EP2593604B1

EP2593604B1 - Surface sizing of paper

Info

Publication number: EP2593604B1
Application number: EP11730659.7A
Authority: EP
Inventors: Ralf KRÜCKEL
Original assignee: Chemische Fabrik Bruehl Mare GmbH
Current assignee: CHEMISCHE FABRIK BRUEHL MARE GmbH
Priority date: 2010-07-13
Filing date: 2011-07-08
Publication date: 2014-05-14
Anticipated expiration: 2031-07-08
Also published as: EP2593604A1; PL2593604T3; PT2593604E; SI2593604T1; ES2478492T3; WO2012007364A1

Description

The invention relates to a surface sizing composition, its preparation and a process for surface treatment of a paper web.
Paper sizing is generally known to refer to the ability of paper (a fibrous substrate) to resist wetting or penetration of a liquid into it. Alkenylsuccinic anhydride-based sizing agents belong to the group of cellulose-reactive sizing agent and have been widely used for internal sizing of a wide variety of paper grades, such as printing and writing grades, and bleached and unbleached board grades. Typically it is assumed that sizing agents, including cellulose-reactive agents like alkenylsuccinic anhydrides, impart hydrophobic properties to the resulting paper and board products.
In internal sizing, the sizing agents are added to at the wet end of the paper machine before the paper web is formed from the pulp. A drawback of internal sizing agents is the size retention which will be normally lower than 100%, the sizing agents thus not being optimally used. Also, the presence of an internal sizing agent may adversely affect the paper web-producing process, specifically it can affect the entanglement and/or bonding of the fibers in the pulp thereby influence wet paper strength and other properties. Also, some of the internal sizing agent will be lost in the white water, which is undesired from both an economical and environmental viewpoint
Alkenylsuccinic anhydride (ASA) is ordinarily used as an internal size agent and applied in the form of an aqueous dispersion, mostly also including a dispersant and/or a stabilizer, such as cationic surfactants and cationic polymers, like modified starches, as well as amphoteric hydrophilic polymers (including starches). For example, EP-A-0151994 discloses the use of an aqueous formulation comprising ASA as an internal sizing agent and a specific polymer is used to emulsify the ASA. Further, WO 2003/022898 discloses an amphoteric promoter resin for sizing agents.
In order to optimize the distribution of the sizing agents over the paper product, sizing agents can be applied to the surface of a paper web, usually immediately or shortly after the web is formed, when the paper is still wet but partially dried. Such sizing agents are referred to as external or surface sizes and are usually applied in the form of an aqueous surface sizing composition.
It has been found that use of ASA as a surface sizing agent under practical paper-making-conditions involves an increased problem with fouling of the paper-making equipment, particularly when calcium ions (Ca²⁺) are present in significant amounts. This fouling is also known as deposit formation on the application equipment.
WO 2004/059082 discloses the use of polymers to emulsify ASA for surface sizing.
US 2006/0060814 discloses forming an emulsion from ASA and a surfactant and combining that emulsion with starch.
However, following the procedures of these disclosures still give significant deposit formation on the application equipment, usually a size press.
JP07-138898 A describes the use of a polymer as processing agent together with ASA for surface sizing of newsprint, but there is no disclosure how to reduce or prevent the formation of deposits on a size press.
According to the present invention it has now been found possible to significantly diminish the problem of fouling, thus opening the possibility to use a regular and well accepted ASA as a surface sizing agent for all paper products.
An aspect of the invention concerns a process for the preparation of surface sizing composition comprising separately adding to an aqueous component being an aqueous solution comprising starch and at least 80 wt% of water:

(a) an aqueous dispersion comprising an alkenylsuccinic anhydride (ASA); and,
(b) a non-ionic, amphoteric, cationic, or anionic polymer.

A further aspect of the invention concerns a sizing composition obtainable by such a process.
Still a further aspect of the invention concerns a process for surface treatment of a paper web, comprising the steps of preparing a surface sizing composition as described herein and applying said surface sizing composition to the surface of the paper web.
The aqueous component can include only small amounts of various unavoidable impurities, such as calcium ions. The aqueous solution comprising starch (referred to herein as surface starch) has preferably a water content of at least 85 wt% or at least 90 wt%, or even at least 95 wt%. The aqueous solution can have at least one further component, wherein the at least one further component may, for example, be at least one of wheat flour, carboxy methyl cellulose (CMC) or any other suitable component, or mixtures thereof. The surface starch may, for example, be anionic, cationic, nonionic or amphoteric starch, particularly anionic, non-ionic or amphoteric starch, from various plants, including corn, potato, wheat, tapioca, or sorghum, optionally modified by enzymes, high temperature or chemical/thermal converting techniques, like oxidized starch, ethylated starch or pearl starch. In some embodiments the surface starch is, for example oxidized starch. The aqueous solution may, for example, comprise a minimum of about 1 wt% starch in water, typically from 3 to 19 wt% or from 5 to 15 wt%. A preferred maximum level of starch in the aqueous solution is about 20% by weight. The pH of the aqueous component, e.g. solution of surface starch, may, for example, be between about 4 and 9, or between 5 and 7. The surface starch may enhance the strength property of the surface fibres of the paper and also serve as a carrier for the ASA.
The aqueous dispersion of the ASA may, for example, comprise ASA in an amount of at least 0.01 wt%, particularly at least 0.1 wt%, or at least 0.3 wt%, and up to 20 wt%, or up to 15 wt. %, based on the total weight of the dispersion. The ASA is generally in the form of finely divided particles or droplets dispersed in an aqueous phase and droplets or particles may, for example, have a size such that the d50 of the droplet size distribution (as determined in the conventional way by laser diffraction, such as Malvern) is from 0.5 microns to less than 5 microns.
The term "dispersion" as used herein is meant to include all kinds of systems in which particles are dispersed in a continuous phase, including emulsions where the dispersed phase is a liquid.
The ASA generally includes alkenylsuccinic anhydride compounds composed of mono unsaturated hydrocarbon chains containing pendant succinic anhydride groups. The alkenylsuccinic anhydride compounds are generally liquid and may be derived from maleic anhydride and suitable olefins, as is well known in the art.
The alkenylsuccinic anhydride compounds may, for example, be made by reacting one or more isomerized C14 - C24 mono olefins, preferably an excess of an internal olefin, with maleic anhydride, at a temperature and for a time sufficient to form the alkenylsuccinic anhydride compound in conventional ways. The ASA referred to herein may also include hydrolyzed alkenylsuccinic anhydride and/or substituted cyclic dicarboxylic acid anhydride. For example, the ASA may contain from 0 to about 30 wt%, based on the total weight of ASA, hydrolyzed alkenylsuccinic anhydride. ASA is commercially available, such as Eka® SA 220 from AkzoNobel.
The dispersions are usually prepared with the aid of a conventional dispersant system, preferably with at least one dispersant which, when used to make an emulsion in accordance with the invention, produces an emulsion that minimizes coalescing and imparts useful sizing properties to a fibrous substrate after the emulsion contacts the fibrous substrate. Generally, the dispersant system may include one or more are anionic, nonionic, or cationic surfactant that can have a wide range of HLB values.
The aqueous dispersion of ASA may comprise components from a dispersant system, such as at least one surfactant. If at least one surfactant is included, the content thereof may, for example be from 0.01 to 10 wt% or from 0.1 to 5 wt%, based on the weight of the total dispersion.
The at least one surfactant may, for example, include alkyl and aryl primary, secondary and tertiary amines and their corresponding quaternary salts, sulfosuccinates, fatty acids, ethoxylated fatty acids, fatty alcohols, ethoxylated fatty alcohols, fatty esters, ethoxylated fatty esters, ethoxylated triglycerides, sulfonated amides, sulfonated amines, ethoxylated polymers, propoxylated polymers or ethoxylated/ propoxylated copolymers, polyethylene glycols, phosphate esters, phosphonated fatty acid ethoxylates, phosphonated fatty alcohol ethoxylates, and alkyl and aryl sulfonates and sulfates.
Examples of preferred suitable surfactants include but are not limited to amides; ethoxylated polymers, propoxylated polymers or ethoxylated/propoxylated copolymers; fatty alcohols, ethoxylated fatty alcohols, fatty esters, carboxylated alcohol or alkylphenol ethoxylates; carboxylic acids; fatty acids; diphenyl sulfonate derivatives; ethoxylated alcohols; ethoxylated fatty alcohols; ethoxylated alkylphenols; ethoxylated amines; ethoxylated amides; ethoxylated aryl phenols; ethoxylated fatty acids; ethoxylated triglycerides; ethoxylated fatty esters; ethoxylated glycol esters; polyethylene glycols; fatty acid esters; glycerol esters; glycol esters; certain lanolin-based derivatives; monoglycerides, diglycerides and derivatives; olefin sulfonates; phosphate esters; phosphorus organic derivatives; phosphonated fatty acid ethoxylates, phosphonated fatty alcohol ethoxylates; polyethylene glycols; polymeric polysaccharides; propoxylated and ethoxylated fatty acids; alkyl and aryl sulfates and sulfonates; ethoxylated alkylphenols; sulfosuccinamates; sulfosuccinates.
The dispersion of ASA may comprise one or more cationic organic compound having a weight average molecular weight less than 10000 or at least one anionic stabiliser, or both, which is most preferred.
The aqueous dispersion of ASA may comprise starch, for example in an amount so the dry weight ratio of the ASA to starch ranges from 1:0.02 to 1:3, or from 1:0.05 to 1:0.5, or from 1:0.1 to 1:0.2.. The starch could be of any kind, such as anionic, cationic, nonionic or amphoteric starch from various plants, including corn, potato, wheat, tapioca, or sorghum, optionally modified by enzymes, high temperature or chemical/thermal converting techniques. In some embodiments, no starch is included in the dispersion of ASA.
The aqueous dispersion of ASA can be produced in a conventional way by homogenising the ingredients to obtain an aqueous dispersion. The homogenization can be achieved in the absence of high shearing forces (low shear conditions), e.g., those shearing conditions are created by a device selected from the group of centrifugal pumps, static in-line mixers, peristaltic pumps, and combinations thereof, but also high shear conditions may be applied (rotor-stator mixers, colloid mills, ultrasonic homogenisers, etc). The temperature during the homogenisation is preferably sufficiently high for the ASA to be liquid, and is in most case a suitable temperature ranges from about 10 to about 100 °C, most preferably from about 20 to about 60 °C.
A process of the invention may thus comprise dispersing ASA in water and optional other components as described above, for example at least one surfactant, to obtain the aqueous dispersion comprising ASA and adding that dispersion to the aqueous component as described herein.
The non-ionic, amphoteric, cationic, or anionic polymer is preferably added as an aqueous solution thereof. The aqueous solution may, for example, comprise from 1 to 60 wt% or from 15 to 30 wt% of at least one such polymer. It is possible to prepare such an aqueous solution by dissolving a solid polymer, but many suitable polymers are also commercially available as aqueous solutions.
The polymer can be selected from a wide variety of non-ionic, amphoteric, cationic and anionic polymers. In some embodiments the polymer is selected from non-ionic, amphoteric, and cationic polymers.
The preferred molecular weight of such a polymer depends on its exact structure but the weight-averaged molecular weight (Mw) is typically from 50,000 to 1,000,000 Dalton (as determined in a conventional way by size exclusion chromatography using polystyrenes as a standard). More specifically, it is preferred to use a polymer with an Mw above 55,000, for example above 60,000 or above 65,000. The higher the Mw, the more difficult it is to process the polymer. Therefore it can be preferred to use a polymer with a Mw less than 900,000, suitably less than 800,000. In some embodiments, the polymer is water-soluble at a pH<6 at 25 °C.
In some embodiments the polymer is a synthetic polymer. In other embodiments the polymer is an optionally modified natural polymer, such as optionally modified starch. Also mixtures of synthetic and natural polymers may be used. It is noted that the same kind of polymer that is used as component (b), i.e. for reducing deposit formation, may also be used in the preparation of the ASA dispersion, but that in such a case the polymer is also added separately to the aqueous component.
In some embodiments, the polymer is selected from polyacrylamides (PAM), for example of core-shell type, particularly having a weight averaged molecular weight (M_w) from 500,000 to 1,000,000, and particularly amphoteric PAM. A suitable amphoteric PAM may, for example, contain anionic acid functions from itaconic acid and/or acrylic acid and cationic quaternary nitrogen groups (also referred to as "quat") from benzyl quat (meth)acrylate or trimethyl quat (meth)acrylate.
An amphoteric polymer, such as amphoteric PAM, may, for example, have a total net charge (cationic minus anionic charges) from 0.1 to 6 or from 0.25 to 3 meq/g, measured by polyelectrolyte titration.
In some embodiments a cationic PAM is used, for example a linear polymer, particularly having an Mw of from 250,000 to 500.000. A cationic PAM may, for example, contain benzyl quat (meth)acrylate or trimethyl quat (meth)acrylate-derived groups for the cationic function.
In some embodiments the polymer is selected from at least one of cationic starch, polyamide amines, or polyamines.
A cationic polymer, such as PAM or polyamine, may, for example, have a total net charge from 0.5 to 8 or from 1 to 6 meq/g, measured by polyelectrolyte titration.
A cationic starch, may, for example, have a total net charge from 0.05 to 0.8 or from 0.25 to 0.5 mol% nitrogen, measured by Kjeldahl method.
Many suitable polymers are commercially available, such as the amphoteric PAM Eka® DS 750 from AkzoNobel and the cationic starches Raisamyl® 142 from Chemigate and Vector® SC 20157 from Roquette, and the polyamine Eka® ATC 4150 from AkzoNobel.
The ASA (component (a)) and the polymer (component (b)) are added to the aqueous component in amounts to provide a composition suitable for surface sizing when applied to a paper web. The amount of ASA in the final composition may, for example, be from 0.005 to 5 wt% or from 0.05 to 1 wt%, calculated as dry ASA on the entire composition. The amount of polymer (component (b)) may, for example, be from 0.0005 to 5 wt% or from 0.005 to 1 wt%, calculated as dry polymer on the entire composition. The weight ratio ASA:to polymer used in final composition may, for example, be from 0.005:1 to 1:0.005 (on a dry weight basis).
According to the invention it was found that polymers as described herein can be used to reduce the amount of deposit formation when ASA is used as a surface sizing agent, particularly when added to the aqueous component separately from the ASA. The polymer and the ASA will then be in contact with each other for only a short time before being contacted with the paper in the size press, usually less than 60 minutes or less than 30 minutes, in most cases less than 15 minutes or less than 10 minutes. Doing so results in excellent paper surface sizing while minimizing deposit formation on the size press.
The application equipment may be part of a continuous operation and in that case the time indicated is to be seen as the time under steady state process conditions. Further, the time indicated is to be seen as the averaged residence time of the ASA and/or the polymer in the application equipment. In most cases, the aqueous component, e.g. an aqueous solution of surface starch, is circulating through the application equipment and the dispersion of ASA and the polymer are continuously added as separate streams to the circulating aqueous component to form the final surface sizing composition applied to the paper web.
The invention is applicable for surface treating of all kinds of paper, but in some embodiments the paper that is surface treated is not newspaper. Furthermore, the invention is, for example, applicable to a process for making paper products that are essentially free from optical brighteners, meaning that less than 0.5 % wt%, preferably less than 0.2 wt%, or less than 0.05 wt%, based on the weight of the dried paper, of the optical brightener is present in the paper that is surface treated in accordance with the invention.
The term "paper", as used herein is meant to include not only paper but all types of cellulose-based products in sheet or web form, including, for example, board and paperboard, which are based on recycled paper fibers. However, the invention is particularly advantageous for preparation of fine paper, which includes graphic paper to be used in all kinds of printing processes, such as ink-jet printing, laser printing, copying, etc. More specifically, fine papers are printing and writing sheets based mainly on chemical pulp. Normally the content of mechanic pulp is below 10 wt% and the amount of fillers is within the range from 5 to 25 wt% based on the dry weight of the paper. The surface sizing process of the invention is of particular interest for making surface-sized liner board and fine paper.
With the exception of the information in the examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term 'about.' Further, where numerical ranges are disclosed they are meant to be continuous ranges that include every value between the minimum and maximum value as presented. The words "dry" and "dried", as used herein, are meant to have their conventional meaning, indicating that the product concerned is to be taken without any (residual) water.
Although not necessary, it can be beneficial to include one or more conventional, cellulose non-reactive sizes in the surface sizing composition, or to add them separately. The use of cellulose non-reactive sizes generally result in improved toner adhesion, little or no effect on coefficient of friction, no effect, or an improved effect on high speed converting, and no size reversion when compared to reactive sizes. However, they are less efficient at sizing than the cellulose reactive sizes.
If used, the weight ratio between the ASA to cellulose non-reactive sizing agent is preferably from about 1:99 to about 99:1, most preferably from about 1:9 to about 9:1. A cellulose non-reactive sizing agent may be added separately to the aqueous component or be included into the aqueous dispersion of ASA, for example in an amount from 0.1 to 50 wt% or from 0.5 to 50 wt% based on the entire composition. Examples of such optional further sizing agents include copolymers of styrene with vinyl monomers such as maleic anhydride, acrylic acid and its alkyl esters, acrylamide, etc., such as those described in in e.g. US Patents No. 6426381 , 5672392 and 6835767 , and in US Patent Applications Publ. No. 2009/0139675 and 2010/0016478 .
The cellulose non-reactive sizes are usually polymeric materials having a molecular weight M_w greater than 1,500. Preferably the molecular weight is greater than 5,000, and more preferably greater than 10,000. Suitable cellulose non-reactive sizing agents are polymeric materials preferably having a weight average molecular weight greater than 50,000. In most cases the molecular weight can be up to 5,000,000.
Suitable water-based non-reactive sizes include dispersions of anionic polymers made from at least one monomer containing at least one carboxyl group. These polymers include copolymers of styrene or substituted styrenes with vinyl monomers containing carboxyl groups. Examples of such monomers include, but are not restricted to maleic anhydride, acrylic acid, methacrylic acid and itaconic acid. Also included are the partially esterified forms of such copolymers. Examples of suitable polymer formulations) are styrene/maleic anhydride resins and their partially esterified counterparts. Examples of polymeric cellulose non-reactive sizes for use in the invention are styrene/maleic anhydride resins
Other examples of suitable non-reactive sizes include, but is not limited to, copolymers of styrene or substituted styrenes with vinyl monomers. Examples of such vinyl monomers include, but are not restricted to maleic anhydride, acrylic acid or its alkyl esters, methacrylic acid or its alkyl esters, itaconic acid, divinyl benzene, acrylamide, acrylonitrile, cyclopentadiene and mixtures thereof. Also included are polyurethanes and copolymers of ethylene with comonomers such as vinyl acetate, acrylic acid and methacrylic acid. Preferred water-insoluble polymers are copolymers made from monomers comprising styrene or substituted styrene, alkyl acrylate or methacrylate and ethylenically unsaturated carboxylic acid, where the styrene or substituted styrene is selected from the group consisting of styrene, α-methylstyrene, vinyl toluene and mixtures thereof, where the alkyl group of the alkyl acrylate or methacrylate contains from 1 to about 12 carbon atoms and where the ethylenically unsaturated carboxylic acid is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid or anhydride, fumaric acid, itaconic acid and mixtures thereof. Particularly suitable polymers include copolymers of styrene or substituted styrenes with at least one other kind of ethylenically unsaturated monomers, preferably comprising monomers containing one or more carboxyl groups. Examples of such monomers include maleic anhydride, acrylic acid, methacrylic acid and itaconic acid, as well as esters, amides and nitrile thereof, of which esters are particularly preferred. Preferred esters are alkyl esters where the alkyl group preferably have from 1 to 12 carbon atoms, most preferably from 1 to 5 carbon atoms. Particularly preferred are esters of acrylic acid or methacrylic acid. Examples of alkyl groups are methyl, ethyl, propyl, n-butyl, iso-butyl, tert-butyl and 2-butyl. A mixture at least two isomeric butyl acrylates or methacrylates, such as n-butyl- and t-butyl acrylate or methacrylate, is particularly preferred. The monomers as described above may also be co-polymerised with other ethylenically unsaturated monomers.
In some embodiments the cellulose non-reactive sizing agent is a copolymer obtained from ethylenically unsaturated monomers comprising from about 20 to about 80 wt%, preferably from about 30 to about 70 wt% of styrene or substituted styrene, from about 20 to about 80 wt%, preferably from about 30 to about 70 wt% of alkyl acrylate or methacrylate, and from 0 to about 15 wt%, preferably from 0 to about 10 wt% of other ethylenically unsaturated monomers.
It is noted that also a further cellulose reactive size can be used in combination with the ASA. For instance, if so desired, conventional alkyl ketene dimer can be used. Such further reactive sizes can be added separately or with the ASA.
As mentioned, Ca²⁺ present in the surface sizing compositions influences the speed and amount of deposit formation. The Ca²⁺ is typically present in the paper pulp and concentrated in the paper product when it is (partially) dried in steps before the surface sizing is supplied to paper web. It will then also be present in the water that is used in the preparation of the various formulations, such as one or more of the ASA dispersion the polymer formulation and the aqueous component to which the ASA and the polymer are added. Consequently, at steady state conditions the surface sizing composition may take up close to the maximum amount of Ca²⁺ that will dissolve in said composition at the conditions prevailing during application to the paper web. Typical Ca²⁺ concentrations in the surface sizing composition may, for example, be from 1 to 1,000 mg/litre, such as between 5 and 200 mg/litre or between 5 and 100 mg/litre. With those typical levels of calcium ions the problems with deposit formation are particularly severe when ASA is used as a surface sizing agent. Accordingly, in some embodiments of the invention, the surface sizing composition, for example a size press solution, at steady state conditions, has a Ca²⁺ level exceeding 5 mg/litre, or exceeding 20 mg/litre.
As mentioned, the pH of the surface sizing composition can influence the speed and amount of deposit formation. The pH is typically dependent on the pH of the paper pulp, of the dilution water, starch quality and other ingredients used. Typically values for the pH may, for example, be between 4 and 8, often between 5 and 7. In the process according to the invention, the surface sizing composition, at steady state conditions and when containing all additives, preferably has a pH lower than 8 or lower than 7, more preferably lower than 6 or even lower than 5. In most cases the pH will be higher than 1.
The surface sizing composition of the invention, or any of the components used for preparing the composition, may contain further conventional additives for surface sizes, such as one or more of biocides, insolubilisers, defoamers, crosslinkers such as inorganic compounds like aluminium or zirconium compounds, stabilisers, optical brightening agents, e.g. in an amount from about 0 to about 2 wt% of amount of paper produced, pigments (e.g. chalk, precipitated calcium carbonate, kaolin, titanium dioxide, barium sulphate or gypsum), e.g. in an amount from about 0 to about 15 g/m² paper produced.
The surface sizing composition may be applied to the paper web by means of any suitable equipment, such as various kinds of size presses, usually positioned near to the end of a paper making process. A size press is typically designed to comprise a two roll press with the paper web running between the rolls, for example with a hydraulic or pneumatic pressure system. Any conventional size press can be used in the present invention and examples thereof include puddle size presses (also referred to pond size presses), film size presses and gate-roll size presses. Optionally the paper web is first coated with surface sizing composition followed by pressing. After application of the surface sizing composition, the paper web is usually dried utilizing any of the conventional drying procedures well known in the art to obtain a desired paper product.
The amount of surface sizing composition transferred to the paper web may, for example, be such that the surface sized paper will contain from 0.001, preferably more than 0.01, more preferably more than 0.05 wt%, up to less than 50, preferably less than 30, more preferably less than 20 wt%, of ASA from the surface sizing composition, expressed as the amount of dry ASA from the composition in the final dried paper.
It is noted that also paper coatings may optionally be applied to the surface of paper, but that such paper coatings are completely different in function and composition from surface sizes. Paper coating compositions have much higher viscosities than surface size compositions, and thus cannot readily be applied by a size press on a typical paper machine. Paper coatings contain pigment at levels 3 to 20 times higher than that of polymeric binder; whereas in a typical surface size pigments are generally not present, although they can be optionally used in low amount. If pigments are used, the amount thereof may, for example be at levels of 0 to 50% by weight or 0 to 30% by weight of the total solids level of the aqueous surface sizing composition.
The invention will now be further described in connections with the following examples which, however, do not intend to limit the scope thereof. Unless otherwise stated, all parts and percentages refer to parts and percent by weight.

Examples

In the examples presented below an investigation was made on the influence of a polymer on the deposit formation on a size press when an ASA formulation was used.
In the tests a modified Einlehner lab size press (vertical rod transfer) with a hot air gun was used. The temperature of the hot air was around 75 °C. The size press was equipped with a size press circulation loop with a circulation rate of ~500 ml per minute. The upper size press roll was protected/covered with the plastic film, fixed with adhesive tape (Tesa® ex Beiersdorf). The weight of the untreated dried plastic film was measured before use.
For deposit formation studies, no paper was treated, but the plastic film was used to simulate a paper stream. This means that in these tests there was no actual pickup of the formulation by paper, the formulations stayed in the puddle for up to one hour, which simulates actual steady state conditions. The plastic film used to simulate paper was a plastic film as used for lasercopier machines supplied by VIP (material number 1200019).
The following materials were used for preparing the surface sizing compositions:

Oxidized potato starch for surface starch (Perfectamyl® P 255 SH ex Avebe)
ASA (Eka® SA 220, ex AkzoNobel)
Calcium chloride, anhydrous powder (ex Merck)
Phosphonated fatty alcohol ethoxylate surfactant (Servoxyl® 99 ex Degussa)
Amphoteric polyacrylamide (Eka® DS 750 ex AkzoNobel, delivered as an 30 wt% aqueous solution)
Cationic starch polymer (Vector® SC 20157 ex Roquette, delivered as an 20 wt% aqueous solution)
Cationic starch polymer (Raisamyl® 142 ex Chemigate), dissolved in water to an 5 wt% solution before use

A surface starch solution was prepared by degradation using cooking conditions at temperature of 95 °C for 45 minutes at a concentration of 22 wt%. The starch was later dissolved to a final concentration of 7 wt%. The water used was treated with calcium chloride in order to obtain the target calcium levels in the final size press liquid, that mimic typical commercial process conditions. Actual Ca²⁺ concentration are presented.
ASA was dispersed in water together with a phosphonated fatty alcohol ethoxylate surfactant in an amount of 1 wt% surfactant based on the weight of the ASA. A Waring® household kitchen blender (model HGBPWTG4, type 8010EG) was used at high speed to make the dispersion at 15 °C. The d50 of the particle size of the resulting dispersed ASA emulsion was below 2 µm as measured by light scattering. The final ASA concentration was 7.5 wt%.
Immediate before testing, 14.5 g ASA dispersion was mixed with 800 g surface starch solution (7 wt% solids), which was premixed with an aqueous solution of the polymer being tested, to obtain a surface sizing composition (also referred to as size press liquid) and, temperature of the composition was adjusted to 55°C. The size press liquid was filled into the size press circulation loop. Since Ca²⁺ is influencing the deposit formation, the amount of Ca²⁺ was controlled by addition of CaCl₂. Unless stated differently, the calcium levels were maintained at 714 mg Ca²⁺/l by addition of the appropriate amount of CaCl₂. The pH was adjusted to 6.0, or the indicated value by use of ammonium hydroxide solution (1 N). The pH was permanently controlled at the target value by use of an automatic titration equipment dosing ammonium hydroxide solution (1 N). Temperature was controlled at 55-60 °C over the test period. The test period was 1 hour. Deposits were formed on the plastic foil, which was removed after the end of the test period, dried and the weight measured again to determine the amount of deposits formed.
In a first test no polymer was used and the amount of deposit found was unacceptably high (>1g). The addition of a polymer of the invention was found to decrease depositions on the size press and post drying section.
In the following tables the amount of deposits is presented when an ASA reactive surface size and a polymer were used. The test was performed at two pH values. In the comparative experiments the ASA was dispersed in an aqueous solution of the polymer and the resulting dispersion then added to the surface starch solution, in amounts corresponding to the amounts when the ASA dispersion and the polymer were separately added to the surface starch solution.
In the following examples 1-2 the weight ratio of ASA to polymer (Eka® DS 750) was 1 : 0.25 (on a dry weight basis). The droplet/particle size of all dispersions was 2-4 microns.

Example pH deposits formed (mg)

Ex 1 4-5 25

Comparative Ex.1 4-5 38

Ex 2 6 79

Comparative Ex 2 6 100
The data shows that using the same chemicals, the experiment according to the invention in which the ASA and the polymer were added separately to the surface starch solution shows much better results than the comparative examples in which ASA was emulsified in the polymer solution.
In the following examples 3-4 the weight ratio of ASA to polymer (Vector® SC 20157) was 1 : 0.5 (on a dry weight basis). The droplet/particle size of all dispersions was 2-4 microns.

Example pH deposits formed (mg)

Ex 3 4-5 58

Comparative Ex 3 4-5 104

Ex 4 6 88

Comparative Ex 4 6 143
In the following examples 5-6 the weight ratio of ASA to polymer (Raisamyl® 142) was (on a dry weight basis). The d50 of the droplet/particle size of all dispersions was 2-4 microns.

Example pH Polymer level (expressed as percent polymer (dry) on ASA (dry) deposits formed (mg)

Ex 5 6 25 335

Comparative Ex 5 6 25 927

Ex 6 6 50 51

Comparative Ex 6 6 50 656
Again, the results show that the polymers could be used to reduce deposit formation and that less deposits were formed when the polymer formulation was added separately to the size press compared to a situation where the ASA was dissolved/dispersed in the polymer solution/dispersion, using otherwise the same chemicals and same conditions. Further, the fact that less deposits are formed shows that a composition prepared by separate addition of ASA and polymer has different properties compared to a composition in which the ASA has been dispersed in a polymer solution.

Claims

A process for the preparation of surface sizing composition comprising separately adding to an aqueous component being an aqueous solution comprising starch and at least 80 wt% of water:
(a) an aqueous dispersion comprising an alkenylsuccinic anhydride (ASA); and,

(b) a non-ionic, amphoteric, cationle, or anionic polymer.
A process as claimed in claim 1, wherein the starch is anionic, amphoteric, or nonionic starch.
A process as claimed in any one of the claims 1-2, wherein aqueous solution comprises from 3 to 19 wt% of starch.
A process as claimed in any one of the claims 1-3, wherein the non-ionic, amphoteric, cationic, or anionic polymer is added as an aqueous solution thereof.
A process as claimed in any one of the claims 1-4, wherein the weight-averaged molecular weight (Mw) of the polymer is from 50, 000 to 1,000,000 Dalton.
A process as claimed in any one of the claims 1-5, wherein the polymer is water-soluble at a pH<6 at 25 °C.
A process as claimed in any one of the claims 1-6, wherein the polymer is selected from the group consisting of amphoteric polyacrylamides (PAM), cationic polyacrylamides, cationic starches, polyamide amines, and polyamines.
A process as claimed in any one of the claims 1-7, wherein the polymer is an amphoteric polymer having a total net charge from 0.1 to 6 meq/g.
A process as claimed in any one of the claims 1-8, wherein the amphoteric PAM contain anionic acid functions from itaconic acid and/or acrylic acid and cationic quaternary nitrogen groups from benzyl quat (meth)acrylate or trimethyl quat (meth)acrylate.
A surface sizing composition obtainable by the process according to any one of the claims 1-9.
A process for surface treatment of a paper web, comprising the steps of preparing a surface sizing composition according to the process of any one of the claims 1-9 and applying said surface sizing composition to the surface of the paper web.
A process as claimed in claim 11, wherein the aqueous component is circulating through an application equipment and the dispersion of ASA and the polymer are continuously added as separate streams to the circulating aqueous component to form the final surface sizing composition applied to the paper web.
A process as claimed in any one of the claims 11-12, wherein the surface sizing composition, at steady state conditions, has a Ca²⁺ level exceeding 5 mg/l.
A process as claimed in any one of the claims 11-13, wherein the surface sizing composition, at steady state conditions, has a pH lower than 8,