BR0003234B1 - dispersion of a solid particulate material in an aqueous medium, and process for reducing the viscosity of a dispersion of a solid particulate material in an aqueous medium. - Google Patents

Description

"DISPERSION OF A SOLID PRIVATE MATERIAL IN A WATER-MEDIUM AND PROCESS TO REDUCE THE VISCOSITY OF A SOLID PARTICULAR MATERIAL IN A WATERY MEDIA".

The present invention relates to dispersions or pastes of a solid particulate material in aqueous medium; in particular to solid desolate dispersions which usually tend to aggregate, deposit or separate asphalts and to a process for inhibiting such phenomena in pastes containing these mineral particles in order to improve the viscosity of such pastes by making them more processable.

The present invention is suitable for producing particulate solid pastes, for example calcium carbonate for the paper industry and clays for use in the ceramics industry, but in fact the invention can be used for the production of a dispersion or a aqueous paste. containing any solid particles at high concentration.

Previous attempts to produce such aqueous dispersions are described, for example, in EP-B-0129329. This document discloses pigment pastes containing water soluble polymers of 1,500 to 6,000 molecular weight, formed from one or more ethylenically unsaturated monomers and containing acidic groups selected from the carboxyl and sulfonic groups. The present invention has improved performance over this prior art.

US-A-4,868,228 describes crushing agents in aqueous suspensions of mineral materials and, in particular, the use of such crushing agents for the production of low-viscosity aqueous suspensions of mineral solids. Grinding agents are described as polymers and / or copolymers of acrylic acid which are completely neutralized by at least one neutralizing agent having a monovalent function and at least one neutralizing agent having a polyvalent function.

EP-A2-0705892 teaches dispersions or pastes of solid particulate materials in an aqueous medium, which also comprise a phosphono carboxylic acid or a water soluble salt thereof, the dispersant having the following formula:

H [CHRCHR] n - PO3M2Zv

wherein at least one R group in each unit is a COOM1 / v group and the other R group is hydrogen or a COOM1 / v hydroxyl, phosphono, sulfono, sulfate, C1-7 alkyl group or a carboxylate-substituted C1-7 alkyl or C1-7 alkenyl group. , phosphono, sulfono, sulfate and / or hydroxy, and each M is a cation such that the phosphonated carboxylate is water soluble, and η (the number of monomer units in polymerized polymer chain form) is from 1 to 6, and preferably less than 5, e.g. from 1 to 3. The solid particles dispersed in this prior art preferably have a particle size of less than 1 mm, for example less than 0.5 mm, preferably from 0.5 to 100 μηι, and especially from 1 to 50 μπι.

The present invention seeks to provide improved dispersions or pastes of solid particles in water. It is well known, for example see PCT / US 91/94539, that it is especially difficult to achieve stable dispersions of fine materials; thus, it is of particular interest to produce stable dispersions of fine solid particles, such as those having a significant proportion with a particle size of less than 2 μιη.

The present invention therefore provides a dispersion of solid particulate material in a water-containing medium and at least one dispersion agent, wherein said dispersing agent comprises a water-soluble polymer comprising: <formula> formula see original document page 4 </formula>

wherein X is Η, Na, K, Ca, Mg, NH 4 + or A; and A is a polymer, copolymer or one of its water-soluble salts comprising one or more of the following monomers in polymerized form:

<formula> formula see original document page 4 </formula>

on what:

R1 is Η, OH, C1 to C9 alkyl or alkoxy or acetoxy or acetate;

R2 is H, C1 to C3 alkyl or alkoxy, COOR3;

R3 is H, Na, K or C1 to C10 alkyl;

hydroxy propyl acrylate propyl methacrylate, 2-acrylamido-2-propane sulfonic acid, sodium styrene sulfonate, disodium allyl sulfonate, sodium methyl sulfonate, vinyl sulfonic acid and salts thereof; acrylamide, methacrylamide, tert-butyl acrylamide, (meth) acrylonitrile, styrene, vinyl acetate, allyloxy-2-hydroxypropyl sulfonate and dialkyl acrylamide; and

A further contains at least 10 monomers in polymerized form.

The number of monomers in the polymerized form may be from 10 to over 100, but preferably from 15 to 85, and most preferably from 25 to 60. Dispersing agents may have a weight average molecular weight of 1,000 to 10,000 and dispersing agents which have a weight average molecular weight of 2,000 to 6,000 are especially preferred. Although stable dispersions with a low viscosity can be obtained with dispersing agents of a higher molecular weight, there is a greater tendency for gel formation with the above molecular weight polymers. than 6,000, which may be disadvantageous in some applications.

The invention is particularly suited for forming very fine particle dispersions, for example those where 70% or more of the particles are below 2 μπι, and preferably those where 70% or more are below 1 μιη. The invention works particularly well with fine particle dispersions, where 95% or more of the particles are below 1 μπι.

The water soluble dispersing agent is preferably an acrylic acid phosphono-terminated homo- or copolymer. The other monomer, if the dispersing agent is a copolymer, may be malamic acid or maleic anhydride, methacrylic acid, unsaturated sulfonic monomers or any unsaturated polymerizable monomers having a COOH group. In some embodiments, a suitable water-soluble dispersing agent is selected from the group consisting of an acrylic acid phosphonate-terminated homopolymer having a weight average molecular weight of 2,000 to 5,800 of a acrylic acid phosphonate-terminated copolymer of a weight average molecular weight. from 2,000 to 5,800. Such polymers may be made, for example, according to US 4,046,707, US 5,376,731, US 5,077,361 and US 5,294,686.

The dispersed or suspended solid may be any particulate solid which is sufficient and chemically inert to be dispersed or suspended in an aqueous medium. The particles are preferably inorganic and substantially insoluble in water. Examples include calcium carbonate, clays, kaolin, talc and metal oxides.

The liquid medium may be water or a water containing solution. This medium may also contain alcohols, glycols, surfactants or wetting agents.

The composition of the present invention provides at least two important advantages, namely a reduction in dispersion viscosity and a reduction in dispersion tendency to form a gel, particularly in fine particle dispersions. Further, these benefits are obtained by systems wherein the weight percentage of solid particles in the dispersion is high, for example, greater than 60%, and preferably greater than 75%.

Finally, the invention also provides a process for reducing the viscosity of a solid particulate material dispersion in an aqueous medium comprising contacting the aqueous medium prior to or after forming the solid particulate material dispersion with an effective amount of at least one dispersing agent. wherein said dispersing agent comprises a water-soluble polymer comprising:

<formula> formula see original document page 6 </formula>

wherein X is H, Na, K, Ca, Mg, NH 4 + or A; and A is a polymer, copolymer or one of its water-soluble salts comprising one or more of the following monomers in polymerized form:

<formula> formula see original document page 6 </formula>

on what:

<formula> formula see original document page 6 </formula>

R1 is Η, OH, C1 to C9 alkyl or alkoxy or acetoxy or acetate;

R2 is H, C1 to C3 alkyl or alkoxy, COOR3: R3 is Η, Na, K or C1 to C10 alkyl;

hydroxyl propyl acrylate, propyl methacrylate, 2-acrylamido-2-propane sulfonic acid, sodium styrene sulfonate, disodium allyl sulfonate, sodium methyl sulfonate, vinyl sulfonic acid and salts thereof; acrylamide, methacrylamide, tert-butyl acrylamide, (meth) acrylonitrile, styrene, vinylacetate, allyloxy-2-hydroxypropyl sulfonate and dialkyl acrylamide; and

A further contains at least 10 monomers in polymerized form.

There are three general processes for making a definite dispersion of sodium carbonate:

1) Combining natural calcium carbonate (including powder), water and dispersing agents together and mixed to form a paste;

2) precipitating calcium carbonate from an aqueous solution of soda lime (calcium hydroxide) and carbon dioxide, collecting the precipitated material and mixing with water and a dispersing agent to form a paste; and

3) grind the calcium carbonate to the desired particle size and mix with water and a dispersing agent to form a paste.

The invention will now be described with reference to the following Examples.

General process (A) for preparing coarse or finely precipitated calcium carbonate dispersions and measuring their viscosity

a) An aqueous solution is formed by dissolving a dispersion agent in water in a beaker.

b) The aqueous solution is then stirred and a mineral solid to be dispersed is added thereto, a slow addition ratio is required to prevent agglomeration. c) Stirring is continued for about 10 minutes after addition of the mineral solid.

d) Finally, viscosity is measured immediately and after 1 hour, 24 hours and 48 hours using conventional viscometers such as Brookfield, Ford glass, etc.

General process (B) for preparing natural-ground calcium carbonate dispersions and measuring their viscosity

(a) water, dispersing agent and natural calcium to be crushed shall be fed into a container containing crushing agents (balls),

b) The solution is then shaken or stirred until the desired particle size is obtained.

c) The viscosity of the solution is then measured immediately and after 1 hour, 24 hours and 48 hours. Viscosity can be measured using conventional viscometers such as Brookfield's, Ford's cup, etc.

Dispersing agents used in the above tests are described in Table 1 below. TABLE 1: Dispersing agent compositions.

<formula> formula see original document page 9 </formula> DISPEX Ν40, DISPEX DP6 and DISPEX2695 are commercially available dispersing agents from Allied Colloids Limited. DISPEX is a registered trademark of Allied Colloids Limited.

AA = acrylic acid

MALAC = maleic acid

AMPS = 2-acrylamido 2-methylpropane sulfonic acid

EA = ethyl acrylate

HEA = hydroxy ethyl acrylate

HPA = hydroxypropyl acrylate

Dispersing agents 1,110 and 11 were prepared using a process well known to those skilled in the art, and using alcohol propyl alcohol (IPA) as the chain transfer agent. Dispersing agents 2, 6 and 9 were prepared using sodium hypophosphite (NaHP) as the chain transfer agent. Dispersing agents 7 and 8 were prepared using sodium metabisulphite (SMBS) and dispersing agents A-I are phosphonate-containing polymers of the present invention and all were prepared using phosphorous acid (H3PO3) as the chain transfer agent.

EXAMPLE 1: Measurement of Viscosity and Gel Tendency for Precipitated Calcium Carbonate Dispersions with 70% Particle Size <2 microns.

Aqueous dispersions of precipitated calcium carbonate having a particle size of 70% <2 microns were prepared using General Process (A) described above. Viscosity and gel formation date results are given in Table 2 below. TABLE 2: Gd Viscosity and Tendency Results for 70% Particle Size Precipitated Calcium Carbonate Dispersions <2 microns.

<formula> formula see original document page 11 </formula>

The above results demonstrate that the dispersing agents used in the present invention, that is, C, D and G, provide dispersions with significantly lower viscosity than dispersing agents 1 and 2.

Also, with dispersing agents C and D, in particular, the tendency to gel formation is much lower than that obtained by similar dispersions using non-phosphonate containing polymers as the dispersing agent.

EXAMPLE 2: Measurement of Viscosity and Gel Formation Tendency for Ground Calcium Carbonate Particle Size 79 to 83% <1 micron.

Aqueous dispersions of milled natural calcium carbonate with a particle size of 79 to 83% <1 micron were prepared using General Procedure (B) described above. The viscosity and gel date results are given in Table 3 below. <table> table see original document page 12 </column> </row> <table> As shown above results, dispersing agent A containing phosphonate groups and in accordance with the present invention, provides favorable viscosity and gel formation tendency when compared with comparative dispersing agents 3, 4, 5 and 6.

EXAMPLE 3: Measurement of Viscosity and Tendency of Gel Formation for Precipitated Calcium Carbonate Dispersions 95% Particle Size <1 micron

Aqueous dispersions of precipitated calcium carbonate having a particle size of 95% <1 micron were prepared using General Process (A) described above. The results of viscosity and gel formation date are shown in Table 4 below. <table> table see original document page 14 </column> </row> <table> From the results of Table 4, it is observed that the Mphosphonopolicarboxylic acids provide a significant improvement in viscosity and tendency to disperse calcium carbonate gel, with 95% of the particles having sizes smaller than 1 micron.

EXAMPLE 4: Comparison of Dispersing Agent Viscosity vs. Dispersing Agent Viscosity 12 (the preferred phosphonated oligomaleate of EP-A-705892, which was prepared according to Example 1 of EP-A-0569731) .

Aqueous 75% dispersions of calcium carbonate using General Procedure (A) described above. 0.8% dispersing agents were used. Viscosity was measured using a Brokfield RV model viscometer (axis 4) at 10, 20, 50 and 100 rpm. Results are shown in Table 5 below.

TABLE 5: Viscosity for Dispersing Agent C Against Dispersing Agent 12.

<table> table see original document page 15 </column> </row> <table>

EXAMPLE 5: Comparison of Dispersing Agent Torque% C vs. Dispersing Agent Torque% 12 (the preferred phosphonated oligomaleate of patent application EP-A-705892, which was prepared according to Example 1 of EP- A-0569731).

75% aqueous dispersions of precipitated calcium carbonate with 90% <1 micron particle size were prepared using. o General Process (A) described above. 0.8% dispersion polymers were used. At this time the percentage of torque was measured in time = zero and after 1, 2 and 7 days using a Brookfield viscometer model RVIII and a helical trajectory axis (1 rpm / 25 seconds - C axis). The results are shown in Table 6 below. Torque is related to the gel transformation procedures of calcium carbonate pastes.

TABLE 6: A Comparison of the Gels Formation Tendency Results Obtained for Dispersing Agent C Compared to Dispersing Agent 12.

<table> table see original document page 16 </column> </row> <table>

As shown by the results in Tables 5 and 6 above, the phosphonated dispersing agents of the present invention provide significantly improved performance compared to the prior art dispersing agents of EP-A-0705892, providing stable dispersions with a lower viscosity, even after decaying. several days.

Claims (6)

Dispersion of a solid particulate material in an aqueous medium, characterized in that it comprises from 0.8% to 2.45% of a dispersing agent, said dispersing agent comprising: a water-soluble polymer, comprising: formula wherein X is H, Na, K, Ca, Mg, NH 4 + or A; eA is a water-soluble polymer, copolymer or salt thereof which comprises one or more of the following monomers in polymerised form: wherein: R1 is Η, OH, alkyl or C1 to C9 alkoxy or acetoxy or acetate R2 is H, C1 to C3 alkyl or alkoxy, COOR3, R3 is H, Na, K or C1 to C4 alkyl, hydroxypropyl acrylate, propyl methacrylate, acid Sulfonic 2-acrylamido-2-propane, sodium styrene sulfonate, disodium allyl sulfonate, sodium methyl sulfonate, vinyl sulfonic acid and salts thereof; acrylamide, methacrylamide, tert-butyl acrylamide, (meth) acrylonitrile, styrene, vinyl acetate, allyloxy-2-hydroxypropyl sulfonate and dialkyl acrylamide; Additionally, A contains at least 10 monomers in polymerized form, wherein the weight percent of said solid particulate material is greater than 60% by weight, and that 70% or more of said solid particulate material is less than 2 microns, and The solid particulate material is selected from the group consisting of calcium carbonate, kaolin, clays, talc and metal oxides. Dispersion according to claim 1, characterized in that the weight average molecular weight of the dispersing agent is from -1000 to 10,000. Dispersion according to claim 1, characterized in that the weight average molecular weight of the dispersing agent is from 2000 to 6000. Dispersion according to Claim 1, characterized in that the dispersing agent is selected from the group consisting of an acrylic acid phosphonate-terminated homopolymer with a weight average molecular weight of 2000 to 5800 and an acrylic acid phosphonate-terminated copolymer and of maleic anhydride having a weight average molecular weight from 2000 to 5800. Process for reducing the viscosity of a dispersion of a solid particulate material in an aqueous medium, characterized in that it comprises contacting the aqueous medium before or after the formation of dispersion of the solid particulate material in an amount of 0.8% by weight. - 2.45% of at least one dispersing agent, wherein said dispersing agent comprises: a water-soluble polymer comprising: wherein X is H, Na, K, Ca, Mg, NH 4 or A; eA is a polymer, copolymer or one of its water-soluble salts comprising one or more of the following monomers in polymerised form: wherein: R1 is H, OH5 alkyl or alkoxy Q to C9 or acetoxy or acetate R2 is H, C1 to C3 alkyl or alkoxy, COOR3, R3 is H, Na, K or C1 to C10 alkyl hydroxy propyl acrylate, propyl methacrylate, 2-acid sulfonic acrylamido-2-propane, sodium styrene sulfonate, disodium allyl sulfonate, sodium methyl sulfonate, vinyl sulfonic acid and salts thereof; acrylamide, methacrylamide, tert-butyl acrylamide, (meth) acrylonitrile, styrene, vinyl acetate, allyloxy-2-hydroxypropyl sulfonate and dialkyl acrylamide; further, A contains at least 10 monomers in polymerized form, wherein weight percent of said solid particulate material is greater than 60% by weight, and that 70% or more of said solid particulate material particles is less than 2 microns, and that The solid particulate material is selected from the group consisting of decalcium carbonate, kaolin, clays, talc and metal oxides. Process according to Claim 5, characterized in that the dispersion comprises at least 60% by weight of the particulate solid.