NO841007L - PROCEDURE FOR AA IMPROVE THE RETENSION OF FILLERS AND MASS FINDS AND INCREASE THE DRAINAGE SPEED IN PAPER MAKING - Google Patents

Description

This invention relates to a method for improving the retention of fillers and pulp fines and increasing the dewatering rate for the starting material in the manufacture of paper, as well as products obtained by the method.

In general papermaking practice, a

aqueous pulp suspension or pulp slurry of cellulose fibres, produced by digesting the wood starting material, hydraulically and mechanically fed to a moving metal wire mesh or wire to produce a wet web of cellulose fibres. The wet fiber web is dewatered on the wire by draining off liquid, after which the wet web can be further treated, dried, calendered and subjected to further treatments as desired.

In normal practice, there are several additives in the starting material that is fed to the wire where the wet web is formed. These additives may include processing aids to improve the operation of the paper machine, as well as paper chemicals to improve the properties of the final paper product. Suitable processing aids may include retention aids for retention of filler additives in and on the resulting web and reduction of the loss of pulp fines from the feedstock during dewatering and drainage aids which improve the rate of feedstock dewatering on the wire. Other additives may include forming aids, flocculants, antifoam agents, additives that improve wet web strength, pitch control agents, slime control agents, creping agents, and the like, which are well known to those skilled in the art.

Functional additives may include fillers, as mentioned, gluing aids and the like. The fillers may include agents that cause optical lightness, agents that cause opacity, and pigments. Sizing agents are used to make the paper product resistant to wetting by liquids, such as printing ink, water and the like, and rosin or wax are typically used for this purpose.

To increase efficiency and facilitate the processing of wishes

one to add retention aids to the starting material before the wet web is formed, in order to neutralize or reduce negative surface charges which are normally present on

cellulose fibers and fines, and to cause co-flocculation of fillers, fibers and fines so that they stick together,

in addition to being bound by the retention agent.

A number of retention aids have been used according to the state of the art, which generally contain amine or quaternary ammonium groups, such as diethylene-triamine-adipic acid polyamide treated with epichlorohydrin, polymers of ethyleneimine and dimethyldiallylammonium chloride, and aminoethyl acrylate copolymers. From the state of the art, it is also known to use hydrated aluminum sulphate, i.e. alum, both alone and in combination with other retention agents.

Furthermore, it is known to use various polymers and copolymers of acrylamide, of ionic and non-ionic types. In particular, cationic polyacrylamides have been used

and anionic type in combination with alum. Although combinations of retention aids have been used to achieve good filler retention, for example by adding a low molecular weight cationic polymer to the pulp or starting material, followed by a high molecular weight anionic polymer, such combinations can have a detrimental effect on paper web formation by that they cause strong flocculation of the cellulose fibres, which must be compensated by agitating treatment of the starting material upstream of the step in the papermaking process in which the wet web is formed.

Likewise, a number of drainage aids have been used in papermaking to achieve increased capacity with respect to the processing speed in the papermaking process in systems where dewatering or liquid drainage is the rate-limiting step in the process.

Although it is generally desirable to maximize the retention and drainage rates in the papermaking system, the additives which have been used for this purpose to date are often prone to interact in a detrimental manner, so that their effectiveness is reduced, as the drainage and increase in retention is of the opposite nature. Many drainage and retention aids that have been used to date also show relatively little activity at lower pH.

Accordingly, it is an object of the present invention to provide an improved method and means for increasing the retention and dewatering rate of the starting material in the manufacture of paper.

According to one aspect of the invention, this relates to an additive to improve the retention of fillers and pulp fines and increase the dewatering rate of the starting material in the manufacture of paper, comprising

(a) a water-soluble copolymer containing from about 2.5

to approx. 35 mol% 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 approx. 100 mol% of repeating units derived from acrylamide, in which the weight ratio between

(a) and (b) are from approx. 8:1 to approx. 0.125:1.

According to another aspect of the invention is provided

an improved method for increasing the retention of fillers and pulp fines and increasing the dewatering rate for the starting material in the manufacture of paper, comprising adding to the starting material before it is dewatered

(a) from approx. 0.05 to 1.5 kg per tonnes of the starting material

of a water-soluble copolymer containing from approx. 2.5 to approx. 35 mol% repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid and (b) from ca. 0.05 to approx. 2.5 kg per tonnes of the starting material of a water-soluble polymer selected from the group consisting of polyacrylamide and copolymers containing from approx. 70 to approx. 100 mol% of repeating units derived from acrylamide.

The invention also relates to a paper product from the method as described in the previous section.

Detailed description of the invention

In connection with the present invention, it has surprisingly and unexpectedly been discovered that the combined use of a water-soluble copolymer containing from approx. 2.5 to approx. 35 mol% of repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid (hereinafter referred to as AMPS) and a water-soluble polymer selected from the group consisting of polyacrylamide and copolymers containing from approx. 70 to approx. 100 mol% of repeating units derived from acrylamide react synergistically, providing a higher retention rate and dewatering rate (drainage rate) than can

is achieved by any of the components used alone.

In contrast to the previously known combination additives

for improving drainage and retention, the agent according to the present invention is also relatively pH-insensitive and is very effective in both acidic and alkaline systems. Although AMPS polymers and copolymers have been proposed as drainage and retention aids in the past, for example in BRD-off.skrift 2 248 752, it has not previously been recognized that such additives could be used in combination with acrylamide polymers or - copolymers in the manner indicated according to the present invention, while obtaining for-

improved drainage and retention as achieved with the agent according to the present invention.

The agent and method according to the present invention

can advantageously be used in connection with masses of different starting materials for papermaking, such as abrasive pulp, thermal-mechanical pulps (TMP), kraft pulps and the like, and is particularly well suited for use in pulps for newsprint containing at least 40% by weight of abrasive pulp.

The AMPS copolymer used in the present invention contains from approx. 2.5 to approx. 35, preferably 5-20

and most preferably 7-15 mol% repeating units derived from AMPS. AMPS is intended herein to denote 2-acryl-amido-2-methylpropanesulfonic acid as well as suitable salts thereof. Suitable AMPS copolymers include those containing, for example, from approx. 65 to approx. 97.5 mol% of repeating units derived from acrylamide, and from approx. 3 to approx. 15 mol% of repeating units derived from acrylic acid. The AMPS copolymer preferably has a molecular weight of from approx. 2 million to approx. 20 million.

Particularly preferred copolymers may, for example, have a

Standard Brookfield viscosity, measured in a 0.20% solution

at 25°C in 0.33 M NaCl with a No. 1 spindle rotating at 60 rpm. minute, of 2-10 centipoise.

The polymeric additive used together with the AMPS copolymer is a water-soluble polymer selected from the group consisting of polyacrylamide and copolymers containing from approx. 70 to approx. 10Q mol% of repeating units derived from acrylamide. This polymer can be non-ionic or ionic in nature and is most preferably cationic. This polymer can conveniently be a cationic emulsion copolymer containing 95 mol% repeating units derived from acrylamide and 5 mol% repeating units derived from dimethylaminoethyl methacrylate quaternized with dimethyl sulfate, the copolymer being emulsified with sorbitan monooleate and containing a suitable emulsion breaking agent . Alternatively, this polymer can be a cationic copolymer of acrylamide and diallyldimethylammonium chloride containing 75-99 mol% repeating units derived from acrylamide and with a molecular weight below approx. 25,000. Other suitable polymers include aminomethylated polyacrylamide and methacrylamidopropyl-trimethylammonium chloride/acrylamide copolymers.

In the method according to the invention, from approx. 0.0 5 to approx. 1.5 kg per tonnes of starting material of the AMPS copolymer, together with from approx. 0.05 to approx. 2.5/kg/ton of the acrylamide polymer or copolymer, preferably from approx. 0.25 to approx. 1.0 kg/tonne of the AMPS copolymer and from approx. 0.25 to approx. 1.0 kg of the acrylamide polymer or copolymer. The weight ratio between the AMPS copolymer and the acrylamide polymer or copolymer added to the starting material is advantageously in the range from approx. 0.125:1 to approx. 8:1.

Although the invention as mentioned has wide application in

acidic and alkaline starting material media, the agent according to the invention is particularly effective at a pH in the range from approx. 4.0 to approx. 5.5. The agent according to the invention can, for example, be used in a starting material containing a rosin glue and alum at pH values below approx. 5. Furthermore, the agent according to the invention can be used together with conventional compounds that promote good retention and drainage, such as diallyldimethylammonium chloride polymers or copolymers and polyethyleneimine.

The following examples illustrate particular aspects of the present invention. In all examples, the percentages and parts given are by weight unless otherwise stated.

EXAMPLE I

The experiments described below were carried out on newsprint starting material with compositions as shown in Table I.

The stated values for consistency were measured by filtration

of a weighed sample of the starting material, after which the retained fiber was dried and weighed. Mobility was measured in units

ym/ second

volts/cm

at the stationary layer in a micro-electrophoresis cell. The values given for "CD" represent the cationic demand of the starting material, measured as the dosage, in kg/ton of starting material, of poly(dimethylamino/epichlorohydrin) necessary to reduce the mobility of the starting material sample to zero. The inlet box samples of the newsprint starting material described in Table I were produced on a two-wire paper machine, which normally has low first pass retention (FPR). The retention in the first pass for the machine is defined as follows:

„_._ _ Inlet box consistency - trough consistency ,.

FPR = ^ - r— ; = :— x 100%

Inlet box consistency

and is thus a measure of the efficiency of the paper machine's forming section in removing suspended material in the headbox feedstock (ie fibres, fines and fillers) from the feedstock. A high first pass retention correlates with a low recycling rate of fines and fillers in the papermaking system and better operation of the wet end of the process.

A Britt jar was used in the following experiments to measure the effect of different additives on the retention in the first passage. The conditions (agitation speed and serum size) were chosen so that the FPR obtained with the Britt jar was the same as the FPR measured on the paper machine. Thereafter, the starting material for which the Britt jar was calibrated was treated with the selected amount of starting material additive and the FPR again measured in the Britt jar.

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

Samples designated in the following table as "control" contained no polymeric additives to increase retention and/or drainage. The other samples contained specified amounts of "Polymer M" and/or "Copolymer A". Polymer M is a cationic emulsion copolymer containing 95 mol% repeating units derived from acrylamide and 5 mol% repeating units derived from dimethylaminoethyl methacrylate quaternized with dimethyl sulfate, which copolymer is emulsified with sorbitan monooleate ("Arlacel" 80, Atlas Division) of ICI Americas, Inc.) and "Alfonic" 1412-60 (Conoco Chemicals Company) as an emulsion breaking agent. Copolymer A is a copolymer according to the present invention containing 20 mol% repeating units derived from AMPS and 80 mol% repeating units derived from acrylamide.

The retention values in the first pass for the Britt jar

and the drainage measurements at the drainage pipe are indicated in table II below.

The results shown in Table II indicate that copolymer A was better than polymer M for providing a high degree of retention and drainage rate, and that the combination of polymer M and copolymer A gave a surprising and marked improvement in retention and drainage compared to each additive alone, calculated on the basis of equivalent total weight of additive. For example, the combination of 0.95 kg per tonne of polymer M and 0.55 kg per tonnes of copolymer A a retention value of 63.4%, while 1.5 kg per tonnes of polymer M gave a retention value of only 42.2%. Likewise, the use of 2.0 kg per tonnes of polymer M in combination with 1.1 kg per tonnes of copolymer A a retention of 81.2%, in comparison with 3.4 kg per tonnes of polymer M, which showed a retention value of 62% in the first pass. With regard to retention data, the combination of polymer M in an amount of 1.05 kg per ton and copolymer A in an amount of 0.57 kg per ton a drainage of 16 ml per 5 seconds, while 1.6 kg per tonnes of polymer M gave a drainage rate of only 9 ml per 5 seconds. In relation to copolymer A alone, which at a concentration of 0.85 kg per ton gave a drainage rate of 10 ml, gave equivalent weight of polymer M (0.55 kg per ton) and copolymer A (0.285

kg per tonne) a drainage rate of 12 ml per 5 seconds,

an improvement of 20%.

EXAMPLE 2

The experiments described below were carried out to determine retention values for different starting materials, including combinations of copolymer A with different co-additive polymers in varying molar ratios. Copolymer A

and polymer M were again separately compared with a control, i.e. starting material without any additive, as well as with starting materials with the following compositions: copolymer A

in combination with polymer M, weight ratio M/A of 2/1 and 1.24/1; copolymer A in combination with a cationic polyacrylamide which had been Manniched to a 70% level by reaction with formaldehyde and dimethylamine, hereinafter referred to as polymer N, in a weight ratio 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 O/A of 1.24/1; copolymer A in combination with a cationic copolymer of acrylamide and diallyldimethylammonium chloride containing 75-99 mol% repeating units derived from acrylamide with a molecular weight of less than approx. 25,000, containing 25% glyoxal for cross-linking the polymer resin, the following designated by polymer P,

at a P/A weight ratio of 1.24/1; and copolymer A in combination with a nonionic polyacrylamide containing 3% "Alfonic" 1412-60, hereinafter referred to as polymer Q, in a weight ratio Q/A of 1.8 2/1.

The starting material used in this series of experiments was newsprint starting material with the following composition: 45% by weight bleached kraft and 55% by weight of abrasive. The retention in the first passage was measured with a Britt jar for the additive compositions indicated in Table III below, where the values for the percentage retention are indicated. The two-wire paper machine for which the Britt jar was calibrated had a measured FPR value of 47.5%, which is high for newsprint due to the large amount of kraft in this feedstock.

As shown in the table, the control sample had a retention of 47.5% in the first pass, and retention levels of 80-85% were achieved using polymer M and copolymer A separately.

The use of copolymer A in combination with the polymers M,

N, O, P and Q in the manner set forth in the present invention nevertheless allowed the achievement of retention levels as high as 90-95% at relatively low additive levels,

and the compositions according to the present invention exemplify the same marked increase in retention level compared to the separate additives copolymer A and polymer M, as discussed above under example I. For example, 1 kg per tonnes of polymer M alone a retention rate of 69.4% in the first pass, while a combination of 0.57 kg per tonne of polymer M and 0.455 kg per tonnes of polymer A, representing approximately the same total weight of additive, a retention rate of 90.1 and 90.4%. Likewise, 1.0 kg per tonnes of copolymer A a retention rate of 8 0.5%, while a combination of 0.57 kg of polymer 0 per tonnes and 0.4 55 kg copolymer A per tonnes gave a retention rate of

88.4%, representing an increase of 10% for the O/A combination compared to copolymer A alone. The given data also show that for copolymer A alone, an increase in the concentration of copolymer A above approx. 0.6 kg per tonnes harmful and results in decreasing retention levels with increasing concentrations of this copolymer.

EXAMPLE III

In this example, the effect of ionic charge on the AMPS copolymer used in the material according to the present invention was investigated using samples of dry polymer. In the evaluation, copolymers of AMPS and acrylamide were used with varying concentrations of AMPS, in starting materials in which the copolymer was used alone and in combination with polymer M, as previously described, in the manner described according to the invention. The starting material used in these experiments was the same as that used in Example II, and the retention in the first passage was evaluated by means of the Britt jar test.

Reference is made to table IV. Copolymer 1 contains 5 mol% AMPS and 95 mol% acrylamide units; copolymer 2 contains

10% AMPS and 90% acrylamide units; copolymer 3 contains

15% AMPS and 85% acrylamide units; Copolymer A is as described in Example I and contains 20% AMPS and 80% acrylamide-

devices; and copolymer 4 contains 25% AMPS and 75% acrylamide units. The percentage charge on the copolymer, due to the repeating AMPS units therein, is given in Table IV, together with first pass retention values for dosages of the respective copolymers of 0.2 kg per ton, 0.4 kg per ton and 0.6 kg per ton. The respective copolymers were also used in combination with polymer M, as described above in example I, in weight ratios M/copolymer of 0.6/0.5 and 1.1/0.9.

The retention values given in Table IV clearly show the marked increase when the copolymer is used in combination with polymer ^M, compared to the use of the copolymer alone. The data further show that there is an optimum with regard to percentage charge on the copolymer, at approx. 10-20% charge, corresponding to 10-20% AMPS in the copolymer. It should be noted that over approx. 2 0% charge (20% AMPS) the degree of retention decreases with increasing charge, both for the copolymer alone and for the copolymer in combination with polymer M.

EXAMPLE IV

The same copolymers tested in Example III were tested for drainage, alone and in combination with polymer M. Data relating to these tests are given in Table V below, where the same starting material compositions

which in example III was used. The 5-second drainage volume for the control sample containing no drainage/retention additives was 22 ml. Each copolymer additive gave significant increases in drainage, which was further increased by combination with polymer M according to the present invention. As shown, polymer M alone gave only a small negative effect on the drainage rate compared to the control sample which did not contain additives.

EXAMPLE V

Retention studies were performed on a starting material

from the same paper machine as in example II, the samples of which contained different additives which are given the same designations as in the previous examples. The additive combinations also included a 70:30 acrylamide:acrylic acid copolymer containing "Alfonic" 1412-60, denoted herein by polymer R; a 16% by weight aqueous solution of poly(dialkyldimethylammonium chloride), here denoted by polymer S. The results are set out in Table VI below.

The stated retention values illustrate the significant improvement achieved with polymer M in combination with copolymer A according to the present invention, which were retention values for newsprint starting material of 96-99%. As will also be apparent from the tabled data, a combination of cationic polyacrylamide with a copolymer of acrylamide and acrylic acid (polymer M/polymer R) resulted in significantly lower retention than the combination of polymer M with copolymer A, even at significantly increased levels of polymer R in the combination with polymer M in relation to the amount of copolymer A that was used in combination with polymer M.

EXAMPLE VII

Drainage studies were carried out on the starting material for wood fiber boards, consisting of refiner-treated pine chips. This starting material contained hydrated aluminum sulfate (alum) and a pitch-rosin glue, at a pH of 4-4.5. Samples of this starting material were tested with different additives, as shown in Table VII, where the different additives are given the same designations as in the previous examples. As shown, the combinations of copolymer A with polymer S and copolymer A with polymer T gave very large increases in the drainage rate compared to polymer M or copolymer A used alone. The combination of polymer T with polymer R, on the other hand, resulted in a reduction of the drainage rate compared to the sample that did not contain drainage/retention additives.

Claims (11)

1. Method for improving the retention of fillers and pulp fines and increasing the dewatering rate for starting material in the manufacture of paper, characterized in that the starting material is added before dewatering (a) from approx. 0.05 to approx. 1.5 kg per tonnes of starting material of a water-soluble copolymer containing from approx. 2.5 to approx. 3 5 mol% repeating units derived from 2-acrylamido-2-methylpropane-sulfonic acid and (b) from approx. 0.05 to approx. 2.5 kg per tonnes of starting material of a water-soluble polymer selected from the group consisting of polyacrylamide and copolymers containing from approx. 70 to approx. 100 mol% repeating units derived from acrylamide. 2. Method according to claim 1, characterized in that from approx. 0.25 to approx. 1.0 kg of said water-soluble copolymer (a) per tonnes of starting material is added to the starting material. 3. Method according to claim 1, characterized in that from approx. 0.25 to approx. 1.5 kg of said water-soluble polymer (b) per tonnes of starting material is added to the starting material. 4. Method according to claim 1, characterized in that the weight ratio between copolymer (a) and polymer (b) added to the starting material is in the range from approx. 8:1 to approx. 0.125:1. 5. Method according to claim 1, characterized in that copolymer (a) also contains from approx. 65 to approx. 97.5 mol% repeating units derived from acrylamide, and from approx. 3 to approx. 15 mol% repeating units derived from acrylic acid. 6. Method according to claim 5, characterized in that copolymer (a) has a molecular weight of from approx. 2 million to approx. 20 million. 7. Method according to claim 5, characterized in that copolymer (a) has a viscosity (Standard Brookfield) of from approx. 2 to approx. 10 centipoise. 8. Method according to claim 1, characterized in that polymer (b) is a cationic copolymer of acrylamide and diallyldimethylammonium chloride containing 75-99 mol% repeating units derived from acrylamide and has a molecular weight less than approx. 25,000. 9. Method according to claim 1, characterized in that the pH of the starting material from the addition of copolymer (a) and polymer (b) through said dewatering is kept in the range from approx. 4.0 to approx. 5.5. 10. Paper product from the method according to claim 1. 11. Additive material to improve the retention of fillers and pulp fines and increase the dewatering rate for starting material in the manufacture of paper, characterized by (a) a water-soluble copolymer containing from approx. 2.5 to approx. 35 mol% 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 approx. 100 mol% repeating units derived from acrylamide where the molar ratio between (a) and (b) is from approx. 0.125:1 to approx. 8:1.