HK1006029B

HK1006029B - Grinding and/or dispersion aid based on polymers and/or copolymers partially neutralised by magnesium for aqueous suspensions of mineral materials which are convenient for pigmentary applications

Info

Publication number: HK1006029B
Application number: HK98105169.7A
Authority: HK
Inventors: Egraz Jean-Bernard; Mongoin Jacques; Ravet Georges
Original assignee: Coatex S.A.S.
Priority date: 1991-11-12
Filing date: 1998-06-11
Publication date: 1999-02-05

Description

The present invention relates to an improved crushing and/or dispersion agent in aqueous suspension of coarse mineral materials, which produces an aqueous suspension of refined mineral particles, for pigment applications such as an aqueous suspension of calcium carbonate with a dry matter content of at least 70% by weight, of which at least 90% of the constituent particles after crushing have a dimension of less than two microns, while at least 60% of them have a dimension of less than one micron.

The invention also relates to a process for grinding in aqueous medium of coarse mineral materials in the presence of this water-soluble grinding agent. The process leads to aqueous suspensions of mineral materials whose viscosity remains stable over time even if the suspensions are not kept agitated, thus providing great ease of handling and application. The process applies particularly well to the grinding of an aqueous suspension of calcium carbonate, the content of which in dry matter is at least 70% by weight, of which at least 90% of the constituent particles after grinding have a dimension of less than two microns, while at least 60% of the suspensions have a dimension of less than one micron. Furthermore, the invention relates to aqueous suspensions of mineral particles obtained by the process and their applications.

Mineral substances such as calcium carbonates and titanium dioxide have long been known to be used in the preparation of industrial products, including paints, paper-induction, rubber and synthetic resin fillings and other products.

But since these mineral substances do not have a natural laminar or laminated structure which facilitates their decomposition, as is the case with certain substances such as aluminium silicates commonly known as kaolin, the artisan must, in order to use them in the pigment field, grind them into a highly fine aqueous suspension, the constituent grains of which have the smallest possible dimension, i.e. less than a few microns.

The number of publications in this field shows the importance and complexity of the aqueous milling of mineral substances to obtain a partially refined quality, allowing a pigment application. Thus, in the particular case of paper induction, it is well known that the induction mass formed of mineral pigments such as kaolins, calcium carbonate and titanium dioxide suspended in water also contains binding and dispersing agents, as well as other adjuvants such as thickening agents and colouring agents.

Thus, up to now, the man of art has known the use of grinding agents and/or aqueous dispersion of mineral particles consisting of acrylic polymers and/or copolymers totally or partially neutralized by various neutralizing agents (patents FR2539137, FR2531444, FR2603042).

The user is also familiar with the use of a grinding and/or dispersion agent consisting of the fraction of alkali acrylic polymers and/or copolymers totally neutralized by a single cation and having a specific viscosity between 0.3 and 0.8 (patent FR2488814) or partially neutralized by a single cation such as sodium, potassium, lithium or ammonium (EP0127388; EP0185458).

These various types of prior art grinding and/or dispersion agents and other treatments or grinding processes known to the art (EP 0278880; FR 2642415) make it possible to obtain aqueous suspensions of refined mineral particles, which have hitherto been considered stable over time, but for which the user has some difficulties in handling because he has to store these suspensions for several days or weeks without agitation and thus is confronted with the problem of freezing, i.e. the increase in the viscosity of the unagitated suspension.

In the past, the viscosity of the aqueous suspension of mineral particles was usually measured by means of a Brookfield viscosimeter of the RVT type at a temperature of 20°C and a rotation rate of 100 rpm: (a) after leaving the crusher, (b) after eight days' rest in the vial and after a prior agitation of the suspended solution.

Err1:Expecting ',' delimiter: line 1 column 112 (char 111)

Faced with these drawbacks, the applicant then found that the mineral aqueous suspensions obtained by the previous method had high Brookfield viscosities if the measurement was made without prior agitation of the suspension, which is usually the case for the user of those suspensions.

On the basis of that finding, the applicant then developed a grinding and/or dispersion agent and a grinding process in the presence of that agent which surprisingly made it possible to produce aqueous mineral suspensions meeting the quality criteria mentioned above.

Surprisingly, the purposes of the invention are achieved when the percentage of neutralization of the active acid sites of the polymer by a neutralizing agent containing the magnesium ion is between 40 and 60%, including terminals, while the percentage of neutralization of the active acid sites of the polymer by a monovalent agent is less than or equal to 60%.

Thus, one of the purposes of the invention is to provide an improved crushing and/or dispersion agent in aqueous suspension of coarse mineral materials without frost effect.

Another purpose of the invention is to provide a process for grinding mineral particles in aqueous suspension.

These suspensions, intended for pigment applications, of which at least 90% of the particles are less than two microns in size and at least 60% of which are less than one micron in size, according to the invention, have a low viscosity and stable over time even without agitation.

Finally, another purpose of the invention concerns the use of these refined mineral aqueous suspensions in the field of bulk loading and coating of paper, as well as in the field of paints and polymers after possibly eliminating the aqueous phase.

These are achieved by the use in the milling process of the invention of the agent of the invention, which results from the polymerisation and/or copolymerisation of acrylic and/or vinyl monomers with acid groups (carboxylic, sulphonic, phosphonic, phosphoric or other), and whose active acid sites are totally or partially neutralized with a neutralization rate of the active acid sites by a neutralizing agent containing the magnesium ion from 40% to 60%, terminals included, and by a neutralizing agent with a monovalent ion, capable of neutralizing up to 60% of the active acid sites of the polymer and/or copolymer.

The grinding and/or dispersing agent of the invention is, as expressed, acrylic polymers and/or copolymers partially or totally neutralized by acidic processes, obtained by known radical polymerization processes, in the presence of polymerization regulators such as organic compounds based on hydroxylamine and in the presence of polymerization initiators such as peroxides and parsley, e.g. water, persulfate, sodium hypophosphite, hypophosphoric acid, from at least one of the following monomers and/or compounds: acrylic/methacrylic, isoconic, isotonic, isotonic, acrylic, or even anhydrous.aconite, mesaconic, synapic, undecylenic, angelic, canellitic, hydroxyacrylic, in acid or partially neutralized form, acroleine, acrylamide, acrylonitrile, esters of acrylic and methacrylic acids, and in particular dimethylaminoethyl methacrylate, vinylpyrrolidone, vinylcaprolactam, ethylene, propylene, isobutylene, diisobutylene, vinyl acetate, styrene, alphamethylstyrene, methylenvinylconazole, a polymerisation medium which may be water, benzene, methylenethyl acetate, methylenethyl acetate, methylenethyl acetate, methylenethyl acetate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methacrylate, methylenethyl methylate, methylenethyl methylate, methylenethyl methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, methylate, metacetic, tartaric, lactic, citric, gluconic, glucoheptonic acids, 2-mercaptopropionic acid, thiodiethanol, halogenated solvents such as carbon tetrachloride, chloroform, methylene chloride, monopropylene glycol ethers, diethylene glycol or a mixture thereof.

The resulting acid polymerase is possibly distilled and then partially or totally neutralized by at least one neutralizing agent containing the magnesium ion, such that the percentage of neutralization of the active acid sites by the magnesium ion varies between 40% and 60%, including the terminals, and by a neutralizing agent with a monovalent ion capable of neutralizing up to 60% of the active acid sites of the said agent.

The monovalent neutralising agent is selected from the group consisting of alkaline cations (in particular sodium, lithium), ammonium, aliphatic and/or cyclic primary, secondary or tertiary amines such as ethanolamines (mono, di, triethanolamine), mono and diethylamine, cyclohexylamine, methylcyclohexylamine.

Polymers and/or copolymers of the invention generally have a specific viscosity of not more than 25, and preferably not more than 10.

Err1:Expecting ',' delimiter: line 1 column 131 (char 130)

A solution of polymerisate is taken to obtain a solution corresponding to 2,5 g of dry polymer and 50 ml of a 60 g/l sodium chloride solution.

Err1:Expecting ',' delimiter: line 1 column 458 (char 457) - What? The capillary tube is generally chosen in such a way that the flow time of the polymer and/or copolymer-free NaCl solution is approximately 90 to 100 seconds, giving very accurate specific viscosity measurements. The polymers and/or copolymers of the invention can also be treated by all known means to isolate them into a fine powder, which can be used in this other form as a grinding agent.

In practice, the milling operation of the mineral substance to be refined consists in grinding the mineral substance with a milling body into very fine particles in an aqueous medium containing the milling agent. An aqueous suspension of the mineral substance to be grinding, the grains of which have an initial dimension not exceeding 50 microns, is formed in such quantity that the dry matter concentration of the suspension is at least 70% by weight.

The grinding body is generally in the form of particles of materials as diverse as silicon oxide, aluminium oxide, zirconium oxide or mixtures thereof, as well as high-hardness synthetic resins, steels, or others. An example of the composition of such preferred grinding bodies is given by patent FR2303681 which describes grinding elements consisting of 30 to 70% by weight of zirconium oxide, 0.1 to 5% of aluminium oxide and 5 to 20% by weight of silicon oxide. The grinding body is preferably added to the grinding body by adding such a quantity of suspension that the ratio of the grinding material is between 5/1, and preferably less than 3/11.

The mixture of suspension and grinding body is then subjected to the mechanical action of brewing, such as occurs in a conventional microelement grinder.

The grinding and/or dispersion agent of the invention is also introduced into the mixture formed by the aqueous suspension of mineral substances and the grinding body at a rate of 0.2 to 2% by weight of the dried fraction of these polymers in relation to the dry mass of the mineral substance to be refined.

The time required to achieve excellent fineness of the mineral substance after grinding varies according to the nature and quantity of the mineral substances to be porphyrised, and according to the agitation method used and the temperature of the medium during the grinding operation.

The mineral substances to be refined can be of a wide variety of origins such as calcium carbonate and dolomite, calcium sulphate, kaolin, titanium dioxide, i.e. all the mineral substances which must be crushed to be used in such diverse applications as paper-induction, pigmentation of paints and coatings, loading of synthetic rubbers or resins, mating of synthetic textiles, etc.

Thus, the application of the crushing and/or dispersion agent of the invention allows the grinding of coarse mineral substances into very fine particles, of which at least 90% have a dimension of less than two microns and at least 60% have a dimension of less than one micron, and to obtain a suspension of very fine mineral substances with a low viscosity and stable in time and no freezing effect.

The scope and interest of the invention will be better understood by the following examples.

Example 1

This example concerns the preparation of a coarse calcium carbonate suspension which has been ground to a fine microparticulate suspension. for test No 1 illustrating the previous art, polyacrylic acid of specific viscosity 0,54 corresponding to a molecular weight of approximately 4 000, obtained by radical polymerisation and totally neutralized by sodium hydroxide,for test No 2 also illustrating the previous art, the same polyacrylic acid (specific viscosity 0,54) as in the previous test,The test method is based on the following equation: the test chemical is completely neutralized by sodium and lime in a ratio corresponding to a neutralization of the active acid sites at a ratio of 70% by sodium - 30% by calcium,for test No 3 still illustrating the previous art, the same polyacrylic acid (specific viscosity 0,54) as in the previous tests, partially neutralized by sodium hydroxide at a rate of 66% of the active acid sites,for test No 4 illustrating the invention, the same polyacrylic acid (specific viscosity 0,54) as in the previous tests, totally neutralized by sodium and magnesium, in a ratio corresponding to a neutralization of the active acid sites at a ratio of 50% by sodium - 50% by magnesium.

For each test, an aqueous suspension of calcium carbonate from the Orgon deposit in France was prepared, with a particle size of less than 10 microns.

The aqueous suspension has a dry matter concentration of 76% by weight of the total mass.

The grinding agent shall be added to this suspension in the quantities shown in the table below, expressed as a percentage by dry weight of the dry calcium carbonate to be ground.

The suspension is moved in a Dyno-Mill type mill with a fixed cylinder and a rotating impeller, the grinding body of which consists of corundum balls of a diameter of between 0.6 mm and 1.0 mm.

The total volume of the grinding body is 1 150 cubic centimetres and its mass is 2 900 g.

The milling chamber has a volume of 1400 cubic centimetres.

The circumferential velocity of the crusher is 10 meters per second.

The calcium carbonate suspension is recycled at a rate of 18 litres per hour.

The output of the Dyno-Mill is equipped with a 200 micron mesh separator to separate the suspension resulting from the grinding and the grinding body.

The temperature during each grinding test shall be maintained at approximately 60°C.

At the end of the milling (To), a sample of the pigment suspension is taken from a vial, 80% of which is less than one micron in size, and the viscosity is measured with a Brookfield viscosimeter of the RVT type at 20°C and a rotation rate of 10 rpm with the appropriate mobile.

After a rest period of 8 days in the vial, the viscosity of the suspension is measured by introducing into the vial the appropriate mobility of the RVT Brookfield viscosimeter at a temperature of 20°C and a rotation rate of 10 revolutions per minute (AVAG viscosity = before agitation).

All experimental results are recorded in Table 1.

Table 1 shows that only the calcium carbonate suspension crushed by the agent of the invention (Test 4) has a Brookfield viscosity measured at 10 rpm after 8 days at rest and without prior agitation, well below 5000 mPa.s, whereas all tests of the samples carried out by a method of the highest art yield viscosities above 5000 mPa.s.

Thus, the grinding process according to the invention allows the viscosity stability of calcium carbonate suspensions to be obtained even before any agitation.

Example 2

A second group of tests (tests Nos 5 to 13) involved the preparation and grinding of the aqueous suspension of the same calcium carbonate at the same dry matter concentration in the presence of the same polyacrylic acid of specific viscosity 0.54 neutralized by varying levels of magnesium.

These tests were carried out according to the same experimental criteria as in Example 1.

All experimental results are recorded in Table 2.

The rheological results of the invention can be seen from Table 2 and the use of the agent according to the invention can be used to achieve a threshold of profitability in practical tests.

Two criteria are taken into account by the user, the economic and the rheological aspects: an overdose of the grinding and/or dispersing agent leads to an additional cost in the production of the refined calcium carbonate suspension.

Thus, the consumption of a grinding agent and/or dispersion agent in the grinding operation must not exceed 1.2% of dry dispersion agent by weight of dry calcium carbonate for the production of a suspension with 80% particles less than 1 micron and a dry matter concentration of 76%.

As regards rheology, the user who has to handle concentrated suspensions stored for several days without agitation will admit that a Brookfield viscosity of less than 5000 mPa.s, measured at 10 T/minute before agitation, is acceptable.

These two economic and rheological criteria mean that calcium carbonate suspensions satisfying these conditions are those of tests Nos 6 to 10 and 13, i.e. those obtained by using as a grinding agent a polyacrylic acid totally or partially neutralized by at least one neutralising agent containing the magnesium ion, such that 40% to 60% of the active acid sites are neutralized by a neutralising agent containing the magnesium ion and up to 60% of the active acid sites are neutralized by a neutralising agent containing a monovalent ion.

Example 3

This example (tests Nos 14 to 16) concerns the preparation and grinding of the aqueous suspension of the same calcium carbonate at the same concentration of dry matter in the presence of the same polyacrylic acid of specific viscosity 0.54 neutralized by different neutralizing agents containing polyvalent ions other than magnesium.

Thus, the grinding of test No 14 is carried out using the above-mentioned polyacrylic acid neutralized by soda and lime in a ratio corresponding to a neutralization of the active acid sites at a rate of 55% by sodium - 45% by calcium, while test No 15 concerns the same polyacrylic acid neutralized by soda and zinc hydroxide in a ratio corresponding to the maximum solubility of zinc hydroxide, i.e. a ratio corresponding to a neutralization of the active acid sites at a rate of 83% by sodium - 17% by zinc.

Similarly, test No 16 is for the grinding agent obtained by neutralization by sodium and aluminium hydroxide in a ratio corresponding to the maximum solubility of aluminium hydroxide, i.e. a ratio corresponding to neutralization of the active acid sites at a rate of 90% by sodium - 10% by aluminium.

All results are recorded in Table 3.

Table 3 shows that the use of other neutralising agents such as calcium (test 14), zinc (test 15), aluminium (test 16) results in calcium carbonate suspensions with a Brookfield viscosity of more than 5000 mPa, measured at 10 rpm after 8 days of rest and without prior agitation, whereas the use of a neutralising agent such as magnesium results in a suspension of viscosity significantly less than 5000 mPa (test 7).

Thus, it can be seen from Table 3 that the use of other versatile neutralising agents other than magnesium does not allow stable suspensions without freezing to be obtained.

Example 4

This example (tests Nos 17 to 19) concerns the preparation and grinding of the aqueous suspension of the same calcium carbonate at the same concentration of dry matter in the presence of the same polyacrylic acid of specific viscosity 0.54 which is 50% neutralized by the magnesium ion and 50% by different neutralizing agents containing a monovalent cation.

These different neutralising agents containing a monovalent cation are ammonium for test No 17, lithium for test No 18, potassium for test No 19.

All results are recorded in Table 4.

It can be seen from Table 4 that sodium ion can be effectively replaced by monovalent neutralising agents such as ammonium ion or lithium ion.

Claims

Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials destined for pigmentary applications, constituted by acrylic and/or vinylic polymers and/or copolymers which include partially or totally neutralised acid groups resulting from the polymerisation and/or copolymerisation of acrylic and/or vinylic monomers, characterised by the fact that the active acid sites of the said agent are totally or partially neutralised by at least one neutralising agent containing the magnesium ion, in such a manner that the percentage of neutralisation of the active acid sites by the magnesium ion varies between 40 and 60%, end sites included, and by a neutralising agent having a monovalent ion able to neutralise up to 60% of the active acid sites of the said agent.
Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials according to claim 1, characterised by the fact that the active acid sites of the said agent are totally neutralised by at least one neutralising agent containing the magnesium ion, in such a manner that the percentage of neutralisation of the active acid sites by the magnesium ion varies between 40 and 60%, end sites included, and by a neutralising agent having a monovalent ion neutralising the 60% to 40% of remaining active acid sites.
Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials according to claim 1, characterised by the fact that the active acid sites of the said agent are partially neutralised by at least one neutralising agent containing the magnesium ion, in such a manner that the percentage of neutralisation of the active acid sites by the magnesium ion varies between 40 and 60%, end sites included, and by a neutralising agent having a monovalent ion able to neutralise up to 60% of the active acid sites.
Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials according to any of claims 1 to 3, characterised by the fact that the monovalent ion of the neutralising agent is chosen from among the sodium ion, the lithium ion, ammonium and the aliphatic and/or cyclic primary, secondary or tertiary amines.
Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials according to any of claims 1 to 4, characterised by the fact that the said agent has a specific viscosity of no more than 25 and preferably no more than 10.
Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials according to claim 5, characterised by the fact that it is a solution.
Agent for crushing and/or dispersion in aqueous suspension of coarse mineral materials according to claim 5, characterised by the fact that it is a powder.
Process for crushing in aqueous suspension of coarse mineral materials destined for pigmentary applications consisting of preparing an aqueous suspension of these materials, introducing a crushing agent composed of acrylic and/or vinylic polymers and/or copolymers which include partially or totally neutralised acid groups resulting from the polymerisation and/or copolymerisation of acrylic and/or vinylic monomers, adding to the suspension a crushing body and subjecting the mixture thus produced to a crushing action, characterised by the fact that the said crushing agent is such as described in any of claims 1 to 7.
Process for crushing in aqueous suspension of coarse mineral materials according to claim 8, characterised by the fact that the crushing agent is introduced into the suspension at the rate of 0.2% to 2% by dry weight of the said polymer in relation to the dry weight of the mineral substance to be crushed.
Process for crushing in aqueous suspension of coarse mineral materials according to either of claims 8 or 9, characterised by the fact that the aqueous suspension of the mineral materials to be crushed includes at least 70% by weight of dry matter.
Aqueous suspension of mineral materials refined by means of the crushing process according to any of claims 8 to 10, characterised by the fact that at least 90% of the particles of the crushed substance have a size of less than two microns.
Aqueous suspension of mineral materials refined according to claim 11, characterised by the fact that the Brookfield viscosity of the said suspension measured without agitation after at least 8 days of storage at 10 revolutions per minute does not exceed 5000 mPa.s.
Application of the aqueous suspension of materials refined according to claims 11 and 12 to the field of mass loading, paper coating, paints and plastics.