US20070277949A1

US20070277949A1 - Sizing of paper

Info

Publication number: US20070277949A1
Application number: US11/809,606
Authority: US
Inventors: Jonas Liesen; Jeanette Risen; Kristina Mohlin; Agneta Lernbrink
Original assignee: Akzo Nobel NV
Current assignee: Akzo Nobel NV
Priority date: 2006-06-01
Filing date: 2007-05-31
Publication date: 2007-12-06

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

FIELD OF THE INVENTION

The present invention generally relates sizing of paper and paper board.

BACKGROUND OF THE INVENTION

Cellulose-reactive sizing agents, such as those based on alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA), are widely used in papermaking at neutral or slightly alkaline stock pH's in order to give paper and paper board some degree of resistance to wetting and penetration by aqueous liquids. Paper sizes based on cellulose-reactive sizing agents are generally provided in the form of dispersions containing an aqueous phase and finely divided particles or droplets of the sizing agent dispersed therein.
Cellulose-reactive sizing agents generally provide good sizing effect using low dosages of the sizing agent when added to the aqueous cellulosic suspension. The sizing effect starts to develop in the drying section of the paper machine. However, since most paper machines operate at maximum speed to optimize the paper production, the time in the drying section is often not long enough to produce sized paper on-machine. Instead the paper has to be allowed to cure for up to 24 hours before a fully sized product can be achieved. This slow development of the sizing effect creates a number of problems. Firstly, subsequent operations such as printing, coating, pasting, etc. may be difficult to handle. Secondly, many paper makers continuously overdose the sizing agents to make sure that a fully sized product is achieved. Consequently, problems in terms of deposits on machine components are usually created.
WO 9710387 discloses a paper sizing enhancer which is a polymerization reaction product of a quaternary diallylammonium monomer and a diallylammonium monomer. The polymerization product has a molecular weight of at least 10,000. WO 9710387 discloses that the paper sizing enhancer may be introduced into a paper furnish during the papermaking process in combination with the paper sizing agent, either separately or as an aqueous medium containing both components.
WO 02081587 discloses a sizing dispersion containing a sizing agent and a non-ionic surface active monoester of glycerol with a fatty acid.
It is an object of this invention to provide a process for the production of paper with improved initial sizing on-machine. It is also an object of the invention to provide faster curing times for sizing agent. Further objects will appear hereinafter.

SUMMARY OF THE INVENTION

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

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention it has surprisingly been found that improved initial sizing, i.e. faster development of the sizing effect or faster curing of paper, in papermaking can be achieved by separately adding to a cellulosic suspension a nitrogen-containing organic compound having a molecular weight of less than 1,000 and a cellulose-reactive sizing agent. It has also been found that improved initial sizing can be achieved by adding to the suspension a pre-mix of the nitrogen-containing organic compound and an aqueous dispersion of a cellulose-reactive sizing agent. Faster curing provides faster feedback on sized products, minimizes the risk of overdosing the sizing agent which, in turn, may result in less deposits in the paper machine. Hereby improved runnability of the paper machine can be achieved. Due to faster curing times, less storage space for paper rolls to be cured will be required. The present invention thus offers substantial economical and technical benefits.
The nitrogen-containing organic compound according to the invention can be selected from primary amines, secondary amines, tertiary amines, quaternary amines, which are also referred to as quaternary ammonium compounds. The nitrogen-containing compound is preferably water-soluble or water-dispersible and it can be aromatic, i.e. containing one or more aromatic groups, or aliphatic; the aliphatic nitrogen-containing water-dispersible organic compounds usually being preferred. The nitrogen-containing organic compound can be uncharged or cationic. Suitable nitrogen-containing organic compounds include acid addition salts of primary, secondary and tertiary amines and, preferably, quaternary ammonium compounds. The nitrogen-containing organic compound may have one or more oxygen-containing substituents, for example with oxygen in the form of hydroxyl groups and/or alkyloxy groups. Examples of preferred substituents of this type include hydroxyl groups, e.g. ethanol groups, and methoxy and ethoxy groups. The nitrogen-containing organic compounds may include one or more nitrogen atoms, preferably one or two. The nitrogen-containing organic compound has a molecular weight of less than 1,000, suitably less than 900 or 800 and preferably less than 750 or 600. 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 a primary, secondary or tertiary amine with methyl chloride, dimethyl sulphate and benzyl chloride. Examples of suitable quaternary ammonium compounds further include compounds having the general formula R₄N⁺ X⁻, wherein each R group is independently selected from (i) hydrogen; (ii) hydrocarbon groups, suitably aliphatic and preferably alkyl groups, having from 1 to about 30 carbon atoms, preferably from 1 to 22 carbon atoms; and (iii) hydrocarbon groups, suitably aliphatic and preferably alkyl groups, having up to about 30 carbon atoms, preferably from 4 to 22 carbon atoms, and being interrupted by one or more heteroatoms, e.g. oxygen or nitrogen, and/or groups containing a heteroatom, e.g. carbonyl and acyloxy groups; where at least one, suitably at least three and preferably all of said R groups contain carbon atoms; suitably at least one and preferably at least two of said R groups containing at least 7 carbon atoms, preferably at least 9 carbon atoms and most preferably at least 12 carbon atoms; and wherein X⁻ is an anion, typically a halide like chloride. The nitrogen-containing organic compound of the invention is preferably substantially free from silica-based particles.
Examples of suitable primary amines, i.e. amines having one organic substituent, include alkylamines, e.g. propylamine, butylamine, cyclohexylamine, alkanolamines, e.g. ethanolamine, and alkoxyalkylamines, e.g. 2-methoxyethylamine. Examples of suitable secondary amines, i.e. amines having two organic substituents, include dialkylamines, e.g. diethylamine, dipropylamine and di-isopropylamine, dialkanolamines, e.g. diethanolamine, and pyrrolidine. Examples of suitable tertiary amines, i.e. amines having three organic substituents, include trialkylamines, e.g. triethylamine, trialkanolamines, e.g. triethanolamine, N,N-dialkylalkanolamines, e.g. N,N-dimethylethanolamine. Examples of suitable quaternary ammonium compounds include methyl bis[ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulphate, dioctyldimethylammonium chloride, didecyldimethylammonium chloride, dicocodimethylammonium chloride, cocobenzyldimethylammonium chloride, coco(fractionated)benzyldimethylammonium chloride, octadecyl trimethylammonium chloride, dioctadecyl dimethylammonium chloride, dihexadecyl dimethylammonium chloride, di(hydrogenated tallow)dimethylammonium chloride, di(hydrogenated tallow)benzylmethylammonium chloride, di(hydrogenated tallow fatty acids-2-hydroxyethyl ester) dimethyl ammonium chloride, (hydrogenated tallow)benzyldimethylammonium chloride, dioleyldimethylammonium chloride, di(ethylene hexadecanecarboxylate)dimethylammonium chloride, (vegetableoil)benzyldimethylammonium chloride, (dodecyl)benzyl-dimethylammonium chloride and quaternised imidazole derivates. Examples of suitable diamines include aminoalkylalkanolamines, e.g. aminoethylethanolamine, piperazine and nitrogen-substituted piperazines having one or two lower alkyl groups of 1 to 4 carbon atoms. Example of suitable imidazoline derivates include quaternary imidazolinium compounds, e.g. 2-(C17 and C17 unsaturated alkyl)-1-[2-(C18 and C18-unsaturated amido) ethyl]-4,5-dihydro-1-methyl, methyl sulfates. Examples of preferred nitrogen-containing organic compounds include methyl bis[ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulphate, di(hydrogenated tallow)dimethylammonium chloride, di(hydrogenated tallow fatty acids-2-hydroxyethyl ester) dimethyl ammonium chloride, didecyldimethylammonium chloride, (vegetableoil)benzyl-dimethylammonium chloride and (dodecyl)benzyl-dimethylammonium chloride.
The cellulose-reactive sizing agent can be selected from the group consisting 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. Suitable ketene dimers have the general formula (I) below, wherein R¹and R²represent saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbons, the hydrocarbon groups suitably having from 8 to 36 carbon atoms, usually being straight or branched chain alkyl groups having 12 to 20 carbon atoms, such as hexadecyl and octadecyl groups. Suitable acid anhydrides can be characterized by the general formula (II) below, wherein R³and R⁴can be identical or different and represent saturated or unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms, or R³and R⁴together with the —C—O—C— moiety can form a 5 to 6 membered ring, optionally being further substituted with hydrocarbon groups containing up to 30 carbon atoms. Examples of acid anhydrides which are used commercially include alkyl and alkenyl succinic anhydrides and particularly isooctadecenyl succinic anhydride.
Suitable ketene dimers, acid anhydrides and organic isocyanates include the compounds disclosed in U.S. Pat. No. 4,522,686, which is hereby incorporated herein by reference.
The dispersions of this invention contain a dispersant or a dispersant system comprising one or more dispersing agents and protective colloids. The dispersing agents and protective colloids can be selected from anionic, non-ionic, cationic and amphoteric compounds which separately or together may function as dispersing agent or dispersant system for the cellulose-reactive sizing agent. The dispersions according to the invention can have contents of cellulose-reactive sizing agents from about 0.1% by weight up to about 30% by weight. The content of cellulose-reactive sizing agent is suitably within the range of from 5 to 25% and preferably from 8 to 20% by weight.
The dispersing agents and protective colloids can be any of those conventionally used in the preparation of aqueous sizing dispersions or emulsions. They can for example be selected from saponified rosin derivatives, alkyl sulphates, alkylaryl sulphates, alkyl sulphonates, alkylaryl sulphonates, etc. Particularly suitable anionic dispersing agents are alkyl sulphates and alkyl sulphonates, e.g. sodium lauryl sulphate, as well as sodium lignosulphonate and sodium naphthalene sulphonate. Examples of suitable protective colloids include water-soluble cellulose-derivatives such as hydroxyethyl- and hydroxypropyl-, methylhydroxypropyl- and ethylhydroxyethylcellulose, methyl- and carboxymethylcellulose, gelatin, starch, guar gum, xanthan gum, polyvinyl alcohol, etc.. Examples of suitable non-ionic dispersing agents can for example be selected from fatty alcohols, ethoxylated fatty alcohols, fatty acids, alkyl phenols or fatty acid amides, ethoxylated or non-ethoxylated glycerol esters, sorbitan esters of fatty acids, etc.. Examples of suitable cationic dispersing agents and protective colloids include water-soluble nitrogen-containing epichlorohydrin resins and cationic starches, etc.. The dispersion may also contain other additives such as preservative agents. Suitably, the amount of dispersing agent is at least 0.5% by weight, based on the amount of sizing agent. Normally, it is not necessary to use more than 10% by weight.
The nitrogen-containing organic compound of the invention and the cellulose-reactive sizing agent can be separately added to the cellulosic suspension in any order. The nitrogen-containing organic compound can be separately added prior to, simultaneously with or after adding the cellulose-reactive sizing agent and preferably prior to adding the cellulose-reactive sizing agent.
The nitrogen-containing organic compound and the aqueous dispersion of cellulose-reactive sizing agent, herein also referred to as sizing dispersion, can also be added to the cellulosic suspension as a pre-mix. In this embodiment, the nitrogen-containing organic compound and the sizing dispersion are mixed to form a pre-mix before addition to the cellulosic suspension. The mixing can be done by bringing into contact some time before the addition the nitrogen-containing organic compound, suitably an aqueous phase thereof and preferably an aqueous stream thereof, and the sizing dispersion, preferably an aqueous stream thereof.
The obtained aqueous phase or stream is then introduced to the cellulosic suspension. Preferably, the contact time, i.e. the time from mixing the nitrogen-containing organic compound and the sizing dispersion to adding the pre-mix so formed to the cellulosic suspension, is short. This period of time can be less than about 20 minutes, suitably less than 4 minutes and preferably less than 2 minutes.
The mixing of aqueous streams of the nitrogen-containing organic compound and the sizing dispersion can be effected by directing the separate streams to be mixed towards each other, allowing them to impinge on each other and introducing the pre-mix stream so formed into the cellulosic suspension. Suitably mixing is carried out under turbulent flow conditions, which promote more intensive and rapid mixing of the streams. The streams can be mixed by means of any mixing device having at least two inlets into which separate streams to be mixed are supplied and having at least one outlet through which the resulting pre-mix is passed and subsequently introduced to the cellulosic suspension. This stream mixing embodiment is advantageous from a practical point of view and confers operational benefits.
The nitrogen-containing organic compound and the cellulose-reactive sizing agent can be added to the cellulosic suspension at any position, e.g. anywhere between the machine chest and the headbox.
The nitrogen-containing organic compound and the cellulose-reactive sizing agent can be added to the cellulosic suspension in amounts that can vary within wide limits, where the dosage is mainly dependent on the quality of the pulp or paper to be sized, the cellulose-reactive sizing agent used and the level of sizing desired. The nitrogen-containing organic compound is suitably added to the cellulosic suspension in an amount of from 0.005 to 0.5% by weight, preferably of from 0.01 to 0.3% by weight and most preferably of from 0.02 to 0.1% by weight based on the dry weight of the cellulosic suspension. The cellulose-reactive sizing agent is suitably added to the cellulosic suspension in an amount of from 0.01 to 1.0% by weight, preferably of from 0.05 to 0.5% by weight based on the dry weight of the cellulosic suspension.
The term “paper”, as used herein, is meant to include not only paper but all types of cellulose-based products in sheet and web form, including, for example, board, paperboard and particularly liquid packaging board. The process according to the invention can be used in the production of paper from different types of cellulosic suspensions of cellulose-containing fibres and the suspensions should suitably contain at least 25% by weight and preferably at least 50% by weight of such fibres, based on dry substance. The suspension can be based on fibres from chemical pulp such as sulphate, sulphite and organosolv pulps, mechanical pulp such as thermomechanical pulp, chemo-thermomechanical pulp, refiner pulp and groundwood pulp, from both hardwood and softwood, and can also be based on recycled fibres, optionally from de-inked pulps, and mixtures thereof. The cellulosic suspension may optionally also contain mineral fillers. Examples of mineral fillers of conventional types include kaolin, china clay, titanium dioxide, gypsum, talc and natural and synthetic calcium carbonates such as chalk, ground marble and precipitated calcium carbonate. The pH of the cellulosic suspension can be within the range of from about 3 to about 10. The pH is suitably above 3.5 and preferably within the range of from 4 to 9.
Chemicals conventionally added to the cellulosic suspension in papermaking such as retention aids, aluminium compounds, dyes, wet-strength resins, optical brightening agents, etc., can of course be used in conjunction with the present dispersions. Examples of aluminium compounds include alum, aluminates and polyaluminium compounds, e.g. polyaluminium chlorides and sulphates. Examples of suitable retention aids include cationic polymers, anionic inorganic materials in combination with organic polymers, e.g. bentonite in combination with cationic polymers, silica-based sols in combination with cationic polymers or cationic and anionic polymers. Particularly good internal sizing can be obtained when using the nitrogen-containing organic compound and the cellulose-reactive sizing agent as described above in combination with retention aids comprising cationic polymers. Suitable cationic polymers include cationic starch, guar gum, acrylate-based and acrylamide-based polymers, polyethyleneimine, dicyandiamide-formaldehyde resins, polyamines, polyamidoamines and poly(diallyldimethyl ammoniumchloride) and combinations thereof. Cationic starch and cationic acrylamide-based polymers are preferably used, either alone or in combination with each other or with other materials.
The invention is further illustrated in the following examples, which, however, are not intended to limit the same.

EXAMPLE 1

AKD sizing of liquid packaging board was performed on an experimental paper machine which comprised a machine chest, two separate pumping arrangements, defoamer, screen, headbox and a wire, where the cellulosic suspension was dewatered to form a sheet.
The nitrogen-containing organic compounds used in the following Examples are those described in Table 1.

TABLE 1

Nitrogen-containing
organic compound	Description	Molecular weight	Trade name

A	Di(hydrogenated	560	Arquad 2HT-75PG
	tallow)dimethylammonium
	chloride
B	Didecyldimethylammonium	360	Arquad 2.10-50
	chloride
C	(Vegetableoil)benzyl-	410	Arquad HTB-75
	dimethylammonium chloride
D	(Dodecyl)benzyl-	420	Croda N-Dodecyl
	dimethylammonium chloride
E	Quaternary imidazolinium	744	Incrosoft CFI-90
			PG
F	polyDADMAC	350,000	Eka ATC 6340
G	Di(hydrogenatedtallow fatty	702	Armosoft DEQ
	acids-2-hydroxyethyl ester)
	dimethyl ammonium
	chloride

The cellulosic suspension comprised 100% bleached CTMP. Two different nitrogen-containing organic compounds were used in the tests: A and E. The addition of the nitrogen containing compound to the cellulosic suspension took place after the machine chest. A reference without addition of nitrogen-containing organic compound was also performed. Cationic starch (Raisamyl 142) was dosed at two points; after the first pumping arrangement (P1) 2 kg/tonne and before the second pumping arrangement (P2) 3 kg/tonne. The AKD (Eka DH 28HF) sizing agent was dosed before the P2 and a silica sol (Eka NP 442) was dosed after the P2 (3 kg/tonne as received). pH at the head box was 8.0.
Edge Wick (EW) tests with lactic acid (1%) were performed on the final paper after 1 h and 24 h, respectively. The results are presented in Table 2.

	TABLE 2

	1 h EW (LA 1%)	24 h EW (LA 1%)
	(kg/m²)	(kg/m²)

	AKD		AKD
Nitrogen-containing	(2	AKD	(2	AKD
organic compound	kg/tonne)	(3 kg/tonne)	kg/tonne)	(3 kg/tonne)

Reference	1.29	0.96	0.68	0.56
E (0.5 kg/tonne)	0.9	0.78	0.63	0.60
A (0.5 kg/tonne)	0.83	0.67	0.6	0.55
A (1.0 kg/tonne)	0.75	0.62	0.63	0.54

As can be seen from Table 2, the tests using nitrogen-containing organic compounds according to the present invention showed lower EW values after 1 hour compared to references which did not contain any nitrogen-containing organic compound. It can be concluded that the addition of nitrogen-containing organic compounds shorten the curing time. After 24 hours, all samples show about the same EW values.

EXAMPLE 2

The papermaking conditions were the same as in Example 1. Two different dosages (0.25 kg/tonne and 0.5 kg/tonne) of the nitrogen-containing organic compounds were tested at two dosage levels of AKD (1 kg/tonne and 1.5 kg/tonne).
Sizing performance was tested as Cobb₆₀-value on the paper directly after it had come off the machine, after 1 h, 3 h, and finally after 24 h according to the standard method Tappi T441. The results are shown in Table 3.

TABLE 3

	Nitrogen-
Nitrogen-	containing
containing	organic	Cobb₆₀(g/m²)

organic	AKD	compound	Off
compound	(kg/tonne)	(kg/tonne)	Machine	1 h	3 h	24 h

Reference	1.0	0	220	127	39	20
A	1.0	0.25	68	39	26	18
B	1.0	0.25	111	47	31	21
C	1.0	0.25	42	30	25	19
D	1.0	0.25	84	41	26	21
Reference	1.5	0	41	29	23	17
A	1.5	0.25	28	24	21	17
B	1.5	0.25	35	24	21	17
C	1.5	0.25	24	22	19	17
D	1.5	0.25	28	24	21	18
A	1.0	0.5	31	26	23	20
B	1.0	0.5	42	30	24	20
C	1.0	0.5	31	26	22	20
D	1.0	0.5	58	40	26	21
A	1.5	0.5	22	20	18	17
B	1.5	0.5	26	21	19	17
C	1.5	0.5	24	19	18	17
D	1.5	0.5	27	23	20	18

Cobb₆₀-values off machine and after 1 h of the paper samples treated with a nitrogen-containing organic compound show lower Cobb₆₀-values compared to Cobb₆₀-values of the reference. After 24 h, all the samples have reached approximately the same sizing degree. From the results of Table 3 it can also be concluded that it is possible to decrease the AKD dosage when a nitrogen-containing organic compound according to the present invention is added to the suspension.
Tensile index (SCAN-P 67:93) was tested on the paper sheets treated with the nitrogen-containing organic compounds and compared with the reference in order to investigate if the nitrogen-containing organic compounds have had a negative effect on the paper strength. The results are shown in Table 4.

TABLE 4

		Nitrogen-containing
Nitrogen-containing	AKD	organic compound	Tensile index
organic compound	(kg/tonne)	(kg/tonne)	(Nm/g)

Reference	1.0	—	29.7
A	1.0	0.25	29.1
B	1.0	0.25	30.6
C	1.0	0.25	29.9
D	1.0	0.25	29.9
Reference	1.5	—	30.9
A	1.5	0.25	27.3
B	1.5	0.25	28.5
C	1.5	0.25	30.0
D	1.5	0.25	30.3
A	1.0	0.50	27.9
B	1.0	0.50	29.6
C	1.0	0.50	28.1
D	1.0	0.50	30.5
A	1.5	0.50	28.3
B	1.5	0.50	30.6
C	1.5	0.50	30.3
D	1.5	0.50	30.5

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

EXAMPLE 3

In this Example, sizing performance was tested as Cobb₆₀-value on paper when nitrogen-containing organic compounds were added in different addition modes. Further, sizing performance was tested when using a nitrogen-containing organic compound according to the present invention and polyDADMAC polymer.
The cellulosic suspension contained 80% hardwood and 20% softwood and had a fiber concentration of 0.5%. No filler was added. The conductivity was 0.3 mS/cm and pH was about 8. Hand sheets were prepared according to the standard method SCAN-C26:76 and sizing property was measured as Cobb₆₀value according to the standard method Tappi T441.
A first retention system was used comprising 0.75 kg/tonne cationic polyacrylamide (Eka PL 1510) and 1 kg/tonne of silica sol (Eka NP 442), calculated as dry substances on dry cellulosic suspension. The results are presented in Table 5. A second retention system was used comprising 5 kg/tonne of cationic potato starch (Perlbond 980) and 1 kg/tonne of silica sol (Eka NP 442), calculated as dry substances on dry cellulosic suspension. The results are presented in Table 6.
The dosage of the cationic polyacrylamide (EKA PL 1510) was reduced to 0.5 kg/tonne in the cases where polyDADMAC (F) was added to the paper fiber suspension.
The sizing agent AKD (Eka DR 28 HF) was added in an amount of 0.45 kg/tonne and the nitrogen-containing organic compound, Arquad HTB-75 (C), according to the invention was either added:
a) 2 minutes before AKD,
b) premixed with AKD,
c) simultaneously 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 the nitrogen-containing organic compound or by addition of the polymer (F) instead of the nitrogen-containing organic compound according to the invention.

	TABLE 5

	Cobb₆₀(g/m²)

		F	C
Addition mode	Reference	(0.25 kg/tonne)	(0.25 kg/tonne)

no addition	63
a) addition before AKD		230	36
b) premixed with AKD			33
c) addition simultaneously		38	32
with AKD
d) addition after AKD			31

	TABLE 6

	Cobb₆₀(g/m²)

		F	C
Addition mode	Reference	(0.5 kg/tonne)	(0.5 kg/tonne)

no addition	98
a) addition before AKD		251	30
b) premixed with AKD			31
c) addition simultaneously		33	31
with AKD
d) addition after AKD			31

EXAMPLE 4

In this Example, liquid packaging board was prepared on an experimental paper machine as described in Example 1 and the sizing performance was tested as Cobb₆₀-value according to the standard method Tappi T441. The cellulosic suspension contained 80% hardwood (40% eucalyptus and 40% birch) and 20% softwood and had a fiber concentration of 1.5%. No filler was added. The pH was 7.1. A retention system was used comprising 0.375 kg/tonne cationic polyacrylamide (Eka PL 1510) and 0.15 kg/tonne silica sol (Eka NP 442), calculated as dry substances on dry cellulosic suspension. A nitrogen-containing organic compound, Arquad HTB-75 (C) or Armosoft DEQ (G), according to the invention was added before the sizing agent AKD (Eka DR 28 HF). In order to investigate the impact of dosing order on the sizing performance, Armosoft DEQ (G) was also added after the addition of the AKD. The sizing results are presented in Table Nos. 7 and 8, respectively. The results can be compared with the results obtained by the absence of the nitrogen-containing organic compound.

TABLE 7

	Nitrogen-
Nitrogen-	containing
containing	organic	Cobb₆₀(g/m²)

organic	compound	AKD	Off				10 min.
compound	kg/t	kg/t	machine	1 h	3 h	24 h	110° C.

—	0	0.5	127	127	102	28	28
—	0	0.75	105	98	46	26	26
—	0	1.0	97	72	48	25	25
C	0.25	0.5	127	93	53	31	29
C	0.25	0.75	76	46	30	24	26
C	0.25	1.0	46	35	28	23	23
C	0.5	0.5	83	56	42	38	45
C	0.5	0.75	49	29	28	24	28
C	0.5	1.0	31	27	24	22	24
G	0.25	0.5	103	76	38	27	25
G	0.25	0.75	45	36	36	25	26
G	0.25	1.0	41	35	27	25	23
G	0.5	0.5	63	35	29	28	28
G	0.5	0.75	38	29	25	24	25
G	0.5	1.0	32	25	27	22	24

It can be seen that the nitrogen-containing organic compounds according to the invention have a positive effect on the initial sizing of AKD. It is possible to reach low Cobb₆₀-values already directly off machine. The final sizing degree is not affected by the addition of the nitrogen-containing organic compound.

TABLE 8

	Nitrogen-
Nitrogen-	containing
containing	organic	Cobb₆₀(g/m²)

—	0	0.5	122	116	96	27	24
—	0	0.75	96	77	41	24	21
—	0	1.0	78	55	35	23	21
G	0.5	0.5	109	80	38	27	23
G	0.5	0.75	60	36	30	23	21
G	0.5	1.0	37	31	30	23	21

In this example it can be seen that it is possible to add the nitrogen-containing organic compound before or after the addition of AKD.

EXAMPLE 5

In this Example, liquid packaging board was prepared on an experimental paper machine as described in Example 1 and the sizing performance was tested as Cobb₆₀-value according to the standard method Tappi T441. The cellulosic suspension comprised 100% bleached CTMP, which had a fiber concentration of 1.35%. No filler was added. The pH was 5.6 and the conductivity was 219 μS/cm. A nitrogen-containing organic compound, Arquad HTB-75 (C) or Armosoft DEQ (G), was used in the tests. The addition of the nitrogen containing compound to the cellulosic suspension took place after the machine chest. A reference without addition of a nitrogen-containing organic compound was also performed. The AKD (Eka DH 28HF) sizing agent was added before the second pumping arrangement (P2). Cationic starch (Raisamyl 142) was added before P2 (5 kg/tonne) and a silica sol (Eka NP 442) was added after the P2 (0.15 kg/tonne), calculated as dry substances on dry cellulosic suspension. The nitrogen-containing organic compound, Arquad HTB-75 (C) or Armosoft DEQ (G), according to the invention was added before the sizing agent AKD (Eka DR 28 HF).

TABLE 9

	Nitrogen-
Nitrogen-	containing
containing	organic	Cobb₆₀(g/m²)

—	0	0.75	338	306	280	33	25
—	0	1.0	294	286	270	33	24
—	0	1.25	261	227	205	29	22
C	0.25	0.75	227	173	64	26	21
C	0.25	1.0	87	54	33	23	23
C	0.25	1.25	64	38	31	21	21
C	0.5	0.75	121	71	46	25	26
C	0.5	1.0	39	30	30	21	24
C	0.5	1.25	30	28	23	20	22
G	0.25	0.75	249	225	92	28	25
G	0.25	1.0	209	177	101	27	26
G	0.25	1.25	76	42	32	23	22
G	0.5	0.75	139	58	56	26	24
G	0.5	1.0	50	33	33	23	19
G	0.5	1.25	36	28	26	23	20

It can be seen that the nitrogen-containing organic compounds according to the invention have a positive effect on the initial sizing of AKD. It is possible to reach low Cobb₆₀-values already after 1 h. The final sizing degree is not affected by the addition of the nitrogen-containing organic compound. The tensile index is not decreased by the addition of the nitrogen-containing organic compounds.
The nitrogen-containing organic compounds according to the invention function together with AKD in amounts of from about 0.05 to about 5 kg/tonne calculated on dry pulp, preferably from about 0.1 to about 3 kg/tonne calculated on dry pulp and most preferably from about 0.2 to about 1 kg/tonne calculated on dry pulp.

Claims

1. 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.

2. Process according to claim 1, wherein the nitrogen-containing organic compound is a quaternary ammonium compound.

4. Process according to claim 1, wherein the nitrogen-containing organic compound is added to the cellulosic suspension prior to adding the cellulose-reactive sizing agent.

5. Process according to claim 1, wherein the nitrogen-containing organic compound is added to the cellulosic suspension simultaneously with the cellulose-reactive sizing agent.

6. Process according to claim 1, wherein the nitrogen-containing organic compound is added to the cellulosic suspension after the cellulose-reactive sizing agent.

7. Process according to claim 1, wherein the nitrogen-containing organic compound comprises any one of methyl bis[ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulphate, di(hydrogenated tallow)dimethylammonium chloride, di(hydrogenated tallow fatty acids-2-hydroxyethyl ester) dimethyl ammonium chloride, didecyldimethylammonium chloride, (vegetableoil)benzyl-dimethylammonium chloride, (dodecyl)benzyl-dimethylammonium chloride or quaternary imidazolinium compound.

8. Process according to claim 1, wherein the cellulose-reactive sizing agent is a ketene dimer.

9. Process according to claim 1, wherein the sizing agent is added as an aqueous dispersion.

10. Process according to claim 1, wherein the nitrogen-containing organic compound is added in an amount of greater than 20% by weight based on the weight of the cellulose-reactive sizing agent.

11. Process according to claim 1, wherein the nitrogen-containing organic compound is added in an amount of 0.005 to 0.5% by weight, based on the dry weight of the aqueous cellulosic suspension.

12. Process according to claim 1, wherein the sizing agent is added in an amount of 0.01 to 1.0% by weight, based on the dry weight of the aqueous cellulosic suspension.

13. 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 which is a quaternary ammonium compound having a molecular weight less than 1,000; and

(ii) an aqueous dispersion of a cellulose-reactive sizing agent which is a ketene dimer; and

(c) dewatering the obtained suspension to form paper.

14. Process according to claim 13, wherein the nitrogen-containing organic compound comprises any one of methyl bis[ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulphate, di(hydrogenated tallow)dimethylammonium chloride, di(hydrogenated tallow fatty acids-2-hydroxyethyl ester) dimethyl ammonium chloride, didecyldimethylammonium chloride, (vegetableoil)benzyl-dimethylammoniumchloride, or (dodecyl)benzyl-dimethylammonium chloride.

15. Process according to claim 13, wherein the nitrogen-containing organic compound comprises quaternary imidazolinium.

16. Process for the production of paper which comprises:

(a) providing a cellulosic suspension;

(b) mixing a nitrogen-containing organic compound having a molecular weight less than 1,000 with an aqueous dispersion of a cellulose-reactive sizing agent to form a pre-mix, wherein the mixing is carried out by bringing an aqueous stream of the nitrogen-containing organic compound into a contact with an aqueous stream of the sizing agent and introducing the resulting stream into the cellulosic suspension;

(c) adding the pre-mix to the suspension; and

(d) dewatering the obtained suspension to form paper.

17. Process according to claim 16, wherein a contact time of the nitrogen-containing organic compound and the aqueous dispersion of the sizing agent in the pre-mixture is less than 20 minutes before the addition.

18. Process according to claim 16, wherein the nitrogen-containing organic compound comprises any one of methyl bis(ethyl (tallowate)]-2-hydroxyethyl ammonium methyl sulphate, di(hydrogenated tallow)dimethylammonium chloride, di(hydrogenated tallow fatty acids-2-hydroxyethyl ester) dimethyl ammonium chloride, didecyldimethylammonium chloride, (vegetableoil)benzyl-dimethylammoniumchloride, (dodecyl)benzyl-dimethylammonium chloride or quaternary imidazolinium compound.

19. Process according to claim 16, wherein the cellulose-reactive sizing agent is a ketene dimer.

20. Process according to claim 16, wherein the nitrogen-containing organic compound is added in an amount of greater than 20% by weight, based on the weight of the cellulose-reactive sizing agent.