KR20090023579A - Sizing of paper - Google Patents

Abstract

The present invention relates to a process for the production of paper which comprises: (a) providing an aqueous cellulosic suspension; (b) separately adding to the suspension: (i) a nitrogen-containing organic compound having a molecular weight less than 1,000; and (ii) a cellulose-reactive sizing agent; and (c) dewatering the obtained suspension to form paper. The invention further relates to a process in which a nitrogen-containing organic compound having a molecular weight less than 1,000 is mixed with an aqueous dispersion of a cellulose-reactive sizing agent to form a pre-mix and which premix is added to the suspension.

Description

Sizing method of paper {SIZING OF PAPER}

The present invention relates to a method of sizing paper and paper board.

Cellulose-reactive sizing agents based on, for example, alkyl ketene dimers (AKDs) and alkenyl succinic anhydrides (ASAs) produce paper at the pH of a neutral or slightly alkaline raw material to produce water and Widely used to provide some resistance to the permeability of aqueous liquids. Paper sizes based on cellulose-reactive sizing agents are provided in the form of a dispersion comprising an aqueous phase and are finely separated into particles or particles of the sizing agent dispersed therein.

Cellulose-reactive sizing agents generally provide a good sizing effect using a small amount of sizing agent when added to an aqueous cellulose suspension. The sizing effect begins to develop in the drying section of the paper machine. However, since most paper machines operate at maximum speed to optimize paper production, the time in the dryer section was not long enough to produce paper sized in the paper machine. Instead, the paper is allowed to cure for up to 24 hours before fully sized product is achieved. The slow development of sizing effects creates a number of problems. First, subsequent work, such as printing, coating, pasting, and the like, can be difficult to handle. Second, many paper manufacturers overload sizing agents to ensure that full size products are achieved. As a result, problems related to deposits in paper machine components usually arise.

WO 9710387 discloses a paper sizing enhancer which is a polymerization reaction product of quaternary diallyl ammonium monomers and diallyl ammonium monomers. The polymerization product has a molecular weight of at least 10,000. In WO 9710387 the paper sizing enhancer can be fed separately with the paper sizing agent to the paper supply during the papermaking process or as an aqueous medium comprising both components.

WO 02081587 describes sizing dispersants comprising sizing agents and nonionic surface active monoesters of fatty acids and glycerol.

It is an object of the present invention to provide a paper making method with improved initial sizing in a machine. It is also an object of the present invention to provide faster curing times for sizing agents. Additional purposes will appear later.

Summary of the Invention

The present invention relates to a method for producing paper,

The method is

(a) preparing an aqueous cellulose suspension;

(b) in the suspension,

    (i) nitrogen-containing organic compounds having a molecular weight of 1,000 or less; And

    (ii) adding cellulose-reactive sizing agents individually; And

(c) dehydrating the suspension obtained to form a paper.

In addition, the present invention relates to a method for producing paper,

The method is

(a) preparing a cellulose suspension;

(b) mixing a nitrogen-containing organic compound having a molecular weight of 1,000 or less with an aqueous dispersion of cellulose-reactive sizing agent to form a pre-mix;

(c) adding the premix to the suspension; And

(d) dehydrating the suspension obtained to form a paper.

According to the present invention surprisingly improved initial sizing in the papermaking process, such as the rapid sizing effect of paper sizing or rapid cure, can be applied to cellulose suspensions with nitrogen-containing organic compounds and cellulose-reactive sizing agents having a molecular weight of 1,000 or less. It has been found that this can be achieved by adding them individually. It has also been found that improved initial sizing can be achieved by adding an aqueous dispersion of cellulose-reactive sizing and premix of nitrogen-containing organic compounds to the suspension. Rapid curing provides rapid feedback in the sized product and can minimize the risk of excessive supply of sizing agent that can result in fewer deposits in the paper machine. By this, improved runnability of the paper machine can be achieved. Faster curing times will require less storage space for the paper roll to be cured. Therefore, the present invention provides a substantial economic and technical advantage.

The nitrogen-containing organic compound according to the invention can be selected from primary amines, secondary amines, tertiary amines, quaternary amines, also called quaternary ammonium compounds. Nitrogen-containing compounds are preferably water-soluble or water-dispersible, and are aromatics (eg, comprising at least one aromatic group) or aliphatic; Aliphatic nitrogen-containing water-dispersible organic compounds are usually preferred. Nitrogen-containing organic compounds may be uncharged or cationic. Suitable nitrogen-containing organic compounds include acid addition salts of primary, secondary and tertiary amines, preferably quaternary ammonium compounds. The nitrogen-containing organic compound may have one or more oxygen-containing substituents, such as oxygen in the form of hydroxyl groups and / or alkyloxy groups. Examples of preferred substituents of this type include hydroxyl groups such as ethanol groups, and methoxy groups and ethoxy groups. The nitrogen-containing organic compound may comprise one or more nitrogen atoms, preferably one or two nitrogen atoms. The nitrogen-containing organic compound has a molecular weight of 1,000 or less, suitably 900 or 800 or less, preferably 750 or 600 or less. Usually, the molecular weight of the nitrogen-containing organic compound is at least 250, preferably at least 330.

Examples of suitable nitrogen-containing organic compounds include compounds prepared by reacting primary, secondary or tertiary amines with methyl chloride, dimethyl sulfate and benzyl chloride. Examples of suitable quaternary ammonium compounds of the general formula R ₄ N ⁺ X ^- comprises a compound having, each R group is independently (i) hydrogen; (ii) a hydrocarbon group having about 1-30 carbon atoms, preferably 1-22 carbon atoms, suitably an aliphatic group, preferably an alkyl group; And (iii) groups having up to about 30 carbon atoms, preferably 4-22 carbon atoms and comprising one or more heteroatoms such as oxygen or nitrogen, and / or heteroatoms (eg, carbonyl and acryloxy groups Is selected from a hydrocarbon group, suitably an aliphatic group, preferably an alkyl group, intercalated by; At least one, suitably at least three, preferably all of said R groups comprise carbon atoms; Suitably at least one, preferably at least two of said R groups comprise at least seven carbon atoms, preferably at least nine carbon atoms, most preferably at least twelve carbon atoms; X ⁻ is an anion, typically a halide such as chloride. It is preferable that the nitrogen-containing organic compound of the present invention is substantially free of silica-based particles.

Examples of suitable primary amines such as amines with one organic substituent include alkylamines such as propylamine, butylamine, cyclohexylamine, alkanolamines such as ethanolamine, and alkoxyalkylamines such as 2-methoxyethylamine It includes. Examples of suitable secondary amines, such as amines with two organic substituents, include dialkylamines such as diethylamine, dipropylamine and di-isopropylamine, dialkanolamines such as diethanolamine and pyrrolidine . Examples of suitable quaternary amines, such as amines having three organic substituents, are trialkylamines such as triethylamine, trialkanolamines such as triethanolamine, N, N-dialkylalkanolamines such as N, N-dimethyl Ethanolamine. Examples of suitable quaternary ammonium compounds include methyl bis [ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulfate, dioctyldimethylammonium chloride, didecyldimethylammonium chloride, dicodimethylammonium chloride, cocobenzyldimethylammonium Chloride, coco (fractionated) benzyldimethylammonium chloride, octadecyl trimethylammonium chloride, dioctadecyl dimethylammonium chloride, dihexadecyl dimethylammonium chloride, di (hydrogenated tallow) dimethylammonium chloride, di (hydrogenated tallow) -benzyl Methylammonium chloride, di (hydrogenated tallow fatty acid-2-hydroxyethyl ester) dimethyl ammonium chloride, (hydrogen tallow) benzyldimethylammonium chloride, dioleyldimethylammonium chloride, di (ethylene hexadecanecarboxylate) dimethylammonium chloride , (Vegetable oil) benzyl-dimethyl Monium chloride, (dodecyl) benzyldimethylammonium chloride and quaternary imidazole derivatives. Examples of suitable diamines include aminoalkylalkanolamines such as aminoethylethanolamine, piperazine and nitrogen-substituted piperazine having 1 or 2 lower alkyl groups of 1-4 carbon atoms. Examples of suitable imidazoline derivatives include quaternary imidazolinium compounds, such as 2- (C17 and C17 unsaturated alkyl) -1- [2- (C18 and C18-unsaturated amido) ethyl] -4,5-dihydro -1-methyl, methyl sulfate. Examples of preferred nitrogen-containing organic compounds include methyl bis [ethyl (tallowate)]-2-hydroxyethylammonium methyl sulfate, di (hydrogenated tallow) dimethylammonium chloride, di (hydrogenated tallow fatty acid-2-hydroxy Ethyl ester) dimethyl ammonium chloride, didecyldimethylammonium chloride, (vegetable oil) benzyl-dimethylammonium chloride and (dodecyl) benzyl-dimethylammonium chloride.

Cellulose-reactive sizing agents consist of hydrophobic ketene dimers, ketene multimers, acid anhydrides, organic isocyanates and mixtures thereof, preferably ketene dimers, ketene multimers and acid anhydrides, most preferably ketene dimers. Can be selected from the group. Suitable ketene dimers have the general formula (I): wherein R ¹ and R ² are saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbons (the hydrocarbon groups have 8-36 carbon atoms, usually 12-20 carbon atoms) Linear or branched alkyl groups such as hexadecyl group and octadecyl group). Suitable acid anhydrides are characterized by the following formula II, wherein R ³ and R ⁴ may be the same or different and represent a saturated or unsaturated hydrocarbon group containing 8-30 carbon atoms, or R ³ and R ⁴ May form a 5- to 6-membered ring with the —COC— component and optionally be further substituted with a hydrocarbon group containing up to 30 carbon atoms. Examples of acid anhydrides used commercially include alkyl and alkenyl succinic anhydrides, in particular isooctadecenyl succinic anhydride.

Suitable ketene dimers, acid anhydrides and organic isocyanates include the compounds described in US Pat. No. 4,522,686, which is incorporated herein by reference.

Dispersions of the invention include dispersants or dispersant systems comprising at least one dispersant and a protective colloid. The dispersant and protective colloid are selected from the group consisting of anionic, nonionic, cationic and amphoteric compounds, which can act individually or together as a dispersant or dispersant system for cellulose-reactive sizing agents. Dispersants according to the invention may have a content of cellulose-reactive sizing agent from about 0.1% to about 30% by weight. The content of cellulose-reactive sizing agent is suitably in the range 5-25% by weight, preferably 8-20% by weight.

Dispersants and protective colloids may be those conventionally used in the preparation of aqueous sizing dispersants or emulsions. These can be selected for example from saponified rosin derivatives, alkyl sulfates, alkylaryl sulfates, alkyl sulfonates, alkylaryl sulfonates and the like. Particularly suitable anionic dispersants are alkyl sulfates and alkyl sulfonates, for example sodium lauryl sulfate, as well as sodium lignosulfonate and sodium naphthalene sulfonate. Examples of suitable protective colloids include water-soluble cellulose-derivatives such as hydroxyethyl- and hydroxypropyl-, methylhydroxypropyl- and ethylhydroxyethylcellulose, methyl- and carboxymethylcellulose, gelatin, starch, guar Gums, xanthan gum, polyvinyl alcohol and the like. Examples of suitable nonionic dispersants may be selected, for example, from fatty alcohols, ethoxylated fatty alcohols, fatty acids, alkyl phenols or fatty acid amides, ethoxylated or nonethoxylated glycerol esters, sorbitan esters of fatty acids and the like. Examples of suitable cationic dispersants and protective colloids include water-soluble nitrogen-containing epichlorohydrin resins, cationic starches and the like. The dispersant may also comprise other additives, such as preservatives. Suitably, the amount of dispersant is at least 0.5% by weight based on the amount of sizing agent. Usually, it is not necessary to use more than 10% by weight.

The nitrogen-containing organic compounds and cellulose-reactive sizing agents of the present invention may be added separately to the cellulose suspension in any order. The nitrogen-containing organic compound may be added separately before, simultaneously with, or after the addition of the cellulose-reactive sizing agent, preferably before the addition of the cellulose-reactive sizing agent.

Aqueous dispersions of nitrogen-containing organic compounds and cellulose-reactive sizing agents (herein referred to as sizing dispersions) may be added to the cellulose suspension as a premix. In this embodiment, the nitrogen-containing organic compound and the sizing dispersion are mixed to form a premix and added to the cellulose suspension. Said mixing may be effected by contacting them at some point before adding the nitrogen-containing organic compound, suitably its aqueous phase, preferably its aqueous stream, and its sizing dispersion, preferably its aqueous stream.

The aqueous phase or stream obtained is then introduced into the cellulose suspension. Preferably, the contact time, for example the time from mixing the nitrogen-containing organic compound and the sizing dispersion until adding the formed premix to the cellulose suspension is short. The period may be about 20 minutes or less, suitably 4 minutes or less, preferably 2 minutes or less.

 Mixing the aqueous streams of the nitrogen-containing organic compound and the sizing dispersion can be carried out by mixing the individual streams with respect to each other, contacting them with each other and introducing the formed premix stream into the cellulose suspension. Suitably, mixing is carried out under vigorous flow conditions, which promotes the streams to be mixed more intensively and quickly. The stream can be mixed by means of a mixing device having at least two inlets through which the individual streams to be mixed are fed and at least one outlet through which the obtained premix passes and which can subsequently be introduced into the cellulose suspension. Such stream mixing embodiments are beneficial in practical terms and provide advantages in operation.

Nitrogen-containing organic compounds and cellulose-reactive sizing agents may be added to the cellulose suspension at any location, for example anywhere between the machine chest and the headbox.

Nitrogen-containing organic compounds and cellulose-reactive sizing agents can be added to the cellulose suspension in amounts that can vary within a wide range, the feed amount being determined for the determination of the pulp or paper to be sized, the cellulose-reactive sizing agent used and the desired It depends mainly on the sizing level. The nitrogen-containing organic compound is added to the cellulose suspension in an amount of 0.005-0.5% by weight, preferably 0.01-0.3% by weight and most preferably 0.02-0.1% by weight based on the dry weight of the cellulose suspension. The cellulose-reactive sizing agent is added to the cellulose suspension in an amount of 0.01-1.0% by weight, preferably 0.05-0.5% by weight based on the dry weight of the cellulose suspension.

The term "paper" as used herein is meant to include all cellulosic product forms (eg, including boards, paperboards and especially liquid packaging boards) in the form of sheets as well as paper. The process according to the invention can be used for the production of paper from different forms of cellulose suspensions of cellulose-containing fibers, which suspension should comprise at least 25% by weight, preferably at least 50% by weight of the fibers, based on dry matter. do. The suspension can be chemical pulp such as sulfate, sulfite and organosolv pulps, mechanical pulp such as thermodynamic pulp, chemical-thermodynamic pulp, refiner pulp and groundwood pulp, softwood and hardwood. Can be based on fibers from, and can optionally be based on recycled fibers from bleached pulp and mixtures thereof, the cellulose suspension optionally comprises mineral fillers. Examples of conventional mineral fillers include kaolin, china clay, titanium dioxide, gypsum, talc and natural and synthetic calcium carbonates such as chalk, marble and precipitated calcium carbonate. The pH of the cellulose suspension is in the range of about 3 to about 10. The pH is suitably in the range of at least 3.5, preferably 4-9.

Chemicals conventionally added to cellulose suspensions in the papermaking process, such as retention aids, aluminum compounds, dyes, wet-enhancing resins, optical brightening agents, etc., can of course be used with the dispersions of the present invention. have. Examples of aluminum compounds include alum, aluminate and polyaluminum compounds such as polyaluminum chloride and sulfate. Examples of suitable retention agents include cationic polymers, anionic inorganic materials combined with organic polymers, such as bentonite combined with cationic polymers, cationic polymers or silica-based sol combined with cationic and anionic polymers. Particularly good internal sizing can be obtained when using nitrogen-containing organic compounds and cellulose-reactive sizing agents as described above in combination with retention agents comprising cationic polymers. Suitable cationic polymers include cationic starch, guar gum, acrylate- and acrylamide-based polymers, polyethyleneimine, dicyandiamide-formaldehyde resins, polyamines, polyamidoamines and poly (diallyldimethyl ammonium chloride) and their Include blends. It is preferable to use cationic starch and cationic acrylamide polymer alone or in combination with each other or in combination with other materials.

The invention is further illustrated by the following examples, but is not limited thereto.

Example 1

AKD sizing of the liquid packaging board is carried out in an experimental paper machine comprising a machine chest, two separate pumping arrangements, an antifoam, a screen, a headbox and a wire, and the cellulose suspension is dehydrated to form a sheet.

The nitrogen-containing organic compounds used in the examples below are described in Table 1 below.

Cellulose suspensions comprise 100% bleached CTMP. Two different nitrogen-containing organic compounds are used in tests A and E. The addition of the nitrogen containing compound to the cellulose suspension is carried out after the machine chest. Reference is also made without the addition of nitrogen-containing organic compounds. Cationic starch (Raisamyl 142) is added at two points; 2 kg / tonne after the first pumping arrangement P1 and 3 kg / tonne before the second pumping arrangement P2. AKD (Eka DH 28HF) sizing agent is added before P2 and silica sol (Eka NP 442) is added after P2 (3 kg / tonne). In the headbox the pH is 8.0.

Edge Wick (EW) tests with lactic acid (1%) are performed on the final paper after 1 hour and 24 hours, respectively. The results are shown in Table 2.

As can be seen from Table 2, tests using nitrogen-containing organic compounds according to the present invention show lower EW values after 1 hour compared to references that do not include nitrogen-containing organic compounds. The addition of nitrogen-containing organic compounds shortens the curing time. After 24 hours, all samples show the same EW value.

Example 2

Papermaking conditions are the same as in Example 1. Two different feeds of nitrogen-containing organic compounds (0.25 kg / tonne and 0.5 kg / tonne) are tested at two feed levels of AKD (1 kg / tonne and 1.5 kg / tonne).

Sizing performance is tested at Cobb ₆₀ -values in paper immediately after the off machine, after 1 hour, after 3 hours and after the last 24 hours according to the standard method Tappi T441. The results are shown in Table 3.

Cobb ₆₀ -values after 1 hour of mechanical off and paper off of paper samples treated with nitrogen-containing organic compounds show a lower Cobb ₆₀ -value compared to the Cobb ₆₀ -value of reference. After 24 hours, all samples reach approximately the same degree of sizing. From the results in Table 3, the AKD feed can be reduced when the nitrogen-containing organic compound according to the invention is added to the suspension.

Tensile index (SCAN-P 67:93) is tested on paper sheets treated with nitrogen-containing organic compounds and compared with references to investigate whether the nitrogen-containing organic compounds have a negative effect on paper strength. . The results are shown in Table 4.

The results show that the nitrogen-containing organic compounds do not have a great effect on the tensile strength and therefore the paper / board quality does not deteriorate.

Example 3

In this example, sizing performance is tested at Cobb ₆₀ -value when nitrogen-containing organic compounds are added in different addition forms. In addition, sizing performance is tested when using nitrogen-containing organic compounds and polyDADMAC polymers according to the invention.

The cellulose suspension comprises 80% hardwoods and 20% conifers and has a fiber concentration of 0.5%. No filler was added. Conductivity is 0.3 mS / cm and pH is about 8. Hand sheets are prepared according to standard method SCAN-C26: 76 and sizing properties are measured in Cobb ₆₀ -values according to standard method Tappi T441.

A first retention system is used which comprises 0.75 kg / tonne of cationic polyacrylamide (Eka PL 1510) and 1 kg / tonne of silica sol (Eka NP 442) calculated as dry material in a dry cellulose suspension. The results are shown in Table 5. Calculated as a dry substance in a dry cellulose suspension, a second retention system is used comprising 5 kg / tonne of cationic potato starch (Perlbond 980) and 1 kg / tonne of silica sol (Eka NP 442). The results are shown in Table 6.

The feed amount of cationic polyacrylamide (EKA PL 1510) is reduced to 0.5 kg / tonne when polyDADMAC (F) is added to the paper fiber suspension.

The sizing agent AKD (Eka DR 28 HF) is added in an amount of 0.45 kg / tonne and the nitrogen-containing organic compound according to the invention, Arquad HTB-75 (C), is added in the following way:

(a) 2 minutes before AKD addition,

(b) premixed with AKD,

(c) concurrent with AKD,

(d) After AKD.

The sizing results obtained by the addition of 0 kg / tonne, 0.25 kg / tonne and 0.5 kg / tonne of the nitrogen-containing organic compound (C) are shown in Tables 5 and 6, respectively. The results can be compared with the results obtained by the absence of nitrogen-containing organic compounds or by the addition of polymer (F) instead of the nitrogen-containing organic compounds according to the invention.

Example 4

In this example, a liquid packaging board is made in an experimental paper machine as described in Example 1, and the sizing performance is tested at Cobb ₆₀ -value according to the standard method Tappi T441. The cellulose suspension comprises 80% hardwoods (40% eucalyptus and 40% birch) and 20% conifers and has a fiber concentration of 1.5%. No filler was added. pH is 7.1. A retention system is used which comprises 0.375 kg / tonne of cationic polyacrylamide (Eka PL 1510) and 0.15 kg / tonne of silica sol (Eka NP 442) calculated as dry material in a dry cellulose suspension. According to the invention a nitrogen-containing organic compound Arquad HTB-75 (C) or Armosoft DEQ (G) is added prior to the addition of the sizing agent AKD (Eka DR 28 HF). Armosoft DEQ (G) is also added after the addition of AKD to investigate the effect of feed order on sizing performance. Sizing results are shown in Tables 7 and 8, respectively. The results can be compared with the results obtained by the absence of nitrogen-containing organic compounds.

It can be seen that the nitrogen-containing organic compound according to the present invention has a positive effect on the initial sizing of AKD. The low Cobb ₆₀ -value can already be reached immediately after the machine is off. The final sizing degree is not affected by the addition of nitrogen-containing organic compounds.

In this example, it can be seen that nitrogen-containing organic compounds can be added before or after the addition of AKD.

Example 5

In this example, a liquid packaging board is prepared in a laboratory paper machine as described in Example 1, and the sizing performance is tested at Cobb ₆₀ -value according to the standard method Tappi T441. Cellulose suspensions comprise 100% bleached CTMP and have a fiber concentration of 1.35%. No filler was added. pH is 5.6 and conductivity is 219 μS / cm. Nitrogen-containing organic compounds, Arquad HTB-75 (C) or Armosoft DEQ (G), are used in the test. The addition of the nitrogen containing compound to the cellulose suspension takes place after the machine chest. Reference is also made without the addition of nitrogen-containing organic compounds. AKD (Eka DH 28HF) sizing agent is added before the second pumping arrangement P2. Calculated as a dry substance in a dry cellulose suspension, cationic starch (Lysamil 142) is added before P2 (5 kg / tonne) and silica sol (Eka NP 442) is added after P2 (0.15 kg / tonne) Is added. Nitrogen-containing organic compounds according to the invention, Arquad HTB-75 (C) or Armosoft DEQ (G), are added before the sizing agent AKD (Eka DR 28 HF).

It can be seen that the nitrogen-containing organic compound according to the present invention has a positive effect on the initial sizing of AKD. A low Cobb ₆₀ -value can already be reached after 1 hour. The final sizing degree is not affected by the addition of nitrogen-containing organic compounds. The tensile index was not reduced by the addition of nitrogen-containing organic compounds.

The nitrogen-containing organic compound according to the invention acts in an amount of about 0.05-5 kg / tonne, preferably about 0.1-3 kg / tonne and most preferably about 0.2-1 kg / tonne, calculated as dry pulp together with AKD. do.

Claims (18)

(a) preparing an aqueous cellulose suspension; (b) in the suspension,     (i) nitrogen-containing organic compounds having a molecular weight of 1,000 or less; And     (ii) cellulose-reactive sizing agents     Adding them separately; And (c) dehydrating the obtained suspension to form a paper. (a) preparing a cellulose suspension; (b) mixing a nitrogen-containing organic compound having a molecular weight of 1,000 or less with an aqueous dispersion of cellulose-reactive sizing agent to form a pre-mix; (c) adding the premix to the suspension; And (d) dehydrating the obtained suspension to form a paper. The method according to claim 1 or 2, The nitrogen-containing organic compound is a quaternary ammonium compound. The method according to claim 1 or 2, The nitrogen-containing organic compound is an amine or acid addition salt thereof. The method according to any one of claims 2 to 4, Mixing is carried out by contacting an aqueous stream of nitrogen-containing organic compounds having a molecular weight of 1,000 or less with an aqueous stream of a dispersion of cellulose-reactive sizing agent and introducing the obtained stream into a cellulose suspension. The method according to any one of claims 2 to 5, Contacting time of the aqueous dispersion of nitrogen-containing organic compound and sizing agent in the premix is 20 minutes or less prior to addition to the suspension. The method of claim 1, Wherein the nitrogen-containing organic compound is added to the cellulose suspension prior to adding the cellulose-reactive sizing agent. The method of claim 1, The nitrogen-containing organic compound is added to the cellulose suspension separately but simultaneously with the cellulose-reactive sizing agent. The method of claim 1, The nitrogen-containing organic compound is added to the cellulose suspension after the addition of the cellulose-reactive sizing agent. The method according to any one of claims 1 to 9, Nitrogen-containing organic compounds include methyl bis [ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulfate, di (hydrogenated tallow) dimethylammonium chloride, di (hydrogenated tallow fatty acid-2-hydroxyethyl ester) Dimethyl ammonium chloride, didecyldimethylammonium chloride, (vegetable oil) benzyl-dimethylammonium chloride or (dodecyl) benzyl-dimethylammonium chloride. The method according to any one of claims 1 to 9, Wherein the nitrogen-containing organic compound comprises quaternary imidazolinium. The method according to any one of claims 1 to 11, The nitrogen-containing organic compound is characterized in that the silica-based particles are substantially free of. The method according to any one of claims 1 to 12, The cellulose-reactive sizing agent is a ketene dimer. The method according to any one of claims 1 to 12, The cellulose-reactive sizing agent is an acid anhydride. The method according to any one of claims 1, 3, 4 and 7 to 14, Sizing agent is added as an aqueous dispersion. The method according to any one of claims 1 to 15, Wherein the nitrogen-containing organic compound is added in an amount of at least 20% by weight based on the weight of the cellulose-reactive sizing agent. The method according to any one of claims 1 to 16, The nitrogen-containing organic compound is added in an amount of 0.005-0.5% by weight based on the dry weight of the aqueous cellulose suspension. The method according to any one of claims 1 to 17, Sizing agent is added in an amount of 0.01-1.0% by weight based on the dry weight of the aqueous cellulose suspension.