Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H19/58—Polymers or oligomers of diolefins, aromatic vinyl monomers or unsaturated acids or derivatives thereof
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper

Definitions

• This invention relates to paper coating and more particularly the modification of paper coating rheology.
• polymeric thickeners are well documented in the prior art. Often these are in the form of aqueous emulsions which are either alkali soluble or alkali swellable.
• WO-A-00/34361 describes a comb polymer comprising a backbone of hydrophilic units and dihalogeno compounds and a moiety contain pendent hydrophobe, being particularly suited as a thickener for latex paints.
• the hydrophobic group is attached to the backbone of the preformed polymer.
• WO-A-02/12360 describes an aqueous dispersion of copolymeric microparticles, useful as an associative thickener in coating compositions such as paints.
• the thickeners exemplified include at least 10% by weight associative monomer.
• US 5478602 describes coating a substrate by applying an aqueous coating composition containing an alkali swellable complex hydrophobe associative thickener. Since the polymer is alkali swellable it must be so substantially cross-linked that the polymer is not soluble.
• associative thickeners bring about low high shear viscosity at small dosages. They can thus give an economic advantage over other types of synthetic thickeners.
• an equally well known problem with associative thickeners is that they provide poor water retention. So the economic advantage of associative thickeners is normally only obtained in conditions where water retention is not important.
• Water retention of coating colours has a profound influence on the runnability of the paper coating process. The coating colour loses a large proportion of the water that it contains as soon as it comes into contact with the surface of the paper owing to capillary action, the extent of which depends on the absorbency of the substrate. The pressure in the nip and under the blade also promotes dewatering. The release of water from the coating colour can have the following consequences:
• the solids content of the wet coating increases which modifies the rheology of the coating before it comes into contact with the blade. In the worst case the coating can form a thick, immobile 'filter cake" which can cause streaking and might even cause the web to break.
• the water taken up by the paper causes a reduction in its internal bonding strength which causes it to tear more easily under tension.
• the solids content of the coating colour re-circulated from the coater head can increase by 5% and more over a period of a few hours because the concentration of water soluble polymer in the coating colour is also much lower if too much water is released. This phenomenon is often observed at the precoating stage.
• the rod pressure of the coating apparatus can increase significantly.
• the coating composition results in poor water retention on the rod pressure tends to be unstable. In both instances in this can result in damage to the coated paper and/or poor runnability of the coater.
• the present invention has been made in order to address this problem.
• composition for modifying the rheology of paper coatings comprising an associative thickener characterised in that the associative content of the thickener is below 10%, the molecular weight of the thickener is below about 1 million, and the acid content is at least 10% by weight.
• Associative thickeners for obtaining low high shear viscosity are well known. They comprise hydrophilic, water soluble polymers with hydrophobic terminal groups or side chains.
• the hydrophobic terminal groups may be aliphatic or aromatic hydrocarbons and they are water insoluble. They can be joined to the hydrophilic polymer backbone by means of a hydrophilic spacer so that they remain flexible. Their structure is similar to that of surfactants. Interaction . between the hydrophobic groups or side chains is what is considered to provide for very high viscosity at low shear.
• associative thickeners there are various types of associative thickeners but those which are generally useful for the purpose of the present invention are formed from ethylenically unsaturated monomers such as (meth) acrylic acid, (meth) acrylates, maleic acid or anhydride, maleates, itaconic acid, itaconates, allyl ethers and vinyl esters.
• monomers such as (meth) acrylic acid, (meth) acrylates, maleic acid or anhydride, maleates, itaconic acid, itaconates, allyl ethers and vinyl esters.
• the choice of monomers is such that the polymer is insoluble in water and at neutral pHs, but dissolves under alkali conditions, for instance pH 8 to 10 or higher.
• the polymers are typically made by aqueous emulsion polymerisation of the monomers to form an aqueous emulsion of a polymer.
• polymers of particular interest in connection with the present invention are the hydrophobic alkali-soluble emulsions in which the hydrophilic polymer backbone comprises an alkali-soluble polyacrylate derived from monomers such as alkyl acrylates for example ethyl acrylate, acrylic acid and methacrylic acid.
• the hydrophibic side chains are attached to the polymer backbone by, for example, a polyoxyethylene oxide spacer.
• the hydrophobic side chains are provided by including ethylenically unsaturated monomers that contain the hydrophobic side chains.
• the hydrophobic side chains are C8-C30 alkyl groups.
• hydrophobic side chain moiety can be bonded to ethylenically unsaturated components such as acrylamido, acrylate or allyloxy etc.
• the thickening effect can be adjusted by altering the ratios of the monomers. All this is well known.
• associative thickeners used as paint thickeners, printing pastes and the like are disclosed in European Patent Specification 0 216 479 A1.
• Other associative thickeners are described in detail in European Patent Specification 0 013 836 A1 and 0 011 806 A1. These can be used in the present invention subject to their being modified in accordance with the definition of the invention as set out above.
• associative thickeners must have the special combination of an acid content of at least 10% by weight and an associative monomer content of below 10% of molecular weight below 1 million.
• Molecular weights of below 700,000 have been found to be particularly suitable for use in the present invention.
• An especially preferred molecular weight range is 70,000 to 150,000, and most preferably 70,000 to below 100,000.
• the polymers may be made by the inclusion of branching or cross-linking agents and/or chain transfer agents. However, it is preferred that the amounts of branching or cross-linking agents are used in amounts such that the polymer is substantially soluble in at least in alkali. Thus the polymer may be substantially linear, branched or slightly cross-linked. Nevertheless, the polymers desirably should not be so cross-linked that it is insoluble.
• the amount of cross linking agent is generally below 2000 ppm (by weight) and preferably below 1000 ppm. Typically the amount of cross-linking agent will be below 500 ppm, for instance in the range of 1 or 2 ppm up to for instance 100 ppm, preferably 5 ppm up to 20 or 30 ppm.
• the cross-linking agent can be a polyethylenically unsaturated monomer, for instance methylene bis acrylamide, butane diol diacrylate and tetra allyl ammonium chloride.
• Preferred thickeners for use in the invention are alkali soluble aqueous emulsions of ethyl acrylate/methacrylic acid/steareth 10 mole ethoxylate allyl ether and having a molecular weight below 1 million and preferably in the range 10,000 to 700,000 and more preferably in the range 50,000 to 200,000 or 250,000, and most preferably 70,000 and to below 100,000.
• Cross linkers and initiators can be included if desired.
• These polymers are mildly associative their associative content being preferably not above 5% and more preferably below 2.5%.
• the acid functionality may be provided by any suitable acid, methacrylic acid, acrylic acid or a mixture thereof being preferred.
• the acid content can be from 10 to 70%, preferably 20 to 50% by weight (based on the weight of polymer). As already indicated the precise values of the above parameters are chosen • having regard to the viscosity and water retention that the particular coating operation demands and to the dosage of the thickener in the coating composition.
• the thickener of the invention is included in a conventionally formulated coating composition for a pre-coat or top coat.
• the dosage of the thickener of the invention in the coating composition is kept as low as possible consistent with the required viscosity being obtained.
• a dosage of thickener of 0.2pph will give a target Brookfield viscosity of about 1000 to 1400 mPas at 100 rpm (typical for "roll and blade” coating method) in combination with good water retention of the order of 100 g/m 2 or lower. Unless otherwise stated the viscosity is measured at 25°C.
• the target viscosity will to some extent be chosen having regard to the coating method that is to be used.
• a target Brookfield viscosity is of the order of 700 to 1000 mPas whereas for a jet applicator the target Brookfield viscosity is of the order of 2000 to 2500 mPas.
• the dosage may need to be altered in order to obtain the required viscosity.
• changing the dosage of thickener to obtain the desired viscosity can also change the water retention.
• adjustment of the acid content of the thickener can, in those circumstances, be used in order to secure good water retention.
• the coating composition is preferably mildly alkaline, of the order of pH 8 to 10, preferably 8.5 to 9.5. Where necessary the pH can be adjusted for example by the addition of an alkali such as sodium hydroxide.
• the invention also provides a method of modifying the rheology of a paper coating composition comprising adding to the coating composition a thickener as defined above.
• the invention provides a paper coating method comprising coating paper or paperboard with a paper coating composition, said composition including a thickener as defined above.
• the thickeners of the invention can be used in all methods of paper coating and at all possible coating weights for example from 2 to 25 g/m 2 .
• the thickeners can be used in coating compositions for pre-coat, middle coat and top coat and can be used with any pigments and binders.
• Example 1 The following examples further illustrate the invention: Example 1
• the contents of the resin pot were heated to 85°C and then degassed with nitrogen for 30 minutes.
• An aqueous emulsion was prepared by mixing 143.75gms ethyl acrylate, lOO.OOgms methacrylic acid, 6.25gms steareth-10 ethoxylate allyl ether and 1.25gms n-dodecyl mercaptan into 10.5gms Disponil FES993 in 162.62gms deionised water.
• An initiator feed was prepared by dissolving O. ⁇ Ogms ammonium persulphate in 37.5gms water.
• the contents of the reactor were held between 83 and 87°C during the feed time and held for a further 1 hour at 85°C to reduce residual monomer content.
• a top coat was prepared according to the following recipe:
• Control Commercially available carboxymethyl cellulose
• HASE B Ethyl acrylate 55% methacrylic acid 40%; steareth 10 ethoxylate allyl ether 5%
• E Ethyl acrylate 58% methacrylic acid 40%; steareth 10 ethoxylate allyl ether 2%
• Compositions B to E also included about 5000 ppm of n-dodecyl mercaptan.
• compositions of the invention were judged by comparison of their viscosity and water retention with the control sample where the thickener was carboxymethyl cellulose and HASE thickener A.
• the thickeners of the invention gave lower high shear viscosity than control and about the same water retention.
• the HASE thickener gave about the same high shear viscosity as the thickeners of the invention, but significantly worse water retention. Note that the dosage of HASE thickeners and the thickeners of the invention was about the same.
• Water Retention GWR (gsm) The water retention was measured in gsm on a gravimetric water retention meter using the parameters of 2 minutes dwell time, 1.5 bar pressure and 5 ⁇ m polycarbonate membrane filters.
• High Shear Viscosity The high shear viscosity was measured in mPas on a cone and plate viscometer at 10000s "1 - Example 3
• Example 2 Certain of the samples used in Example 2 were added to a top coat composition. The dosages and the resultant viscosity and water retention are shown in the following Table 2.
• Example 2 The results confirm the results of Example 2, i.e. with the thickeners of the invention (B and C) it is possible to get low high shear and good water retention.
• typical HASE thickener (A) also gives low high shear viscosity but poor water retention.
• ACAV measured with a capillary viscometer in which pressure in a cylinder forces the sample through a capillary.
• a pre-coat formulation was prepared as follows:
• a pre-coat formulation was made up as follows: 100 parts CaC0 3 6 parts SB latex 6 parts starch
• compositions selected from a commercial HASE thickener, a commercial ASE thickener and in a thickener composition according to the invention.
• the composition of the coating formulation is a shown in Table 5.
• Sample F Ethyl acrylate 57.5% methacrylic acid 40%; steareth 20 ethoxylate allyl ether 2.5%
• sample F provides an excellent combination of low high shear viscosity and water retention values.
• sample F exhibits significantly improved water retention than the conventional associative thickener (commercial HASE). This is also clear from Figure 1.
• Example 7 Thickener composition sample F was used in and in a coating foimulation to coat paper in a pilot trial.
• Coating unit Film press, one-sided
• Thickener composition sample F and various other thickener compositions were used in coating formulations to coat paper in a pre coating pilot trial.
• Base paper Uncoated, 52 g/m2 (base paper for 90 g/m2 grade)
• Pre-coating conditions pH: ca. 8.5
• the thickener according to the present invention exhibits the best combination of low high shear viscosity and water retention over CMC or commercial ASE thickener. It can be seen that the CMC gave low high shear viscosity but poor water retention. The dose of commercial ASE thickener that provides low high shear viscosity gives poor water retention whereas a dose and of the same thickener and that provides good water retention exhibits poor high shear viscosity. Furthermore, the coating composition made using the thickener of the present invention provided better runability and no or low misting. Example 9
• Thickener composition sample F and various other thickener compositions were used in coating formulations to coat paper in a top coating pilot trial.
• Base paper Pre-coated, 52 g/m2 (pre-coated paper for 65 g/m2 grade)

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Paper (AREA)
• Paints Or Removers (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2003
  • 2003-02-26 GB GBGB0304354.4A patent/GB0304354D0/en not_active Ceased
• 2004
  • 2004-02-16 BR BRPI0407872-1A patent/BRPI0407872A/pt not_active IP Right Cessation
  • 2004-02-16 NZ NZ541746A patent/NZ541746A/en unknown
  • 2004-02-16 WO PCT/EP2004/001426 patent/WO2004076743A2/en active Application Filing
  • 2004-02-16 RU RU2005129548/04A patent/RU2005129548A/ru unknown
  • 2004-02-16 AU AU2004215224A patent/AU2004215224A1/en not_active Abandoned
  • 2004-02-16 KR KR1020057015788A patent/KR20050104398A/ko not_active Application Discontinuation
  • 2004-02-16 CN CNB2004800051756A patent/CN100385074C/zh not_active Expired - Fee Related
  • 2004-02-16 EP EP04711354A patent/EP1611283A2/de not_active Withdrawn
  • 2004-02-16 PL PL377002A patent/PL377002A1/pl unknown
  • 2004-02-16 US US10/545,754 patent/US20060148938A1/en not_active Abandoned
  • 2004-02-16 CA CA002517055A patent/CA2517055A1/en not_active Abandoned
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  • 2004-02-16 JP JP2006501853A patent/JP2006519280A/ja active Pending
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• 2005
  • 2005-08-24 NO NO20053948A patent/NO20053948L/no not_active Application Discontinuation

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