NO326100B1 - Process for the preparation of paper using hydrophilic dispersion polymers of diallyldimethylammonium chloride and acrylamide as retention and dewatering agents - Google Patents

Description

The invention relates generally to the field of papermaking and, more particularly, to a method for improved retention and drainage performance in a papermaking process using hydrophilic dispersion copolymers of diallyl-N,N-disubstituted ammonium halide and (meth)acrylamide as retention- and dewatering agents.

Background for the invention

In the production of paper, an aqueous cellulose suspension or slurry is formed into a sheet of paper. The cellulose slurry is usually diluted to a consistency (percent dry weight of solids in a slurry) of less than 1%, and often less than 0.5%, ahead of the paper machine, while the finished sheet must have less than 6% water by weight. Thereby the dewatering aspect of the manufacture of paper is extremely important to the efficiency and cost of manufacture.

The least expensive dewatering method is drainage, and then more expensive methods are used, including vacuum pressing, felt blanket removal and pressing, evaporation and the like, and any combination of such methods. Because drainage is both the first dewatering method used and the least expensive, improvements in the efficiency of drainage will reduce the amount of water required to be removed by other methods and improve the overall efficiency of dewatering, thereby reducing its costs.

Another aspect of papermaking that is extremely important to the efficiency and cost of manufacture is the retention of pulp components on and within the fiber mat formed during papermaking. A paper pulp contains particles ranging in size from about 2 to 3 mm the size of cellulose fibers to fillers measuring only a few microns. Within this range are cellulose fillers, mineral fillers (used to increase opacity, brightness and other paper characteristics) and other small particles that would normally, without the inclusion of one or more retention agents, pass through the openings (pores) between the cellulose fibers in the resulting fiber mat .

One method to improve the retention of cellulose fines, mineral filler and other pulp components on the fiber mat is to use a coagulant/flocculant system, which is added at the front of the paper machine. In such a system, a coagulant such as a low molecular weight, cationic synthetic polymer or a cationic starch is first added to the pulp. The coagulant usually reduces the negative surface tension present on the particles in the pulp, especially cellulose fines and mineral filler, and thereby agglomerates such particles. The coagulant is followed by the addition of a flocculant. The flocculant is usually a high molecular weight cationic or anionic synthetic polymer that bridges the particles and/or agglomerates from one surface to another, thereby binding the particles into large agglomerates. The presence of such large agglomerates in the pulp increases retention. The agglomerates are filtered out of the water in the fiber net, where unagglomerated particles would otherwise pass.

Although a flocculated agglomerate does not usually affect the drainage of the fiber mat to the extent that would occur if the mass became gel-like or contained gelatinous material, when such flocculations are filtered by the fiber net, the pores thereof are reduced, thereby reducing the drainage efficiency. This increases retention at the expense of a reduction in drainage.

Systems, such as those described in U.S. Pat. Patent Nos. 4,753,710 and 4,913,775, have been used to provide an improved combination of retention and dewatering. Briefly, these patents call for first adding to the aqueous cellulosic paper use suspension a high molecular weight linear cationic polymer prior to shearing the suspension, followed by the addition of bentonite after shearing. The cutting is usually provided by one or more of the cleaning, mixing and pumping steps of the papermaking process. The cutting breaks down the large flocs formed by high molecular weight polymers into micro flocs, and further agglomeration follows with the addition of bentonite clay particles.

Another system, described in the U.S. patent no. 4,388,150 uses the combination of cationic starch followed by colloidal silica to increase the amount of material retained on the mat by charge neutralization and adsorption of smaller agglomerates.

U.S. Patent Nos. 5,098,520 and 5,185,062 describe methods for improving dewatering in the papermaking process.

U.S. patent no. 5,266,164 describes a method for improving the retention of mineral fillers and cellulose fibers on a cellulose fiber sheet.

EP-A2-0760406 describes a method for minimizing particle deposits of pitch, ink and sticky materials in the papermaking process by the retention of such particles on top of fiber.

CA-A1-2102742 describes a process for improving retention and/or drainage in papermaking by adding diallyldimethylammonium chloride (DADMAC)/acrylamide copolymer to a fiber suspension.

Despite these prior systems, there is still a need for new methods using hydrophilic dispersion polymers to improve retention and dewatering performance, especially without the undesirable addition of oils and surfactants contained in the conventional latex polymers. As used herein, "latex" is defined to mean an inverse water-in-oil emulsion polymer. There is also a need for dispersion polymers that do not require an inverter system and that can be introduced into the papermaking process using simple dosing equipment.

Summary of the invention

The process of the invention requires forming an aqueous cellulose slurry for papermaking, adding an effective amount of a hydrophilic dispersion polymer to the slurry, draining the slurry to form a sheet, and drying the sheet.

More specifically, the present invention provides a method for improved retention and drainage performance in a papermaking process comprising the steps of: a) forming an aqueous cellulose slurry for papermaking; b) adding from 0.02-2.3 kg of a hydrophilic dispersion polymer per 907 kg of slurry solids to the slurry, wherein the hydrophilic dispersion polymer has a cationic charge of from 1 mole percent to 50 mole percent, an intrinsic viscosity of from 0.5 to 10 deciliters per gram and which results from the polymerization of: i) a cationic monomer diallyl-N,N-disubstituted ammonium halide in which the substituents of the disubstituted ammonium halide are selected from the group consisting of C1-C20 alkyl groups, aryl groups, alkylaryl groups and arylalkyl groups,

ii) a second monomer of the formula

wherein R 1 and R 2 are selected from the group consisting of hydrogen, C 1 -C 10 alkyl groups, aryl groups and alkylaryl groups; R3 is selected from the group consisting of hydrogen and methyl groups and R4 and R5 are selected from the group consisting of C1-C10 straight chain or branched alkylene groups and hydrogen, in an aqueous solution of a polyvalent anionic salt, wherein the polymerization is carried out in the presence of a dispersant ;

c) draining the slurry to form a sheet; and

d) drying the sheet.

This method improves retention and dewatering performance without the unwanted addition of oils and surfactants. Furthermore, the hydrophilic dispersion polymers used in the present invention do not require an inversion system and can be added to the papermaking process using simple dosing equipment.

Detailed description of the invention

As stated above, the present invention is directed to a method for improved retention and drainage performance in a process for making paper comprising forming an aqueous cellulose slurry for making paper, adding a hydrophilic dispersion polymer to the slurry, and draining the slurry to form a sheet and then to dry the sheet.

The hydrophilic dispersion polymer of the invention is a copolymer of diallyl-N,N-disubstituted ammonium halide cationic monomer and (meth)acrylamide. A preferred copolymer is formed from diallyldimethylammonium chloride (DADMAC) and acrylamide (AcAm). It has been found that the polymer described above provides advantages for use in a papermaking process. In particular, the hydrophilic dispersion polymers of the invention show improved or equal activity in terms of retention and dewatering performance without the undesirable addition of oils and surfactants compared to conventional cationic latex polymers. In addition, these polymers do not require an inverter system and can be introduced into the papermaking process using simple dosing equipment.

Another advantage relates to the method of adding the dispersion polymers. In most cases, conventional water-soluble polymers are now commercially available in powder form. Before use, the polymeric powder must be dissolved in an aqueous medium for the application in question. The polymer swells in an aqueous medium, and the dispersed particles flocculate.

It is typically very difficult to dissolve the conventional polymers in an aqueous medium. In contrast, the dispersion polymers of this invention by this nature avoid dissolution-related problems.

Furthermore, the dispersion copolymers formed from DADMAC and AcAm have the advantageous flexibility in that they can be used either as the only polymeric treatment, or as a component in a conventional dual polymer program that requires both a conventional coagulant and a flocculant.

The dispersion copolymers of the present invention, if required in the form of an aqueous solution resulting from dilution with water, can be advantageously used in a number of technological fields such as flocculants, thickeners, soil improvers, adhesives, food additives, dispersants, cleaning agents, additives for medicines or cosmetics.

The monomers

Example 1 outlines the process for preparing copolymers at various ratios of the monomer components in the range of from about 1:99 to about 99:1 of acrylamide type monomer to diallyl-N,N-disubstituted ammonium halide. Each of the two types of monomers used to form the dispersion polymers of this invention will be described below in greater detail.

In the case of the diallyl-N,N-disubstituted ammonium halide, the disubstituents of the monomer may be C1-C20 alkyl groups, aryl groups, alkylaryl groups or arylalkyl groups. Furthermore, each of the disubstituents can be a different group. For example, an intended halide is N-methyl-N-ethyl-N,N-diallyl-ammonium chloride.

A specific example of a useful halide is DADMAC. Preferably, the amount of DADMAC present in the copolymer is from about 5 mol% to about 30 mol%. Diallyl-N,N-disubstituted-ammonium halides, particularly DADMAC are well known and commercially available from a variety of sources. In addition to chloride, the counterion can also be bromide, sulphate, phosphate, monohydrogen phosphate and nitrate, among others. A method for the production of DADMAC is described in US patent no. 4,151,202.

In the case of acrylamide type monomers, substituted (meth)acrylamide monomers can have either straight chains or branched alkyl groups. Useful monomers include, but are not limited to, ethylhexyl(meth)acrylamide, diethylaminopropyl(meth)acrylamide, dimethylaminohydroxypropyl-(meth)acrylamide, N-isopropyl(meth)acrylamide, N-tert-butyl-(meth)acrylamide, C1-C10 N-alkylacrylamide, C1-C10 N-alkylmethacrylamide, N-arylacrylamide, N-arylmethacrylamide, N-arylalkylacrylamide, N-isopropyl(meth)acrylamide, N,N-dimethylacrylamide (meth)acrylamide, C1-C10 N,N-dialkylacrylamide, C1-C10 N,N-dialkylmethacrylamide, N,N-diarylacrylamide, N,N-diarylmethacrylamide, N,N-diallylalkylacrylamide and N,N-diarylalkylmethacrylamide. As used herein, the term "arylalkyl" is intended to include benzyl groups and phenethyl groups. Pendant amine refers to an NH2 group attached to the main polymer chain.

The polyvalent anionic salts

A polyvalent anionic salt is contained in an aqueous solution. According to the present invention, the polyvalent anionic salt is conveniently sulfate, a phosphate or a mixture thereof. Preferred salts include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogen phosphate, sodium hydrogen phosphate and potassium hydrogen phosphate. In the present invention, each of these salts can be used as an aqueous solution thereof with a concentration of 15% or more.

The dispersion medium

A dispersion polymer is present in an aqueous anionic salt solution in which the polymerization of the above-mentioned monomers takes place. The dispersion polymer is a water-soluble high molecular weight cationic polymer, and is preferably soluble in the above-mentioned aqueous salt solutions. It is preferred that the dispersion polymer is used in an amount of from about 1 to 10% by weight based on the total weight of the hydrophilic dispersion polymer.

The dispersion polymer consists of 20 mol% or more of cationic monomer units of diallyl disubstituted ammonium alide or N,N-dialkylaminoethyl (meth)acrylates and their tetravalent salts. Preferably, the residual mol% is AcAm or (meth)AcAm. The performance of the dispersant is not greatly affected by molecular weight. In contrast, the molecular weight of the dispersant is preferably in the range of approximately 10,000 to 10,000,000. Preferred dispersants include homopolymers of diallyl dimethyl ammonium chloride, dimethyl aminoethyl acrylate methyl chloride quaternary salt and dimethyl aminoethyl methacrylate methyl chloride quaternary salt.

According to one embodiment of the invention, a multifunctional alcohol such as glycerine or polyethylene glycol coexists in the polymerization system. The deposition of fine particles is easily carried out in the presence of these alcohols. Furthermore, polysaccharides, such as starch, dextran, carbo-methoxycellulose and pullulan, among others, can also be used as stabilizers either alone or in conjunction with other organic cationic flocculants.

The dispersion polymers

For the polymerizations, a common water-soluble radical agent can be used, but preferably water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane) hydrochloride and 2,2'-azobis(N,N'-dimethylisobutylamine) hydrochloride are used .

According to one embodiment of the invention, a

graft polymer before the start of the polymerization of the above-mentioned monomers with the intention of obtaining a fine dispersion. The graft polymer is a water-soluble cationic polymer, insoluble in the aqueous solution of the polyvalent anion salt.

The graft polymer is preferably a polymer produced from the above-mentioned monomer mixtures by the method described herein. Even so, the monomer composition of the graft polymer need not always be the same as the water-soluble cationic polymer formed during polymerization. In contrast, as the water-soluble polymer formed during polymerization, the graft polymer should contain at least mol% of cationic monomer units of diallylmethyl ammonium halide. According to one embodiment of the invention, the graft polymer used in a polymerization reaction is a water-soluble polymer produced in a previous reaction that used the same monomer mixture.

The procedure

An aqueous cellulose slurry is first formed by any conventional method commonly known to those skilled in the art. A hydrophilic dispersion polymer is then added to the slurry.

The hydrophilic dispersion polymer is formed by the polymerization of

1) a cationic monomer diallyl-N,N-disubstituted

ammonium halide wherein the substituents of the disubstituted ammonium halide are selected from the group consisting of C1-C20 alkyl groups, aryl groups, alkylaryl groups and arylalkyl groups,

2) a second monomer with the formula

wherein R 1 and R 2 are selected from the group consisting of hydrogen, C 1 -C 10 alkyl groups, aryl groups and alkyl-aryl groups; R3 is selected from the group consisting of hydrogen and methyl groups and R4 and R5 are selected from the group consisting of C1-C10 straight chain or branched alkylene groups and hydrogen, in an aqueous solution of a polyvalent anionic salt, wherein the polymerization is carried out in the presence of a dispersant .

The papermaking cellulose slurry is then drained to form a sheet and then dried. The steps of draining and drying may be carried out in any conventional manner commonly known to those skilled in the art. The cationic monomer can be DADMAC and the other monomer can be AcAm. The hydrophilic dispersion polymer can have a cationic charge of from about 1 mol% to about 50 mol%.

In addition, conventional coagulants, conventional flocculants, alum, cationic starch or a combination thereof can also be used as accessories with dispersion polymers, although it must be emphasized that the dispersion polymer does not need any accessories for effective retention and drainage activity.

Furthermore, the range of intrinsic viscosities of the hydrophilic dispersion polymers of the invention is from about 0.5 to about 10 dl/g, preferably from about 1.5 to about 8.5 dl/g and most advantageously from about 2.5 to about 7, 5 dl/g. Depending on the conditions at the individual factory, the preferred dosage is from about 0.02 to about 2.3 kg of active substance per 907 kg of slurry solids.

EXAMPLES

The following examples are intended to be illustrative of the present invention and to teach a person skilled in the art how to make and manufacture the invention.

Example 1

A dispersion copolymer of 30 mol% diallyldimethylammonium chloride and acrylamide was synthesized as follows. 25.667 g of a 49.0% solution of acrylamide (0.1769 mol), 161.29 g of a 62.0% solution of DADMAC (0.6192 mol), 200 g of ammonium sulfate, 40 g of sodium sulfate, 303, 85 g of deionized water, 0.38 g of sodium formate, 45 g of a 20% solution of poly(DMAEA.MCQ) (dimethylaminoethyl acrylate methyl chloride tetravalent salt, IV = 2.0 dl/gm) and 0.2 g of EDTA was added to a two liter resin reactor equipped with a stirrer, temperature control, and water-cooled condenser. The mixture was heated to 48°C and 2.50 g of a 4% solution of 2,2-azo-bis(2-amidinopropane)dihydrochloride and 2.50 g of a 4% solution of 2,2-azobis( N,N'-dimethylisobutryramidine) and 2.50 g of a 4% solution of 2,2'-azobis(N,N'-dimethylisobutryramidine) dihydrochloride were added. The resulting mixture was aerated with 1000 cc/min of nitrogen. After 15 minutes, polymerization began and the solution became viscous. During the next 4 hours the temperature was maintained at 50°C and a solution containing 178.42 g of 49.0 AcAm (1.230 mol) and 0.2 g of EDTA was pumped into the reactor using a syringe pump. The resulting polymer dispersion had a Brookfield viscosity of 4200 eps. The dispersion was then further reacted for 2.5 hours and at a temperature of 55°C. The resulting polymer dispersion had a Brookfield viscosity of 3300 eps. 10 g of 99% adipic acid, 10 g of ammonium sulfate and 12.5 g of a 60% aqueous solution of ammonium thiosulfate were added to the polymer dispersion. The resulting dispersion had a Brookfield viscosity of 1312.5 eps and contained 20% of a 50% by weight copolymer of DADMAC and AcAm with an intrinsic viscosity of 6.32 dl/gm in 1.0 molar NaNO 3 .

The polymers used in this invention and their respective descriptions are summarized in Table 1.

Example 2

To determine the activity of the hydrophilic dispersion polymers synthesized according to Example 1, the following procedure was used. The vacuum drainage tester (VDT) was used to evaluate the drainage performance. Thin stock for the VDT tests was obtained from a Southern linerboard papermill at a sampling point just before the basesheet inlet box. Because no retention/drainage aids were used on the paper machine, the pulp was tested as is.

The pulp was processed in a Britt jar stirrer at 1000 rpm. The VDT tests were conducted by the normal procedure of transferring the treated pulp to the VDT chamber, then filtering under 15 in. Hg (7.84 psi) vacuum through Filpaco No. 716 paper. The test conditions are given in Table II. The drainage rates are expressed in terms of the time it took to collect 100 ml filtered volumes.

Cationic polymer programs showed activity with the basesheet pulp in relation to untreated sample (Blank). Table III shows VDT drainage data for polymers listed in Table I. A lower drainage time (for a constant volume of 100 ml) indicates a higher drainage rate. Therefore, the higher the drainage rate, the more effective the treatment. The results in Table III demonstrate that the hydrophilic DADMAC/AcAm dispersion polymer (Dispersion I) is superior to conventional treatments. Furthermore, the drainage performance of Dispersion I was better than its latex analogue, Polymer I. In addition, the turbidity of the filtrate obtained with Dispersion I was clearly clearer than the other polymers tested, suggesting better retention.

Example 3

A series of VDT drainage experiments were conducted using the hydrophilic dispersion DADMAC/AcAm polymer (Dispersion I) with pulp obtained from a Midwestern boxboard papermill. The mass was processed in a Britt jar stirrer at 1000 rpm. The VDT tests were performed by the normal procedure of transferring the treated pulp to the VDT chamber, then filtering under 15 in. Hg (7.84 psi) vacuum through Filpaco No. 716 paper. The test conditions are shown in Table IV.

The results are summarized in Table V. The drainage rates are expressed in terms of time taken to collect 400 ml filtrate volumes. A lower drain time to collect a constant volume of 400 ml indicates better performance. The data in Table V show the flexibility of the hydrophilic dispersion polymer in that it can be used either as the only polymeric treatment (flocculant) or as a coagulant in a dual program with conventional flocculants (Polymer Q, Polymer N).

Claims (8)

1. A method for improved retention and drainage performance in a paper making process comprising the steps of: a) forming an aqueous cellulose slurry for making paper; b) adding from 0.02-2.3 kg of a hydrophilic dispersion polymer per 907 kg of slurry solids to the slurry, wherein the hydrophilic dispersion polymer has a cationic charge of from 1 mole percent to 50 mole percent, an intrinsic viscosity of from 0.5 to 10 deciliters per gram and which results from the polymerization of: i) a cationic monomer diallyl-N,N-disubstituted ammonium halide in which the substituents of the disubstituted ammonium halide are selected from the group consisting of C1-C20 alkyl groups, aryl groups, alkylaryl groups and arylalkyl groups, ii) a second monomer with the formula wherein R 1 and R 2 are selected from the group consisting of hydrogen, C 1 -C 10 alkyl groups, aryl groups and alkylaryl groups; R3 is selected from the group consisting of hydrogen and methyl groups and R4 and R5 are selected from the group consisting of C1-C10 straight chain or branched alkylene groups and hydrogen, in an aqueous solution of a polyvalent anionic salt, wherein the polymerization is carried out in the presence of a dispersant ; c) draining the slurry to form a sheet; and d) drying the sheet. 2. Process according to claim 1, characterized in that the cationic monomer is diallyldimethylammonium chloride and the other monomer is acrylamide. 3. Method according to claim 1 or 2, characterized in that the hydrophilic dispersion polymer has an intrinsic viscosity of from 1.5 to 8.5 deciliters per gram. 4. Method according to claim 3, characterized in that the hydrophilic dispersion polymer has an intrinsic viscosity of from 2.5 to 7.5 deciliters per gram. 5. Method according to any one of claims 1-4, characterized in that it further comprises the addition of a coagulant in step b). 6. Method according to any one of claims 1-5, characterized in that it further comprises the addition of a flocculant in step b). 7. Method according to any one of claims 1-6, characterized in that it further comprises the addition of alum in step b). 8. Method according to any one of claims 1-7, characterized in that it comprises the addition of a cationic starch in step b).