EP0600801B1 - Latex binder for a paper coating composition - Google Patents

Abstract

A binder for paper-coating composition, characterised in that it comprises: A) from 97 to 99.9 %, preferably from 97.5 to 99.5 % (calculated on the basis of the weight of the solids content) of a film-forming aqueous dispersion of a latex of an organic copolymer chosen from a styrene-butadiene, styrene/acrylate and styrene/butadiene/acrylate copolymer, B) from 3 to 0.1 %, preferably from 2.5 to 0.5 % (calculated on the basis of the weight of the solids content) of an aqueous emulsion of an aromatic epoxy resin and of a nonionic surface-active agent. The paper coated with the coating composition according to the invention exhibits, in particular, a better wet pick resistance.

Description

The present invention relates to a latex binder for a paper coating composition comprising an aromatic epoxy resin emulsion.

By composition for coating paper, is generally meant an aqueous coating composition essentially containing a filler (pigment), a binder and possibly various adjuvants.

Such a composition is applied to the paper in order to modify the surface properties, in particular the whiteness, the gloss, the printability, etc. It is now in common use in the paper industry to use as essentially binding a latex of organic, synthetic, film-forming polymer, in the form of an aqueous emulsion.

Among the properties that coated paper must have for offset printing, wet peel resistance (RAH) is of particular importance. The offset printing process, which is based on the repulsion of water by fatty inks, actually uses water. In four-color offset printing, we are therefore led to print the second, third or fourth color in a previously wet location. It is therefore important, in order to avoid the phenomena of peeling in the wet state, which result in fouling of the blanket of the offset presses, that the coated paper has sufficient wet peel resistance.

An important property is the binding power of latex, characterized by the measurement of dry peel (RAS) and / or wet (RAH). The higher this binding power, the more a lower latex content can be used in the coating composition while maintaining the same quality.

The improvement in the resistance to dry stripping (RAS) and / or wet (RAH) is unfortunately often accompanied by a degradation of the porosity in inks of the layer or a degradation of the storage stability of the binder. or a degradation of the storage stability of the coating composition.

The main aim of the present invention is precisely to provide an organic copolymer binder for coating composition giving the coating both a wet and dry peel resistance very improved in combination with good coating porosity and good stability to storage of the binder and the coating composition.

• A) de 97 à 99,9 %, de préférence 97,5 à 99,5 % (calculés sur la base du poids de l'extrait sec), d'une dispersion aqueuse filmogène d'un latex d'un copolymère organique choisi parmi un copolymère styrène/butadiène, styrène/acrylate et styrène/butadiène/acrylate et,
• B) de 0,1 à 3 %, de préférence de 0,5 à 2,5 % en poids (calculés sur la base du poids de l'extrait sec) d'une émulsion aqueuse d'une résine époxy aromatique et d'un agent tensio-actif non ionique.

This object and others is achieved by the present invention which in fact relates to a binder for a paper coating composition comprising:

• A) from 97 to 99.9%, preferably 97.5 to 99.5% (calculated on the basis of the weight of the dry extract), of a film-forming aqueous dispersion of a latex of organic copolymer chosen from a styrene / butadiene, styrene / acrylate and styrene / butadiene / acrylate copolymer and,
• B) from 0.1 to 3%, preferably from 0.5 to 2.5% by weight (calculated on the basis of the weight of the dry extract) of an aqueous emulsion of an aromatic epoxy resin and of a nonionic surfactant.

If the content of emulsion B is less than 0.1%, the expected effect is not obtained in particular at the level of the RAH. If the content of B is greater than 3%, the binder obtained has too great an instability of the viscosity over time (in fact an increase) making it unsuitable for use in a coating composition.

The aromatic epoxy resin is preferably chosen from epoxy resins of the bisphenol type, in particular bisphenol A, epoxy resins of the novolak type and their mixtures.

Bisphenol A (2,2-bis (4'-hydroxyphenyl) propane) type epoxy resins is the product of the reaction of bisphenol A with epichlorohydrin. These resins are products commercially available in particular under the registered trademarks Epikote (Shell), DER (Dow Chemical), Araldite (Ciba) and ERL (UCC).

Novolak type epoxy resins are also commercially available products, in particular under the registered trademarks Epikote, DEN and EPN.

It is recommended to use a mass epoxy resin in epoxy equivalent between 160 and 2000, preferably between 180 and 300.

These aromatic epoxy resins can be emulsified, generally without difficulty, using nonionic surfactants. As nonionic surfactants which can be used, mention may be made of polyethers such as polyethylene and / or polypropylene oxides, alkylaromatic ethers of polyethylene and / or polypropylene glycol. Other usable surfactants are the polyoxyalkylene derivatives of hexitol including sorbitans and mannitans, some of which are marketed under the registered trademark "Tween" by Atlas Powder Company. Other usable surfactants are adducts of polyoxyethylene glycol and of glycidyl polyethers of polyhydric phenols. It is recommended according to the invention to use from 1 to 20%, preferably from 3 to 10% by weight of surfactant relative to the weight of aromatic epoxy resin during the aqueous emulsion of said resin.

The preferred nonionic surfactants are polyoxyalkylene glycol, the straight or branched alkylene part of which has between 2 and 6 carbon atoms.

The aromatic resins and the surfactants which can be used are in particular described in US Pat. No. 4,073,762 cited as a reference.

According to a particular and preferred embodiment, all or part of the polyoxyalkylene glycol, the straight or branched alkylene part of which comprises between two and six carbon atoms, is grafted by means of a covalent bond onto the aromatic epoxy resin.

• A) de 97 à 99,9 % , de préférence de 99,5 à 97,5 % d'une dispersion aqueuse filmogène d'un latex d'un copolymère organique telle que définie ci-dessus et,
• B) de 0,1 à 3, de préférence de 0,5 à 2,5 % (calculés sur la base de du poids de l'extrait sec) d'une émulsion aqueuse d'une résine époxy qui est le produit d'addition de réactifs comportant :
  • a) un éther diglycidyle d'un dérivé phénolique dihydroxylé,
  • b) un dérivé phénolique dihydroxylé,
  • c) un éther diglycidyle d'un polyoxyalkylèneglycol.

The present invention therefore also relates to a composition for paper comprising:

• A) from 97 to 99.9%, preferably from 99.5 to 97.5% of a film-forming aqueous dispersion of a latex of an organic copolymer as defined above and,
• B) from 0.1 to 3, preferably from 0.5 to 2.5% (calculated on the basis of the weight of the dry extract) of an aqueous emulsion of an epoxy resin which is the product of addition of reagents comprising:
  • a) a diglycidyl ether of a dihydroxylated phenolic derivative,
  • b) a dihydroxy phenolic derivative,
  • c) a diglycidyl ether of a polyoxyalkylene glycol.

Compounds a) and b) of the epoxy resin may contain other substituents of the alkyl, aryl, sulfonyl and the like type.

The preferred compounds b) are bisphenol A (2,2'-bis (4'-hydroxyphenyl) propane) and bis (4-hydroxyphenylmethane).

The diglycidyl ethers a) are prepared by reaction of b) with an epoxy containing a halogen according to for example the teaching of patents US-A 2,582,985, US-A 2,615,007 and US-A 2,633,458.

The aqueous dispersion of epoxy resin is made stable by the incorporation into the resin of a diglycidyl ether of a polyoxyalkylene glycol.

Compound c) is prepared by reacting the epichlorohydrin with a polyoxyalkylene glycol in a molar ratio making it possible to obtain c).

The preferred polyoxyalkylene glycols are those prepared by reaction of ethylene oxide and / or propylene oxide with an aliphatic dialcohol such as glycol and having a molecular weight of between 5000 and 10000. The aqueous dispersion B) generally comprises 30 80% dry matter, preferably 50-70%. The epoxy resin in aqueous dispersion in B) preferably has a molecular weight of between 500 and 20,000.

• 40 à 90 parties en poids de a),
• 3 à 35 parties en poids de b) et,
• 1 à 25 parties en poids de c).

Preferably, this epoxy resin is the product of addition of:

• 40 to 90 parts by weight of a),
• 3 to 35 parts by weight of b) and,
• 1 to 25 parts by weight of c).

According to a preferred embodiment and in order to improve the stability of the aqueous dispersion B), this aqueous dispersion also comprises a stabilizing amount of a reactive diluent d) with a content in B) preferably between 1 and 25, preferably 5 to 20%, by weight relative to the weight of dry epoxy resin contained in B).

Examples of reactive diluents are unsaturated, epoxidized hydrocarbons and glycidyl ethers of C ₈ -C ₁₇ aliphatic alcohols such as 2-ethyl hexanol, dodecanol and eicosanol.

The emulsion may contain a crosslinking agent preferably chosen from alkylene polyamines such as ethylene diamine and diethylamine diamine and polyaminoamines.

However, the presence of such a catalyst is not essential especially in the case where the aqueous latex dispersion comprises a polymer having in its chain organic groups capable of reacting with epoxy groups such as carboxylic groups and amine groups primary and secondary.

The aqueous dispersions B) of epoxy resin which can be used in the context of the present invention are more particularly described in US Pat. No. 4,315,044 cited as reference.

The aqueous dispersion A) film-forming of a styrene / butadiene, styrene / acrylate and styrene / butadiene / acrylate latex copolymer can be any aqueous dispersion of this type known and usable as a binder in coating compositions for paper.

The polymerizable base monomers are chosen from, styrene, butadiene and acrylic esters, the copolymer always comprising styrene.

The styrene can be replaced in whole or in part by alphamethylstyrene or vinyltoluene. By acrylic esters, we mean the esters of (meth) acrylic acid with C ₁ -C ₁₂ , preferably C ₁ - alcohols C ₈ such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, isobutyl methacrylate .....

• les nitriles vinyliques, en particulier l'acrylonitrile et le méthacrylonitrile,
• les acides mono-et-di carboxyliques monomères éthyléniquement insaturés utilisables seuls ou en mélange comme l'acide acrylique, l'acide méthacrylique ou son dimère, l'acide fumarique, l'acide crotonique, l'acide itaconique, l'acide maléique ainsi que les monoesters des acides ci-dessus avec des alcools de préférence en C₁ - C₄, et leurs dérivés N-substitués tels que l'acrylate de méthyle, l'acrylate d'éthyle, l'acrylate de propyle, l'acrylate de n-butyle, le méthacrylate de méthyle, le méthacrylate d'éthyle et le méthacrylate de n-butyle,
• les amides des acides carboxyliques insaturés comme l'acrylamide, le méthacrylamide, le N-méthylol(méth)acrylamide,
• les monomères éthyléniques comportant un groupe sulfonique et leurs sels alcalins ou d'ammonium tels que le méthallylsulfonate, le sulfo éthylméthacrylate, l'acide vinylsulfonique,
• les monomères éthyléniques insaturés comportant un groupe amino secondaire tertiaire ou quaternaire ou un hétérocycle contenant de l'azote tel que le vinylimidazole, le diméthylaminoéthyl(méth)acrylate, le ditertio buthylamino(méth)acrylate, le diméthylaminométhyl(méth)acrylamide,

Among the ethylenically unsaturated monomers which can be polymerized with the above monomers, and the amount of which can generally range up to 30% by weight of the total of the monomers, there may be mentioned:

• vinyl nitriles, in particular acrylonitrile and methacrylonitrile,
• mono-and-di-carboxylic acid ethylenically unsaturated monomers which can be used alone or as a mixture such as acrylic acid, methacrylic acid or its dimer, fumaric acid, crotonic acid, itaconic acid, acid maleic as well as the monoesters of the above acids with preferably C ₁ - C ₄ alcohols, and their N-substituted derivatives such as methyl acrylate, ethyl acrylate, propyl acrylate, l n-butyl acrylate, methyl methacrylate, ethyl methacrylate and n-butyl methacrylate,
• amides of unsaturated carboxylic acids such as acrylamide, methacrylamide, N-methylol (meth) acrylamide,
• ethylenic monomers containing a sulfonic group and their alkali or ammonium salts such as methallylsulfonate, sulfo ethyl methacrylate, vinyl sulfonic acid,
• unsaturated ethylenic monomers comprising a tertiary or quaternary secondary amino group or a nitrogen-containing heterocycle such as vinylimidazole, dimethylaminoethyl (meth) acrylate, ditertio buthylamino (meth) acrylate, dimethylaminomethyl (meth) acrylamide,

Latex A is preferably a copolymer based on styrene / 1,3-butadiene. More particularly suitable are copolymers based on 25 to 60% by weight of butadiene, 40 to 75% by weight of styrene and 0 to 6% of ethylenically unsaturated monomers comprising at least one carboxylic acid function and their monoesters with an alkanol in C ₁ - C ₈ and from 0 to 3% of an ethylenically unsaturated monomer with a sulfate or sulfonate function, in particular metallylsulfonate and sulfoethylmethacrylate.

The latex of copolymer A is prepared in a manner known per se by polymerization in aqueous emulsion of butadiene and / or styrene and / or acrylate and optionally of at least one other monomer, in the presence of at least one initiator and d '' at least one emulsifying agent with a mixture concentration of the monomers in the reaction medium generally between 20 and 60% by weight.

The monomers used can be introduced as a mixture or separately and simultaneously into the reaction medium, either before the start of polymerization in one go, or during polymerization by successive fractions or continuously.

As an emulsifying agent, the conventional anionic agents are used, represented in particular by fatty acid salts, alkylsulfates, alkylsulfonates, arylsulfates, arylsulfonates, alkylarylsulfates, alkylarylsulfonates, sulfosuccinates, alkylphosphates alkaline, salts of abietic acid, hydrogenated or not. They are used in an amount of 0.01 to 5% by weight relative to the total weight of the monomers.

The initiator, which is water-soluble, is more particularly represented by hydroperoxides such as hydrogen peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide, and by persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate. It is used in amounts of between 0.05 and 2% by weight relative to the total of the monomers. These initiators are optionally combined with a reducing agent, such as sodium bisulfite or formaldehyde sulfoxylate, polyethyleneamines, sugars: dextrose, sucrose, metal salts. The amounts of reducing agent used vary from 0 to 3% by weight relative to the total weight of the monomers.

The reaction temperature, depending on the initiator used, is generally between 0 and 100 ° C, and preferably between 30 and 70 ° C.

The transfer agent used in proportions ranging from 0 to 3% by weight relative to the monomer (s) is generally chosen from mercaptans such as N-dodecylmercaptan, tertiododecylmercaptan cyclohexene: halogenated hydrocarbons such as chloroform, bromoform, carbon tetrachloride. It makes it possible to adjust the proportion of grafted polymer and the length of the grafted molecular chains. It is added to the reaction medium either before the polymerization, or during polymerization.

The latexes thus obtained can be used in particular as binders for the preparation of aqueous compositions for coating paper and more particularly paper for offset printing.

To prepare the binder according to the invention, it is recommended to adjust the pH of the dispersion A) of latex and the emulsion B) of epoxy resin to a similar value before mixing, this value being preferably less than 7, preferably less than 6.

To prepare the paper coating compositions, pigments are mixed with the binder and various additives are added. The most commonly used pigment is mineral clay such as kaolin. It is also possible to use, alone or as a mixture with mineral clay, other pigments such as calcium carbonate, titanium oxide, white satin, hydrargillite, talc, barium sulphate and plaster. These pigments are dispersed in water, generally in an alkaline medium and in the presence of dispersing agents, the most important of which are tetrasodium pyrophosphate, sodium hexametaphosphate, low molecular weight polyacrylates at levels between 0, 2 and 0.5% by weight relative to the pigments. These pigments are fixed to the paper by means of binders. As a binder for this application, aqueous latexes of a synthetic polymer have already been proposed, used either alone or in admixture with natural binders such as starches, proteins, casein, or synthetics such as polyvinyl alcohols. It is also possible to associate with latex products capable of improving the water retention properties of coating compositions such as carboxymethylcelluloses or alginates, or a latex of an alkali-swelling or alkali-soluble polymer.

• 100 parties en poids de pigment,
• 5 à 25, de préférence 8 à 15 parties en poids de liant selon l'invention,
• 1 à 10, de préférence 2 à 8 parties en poids d'adjuvants divers en particulier ceux cités ci-dessus.

The coating composition generally comprises:

• 100 parts by weight of pigment,
• 5 to 25, preferably 8 to 15 parts by weight of binder according to the invention,
• 1 to 10, preferably 2 to 8 parts by weight of various additives, in particular those mentioned above.

According to a preferred embodiment of the present invention, it is recommended to use as pigment at least 40% by weight of calcium carbonate Ca CO ₃ relative to the total weight of pigment used. The rest of the pigment is then chosen from the mineral pigments usually chosen for coating and, in particular, those mentioned above. Preferably all the pigment consists of crushed Ca CO ₃ and / or precipitation. It has indeed been surprisingly found that the beneficial effect of the use of an epoxy resin emulsion is even greater, in particular at the level of the RAH, in the case of the use of Ca CO ₃ .

The coating compositions may finally contain other various ingredients such as in particular crosslinking agents, anti-foaming agents, slip agents, optical brighteners.

The coating of the paper using the coating compositions according to the invention is carried out by means of a bedding machine according to various techniques using various devices among which mention may be made of those known industrially under the following names: the blade d , the size press, the Champion coater, the roller coater, the trailing blade and the rotary bar. After coating, the paper undergoes a drying operation generally followed by a calendering operation.

The present invention therefore also relates to a process for coating paper, characterized in that at least one of the two faces of the paper is coated with 5 to 30 g / m ² of coating composition according to the invention.

In all that follows or all of the above, unless otherwise indicated, the percentages and parts are by weight.

The following examples illustrate the invention without limiting its scope.

EXAMPLE 1 : a) Preparation of An dispersions: a1) Preparation of the dispersion A 1:

• 59,0 parties en poids de styrène,
• 37,0 parties en poids de butadiène-1,3,
• 2,0 parties en poids d'acide acrylique,
• 2,0 parties en poids d'acide fumarique,
• 1,0 partie en poids de métallylsulfonate de sodium,
• 1,0 partie en poids de tert-dodécylmercaptan,
• 110 parties en poids d'eau,
• 0,5 partie en poids de lauryl sulfate d'ammonium,
• 1,10 parties en poids de persulfate d'ammonium.

In a stainless steel autoclave, fitted with an agitator, are introduced:

• 59.0 parts by weight of styrene,
• 37.0 parts by weight of 1,3-butadiene,
• 2.0 parts by weight of acrylic acid,
• 2.0 parts by weight of fumaric acid,
• 1.0 part by weight of sodium metallylsulfonate,
• 1.0 part by weight of tert-dodecylmercaptan,
• 110 parts by weight of water,
• 0.5 part by weight of ammonium lauryl sulfate,
• 1.10 parts by weight of ammonium persulfate.

The mixture is heated to about 60 ° C for the duration of the reaction (about 12 h). The conversion rate is around 98%.

• Extraits secs (ES)   50 %,
• pH   5,2,
• Viscosité Brookfield à 20°C (50 t/mn)   165 mPa.s
• Diamètre moyen des particules de polymère   150 nm,
• Tg du polymère   0°C.

The dispersion A1 of styrene / butadiene latex thus obtained has the following characteristics:

• Dry extracts (ES) 50%,
• pH 5.2,
• Brookfield viscosity at 20 ° C (50 rpm) 165 mPa.s
• Average diameter of the polymer particles 150 nm,
• Tg of the polymer 0 ° C.

a2) Preparation of dispersion A2:

The procedure is exactly as for A1 except that 1.5 parts of tert-dodecylmercaptan and 0.25 parts of ammonium lauryl sulfate are used. The latex dispersion A2 thus obtained has the same properties as A1 except that the viscosity is 120 mPa.s and the average diameter of the joints is 170 nm.

a3) Preparation of dispersion A3:

• 36,7 parties en poids de styrène,
• 60 parties en poids d'acrylate de n-butyle,
• 3,3 parties en poids d'acide acrylique,
• 0,5 partie en poids de méthallylsulfonate de sodium,
• 0,5 partie en poids d'acrylamide,
• 110 parties en poids d'eau,
• 0,7 partie en poids de persulfate d'ammonium,
• 0,1 partie d'alkylsulfonate,

In a stainless steel autoclave fitted with an agitator, the following are introduced:

• 36.7 parts by weight of styrene,
• 60 parts by weight of n-butyl acrylate,
• 3.3 parts by weight of acrylic acid,
• 0.5 parts by weight of sodium methallylsulfonate,
• 0.5 part by weight of acrylamide,
• 110 parts by weight of water,
• 0.7 part by weight of ammonium persulfate,
• 0.1 part of alkylsulfonate,

The mixture is heated to 60 ° C during the reaction. The conversion rate is around 97%.

• ES   50 %
• pH   2,0
• Viscosité   430 mPa.s
• Diamètre des particules   130 nm
• Tg   0°C

The latex dispersion thus obtained has the following characteristics:

• ES 50%
• pH 2.0
• Viscosity 430 mPa.s
• Particle diameter 130 nm
• Tg 0 ° C

b) Aromatic epoxy resin emulsion Bn :

b1) CMD W 60-3515 emulsion:

The epoxy resin emulsion based on bisphenol A is used, sold by the company Hi-Tek Polymers: Louisville, USA under the trade name CMD W 60-3515.

This emulsion epoxy resin is the addition product of bisphenol A glycidyl ether, bisphenol A and diglycidyl ether of a copolymer of ethylene oxide and propylene oxide.

• ES : 63 %,
• MEE (masse en équivalent époxy basée sur la résine sèche) : 250,
• Tg (température de transition vitreuse)   7°C.
• Viscosité Brookfield (aiguille 5, 10 t/mn à 25°C) : 11000 mPa.s,
• pH   3,7.
• 2 groupes époxy par molécule.

The CMD W 60-3515 emulsion has the following characteristics:

• ES: 63%,
• MEE (mass in epoxy equivalent based on dry resin): 250,
• Tg (glass transition temperature) 7 ° C.
• Brookfield viscosity (needle 5, 10 rpm at 25 ° C): 11000 mPa.s,
• pH 3.7.
• 2 epoxy groups per molecule.

b2) W60-3510 CMD emulsion:

• ES : 65 %,
• MEE : 195,
• tg: - 5°C,
• Viscosité: 10 000 mPa.s,
• pH :3,5
• 2 groupes époxy par molécule.

This emulsion marketed by Hi-Tek is of the same type as the emulsion b1) and it has the following characteristics:

• ES: 65%,
• MEE: 195,
• tg: - 5 ° C,
• Viscosity: 10,000 mPa.s,
• pH: 3.5
• 2 epoxy groups per molecule.

b3) Epi-Rez 35201 emulsion:

• ES : 60 %,
• MEE : 700,
• Tg : 32 °C,
• Viscosité: 11 000 mPa.s,
• pH : 8,0
• 2 groupes époxy par molécule.

This emulsion marketed by Hi-Tek is of the same type as the emulsion b1) and it has the following characteristics:

• ES: 60%,
• MEE: 700,
• Tg: 32 ° C,
• Viscosity: 11,000 mPa.s,
• pH: 8.0
• 2 epoxy groups per molecule.

b4) Epi-Rez W55-5003 emulsion:

• ES :57 %,
• MEE : 205,
• Tg : 14°C,
• Viscosité: 11 000 mPa.s,
• pH :7,0,
• 3 groupes époxy par molécule

This emulsion is also marketed by the Hi-Tek Company and it has the following characteristics:

• ES: 57%,
• MEE: 205,
• Tg: 14 ° C,
• Viscosity: 11,000 mPa.s,
• pH: 7.0,
• 3 epoxy groups per molecule

c) Preparation and stability of the binder:

A mixture of 98% latex A1, A2 and A3 prepared under a) above is carried out in a propeller mixer at room temperature with 2% of emulsion B (B1, B2, B3 and B4 of epoxy resin defined under b ) above), the percentages being calculated on the basis of the weight of the dry extracts of A and B to assess the stability of the binder L ₁ thus obtained, its viscosity is measured at time 0, at 2 days, 30 days and 78 days (Brooklfield viscosity at 50 rpm at 20 ° C). The results are collated in Table 1 below:

These measurements collected in Table 1 demonstrate the good storage stability of the binder.

d) Preparation of a coating composition C1 pigmented with calcium carbonate :

The following ingredients are mixed in a mixer at high speed:

A control coating composition C1 (0) is prepared having exactly the same composition as C1 except that L1 (n) is replaced by dispersion A1 prepared in point a) above.

On the 2 coating baths, ES is measured, the pH at time 0, the viscosity at time 0 and at 24 h.

A layer of 20 g / m2, expressed as dry matter, is applied using an air layer coater, on one side of a 50 g / m2 SIBILLE® paper, on a DIPROMA® coating machine. . The coated paper is dried in a tunnel oven at a temperature of 120 ° C and then undergoes calendering consisting of 8 successive passes between 2 cylinders under a force of 30 KN per meter.

- Measurement of resistance to wet lifting (RAH) :

The RAH is determined using a PRUFBAU® press under a printing force of 0.8 KN at a speed V of 0.5 m / s.

To determine the RAH, we therefore put a sample of coated paper in contact, on which a thin film of water has previously been deposited, with an ink wheel whose printing force on the sample is adjusted to a chosen value. . The "3802" ink sold by the Etablissements Lorilleux Lefranc (Paris) is used. The RAH is evaluated by the ratio of the optical density (OD) of the wet range to the OD of the dry range, said ratio being multiplied by 10. The results are expressed by a value ranging from 0 to 10. The resistance to l wet peeling is higher the closer the value is to 10, the value 0 corresponding to a paper having very poor resistance and the value 10 to a paper having excellent resistance.

- Measurement of resistance to dry lifting :

On coated paper, we also appreciate the resistance to dry peeling (RAS) according to TAPPI Standard T-499. LORILLEUX® 3803 ink is used for this using an electric IGT-AiC2-5 press, the final speed of which is set at 1 m / s.

The IGT press was developed by the "Institut von Grafische Technik" in Amsterdam (Netherlands).

- Measurement of the porosity of the coating with porometric ink P :

It is appreciated by measuring the optical density (O.D.) after printing the paper coated with a porometric ink and wiping the printed paper at 7 s, 30 s and 120 s.

The composition of the coating bath and the properties of the coated papers are collated in Table 2 below.

EXAMPLE 2:

Preparation of the coating composition C2:

The control coating composition C2 (0) is the same as C1 (0) described in Example 1.

To prepare C2, the procedure of Example 1 is followed except that a binder L2 is used which is a mixture of dispersion A1 with 2% (calculated as dry) of emulsion B2. The paper is coated and the properties of the coated papers are measured as described in Example 1 above. The results are collated in Table 3 below.

EXAMPLE 3:

Preparation of a C3 coating composition:

Composition C3 is prepared like compositions C1 or C2 except that one starts from the binder L3 which is a mixture of dispersion A2 with the emulsion B1.We also prepare a control coating composition C3 (0) having exactly the same composition as C3 , except that the binder is only formed by the dispersion A2 prepared in point a2) of Example 1 above.

Using compositions C3 and C3 (0), the paper is coated and the properties of the coated papers are measured as described in Example 1 above.

The results are collated in Table 4 below.

EXAMPLE 4:

Preparation of a C4 coating composition.

The procedure is as in Example 1 except that a mixture of A2 with 2% of B2 is used as binder L4. The control composition C4 (0) has as binder only A2. The results are collated in Table 5 below.

EXAMPLE 6

Preparation of a coating composition C5.

The procedure is as in Example 1, except that one starts from a binder which is a mixture of dispersion A3 with emulsion B1 or B2. The control composition C5 (0) has as a binder only A3.

The results are collated in Table 6 below.

From Tables 1 to 5 it appears that the coating compositions according to the invention exhibit suitable stability linked to a substantial improvement in the SAR and the RAH without concomitant degradation of the porosity of the inks. TABLE 1 BINDER A1 to 2% B2 A1 to 2% B4 A1 to 2% B1 A1 to 2% B3 A2 at 2% B2 A3 at 2% B2 ES (%) 50 50 50.1 49.85 50.3 50 pH (0h) 5.5 5.6 5.5 6 8 5 pH (48h) 6 6 5.5 6 8 5 Brookfield viscosity 50 rpm 0 hour 288 248 276 260 640 165 2 days 328 260 300 292 645 175 30 days 304 280 304 284 650 180 78 days 320 264 292 288 665 185 L1 A1 A1 to 1% B1 A1 to 2% B1 ES (%) 67.1 67 67 pH 0 h (initial) 9 9 9 Viscosity 0 h (10t / mn) 4750 5300 5750 (mPa.s) 0h (100 rpm) 765 850 880 (mPa.s) 24 h (10t / mn) 4850 5450 5750 (mPa.s) 24 h (100t / mn) 800 880 905 RAS (cm / s) ink 3803 37 37 41 RAH ink 3802 3 6 7 P (DO) 7s 0.35 0.35 0.36 30 s 0.46 0.46 0.46 120s 0.62 0.61 0.57 L2 A1 A1 to 2% B2 ES (%) 67.1 67.4 pH 0 h (initial) 9 9 Viscosity 0 h (10t / mn) 4750 6050 (mPa.s) 0h (100 rpm) 765 915 (mPa.s) 24 h (10t / mn) 485 6100 (mPa.s) 24 h (100t / mn) 800 965 RAS (cm / s) ink 3803 37 38 RAH ink 3802 3 8 P (DO) 7s 0.35 0.34 30 s 0.48 0.49 120s 0.62 0.61 L3 A2 A2 at 1% B1 A2 at 2% B1 ES (%) 67 66.9 66.9 pH 0 h (initial) 10.1 10.2 10.2 Viscosity 0 h (10t / mn) 4500 4550 4650 (mPa.s) 0h (100t / mn) 725 745 770 (mPa.s) 24 h (10t / mn) 4500 4550 4650 (mPa.s) 24 h (100t / mn) 785 790 795 RAS (cm / s) ink 3803 33 35 35 RAH ink 3802 2 3 4 P (DO) 7s 0.25 0.25 0.26 30 s 0.32 0.32 0.31 120s 0.40 0.40 0.39 L4 A2 A2 at 2% B2 ES (%) 67 66.9 pH 0 h (initial) 10.1 10.2 Viscosity 0 h (10t / mn) 4500 4950 (mPa.s) 0h (100t / mn) 725 805 (mPa.s) 24 h (10t / mn) 4500 4950 (mPa.s) 24 h (100t / mn) 785 840 RAS (cm / s) ink 3803 33 35 RAH ink 3802 2 6 P (DO) 7s 0.25 0.26 30 s 0.32 0.31 120s 0.40 0.39 L5 A3 A3 at 1% B1 A3 at 2% B1 A3 at 2% B2 ES (%) 66.7 66.9 66.8 67 pH 0 h (initial) 9 9 9.1 9 Viscosity 0h (10 rpm) 4950 5250 5950 6200 0h (100 rpm) 750 825 865 905 (mPa.s) 24h (10 rpm) 4950 5250 5950 6200 (mPa.s) 24h (100 rpm) 800 860 940 960 RAS (cm / s) ink 3803 23 25 25 23 RAH ink 3802 2 4 4 5 P (DO) 7s 0.41 - - - 30s 0.57 - - - 120s 0.73 - - -

Claims (16)

1. A binder for a paper coating composition, characterized in that it comprises:

   A) 97% to 99.9%, preferably 97.5% to 99.5% (calculated on the basis of the weight of dry extract) of an aqueous film-forming dispersion of an organic copolymer latex selected from a styrene-butadiene copolymer, a styrene-acrylate copolymer and a styrene-butadiene-acrylate copolymer;

   B) 3% to 0.1%, preferably 2.5% to 0.5% (calculated on the basis of the weight of dry extract) of an aqueous emulsion of an aromatic epoxy resin and a non-ionic surfactant.
2. A binder according to claim 1, characterized in that the aromatic epoxy resin is selected from bisphenol type epoxy resins, novolac type epoxy resins, and mixtures thereof.
3. A binder according to claim 1 or claim 2, characterized in that the surfactant of emulsion B is a polyoxyalkylene glycol in which the linear or branched alkylene portion contains 2 to 6 carbon atoms, all or part of the surfactant being grafted onto the aromatic epoxy resin.
4. A binder according to any one of claims 1 to 3, characterized in that the epoxy resin has an epoxy equivalent mass which is in the range 160 to 2000, preferably in the range 180 to 300.
5. A binder according to any one of claims 1 to 4, characterized in that the epoxy resin of emulsion B is a self-emulsifying epoxy resin which is the addition product of reagents comprising :

   a) a diglycidyl ether of a dihydroxylated phenolic derivative;

   b) a dihydroxylated phenolic derivative;

   c) a diglycidyl ether of a polyoxyalkylene glycol.
6. A binder according to claim 5, characterized in that the epoxy resin is the addition product of:

   40 to 90 parts by weight of a);

   3 to 35 parts by weight of b); and

   1 to 25 parts by weight of c).
7. A binder according to claim 5 or claim 6, characterized in that compound b) is selected from bisphenol A and bis(4-hydroxyphenylmethane).
8. A binder according to any one of claims 5 to 7, characterized in that compound c) is the product of the reaction of epichlorohydrin with a polyoxyalkylene glycol with a molecular weight which is in the range 5000 to 10000.
9. A binder according to any one of the preceding claims, characterized in that aqueous dispersion B) contains 30% to 80% of dry matter.
10. A binder according to any one of claims 5 to 8, characterized in that the epoxy resin has a molecular weight which is in the range 500 to 20000.
11. A binder according to any one of the preceding claims, characterized in that aqueous dispersion B) also contains 1% to 25% by weight, with respect to the dry epoxy resin weight, of a reactive diluent selected from epoxy hydrocarbons and glycidyl ethers of aliphatic C₈-C₁₇ alcohols.
12. A binder according to any one of the preceding claims, characterized in that the latex copolymer results from copolymerisation of:

    • 25% to 60% by weight of butadiene;

    • 40% to 75% by weight of styrene;

    • 0 to 6% of at least one monomer selected from monomers containing an ethylenic unsaturation having at least one carboxylic acid function and their monoesters with a C₁-C₈ alkanol;

    • 0 to 3% of a monomer containing an ethylenic unsaturation and a sulphate or sulphonate function, in particular methallylsulphonate or sulphoethylmethacrylate.
13. A coating composition for paper comprising pigments and normal additives, characterized in that it contains a binder which is as defined in any one of claims 1 to 11.
14. A coating composition according to claim 13, characterized in that at least 40% by weight of the pigment is calcium carbonate.
15. A coating composition, characterized in that it comprises 100 parts by weight of pigment, 5 to 25 parts by weight of a binder as defined in any one of claims 1 to 12, and 1 to 10 parts by weight of additives.
16. A paper coating process, characterized in that at least one face of the paper is coated with a coating composition as defined in any one of claims 13 to 15 in an amount of 5 to 30 g/m² per paper face.