EP0261039A1 - Complex pigmentary compositions for coating paper - Google Patents

Abstract

Complex pigment compositions for coating paper comprising an aqueous phase, at least one pigment of mineral origin, a binding agent, optionally various usual additives and a dispersing agent consisting of water-soluble carboxylic polymers in a salified form obtained by known processes which are characterized in that the dispersing agent: a) has a specific viscosity of between 0.25 and 2 (measured in the form of a sodium salt), b) is salified at a rate of at least 0.60 by at least one salifying agent having a versatile function. These complex pigment compositions which offer very low viscosities can simultaneously contain pigments as diverse as kaolin, titanium dioxide, calcium carbonate, while eliminating the usual increases in viscosity and the risks of solidification.

Description

The invention relates to complex pigment compositions for coating paper, containing one or more pigments in high concentration and having a low viscosity which is stable over time.

For a long time already, those skilled in the art have had for the coating of paper pigment compositions comprising pigments, more generally of a given type such as kaolin, containing more or less significant amounts of clays, a phase aqueous in which these pigments are dispersed, at least one binding agent which can be water-dispersed or water-soluble, of natural origin such as starch, casein, carboxymethylcellulose, and / or synthetic such as styrene-butadiene emulsions, styrene- acrylate, vinyl copolymers, and a dispersing agent such as for example a polyphosphate.

However, since the techniques for coating paper have rapidly evolved because the appropriate technologies have improved and the coating speeds have increased, it became obvious to the user that the pigment compositions for coating the paper had to simultaneously contain the smallest amount of water possible to decrease the thermal energy consumed during drying and have the most favorable rheological characteristics for the coating operation, that is to say being in a state of low viscosity at a high speed gradient to allow a much faster coating or alternatively allow at low shear rate to always have a low viscosity in order to be able to easily handle the coating composition, in particular in the sieving operations preceding the operation d coating.

Pigment compositions for coating paper have evolved considerably in recent years to meet technological progress (significant increase in speeds) and the imperatives of productivity, quality and costs. This evolution of the coating compositions is manifest, not only by the reduction in the amount of water, that is to say by the increase in the concentration of pigment materials, but also by the use of polyacrylates of alkali metals. or ammonium as dispersing agents. Thus, and by these means, the pigments should be maintained after their mechanical disintegration in a satisfactory dispersed state so that the coating composition is sufficiently fluid.

As such, French patent 2,185,721 describes pigment compositions for coating paper, the dispersing agent of which is chosen from acrylic acid polymers completely neutralized by an alkaline solution of sodium hydroxide. However, such dispersing agents have drawbacks which are considered to be major because they have proved difficult to use in certain pigment compositions currently used in the coating of paper, as they have been shown to be sensitive to variations in the pH of the aqueous phase. of the pigmentary dispersion of the ionic environment of said compositions, this sensitivity being detected by the rapid and irreversible increase in viscosity and, in certain cases, solidification of the coating compositions.

Because the pigment compositions currently available to those skilled in the art for coating paper have also evolved considerably by their pigment formulation, it being understood that they increasingly use mixtures of pigments comprising , no longer kaolin alone or associated with clays, but kaolin and / or pigmentary calcium carbonate and / or talc and / or titanium dioxide, changing the state ionic phase of the aqueous phase and that, during their preparation and mixing prior to the coating of the paper and / or their storage, the already mentioned increase in viscosities and the solidification in certain cases of said compositions is manifested, in especially when there is a mixture of pigments.

Thus, these dispersing agents have been revealed in use incapable of solving or overcoming the drawbacks caused within compositions for coating paper by the presence of mixtures of pigments which are more or less compatible with each other, but whose presence is necessary in said compositions for the quality of the paper after coating.

However, in another field, the Applicant, which has previously encountered the phenomenon of increased viscosities during the grinding of mineral materials in an aqueous medium, has already successfully advocated the use of a grinding, ethylenic polymer, making it possible to increase the concentration of mineral matter in the suspension subjected to grinding while maintaining a low viscosity and stable over time, that is to say during grinding and prolonged storage (one month) crushed suspensions.

In this regard, French patent 2,531,444 describes a grinding agent consisting of a polymer and / or copolymer of ethylenic acids whose acid functions are partially neutralized by at least one neutralizing agent having at least one monovalent function with a neutralization rate which can vary between 0.40 and 0.96 and preferably between 0.50 and 0.75, the nature of the neutralizing cation not being essential, the important character being the free acidity after neutralization.

However, when said grinding agent, as recommended by the prior art, is introduced into a pigment composition intended for coating paper comprising at the highest concentration, for example 70%, a single pigment, such as for example kaolin, or several pigments, such as for example pigmentary calcium carbonate and titanium dioxide, there is a very significant increase in viscosity ranging in certain extreme cases until the setting of said composition, while, due to its behavior as a grinding agent, one could expect a decrease in viscosity.

In this same regard, French patent 2,539,137 also describes a grinding agent formed from a polymer and / or from a copolymer of ethylene acids, the acid functions of which are completely and simultaneously neutralized by at least one neutralizing agent having of a monovalent function and by at least one neutralizing agent having a polyvalent function, the neutralization rate of the agent having a monovalent function being between 0.40 and 0.95, preferably between 0.60 and 0.90 and the neutralization rate of the agent having a polyvalent function being between 0.60 and 0.05, preferably between 0.40 and 0.10.

However, when this grinding agent is used according to the practice of the prior art as a dispersing agent in pigment compositions intended for coating paper comprising at a higher concentration a single pigment (kaolin, for example Dinkie A lump at 68% concentration) or a mixture of several pigments (calcium carbonate and titanium dioxide), there is a rapid and irreversible evolution of the rheological characteristics of these compositions, manifested by a strong increase in their viscosity and, in certain case, by their solidification, in especially when there is a mixture of pigment, even when one of them is present in very small proportion.

Therefore, the invention aims to remedy the aforementioned drawbacks by developing complex pigment compositions for coating paper, into which is introduced a dispersing agent giving said compositions a low viscosity and stable over time and excellent compatibility between pigments, avoiding any solidification.

• a) dispose d'une viscosité spécifique comprise entre 0,25 et 2 (mesurée sous la forme de sel de sodium),
• b) est salifié à un taux d'au moins 0,60 par au moins un agent de salification disposant d'une fonction polyvalente.

According to the invention, complex pigment compositions for coating paper, comprising an aqueous phase, at least one pigment of mineral origin, a binding agent, various usual well-known additives and a dispersing agent consisting of water-soluble carboxylic polymers under a salified form, obtained by known methods of polymerization, are characterized in that the dispersing agent:

• a) has a specific viscosity of between 0.25 and 2 (measured in the form of the sodium salt),
• b) is salified at a rate of at least 0.60 by at least one salifying agent having a versatile function.

To allow a better understanding of the subject of the invention, it is desirable to recall that a polyvalent salification agent has the capacity to associate with as many carboxylic functions of the polymer as its cation has valences.

Similarly, to measure the full scope and richness of the invention, it is useful to specify that, under the expression "complex pigment compositions", it is intended to define all the pigment formulations containing a pigment at a higher concentration than prior art or a mixture of several pigments whose incompatibility is evident in the presence of a dispersing agent of the prior art.

Among the pigments used in the context of the invention alone or as a mixture, mention may be made of kaolins, titanium oxides, talcs, natural or precipitated carbonates, aluminum hydroxides, satin white (double sulfate aluminum and hydrated calcium), natural or synthetic gypsum.

Because the Applicant was led to continue its research in the field of dispersing agents intended for pigment compositions for the coating of paper and, thereby, to increase industrial tests, it was led to observe first and then to then check that it was possible to produce pigmentary compositions for coating paper more concentrated in dry materials than those produced according to the prior art, of complex pigmentary formulation using mixtures of pigments and of low and very stable viscosity in time free from any solidification. These conditions are obtained when the dispersing agent is a water-soluble carboxylic polymer of which at least 60% of the carboxylic functions are salified with an appropriate salifying agent having a polyvalent function, it being found that at least 60% of the carboxylic functions salified with said agent and, a fortiori with a monovalent agent, said polymer used as a dispersing agent in complex pigment compositions intended for coating paper causes an increase in their viscosity and their solidification in certain cases.

The carboxylic polymers constituting the dispersing agent according to the invention result from the polymerization in the presence of transfer agents according to known methods in aqueous, alcoholic, hydroalcoholic, aromatic or aliphatic medium of at least one of the following monomers:
acrylic, methacrylic, itaconic, crotonic, fumaric, maleic anhydride or isocrotonic, aconitic, mesaconic, sinapic, undecylenic, angelic, hydroxy-acrylic, acrolein, acrylamide, acrylonitrile, esters of acrylic and methacrylic acids and, in particular, methyl, ethyl and propyl acrylates and methacrylates, dimethylaminoethyl methacrylate, imidazoles, vinylpyrolidone, vinylcaprolactam, ethylene, propylene, isobutylene, diisobutylene, vinyl acetate, styrene , alphamethylstyrene, methylvinyl ketone.

The transfer agents used during the polymerization are those well known to those skilled in the art such as for example isopropanol, tertiododecylmercaptan, thioglycolic acid and its esters, n-dodecylmercaptan, 2 mercaptopropionic acid, thiodiethanol.

Thus, the polymerization medium can be water, methanol, ethanol, propanol, isopropanol, butanols, or even dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, hexane, heptane, benzene, toluene, xylene, acetic acids, tartaric, lactic, citric, gluconic, glucoheptonic, halogenated solvents such as carbon tetrachloride , chloroform, methylene chloride, methyl chloride, ethers of ethylene glycol and propylene glycol.

The water-soluble carboxylic polymers according to the invention generally have a specific viscosity (measured in the form of the sodium salt) preferably between 0.30 and 1.0.

The specific viscosity of the carboxylic polymers and / or copolymers, which is symbolized by the letter "η", is determined as follows:
a solution of 100% neutralized carboxylic polymer and / or copolymer is prepared (neutralization rate: 1) with sodium hydroxide for the measurement, by dissolving 50 g dry of the polymer and / or copolymer in one liter of a distilled water solution containing 60 g of NaCl. Then a capillary viscometer with a Baume constant equal to 0.000105 placed in a bath thermostatically controlled at 25 ° C. is measured the flow time of a given volume of the above-mentioned solution containing the alkaline carboxylic polymer and / or copolymer, as well as the flow time of the same volume of aqueous sodium chloride solution devoid of said polymer and / or copolymer. It is then possible to define the viscosity "η" using the following relation:

The capillary tube is generally chosen in such a way that the flow time of the NaCl solution, devoid of polymer and / or copolymer, is approximately 90 to 100 seconds, thus giving very precise measurements of specific viscosity. precision.

The salifying agent having a versatile function is chosen from the group consisting of at least one of the divalent alkaline earth cations, in particular calcium, magnesium, zinc, copper, lead, as well as by trivalent cations including in particular aluminum, chromium, or even by cations of higher valence.

The salification of the dispersing agent according to the invention with at least one salifying agent having a polyvalent function can be carried out at a rate ranging from 0.6 to 1.0.

As soon as the salification of at least 60% of the acid sites with at least one salifying agent having a polyvalent function is carried out, the remaining acid sites can be maintained in this acid state or else completely salified according to the known art by a any salifying agent with a monovalent function, such as alkali cations, in particular lithium, sodium, potassium and by assimilation ammonium or even with an amine.

The dispersing agent is introduced into the pigment compositions at a concentration of 0.10 to 1.5 and preferably from 0.15 to 1.0 percent by weight relative to the dry pigments.

In addition to the dispersing agent according to the invention, said compositions contain pigments, alone or as a mixture, chosen from those known to those skilled in the art, such as for example kaolin, calcium carbonate, talc, titanium dioxide, hydroxide 'aluminum.

In addition, the pigmentary compositions according to the invention contain at least one binding and / or water-retaining agent chosen from binders of natural or synthetic origin, the former such as for example starch, carboxymethylcellulose, alcohol polyvinyl which also play the role of water retentive, being put in aqueous solution, the others such as for example styrene-butadiene or styrene-acrylate copolymers, being in the form of an aqueous emulsion.

The binding agent and / or water expander is introduced into the pigment compositions according to the invention in an amount of 7 to 20 percent by weight relative to the dry pigments.

Likewise, the pigment compositions according to the invention may also contain conventional additives in a known manner, such as anti-foaming agents, optical brighteners, biocidal agents, dyes, alkali hydroxides, etc.

The usual additives are introduced into the pigment compositions in the amounts necessary for each case to obtain the properties desired by the formulator, these amounts being well known to those skilled in the art.

• a) de 0,10 à 1,5 et préférentiellement de 0,15 à 1,0 pour cent de l'agent dispersant,
• b) de 7 à 20 pour cent de l'agent liant et/ou rétenteur d'eau,
• c) éventuellement des additifs usuels selon les pour cent connus.

In practice, the pigment compositions according to the invention may contain, expressed in percent by weight relative to the anhydrous mineral pigment mass:

• a) from 0.10 to 1.5 and preferably from 0.15 to 1.0 percent of the dispersing agent,
• b) from 7 to 20 percent of the binding agent and / or water-retaining agent,
• c) optionally usual additives according to the known percent.

The pigment compositions according to the invention are prepared according to methods known to those skilled in the art.

Thus, and unlike the prior art, the pigment compositions according to the invention constitute considerable progress in the field of coating of paper by the facts, not only that they contain a complex pigment formulation (mixture of pigments) and to higher concentration, but still that they have the most favorable rheological characteristics for the coating operation, that is to say being in a state of low viscosity at high speed gradient but also the most favorable for the operations handling such as sieving, transfer by pump, that is to say allowing to always have a low viscosity at low shear rate.

The invention will be better understood thanks to the illustration which is made thereof through the following examples.

Example 1

This example pursues the aim of illustrating comparatively the prior art and the invention.

To do this, pigment compositions for coating paper were prepared according to known methods, making use, for some of the well-known dispersing agents, for the others of dispersing agents which are objects of the invention.

In a first group of tests (tests 1 and 2), was determined for a given pH conventionally practiced in the paper industry, the optimum concentration range of dispersing agent according to the invention to be introduced into said compositions for their impart a very low and constant viscosity.

Test 1 concerns pigment compositions whose pigment, kaolin Dinkie A lump (English China Clay, Great Britain), is suspended in water at a rate of 71% by weight relative to the total mass in the presence of polyacrylate sodium of specific viscosity 0.4 (salification rate 1), dispersing agent of the prior art introduced into said compositions at increasing rates expressed in percent by weight of dry / dry.

Test 2 relates to pigment compositions containing 71% by weight relative to the total mass of kaolin Dinkie A lump suspended in water in the presence of an acrylic polymer of specific viscosity 0.4, salified at a rate of 0 , 7 per Ca² and at a rate of 0.3 per Na ±, dispersing agent according to the invention introduced into said compositions according to increasing rates expressed in percent by weight of dry / dry.

The pH of these compositions was adjusted to 7.4 ± 0.1.

All these pigment compositions were subjected to Brookfield viscosity measurements at rotational speeds of 10 revolutions and 100 revolutions per minute with an appropriate mobile according to the viscosities, these viscosities being measured at the end of the preparation.

All the results relating to the abovementioned compositions have been recorded in Table I below and are illustrated by FIG. 1.

Table I shows that at equal concentrations of dispersing agents:
the viscosity of the pigment compositions is always lower for those forming the subject of the invention,
the viscosity of the pigment compositions according to the invention remains constant from a threshold of 0.22% up to 0.25% by weight of dry / dry in dispersing agent, the most favorable interval for the user, then that that of the compositions of the prior art increases when the amount of dispersing agent.

In a second group of tests (tests 3 and 4), a pH interval was studied for a given concentration of dispersing agent, this interval corresponding to the pH of the components used in the paper industry for the preparation of coating compositions.

Because, it is known that in coating compositions belonging to the prior art, a person skilled in the art adjusts the pH of the kaolin compositions to around 7.3 value for which the viscosity is the lowest and that the adjustment the pH of the various components used in said coating compositions avoids shocks due to these differences in pH which would materialize by an undesirable increase in viscosity.

Test 3 relates to pigment compositions containing 71% by weight relative to the total mass of Dinkie A lump kaolin suspended in water in the presence of the same sodium polyacrylate (salification rate 1) as test 1, agent dispersant of the prior art introduced into said compositions at a constant rate of 0.25% by weight expressed in sec / sec, the pH of said compositions varying between 7.35 and 10.25.

Test 4 relates to pigmentary compositions also containing 71% by weight relative to the total mass of kaolin Dinkie A lump suspended in water in the presence of the same calcium and sodium polyacrylate from test 2, dispersing agent according to l he invention introduced into said compositions at a constant rate of 0.25% by weight expressed in sec / sec, the pH of said compositions varying between 7.35 and 10.25.

These pigment compositions were subjected to the same Brookfield viscosity measurements as those carried out for tests 1 and 2.

All the results concerning these compositions have been recorded in Table II below and are illustrated by FIG. 2.

Table II reveals that by changing the pH of the above-mentioned pigment compositions for the same concentration of dispersing agent:
the viscosity of the compositions according to the invention is always lower than that of the compositions according to the prior art regardless of the pH value,
- The viscosity of the compositions according to the invention is stable whatever the pH while that of the compositions according to the prior art increases with the pH.

Example 2

This example, the aim of which is to illustrate the invention, relates to the preparation of pigmentary compositions for coating paper making use of dispersing agents which are acrylic polymers of specific viscosities (measured in the form of sodium salt) included in the preferential range of 0.3 to 1, salified at a rate of at least 0.60 by at least one salifying agent having a divalent function.

Test 5 relates to a pigment composition for coating paper comprising 72% by weight of TiO₂ (titanium dioxide Anatase from THANN AND MULHOUSE) relative to the total mass in the presence of 0.35% by weight (relative to the pigment mass) of dispersing agents (acrylic polymers) which, according to the prior art, are completely salified with sodium ion.

Tests 6 to 24 relate to pigmentary compositions for coating the paper conform to the invention, comprising 72% by weight of TiO₂ (titanium dioxide Anatase from THANN AND MULHOUSE) relative to the total mass in the presence of 0.35% by weight (relative to the dry weight of pigment) of dispersing agents (acrylic polymers) salified at a rate of at least 0.6 by a salifying agent having a divalent function.

All the pigment compositions were subjected to viscosity measurements at rotational speeds of 10 revolutions and 100 revolutions per minute (Brookfield viscometer) with an appropriate mobile according to the viscosities, these viscosities being measured at the end of the preparation.

In addition, to highlight the harmful effects occurring in industrial installations, in particular in pipes, pumps, storage tanks during successive passages in these installations of different pigment compositions, for example one based on carbonate of calcium, the other based on titanium dioxide, a compatibility test between these two compositions was carried out in the laboratory.

This test consists in introducing into a pigment composition based on titanium dioxide a very small amount (1% by weight relative to the mass of TiO₂) of an aqueous suspension of finely ground calcium carbonate (H-90 from OMYA France ), said suspension of calcium carbonate having a concentration of 75% by weight relative to its total mass, then to observe after this introduction the evolution of the viscosity of said pigment composition which may lead to solidification.

All the parameters and results relating to the abovementioned compositions have been recorded in Table III below.

AA = Prior Art
INV = Invention
(A) = no increase in viscosity
(B) = less than 20% increase in viscosity
(C) = solidification

Table III shows by comparison of test 5 with tests 6 to 24:
- The significant decrease in the viscosities of the pigment compositions which become measurable when moving from the prior art to the subject of the invention. The pigments can be used at this concentration as opposed to the prior art,
- the very beneficial influence of the salification of dispersing agents at a rate of at least 0.6 by at least one polyvalent salification agent,
- the good compatibility between pigments (titanium dioxide anatase and calcium carbonate) for the pigment compositions according to the invention.

Example 3

This example pursues the aim of showing the universal character of the invention by the use in pigmentary compositions of titanium dioxide of various origins.

To do this, pigmentary compositions for coating paper, the pigment of which is titanium dioxide, were prepared according to known methods (tests 25 to 27, TiO₂ AHR of TIOXIDE and tests 28 to 30, TiO₂ A KRONOS) suspended in water at a rate of 72% by weight relative to the total mass in the presence of a dispersing agent which is either a sodium polyacrylate (specific viscosity 0.4 and salification rate 1) in the case tests relating to the prior art (tests 25, 26, 28, 29), ie an acrylic polymer (specific viscosity 0.4) salified at a rate of 0.7 per Ca²⁺ and at a rate of 0.3 per Na⁺ in the case of tests relating to the invention (tests 27 and 30).

All the pigment compositions were subjected to the same viscosity measurements and to the same compatibility tests as those practiced in Example 2.

All the results relating to the abovementioned compositions have been introduced in Table IV below.

AA = Prior Art
INV = Invention
(A) = no increase in viscosity
(B) = less than 20% increase in viscosity
(C) = solidification

Table IV confirms the conclusions of Table III of Example 2 which are particularly favorable to the subject of the invention.

Example 4

This example illustrates the universal nature of the invention by the use in kaolin pigment compositions as pigments of an origin other than that used in Example 1.

To this end, pigmentary compositions for the coating of paper based on kaolin Alphacoat (ANGLO AMERICAN CLAYS CORP.) Have been prepared according to known methods, using, for some, a dispersing agent belonging to the prior art, for the others a dispersing agent belonging to the invention.

Test 31 relates to pigment compositions comprising kaolin Alphacoat in suspension in water at a rate of 68% by weight relative to the total mass and a dispersing agent according to the prior art which is a sodium polyacrylate of specific viscosity 0 , 4 introduced into said compositions according to increasing rates expressed in percent by weight of dry / dry.

Test 32 relates to pigment compositions comprising the same kaolin Alphacoat suspended in water at the same concentration and a dispersing agent according to the invention which is an acrylic polymer (specific viscosity 0.4) salified at a rate of 0, 7 with Ca²⁺. and a rate of 0.3 per Na⁺ introduced into said compositions according to increasing rates.

The pH of these compositions was adjusted to 7.1 ± 0.1.

All these pigment compositions were subjected to Brookfield viscosity measurements and the results relating to them were collated in Table V below and are illustrated by FIG. 3.

This table confirms the conclusions extracted from Table I which concerned a Dinkie A lump kaolin.

Test 33 relates to pigment compositions comprising the same Alphacoat kaolin suspended in water at the same concentration of 68% and a dispersing agent of the prior art which is the same as that of test 31, introduced into said compositions at a rate of 0.25% by weight expressed as dry / dry, the pH of said compositions varying between 6.7 and 10.25.

Test 34 relates to pigment compositions comprising the same Alphacoat kaolin in suspension in water at the same concentration of 68% and a dispersing agent according to the invention which is the same calcium and sodium polyacrylate as in test 32 , introduced into said compositions at a constant rate of 0.25% by weight expressed in sec / sec, the pH of said compositions varying from 6.5 to 10.0.

The results relating to these pigment compositions have been collated in Table VI below and are illustrated in FIG. 4.

This table brings the same conclusions as Table II concerning a Dinkie A lump kaolin.

Example 5

This example, which illustrates the invention compared to the prior art, relates to the preparation of pigmentary compositions for coating paper using dispersing agents which are acrylic polymers with a specific viscosity 0.4 (measured in the form of sodium salt).

Tests 35 and 37 relate to aqueous pigment compositions for coating paper comprising natural calcium carbonate (from OMYA with a specific surface BET of 7 m² / g: test 35) or precipitated calcium carbonate (Socal P3 from SOLVAY: test 37, with a BET specific surface area of 14 m² / g) in the presence of a dispersing agent (above-mentioned acrylic polymer) which, according to the prior art, is completely salified with sodium ion.

Tests 36 and 38 relate to aqueous pigmentary compositions for coating the paper in accordance with the invention, comprising these same natural calcium carbonates (test 36) or precipitated calcium (test 38) in the presence of a dispersing agent ( aforementioned acrylic polymer) which, according to the invention, is salified at a rate of 0.7 per Ca²⁺ and a rate of 0.3 per Na⁺.

The results relating to these compositions are collated in Table VII below.

The comparison of tests 35 and 37 (prior art) with tests 36 and 38 (invention) confirms the significant improvements obtained thanks to the invention, in particular when the BET specific surface area of pigments increases significantly, causing in this case well known difficulties of implementation.

Example 6

This example illustrates the implementation according to the invention in an aqueous pigment composition of a dispersing agent which is an acrylic polymer of specific viscosity 0.4, partially salified at the rate of 0.7 with Ca²⁺, the other functions - COOH remaining free.

In this regard, test 39 relates to the preparation of an aqueous pigment composition of 72% by weight relative to the total mass of TiO₂ (titanium dioxide Anatase from THANN AND MULHOUSE) in the presence of 0.35% by weight. relative to the dry weight of the pigment of a dispersing agent (acrylic polymer) mentioned above (Ca²⁺ / -COOH = 0.7 / 0.3).

The results relating to this composition as well as to the control composition (test 5 of the prior art) are collated in Table VIII below.

Thus, provided that the dispersing agent (acrylic polymer) is salified at a rate of at least 0.6 by a salifying agent having a polyvalent function, the free acid functions (-COOH) in no way affect the very positive effects observed for the pigment compositions according to the invention.

Example 7

The purpose of this example is to illustrate comparatively complex pigment compositions (mixture of two pigments) for coating paper according to the prior art and according to the invention.

To do this, complex pigmentary compositions in which the dispersing agent is, for some known types (sodium polyacrylate) and for others a salified polymer according to the invention (salification rate: 0.7 Ca²⁺ and 0.3 Na⁺).

Test 40 relates to a complex pigment composition according to the prior art containing:
- 70% by weight of Dinkie A lump kaolin, introduced in the form of an aqueous suspension of said kaolin at 71% by weight of concentration containing, as dispersing agent, 0.25% by dry / dry weight of a polyacrylate of sodium with specific viscosity 0.4 (salification rate 1).
- 30% by weight of pigmentary calcium carbonate introduced in the form of an aqueous suspension of said calcium carbonate at a concentration of 74.3% by weight containing 0.6% by dry / dry weight of a dispersing agent which is a acrylic polymer of specific viscosity 0.56, salified at a rate of 0.3 with the Ca²⁺ ion and at a rate of 0.7 with the Na⁺ ion, in accordance with the prior art.

Test 41 relates to a complex pigment composition according to the invention, containing:
- 70% by weight of Dinkie A lump kaolin, introduced in the form of an aqueous suspension of said kaolin at 71% by weight of concentration containing as dispersing agent 0.25% by dry / dry weight of an acrylic polymer of specific viscosity 0.40 salified at a rate of 0.7 with the Ca²⁺ ion and at a rate of 0.3 with the Na⁺ ion
- 30% by weight of pigmentary calcium carbonate, introduced in the form of an aqueous suspension described in test 40.

At the end of these two pigment mixes, compositions for coating the paper were prepared by adding to tests 40 (prior art) and 41 (invention) per 100 parts by weight of dry pigments:
- 0.5 part by weight of a water-retaining agent (carboxymethylcellulose)
- 10.5 parts by weight of a latex, an anionic aqueous emulsion of an acrylic copolymer sold under the name ACRONAL S 360 D by BASF

The pH of these coating compositions was adjusted to 8.6 ± 0.1 and the oncentration in% by weight of dry matter was 69%.

The coating compositions were subjected to Brookfield viscosity measurements at rotational speeds of 10 rpm and 100 rpm with an appropriate mobile.

All the results relating to these compositions are recorded in Table IX below.

The table by comparison of the two compositions for coating the paper confirms that at equal concentrations of pigments and dispersing agents, the viscosities of the composition for coating the paper according to the invention are always much lower (approximately 60%) than the composition for coating according to the prior art.

Example 8

This example illustrates by comparison complex pigment compositions (mixture of three pigments) intended for the coating of paper, prepared according to known methods and making use for some of the dispersing agents belonging to the prior art and for the others of salified dispersing agents according to the invention.

• a) d'abord de 10% en poids de dioxyde de titane (Anatase ATl de la société THANN ET MULHOUSE) sous la forme d'une suspension aqueuse à 72% en poids de concentration contenant également comme agent dispersant 0,1% en poids sec/sec d'un polyacrylate de sodium de viscosité spécifique 0,4 (taux de salification 1)
• b) ensuite de 20% en poids de carbonate de calcium pigmentaire sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• c) enfin de 70% en poids de kaolin sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.

Test 42 relates to a complex composition according to the prior art prepared by the introduction:

• a) first of 10% by weight of titanium dioxide (Anatase AT1 from the company THANN ET MULHOUSE) in the form of an aqueous suspension at 72% by weight of concentration also containing as dispersing agent 0.1% by weight dry / dry sodium polyacrylate with specific viscosity 0.4 (salification level 1)
• b) then 20% by weight of pigmentary calcium carbonate in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• c) finally 70% by weight of kaolin in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.

• a) d'abord de 10% en poids de dioxyde de titane (Anatase ATl de la société THANN ET MULHOUSE) sous la forme d'une suspension aqueuse à 72% en poids de concentration contenant également comme agent dispersant, selon l'invention, 0,35% en poids sec/sec d'un polymère acrylique de viscosité spécifique (mesurée sous la forme de sel de sodium) 0,4 et salifié à un taux de 0,7 par l'ion Ca²± et à un taux de 0,3 par l'ion Na±.
• b) ensuite de 20% en poids de carbonate de calcium pigmentaire sous la forme de la même suspension aqueuse que celle de l'essai 42, paragraphe (b).
• c) enfin de 70% en poids de kaolin sous la forme de la même suspension aqueuse que celle de l'essai 42, paragraphe (c).

Test 43 relates to a complex composition according to the invention prepared by the introduction:

• a) first of 10% by weight of titanium dioxide (Anatase AT1 from the company THANN ET MULHOUSE) in the form of an aqueous suspension at 72% by weight of concentration also containing as dispersing agent, according to the invention, 0.35% by dry / dry weight of an acrylic polymer of specific viscosity (measured in the form of sodium salt) 0.4 and salified at a rate of 0.7 with the ion Ca² ± and at a rate of 0.3 per Na ± ion.
• b) then 20% by weight of pigmentary calcium carbonate in the form of the same aqueous suspension as that of test 42, paragraph (b).
• c) finally 70% by weight of kaolin in the form of the same aqueous suspension as that of test 42, paragraph (c).

• a) d'abord de 10% en poids de dioxyde de titane (Anatase ATl de la société THANN ET MULHOUSE) sous la forme d'une suspension aqueuse à 72% en poids de concentration contenant également comme agent dispersant 0,35% en poids sec/sec d'un polymère acrylique de viscosité spécifique (mesurée sous la forme du sel de sodium) 0,4 et salifié à un taux de 0,7 par l'ion Ca²⁺ et à un taux de 0,3 par l'ion Na⁺.
• b) ensuite de 20% en poids de carbonate de calcium pigmentaire sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• c) enfin de 70% en poids de kaolin sous la forme d'une suspension aqueuse à une concentration de 71% en poids contenant comme agent dispersant 0,25% en poids sec/sec d'un polymère acrylique de viscosité spécifique 0,4 salifié à un tau x de 0,7 par l'ion Ca²⁺ et à un taux de 0,3 par l'ion Na⁺.

Test 44 relates to a complex composition according to the invention prepared by the introduction:

• a) first of 10% by weight of titanium dioxide (Anatase AT1 from the company THANN ET MULHOUSE) in the form of an aqueous suspension at 72% by weight of concentration also containing as dispersing agent 0.35% by weight dry / dry of an acrylic polymer of specific viscosity (measured in the form of the sodium salt) 0.4 and salified at a rate of 0.7 with the Ca²⁺ ion and at a rate of 0.3 with Na⁺ ion.
• b) then 20% by weight of pigmentary calcium carbonate in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• c) finally 70% by weight of kaolin in the form of an aqueous suspension at a concentration of 71% by weight containing as dispersing agent 0.25% by dry / dry weight of an acrylic polymer of specific viscosity 0.4 salified at a tau x of 0.7 with the Ca²⁺ ion and at a rate of 0.3 with the Na⁺ ion.

• a) d'abord de 70% en poids de kaolin sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• b) ensuite de 20% en poids de carbonate de calcium pigmentaire sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• c) enfin de 10% en poids de dioxyde de titane (Anatase Atl de la société THANN ET MULHOUSE) sous la forme d'une suspension aqueuse à 72% en poids de concentration contenant également comme agent dispersant 0,1% en poids sec/sec d'un polyacrylate de sodium de viscosité spécifique 0,4 (taux de salification 1)

Test 45 relates to a complex composition according to the prior art prepared by the introduction:

• a) first of 70% by weight of kaolin in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• b) then 20% by weight of pigmentary calcium carbonate in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• c) finally 10% by weight of titanium dioxide (Anatase Atl from the company THANN ET MULHOUSE) in the form of an aqueous suspension at 72% by weight of concentration also containing as dispersing agent 0.1% by dry weight / dry sodium polyacrylate with specific viscosity 0.4 (salification rate 1)

• a) d'abord de 70% en poids de kaolin sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• b) ensuite de 20% en poids de carbonate de calcium pigmentaire sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• c) enfin de 10% en poids de dioxyde de titane (Anatase ATl de la société THANN ET MULHOUSE) sous la forme d'une suspension aqueuse à 72% en poids de concentration contenant comme agent dispersant, selon l'invention, 0,35% en poids sec/sec d'un polymère acrylique de viscosité spécifique 0,4 salifié au taux de 0,7 par l'ion Ca²⁺ et au taux de 0,3 par l'ion Na⁺.

Test 46 relates to a complex composition according to the invention prepared by the introduction:

• a) first of 70% by weight of kaolin in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• b) then 20% by weight of pigmentary calcium carbonate in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• c) finally 10% by weight of titanium dioxide (Anatase AT1 from the company THANN ET MULHOUSE) in the form of an aqueous suspension at 72% by weight of concentration containing, as dispersing agent, according to the invention, 0.35 % by dry / dry weight of an acrylic polymer of specific viscosity 0.4 salified at the rate of 0.7 with the Ca²⁺ ion and at the rate of 0.3 with the Na⁺ ion.

• a) d'abord de 70% en poids de kaolin sous la forme de la suspension aqueuse à une concentration de 71% en poids contenant comme agent dispersant 0,25% en poids sec/sec d'un polymère acrylique de viscosité spécifique 0,4 salifié à un taux de 0,7 par l'ion Ca²⁺ et à un taux de 0,3 par l'ion Na⁺.
• b) ensuite de 20% en poids de carbonate de calcium pigmentaire sous la forme de la suspension aqueuse décrite dans l'essai 40, l'agent dispersant appartenant à l'art antérieur.
• c) enfin de 10% en poids de dioxyde de titane (Anatase ATl de la société THANN ET MULHOUSE) sous la forme d'une suspension aqueuse à une concentration de 72% en poids contenant également comme agent dispersant, selon l'invention, 0,35% en poids sec/sec d'un polymère acrylique de viscosité spécifique 0,4 salifié à un taux de 0,7 par l'ion Ca²⁺ et un taux de 0,3 par l'ion Na⁺.

Test 47 relates to a complex composition according to the invention prepared by the introduction:

• a) first of 70% by weight of kaolin in the form of the aqueous suspension at a concentration of 71% by weight containing as dispersing agent 0.25% by dry / dry weight of an acrylic polymer of specific viscosity 0, 4 salified at a rate of 0.7 with the Ca²⁺ ion and at a rate of 0.3 with the Na⁺ ion.
• b) then 20% by weight of pigmentary calcium carbonate in the form of the aqueous suspension described in test 40, the dispersing agent belonging to the prior art.
• c) finally 10% by weight of titanium dioxide (Anatase AT1 from the company THANN ET MULHOUSE) in the form of an aqueous suspension at a concentration of 72% by weight also containing as dispersing agent, according to the invention, 0 , 35% by dry / dry weight of an acrylic polymer of specific viscosity 0.4 salified at a rate of 0.7 with the Ca²⁺ ion and a rate of 0.3 with the Na⁺ ion.

After having made these various pigmentary mixtures, compositions for coating the paper were prepared by adding to tests 42 to 47, per 100 parts by weight of dry pigments:
- 0.5 part by weight of a water retentant (carboxymethylcellulose),
- 10.5 parts by weight, of the latex described in Example 7.

The pH of these compositions was adjusted to 8.6 ± 0.1 and the dry matter concentration to 68.7% ± 0.2%.

The coating compositions thus prepared were subjected to Brookfield viscosity measurements at rotational speeds of 10 rpm and 100 rpm

All the results relating to these compositions have been collated in Table X below.

From this table and by comparison between the tests relating to the prior art and those relating to the invention, it appears that:
in the prior art , the order of introduction of the aqueous pigmentary suspensions during the preparation of the complex compositions for coating the paper is important because it results either in solidification (test 42) or in very high viscosities (test 45) of said compositions, revealing an incompatibility between the various pigments
- In the invention , the aqueous pigment suspensions produced in the presence of at least one dispersing agent according to the invention become compatible with one another during their mixing thanks to the presence of said agent. Such mixtures no longer solidify regardless of the order of introduction of the pigment suspensions, and give said complex compositions thus prepared viscosities much lower than in the prior art.

Claims (12)

1 - Complex pigment compositions for coating paper comprising an aqueous phase, at least with a pigment of mineral origin, a binding agent, optionally various usual additives and a dispersing agent constituted by the water-soluble carboxylic polymers in a salified form, obtained by known methods of polymerization, characterized in that the dispersing agent: a) has a specific viscosity of between 0.25 and 2 (measured in the form of a sodium salt), b) is salified at a rate of at least 0.60 by at least one salifying agent having a versatile function. 2 - Pigment compositions for coating the paper according to claim 1, characterized in that the dispersing agent results from the polymerization or copolymerization according to known methods of at least one of the monomers belonging to the group of acrylic or methacrylic acids, itaconic, crotonic, fumaric, maleic anhydride or isocrotonic, aconitic, mesaconic, sinapic, undecylenic, angelic, hydroxy-acrylic; acrolein; acrylamide; acrylonitrile; esters of acrylic and methacrylic acids, and in particular methyl, ethyl, propyl acrylates and methacrylates, dimethylaminoethyl methacrylate; imidazoles; vinylpyrolidone; vinylcaprolactam; ethylene, propylene, isobutylene, diisobutylene ; vinyl acetate, styrene, alphamethylstyrene, methylvinyl ketone. 3 - Pigmentary compositions for coating the paper according to claim 2, characterized in that the dispersing agent results from the polymerization or copolymerization, according to the processes preferably known of at least one of the acrylic, methacrylic, itaconic acid monomers, crotonic, fumaric and maleic anhydride. 4 - Pigment compositions for coating the paper according to any one of claims 1 or 3, characterized in that the dispersing agent has a specific viscosity measured in the form of a sodium salt, preferably between 0.30 and 1.0. 5 - Pigment compositions for coating paper according to any one of claims 1 to 4, characterized in that the salifying agent having a versatile function belongs to the group consisting of divalent and trivalent cations and preferably chosen from calcium, magnesium, zinc, copper, lead, aluminum or chromium. 6 - Pigmentary compositions for coating paper according to any one of claims 1 to 5, characterized in that the salification of the dispersing agent with at least one salifying agent having a versatile function is carried out at a rate between 0.6 and 1. 7 - Pigment compositions for coating the paper according to claim 6, characterized in that the salification of the dispersing agent with at least one salification agent having a function polyvalent is carried out at a rate of at least 0.6, the non-salified acid sites remaining in said acid state. 8 - Pigment compositions for coating the paper according to claim 6, characterized in that the salifaction of the dispersing agent with at least one salifying agent having a polyvalent function is carried out at a rate of at least 0, 6, the still free acidic sites being salified by a salifying agent having a monovalent function chosen from the group consisting of lithium, sodium, potassium, ammonium, an amine. 9 - Pigmentary compositions for coating paper according to any one of claims 1 to 8, characterized in that the dispersing agent is used in said compositions at a concentration of 0.10 to 1.5 percent and preferably from 0.15 to 1 percent by weight relative to the dry pigment. 10 - Pigment compositions for coating the paper according to any one of Claims 1 to 9, characterized in that they contain in percent by weight relative to the anhydrous mineral pigment mass, in addition to the aqueous phase: a) from 0.10 to 1.5 percent and preferably from 0.15 to 1.0 percent of the dispersing agent, b) from 7 to 20 percent of a binder and / or water-retaining agent, c) optionally usual additives according to known percent. 11 - Pigment compositions for coating the paper according to any one of claims 1 to 10, characterized in that the pigments used alone or as a mixture are chosen from the group consisting of kaolins, titanium oxides, talcs, natural or precipitated carbonates, aluminum hydroxides, double hydrated aluminum and calcium sulphate. 12 - Pigmentary compositions for coating paper according to any one of claims 1 to 11, characterized in that the binding agent and / or water-retaining agent is chosen from the group consisting of starch, carboxymethylcellulose, polyvinyl alcohol, styrene-butadiene and styrene-acrylate copolymers.

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