Compatibility agent for aqueous polypigmentary suspensions containing hydrated calcium sulfate

Abstract

Copolymers having the general formula: ##STR1## are useful as compatibility, dispersion and grinding agents for aqueous pigmentary suspensions formulated from a mixture of mineral pigments, at least one of which is hydrated calcium sulfate. These suspensions are useful in papermaking.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compatibility, dispersion and/or grinding agent for aqueous pigmentary suspensions formulated from a mixture of mineral pigments, at least one of which is hydrated calcium sulfate. The invention also relates to aqueous pigmentary suspensions containing the dispersion and/or grinding agent formulated from a mixture of pigments, at least one of which is hydrated calcium sulfate, a method for preparing such suspensions, a method of papermaking, using the above-identified aqueous pigmentary suspensions, and the paper made by such a process.

Background of the invention

When aqueous pigmentary suspensions are prepared from a mixture of mineral pigments, there frequently occurs an extremely rapid and considerable increase in their viscosity, which can reach the solidification point of said suspensions.

This phenomenon, which is linked to the incompatibility of the pigments with one another, occurs for example in suspensions containing a mixture of CaCO.sub.3 and titanium oxide, CaCO.sub.3 and kaolin, and CaCO.sub.3 and titanium oxide and kaolin.

Known to the skilled artisan by the term "shock effect", this viscosifying effect also occurs, but to a greater extent, in the case of aqueous pigmentary suspensions containing both hydrated calcium sulfate and calcium carbonate, or even hydrated calcium sulfate, kaolin and calcium carbonate.

Hydrated calcium sulfate is a mineral pigment which has not yet been greatly exploited as such, but possesses interesting qualities in the field of mass charge or coating of the paper with a view to improving the opacity, shine, reaction to water, printing and whiteness thereof (Patents FR 2,370,124; FR 2,343,082; FR 2,440,437; FI 67.568).

In addition, for the satisfactory use of aqueous pigmentary suspensions formulated from a mixture of mineral pigments, at least one of which is hydrated calcium sulfate, it is desirable to be able to use an agent which is capable of both promoting the dispersion of the pigmentary particles and of eliminating the shock effect by rendering the pigments compatible with one another.

For many years the specialized literature has discussed the research carried out to eliminate the shock effect occurring between the hydrated calcium sulfate and other pigments when they are used together in aqueous pigmentary suspensions.

A first reference (EP 0 216 516) describes a compatibility agent which enables the preparation of aqueous suspensions containing as pigments a mixture of gypsum (in which 70% of the particles have a size of less than 2 microns), kaolin (in which 80% of the particles have a size of less than 2 microns) and calcium carbonate (in which 86% of the particles have a size of less than 2 microns). The recommended compatibility agent is formed from an alkylphosphate ester or a polyacrylate, in which at least 15% of the carboxylic sites are esterified.

In this manner, aqueous suspensions containing a mixture of hydrated calcium sulfate and calcium carbonate or kaolin were prepared in the presence of the above-identified compatibility agent, whether it be an alkylphosphate ester or a partially esterified polyacrylate. However, in order to achieve reasonable viscosities for industrial use, the concentration of these suspensions was unable to go beyond 56% by weight of dry material.

In addition and in the case of the use of an alkylphosphate ester as the compatibility agent, there appears a new restriction of having to operate in a medium with a pH of at most equal to 7 in order for the rheology of the pigmentary suspension to remain within acceptable values for the applications planned. Moreover, when the pH exceeds 7, it is no longer possible to control the viscosity of the mixture of pigments in suspension, with this viscosity increasing very rapidly in a detrimental manner.

Therefore, as the aqueous pigmentary suspensions for the coating of the paper must normally have a concentration of dry material of at least 65% and a pH of between 8 and 11, the compatibility agent recommended in said patent is unusable in the field of paper coating.

In EP 0 227 623, a compatibility agent is proposed which is selected from the acid alkylamine salts in order to regulate the viscosity of aqueous pigmentary suspensions intended for paper coating and containing a mixture of calcium sulfate, kaolin and/or calcium carbonate. However, it has not been possible to bring the content of dry material of these suspensions to a value greater than 56% by weight without causing an increase in viscosity which is prohibitive for paper coating applications.

FR 2,370,124 discloses the use of a compatibility agent to stabilize aqueous pigmentary suspensions intended for paper coating and containing a mixture of aluminum trihydroxide and dihydrated calcium sulfate with a grain size of less than 20 micrometers, with said pigment compatibility agent being a phosphate-ester of depolymerized starch, possibly in combination with a conventional dispersion agent.

However, such pigmentary compositions can be used in the paper coating field only if the user is satisfied with a low content of dry material (on the order of 50 by weight) in order to control the rheology, which fact is certainly a disadvantage.

GB 2,173,781 discloses, for the manufacture of a hydrated calcium sulfate slurry, to use as a dispersing agent a mixture of a surfactant agent with a high concentration, selected from the group of organic sulfates or sulfonates, and a complexing agent selected from the inorganic phosphates and the amines. However, as the present applicants have found, such a mixture of surfactant and complexing agents does not enable the compatibility sought between the hydrated calcium sulfate and the other pigments normally used for paper coating to be achieved.

SUMMARY OF THE INVENTION

Therefore, a first object of the present invention is to provide a compatibility agent which eliminates the previously mentioned shock effect and renders possible the simultaneous presence of hydrated calcium sulfate and other pigments in aqueous pigmentary suspensions without causing the increase in viscosity which is normally observed.

Another object of the present invention is to provide a compatibility agent which eliminates the shock effect and which is also an effective grinding-agent for the refinement of coarse hydrated calcium sulfate, alone or in a mixture with other mineral materials.

Another object of the present invention is to provide aqueous pigmentary suspensions which are more concentrated than in the prior art and which are prepared from mixtures of mineral pigments at least one of which is hydrated calcium sulfate.

Another object of the present invention is to provide a method for preparing aqueous pigmentary suspensions which contain hydrated calcium sulfate.

Another object of the present invention is to provide a method of papermaking using aqueous pigmentary suspensions containing hydrated calcium sulfate.

Another object of the present invention is to provide paper made by a process using aqueous pigmentary suspensions containing hydrated calcium sulfate.

These and other objects, which will become apparent during the course of the following detailed description, have been achieved by the inventors' discovery that copolymers having the general formula (I): ##STR2## symbolized by the formula:

--A--.sub.K --B--.sub.L --C--.sub.M wherein (B) is an ethylene monomer having a phosphate or phosphonate function, (A) is an ethylene monomer having a carboxylic acid group, and (C) is an ethylene monomer of the ester or substituted type, and wherein L is a value such that (B) is present in an amount of between 5 and 95.parts by weight, based on the sum of the amounts of (A), (B), and (C), and one of K and M may be 0, are effective compatibility, dispersion, and grinding agents for pigmentary suspensions which contain hydrated calcium sulfate and which may be used in papermaking.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Thus, while the previous reports basically describe compatibility or dispersion agents resulting from mixtures of known products, the agent in accordance with the present invention is distinguished by the fact that it concentrates, due to a single molecular structure, all the functions peculiar to creating interpigmentary effects of compatibility and permitting the dispersion and the grinding of pigments, at least one of which is calcium sulfate.

In addition, whereas the prior art reveals only the placing in suspension of a mixture of pigments containing coarse hydrated calcium sulfate at concentrations not exceeding 56% by weight of dry material, the agent in accordance with the present invention gives rise to a synergistic effect simultaneously providing the refinement and the acquisition of the interpigmentary compatibility effect at concentrations greater than those of the prior art, while favorably controlling the rheology of the suspensions for the papermaking industry.

In the above-given formula of the agent in accordance with the invention, R.sub.1 can be hydrogen or a carboxylic acid group, which may or may not be esterified with a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alcohol.

R.sub.2 can be hydrogen or a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl group.

R.sub.3 and R'.sub.3 can be hydrogen, a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl group, a substituted or an unsubstituted aryl, a carboxylic acid group, or a halogen.

R.sub.4 can be hydrogen, a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl group, a substituted or an unsubstituted aryl, or a carboxylic acid group which may or may not be esterified with a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alcohol.

R.sub.5 is a group of atoms binding the phosphorus to the polymeric chain by a phosphate function ##STR3## or by a phosphonate function ##STR4##

Where the function is of the phosphate type, R.sub.5 can be:

either an ethylene oxide or a propylene oxide carboxylic ester of the formula: ##STR5##

in which R.sub.10 can be hydrogen or a methyl group and n can take on values in the range of 1 to 50, preferably 1 to 10;

an alkyl, aryl or aralkyl carboxylic ester of the formula: ##STR6## in which R.sub.11 can contain 1 to 12 carbon atoms;

a substituted amide of the formula: ##STR7## in which R.sub.12 is hydrogen, C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl, a substituted or unsubstituted C.sub.5 or C.sub.6 aryl group, or an aralkyl group, and R.sub.13 can be C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl, substituted or unsubstituted C.sub.5 or C.sub.6 cycloalkyl, such as cyclohexyl and cyclopentyl, C.sub.5 or C.sub.6 cycloalkenyl, such as cyclopentadienyl, aryl, such as phenyl or aralkyl; or

oxygen.

In the case where the function is of the phosphonate type, R.sub.5 can be C.sub.1 to C.sub.12, preferably Cl to cycloalkyl, substituted or unsubstituted C.sub.5 to C.sub.6 cycloalkenyl, substituted or unsubstituted aryl, aralkyl, a C.sub.1 to C.sub.12, preferably a C.sub.1 to C.sub.3, ester, or a substituted amide.

R.sub.6 can be hydrogen, a cation, an ammonium group, an amine, C.sub.1 to C.sub.3 alkyl, substituted or unsubstituted C.sub.5 or C.sub.6 cycloalkyl, substituted or unsubstituted C.sub.5 to C.sub.6 cycloalkenyl, substituted or unsubstituted aryl, aralkyl, a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, ester, or a substituted amide.

R.sub.7 can be hydrogen, a carboxylic group, a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, ester, C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl, C.sub.5 or C.sub.6 cycloalkyl, C.sub.5 or C.sub.6 cycloalkenyl, aryl, or aralkyl.

R.sub.8 can be hydrogen, a carboxylic group, C.sub.1 to C.sub.3 alkyl, or a halogen.

R.sub.9 can be a C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.5, ester, a substituted or an unsubstituted amide, C.sub.1 to C.sub.12, preferably C.sub.1 to C.sub.3, alkyl, C.sub.5 or C.sub.6 cycloalkyl, C.sub.5 or C.sub.6 cycloalkenyl, aryl, aralkyl, a halogen, a carboxylic group, or a sulfonated or sulfated alkyl or aryl group.

These acid copolymers may be prepared by copolymerization in accordance with conventional methods, in the presence of appropriate initiators and regulators, in an aqueous, alcoholic, hydroalcoholic, aromatic or aliphatic medium or in a halogenated solvent, of at least two ethylenically unsaturated monomers one of which has a phosphate or phosphonate function, at atmospheric or over pressure. That is, the present copolymers may be prepared by the copolymerization of an ethylenically unsaturated monomer corresponding to unit (B) in formula (I) with at least one ethylenically unsaturated monomer corresponding to either unit (A) or (C) in formula (I).

Preferred monomers corresponding to unit (A) include acrylic acid, methacrylic acid, itaconic acid, and maleic acid. Preferred monomers corresponding to unit (C) include esters of acrylic and methacrylic acid, such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate.

Thus, the polymerization medium can be water, methanol, ethanol, propanol, isopropanol, butanols, or even dimethylformamide, dimethylsulfoxide, tetrahydrofuran, acetone, methylethylketone, ethyl acetate, butyl acetate, hexane, heptane, benzene, toluene, ethylbenzene, xylene, mercaptoethanol, tert-iododecylmercaptan, thioglycolic acid and esters thereof, n-dodecylmercaptan, acetic acid, tartaric acid, lactic acid, citric acid, gluconic acid, glucoheptonic acid, 2-mercaptopropionic acid, thiodiethanol, halogenated solvents such as carbon tetrachloride, chloroform, methylene chloride, methyl chloride, monopropyleneglycol ether or diethyleneglycol ether.

The copolymers intended to be used as a compatibility, dispersion and grinding agent in accordance with the present invention are generally selected from among those having a specific viscosity of between 0.2 and 10.0 and preferably between 0.25 and 5.0, and most preferably between 0.4 and 1.2.

The specific viscosity of the copolymers, which is symbolized by the letter ".eta." was determined in the following manner:

A copolymer solution in sodium salt form was prepared by dissolving 50 g of dry copolymer in one liter of a solution of distilled water containing 60 g of sodium chloride.

Then, using a capillary viscometer placed in a 25.degree. C. thermostatted bath, the flow time of a given volume of the above-identified solution containing the alkaline copolymer was measured, as was the flow time of the same volume of aqueous solution of sodium chloride without said copolymer. It was then possible to define the specific viscosity ".eta." using the following equation: ##EQU1##

The capillary tube is generally selected such that the flow time of the NaC.sub.1 solution without the copolymer is approximately 90 to 100 seconds, thus giving very accurate measurements of specific viscosity.

At the end of the polymerization, the acid copolymers in accordance with the invention in the aqueous solution are collected and can be used in this form.

In accordance with one alternative, which has been shown to be very interesting, the copolymers in accordance with the invention in the aqueous solution can be totally or partially neutralized by a neutralizing agent having a monovalent function. In addition, a neutralizing agent having a polyvalent function can be combined with this monovalent agent.

In the first case, the neutralizing agent is desirably selected from the group consisting of alkaline and similar cations, particularly lithium, sodium, potassium, ammonium or amine polysubstituted or not. This agent, in the second case, can be combined with an agent from the alkaline earth or similar group, preferably calcium and magnesium.

In practice, the liquid phase resulting from the copolymerization and containing the acid copolymer can be used in a salified form as a slurrying or grinding agent, but it can also be dried by any known means in order to remove said liquid and isolate the copolymer in the form of a fine powder and can be used in this other form as a compatibility, dispersion or grinding agent.

In another embodiment, the agent in accordance with the invention can be used in accordance with a method for the preparation of aqueous pigmentary suspensions, containing at least hydrated calcium sulfate, comprising the following steps:

(a) The preparation by slurrying of an aqueous suspension of hydrated calcium sulfate, alone or mixed, is carried out under stirring by first placing all or part of the agent in accordance with the invention into the aqueous phase, and then introducing the pigment(s) so as to obtain a fluid and desirably homogeneous suspension;

(b) The suspension prepared in accordance with step a) is continuously introduced into a grinding zone composed of a grinder with microelements;

(c) The temperature of the suspension during grinding is kept at a level below 100.degree. C. and preferably between room temperature and 80.degree. C;

(d) The suspension is ground in the presence of the microelements for the time necessary to obtain the desired particle size;

(e) During the grinding, an additional fraction of the agent is possibly introduced, in at least one step;

(f) On exiting the grinder, the finely ground suspension of CaSO.sub.4 .multidot.2H.sub.2 O, alone or in a mixture, is continuously separated from the grinding elements and the particles which are rejected as being too coarse; and

(g) At least one rheology-modifying agent is possibly introduced into the finely ground suspension.

If the pigment or pigments used have a grain size distribution which conforms to the requirements of the user, only step (a) is carried out. In the contrary case, the following steps are carried out, that is (b) to (g), so as to produce an aqueous suspension of pigments refined by grinding and rendered compatible with each other.

The agent in accordance with the invention is introduced into the aqueous pigmentary suspension in an amount of 0.05 to 4% by weight of active material in relation to the dry weight of the mineral materials, and preferably in an amount of 0.5 to 2.5%.

The suspension collected after the slurrying and/or the grinding generally has a concentration of at least 65% dry material, and preferably in the range of 70 to 80% by weight, with the size of the pigmentary particles obtained being defined by the user in the case of grinding.

The pigmentary suspension refined in this manner, due to the presence of the agent in accordance with the invention, can be preferably used as a pigmentary charge in the manufacture of paper, paint and plastic materials.

Other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof.

EXAMPLES

Example 1

This example, the object of which is to illustrate the effects of the known agents, relates to the preparation of a suspension of hydrated calcium sulfate using slurrying.

For this purpose, several suspensions of hydrated calcium sulfate were prepared with 19 types of known dispersion or compatibility agents.

All the suspensions (Tests 1 to 19) were carried out with the same calcium sulfate having an average grain size on the order of 15 micrometers, with the concentration of the suspensions being fixed at 68% by weight of dry material and the amount of the agent adjusted to 1% by weight of active material in relation to the pigmentary material.

The suspensions were prepared in the same apparatus as in step a) of the previously described method at room temperature.

The properties and results of Tests 1 to 19 are given in Table 1.

TABLE 1__________________________________________________________________________Slurrying of CaSO.sub.4.2H.sub.2 O with Known Agents BROOKFIELD CONCENTRATION AVERAGE DIAMETER VISCOSITY PERCENTAGE OF THE OF PARTICLES IN after 24 hrsNUMBER TYPE OF POLYMER OF AGENT SUSPENSION MICROMETER 10 REVS 100__________________________________________________________________________ REVS 1 Sodium polyacrylate - 1 68 15 2000 650 Specific viscosity 0.40 2 Sodium polyacrylate - 1 68 15 1800 700 Specific viscosity 0.57 3 Sodium polyacrylate - 1 68 15 2700 770 Specific viscosity 0.30 4 Sodium polyacrylate - 1 68 15 3700 1300 Specific viscosity 0.70 5 Sodium polymethacrylate - 1 68 15 18000 3900 Specific viscosity 0.55 6 Chromium lignosulfonate 1 68 15 10200 1600 7 C.sub.6 -Alcohol phosphate 1 68 15 2100 800 monoester acid 8 C.sub.10 -Alcohol phosphate 1 68 15 4100 1450 monoester acid 9 C.sub.6 -Alcohol phosphate 1 68 15 SET IN MASS monoester sodium salt10 C.sub.10 -Alcohol phosphate 1 68 15 SET IN MASS sodium salt11 Calcium dodecyl 0.6 68 15 8400 1680 benzenesulfonate + 0.4 Sodium pyrophosphate12 Sodium C.sub.16 -olefinsul- 0.6 68 15 7200 950 fonate + Sodium 0.4 pyrophosphate13 Carboxy methyl 0.6 68 15 8100 1120 cellulose + 0.4 C.sub.6 -Alcohol monoester phosphate acid14 Carboxy methyl 0.6 68 15 10200 1700 cellulose + 0.4 C.sub.10 -Alcohol monoester phosphate acid15 Ethylene glycol 0.6 68 15 7800 1080 methacrylate monoester 0.4 phosphate + Carboxy methyl cellulose16 Oxyethyl 18-tristyryl- 1 68 15 5300 920 phenol phosphate17 2-methylpropanesulfonic 1 68 15 9500 1540 acrylamide copolymer (30) Acrylic acid (37) Methacrylic acid (33) Specific viscosity: 0.418 Itaconic acid copolymer 1 68 15 10800 2700 (15) Methacrylic acid (40) Acrylic acid (45) Specific viscosity: 0.419 Phosphonic salt (Dequest 1 68 15 8000 950 160 from Monsanto) 0.4 + Copolymer No. 18__________________________________________________________________________

Table 1 demonstrates that the viscosities at 10 and 100 revolutions are fairly high for a monopigment, in certain cases resulting in setting.

EXAMPLE 2

This example, which is intended to illustrate the object of the invention, relates to the slurrying of hydrated calcium sulfate (of the same origin as in Example 1) in the presence of the agent in accordance with the invention in the case where the copolymer does not contain monomer (C) (that is M=0).

Through Tests 20 to 29, the formula of the copolymer was modified by qualitatively and quantitatively varying the various radicals as well as the specific viscosities of the copolymers used, it being understand that said copolymers had been at least partially salified with sodium cations until a pH of between 7 and 8 on average was obtained

The properties of the suspensions prepared (Tests 20 to 29) and the results obtained are collected in Table 2.

TABLE 2 Slurrying of CaSO.sub.4.2H.sub.2 O According to the Present Invention Average Brookfield Concentration Diameter Viscosity of the of the after 24 hrs Example A B C Specific Percentage suspension Particles (cP) No R1 R2 M1 k R3 R4 R5 R6 M2 l R7 R8 R9 m Vicosity of Agent (%) (micrometers) 10 rev 100 rev 20 H H Na 90 H CH.sub.3 ##STR8## Na Na/H 10 0 0,65 1 68 15 800 520 21 H H Na 85 H CH.sub.3 ##STR9## Na Na/H 15 0 0,58 1 68 15 200 120 22 H H Na 85 H H ##STR10## Na Na/H 15 0 0,74 1 68 15 800 440 23 H H Na 70 H CH.sub.3 ##STR11## Na Na/H 30 0 0,76 0,3 68 15 850 600 24 H H Na 70 H CH.sub.3 ##STR12## Na Na/H 30 0 0,5 0,4 68 15 1050 750 25 H H Na 60 H CH.sub.3 ##STR13## Na Na/H 40 0 0,56 0,1 68 15 950 485 26 H H Na 50 H CH.sub.3 ##STR14## Na Na/H 50 0 0,43 0,1 68 15 800 400 27 H CH.sub. 3 Na 60 H CH.sub.3 ##STR15## Na Na/H 40 0 0,41 0,1 68 15 850 420 28 H HCH.sub.3 NaNa 4515 H CH.sub.3 ##STR16## Na Na/H 40 0 0,51 0,1 68 15 750 360 29 H H Na 20 H CH.sub.3 ##STR17## Na Na/H 40 0 insoluble 0,1 68 15 720 320 H H ##STR18## Na Na/H 40

From Table 2 and the comparison with Table 1, it is apparent that the viscosities of the suspensions in accordance with the invention measured under the same conditions as those of Example 1 are considerably lower than obtainable by the known agents. Therefore, it was possible to lower the concentration of compatibility agent by large amounts, possibly by a ratio of 10/1.

Example 3

This example, which is intended to illustrate the object of the invention, relates to the slurrying of hydrated calcium sulfate (of the same origin as in Example 1) in the presence of the agent in accordance with the invention, in the case where the copolymer does not contain monomer (A) (that is K=0).

Through Tests 30 to 35, the formula of the copolymer was modified by qualitatively and quantitatively varying the various radicals as well as the specific viscosities of the copolymers used, it being understand that said copolymers had been a least partially salified with the sodium cation until a pH of between 7 and 8 on average was obtained.

The properties of the suspensions prepared (Tests 30 to 35) and the results obtained are collected in Table 3.

TABLE 3 Slurrying of CaSO.sub.4.2H.sub.2 O According to the Present Invention Average Brookfield Concentration Diameter Viscosity of the of the after 24 hrs Example A B C Specific Percentage suspension Particles (cP) No R1 R2 M1 k R3 R4 R5 R6 M2 l R7 R8 R9 m Vicosity of Agent (%) (micrometers) 10 rev 100 rev 30 0 H CH.sub.3 ##STR19## Na Na/H 40 H H ##STR20## 60 1 68 15 650 430 31 0 H CH.sub.3 ##STR21## Na Na/H 30 H HCH.sub.3 CO(CH.sub.2).sub.2 OHOCH.sub.3 4525 1 68 15 500 310 32 0 H CH.sub.3 -- Na Na/H 40 H H ##STR22## 60 0,6 0,5 68 15 1040 420 33 0 H CH.sub.3 -- Na Na/H 40 H CH.sub.3 ##STR23## 60 0,55 0,5 68 15 950 370 34 0 H CH.sub.3 -- Na Na/H 40 H HCH.sub.3 ##STR24## 4515 0,7 0,5 68 15 1000 405 35 0 H H ##STR25## Na Na/H 30 H H ##STR26## 70 0,65 1 68 15 900 560

From Table 3 and the comparison with Table 1, it is apparent that the viscosities of the suspensions in accordance with the present invention, measured under the same conditions as those of Example 1, are considerably lower than obtainable by the known agents Therefore, it was possible to lower the concentration of compatibility agent by large amounts, possibly by a ratio of 2/1.

Example 4

This example, which is intended to illustrate the object of the invention, relates to the slurrying of hydrated calcium sulfate (of the same origin as in Example 1) in the presence of the agent in accordance with the invention, in the case where the copolymer prepared contains the three monomers (A), (B) and (C), that is when K and M are simultaneously not equal to 0.

Through Tests 36 to 60, the formula of the copolymer was modified by qualitatively and quantitatively varying the various radicals as well as the specific viscosities of the copolymers used, it being understand that said copolymers had been at least partially salified with the sodium cation until a pH of between 7 and 8 on average was obtained.

The properties of the suspensions prepared (Tests 36 to 60) and the results obtained are collected in Table 4.

TABLE 4 Slurrying of CaSO.sub.4.2H.sub.2 O According to the Present Invention Per- Average Brookfield Ex- cen- Concentra- Diameter Viscosity am- tage tion of the of the after 24 hrs ple A B C Specific of suspension Particles (cP) No R1 R2 M1 k R3 R4 R5 R6 M2 l R7 R8 R9 m Vicosity Agent (%) (micrometers) 10 rev 100 rev 36 H H Na 70 H CH.sub.3 ##STR27## Na Na/H 15 H CH.sub.3 ##STR28## 15 0,46 0,5 68 15 910 630 37 H H Na 65 H CH.sub.3 ##STR29## Na Na/H 20 H CH.sub.3 ##STR30## 15 0,5 0,5 68 15 840 560 38 H H Na 55 H CH.sub.3 ##STR31## Na Na/H 30 H CH.sub.3 ##STR32## 15 0,66 0,3 68 15 680 340 39 H H Na 40 H CH.sub.3 ##STR33## Na Na/H 30 H CH.sub.3 ##STR34## 30 0,6 0,3 68 15 600 320 40 H H Na 45 H CH.sub.3 ##STR35## Na Na/H 40 H CH.sub.3 ##STR36## 15 0,54 0,1 68 15 710 450 41 H H Na 55 H H ##STR37## Na Na/H 15 H CH.sub.3 ##STR38## 30 0,55 0,5 68 15 1020 730 42 H H Na 30 H H ##STR39## Na Na/H 40 H CH.sub.3 ##STR40## 30 0,53 0,3 68 15 700 440 43 H CH.sub.3 Na 45 H CH.sub.3 ##STR41## Na Na/H 40 H CH.sub.3 ##STR42## 15 0,49 0,2 68 15 680 470 44 H H Na 45 H CH.sub.3 ##STR43## Na Na/H 40 H H ##STR44## 15 0,60 0,1 68 15 780 510 45 H H Na 45 H CH.sub.3 ##STR45## Na Na/H 40 H H ##STR46## 15 0,55 0,1 68 15 820 550 46 H H Na 55 H CH.sub.3 ##STR47## Na Na/H 30 H H CO(CH.sub.2).sub.2CH.sub.3 15 0,52 0,2 68 15 920 590 47 H H Na 50 H CH.sub.3 ##STR48## Na Na/H 40 H H CO(CH.sub.2 CH.sub.2 O).sub.4 (CH.sub.2).sub.11CH.sub.3 10 0,50 0,4 68 15 840 530 48 H H Na 45 H CH.sub.3 ##STR49## Na Na/H 40 H H CN 15 0,56 0,2 68 15 780 470 49 H H Na 45 H CH.sub.3 ##STR50## Na Na/H 40 H CH.sub.2 COOH COOH 15 0,55 0,3 68 15 720 510 50 H H Na 45 H CH.sub.3 ##STR51## Na Na/H 40 H CH.sub.3 ##STR52## 15 0,48 0,2 68 15 690 450 51 H H Na 45 H CH.sub.3 ##STR53## Na Na/H 40 H H C.sub.6 H.sub.5 15 0,7 0,1 68 15 850 540 52 H H Na 45 H CH.sub.3 -- Na Na/H 40 H CH.sub.3 ##STR54## 15 0,65 0,1 68 15 750 520 53 H H Na 45 H CH.sub.3 ##STR55## Na Na/H 40 H CH.sub.3 ##STR56## 15 0,7 0,4 68 15 910 670 54 H H Na 45 H H CH.sub.2 O Na Na/H 40 H CH.sub.3 ##STR57## 15 0,8 0,4 68 15 860 590 55 H H Na 45 H C.sub.6 H.sub.5 -- Na Na/H 40 H CH.sub.3 ##STR58## 15 Insoluble 0,3 68 15 780 460 56 H H Na 45 H H ##STR59## Na Na/H 40 H CH.sub.3 ##STR60## 15 0,68 0,4 68 15 990 600 57 H H Na 55 ##STR61## H ##STR62## Na Na/H 30 H CH.sub.3 ##STR63## 15 0,50 0,4 68 15 850 540 58 ##STR64## H Na 45 H CH.sub.3 ##STR65## Na Na/H 40 H CH.sub.3 ##STR66## 15 0,75 0,3 68 15 930 625 59 H H Na 45 H CH.sub.3 ##STR67## Na Na/H 40 H H ##STR68## 15 0,5 0,3 68 15 720 440 60 H H Na 45 H CH.sub.3 ##STR69## Na Na/H 40 ##STR70## H ##STR71## 15 0,58 0,6 68 15 970 640

From Table 4 and the comparison with Table 1, it is apparent that the viscosities of the suspensions in accordance with the present invention, measured under the same conditions as those of Example 1, are considerably lower than obtainable by the known agents. Therefore, it was possible to lower the concentration of compatibility agent by large amounts, possibly by a ratio of 10/1.

Example 5

This example, which is intended to illustrate the object of the present invention, relates to the slurrying of hydrated calcium sulfate (of the same origin as in Example 1) in the presence of the agent in accordance with the invention, copolymer with the formula described in Example 4 and with a specific viscosity varying from 0.27 to 2.5 and salified with the sodium cation.

In this case, several tests were carried out (Tests 40/01 to 40/10), with the aqueous suspensions of hydrated calcium sulfate subjected to slurrying in the presence of said agent in an amount of 0.1% by weight of dry material in relation to the weight of the dry pigment, with the concentration of the suspension always being fixed at 68% by weight of said sulfate.

The properties of the suspensions prepared (Tests 40,,01 to 40/10) and the results obtained are collected in Table 5.

TABLE 5______________________________________Influence of the Specific Viscosity of the Agent on theRheology of the Pigmentary SuspensionTest Specific Brookfield Viscosity after 24 hours (in cP)No. Viscosity 10 rpm 100 rpm______________________________________40/01 0.27 1330 91040/02 0.45 850 52040/03 0.5 840 48540/04 0.54 710 45040/05 0.6 700 41040/06 0.7 650 37040/07 0.76 630 34040/08 0.9 750 46040/09 1.17 900 54040/10 2.5 1250 830______________________________________

From Table 5 and the comparison with Table 1, it is apparent that the viscosities of the suspensions in accordance with the present invention, measured under the same conditions as those of Example 1, are considerably lower than obtainable by the known agents, even within the claimed limits of specific viscosities. Therefore, it was possible in all cases to lower the concentration of compatibility agent by a ratio of 10/1.

Example 6

This example, which is intended to illustrate the object of the present invention, relates to the slurrying of the same hydrated calcium sulfate used in the preceding examples in the presence of the agent composed of a copolymer with the same specific viscosity and with the same composition but salified with sodium, lithium, ammonium, potassium, calcium and magnesium, or in an acid form, or salified by an amine.

In this case, several tests were carried out (Tests 61 to 69), with the aqueous suspensions subjected to slurrying in the presence of said agent having concentrations of dry material which were fixed at 68% by weight and the amount of the agent being fixed at 0.1% by weight of dry material.

The properties of the suspensions prepared (Tests 61 to 69) and the results obtained are collected in Table 6.

TABLE 6 Slurrying of CaSO.sub.4.2H.sub.2 O According to the Present Invention Average Brookfield Concentration Diameter Viscosity of the of the after 24 hrs Example A B C Specific Percentage suspension Particles (cP) No R1 R2 M1 k R3 R4 R5 R6 M2 l R7 R8 R9 m Vicosity of Agent (%) (micrometers) 10 rev 100 rev 61 H H Na 45 H CH.sub.3 ##STR72## Na Na/H 40 H CH.sub.3 ##STR73## 15 0,54 0,1 68 15 710 450 62 H H NH.sub.4 45 H CH.sub.3 ##STR74## NH.sub.4 NH.sub.4 /H 40 H CH.sub.3 ##STR75## 15 0,54 0,1 68 15 820 490 63 H H K 45 H CH.sub.3 ##STR76## K K/H 40 H CH.sub.3 ##STR77## 15 0,54 0,1 68 15 1200 790 64 H H Li 45 H CH.sub.3 ##STR78## Li Li/H 40 H CH.sub.3 ##STR79## 15 0,54 0,1 68 15 650 400 65 H H Ca 45 H CH.sub.3 ##STR80## Ca Ca/H 40 H CH.sub.3 ##STR81## 15 0,54 0,1 68 15 1800 950 66 H H NaMg 45 H CH.sub.3 ##STR82## Na/Mg Na/Mg/H 40 H CH.sub.3 ##STR83## 15 0,54 0,1 68 15 1600 920 67 H H TEA 45 H CH.sub.3 ##STR84## TEA TEA/H 40 H CH.sub.3 ##STR85## 15 0,54 0,1 68 15 1560 880 68 H H H 45 H CH.sub.3 ##STR86## H H 40 H CH.sub.3 ##STR87## 15 0,54 0,1 68 15 1100 720 69 H H Na 45 H CH.sub.3 ##STR88## Na Na 40 H CH.sub.3 ##STR89## 15 0,54 0,1 68 15 700 430

From Table 6 and the comparison with Table 1, it is apparent that the viscosities of the suspensions in accordance with the present invention are considerably lower than obtainable by the known agents, even though the concentration of the compatibility agent was decreased by a ratio of 10/1.

Example 7

The object of this example is to compare the compatibility of aqueous polypigmentary suspensions containing two pigments, at least one of which is hydrated calcium sulfate, for coating paper, using a known compatibility agent (Table 7-2, Tests 70 to 79) and an agent in accordance with the present invention (Table 7-2, Tests 80 to 88).

For this purpose, aqueous monopigmentary suspensions of calcium carbonate, hydrated calcium sulfate, kaolin, and titanium oxide in the presence of a known compatibility agent (types A, B.sub.1, C, and D) and an agent in accordance with the present invention (type B.sub.2) with similar specific viscosities were prepared by slurrying.

The characteristics of the aqueous pigmentary suspensions prepared in this manner and the results obtained are collected in Table VII-1 below, indicating in particular the viscosities of the suspensions at 10 and 100 revolutions per minute.

TABLE 7-1__________________________________________________________________________Properties of the Suspensions Used in Table 7-2 Suspension Average Brookfield viscosity Agent Concentration diameter (cP)Suspension of: Type % (%) (microns) 10 rpm 100 rpm__________________________________________________________________________CaCO.sub.3 H 90 A Sodium polyacrylate 0.4 75 1 700 300from OMYA Co. Specific viscosity: 0.55CaSO.sub.4.2H.sub.2 O B1 Polyacrylate 1 70 15 2700 980 Specific viscosity: 0.6 B2 Agent of the invention 1 70 15 200 150 Test 40/07SPS kaolin C Sodium polyacrylate 0.2 66 3.5 600 300from ECC Specific viscosity: 0.40AT1 titanium D Sodium and calcium 0.35 73 0.5 6600 1200from Thann polyacrylateand Mulhouse Specific viscosity: 0.4__________________________________________________________________________ The mixtures of the suspensions were prepared by adjusting the amount of agent to 1%: - for the prior art with sodium polyacrylate with a specific viscosity of 0.55 - for the invention with 40/07.

Then, in order to compare the efficacy of the compatibility agents used, the preparation of aqueous polypigmentary suspensions was carried out by mixing the above-identified suspensions of calcium carbonate, kaolin, and titanium oxide with the hydrated calcium sulfate suspensions.

The properties of the polypigmentary suspensions prepared in this manner and the results obtained from the experiments are provided in Table 7-2.

TABLE 7-2__________________________________________________________________________Test for Compatibility by Mixing % by weight of the mixture of suspensions Brookfield viscosity Dry of of of of of the mixtureTest extract CaCO.sub.3 CaSO.sub.4.2H.sub.2 O titanium kaolin (in cP)number (%) A B2 B1 D C 10 rpm 100 rpm__________________________________________________________________________PRIOR ART70 74.5 90 10 0 0 Set in mass71 74 80 20 0 0 "72 73.5 70 30 0 0 48000 720073 66.4 0 10 0 90 Set in mass74 66.8 0 20 0 80 "75 67.2 0 30 0 70 "76 67.6 0 40 0 60 100000 1000077 68 0 50 0 50 75000 1000078 72.7 0 10 90 0 Set in mass79 72.4 0 20 80 0 Set in massINVENTION80 66.4 0 10 0 90 33000 520081 66.8 0 20 0 80 16000 350082 67.2 0 30 0 70 6200 130083 74.5 90 10 0 0 35000 400084 74 80 20 0 0 22000 284085 73.5 70 30 0 0 14000 200086 72.7 0 10 90 0 6250 81587 72.4 0 20 80 0 2700 46088 72.1 0 30 70 0 1600 295__________________________________________________________________________

Table 7-2 leads to the following observations. The hydrated calcium sulfate, due to its greater solubility in the aqueous medium, is the pigment which generates the shock effect during the preparation of polypigmentary suspensions. However, it should be recalled that for the coating of the paper, it is the polypigmentary suspensions with a low content of hydrated calcium sulfate which are used and which have been shown to be the most sensitive to the shock effect.

For Tests 70 to 79, which represent the effect of known agents to which the invention is compared, the polypigmentary suspensions, obtained by mixing, practically all manifest setting during the mixing of the constituent suspensions. These results reveal the inability of the known compatibility agents to overcome the shock effect caused by the hydrated calcium sulfate.

For Tests 80 to 88, which illustrate the present invention, the polypigmentary suspensions obtained by mixing all have a reasonably decreased viscosity, rendering them suitable to use for the coating of paper. The phenomenon observed of the substantial lowering of the viscosities shows the ability of the present compatibility agent to overcome the shock effect caused by the hydrated calcium sulfate. Therefore, the present compatibility agent enables the preparation of polypigmentary suspensions containing hydrated calcium sulfate with concentrations of dry material which are adequate for papermaking applications.

All the above results were able to be compared by using identical dry extracts, percentages of compatibility agent and identical amounts of pigmentary mixtures for both the known agents and the present agents.

Example 8

The object of this example is to illustrate, in a comparative manner, the ability of the present agent to be the compatibility, the dispersion, and the grinding agent simultaneously.

For this purpose, coarse suspensions of hydrated calcium sulfate from the same origin were prepared by using known compatibility agents (Tests 89 to 92) and compatibility agents according to the present invention (Tests 93 to 98).

Known Compatibility Agents:

Test 89: sodium polyacrylate.

Test 90: sodium polymethacrylate.

Test 91: copolymer of acrylic acid and methallyl sulfonate neutralized with the sodium ion.

Test 92: copolymer of acrylic acid and dimethylaminoethyl methacrylate neutralized with the sodium ion.

Compatibility Agents From the Present Invention

Test 93: copolymer of acrylic acid and ethylene glycol methacrylate phosphate neutralized with the sodium ion.

Test 94: copolymer of methyl methacrylate, ethylene glycol methacrylate phosphate and acrylic acid neutralized with the sodium ion.

Test 95: copolymer of ethylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate and acrylic acid neutralized with the sodium ion.

Test 96: copolymer of ethylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate and methyl methacrylate neutralized with the sodium ion.

Test 97: copolymer of ethylene glycol methacrylate phosphate, acrylic acid and acrylamide neutralized with the sodium ion.

Test 98: copolymer of methyl methacrylate, ethylene glycol methacrylate phosphate and acrylic acid neutralized with the lithium ion.

The average diameter of the hydrated calcium sulfate before grinding was 15 micrometers.

These tests were all carried out using the same experimental procedures, carrying out the grinding in the same apparatus, in order that the results obtained could be directly compared.

For each test, an aqueous suspension of hydrated calcium sulfate with an average diameter of 15 micrometers was prepared.

The aqueous suspension had a concentration of 68% of dry material expressed as a percentage by weight.

The grinding agent was present in the suspensions in an amount of 1% by weight of dry material in relation to the mass of hydrated calcium sulfate to be ground.

Each suspension prepared in this manner was placed in a Dyno-Mill type grinder with a fixed cylinder and a rotating impeller, the grinding body of which was composed of corundum bearings of a diameter in the range of 0.6 millimeter to 1.0 millimeter.

The total volume occupied by the grinding body was 5,000 milliliters, while its weight was 10 kilograms.

The grinding chamber had a volume of 5,000 milliliters. The circumference speed of the grinder was 10 meters per second.

The hydrated calcium sulfate suspension was recycled at a rate of 50 liters per hour.

The exit of the Dyno-Mill grinding was provided with a 300 micron mesh separator, enabling the separation of the suspension resulting from the grinding and the grinding body.

The temperature during each grinding test was maintained at 25.degree. C.

At the end of the grinding, the viscosity of the microparticulate suspension was measured using a Brookfield viscosimeter, at a temperature of 20.degree. C. and at rotation speeds of 10 and 100 revolutions per minute.

Similarly, at the end of the grinding, the grain size was determined using a Cilas Alcatel 715 laser granulometer.

The properties of the ground suspensions and the results obtained after grinding are given in Table 8.

TABLE 8__________________________________________________________________________ Grain size Brookfield viscosityTest Specific Average diameter (in cP)number Composition of the agent viscosity (in microns) 10 rpm 100 rpm__________________________________________________________________________PRIOR ART89 100% AA neutralized 100% Na 0.55 8 17000 270090 100% AMA neutralized 100% Na 0.5 9 18000 398091 85% AA neutralized 100% Na 0.4 9 12500 2300 15% MTAS92 50% AA neutralized 100% Na 0.4 8 16500 2600 50% MADAMINVENTION93 70% AA neutralized 100% Na 0.76 5 6000 1000 30% PO.sub.4 MAEG94 15% MAM neutralized 100% Na 0.76 3 7500 1120 40% PO.sub.4 MAEG 45% AA95 40% PO.sub.4 MAEG neutralized 100% Na 0.6 4 10000 1480 40% PO.sub.4 AEG 20% AA96 40% PO.sub.4 MAEG neutralized 100% Na 0.74 5 9500 1300 40% PO.sub.4 AEG 20% MAM97 40% PO.sub. 4 MAEG neutralized 100% Na 0.62 4 7800 1100 45% AA 15% Acrylamide98 15% MAM Neutralized 0.76 3 7000 950 40 PO.sub.4 MAEG 100% Li 45% AA__________________________________________________________________________

The results given in Table 8 lead to the following observations. For Tests 89 to 92 which represent suspensions of hydrated calcium sulfate ground in the presence of known compatibility agents, it is seen that the average diameter of the ground pigment remains coarse and that the viscosity of the suspensions obtained is high. Thus, these suspensions are unsuitable for papermaking applications.

For Tests 93 to 98 which represent suspensions of hydrated calcium sulfate ground in the presence of the compatibility agent of the present invention, it is observed that the average diameter of the ground pigment is very fine and that the viscosity of the suspensions obtained is much lower than that obtained by the prior art, even with the consequent decrease in the average diameter.

The favorable development of these two characteristics renders the present suspensions particularly suitable for papermaking applications.

Example 9

The object of this example is to illustrate the capability of the present compatibility agent to enable the grinding of aqueous polypigmentary suspensions containing a pigmentary mixture of hydrated calcium sulfate and calcium carbonate.

For this purpose, mixed suspensions of coarse hydrated calcium sulfate (average diameter of 15 micrometers) and coarse calcium carbonate (average diameter of 30 micrometers) were prepared using a known compatibility agent (Tests 99 to 101) and a compatibility agent in accordance with the present invention (Tests 102 to 104).

Each aqueous suspension had a concentration of 70% by weight of dry material, with the composition of the pigmentary mixture being prepared according to the ratios indicated in Table 9 and the compatibility agent being present in an amount of 1% by weight of dry material in relation to the dry pigments.

The grinding tests were carried out using the same experimental procedures as those described in Example 8.

The properties of the ground suspensions and the results obtained after grinding are given in Table 9.

TABLE 9__________________________________________________________________________Cogrinding of CaSO.sub.4.2H.sub.2 O and CaCO.sub.3Test Type Percentage Average diameter Viscosity after grindingnumber of agent of agent after grinding CaSO.sub.4.2H.sub.2 O CaCO.sub.3 10 revs. 100 revs.__________________________________________________________________________PRIOR ART 99 Sodium 1 GRINDING 70 30 GRINDING polyacrylate IMPOSSIBLE IMPOSSIBLE100 Specific 1 50 50 viscosity: 0.55101 1 30 70INVENTION102 AGENT OF THE 1 1.3 70 30 14000 1320103 INVENTION 1 1.4 50 50 14000 1600104 TEST 40-07 1 1.5 30 70 6000 1160__________________________________________________________________________

The results given in Table 9 lead to the following observations: For Tests 99 to 101 which represent the aqueous polypigmentary suspensions using known agents, grinding is impossible due to the rapid increase in viscosity until a paste state is reached.

For Tests 102 to 104 which represent the aqueous polypigmentary suspensions in accordance with the present invention, it can be seen that the average diameter of the two types of ground pigments is very close to one micrometer, revealing not only a remarkable improvement in relation to the pigmentary suspensions of the prior art but also in relation to the ground monopigmentary suspensions of Example 8. In addition, the viscosities after grinding of said suspensions remain reasonable, even low, in spite of the increased fineness of the co-ground pigments.

Example 10

The object of this example is to illustrate the compatibility between pigments which are different in composition when they are used together in an aqueous polypigmentary suspension, due to the presence of the present agent.

For this purpose, monopigmentary suspensions of calcium carbonate and hydrated calcium sulfate were first prepared by grinding in an aqueous medium (using the procedures of Example 8) in the presence of a known compatibility agent (suspension types E and G) and an agent in accordance with the present invention (suspension types F and H). The properties of the monopigmentary suspensions and the results obtained are given in Table 10-1.

TABLE 10-1__________________________________________________________________________Properties of the Suspensions of Table 10-2 Suspension of CaCO.sub.3 Suspension of CaSO.sub.4.2H.sub.2 OReference E F G H__________________________________________________________________________Type of agent Sodium polyacrylate Agent of the invention. Sodium polyacrylate Agent of the invention. Test 40/07 Test 40/07specific viscosity 0.55 0.76 0.55 0.76Concentration of the 75 75 68 68suspension (%)Average diameter 1 1.5 8 3(microns)Brookfield viscosity of 10 rpm 100 rpm 10 rpm 100 rpm 10 rpm 100 rpm 10 rpm 100 rpmthe suspensions (cP) 700 300 3000 1200 17000 2700 7500 1170__________________________________________________________________________

In order to comparatively test the efficacy of the compatibility agents, the preparation of aqueous polypigmentary suspensions was carried out by mixing suspensions of calcium carbonate and hydrated calcium sulfate, containing on the one hand the known compatibility agent and on the other hand the compatibility agent in accordance with the present invention.

Tests 105 to 108 represent the suspensions with known agents and Tests 109 to 112 represent those of the present agent.

The properties of the polypigmentary suspensions prepared and the results obtained collected in Table 10-2.

TABLE 10-2______________________________________Dry extract % by wt. of the Brookfieldof the mixture of suspensions viscosityTest mixture CaCO.sub.3 CaSO.sub.4.2H.sub.2 O (in cP)No. (%) E F G H 10 rpm 100 rpm______________________________________Prior Art105 74.3 90 0 10 0 75000 >10000106 73.6 80 0 20 0 62000 >10000107 72.9 70 0 30 0 45000 >10000108 72.2 60 0 40 0 37000 8000Invention109 74.3 0 90 0 10 3000 740110 73.6 0 80 0 20 1600 360111 72.9 0 70 0 30 400 230112 72.2 0 60 0 40 280 200______________________________________

The results given in Table 10-2 lead to the following observations. For tests 105 to 108, the known compatibility agent does not eliminate the interpigmentary shock effect during the mixing of the monopigmentary suspensions: the viscosities of the known agent-containing polypigmentary suspensions are exacerbated to the extreme with the occurrence of a pasty appearance.

For Tests 109 to 112, the present compatibility agent eliminates the interpigmentary shock effect during the mixing of the monopigmentary suspensions; the viscosities of said polypigmentary suspensions are very low, even lower than those observed in Table 7-2 of Example 7 (polypigmentary suspensions obtained by mixing unground monopigmentary suspensions).

Example 11

The object of this example is to illustrate the capability of hydrated calcium sulfate to be substituted as a pigment for titanium oxide in a polypigmentary suspension, in the coating of paper, due to the presence of the agent in accordance with the present invention.

For this purpose, two aqueous polypigmentary suspensions were prepared: one containing kaolin, calcium carbonate, and titanium oxide dispersed in the aqueous phase by means of a known compatibility agent; the other containing kaolin, calcium carbonate and hydrated calcium sulfate dispersed in the aqueous phase by means of the present compatibility agent.

To these aqueous polypigmentary suspensions, the various components were added which were necessary for their transformation into paper-coating formulas, with the components being introduced in identical amounts so that the two formulas could be distinguished from one another only by the presence of TiO.sub.2 in one, and by the presence of hydrated calcium sulfate and the compatibility agent of the present invention in the other.

These two formulas were used for coating a cardboard on a flat table machine built by the Allimand company.

Using a trailing blade, a coat of 11 to 12 g.m.sup.-2 of each formula was deposited on a cardboard support (170 g.m.sup.-2) at an application speed of 380 meters per minute in a width of 3.2 meters. At the exit of the Allimand machine, a coated cardboard of 181 to 182 g.m.sup.-2 was obtained.

The properties of the coating formulas and the coated cardboards are given in Table 11.

TABLE 11______________________________________Coating Formulas and Industrial Tests______________________________________Kaolin from the 65 65ECC CompanyCaCO.sub.3 Hydrocarb 90 25 25from OMYATiO.sub.2 RL 68 from Thann 10 0and MulhouseCaSO.sub.4.2H.sub.2 O 0 10Compatibility agent of the 0 4% in dry/dry ininvention 40/07; addition relation to the sulfateCMC Finnfix 5 (water 0.5% on dry 0.5% on dryretainer) from pigment pigmentMetralliiton TilisuusAcrylic styrene latex SD 15% 15%215 from Rhone PoulencUrecoll S (rendering the 10% in relation to 10% in relation tolayer insoluble) from the dry latex the dry latexBASFNaOH, quantity sufficient 8.5-8.7 8.5-8.7for a pH of:Water, quantity sufficient 65% 65%for a dry extract of:Leucophor CK bluing 1% as is on the 1% as is on theagent from Sandoz dry pigment dry pigmentBrookfield viscosity 10 revs. 7600 6000100 revs. 1280 1000Whiteness 84.5 89.7Brilliance under ultra- 29 27violetPause opacity index -0.8 -8.64Ink absorption - Drying 12/15 seconds 4/5 secondstimeBehavior on the machine Slight clogging Perfectly smooth of the blade blade______________________________________

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A process for making paper, comprising the step:

(i) coating a paper support with a suspension comprising hydrated calcium sulfate and a water-soluble copolymer having the formula (I): ##STR90## wherein L is a value such that the amount of the comonomer of the formula ##STR91## is between 5 and 95 parts by weight, based on the total weight of said copolymer, and one of K and M may be 0 and the sum of K, L, and M equals 100 parts by weight;

wherein R.sub.1 is one member selected from the group consisting of hydrogen and a carboxylic acid group which may be esterified with a C.sub.1 to C.sub.12 alkyl group;

R.sub.2 is one member selected from the group consisting of hydrogen and C.sub.1 -C.sub.12 alkyl;

R.sub.3 and R'.sub.3 are each, independently, one member selected from the group consisting of hydrogen, a carboxylic acid group, halogen, C.sub.1 -C.sub.12 alkyl, and substituted or unsubstituted aryl;

R.sub.4 is one member selected from the group consisting of hydrogen, C.sub.1 -C.sub.12 alkyl, substituted or unsubstituted aryl, and a carboxylic acid group which may be esterified with a C.sub.1 14 C.sub.12 alkyl group;

R.sub.5 is one member selected from the group consisting of an ester group, a substituted amide, oxygen, C.sub.1 -C.sub.12 alkylene, substituted or unsubstituted arylene, substituted or unsubstituted cycloalkylene, substituted or unsubstituted cycloalkenylene and substituted or unsubstituted aralkylene, an ethylene or propylene oxide carboxylic ester of the formula: ##STR92## in which R.sub.10 is hydrogen or methyl and n has a value of between 1 and 50, an alkyl, aryl, or aralkyl carboxylic ester of the formula: ##STR93## wherein R.sub.11 contains 1 to 12 carbon atoms, and a substituted amide of the formula: ##STR94## wherein R.sub.12 is hydrogen, C.sub.1-C.sub.12 alkyl, substituted or unsubstituted aryl, or aralkyl, and R.sub.13 is C.sub.1 -C.sub.12 alkylene substituted or unsubstituted arylene, substituted or unsubstituted cycloalkylene, substituted or unsubstituted cycloalkenylene, or substituted or unsubstituted aralkylene;

R.sub.6 is one member selected from the group consisting of hydrogen, a cation, an amine, C.sub.1 -C.sub.3 alkyl, substituted or unsubstituted aryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted cycloalkenyl, substituted or unsubstituted aralkyl, a C.sub.1 -C.sub.12 ester, and a substituted amide;

R.sub.7 is one member selected from the group consisting of hydrogen, a carboxylic acid group, a C.sub.1 -C.sub.12 ester, C.sub.1 -C.sub.12 alkyl, aryl, cycloalkyl, cycloalkenyl, and aralkyl;

R.sub.8 is one member selected from the group consisting of hydrogen, a carboxylic acid group, C.sub.1 -C.sub.3 alkyl, and halogen; and

R.sub.9 is one member selected form the group consisting of a C.sub.1 -C.sub.12 ester, substituted or unsubstituted amide, C.sub.1 -C.sub.12 alkyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, halogen, --CO.sub.2 H, and a sulfonated or sulfated alkyl or aryl group.

2. Paper, produced by the process, comprising the steps of

(i) coating a paper support with a suspension comprising hydrated calcium sulfate and a water-soluble copolymer having the formula (I): ##STR95## wherein L is a value such that the amount of the comonomer of the formula ##STR96## is between 5 and 95 parts by weight, based on the total weight of said copolymer, and one of K and M may be 0 and the sum of K, L, and M equals 100 parts by weight;

wherein R.sub.1 is one member selected from the group consisting of hydrogen and a carboxylic acid group which may be esterified with a C.sub.1 to C.sub.12 alkyl group;

R.sub.2 is one member selected form the group consisting of hydrogen and C.sub.1 -C.sub.12 alkyl;

R.sub.3 and R'.sub.3 are each, independently, one member selected from the group consisting of hydrogen, a carboxylic acid group, halogen, C.sub.1 -C.sub.12 alkyl, and substituted or unsubstituted aryl;

R.sub.4 is one member selected for the group consisting of hydrogen, C.sub.1 -C.sub.12 alkyl, substituted or unsubstituted aryl, and a carboxylic acid group which may be esterified with a C.sub.1 -C.sub.12 alkyl group;

R.sub.5 is one member selected from the group consisting of an ester group, a substituted amide, oxygen, C.sub.1 -C.sub.12 alkylene, substituted or unsubstituted arylene, substituted or unsubstituted cycloalkylene, substituted or unsubstituted cycloalkenylene and substituted or unsubstituted aralkylene, an ethylene or propylene oxide carboxylic ester of the formula: ##STR97## in which R.sub.10 is hydrogen or methyl and n has a value of between 1 and 50, an alkyl, aryl, or aralkyl carboxylic ester of the formula: ##STR98## wherein R.sub.11 contains 1 to 12 carbon atoms, and a substituted amide of the formula: ##STR99## wherein R.sub.12 is hydrogen, C.sub.1 -C.sub.12 alkyl, substituted or unsubstituted aryl, or aralkyl, and R.sub.13 is C.sub.1 -C.sub.12 alkylene, substituted or unsubstituted arylene, substituted or unsubstituted cycloalkylene, substituted or unsubstituted cycloalkenylene, or substituted or unsubstituted aralkylene;

R.sub.6 is one member selected form the group consisting of hydrogen, a cation, an amine, C.sub.1 -C.sub.3 alkyl, substituted or unsubstituted aryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted cycloalkenyl, substituted or unsubstituted aralkyl, a C.sub.1 -C.sub.12 ester, and a substituted amide;

R.sub.7 is one member selected from the group consisting of hydrogen, a carboxylic acid group, a C.sub.1 -C.sub.12 ester, C.sub.1 -C.sub.12 alkyl, aryl, cycloalkyl, cycloalkenyl, and aralkyl;

R.sub.8 is one member selected from the group consisting of hydrogen, a carboxylic acid group, C.sub.1 -C.sub.3 alkyl, and halogen; and `R.sub.9 is one member selected from the group consisting of a C.sub.1 -C.sub.12 ester, substituted or unsubstituted amide, C.sub.1 -C.sub.12 alkyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, halogen, --CO.sub.2 H, and a sulfonated or sulfated alkyl or aryl group.