CA2336660A1 - The use of modified starch products as retention agents in the production of paper - Google Patents

Abstract

The invention relates to the use of modified starches as retention agents for pigments, inorganic fillers and fines in the production of paper. Said modified starches are obtained by decomposing starch, starch derivatives and/or breakdown products thereof in aqueous solution in the presence of at least one cationic polymer made up of at least 20 wt. % polymerised, protonised or quarternised dialkylaminoalkyl(meth)acrylic acid amide units and at least one inorganic mineral substance.

Description

The Use of Modified Starch Products as Retention Agents in the Production of Paper The invention relates to the use of starch or starch derivatives, which have been modified with polyelec-trolytes based on dialkylaminoalkyl(meth)acrylamides and pulped in the presence of inorganic additives, as retention agents for pigments, mineral fillers, and fibrous fines in paper manufacturing.
Pigments and fillers are added as essential paper components in the production of the paper pulp dispersion and bound using retention aids during sheet forming. Ac-cording to the statements in Wochenblatt fur Papierfabrika-tionen 5 (1991), pp. 149-154, for example, cationic bulk starches are extensively used as colloidal auxiliary agents to improve the retention, draining and strength of the paper where, in particular, by using cationic starch ethers according to Ullmann, 4th edn., 1979, Vol. 17, p. 581, the retention of pigments and fines is improved.
The retentive effect of starch ethers is limited, however, and therefore, high molecular weight, cationic polyelectrolytes having higher charge density are also used as retention agents. For example, these high molecular weight polyelectrolytes are copolymers of acrylamide and esters of (meth)acrylic acid with di(C1-C2)alkylamino-(Cz-C6)alkylalcohols or copolymers of acrylamide and amides of (meth) acrylic acid with di (C1-CZ) alkylamino (Cz-C6) alkyl-amines, each of which is present in protonated or qua-ternized form. Retention agents based on such a,(3-unsaturated N-substituted carboxylic acid amides have been described in EP-A-0,038,573.

According to WO 86/00100, a process for the produc-tion of paper is known wherein, in order to improve the re-tention, the paper pulp is added with colloidal binders ob-tained on the basis of silicic acid modified with aluminum silicate on the surface thereof and cationic or amphoteric carbohydrates, preferably such as starch or amylopectin.
EP-A-0,703,314 and WO 97/04168 suggest the use of special cationic amylopectin starches to improve the reten-tion, optionally using colloidal silicic acid, anionic polyacrylamides or bentonite.
Furthermore, microparticle systems are known as re-tention agents from Wochenblatt fur Papierfabrikationen 20, 1994, pp. 785-790, where a paper pulp dispersion initially is pretreated using cationic starch or cationic polyacryl-amides, flocculated and dispersed, and subsequently reflocculated prior to sheet forming, using silica microparticle systems or by adding bentonite or aluminum salts. The mufti-stage processing mode leads to improved retention values.
Furthermore, a process for the production of paper has been described in EP-B-0,227,465 wherein, using complex partial steps, the pulp and separately, the mineral filler as well are initially treated with a synthetic polyelectro-lyte of same charge each time and subsequently, the treated filler is subjected to a treatment using a polymer poly-electrolyte of opposite charge.
Likewise, a mufti-stage process for improving the retention is known from US-A-5,126,014, wherein the paper pulp, prior to an optional mufti-stage shear treatment, is added with calcium carbonate as filler, cationic starch, a cationic coagulant, and an anionic flocculant and, follow-ing at least one shear treatment stage, bentonite or col-loidal silicic acid are added thereto.
Also, the modification of starch products using cationic polyelectrolytes is known from prior art.
A process for the production of cationic starch is known from EP-A-0,803,512, according to which the starch in dry state is roasted with cationic polymers at temperatures of from 60 to 200°C for a period of from 10 minutes to 5 hours, to be used as paper strengthening agent.
Furthermore, the modification of starch using ionic, particularly cationic polyelectrolytes has been de-scribed in EP-B-0,282,761, WO 96/05373 and WO 96/13525. To this end, according to EP-B-0,282,761, cationic polymers of diallyldimethylammonium chloride, N-vinylamine or N-vinyl-imidazoline are heated with native potato starch or one already pulped, while according to WO 96/05373, cationic polymers are reacted with preferably anionic starch, and according to WO 96/13525, preferably hydrolyzed, cationic polymers of N-vinylformamide, polyethyleneimines or poly-alkylamines are reacted with starches of any type. These reaction products, as is the case, with starches modified with copolymers of (meth)acrylamide and dialkylaminoalkyl-(meth)acrylamide, are only recommended as dry strengthening agents for paper manufacturing.
More and more waste paper and wood pulp dispersions are being processed in paper manufacturing and therefore, the level of fines such as cellulose short fibers and min-eral fillers in the paper pulp dispersions is increasing.
Furthermore, and as a general rule, the level of inorganic fillers and pigments has to be increased further in order to obtain a paper of an appearance accepted on the market .
It is well-known, however, that the strength of paper is adversely affected with increasing levels of fines and, in particular, of mineral fillers and pigments. Thus, for ex-ample, it is evident from the publication by K. Ritter and H. Forkel, "Papierfaserstofftechnik" Symposium 1997, 21, p.
4, that the tear resistance of paper as a measure for the strength thereof decreases with increasing ash content in the paper, which is regarded as a measure for the content of mineral fillers and pigments in the paper.
It was therefore the object of the present inven-tion to improve the retention of pigments, fillers and fines in well-known paper manufacturing, preferably using waste paper, with no additional processing steps, i.e., without the partial steps mentioned above, and without ad-versely affecting the mechanical strength of the paper.
According to the invention, this is accomplished by using modified starch as retention agent for pigments, in-organic fillers and fines in paper manufacturing, said modified starch being obtained by pulping starch, starch derivatives and/or degradation products thereof in aqueous solution and in the presence of at least one cationic poly-mer constituted of at least 20 wt.-o of polymerized dial-kylaminoalkyl(meth)acrylic acid amide moieties present in protonated, preferably quaternized form, and with addition of at least one particulate additive based on an inorganic mineral substance prior to, during, or after pulping.
Native starches, such as potato starch, wheat starch, cereal flour, corn starch, tapioca starch, sago starch, as well as starches having an increased hydrolysis content, rice starch, pea starch and/or mixtures thereof, starch degradation products, particularly dextrins or oxi-dized starches such as dialdehyde starch, starch deriva-tives like chemically modified starches, particularly ani-onic starches such as carboxystarch and starch degraded by persulfate, anionic starch esters such as starch phosphoric acid mono- or diesters, starch acetates and starch cit-rates, anionic starch ethers such as carboxymethylstarch, carboxymethyl-2-hydroxyethylstarch, or carboxymethyl-3-hy-droxypropylstarch, or cationic starch derivatives such as N-containing starch ethers, particularly starches having primary or secondary amino or imino groups, and tertiary amino groups positively charged by protonation with acids, and quaternized ammonium groups are employed as starch com-ponent.
Native starches such as potato starch, wheat starch, corn starch, rice starch, pea starch, and/or mix-tures thereof, as well as anionic starches and/or cationic N-containing starch ethers are preferably used.
Homo- or copolymers of dialkylaminoalkyl(meth)-acrylic acid amides are preferably used as cationic polymers, including at least 20 wt.-o of polymerized amide moieties of (meth)acrylic acid and/or acrylic acid and preferably di (C1-CZ) alkylamino (Cz-C6) alkylamines, each one being present in protonated or quaternized form. Their production has been reported in EP-A-0,013,416 or in EP-A-0,113,038, for example, the corresponding disclosure of these publications hereby being incorporated by reference.
Preferably, these polymerized moieties are derived from protonated or quaternized N-dialkyl-substituted (meth)acrylic acid amides such as dimethylaminoethylacryl-amide or -methacrylamide, dimethylaminopropylacrylamide or -methacrylamide, diethylaminopropylacrylamide or -meth-acrylamide, diethylaminoethylacrylamide or -methacrylamide, diethylaminomethylacrylamide or -methacrylamide, as well as N',N'-dimethylamino-2,2-dimethylpropylacrylamide or -meth-acrylamide or mixtures thereof, reacted with well-known quaternizing agents. For example, dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride, preferably di-methyl sulfate or methyl chloride are possible as qua-ternizing agents.
The polyelectrolytes may include additional moie-ties of unsaturated monomers, e.g. diallyldimethylammonium chloride. These monomers incorporated by polymerization may also be water-soluble, non-ionogenic monomers such as acrylamide, methacrylamide, N-(C1-Cz)-alkylated (meth)-acrylamides, N-vinylamide, vinylformamide, N-vinylacet-amide, N-vinyl-N-methylacetamide, N-vinylpyrrolidone. In addition, suitable water-soluble monomers are N-methylol-acrylamide, N-methylolmethacrylamide, as well as N-meth-ylol(meth)acrylamides partially or completely etherified with monohydric C1-C9 alcohols .
Likewise, the copolymers may include limited amounts, preferably up to 10 wt.-o, of sparingly water-soluble and/or water-insoluble monoethylenically unsatu-rated monomers such as (meth)acrylic acid alkyl esters and vinyl acetate, as long as the solubility of the copolymers in water is retained.
The polymer products to be used according to the invention preferably have a molecular weight m.w. (g/mol) in a range of from 1.0 x 105 to 40 x 106, more preferably in a range of from 2.0 x 106 to 15 x 106, with 5.0 x 106 to 15 x 106 being particularly preferred.
The viscosity was determined using a to polymer so-lution in loo NaCl solution on a Brookfield RVT viscometer, spindle 1-3/10 r.p.m. at 20°C, indicating >10 mPa~s for the polymers being used.
Clay, preferably swellable, silicic acid, prefera-bly silicic acid sol and/or polysilicates modified with -aluminum, polyorthosilicic acid, polyorthosilicic acid modified with aluminum, bentonite, titanium dioxide, or talc are possible as particulate additives based on inorganic mineral substances, i.e., which may also consist thereof. These materials preferably are present as micro-particles or microgels. It is particularly preferred to use bentonite, talc, titanium dioxide, or silicic acid sol.
The reaction of the starch component with the cati-onic homo- or copolymers of preferably protonated or qua-ternized dialkylaminoalkyl(meth)acrylic acid amides can be effected in aqueous dispersion and in batchwise fashion in a reaction vessel, or in a continuous-flow process, e.g. in a jet boiler under heat exposure at temperatures of from 70 to 130°C, preferably 90-100°C, with addition of the inor-ganic additive and optionally under pressure, thus pulping the starch component. The reaction conditions and suitable apparatus-related conditions are in accordance with the statements in Wochenblatt fur Papier 4, 1991, pp. 127-130, the disclosure of which is hereby incorporated by refer-ence.
The addition of additives based on inorganic min-eral substances in amounts of from,0.l to 15 wt.-o, pref-erably from 3 to 15 wt.-o, more preferably from 5 to 13 wt.-%, relative to the modified starch component, in the production of these modified starch components prior to starch pulping or during starch pulping, preferably prior to the modifying reaction and pulping with the cationic homo- or copolymer, provides a retention agent having im-proved effectiveness as to the retention capacity for fill-ers and fines.
The aqueous dispersion of the starch component em-ployed in the modification and not pulped yet preferably has a content of from 0.5 to 20 wt.-%, more preferably from - g -0.5 to 10 wt.-o, and highly preferably from 2.0 to 10 wt.-o of starch component. The aqueous solution of the polyelec-trolyte used in the modification has a content of from 0.1 to 2.0 wt.-%, preferably from 0.1 to 0.5 wt.-o, and highly preferably from 0.1 to 0.3 wt.-o of cationic homo- or co-polymers. In said modification, the weight ratio of starch component to cationic polyelectrolyte ranges from 4:1 to 25:1, preferably from 10:1 to 25:1, and more preferably from 14:1 to 20:1.
The modified starch products, together with the in-organic additives, preferably in the form of an aqueous so-lution, can be used as retention agents in the production of all paper grades and cardboards. Preferably, they are suited for use in the production of paper based on sulfite or sulfate cellulose in bleached or non-bleached condition;
such a fibrous material may consist of up to 100 wt.-o of wood pulp and/or waste paper, and for this reason alone has a high level of mineral fillers, pigments and fibrous fines.
According to the invention, the retention agent of the invention is added to the aqueous paper pulp dispersion in an amount of from 0.1 to 10 wt.-o solids, preferably from 0.5 to 5 wt.-%, and more preferably from 1.0 to 3 wt.-o, relative to the dry mass or paper pulp mass, up-stream from the stock inlet of the paper machine, and pref-erably as an aqueous solution with stirring. The addition is made to the aqueous dispersion which may already contain calcium carbonate, kaolin, aluminum silicate and oxide hydrate, satin white, talc, gypsum, barite, calcium sili-cate, lithopone, and kieselguhr as fillers, as well as syn-thetic, organic fillers from the recycling material, or has been added therewith.

Advantageously, the retention agent of the inven-tion is added to the pulp dispersion in the machine chest, upstream from the vertical separator, and upstream or down-stream from the stock flow pump, prior to sheet forming.
Using the retention agent of the invention based on modified starch and inorganic additives, excellent reten-tion of the fillers is achieved and surprisingly, despite increased filler and thus, ash content of the paper, a de-terioration of the strength values is avoided. In particu-lar, this is the case when using paper pulp dispersions containing percentages of waste paper or wood material such as wood pulp and thermomechanical pulp (TMP) or consisting thereof.
It has also been determined that the use of the re-tention agent according to the invention does not interfere with the effect of optical brighteners added to improve the whiteness of the paper pulp.
The invention will be illustrated in more detail with reference to the following Examples.
Examples 1 to 4:
A In a heatable vessel, 250 g of an aqueous 4.0 wt.-o dispersion of native potato starch, product name C*Gel 30002, Co. Cerestar Holding B.V., was mixed with 250 g of a 0.25 wt.-o solution of a water-soluble cationic polymer with stirring, added with varying amounts of bentonite, respectively with addition of talc, and heated at a temperature of from 95 to 100°C. No mineral substance was added in Comparative Example 1. The mix-ture was maintained in said temperature range for 15 to 20 minutes, then cooled, and used as retention agent.

Copolymers of trimethylammoniumpropylacrylamide chlo-ride and acrylamide having a quaternized monomer per-centage of 70 wt.-o were used as water-soluble cationic polymers.
B A 4.0 wt.-o pulp suspension made of 100 wt.-o waste pa-per was diluted with water to a content of 1 wt.-o and added with stirring with the retention agent produced according to A. The retention agent was added in an amount of 2.125 wt.-o, relative to the dry content of the pulp suspension.
C Using the pulp suspension obtained according to B, test sheets having a gram weight of about 100 g/cm' were pro-duced in a laboratory using the Rapid-Kothen process in accordance with DIN 54358 on a sheet forming apparatus model 20-12 MC from the Haage company. The sheets were dried and stored overnight under normal conditions at 23°C and 50o relative humidity.
After weighing the papers, gram weight, ash content according to DIN 54373 and bursting pressure according to DIN 63141 were determined.
The overall retention indicates the ratio of the amount of dry material employed in paper manufacturing to the amount of material remaining in the final paper. This can be determined by weighing the respective amounts of ma-terial.
The ash retention indicates the ratio of the ash content of the amount of (dry) material employed in paper manufacturing to the ash content of the final paper. This is determined by determining the respective ash content.

The retention of fines indicates the ratio of the fines content in the amount of (dry) material employed in paper manufacturing to the fines content in the final pa-per.
Using a Britt Dynamic drainage jar, the respective amounts of fines are determined as follows:
An aqueous paper pulp suspension including 0.5 g of dry pa-per material, from which suspension the paper is produced (StWG), is diluted to about 1 wt.-% using tap water. This suspension is stirred at 750 r.p.m. for some seconds and then drained with stirring. The residue is added with an-other 500 ml of water, stirred, and drained. The process is repeated 4-5 times until the filtrate is completely clear, i.e., no fine fibers can be washed out anymore. The residue on the screen is placed on a tared filter and determined gravimetrically (drying at 110°C).
Calculation of fines content: Fines content = 100 - amount of coarse material (%) The amount of coarse material corresponds to the amount of fibers present on the filter.
Amount of coarse material in g Fines content = 100 -0.5 g x 1 wt.-The corresponding values from Comparative Example 1 and Examples 1 to 4 are given in Table 1.

Table 1 Comparative Example Ash content Overall retentionBursting pressure Exam les 1 to 4 wt.-% wt.-% kPa Mod. starch with 93.3 89.1 95 no min-eral substance added Mod. starch 9.7 95.3 90.7 104 Bentonite 0.3 Mod. starch 9.5 95.2 92.1 106 Bentonite 0.5 Mod. starch 9.0 97.6 96.7 92 Bentonite 1.0 Mod. starch 9.0 95.3 94.0 -Talc 1.0 Comparative Example 2 The procedures A, B and C of Examples 1 to 4 were the same, but the cationic polymer specified in A of Exam-ples 1 to 4 was tested as such as retention aid in sheet forming.
The corresponding values are given in Table 2.
Table 2 Comparative Cationic Ash contentOverall retentionBursting pressure ratio Example in copolymer(wt.-%) (wt.-%) (kPa) wt.-2* 70 0 44.8 60 * With no starch component

Claims (17)

Claims:

1. Use of modified starch as retention agent for pigments, inorganic fillers and fines in paper manufac-turing, said modified starch being obtained by pulping starch, starch derivatives and/or degradation products thereof in aqueous solution and in the presence of at least one cationic polymer constituted of at least 20 wt.-% of polymerized dialkylaminoalkyl(meth)acrylic acid amide moieties, with addition of at least one par-ticulate additive based on an inorganic mineral sub-stance prior to or during pulping.

2. The use according to claim 1, characterized in that protonated or quaternized di (C1-C2) alkylamino-(C2-C6)alkyl(meth)acrylamide moieties are present as dialkylaminoalkyl(meth)acrylic acid amide moieties.

3. The use according to claim 1 or 2, character-ized in that quaternized, polymerized moieties of di-methylaminoethylacrylamide or -methacrylamide, diethyl-aminopropylacrylamide or -methacrylamide, diethylamino-ethylacrylamide or -methacrylamide, diethylaminomethyl-acrylamide or -methacrylamide, dimethylaminopropyl-acrylamide or -methacrylamide, dimethylaminomethyl-acrylamide or -methacrylamide, N,N-dimethylamino-2,2-dimethylpropylacrylamide or -methacrylamide or mixtures there of are present as quaternized di(C1-C2)alkyl-amino(C2-C6)alkyl(meth)acrylamide moieties.

4. The use according to claim 3, characterized in that the moieties have been reacted with dimethyl sul-fate or methyl chloride as quaternizing compounds.

5. The use according to one or more of claims 1 to 4, characterized in that trimethylammoniumpropylacryl-amide chloride moieties are present as quaternized di-alkylaminoalkylacrylic acid amide moieties.

6. The use according to one or more of claims 1 to 5, characterized in that the cationic polymers include additional polymerized moieties of water-soluble, un-saturated monomers, preferably of .alpha.,.beta.-unsaturated am-ides, N-vinylamides, N-hydroxyalkylamides optionally etherified partially or completely, N-vinylpyrrolidone and/or dialkyldimethylammonium chloride.

7. The use according to claim 6, characterized in that the amide moieties are derived from acrylamide or methacrylamide, preferably from acrylamide.

8. The use according to one or more of claims 1 to 7, characterized in that the cationic polymers include up to 10 wt.-% of moieties of .alpha.,.beta.-unsaturated monomers sparingly soluble or insoluble in water, preferably of (meth)acrylic acid alkyl ester or vinyl acetate.

9. The use according to one or more of claims 1 to 8, characterized in that the cationic polymer has a mo-lecular weight m.w. (g/mol) of from 0.1 to 20 millions.

10. The use according to one or more of claims 1 to 9, characterized in that native starches, preferably potato starch, cereal flour, wheat starch, corn starch, rice starch, pea starch, and/or mixtures thereof, ani-onic starches or cationic N-containing starch ethers are used as starch.

11. The use according to one or more of claims 1 to 10, characterized in that the starch component is pulped in the presence of microparticles of at least one additive based on an inorganic mineral substance, preferably clay, silicic acid optionally modified with aluminum, polysilicates optionally modified with alumi-num, or polyorthosilicic acid, bentonite, titanium di-oxide, or talc.

12. The use according to one or more of claims 1 to 11, characterized in that the inorganic additive is em-ployed in amounts of from 0 . 1 to 15 wt.-%, relative to the modified starch component.

13. The use according to one or more of claims 1 to 12, characterized in that the weight ratio of starch component to cationic homo- or copolymer ranges from 4:1 to 25:1, preferably from 10:1 to 25:1, more pref-erably from 14 : 1 to 20: 1 when performing the modifica-tion.

14. The use according to one or more of claims 1 to 13, characterized in that the starch component has been pulped at temperatures of from 70 to 150°C, preferably from 90 to 100°C.

15. The use according to one or more of claims 1 to 14, characterized in that the retention agent is added to the paper pulp suspension prior to sheet forming.

16. The use according to one or more of claims 1 to 15, characterized in that the retention agent is added in amounts of from 0.1 to 10 wt.-%, preferably from 0.5 to 5 wt.-% solids, relative to the paper pulp.

17. The use according to one or more of claims 1 to 16, characterized in that waste paper is used in paper manufacturing.