N-vinylamide monomers and the like. In general, lower temperature and higher monomer concentration produce a higher molecular weight polymers while higher temperature and lower monomer concentration produce lower molecular weight polymers. It is considered an important feature of the invention that the N-vinylamide polymers have absolute molecular weights (as determined by light scattering or equivalent methods) of at least 10,000, and can be as high as 4 million. However, due to solubility and handling considerations, the preferred N-vinylamide polymers of the present invention generally have absolute molecular weights in the range of from 10,000 to 1 million, preferably from 20,000 to 500,000 and most preferably from 50,000 to 100,000.

The N-vinylamide polymers, prior to their addition to the aqueous pulp suspensions are hydrolyzed with an acid or a base, either partially to form N-vinylamide/ vinylamine copolymers, or completely to form vinylamine homopolymers. Generally, partial hydrolysis is preferred with a suitable acid such as hydrochloric acid, sulfuric acid, nitric acid, and the like. Copolymers having different molar ratios of N-vinylamide to vinylamine are obtained by controlling the amount of acid, reaction temperature and reaction time.

It has now been discovered that the effectiveness of these polymers for use as drainage/retention aids can be optimized by hydrolyzing the N-vinylamide polymers to provide a charge density in the range 5 mEq/g to 24 EQ./?/, preferably 8 to 20 mEq/g, most preferably 10 to 18 mEq/g as determined at pH 4. A charge density of 5 mEq/g generally corresponds to 25% hydrolysis of the N- vinylamide polymer. These charge densities cause the polymer to expand in size and effectively increases the apparent molecular weight of the resultant hydrolyzed polymer by a factor of up to forty times. Thus, a homopolymer of N-vinylamide, having an absolute molecular weight of 10,000 (as determined by light scattering or other equivalent means) , when hydrolyzed, will possess an apparent molecular weight of about 400,000 (as determined by gel permeation chromatography or other equivalent means) . Accordingly, the above preferred polymers of the invention, when hydrolyzed, will possess apparent molecular weights in the range 100,000 to 3 million, preferably 200,000 to 2 million, and most preferably between 300,000 and 1 million. These highly cationically charged, high apparent molecular weight polymers are readily soluble in aqueous papermaking systems, do not present handling problems to papermakers, and surprisingly provide enhanced drainage and retention properties over other conventional cationic polymeric drainage retention aids having equivalent or higher absolute molecular weights.

For purposes of explanation, and not limitation, it is believed that the use of these expanded polymer chains favors the mechanism of bridging flocculation, and thus enables these relatively low absolute molecular weight polymers to perform with similar effectiveness as higher molecular weight polymers for drainage/retention. Therefore, the invention prefers, employing relatively low molecular weight N-vinylamide polymers which are then hydrolyzed to provide a high degree of charge density as drainage/retention agents in paper or paperboard making processes.

The polymers and microparticles of this invention are generally prediluted in separate aqueous solutions which may then be added tr in aqueous pulp suspension in any order and at any poin in the papermaking process prior to the headbox, either before or after one of the several shear stages. Shear stages include the cleaning, mixing and/or pumping stage. Due to the low molecular weight of the polymers of the invention, excessive shear of the drainage/retention in the aqueous pulp suspension is not essential for effective drainage/retention. Best results are achieved when the polymer is added to the thin stock rather than to thick stock, and the microparticles are added after the addition of the polymer solution. Typically, both components are added close to the head box prior to sheet formation.

The dosage amounts of polymer and microparticle added to the system can vary widely depending on the nature of the aqueous pulp suspension and the degree of drainage or retention desired. Those of ordinary skill in the art can readily determine appropriate dosage amounts by conventional techniques. Thus, the exact dosage amounts are not critical to the invention, per se, and are generally added in amounts effective to provide enhanced drainage or retention relative to the absence of these materials. Typical dosage amounts of polymers range from 0.005 to 0.5%, preferably from 0.01 to 0.3% and most preferably from 0.02 to 0.1% on a weight basis relative to the dry paper stock. Typical dosage amounts for microparticles range from 0.005 to 3% on a weight basis relative to the dry paper stock. When the microparticles are inorganic, the dosage is preferably from 0.1 to 1.5% and most preferably from 0.2 to 1% on a weight basis. When the microparticle is an organic polymeric microparticle, the dosage is preferably from 0.01 to 1%, most preferably from 0.02 to 0.5%. In accordance with the present invention, the polymer and microparticle solutions can also be added in several increments.

The drainage/retention aids of the present invention may optionally be used in combination with other paper making additives including but not limited to other water soluble non-acrylamide or methacrylamide based polymers, enzymes, fillers, coagulants, wet and dry strength additives, sizing agents, starches and the like, and mixtures thereof. Suitable enzymes include cellulolytic enzyme (e.g., cellulases and/or hemicellulases) , glucose isomerase, e.g. derived from Streptomyces, Bacillus or Actinoplanes, Aminopeptidase, e.g. derived from Pseudomonas, Penicillin acylase, e.g. derived from Fusarium, Nitrilase, e.g. from Rhodococcus, from Pseudomonas or from Brevibacterium, Fructosyl tranferase. e.g. from Aspergillus, Invertase, e.g. from Saccharomyces, Lactase, e.g. from Kluyveromyces, Cyanidase, e.g. from Alcaligenes, and mixtures thereof. These enzymes are more fully disclosed in U.S. Patent Nos. 4,923,565, and 5,169,497 and International

Publication Number WO 91/08287 which are incorporated herein by reference in their entirety.

The following examples are provided to illustrate the present invention in accordance with the principles of this invention, but are not to be construed as limiting the invention in any way except as indicated in the appended claims. All parts and percentages are by weight unless otherwise indicated.

Example 1

This example shows the effect of hydrolysis of N- vinylformamide homopolymer on the charge density and molecular weight of the polymer. The weight average molecular weight was determined by size exclusion chromatography. The charge density was measured at pH 4 by colloidal titration using zero streaming potential as the end point of the titration. It was found that the hydrolysis increases the charge density of the polymer, and also expands the polymer chain as indicated by the significant increase of apparent molecular weight.

polymer A is a N-vinylformamide homopolymer polymer B is 20% hydrolyzed polymer A polymer C is 37% hydrolyzed polymer A polymer D is 50% hydrolyzed polymer A polymer E is 78% hydrolyzed polymer A polymer F is 89% hydrolyzed polymer A

Example 2 This example reports a drainage test using the Canadian freeness tester. The stock suspension tested was a bleached kraft pulp containing 30% ground calcium carbonate as filler. The pH of the stock was 8.2, with consistency of 0.48%. In the drainage test, 1 liter stock was used and polymer and bentonite was added in sequence to the stock. The liquid volume collected from the tester was reported as freeness in mililiter. Tests 7 to 11 involve the invention system, test 12 is based on the EP 235893 formula and tests 16, 17 are based on the US 5098521 system. Tests 13 to 15 involve other commonly used commercial polymers. A surprising synergistic effect offered by the invention between N-vinylformamide- vinylamine copolymers and bentonite can be clearly seen as compared to all other systems tested.

Table 2. Drainage Test

Freeness (ml)

Test System

0.05% 0.05% Polymer Polymer

0.4%

Inorganic

Particle

7 Blank 390

8 polymer B 410 525

9 polymer D 415 558

10 polymer G 430 552

11 polymer H 490 600

12 polymer I 490 475

13 polymer J 385 430

14 polymer K 400 440

15 polymer L 390 430

16 M 420

17 N 405

blank means no additives used polymer G is a polyvinylamine homopolymer with molecular weight less than 500,000 polymer H is a copolymer of N- vinylformamide/ vinylamine with 77% hydrolysis with molecular weight about 800,000 polymer I is a high M.W. cationic polyacrylamide with molecular weight above millions polymer J is a polydiallyl dimethyl ammonium chloride polymer (Agefloc PC2206) polymer K is polyethyleneimine polymer L is polymin SK system M involves addition of 0.5% bentonite, 0.06% polymer L and 0.02% polymer I in sequence system N involves addition of 0.5% bentonite, 0.06% polymer K and 0.02% polymer I in sequence

Example 3

This example shows the drainage test on a bleached kraft pulp containing no filler. The pH of the stock was 8 and the consistency was 0.51%. The inorganic particle tested was bentonite.

Table 3. Drainage Test

Freeness (ml)

Test System

0.05% 0.05% Polymer Polymer

0.4%

Inorganic

Particle

18 Blank 350

19 polymer A 335 330

20 polymer B 360 525

21 polymer D 365 530

22 polymer G 360 524

23 polymer H 400 595

24 polymer I 330 440

25 polymer J 330 395

26 polymer K 345 410

27 polymer L 345 400

28 M 325

29 N 355

Example 4 This example reports the retention tests using the standard dynamic Britt jar to compare the invention system (tests 31 to 33) to the systems described in US 4,749,444 (tests 34 & 35). The stock was a bleached kraft pulp containing 30% ground calcium carbonate, with pH around 8.3 and consistency around 0.48%. The inorganic particle tested was bentonite.

Table 4. Retention Test

Test System First Pass Retention (%)

30 blank 23.6

31 0.05% 88.3 polymer B

0.5% inorganic particle

32 0.05% 85.9 polymer F

0.5% inorganic particle

33 0.05% 95.1 polymer H

0.5% inorganic particle

34 M 63.7

35 N 72.2

Example 5 This example shows the retention tests using the same stock in Example 4 to compare the invention system (tests 37 to 40) to the system described in EP 235,893 (test 41) and other commercial polymers (tests 42 to 44) . The inorganic particle tested was bentonite.

Table 5. Retention Test

First Pass Retention

Test Polymer (%)

0.05% 0.05% Polymer Polymer

0.2%

Inorganic

Particle

36 Blank 23.6

37 B 54.1 72.8

38 D 78.3 81.6

39 F 74.8 90.5

40 G 82.2 90.5

41 I 67.4 87.5

42 J 40.9 62.4

43 K 43 51.6

44 L 60.3 58

Example 6 This example shows the retention tests to compare the invention system (tests 46 to 48) to the system described in EP 235,893 (test 49) and other commercial polymers (tests 50 to 52) . The stock was a bleached kraft pulp containing 30% precipitated calcium carbonate. with pH around 8.4 and consistency around 0.5%. The inorganic particle was bentonite.

Table 6. Retention Test

First Pass Retention

Test Polymer (%)

0.05% 0.05% Polymer Polymer

0.4%

Inorganic

Particle

45 Blank 26.2

46 C 67.7 87.5

47 D 68.4 89.2

48 F 82.2 89

49 I 41.3 82.7

50 J 22.9 69

51 K 41.9 80.8

52 L 40 72.6

Example 7 This example shows the retention tests to compare the invention system (tests 54 to 55) to commercial polymers (tests 56 to 58) . The stock was a bleached kraft pulp, with pH around 5.1 and consistency around 0.53%. The inorganic particle was bentonite. Table 7. Retention Test

First Pass Retention

Test Polymer (%)

0.05% 0.05% Polymer Polymer

0.4%

Inorganic

Particle

53 Blank 67

54 D 68 85.4

55 G 76.7 85.1

56 J 66.3 66.9

57 K 64.7 73.7

58 L 70 78

Example 8 This example shows the effect of different retention aid systems on the first pass retention of ground calcium carbonate. Standard Britt jar tests were carried out on a bleached kraft stock containing 30% ground calcium carbonate. The pH of the stock was 8, with consistency around 0.5%. Tests 59 to 61 used the invention retention system. Tests 62 to 64 employed widely used commercial retention systems with molecular weight less than 500,000. Tests 65 and 66 applied retention systems with molecular weight well above 500,000. The results clearly demonstrate the superior retention achieved by the invention. Table 8. Retention Test

Test 0.05% Ho 0.2% 0.4% Polymer Inorganic Inorganic Inorganic

Particle Particle Particle

59 G 47.4 71.9 84

60 F 66.9 79.6 81.4

61 E 26.5 75.7 88.9

62 J 27.4 42.1 60.3

63 L 26.8 49.9 59.7

64 0 30.1 40.9 41.9

65 P 45.9 62.4 70

66 Q 59.4 70.3 77.6

polymer 0 is polyethyleneimine (Darafloc 952, Grace) polymer P is a copolymer of acrylamide and acryloxy- ethyltrimethylammonium chloride with molecular weight above 500,000 polymer Q is a copolymer of acrylamide and acryloxy- ethyltrimethylammonium chloride with molecular weight above 500,000

Example 9 This example shows the effect of various retention aid systems on the first pass retention of kaolin. The stock and experiments were the same as Example 8, except 30% kaolin was used. The inorganic particle used was bentonite. Table 9 also shows the superior retention results achieved by the invention (tests 67,68). Table 9. Retention Test

Test 0.1% NO 0.4% 0.8% Polymer Inorganic Inorganic Inorganic

Particle Particle Particle

67 G 64.5 74 72.7

68 J 38 61.8 68.7

69 L 26.3 31.4 41.3

70 0 26.2 29.9 37.5

71 P 43.3 47.7 58.5

Example 10 Retention tests were carried out to show an unexpected synergism between a relatively high apparent molecular weight (about 800,000 - 1 million), high charge density (21 mEq/g at pH 4) polyvinyla ine (polymer R) and Polyflex CP on filler retention. Polyflex CP is a polymeric particulate manufactured by Cytec. The pulp slurry tested was a bleached kraft containing 30% ground calcium carbonate. 0.03% (on dry paper weight base) Polymer R was first added to the stock, followed by the addition of Polyflex CP at different concentration levels. The first pass retention (FPR) of fine and filler is shown in Table 10.

TABLE 10

Polyflex CP concentration 0% 0.03% 0.09% 0.18%

FPR 35.7% 94% 92% 82% Example 11 (comparative) Retention tests similar to Example 10 were carried out using a high molecular weight (greater than 1 million) cationic polyacrylamide polymer (Polymer S commercially available under the tradename Percol manufactured by Allied Colloids) , and Polyflex CP. The concentration of Polymer S was 0.03%.

TABLE 11

Polyflex CP concentration 0% 0.03% 0.09% 0.18%

FPR 16.7% 46% 48% 33%

Example 12 (comparative) Retention tests similar to Example 10 were carried out using 0.03% Polymer R and bentonite.

TABLE 12

Bentonite concentration 0% 0.03% 0.09% 0.18%

FPR 35.7% 44% 48% 63%

Example 13 This example reports a drainage test using the Canadian freeness tester. An unexpected synergism was observed using 0.03% Polymer R and 0.03% Polyflex CP on freeness of a bleached kraft containing 30% ground calcium carbonate as filler. The consistency of the stock was 0.44%. The liquid volume collected from the side discharge of the tester out of 1 liter stock was reported as the freeness in milliliter. TABLE 13

Polyflex CP concentration 0% 0.03%

Freeness (ml) 519 675

Example 14 (comparative) A drainage test similar to Example 13 using 0.03% Polymer S and 0.03% Polyflex CP was carried out.

TABLE 14

Polyflex CP concentration 0% 0.03%

Freeness (ml) 450 475

Example 15 (comparative) A drainage test similar to Example 13 using 0.03% Polymer R and 0.03% bentonite was carried out.

TABLE 15

Polyflex CP concentration 0% 0.03%

Freeness (ml) 519 549

Claims

IN THE CLAIMS :

1. A method for the production of paper or paperboard from an aqueous pulp suspension which comprises adding to the pulp suspension, in an amount effective to enhance the retention and drainage of the pulp suspension, a drainage/retention aid which further comprises; a) microparticles; and b) a polymer derived from a homopolymer of N- vinylamide having recurring units of the general formula:

wherein each R is independently selected from H or C-. to C₃ alkyl and wherein n is an integer such that the absolute molecular weight of the polymer is at least 10,000 and which, prior to its addition to the pulp suspension, said polymer has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g.

2. A method according to Claim 1 wherein the charge density is in the range 8 to 20 mEq/g.

3. A method according to Claim 1 wherein the charge density is in the range 10 to 18 mEq/g.

4. A method according to Claim 1 wherein each R is

H.

5. A method according to Claim l wherein the hydrolyzed polymer has an apparent molecular weight in the range 100,000 to 3 million.

6. A method according to Claim l wherein the hydrolyzed polymer has an apparent molecular weight in the range 200,000 to 2 million.

7. A method according to Claim 1 wherein the hydrolyzed polymer has an apparent molecular weight in the range 300,000 to 1 million.

8. A method according to Claim l wherein the microparticles are inorganic particles selected from the group consisting of siliceous materials, alumina, bentonite, china clay, titanium, zirconium, tin, borium, calcium carbonate compounds and mixtures thereof.

9. A method according to Claim 8 wherein the inorganic particles are modified with a low molecular weight, high charge density polymer.

10. A method according to Claim 9 wherein the inorganic particles are bentonite.

11. A method according to Claim 1 wherein the microparticles are organic polymeric microparticles.

12. A method according to Claim 1 wherein the amount of polymer added to the aqueous pulp suspension is from 0.005% to 0.5% on a weight basis.

13. A method according to Claim 1 wherein the amount of polymer added to the aqueous pulp suspension is from 0.01% to 0.3% on a weight basis.

14. A method according to Claim 1 wherein the amount of polymer added to the aqueous pulp suspension is from 0.02% to 0.1% on a weight basis.

15. A method according to Claim 1 wherein the amount of microparticles added to the aqueous pulp suspension is from 0.005% to 3%.

16. A method according to Claim 15 wherein the microparticles are inorganic particles and are added to the aqueous pulp suspension in an amount from 0.1% to 1.5%.

17. A method according to Claim 16 wherein the inorganic microparticles are added to the aqueous pulp suspension in an amount from 0.2 to 1%.

18. A method according to Claim 15 wherein the microparticles are organic polymeric microparticles and are added to the aqueous pulp suspension in an amount from 0.01 to 1%.

19. A method according to Claim 15 wherein the microparticles are organic polymeric microparticles and are added to the aqueous pulp suspension in an amount from 0.02 to 0.5%.

20. A method according to Claim 1 which further comprises adding one or more additives selected from the group consisting of water soluble non-acryla ide or methacrylamide based polymers, enzymes, fillers, coagulants, wet strength additives, dry strength additives, sizing agents, starches and mixtures thereof.

21. A paper or paperboard product containing a drainage/retention aid comprising; a) microparticles; and b) a polymer derived from a homopolymer of N- vinylamide having recurring units of the general formula:

wherein each R is independently selected from H or C to C₃ alkyl and wherein n is an integer such that the absolute molecular weight of the polymer is at least 10,000 and which, prior to its addition to the pulp suspension, said polymer has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g.

22. A paper or paperboard product according to

Claim 21 wherein the hydrolyzed polymer has a charge density in the range 8 to 20 mEq/g.

23. A paper or paperboard product according to Claim 21 wherein the hydrolyzed polymer has a charge density in the range 10 to 18 mEq/g.

24. A paper or paperboard product according to Claim 21 wherein each R is H.

25. A paper or paperboard product according to Claim 21 wherein the hydrolyzed polymer has an apparent molecular weight in the range 100,000 to 3 million.

26. A paper or paperboard product according to Claim 21 wherein the hydrolyzed polymer has an apparent molecular weight in the range 200,000 to 2 million.

27. A paper or paperboard product according to Claim 21 wherein the hydrolyzed polymer has an apparent molecular weight in the range 300,000 to 1 million.

28. A paper or paperboard product according to Claim 21 wherein the microparticles are inorganic particles selected from the group consisting of siliceous materials, alumina, bentonite, china clay, titanium, zirconium, tin, borium, calcium carbonate compounds and mixtures thereof.

29. A paper or paperboard product according to Claim 28 wherein the inorganic particles are modified with a low molecular weight, high charge density polymer.

30. A paper or paperboard product according to Claim 29 wherein the inorganic particle is bentonite.

31. A paper or paperboard product according to

Claim 21 wherein the microparticles are organic polymeric microparticles.

32. A drainage/retention aid comprising: a) microparticles; and b) a polymer derived from a homopolymer of N- vinylamide having recurring units of the general formula:

wherein each R is independently selected from H or C_x to C₃ alkyl and wherein n is an integer such that the absolute molecular weight of the polymer is at least 10,000 and which, prior to its addition to the pulp suspension, said polymer has been hydrolyzed to provide a charge density in the range 5 to 24 mEq/g.

33. A drainage/retention aid according to Claim 32 wherein the hydrolyzed polymer has a charge density in the range 8 to 20 mEq/g.

34. A drainage/retention aid according to Claim 32 wherein the hydrolyzed polymer has a charge density in the range 10 to 18 mEq/g.

35. A drainage/retention aid according to Claim 32 wherein each R is H.

36. A drainage/retention aid according to Claim 32 wherein the hydrolyzed polymer has an apparent molecular weight in the range 100,000 to 3 million.

37. A drainage/retention aid according to Claim 32 wherein the hydrolyzed polymer has an apparent molecular weight in the range 200,000 to 2 million.

38. A drainage/retention aid according to Claim 32 wherein the hydrolyzed polymer has an apparent molecular weight in the range 300,000 to 1 million.

39. A drainage/retention aid according to Claim 32 wherein the microparticle is an inorganic particle and is selected from the group consisting of siliceous materials, alumina, bentonite, china clay, titanium, zirconium, tin, borium, calcium carbonate compounds and mixtures thereof.

40. A drainage/retention aid according to Claim 39 wherein the inorganic particle is modified with a low molecular weight, high charge density polymer.

41. A drainage/retention aid according to Claim 41 wherein the inorganic particle is bentonite.

42. A drainage/retention aid according to Claim 32 wherein the microparticle is an organic polymeric microparticle.