WO2000047819A1

WO2000047819A1 - Sizing dispersion

Info

Publication number: WO2000047819A1
Application number: PCT/SE2000/000234
Authority: WO
Inventors: Che On Au; Tina Goodall; Nicholas Morgan; David Weekes
Original assignee: Akzo Nobel N.V.; Eka Chemicals Ab
Priority date: 1999-02-15
Filing date: 2000-02-07
Publication date: 2000-08-17
Also published as: AU2953900A

Abstract

The present invention relates to an aqueous dispersion of a sizing agent and a process for the production of paper using the aqueous dispersion, whereby the dispersion comprises a polymeric aluminium compound comprising silicon such as polynucleate aluminium hydroxy silicate sulphate.

Description

Sizing dispersion The present invention relates to an aqueous dispersion comprising a sizing agent, an aluminium compound and a polymeric aluminium compound comprising silicon Furthermore, the use of the dispersion in a process for production of paper is also contemplated Background

Aqueous dispersions comprising sizing agents such as those based on alkyl ketene dimer (AKD) and/or alkenyl succiπic anhydride (ASA) comprising amphotenc polymer are well-known and used in papermaking at neutral or slightly alkaline stock pH s thereby giving paper and paper board resistance to wetting and aqueous liquid penetration

Dispersions comprising sizing agents contain generally an aqueous phase and finely divided particles or droplets of the sizing agent dispersed therein The dispersions are usually prepared by homogenising the sizing agent which is water insoluble in an aqueous phase in the presence of a dispersing agent such as an amphotenc polymer using shear forces and fairly high temperatures Aqueous sizing dispersions usually exhibit poor stability and high viscosity, even at relatively low solids contents, which evidently lead to difficulties to handling the dispersions such as storage an in use A further drawback is that the products have to be supplied as low concentration dispersions which further increases the costs of transportation of the aqueous sizing dispersion

In the papermaking process when using alkyl ketene dimers (AKD) as sizing agents, it is believed that there are two reactions that AKD can undergo The preferred reaction is that AKD reacts with hydroxyl-groups of the cellolose to form a β-keto ester often referred to as reacted or bound AKD The other competing reaction is the hydrolysis process whereby inter alia ketone is formed Sizing agents which are not retained during the paper formation are preferably recirculated back to the papermaking system as part of the white water Failure to retain the unreacted AKD (ketone) in the paper web will thus lead to agglomeration of the unreacted AKD (ketone) in the white water loop, with the consequence of causing deposits either on the paper forming wire and/or on the press section

The problem is even more pronounced in paper mills where white water is extensively recirculated with the introduction of only minor amounts of fresh water into the process, thereby increasing the concentration of sizing agent and/or ketones

Fatty acid ketones derived from AKD migrate from the surface of the paper at high temperature (approx 120 °C) across the transfuse belt to the photoconductive belt where the ketones crystallise At the photoconductive belt, the ketones cause wear on the belt and eventually the need for replacement of the photoconductive belt at high expense and reduced uptime of the copier The paper may have low levels of ketones but still show a great tendency of ketone migration Thus low levels of ketones (i e efficient sizing) in the paper is not a prerequisite for reduced migration of ketones EP 0677125 B1 discloses a sizing composition comprising an amphotenc starch and a polyaluminium compound for example polyaluminium chloride and polyaluminium chlorides containing sulphate and polyaluminium sulphates

WO 9617127 discloses an anionic sizing dispersion comprising colloidal anionic aluminium-modified silica particles The silica particles are surface modified with aluminium

US 5149400 refers to a papermaking process where a basic polynucleate aluminium hydroxy silicate sulphate compound is added to the furnish before draining The invention

In accordance with the present invention it has surprisingly been found that the amount of ketones in the paper and/or migration of ketones in the paper is reduced by means of an aqueous dispersion according to the claims More specifically, the present invention relates to an aqueous dispersion of a sizing agent containing an aluminium compound and an amphotenc polymer whereby the dispersion contains a polymeric aluminium compound comprising silicon Commonly used fillers when preparing paper stocks are different kinds of calcium carbonates It has been found that the amount of ketones in the paper and the migration of ketones is reduced when using the claimed aqueous dispersion on wet stocks comprising calcium carbonate

The claimed size dispersions makes it possible to produce paper with improved sizing over conventional size dispersions at corresponding dosage of cellulose-reactive sizing agent and to use lower dosage of cellulose-reactive sizing agent to attain corresponding level of sizing The possibility of using lower amounts of sizing agent to attain in-specification sizing reduces the risk for accumulation of non-adsorbed sizing agents in the white water recirculating in the process The invention further provides aqueous dispersions of sizing agents with improved stability and viscosity properties

In a preferred embodiment of this invention the sizing agent is suitably a cellulose- reactive sizing agent which can be selected from any of the cellulose-reactive sizing agents known in the art Suitably the cellulose-reactive sizing agent is selected from the group consisting of hydrophobic 2-oxetanones, e g ketene dimers and ketene multimers, acid anhydrides, organic isocyanates carbamoyl chlorides and mixtures thereof, preferably 2- oxetanones and acid anhydrides most preferably ketene dimers Suitable ketene dimers have the formula (I) below wherein R and R² represent independently linear branched c unsaturated hydrocarbon groups suitably having from 8 to 36 carbon atoms (for example isosteaπc ketene dimers or oleic ketene dimers) usually being alkyl grouDS having 12 to 2C carbon atoms, such as tetradecyl and hexadecyl groups Suitable acid anhydrides can be characterized by the general formula (II) below wherein R³ and R⁴ can be identical or different and represent saturated or unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms, or R³ and R⁴ together 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 cyclic dicarboxylic acid anhydrides which are used commercially include alkyl and alkenyl succmic anhydrides and particularly isooctadecenyl succinic anhydride

(I) R¹ — CH = C — CH — R² (II) O O

O — C : R³ — C — O — C — R⁴

Suitable ketene dimers, acid anhydrides and organic isocyanates include the compounds disclosed in U S Pat No 4,522,686, which is hereby incorporated by reference Examples of suitable carbamoyl chlorides include those disclosed in U S Pat No 3,887,427 which is also incorporated herein by reference

In another embodiment of this invention, the sizing agent is preferably a non- cellulose-reactive agent which car; be selected from any of the non-cellulose-reactive sizing agents known in the art Suitably the non-cellulose-reactive sizing agent is selected from the group consisting of hydrophobes based on rosin, e g rosin disproportionated rosin, hydrogenated rosin, polymerised rosin, formaldehyde-treated rosin, estenfied rosin, fortified rosin and mixtures of such treatments and so treated rosins, fatty acids and derivatives thereof, e g fatty acid esters and amides like bis-stearamide, resin and derivatives thereof, e g. hydrocarbon resins, resin acids, resin acid esters and amides, waxes, e g crude and refined paraffin waxes, synthetic waxes, naturally occurring waxes, etc

The aqueous dispersion according to the present invention contains an amphotenc polymer The term amphotenc polymer used herein refers to polymers containing both anionic and cationic groups Suitable polymers are amphotenc starch or amphotenc acryiamide based polymers Amphotenc starch is preferred and for this the anionic groups can for example be phosphate, phosphonic acid, phosphonate, sulphate sulphonate or carboxylic acid groups and they are preferably phosphate groups The cationic groups are preferably tertiary amine or quaternary ammonium groups. Any starch containing anionic and cationic groups can be used and the starch itself can originate from inter alia potato, corn, wheat, tapioca, rice, waxy maize. The anionic groups in the starch can be native and/or introduced by chemical treatment of the starch. It is particularly suitable to use cationised potato starch since native potato starch contains a substantial amount of covalently bound phosphate monoester groups.

The amphoteric polymers can also be an acrylamide based polymers, which are water soluble polymers with acrylamide and/or methacrylamide as the main monomeric unit. These polymers can have molecular weights from about 10000 to about 1500000, suitably from about 300000 to about 800000. Amphoteric acrylamide based polymers can be prepared by introduction of ionic groups in a polymer containing (meth)acrylamide as the main component. Cationic groups can be introduced by different methods such as Hofmann-degradation and Mannich reaction and anionic groups can for example be introduced by hydrolysis or sulphomethylation reaction. Amphoteric acrylamide based polymers can also be prepared by co-polymerisation of (meth)acrylamide and a monomer mixture containing both anionic and cationic monomers.

The degree of cationic substitution (DSc) of the amphoteric polymer can vary over a wide range, usually the degree of substitution is from 0.01 to 0.20, suitably from 0.01 to 0.15, preferably from 0.040 to 0.15 and more preferably from 0.045 to 0.15. In a particularly preferred embodiment the degree of cationic substitution is from 0.05 up to 0.12.

The ratio between the number of anionic and cationic groups in the amphoteric polymer can be within the range from 0.025: 1 up to 90:1 , preferably within the range from 0.4:1 up to 40:1.

The aqueous dispersion of sizing agent comprises an aluminium compound which is a polymeric aluminium compound comprising silicon. Preferably, the aluminium compound is a polymeric aluminium compound comprising silicate. Furthermore, the dispersion may have a weight ratio of aluminium to silicon from 1.0:0.001 up to 1.0:2.0, suitably from 1.0:0.005 up to 1.0: 0.5 and more preferably from 1.0: 0.01 up to 1.0: 0.1. More specifically, the aluminium compound comprised in the dispersion can be a polynucleate aluminium hydroxy silicate sulphate compound. The polynucleate aluminium hydroxy silicate sulphate compound suitably has an average composition as follows: AI_A(OH)_B(SO₄)_c(SiO_x)_D(H₂0)_E wherein A is 1.0 B ranges from 0.75 to 2.0, preferably from 1.2 to 1.8 C ranges from 0.30 to 1.12, preferably from 0.53 to 0.90 D ranges from 0 005 to 0 1 , preferably from 0 033 to 0 070

X is greater than 2 0 but less than or equal to 4 0, preferably less than or equal to 3 0 such that 3 = B+2C+2D(X-2), and E is larger than 4 In a preferred embodiment the silicon compound is bonded to the polymeric aluminium compound The basicity of the aqueous forms of the aluminium containing compound generally range from 20 up to 80 % more preferably from 30 up to 60% Suitable aluminium compounds comprised in the dispersion include the compounds disclosed in EP-A-0372715 which is hereby incorporated by reference

The aluminium compound may also include other anions in amounts ranging from traces up to 10 mol % calculated on the basis of sulphate, such as phosphates chlorides, acetates, borates, carbonates or salts of organic or inorganic acids

Furthermore, the aluminium compound can contain minor or substantial amounts, ranging from traces up to 10 mol %, calculated on the basis of Al of such cations as iron, magnesium, calcium, zinc and zirconium It has been found that the present aqueous sizing dispersion can be prepared in high solids contents and yet exhibit very good stability on storage and low viscosity Accordingly, this invention provides size dispersions with improved storage stability, higher solids content and/or lower viscosity A further benefit observed with the sizing dispersion is improved dilute stability which means less aggregation of the particles or droplets of sizing agent, thereby forming lower levels of bigger aggregates having lower sizing efficiency, as well as less deposits of the hydrophobic sizing agent on the paper machine and less wire contamination, thereby reducing the need for maintenance of the paper machine The present dispersions generally caη have sizing agent contents of from about 0 1 to about 50% by weight and suitably above 20% by weight Aqueous dispersions containing a 2- oxetaπone sizing agent, for example ketene dimer, according to the invention may have ketene dimer contents within the range of from 5 to about 50% by weight and preferably from about 10 to about 35% by weight Dispersions, or emulsions, containing an acid anhydride sizing agent according to the invention may have acid anhydride contents within the range from 0 1 to about 30% by weight and usually from about 1 to about 20% by weight Aqueous dispersions of non-cellulose-reactive sizing agents generally can have sizing agent contents of from 5 to 50% by weight and preferably from 10 to 35% by weight

The amphoteric polymer can be present in the dispersion in an amount of up to 100% by weight, suitably from 0 1 to 20% by weight and preferably from 1 to 10% by weight, based on the sizing agent The aluminium compound can be present in the dispersions in comparatively high amounts and suitably in an amount of from 0 1 up to 10% by weight, calculated as Al₂0₃ on the sizing agent, and preferably the amount of aluminium compound is within the range of from 0.5 up to 5% by weight. Despite the high amounts of aluminium compound the dispersions show good stability.

The aqueous dispersions according to the invention can be produced by mixing an aqueous phase with an amphoteric polymer and the sizing agent, preferably at a temperature where the sizing agent is liquid, and homogenising the mixture so obtained, suitably under pressure. Suitable temperatures for ketene dimer sizing agents are from about 55°C to 95°C whereas lower temperatures can be employed for acid anhydrides. The obtained emulsion, which contains droplets of sizing agent normally having a suitable size of from 0.1 to 3.5 μm in diameter, is then cooled. In addition to the above-mentioned components other substances can also be incorporated into the size dispersions, for example dispersing agents and surface active agents such as sodium lignosulphonate and naphthalene sulphonates and extenders such as urea and urea derivatives etc.

Cyclic dicarboxylic acid anhydrides such as ASA are liquid at room temperature. In commercial ASA-products an emulsifier is usually present. Aqueous compositions of cyclic dicarboxylic acid anhydrides are emulsions and compositions according to the invention can be prepared by mixing the liquid acid anhydride with a solution of the amphoteric polymer, whereby the aluminium compound is suitably present in the solution. The solution should be kept at a temperature of about 20°C. Compositions of cyclic dicarboxylic acid anhydrides according to the invention suitably contain the acid anhydride and the amphoteric polymer in a weight ratio of from 1:1 to 1:4. ASA-emulsions are normally produced at the paper mill in direct connection to its use as sizing agent at the paper production.

The aqueous dispersions of sizing agent according to the invention can be used in conventional manner in the production of paper using any type of cellulosic fibres and they can be used both for surface sizing and internal or stock sizing. 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, cardboard and paperboard. The stock contains cellulosic fibres, optionally in combination with mineral fillers, and usually the content of cellulosic fibres is at least 50% by weight, based on dry stock. 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 present invention preferably relates to a method for the production of paper in which an aqueous dispersion, as defined above, is used as a surface or stock size. Suitably the amount of sizing agent either added to the stock containing cellulosic fibres, and optional fillers, to be drained on a wire to form paper, or applied on the paper surface as a surface size usually at the size press, is from 0 01 to 1 0% by weight based on the dry weight of cellulosic fibres and optional fillers preferably from 0 05 to 0 5% by weight, 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 dispersions according to the present invention are preferably used in the production of paper where the stock comprises calcium carbonate such as chalk preferably precipitated calcium carbonate (PCC) or ground calcium carbonate (GCC) Whereas chalk and other ground carbonates are produced by the mechanical treatment such as crushing and grinding, of naturally occurring materials precipitated calcium carbonate is a different material produced synthetically in a chemical precipitation process usually the carbonation process, where calcium hydroxide is converted to calcium carbonate by reaction with carbon dioxide The stock can contain calcium carbonate like PCC in an amount up to about 35% by weight based on dry weight of cellulosic fibres, suitably from 5 to 30% by weight and preferably from 10 to 25% by weight Further additives which are conventional in papermaking may also be comprised in the stock whereto the aqueous dispersion is added such as dry drainage and retention agents, strength agents, wet strength agents, optical brightening agents, dyes, etc

The invention is further illustrated in more detail by the following examples which, however, are only intended to illustrate the invention and are not intended to limit the same

Example 1

An aqueous dispersion (no 1) of a sizing agent according to the invention was prepared by mixing 48 g of potatq starch with a degree of cationic substitution of (DSc) of 0.11 with naphthalene sulphonate sodium salt as dispersing agent in 800 g of water This is heated to near boiling point and maintained at this temperature for approximately 30 minutes. Subsequent, 150 g of AKD wax is mixed with above aqueous phase at a temperature of 75 ^CC The mixture was homogenised at a pressure of 200 bar and cooled After cooling 15 g of a polyaluminium silicate sulphate solution was added

Example 2

Sizing efficiency of the aqueous dispersion according to example 1 was evaluated in this example and compared with a reference dispersion (ref ) according to the disclosure of EP-A-677125, containing polyaluminium chloride and amphoteric potato starch in corresponding amounts Paper sheets were prepared with a target cobb value of around 25 gsm on a test paper machine The cobb values were measured according to T441 om- 98(TAPPI) The papermaking stock used contained pulp fibre comprising a mixture of soft wood and hard wood and around 18% of PCC The aqueous dispersions were used in con_junction with a commercial retention and dewatenng system, Compozil™, comprising cationic starch and an anionic aluminium-modified silica sol which were added to the stock separately; the cationic starch was added in an amount of 10-12 kg/t based on dry stock, and the silica sol was added in an amount of 0 2-0.5 kg/t, calculated as Sι0₂ and based on dry stock.

Table 1

Dispersion No. AKD dosage [kg/ton] Cobb 60 [g/m²]

1 0,64 24

1 0,54 27

1 0,62 26 ref. 0,75 25 ref. 0,75 24 ref. 0,89 23

Table 2 demonstrates corresponding or improved sizing efficiency at lower dosage levels of AKD when using a sizing dispersion according to the invention.

Example 3

The amount of ketone and the migration of ketones into a copy press system of the paper obtained in example 2 was measured. The migration of ketones was evaluated by measuring the amount of ketones in a fuserbelt after 20000 copies.

Table 3

Dispersion No. Ketone in paper Ketone in fuser belt

[mg/g paper] [mg/g rubber]

1 0,16 0,40 ref. 0,34 1 ,20

Table 3 clearly shows decreased amount of ketones in the in paper as well as a reduced migration of ketones when the sizing dispersions according to the invention are used.

Claims

1. Aqueous dispersion of a sizing agent containing an aluminium compound ana an amphoteric polymer ch a ra cte ri s e d in that the dispersion contains a polymeric aluminium compound comprising silicon.

2. Aqueous dispersion according to claim 1 c h a ra cte ri s e d in that the dispersion contains a polymeric aluminium compound comprising silicate.

3. Aqueous dispersion according to claim 1 cha racterised in that the dispersion has a weight ratio of aluminium to silicon (AI:Si) from 1.0 ' 0.001 up to 1.0 ' 2.0.

4. Aqueous dispersion according to any of the preceding claims ch a ra cte ri se d in that the dispersion comprises an aluminium compound which has the average composition:

AI_A(OH)_B(S0₄)c(SiO_x)_D(H₂0)_E wherein A is 1.0

B ranges from 0.75 to 2.0,

C ranges from 0.30 to 1.12,

D ranges from 0.005 to 0.1,

X is greater than 2.0 but less than or equal to 4.0, such that 3 = B+2C+2D(X-2), and E is larger than 4.

5. Aqueous dispersion according to any of the preceding claims, ch a racte rised in that the amphoteric polymer has a degree of cationic substitution (DSc) from 0.040 to 0.15.

6. Aqueous dispersion according to any of the preceding claims ch a racteri sed in that the amphoteric polymer is amphoteric starch or amphoteric polyacrylamide.

7. Aqueous dispersion according to any of the preceding claims ch a ra cterised in that the amphoteric polymer is amphoteric potato starch.

8. Aqueous dispersion according to any of the preceding claims, ch a ra cte ri sed in that the aluminium compound is present in an amount from about 0.1 up to about 10% by weight, calculated as Al₂0₃ on the sizing agent.

9. Aqueous dispersion according to any of the preceding claims ch aracterised in that the sizing agent is a cellulose-reactive sizing agent.

10. Aqueous dispersion according to any of the preceding claims characterised in that the sizing agent is ketene dimer. 11 Aqueous dispersion according to claim 10, c h a ra cte ri s e d in that the amount of ketene dimer is from about 10 up to about 35% by weight

12 Aqueous dispersion according to any of the preceding claims ch a ra cte ri sed in that the amphoteric polymer is present in an amount from about 01 up to about 20% by weight based on the ketene dimer

13 A process for the production of paper whereby a sizing agent is added either to the stock or applied as a surface sizing agent, c h a ra cte ri sed in that the sizing agent is an aqueous dispersion as defined in any of claims 1 to 12

14 A process according to claim 13 ch a ra cte ri s ed in that the stock or paper comprises calcium carbonate