EP0106763B1 - Composition and process for coating paper and board, process for preparing the composition and paper and board thus obtained - Google Patents

Abstract

The invention relates to a coating composition for paper and cardboard comprising, besides the usual pigments, a fluidizing agent and, by way of binder, an undepolymerized starch possibly modified, as well as, generally, one or several synthetic products and/or one or several proteins.

Description

The present invention relates to an aqueous composition for coating paper and cardboard.

It also relates to a process for coating the paper using said composition, as well as a process for preparing it.

Finally, it relates to the paper and cardboard obtained, that is to say "coated using this composition.

The technical term "coating" denotes the operation consisting in depositing on one or both sides of a support sheet of paper or cardboard, a coating composition forming a coating; this coating gives the treated sheet a particularly regular surface condition and therefore capable of receiving a fine impression, while improving the opacity and appearance of the paper (whiteness, smoothness, gloss).

A coating composition comprises at least two components, namely a pigment and a binder also called an adhesive.

The first of these constituents, the pigment, intervenes as follows during the coating operation.

The paper is made up of fibers of variable dimensions which, despite the usual satin-finishing operation, allow cavities, the dimensions of which are of the order of 50 to 100 μrn, to remain on the surface and, on the other hand , in the thickness of the paper, more or less wide channels, designated by the term of macro-capillaries. When, during the coating operation, the surface is covered with a coating based on very fine pigments, these fill the cavities by leveling the surface; the channels comprised by the layer thus placed are extremely thin, they are micro-capillaries with a width of the order of 2 to 5 μm. When printing coated papers, the ink pigments, which are larger than the channels of the layer, remain on the surface while the ink pigment support which is made up of oils and solvents is easily absorbed by micro-capillaries, which improves the quality of printing.

To constitute the pigment of the coating composition, use is generally made of an aqueous dispersion of kaolin; it is also possible to use either separately, or most often in admixture with kaolin, other pigments such as in particular calcium carbonate, titanium oxide, calcium sulfate, satin white (SO _A Ca + A1 ₂ 0 ₃ ) or very fine talc.

To constitute the binder of the coating composition, use is generally made of starches, proteins such as casein or soy protein, or of synthetic products such as polyvinyl alcohol, polyvinyl acetate, acrylic products. , styrene-butadiene; the composition may contain only one of these products, but often they are used as a mixture. The amount of binder generally represents from 5 to 30% of the weight of pigment. This quantity is chosen in particular as a function of the nature of the pigment, as a function of the coating process used and as a function of the qualities sought for paper or cardboard. By way of example, it is pointed out that it is necessary to use more binder in the case of carbonate and satin white than in the case of kaolin, in the case of divided charges than in the case of coarse charges .

In addition to the pigment and the binder, a coating composition comprises various complementary agents among which mention may be made of foam reducers, preservatives, dyes, dispersants or deflocculants such as tripolyphosphate, pyrophosphate or hexametaphosphate and salts polycarboxylic acids which retard in particular the sedimentation of the suspensions.

The formulation of the coating composition varies according to the application technique, the qualities of the backing paper or the desired properties, the latter being different according to the printing mode (rotogravure, letterpress printing, offset, flexographic printing, screen printing) for which coated papers are intended.

Finally, it should be noted that the simple energy aspect leads to the search, for a given viscosity, for coating compositions having the highest possible dry extract, so that the energy expenditure necessary for obtaining a dry coated paper is as low as possible.

The starches used up to now, alone or in admixture with the above-mentioned proteins or synthetic products to constitute the binder of the coating composition, are depolymerized starches, optionally further modified by etherification or esterification.

Thus, patent FR-A-2447388 describes a product formed of particles comprising a support on which are fixed or retained the constituents of a hydrogenated starch hydrolyzate, said product being able to be used as plasticizer in the paper industry, as indicated in Example 7, but then the support is a white dextin, therefore a depolymerized starch and, moreover, the proportion of hydrolyzate relative to the pigment is of the order of 0.1 part per 100 parts of pigment, c that is to say about four times lower than the lower limit provided in accordance with the invention.

• - le brevet US-A-3 222 220 qui concerne un mélange formé, d'une part, d'amidon à haute teneur en amylose - donc très différent de ce que l'on désigne généralement sous le terme « amidon (cf. col. 6, 1. 28-30) et qui, de plus, peut être considéré comme au moins partiellement dépolymérisé par suite du traitement de cisaillement (cf. col. 2, 1. 28-30) -, cet « amidon étant dispersible dans l'eau chaude, et d'autre part de 10 à 75 % en poids de sorbitol par rapport à l'amidon ; ce mélange forme, grâce à la présence du sorbitol, des pellicules de résistance accrue ; la possibilité d'utiliser ces mélanges dans diverses applications alimentaires, textiles ou papetières est mentionnée sur un plan tout à fait général ;
• - l'article extrait de la revue « Die Stärke », vol. 31 (1979), mai n° 5, pages 163-165, qui concerne simplement des pellicules d'amidon et d'alcools polyvinyliques et examine l'effet de divers agents plastifiants dont le sorbitol ;
• - le brevet FR-A-2 411 866 qui décrit une composition pigmentée de couchage à base d'amidon pour le papier, différente de celle conforme à l'invention.

We also know

• - US-A-3,222,220 which relates to a mixture formed, on the one hand, of starch with a high amylose content - therefore very different from what is generally designated by the term "starch (cf. col . 6, 1. 28-30) and which, moreover, can be considered as at least partially depolymerized as a result of the shearing treatment (cf. col. 2, 1. 28-30) -, this "starch being dispersible in hot water, and on the other hand from 10 to 75% by weight of sorbitol relative to the starch; this mixture forms, thanks to the presence of sorbitol, films of increased resistance; the possibility of using these mixtures in various food, textile or paper applications is mentioned on a very general plan;
• - the article extracted from the magazine "Die Stärke", vol. 31 (1979), May No. 5, pages 163-165, which simply relates to films of starch and polyvinyl alcohols and examines the effect of various plasticizing agents including sorbitol;
• - Patent FR-A-2 411 866 which describes a pigmented coating composition based on starch for paper, different from that according to the invention.

It has indeed been very difficult, if not practically impossible, to use non-depolymerized starch in coating compositions, in particular because of the difficulty of obtaining, from an unpolymerized starch, a colloidal solution. correct, since non-depolymerized starch soils cooked for 90 minutes in a water bath still have highly swollen granules. And even when correct non-depolymerized starch soils are obtained, they exhibit excessive viscosity, aggravated by the tendency of molecules to reassociate or retrogradate, which in fact prevents their practical application in coating compositions.

The starches currently used in coating are depolymerized either by acid or enzymatic hydrolysis, or by oxidation, or by dextrinification, some of these degradations (enzymatic or oxidizing) being able to be carried out directly at the user. It is to improve certain properties (such as the binding or “smoothness” properties) of the layers containing starch as a binder, that it is possible, either before or after the depolymerization reaction, to chemical modifications such as etherification or esterification (acetylation, cationization, hydroxyethylenation or hydroxypropylenation for example).

It turns out that currently users prefer to reduce the proportion of depolymerized starch present in the binder constituting the coating compositions in favor of the synthetic products identified above; the latter even enter alone into the constitution of the binders used in the coating compositions used in certain appropriate installations.

• - à leur pouvoir liant relativement peu élevé,
• - à leurs propriétés médiocres de rétention d'eau dues à la taille réduite des molécules d'amidon dépolymérisé, cette taille réduite favorisant par ailleurs la pénétration de l'enduit de couchage dans la feuille traitée en diminuant la solidité et la résistance de la couche.

This disaffection with depolymerized starches should be attributed, among other things:

• - their relatively low binding power,
• - their poor water retention properties due to the reduced size of the depolymerized starch molecules, this reduced size also promoting the penetration of the coating coating into the treated sheet by reducing the strength and resistance of the layer .

In addition, migration phenomena, mainly during drying, are important.

However, the cost of synthetic products is very high and in any case much higher than that of depolymerized and possibly modified starches.

It follows that there exists in the paper and cardboard industry the need for a product which can constitute the binder of coating compositions which is more economical than the synthetic products currently increasingly used and which does not have the defects of depolymerized starches, the main ones of which are recalled above.

The well-known properties of non-depolymerized starches mean that the latter would meet the aforesaid need if the practically insurmountable difficulties of preparing correct soils of acceptable viscosity based on these non-depolymerized starches prevented their application.

However, the Applicant Company had the merit of finding that, surprisingly and unexpectedly, it was possible to use non-depolymerized starches in the constitution of binders for coating compositions as soon as these non-depolymerized starches were used. at the same time as an effective proportion of at least one agent known as a "fluidizer" chosen from the group consisting of hydrogenated sugars comprising sorbitol, mannitol, maltitol, xylitol, lactitol and hydrogenated starch hydrolysates.

• - un ou plusieurs agents fluidifiants choisis dans le groupe constitué par les sucres hydrogénés comprenant notamment le sorbitol, le mannitol, le maltitol, le xylitol, le lactitol et les hydrolysats d'amidon hydrogénés, la proportion d'agent fluidifiant étant de 0,40 à 20 parties en poids pour 100 parties de pigment, et
• - à titre de liant, un ou plusieurs amidons non dépolymérisés, éventuellement modifiés par éthérification, estérification ou réticulation, en une quantité correspondant à un pourcentage exprimé en sec/sec par rapport au poids de pigment compris entre 0,2 et 30 %.

The aqueous coating composition according to the invention is therefore characterized in that it comprises, in addition to the pigment:

• one or more thinning agents chosen from the group consisting of hydrogenated sugars comprising in particular sorbitol, mannitol, maltitol, xylitol, lactitol and hydrogenated starch hydrolysates, the proportion of thinning agent being 0.40 20 parts by weight per 100 parts of pigment, and
• - As a binder, one or more non-depolymerized starches, optionally modified by etherification, esterification or crosslinking, in an amount corresponding to a percentage expressed as dry / dry relative to the weight of pigment between 0.2 and 30%.

Generally, this composition also comprises one or more synthetic products from the group comprising in particular polyvinyl alcohol, polyvinyl acetate, acrylic products, styrene-butadiene, synthetic copolymers and / or one or more proteins chosen in particular from group comprising casein and soy protein.

The expression “non-depolymerized starches” denotes starches which have not undergone a depolymerization treatment such as in particular acid or enzymatic hydrolyses, oxidative degradation or dextrinification. They can be chosen from starches from all sources and in particular from corn starches, optionally hybrid, wheat and rice starch, potato starch, cassava starch. In addition, as already mentioned previously, these starches may have been etherified, esterified or crosslinked in order to modify some of their properties such as for example their stability in solution.

The presence of the thinning agents makes it possible to give the coating composition a viscosity and a texture perfectly suited to the coating of paper.

The use of non-depolymerized starches overcomes all the drawbacks described above, attached to the use of degraded starches, and in particular allows to obtain a higher binding power, better layer resistance, better retention of water and better homogeneity of the surface.

It should be emphasized that the effect of the thinning agents used in accordance with the invention is very different from the effect of the dispersing or deflocculating agents commonly used in pigment dispersions and which will be discussed.

A given pigment is essentially characterized, not only by its chemical composition, but also by the size and arrangement of its constituent particles.

In general, these are contiguous to each other, and the number of assembly possibilities is unlimited so they can be grouped in "clusters" bringing together few or many individual particles more or less tightly packed against each other.

The description of the behavior of the particles in the cluster is also important: number of particles, mobility or lack of mobility, resistance to rupture or rearrangement of the cluster and surface condition of the cluster.

It is recognized that the dispersion of the pigment is carried out when the clusters of pigment particles are ruptured.

The constituent particles of the cluster can be linked to each other by chemical bonds at the contact points, giving the clusters a resistance roughly equal to that of individual particles of the same size; they can also be quite weakly linked to each other as if they were attracted by magnetic or gravitational forces (Van der Waals force), these particular arrangements can be "disturbed or broken by the application of a force.

The dislocation of clusters of particles linked by chemical bonds to their contact points is called the "disintegration". After disintegration or separation of the particles, the links are not reformed, the disintegration process therefore being irreversible.

The dislocation of clusters of particles linked by Van der Waals type forces is designated by the term "deflocculation". This phenomenon is reversible. This reversibility is prevented by introducing chemicals into the pigment system that act on the particle surfaces so that they repel each other.

The use of dispersing agents is therefore an essential part of the dispersion process which makes the use of mechanical energy efficient and which reduces the viscosity of the suspension of the pigments.

A coating composition comprises pigment particles and a binder, in aqueous solution forming a fluid medium, in which the pigment particles are in suspension. The fluid medium comprises not only the binder or adhesive but also all the other dissolved materials, in particular the fluidizing agents used in accordance with the invention.

Starch or casein, for example, although in colloidal solution, are in a state of sufficient solubility for them to be clearly considered as part of the fluid.

The fluid medium acts as a lubricant between the particles and allows them to slide over each other much more easily than they could if they were dry.

The small size of the fluidizing agent molecules used in accordance with the invention means that they exhibit significant mobility, but, despite this reality, it is surprising to note that the addition of any one of these agents or of several of them, an addition which leads to an increase in the dry matter content of the whole, results in a decrease in viscosity such that the term "fluidifying agent appears to be essential to designate the agents entering, in accordance with the invention, in the constitution of the binder.

This viscosity reduction effect is not achieved by increasing the level of dispersing or deflocculating agents commonly used in pigment dispersions; on the contrary, it is known that increasing the rate of incorporation of these products leads, beyond the optimal rate of use, a very rapid increase in the viscosity of the coating preparation.

It is therefore the selection of the thinning agents used in accordance with the invention which allows the use, as binding agent, of non-depolymerized starches.

The process for coating paper or cardboard according to the invention is characterized in that the aqueous coating composition according to the invention is applied to one or both sides of the paper and cardboard.

All conventional devices and apparatus such as brush coater, CHAMPION brand coater, air knife or trailing scraper coater, multiple roller coater or engraved roller coater, BILLBLADE coater and others can be used for this application.

The process for preparing the aqueous coating composition according to the invention is characterized in that, on the one hand, a non-depolymerized starch glue is prepared, on the other hand, a pigment dispersion, which the starch glue and the pigment dispersion are mixed, and an effective proportion of fluidizing agent chosen from the group consisting of hydrogenated sugars comprising in particular sorbitol, mannitol, maltitol, xylitol, lactitol and hydrogenated starch hydrolysates, by addition either in water used for the preparation of the starch glue and / or the dispersion of pigment, either in starch glue, or in the pigment dispersion, or in the mixture of the two or in the final coating preparation.

The cooking of the non-depolymerized starch can be carried out by any suitable technique and in particular by cooking in a device with injection of live steam.

Preferably, this cooking is carried out by passing a suspension of non-depolymerized starch in an apparatus of the type known in the art under the expression “Jet Cooker well known to starch manufacturers, in which the cooking of starch is obtained by introduction of steam at a pressure higher than atmospheric pressure. Preferably always, the cooking of the non-depolymerized starch is carried out with a dry matter of between 5% and 30%, at a temperature above 120 ° C and in a time generally greater than 20 seconds, which makes it possible to obtain a non-depolymerized starch glue comprising practically no more highly swollen but unexploded granules, responsible for the development of viscosity and a lack of stability.

Among the fluidizing agents identified above, sorbitol or hydrogenated starch hydrolysates are preferably used, obtained by acid and / or enzymatic hydrolysis of all starches followed by hydrogenation. These hydrogenated starch hydrolysates consist mainly and in variable proportions depending on the mode of hydrolysis applied by sorbitol, maltitol, isomaltitol and hydrogenated oligo- and polysaccharides.

Even more preferably, use is made of sorbitol or of hydrogenated starch hydrolysates prepared from starch hydrolysates having a D.E. (Dextrose Equivalent) greater than 25; particularly preferred are hydrolysates having a percentage of sorbitol greater than 60% expressed on the dry matter.

Expressed as dry matter relative to the amount of pigment, the proportion of fluidifying agent entering into the coating composition according to the invention is approximately 0.40% to 20% by weight, preferably from 0.50% to 15% by weight, and more preferably still from 0.50% to 7.5% by weight.

The amounts of binders used in the coating compositions according to the invention are from 5 to 30% by weight relative to the weight of the pigments.

For the constitution of the binder, one can have recourse only to non-depolymerized starches but generally one uses at the same time the other conventional binding agents.

The proportion of non-depolymerized starch present in the coating compositions according to the invention is established, the percentages being expressed dry / dry, between 0.2 and 30% and, preferably, between 0.5 and 30% relative by pigment weight.

The coating compositions according to the invention, the binder of which consists at least in part of non-depolymerized starch, can be formulated at very high dry matter contents, of the order of 60 to 70%, while having a viscosity compatible with their application on existing coating machines and while not causing any difficulty, for example during the final operation of filtration of the coating composition, an operation which consists in ridding the composition in particular of the agglomerates which it can contain.

It is moreover in the case of coating compositions having a high dry matter, greater than about 53%, that the effect of the addition of the fluidizing agents used in accordance with the invention appears to be most effective.

Another advantage inherent in the use of the coating compositions according to the invention lies in the better plasticization of the layer, provided by the presence in the compositions of hydrogenated sugars and more particularly of sorbitol.

The invention can be better understood using the following examples.

Example 1

Comparison between two coating compositions according to the prior art comprising as binding systems respectively a depolymerized starch and a latex for the first, a non-depolymerized starch and a latex for the second.

The pigments used are natural calcium carbonate and kaolin, and the dispersant used consists of a polyacrylate, sold under the brand "DISPEX N 40 by the company ALLIED COLLOIDS.

The first composition was prepared from enzymatically depolymerized starch.

To do this, a suspension of corn starch was treated in a continuous enzymatic converter as constructed according to French patent No. 1,391,011 and marketed by the Applicant Company, the enzymatic transformation being carried out for 30 minutes at 85 ° C. in the presence of 1.4 parts of alpha-amylase per 1000 parts of starch. The inhibition of the enzyme was carried out on the device by a thermal flash at 140 ° C for 90 seconds.

• eau potable 3 600 g
• - « DISPEX N 40 » 35 g
• - kaolin (de marque « DINKIE A », commercialisé par la Société ENGLISH CHINA CLAYS) 6 030 g
• - ammoniaque 80 ml
• - carbonate de calcium (commercialisé sous la marque « OMYALITE 90 par la Société OMYA) 2 590 g

en traitant le mélange par passage dans un déliteur de marque « CELLIER » pendant 15 minutes.Furthermore, a dispersion of the pigments was prepared from the following constituents:

• drinking water 3,600 g
• - "DISPEX N 40" 35 g
• - kaolin (brand "DINKIE A", marketed by ENGLISH Company CHINA CLAYS) 6,030 g
• - 80 ml ammonia
• - calcium carbonate (sold under the brand name "OMYALITE 90 by the company OMYA) 2,590 g

by treating the mixture by passage through a deliter of the “CELLIER” brand for 15 minutes.

To the pigment dispersion thus obtained, 2153 g of the abovementioned enzymatically depolymerized starch glue was first added, having a dry matter content of 28%, ie 7% of "dry matter / dry matter" ( hereinafter referred to as "dry / dry for the sake of simplicity" with respect to the pigment. Then added 1,380 g of latex SB 024 (sold by the company RHONE POULENC) at 50% dry matter, which is equivalent to 8% dry / dry with respect to the pigment.

To prepare the second coating composition, 1,725 g of a non-depolymerized starch glue having a dry matter of 20% (which is equivalent to 4 parts of starch counted as dry per 100 parts of pigment) was added, to a dispersion of pigments prepared in the same manner as above. Then added 1,380 g of latex SB 024 at 50% dry matter, ie 8% dry / dry with respect to the pigment.

The non-depolymerized starch glue was prepared by passing native corn starch over a Jet-Cooker at a temperature of 150 ° C. and for 3 minutes under a pressure of 5 bars.

The viscosities of the two above-mentioned starch adhesives were measured on a viscometer of the BROOKFIELD brand of the RVT type, for a speed of 20 revolutions per minute; then they were measured again, the starch adhesives having been kept in a water bath for 24 hours at 90 ° C. without and with slight stirring. These recorded viscosities are collated in Table I.

The viscosities of the two coating compositions were then measured at 30 ° C, storage being carried out with and without stirring.

The water retention was measured on a ramp and conventional FANN brand filters of the type used for studying drilling muds, under a pressure of 6.9 bars.

In Table II, the results obtained are collated.

It is found that the viscosity of the coating composition based on non-depolymerized starch is much higher than that of the composition based on enzymatically depolymerized starch. The HERCULES viscosity, very representative given the shear applied, is thus practically double that obtained with depolymerized starch; such a viscosity makes practically inapplicable the use of the corresponding composition for coating paper and cardboard. In particular, filtration of the composition intended to rid it of any agglomerates present is made extremely difficult.

We also note that we obtain, with the non-depolymerized starch-based composition, a very correct water retention, despite the use of a significantly lower starch content (4% instead of 7% ).

This confirms the advantage of using non-depolymerized starch, provided that the viscosity can be reduced without adversely affecting the other characteristics.

Example 2

This example illustrates the effect of the addition of sorbitol as a function of the time chosen for this addition to a coating composition containing non-depolymerized starch as a binder.

• - dispersant « DISPEX N 40 » 35 g
• - kaolin « DINKIE A 6 030 g
• - ammoniaque 80 ml
• - « OMYALITE 90 2 590 g

en utilisant un appareil du type CELLIER pendant 30 minutes.To prepare the coating composition, the following products were dispersed in 3,500 g of water:

• - dispersant "DISPEX N 40" 35 g
• - kaolin "DINKIE A 6 030 g
• - 80 ml ammonia
• - "OMYALITE 90 2,590 g

using a CELLIER type device for 30 minutes.

Was then added to the dispersion about 1,725 g of a non-depolymerized corn starch glue with 20% dry matter, prepared on Jet-Cooker under the same conditions as in Example 1, ie 4% of 'dry starch compared to pigments.

Finally, 1,380 g of SB 024 latex was added, ie 8% on a dry basis relative to the pigments.

• - addition dans la dispersion de pigments, après 25 minutes de dispersion (préparation A)
• - addition à la fin de la préparation, après l'introduction du latex (préparation B)
• - addition à la fois dans la dispersion de pigments et dans la préparation finale après l'introduction du latex, en deux parties égales, soit 80 g dans la dispersion et 80 g dans la préparation finale (préparation C).

To several samples of this composition, 160 g of a solution of sorbitol NEOSORB 70/02 ⁸ at 70% of dry matter, or 0.7% of dry sorbitol relative to the whole of the composition, were added each time. 1.29% dry / dry compared to the pigments, the sorbitol additions being carried out at different stages of the preparation, namely:

• - addition in the dispersion of pigments, after 25 minutes of dispersion (preparation A)
• - addition at the end of the preparation, after the introduction of the latex (preparation B)
• - Adding both in the dispersion of pigments and in the final preparation after the introduction of the latex, in two equal parts, ie 80 g in the dispersion and 80 g in the final preparation (preparation C).

For the preparation without sorbitol and for each of the other preparations thus produced, the viscosities as well as the water retention were measured and the figures are collated in Table III.
(Siehe Tabelle III Seite 8 f.)

It is found that, whatever the introduction phase, the addition of 0.7% of sorbitol in the coating composition makes it possible to reduce the viscosity very significantly.

The water retention and migration characteristics are also not affected by the addition of sorbitol.

Example 3

Influence of the proportion (increasing levels) of sorbitol in a coating composition containing non-depolymerized starch as a binding agent.

• - eau 5 400 g
• - « DISPEX N 40 52,5 g
• - kaolin « DINKIE A 9 045 g
• - ammoniaque 120 ml
• - « OMYALITE 90 » 3 860 g

We use the following formula:

• - water 5,400 g
• - "DISPEX N 40 52.5 g
• - kaolin “DINKIE A 9 045 g
• - 120 ml ammonia
• - "OMYALITE 90" 3 860 g

Kaolin therefore represents 70% of the total charge and calcium carbonate 30%.

The dispersion of the pigments was carried out in 15 minutes at high speed on a CELLIER deliter.

Then added to the dispersion of pigments thus obtained, an unpolymerized corn starch glue with 20% dry matter, prepared under the same conditions as in Example 1, the amount added being 2,587 g, or 4% dry / dry compared to pigments.

To the whole, 2,070 g of latex SB 024 was added, that is to say 8% dry / dry.

To different identical samples of the composition thus prepared, increasing proportions of sorbitol were then added in the form of a 70% solution of dry matter such as that sold by the Applicant Company under the brand NEOSORB 70 / 02®. The introduction rate was 0 to 2.1% dry sorbitol based on the entire coating preparation.

The viscosity measurements are collated in Table IV.

Upon examination of these results, it is found that the effect of sorbitol increases with the percentage introduced, the fluidizing action not passing through a maximum. This is a fundamental difference from the effects recorded only under the influence of pigment dispersing agents.

In particular, for a sorbitol level of 2.1% relative to the whole of the formula, the viscosity is reduced by half.

During these measurements, the pH was 8.8 and the dry matter content of about 62%.

Water retention was then studied on the same compositions using a ramp and FANN filters. The pressure was 6.9 bars, obtained using compressed air.

The results are collated in Table V.

It is noted, in view of these results, that water retention is not disturbed by the presence of sorbitol, even in large quantities.

In addition, it is found that the compositions according to the invention do not give rise to harmful migration effects.

Then and still with the aid of the above compositions, coating tests were carried out on a paper support previously coated with 70 g / m ² .

The speed of the coating machine was 140 meters / minute, the temperature of the dryer 170 ° C and the deposit (quantity of composition per unit area) of 12 g / m ² .

• - le test dit aux « Cires Dennison (cf. norme TAPPI T 459 os 75),
• - le test dit « IGI-encre 3805 (cf. norme TAPPI T 499 su 64) et
• - le test dit « IGI humide-encre 3801 » (cf. norme TAPPI T 499 su 64).

The tests to which the papers thus "coated" were subjected are:

• - the test said to “Dennison Waxes (cf. TAPPI standard T 459 os 75),
• - the so-called “IGI-ink 3805 test (cf. TAPPI T 499 su 64 standard) and
• - the so-called “IGI wet-ink 3801” test (cf. TAPPI T 499 su 64 standard).

The results obtained in these tests are collated in Table VI.

It is observed that the DENNISSON wax test is slightly improved by the use of sorbitol. It follows that the surface resistance is better.

The IGT test is also significantly improved.

Example 4

Comparison between the viscosity of a coating composition based on non-depolymerized starch containing no fluidizing agent and the viscosities of different coating compositions according to the invention comprising various hydrogenated sugars.

The formula and the method of preparation of the control coating composition are the same as in Example 2.

The incorporation rate of the various fluidizing agents tested was in all cases 1.29% dry / dry with respect to the pigments, the fluidizing agents having been added in the final preparation.

• - une solution de sorbitol commercialisée sous la marque de fabrique NEOSORB 70/02®,
• - un hydrolysat d'amidon hydrogéné n° 1,
• - un hydrolysat d'amidon hydrogéné n° 2,
• - le mannitol,
• - le xylito'l.

The fluidizing agents tested are:

• - a sorbitol solution sold under the trademark NEOSORB 70 / 02®,
• - a hydrogenated starch hydrolyzate n ° 1,
• - a hydrogenated starch hydrolyzate No. 2,
• - mannitol,
• - xylito'l.

• - sorbitol 74 %
• - disaccharides hydrogénés 20 %
• - autres saccharides hydrogénés 6%

The hydrogenated starch hydrolyzate No. 1 corresponds to that sold by the Applicant Company under the trademark NEOSORB 70170®; it has the following composition, the percentages being expressed on the dry matter:

• - sorbitol 74%
• - hydrogenated disaccharides 20%
• - other hydrogenated saccharides 6%

• - sorbitol 6,5 %
• - maltitol 26 %
• - DP 3 (produit de degré de polymérisation égal à 3) 20 %
• ―DP 4 10%
• - DP 5 à DP 9 16%
• - DP 10 à DP 20 14%
• - DP supérieur à 20 7,5 %

The hydrogenated starch hydrolyzate No. 2, obtained by hydrogenation of a starch hydrolyzate of DE equal to 33, has the following composition:

• - sorbitol 6.5%
• - maltitol 26%
• - DP 3 (product with a degree of polymerization equal to 3) 20%
• ―DP 4 10%
• - DP 5 to DP 9 16%
• - DP 10 to DP 20 14%
• - DP greater than 20 7.5%

The results of the viscosity measurements are collated in Table VII.

It is found, on examination of these results, that the coating compositions in accordance with the invention have a viscosity very much lower than the control composition, which makes it possible to use them in the coating of paper.

Claims (6)

1. Aqueous coating composition for paper and cardboard, comprising pigment and a binding agent at least partially constituted by undepolymerized starch, characterized by the fact that it comprises, besides the pigment :

- one or several fluidizing agents selected from the group constituted by hydrogenated sugars comprising particularly sorbitol, mannitol, maltitol, xylitol, lactitol and by hydrogenated starch hydrolysates, the proportion of fluidizing agents being from 0.40 to 20 parts by weight per 100 parts of pigment, and

- one or several undepolymerized starches, possibly modified by etherification, esterification or crosslinking, in an amount corresponding to a percentage, expressed dry/dry with respect to the weight of pigment, comprised between 0.2 and 30 %.

2. Composition according to claim 1, characterized by the fact that the binding agent comprises, besides the undepolymerized starch or starches, one or several synthetic products of the group comprising particularly polyvinyl alcohol, polyvinyl acetate, acrylic products, styrene-butadiene, synthetic copolymers and/or one or several proteins selected particularly from the group agent being present in an amount corresponding to a percentage from 5 to 30 % by weight with respect to the weight of pigment.

3. Aqueous coating composition according to one of claims 1 and 2, characterized by the fact that the proportion of fluidizing agent is from 0.50 to 15 % by weight and, preferably, from 0.50 to 7.5 % by weight with respect to the amount of pigment.

4. Aqueous coating composition according to one of claims 1 to 3, characterized by the fact that the proportion of undepolymerized starch is from 0.5 to 30 % with respect to the weight of pigment.

5. Method for preparing an aqueous coating composition according to one of claims 1 to 4, characterized by the fact that there is prepared, on the one hand, a glue with undepolymerized starch, on the other hand, a pigment dispersion, that there is formed the mixture of the starch glue and of the pigment dispersion in such proportions that the undepolymerized starch represents a proportion, expressed dry/dry with respect to the weight of pigment, comprised between 0.2 to 30 %, and that there is introduced an amount from 0.40 to 20 parts by weight per 100 parts of pigment, of a fluidizing agent selected from the group constituted by hydrogenated sugars comprising particularly sorbitol, mannitol, maltitol, xylitol, lactitol and by hydrogenated starch hydrolysates, either into the water serving for the preparation of the starch glue and/or of the pigment dispersion, or into the starch glue, or into the pigment dispersion, or into the mixture of the two or in the final coating preparation.

6. Method of coating paper and cardboard, characterized by the fact that there is applied, to one or both surfaces of the paper or of the cardboard, the aqueous coating composition according to one of claims 1 to 4.