ITVA20090020A1 - COMPOSITIONS FOR PAPER COATING - Google Patents

Description

Description

COMPOSITIONS FOR PAPER COATING

TECHNICAL FIELD.

The present invention relates to compositions for paper coating containing as de-flocculants and water-retention agents water-soluble (hydrophilic) comb polyurethanes containing polyoxyethylene side chains.

STATE OF THE ART

It is well known that the surface of printing paper sheets is commonly coated with a coating formulation in order to improve printability and to make it smooth and glossy.

Paper coating compositions generally contain fillers or pigments dispersed in water, polymeric binders, rheology modifiers, water retention agents and dispersing agents.

Dispersing agents are essential to reduce viscosity in the presence of the high solid content that is typical of paper coating compositions and to maintain constant viscosity suitable for the process; examples of conventional dispersing agents are complex phosphates, polyphosphoric acid salts and polycarboxylic acid salts.

Water retention agents prevent dehydration of the coating composition upon contact with the surface of the paper sheet; a typical water retention agent in the paper coating composition is carboxymethyl cellulose.

Rheology modifiers are used to modulate the viscosity of the paper coating.

The binders are responsible for the cohesion of the final patina and the adhesion to the paper layer.

Some conventional paper coating additives are known for their ability to have more than one function; for example carboxymethyl cellulose acts both as a rheology modifier and as a water retention agent, polyvinyl alcohol acts as a water retention agent and an enhancer of optical brilliance.

WO 01/96007, WO 2004/044022, WO 2004/041883 and WO 2007/069037 describe the use of polyacrylic anionic copolymers in the paper industry, for the production or coating of paper; these polyacrylic anionic copolymers contain at least one ethylenically unsaturated anionic monomer having monocarboxylic functionality and at least one ethylenically unsaturated nonionic monomer with poly (C2-4alkylene oxide) chains. Copolymers are said to be useful as dispersing agents and / or as grinding additives, as optical brightening agents, as water retention agents, to improve viscosity and gloss.

Unfortunately, when the known ionic substances are used in the aqueous dispersions according to the prior art, their effectiveness depends on the pH value of the dispersion.

It has now been found that specific comb polyurethanes are suitable as water retention agents and gloss enhancers in paper coating compositions; the compositions for the coating of the paper of the invention are stable over a wide viscosity range regardless of their pH and give a good printability and degree of gloss to the coated paper.

Comb-type hydrophilic polyurethanes containing polyoxyethylene side chains are known and described in the patent literature.

EP 60430 reports a process for the preparation of a polyurethane with polyoxyalkylene side chains; however, in EP 60430 there is no mention of the use of polyurethanes in compositions for the coating of paper.

WO 03/046038 describes a wide family of polyurethane dispersants which contain from 35 to 90% by weight of poly (C2-C4alkylene oxide) on the total weight of polyurethane polymer; however, WO 03/046038 does not disclose the paper coating compositions of the present invention.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a composition for the coating of paper containing a) from 30 to 80% by weight of an inorganic pigment; b) from 0.05 to 3.0 parts by weight per 100 parts by weight of pigment of at least one water-soluble comb polyurethane containing polyoxyethylene side chains having a molecular weight greater than 500, preferably between 2,000 and 20,000 and ethylene oxide content included between 80 and 99.9% by weight; c) at least 15% by weight of water.

DETAILED DESCRIPTION

The compositions for the coating of the paper of the invention contain: a) from 30 to 80% by weight of an inorganic pigment; b) from 0.05 to 3.0 parts by weight per 100 parts by weight of pigment of the comb polyurethane described above; c) at least 15% by weight of water, and have Brookfield® viscosity at 25 ° C and 100 rpm lower than 3,000 mPa * s, preferably between 500 and 2,000 mPa * s.

The compositions for the paper coating of the invention also contain from 0.01 to 3% by weight of a dispersing agent, because the polyurethane comb does not behave itself as a dispersant of the pigment, and may also contain a specific rheology modifier .

Examples of usable dispersing agents are non-crosslinked anionic polyacrylates, such as a sodium polyacrylate, with a molecular weight of between 5,000 and 40,000.

Typical rheology modifiers that can be used are carboxymethyl cellulose, hydroxypropyl guar, hydroxypropyl methyl cellulose, xanthan, ASA polymers (ie â € œacrylic polymers that swell in the presence of alkaliâ €).

Dispersing agents, which are common ingredients in paper coating compositions, are generally unable to prevent flocculation of the finer particles of the dispersion, particularly when paper coating compositions are applied to paper sheets. , ie under high stress conditions and particle flocculation is detrimental to the smoothness and gloss of the resulting coated paper.

Comb polyurethanes containing polyoxyethylene side chains with a molecular weight greater than 500, preferably between 2,000 and 20,000 and ethylene oxide content between 80 and 99.9% by weight, are particularly effective as de-flocculants, avoiding the formation of particle aggregates fines, which may tend to settle, and characterize the compositions for the coating of the paper of the present invention.

The inorganic pigments of the compositions for the coating of paper of this invention, which preferably have from 40 to 90% of the particles with a size of less than 2 microns, are those normally used in the coating of paper and are in particular kaolin, calcium carbonate, talc , titanium dioxide, barium sulfate, gypsum, or mixtures thereof.

The compositions for the coating of the paper of the invention also normally contain from 1 to 15% by weight of a binder, preferably an acrylic polymeric binder.

Among the acrylic polymeric binders preferred for the realization of the invention we mention the polymers of the esters of methacrylic or acrylic acids, the copolymers deriving from monomers of acrylic esters with vinyl acetate, with styrene, with butadiene or with their mixtures.

Other conventional additives may be present in the paper coating compositions, such as antifoamers, biocides, optical brighteners. The water-soluble comb polyurethane useful for the realization of the present invention contains a main chain (backbone), which comprises urea and urethane bonds, with trifunctional nodes from each of which linear polyoxyethylene side chains depart.

The expression â € œpolyoxyethylene side chainsâ € indicates in this text side chains containing units â € “(CH2CH2O) n- with n> 9.

The main chain of the polyurethane containing urea and urethane bonds has uniformly spaced branch points, the distribution of which can be predicted based on the molar ratios and the chemical nature of the reactants and does not depend on the reaction conditions or the catalysts used.

Consequently, the fine structure of the polyurethane comb can be reproduced without great difficulty and possibly modulated as needed.

The main chain of the polyurethane is itself insoluble in water and preferably does not contain any internal or terminal chains of the polyoxyethylene type.

In the comb polyurethane the total content of ethylene oxide, ie the sum of the units - (CH2CH2O) -, is preferably greater than 50% by weight, more preferably greater than 70% by weight.

The preferred comb polyurethanes have a molecular weight greater than 100,000, more preferably between 300,000 and 3,000,000, and polyoxyethylene side chains with a molecular weight between 2,000 and 20,000 and ethylene oxide content between 80 and 99.9% by weight.

The polyoxyethylene side chains of the comb-like polyurethane are distributed along the main chain at intervals of less than 100, preferably less than 50, covalent bonds.

The high molecular weight polyurethane comb can be prepared by any of the methods known to those skilled in the art.

The polyoxyethylene side chains of the comb-shaped polyurethane are generally introduced by reacting in one of the stages of the preparation an organic isocyanate with at least one compound having a molecular weight higher than 500, preferably between 2,000 and 20,000, more preferably between 4,000 and 6,000, and a content of ethylene oxide comprised between 80 and 99.9% by weight, preferably between 90 and 99.9% by weight, and having a group which reacts with isocyanates.

Comb polyurethanes that have polyoxyethylene side chains with molecular weight between 2,000 and 20,000 and ethylene oxide content between 90 and 99.9% by weight are preferred for use in paper coating compositions, because they impart a better water retention, at the expense of a minimum loss of gloss.

Any compound having a molecular weight greater than 500, and ethylene oxide content between 80 and 99.9% by weight and with a group capable of reacting with isocyanates can be used to introduce the polyoxyethylene side chains into the polyurethane of the comb. Examples of suitable compounds are C1-C4 monoalkyl ethers of poly (ethylene oxide), such as monomethyl ether of poly (ethylene oxide) and monobutyl ether of poly (ethylene oxide); poly (ethylene oxide) monomethyl ether with molecular weight between 4,000 and 6,000 is the most preferred compound. The term molecular weight used in this text indicates, when speaking of polymers, the number average molecular weight.

The methods of preparation of comb polyurethanes comprise as a key intermediate a bi-functional isocyanate, containing polyoxyethylene side chains having a molecular weight greater than 500, preferably between 2,000 and 20,000 and ethylene oxide content between 80 and 99.9% by weight, which is reacted with one or more compounds of molecular weight from 34 to 300 which have two reactive groups towards the isocyanic groups, in order to extend the main chain, increase the molecular weight of the bifunctional isocyanate and obtain a comb-like polyurethane having a high molecular weight.

According to a preferred preparation method (Method A), the comb polyurethane is obtained by reacting in a first stage about one mole of a compound with three reactive groups towards the isocyanic groups and which has a molecular weight from 92 to 1,200 with about 3 moles of a diisocyanate (stage a1); in a second stage the trifunctional isocyanate thus obtained is reacted with an equimolar quantity of one or more compounds having a molecular weight greater than 500, preferably between 2,000 and 20,000, ethylene oxide content between 80 and 99.9% by weight and containing a reactive group towards isocyanic groups (stage a2); in a third stage, the bifunctional isocyanate thus obtained is reacted with one or more compounds with molecular weight from 34 to 300 which have two groups reactive towards the isocyanic groups (stage a3). According to another preferred preparation method (Method B) the comb polyurethane is obtained by reacting in a first stage a polyisocyanate with one or more compounds having a molecular weight higher than 500, preferably between 2,000 and 20,000, ethylene oxide content comprised between 80 and 99.9% by weight and having a reactive group towards the isocyanic groups, so as to obtain on average a bi-functional isocyanate (stage b1); in a second stage, the bifunctional isocyanate thus obtained is reacted with one or more compounds with molecular weight from 34 to 300 which have two groups reactive towards the isocyanic groups (stage b2).

According to a further preferred preparation method (Method C), the comb polyurethane is obtained by reacting in a first stage a diisocyanate with equimolar quantities of one or more compounds having a molecular weight greater than 500, preferably between 2,000 and 20,000, of ethylene oxide from 80 to 99.9% by weight and having a reactive group towards isocyanic groups (stage c1); in a second stage, the monofunctional isocyanate thus obtained is reacted with an equimolar quantity of one or more compounds with molecular weight from 34 to 300 which have at least one - NH- reactive group towards the isocyanic groups and at least two hydroxyl groups reactive towards isocyanic groups (stage c2); in a third stage, the compound thus obtained, which has two functional groups reactive towards the isocyanic groups, is reacted with diisocyanates in order to obtain an intermediate compound terminated with two lateral isocyanic groups (stage c3); in a fourth stage, the bifunctional isocyanate thus obtained is reacted with one or more compounds with molecular weight from 34 to 300 which have two groups reactive towards the isocyanic groups (stage c4).

The compound of stage a1 with a molecular weight from 92 to 1,200 and which has three groups reactive towards the isocyanic groups is preferably a trifunctional alcohol.

Examples of usable trifunctional alcohols are polypropylene glycol triol, glycerin, trimethylol propane, trimethylol ethane.

Any organic diisocyanate that has a molecular weight of less than 500 and functionality - NCO between 2.0 and 2.1 can be used in stage a1 and c1 as a diisocyanate.

Examples of usable diisocyanates are 1,6-hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, 1-isocyanate-3-isocyanate-methyl-3,5,5-trimethyl-cyclohexane (or isophorondisocyanate) (IPDI), 4,4â € ™ -dicyclohexylmethane diisocyanate, 2,4-toluene diisocyanate alone or in admixture with 2,6-toluene diisocyanate (TDI), 4,4'-diphenyl-metanediisocyanate (MDI), metatetramethylxylenediisocyanate (TMXDI), 1,5 naphthalene of isocyanate, and their mixtures ; Aliphatic and cycloaliphatic diisocyanates are preferred, the most preferred being the IPDI.

The compounds having molecular weight from 34 to 300 and two groups which reactive towards the isocyanic groups used in the stages a3, b2 and c4 are preferably diamines.

Examples of usable diamines are hydrazine, ethylene diamine, piperazine, 1,5-diamino pentane, 1,6-diamino hexane, isophorondiamine, diethylenetriamine.

Steps a3, b2 and c4 are preferably carried out by dispersing the bifunctional isocyanate in water and adding the diamine, optionally dissolved in water, to the dispersion.

The compound with molecular weight from 34 to 300 of stage c2 is preferably diethanolamine.

Any polyisocyanate with a -NCO functionality between 2.4 and 3.8 (trifunctional isocyanate), with a molecular weight less than 800 can be used in stage b1.

Examples of trifunctional isocyanates are compounds obtained from trimerization, biuretization, urethanization or alloophanation of bifunctional isocyanates such as those mentioned above, and their mixtures.

Usable trifunctional isocyanates are HDI biuret, HDI isocyanurate, IPDI trimers and combinations of these trifunctional isocyanates with diisocyanates.

The preferred trifunctional isocyanates are isocyanurate and hexamethylene diisocyanate biuret, for example HDI isocyanurate in asymmetrical form, HDI biuret with low viscosity and those obtained from combinations of IPDI and HDI trimers.

For the purposes of the invention, wishing to obtain comb polyurethanes with high molecular weight, it is preferable to minimize the quantity of diisocyanates which may be present in the trifunctional isocyanates during stage b1, as is well known to those skilled in the art.

For the purposes of the invention, the ratio between the equivalents of isocyanic groups and the equivalents of reactive groups towards the isocyanic groups during the c3 stage is between 1.1 and 2.3.

The water-soluble comb polyurethanes are preferably non-ionic compounds, free of acid groups, such as carboxylic and sulphonic groups.

Suitable solvents can be used in the preparation stages, but it is also possible to carry out all the preparation stages with pure reagents, without the use of water or organic solvents.

The water-soluble comb polyurethanes described above are useful as water retention agents, de-flocculants and viscosity stabilizers in paper coating compositions and help provide coated paper with excellent printability, whiteness and gloss.

Another advantageous feature of the polyurethanes described above is the fact that they act as rheology and water retention pads for different industrial batches of compositions for the coating of paper with the same recipe; this means that, in the industrial coating process, the usual deviations from the theoretical quantities of the coating ingredients have no effect on the water retention and rheology characteristics of the patina.

EXAMPLES

The following products were used in the examples:

TRIOL1: polypropylene glycol triol, molecular weight 1,000 g / mol, Voranol CP 1055 from Dow Chemical Co.

ETHOXY1: Polyethoxylated butanol, molecular weight 3000 g / mol ETHOXY2: Polyethoxylated methanol, molecular weight 5000 g / mol ETHOXY3: Polyethoxylated butanol, molecular weight 5000 g / mol ETHOXY4: Polyethoxylated methanol, molecular weight 750 g / mol DIISOCYANATE1: Isophorone, molecular weight 222.3 g / mol, Desmodur I, from Bayer Material Science

TRIISOCYANATE1: trimer from hexamethylene diisocyanate, NCO content 24.0%, NCO 3.1 functionality, Desmodur XP2410, from Bayer Material Science

AMINE1: Isophorondiamine, molecular weight 170.3 g / mol, from Sigma Aldrich

AMINE2: Diethanolamine, molecular weight 105.14 g / mol, from Sigma Aldrich

AMINE3: Ethylenediamine, molecular weight 60.10 g / mol, from Sigma Aldrich

AMINE4: Hydrazine Hydrate, 24% solution, molecular weight 32.3 g / mol, from Sigma Aldrich

EXAMPLE 1

Preparation of a polyurethane comb with Method A.

In a reactor equipped with stirrer, thermometer and condenser 100.0 g of TRIOL1 and 300.0 g of ETHOXY1 are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 0.15 g of 85% phosphoric acid are added. At 85 ° C, 69.0 g of DIISOCYANATE1 are added to the homogeneous mixture, under stirring; after 20 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 1.7% (value determined in this as in the following examples in accordance with the standard method ASTM D2572).

300 g of the obtained product are dispersed with vigorous stirring in 890 g of water cooled to 18 ° C. After 20 minutes 9.7 g of AMINE1 dissolved in 39.3 g of water are dropped into the reactor.

The product obtained has a dry% equal to 25.55, Brookfield® viscosity at 20 rpm equal to 48 mPa * s and pH 6.5.

EXAMPLE 2

Preparation of a polyurethane comb with Method A.

In a reactor equipped with stirrer, thermometer and condenser, 50.0 g of TRIOL1 and 250.0 g of ETHOXY2 are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 0.11 g of 85% phosphoric acid are added. At 85 ° C 34.5 g of DIISOCYANATE1 are added to the homogeneous mixture, under stirring; after 20 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 1.26%.

300 g of the obtained product are dispersed with vigorous stirring in 893.1 g of water cooled to 18 ° C. After 20 minutes 6.9 g of AMINE1 dissolved in 27.4 g of water are dropped into the reactor.

The product obtained has a dry% equal to 26.15, Brookfield® viscosity at 20 rpm equal to 62 mPa * s and pH 6.4.

EXAMPLE 3

Preparation of a polyurethane comb with Method B.

In a reactor equipped with stirrer, thermometer and condenser, 300.0 g of ETHOXY1 and 0.11 g of 85% phosphoric acid are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 56.6 g of TRIISOCYANATE1 are added; after 20 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 2.5%.

300 g of the obtained product are dispersed with vigorous stirring in 862.6 g of water cooled to 18 ° C. After 20 minutes 12.8 g of AMINE1 dissolved in 51.5 g of water are dropped into the reactor.

The product obtained has a dry% equal to 25.98, Brookfield® viscosity at 20 rpm equal to 196 mPa * s and pH 6.6.

EXAMPLE 4

Preparation of a polyurethane comb with Method B.

In a reactor equipped with stirrer, thermometer and condenser, 274.5 g of ETHOXY2 and 0.11 g of 85% phosphoric acid are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 31.1 g of TRIISOCYANATE1 are added; after 20 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 1.6%.

275 g of the obtained product are dispersed with vigorous stirring in 795.3 g of water cooled to 18 ° C. After 20 minutes 7.6 g of AMINE1 dissolved in 30.2 g of water are dropped into it.

The product obtained has a dry% equal to 25.51, Brookfield® viscosity at 20 rpm equal to 246 mPa * s and pH 5.5.

EXAMPLE 5

Preparation of a polyurethane comb with Method B.

In a reactor equipped with stirrer, thermometer and condenser, 300.0 g of ETHOXY3 and 0.11 g of 85% phosphoric acid are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 22.0 g of TRIISOCYANATE1 and 10.1 g of DIISOCYANATE1 are added; after 20 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 1.8%.

280 g of the obtained product are dispersed with vigorous stirring in 826.4 g of water cooled to 18 ° C. After 20 minutes 7.6 g of AMINE4 dissolved in 9.8 g of water are dropped into the reactor.

The product obtained has a dry% equal to 26.07, Brookfield® viscosity at 20 rpm equal to 412 mPa * s and pH 6.8.

EXAMPLE 6

Preparation of a polyurethane comb with Method B.

In a reactor equipped with stirrer, thermometer and condenser, 300.0 g of ETHOXY3 and 0.11 g of 85% phosphoric acid are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 22.0 g of TRIISOCYANATE1 and 10.1 g of DIISOCYANATE1 are added; after 20 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 1.8%.

280 g of the obtained product are dispersed with vigorous stirring in 838.1 g of water cooled to 18 ° C. After 20 minutes 2.7 g of AMINE3 dissolved in 10.0g of water are dropped into the reactor.

The product obtained has a dry% equal to 25.84, Brookfield® viscosity at 20 rpm equal to 256 mPa * s and pH 6.8.

EXAMPLE 7

Preparation of a polyurethane comb with Method C.

In a reactor equipped with stirrer, thermometer and condenser, 300.0 g of ETHOXY2 and 0.11 g of 85% phosphoric acid are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 15.3 g of DIISOCYANATE1 are added; after 10 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value equal to 0.9%.

The mixture is then cooled to 55 ° C and 6.6 g of AMINE2 dissolved in 6.6 g of N-methylpyrrolidone are dropped into the reactor.

After 20 minutes, the measurement by titration of the residual NCO groups gives a value equal to 0.0%.

The temperature is then brought to 85 ° C and 28.5 g of DIISOCYANATE1 are loaded and allowed to react up to a value of - residual NCO equal to 1.5%.

300 g of the obtained product are dispersed with vigorous stirring in 898.0 g of water cooled to 18 ° C. After 20 minutes 2.9 g of AMINE3 dissolved in 10.7 g of water are dropped into the reactor.

The obtained product has a dry% equal to 24.99, Brookfield® viscosity at 20 rpm equal to 194 mPa * s and pH 6.3.

EXAMPLE 8

Preparation of a polyurethane comb with Method B.

In a reactor equipped with stirrer, thermometer and condenser, 300.0 g of ETHOXY4 and 0.11 g of 85% phosphoric acid are charged in a nitrogen atmosphere and at room temperature. The mixture is heated under stirring up to 85 ° C and 226.2 g of TRIISOCYANATE1 are added; after 10 minutes, 0.3 g of tin dibutyllaurate are added.

It is left at 85 ° C until the measurement by titration of the free residual NCO groups gives a calculated value of 5.9%.

470 g of the obtained product are dispersed with vigorous stirring in 1360 g of water cooled to 18 ° C. After 20 minutes, 16.7 g of AMINE3 dissolved in 62.1 g of water are dropped into the reactor.

The obtained product has a dry% equal to 25.1.

APPLICATION EXAMPLES

Some compositions for coating paper based on 100% carbonate (Hdrocarb 90, by OMYA, CH) were prepared using the comb polyurethanes of Examples 1-8 and a water retention agent of the prior art ( Viscolam GP37).

The compositions of the compositions for the paper coating are reported in Table 1; the quantities of the ingredients are in parts by weight. The paper coating compositions were characterized by making the following measurements:

ï ‚· pH

ï ‚Brookfield® viscosity at 100 rpm

ï ‚dry%

ï ‚· water retention, according to the T710 Caps method

The patinas were finally applied (13 g / m <2>) on an offset support of 80 g / m <2>; The sheets were conditioned for 24 h at 21 ° C and 50% R.H. and then Calendered (cylinder temperature 55 ° C, pressure 67.5 Kg / cm; Nip 4), and finally the White and Glossy degree readings were carried out.

Table 1

COMPOSITION: 1 2 3 4 5 6 7 8 9 <6)> HYDROCARB 90 100 100 100 100 100 100 100 100 100 DOW L <ATEX> 935 <1)> 10 10 10 10 10 10 10 10 10 REOTAN A <2) > 0.045 0.045 0.045 0.045 0.045 0.045 0.045 0.045 0.045 DEFOMEX 108 <3)> 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 TINOPAL ABP-Z <4)> 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 ES.1 0.45 / / / / / / / / ES.2 / 0.45 / / / / / / / ES.3 / / 0.45 / / / / / / ES.4 / / / 0.45 / / / / / ES.5 / / / / 0.45 / / / / ES.6 / / / / / 0.45 / / / ES.7 / / / / / / 0.45 / /ES.8 / / / / / / 0.45 </> Viscolam GP37 <5)> / / / / / / / /<0.15> CHARACTERISTICS OF THE COMPOSITIONS

Dry (%) 70.32 70.40 70.18 70.16 69.95 69.95 69.97 70.21 70.18 pH 8.85 9.02 8.85 8.91 8.97 9.08 9.06 8.87 8.95 Viscosity (mPa * s) 550 655 570 650 600 770 650 450 960 Water retention

(g / m <2>) <150 140 155 145 130 145 140 165 112> 1) Binder, styrene butadiene latex (Dow Chemical Co. US)

2) Dispersant, sodium polyacrylate (Lamberti SpA, IT)

3) Antifoam, (Lamberti SpA, IT)

4) Optical brightener (CIBA, CH)

5) ASE thickener (Lamberti SpA)

6) comparative

Table 2

COMPOSITION: ° White <1)> Glossy @ 75 ° <2)> 1 100.8 72.5

2 100.6 72.1

3 101.1 72.8

4 100.5 72.0

5 100.3 72.4

6 100.4 72.7

7 100.9 72.6

8 100.6 75.2

9 <3)> 99.2 65.8

1) White according to T452 Cap Method

2) Polished at 75 ° according to the T480 Cap Method

3) comparative

Claims (8)

CLAIMS 1. Compositions for the coating of paper containing a) from 30 to 80% by weight of an inorganic pigment; b) 0.05 to 3.0 parts by weight per 100 parts by weight of pigment of at least one water-soluble comb polyurethane containing polyoxyethylene side chains having a molecular weight greater than 500 and ethylene oxide content between 80 and 99.9% by weight ; c) at least 15% by weight of water, and having Brookfield® viscosity at 25 ° C and 100 rpm lower than 3,000 mPa * s. 2. Compositions for paper coating according to claim 1, wherein the comb polyurethane has a total ethylene oxide content greater than 50% by weight. 3. Paper coating compositions according to claim 2, wherein the comb polyurethane has a total ethylene oxide content greater than 70% by weight. 4. Compositions for paper coating according to claim 2 or 3, in which the comb polyurethane has a molecular weight greater than 100,000 and polyoxyethylene side chains with a molecular weight between 2,000 and 20,000 and an ethylene oxide content between 90 and 99.9% by weight. 5. Compositions for paper coating according to claim 1, in which the polyurethane is obtained by reacting a bifunctional isocyanate, containing polyoxyethylene side chains having a molecular weight higher than 500 and ethylene oxide content between 80 and 99.9% by weight, with one or more compounds of molecular weight from 34 to 300 which have two groups reactive towards the isocyanic groups. 6. Paper coating compositions according to any one of the preceding claims which contain from 0.01 to 3% by weight of a dispersing agent and from 1 to 15% by weight of a binder. 7. Paper coating compositions according to claim 6., in which the dispersing agent is an anionic non-cross-linked polyacrylate with a molecular weight of between 5,000 and 40,000 and the binder is a polymeric binder of an acrylic nature. 8. Compositions for the coating of paper according to claim 1, in which the inorganic pigment has from 40 to 90% by weight of the particles with a particle size lower than 2 microns and is selected from kaolin, calcium carbonate, talc, dioxide titanium, barium sulfate, gypsum and their mixtures.