WATER-SOLUBLE COPOLYMER AND USE THEREOF AS DISPERSANT FOR SUSPENSION OF PARTICLES

Abstract

The invention relates to the field of preparing aqueous dispersions of organic, organometallic or inorganic particles. In particular, the invention relates to the preparation of aqueous suspensions comprising organic, organometallic or inorganic particles and at least one particular copolymer obtained by polymerization of at least one acid and at least one compound or at least one ester derived from a particular acid, in the presence of water, at least one initiator compound and at least one activator compound, followed by total or partial neutralization by means of at least one compound chosen from alkali metal hydroxides, alkaline earth metal hydroxides, alkaline earth metal dihydroxides and mixtures thereof. The invention relates to such a particular copolymer having a low polydispersity index and weight-average molecular weight, the preparation process thereof and the use thereof, especially for the preparation of an aqueous paint composition.

Claims

1. A copolymer obtained by a process comprising: conducting a polymerization reaction of compound (a) and compound (b) in the presence of water, an initiating compound, and an activating compound, thereby forming a polymerized compound, wherein the compound (a) is at least one acid selected from the group consisting of acrylic acid and methacrylic acid; the compound (b) is at least one compound derived from an acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and maleic acid or at least one ester of a compound derived from an acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and maleic acid; the initiating compound is at least one compound selected from the group consisting of hydrogen peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate and the activating compound comprises an alkali metal hypophosphite; and neutralizing the polymerized compound completely or partially with at least one compound selected from the group consisting of MgO, CaO, an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal dihydroxide.

2. The copolymer as claimed in claim 1, wherein the compound (a) is acrylic acid, methacrylic acid or their mixtures, or optionally combined with at least one other acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and maleic acid.

3. The copolymer as claimed in claim 1, wherein the polymerization reaction employs from 10% to 90%, by weight of the compound (a), with respect to a total amount by weight of the compounds (a) and (b).

4. The copolymer as claimed in claim 1, wherein the compound (b) is a compound of formula (A): ##STR00005## wherein each X, independently represents a linear or branched C.sub.1-C.sub.10-alkylene group; n represents a whole or decimal number ranging from 1 to 5; Q represents C(O), CH.sub.2, CH.sub.2, CH.sub.2O or (CH.sub.2).sub.4O; L represents a direct bond or a CH.sub.2 group; R.sup.1 represents H, CH.sub.3 or C(O)OH; and R.sup.2 represents H or C(O)OH.

5. The copolymer as claimed in claim 1, wherein the compound (b) is a compound of formula (I), (II), (III) or (IV): ##STR00006## wherein each X, independently represents a linear or branched C.sub.1-C.sub.10-alkylene group; n represents a whole or decimal number ranging from 1 to 5; L represents a direct bond or a CH.sub.2 group; R.sup.1 represents H, CH.sub.3 or C(O)OH; and R.sup.2 represents H or C(O)OH.

6. The copolymer as claimed in claim 1, wherein the compound (b) is a compound of formula (A), (I), (II), (III) or (IV): ##STR00007## wherein: each X, independently represents a linear or branched C.sub.1-C.sub.10-alkylene group; n represents a whole or decimal number ranging from 1 to 5, wherein: L represents a direct bond, R.sup.1 represents H and R.sup.2 represents H; L represents a direct bond, R.sup.1 represents CH.sub.3 and R.sup.2 represents H; L represents a direct bond, R.sup.1 represents H and R.sup.2 represents C(O)OH; or L represents a CH.sub.2 group, R.sup.1 represents C(O)OH and R.sup.2 represents H.

7. The copolymer as claimed in claim 1, wherein the polymerization reaction employs from 10% to 90%, by weight of the compound (b), with respect to a total amount by weight of the compounds (a) and (b).

8. The copolymer as claimed in claim 1, wherein a weight-average molecular weight (M.sub.w) of the copolymer ranges from 1000 to 6000 g/mol.

9. A process for preparing a copolymer, the process comprising: conducting a polymerization reaction of compound (a) and compound (b) in the presence of water, an initiating compound, and an activating compound, thereby forming a polymerized compound, wherein the compound (a) is at least one acid selected from the group consisting of acrylic acid and methacrylic acid; the compound (b) is at least one compound derived from an acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and maleic acid or of at least one ester of a compound derived from an acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and maleic acid; the initiating compound is at least one compound selected from the group consisting of hydrogen peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate and the activating compound comprises an alkali metal hypophosphite and neutralizing the polymerized compound completely or partially with at least one compound selected from the group consisting of MgO, CaO, an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal dihydroxide.

10. A process for preparing an aqueous dispersion, the process comprising: contacting organic, organometallic or inorganic particles with the copolymer of claim 1.

11. An aqueous dispersion, comprising: organic, organometallic or inorganic particles and the copolymer as claimed in claim 1.

12. An aqueous slurry, comprising: organic, organometallic or inorganic particles and the copolymer as claimed in claim 1.

13. An aqueous adhesive composition or an aqueous coating composition, comprising the copolymer as claimed in claim 1.

14. A water-based paint composition, comprising: a film-forming copolymer latex; an organic or inorganic pigment; and the copolymer as claimed in claim 1.

Description

EXAMPLE 1

Process (1) for the Preparation of Copolymers According to the Invention

[0118] The following are weighed into a 1000 ml glass reactor equipped with a mechanical stirring system and with a heating system of oil bath type: [0119] 310 grams of water, [0120] 0.134 g of iron sulfate heptahydrate, [0121] 0.02 g of copper sulfate pentahydrate.

[0122] The combined mixture is then heated to 95 C.2 C. and the following reactants are then added using three peristaltic pumps with continuous additions over two hours at 95 C.: [0123] Pump 1: the monomers: [0124] acrylic acid: 284.04 g [0125] 2-hydroxypropyleneoxy acrylate: 180 g [0126] water: 31.6 g [0127] Pump 2: the initiating compound: [0128] 130-volume aqueous hydrogen peroxide solution: 37 g [0129] water: 45 g [0130] Pump 3: the reducing activating compound: [0131] 50% sodium hypophosphite solution: 96 g.

[0132] After rinsing the pumps, the combined mixture is subsequently heated at 95 C. for 45 min.

[0133] A polymer is obtained which is then analyzed: [0134] residual monomers: acrylic acid=30 ppm and 2-hydroxypropyl acrylate<60 ppm, [0135] M.sub.w=2795 g/mol, [0136] I.sub.p=2.

[0137] This polymer is subsequently neutralized at pH=80.5 in two forms and for a solids content of 45%0.5%: [0138] neutralization with sodium hydroxide in order to obtain the copolymer 1-1, [0139] neutralization with potassium hydroxide in order to obtain the copolymer 1-2.

EXAMPLE 2

Process (2) for the Preparation of Comparative Copolymers

[0140] The following are weighed into a 1000 ml glass reactor equipped with a mechanical stirring system and with a heating system of oil bath type: [0141] 310 grams of water, [0142] 0.134 g of iron sulfate heptahydrate, [0143] 0.02 g of copper sulfate pentahydrate.

[0144] The combined mixture is then heated to 95 C.2 C. and the following reactants are then added using three peristaltic pumps with continuous additions over two hours at 95 C.: [0145] Pump 1: the monomers: [0146] acrylic acid: 284.04 g [0147] 2-hydroxypropyleneoxy acrylate: 180 g [0148] water: 31.6 g [0149] Pump 2: the initiating compound: [0150] 130-volume aqueous hydrogen peroxide solution: 37 g [0151] water: 45 g [0152] Pump 3: the reducing activating compound: [0153] 50% sodium hypophosphite solution: 96 g.

[0154] After rinsing the pumps, the combined mixture is subsequently heated at 95 C. for 45 min. A polymer is obtained which is then analyzed: [0155] residual monomers: acrylic acid=30 ppm and 2-hydroxypropyl acrylate<60 ppm, [0156] M.sub.w=2755 g/mol, [0157] I.sub.p=3.

[0158] This polymer is subsequently neutralized at pH=80.5 and for a solids content of 45%0.5% by neutralization with ammonia in order to obtain the copolymer 2-1.

EXAMPLE 3

Process (3) for the Preparation of Comparative Copolymers

[0159] The following are weighed into a 1000 ml glass reactor equipped with a mechanical stirring system and with a heating system of oil bath type: [0160] 180 grams of water, [0161] 0.003 g of iron sulfate heptahydrate.

[0162] The combined mixture is then heated to 73 C.2 C. and the following reactants are then added using three peristaltic pumps with continuous additions over two hours at 73 C.: [0163] Pump 1: the monomers: [0164] acrylic acid: 245 g [0165] 2-hydroxypropyleneoxy acrylate: 159.89 g [0166] water: 60 g [0167] Pump 2: the initiating compound: [0168] ammonium persulfate: 5.88 g [0169] water: 60 g [0170] Pump 3: the reducing activating compound: [0171] 40% sodium bisulfite solution: 142 g.

[0172] The monomers and the reducing compound are added over 3 h 30 min; the initiating compound is added over 3 h 35 min. After rinsing the pumps, the combined mixture is subsequently heated at 73 C. for 60 min. A polymer is obtained which is then analyzed: [0173] residual monomers: acrylic acid=60 ppm and 2-hydroxypropyl acrylate<60 ppm, [0174] M.sub.w=3115 g/mol, [0175] I.sub.p=2.4.

[0176] This polymer is subsequently neutralized at pH=80.5 in two forms and for a solids content of 45%0.5%: [0177] neutralization with sodium hydroxide in order to obtain the copolymer 3-1, [0178] neutralization with potassium hydroxide in order to obtain the copolymer 3-2.

EXAMPLE 4

Process (4) for the Preparation of Comparative Copolymers

[0179] The following are weighed into a 1000 ml glass reactor equipped with a mechanical stirring system and with a heating system of oil bath type: [0180] 180 grams of water, [0181] 0.003 g of iron sulfate heptahydrate.

[0182] The combined mixture is then heated to 73 C.2 C. and the following reactants are then added using three peristaltic pumps with continuous additions over two hours at 73 C.: [0183] Pump 1: the monomers: [0184] acrylic acid: 245 g [0185] 2-hydroxypropyleneoxy acrylate: 159.89 g [0186] water: 60 g [0187] Pump 2: the initiating compound: [0188] ammonium persulfate: 5.88 g [0189] water: 60 g [0190] Pump 3: the reducing activating compound: [0191] 40% sodium bisulfite solution: 142 g.

[0192] The monomers and the reducing compound are added over 3 h 30 min; the initiating compound is added over 3 h 35 min. After rinsing the pumps, the combined mixture is subsequently heated at 73 C. for 60 min. A polymer is obtained which is then analyzed: [0193] residual monomers: acrylic acid=60 ppm and 2-hydroxypropyl acrylate<60 ppm, [0194] M.sub.w=2640 g/mol, [0195] I.sub.p=2.1.

[0196] This polymer is subsequently neutralized at pH=80.5 and for a solids content of 45%0.5% by neutralization with ammonia in order to obtain the copolymer 4-1.

[0197] The molecular weights of the copolymers are determined by size exclusion chromatography (SEC) or gel permeation chromatography (GPC). This technique employs a Waters brand liquid chromatography device provided with a detector. This detector is a Waters brand refractometric concentration detector. This liquid chromatography equipment has a size exclusion column in order to separate the different molecular weights of the copolymers studied. The liquid elution phase is an aqueous phase adjusted to pH 9.00 using 1N sodium hydroxide containing 0.05M of NaHCO.sub.3, 0.1M of NaNO.sub.3, 0.02M of triethanolamine and 0.03% of NaN.sub.3.

[0198] According to a first stage, 0.9% of the copolymer solution on a dry basis is diluted in the dissolution solvent of the SEC, which corresponds to the liquid elution phase of the SEC, to which is added 0.04% of dimethylformamide, which acts as marker of flow rate or internal standard. Filtration is then carried out using a 0.2 m filter. 100 l are subsequently injected into the chromatography device (eluent: an aqueous phase adjusted to pH 9.00 with 1N sodium hydroxide containing 0.05M of NaHCO.sub.3, 0.1M of NaNO.sub.3, 0.02M of triethanolamine and 0.03% of NaN.sub.3).

[0199] The liquid chromatography device contains an isocratic pump (Waters 515), the flow rate of which is adjusted to 0.8 ml/min. The chromatography device also comprises an oven which itself comprises, in series, the following system of columns: a precolumn of Waters Ultrahydrogel Guard Column type with a length of 6 cm and an internal diameter of 40 mm, and a linear column of Waters Ultrahydrogel type with a length of 30 cm and an internal diameter of 7.8 mm. The detection system is composed of a Waters 410 refractometric detector of RI type. The oven is brought to a temperature of 60 C. and the refractometer is brought to a temperature of 45 C.

[0200] The chromatography device is calibrated by means of powdered sodium polyacrylate standards of different molecular weights certified by the supplier: Polymer Standard Service or American Polymer Standards Corporation.

[0201] The characteristics of the copolymers prepared are presented in table 1.

TABLE-US-00001 TABLE 1 Copolymer According to the invention Comparative 1-1 1-2 2-1 3-1 3-2 4-1 M.sub.w (g/mol) 2795 2795 2755 3115 3115 2640 I.sub.p 2 2 3 2.4 2.4 2.1 Specific viscosity 0.320 0.320 0.337 0.273 0.327 0.327 Appearance after clear clear clear cloudy phase- clear neutralization separated

[0202] During the implementation of the process (1), solutions which are clear and stable on storage are obtained. During the implementation of the process (2), only the polymer neutralized with ammonia is clear.

[0203] Thus, the polymerization according to the invention, which employs an initiating compound of sodium hypophosphite type, makes it possible to obtain copolymers of use as acrylic dispersants, with high and commercially advantageous concentrations (>35%, indeed even than 40% or else than 43%, for example) and with alkali metal cations resulting from the neutralization.

[0204] It is not possible to obtain such results when the reducing initiating compound is sodium bisulfite, unless ammonia is used during the neutralization of the copolymer, then resulting in the presence of a release of volatile organic compounds during the use of these polymers.

EXAMPLE 5

Use of the Copolymers in the Preparation of Paint Compositions and Evaluation of the Properties of the Paint

[0205] Three paint formulations are prepared by mixing the constituents presented in table 2.

TABLE-US-00002 TABLE 2 Amount Composition (kg) Pasting phase Water 37.78 Sequestering agent Potassium tripolyphosphate (KTPP) 0.45 Dispersing copolymer according to the invention 2.09 1-1, 1-2 or 2-1 or comparative Surface-active agent Triton CF-10 1.36 Antifoaming agent Rhodaline 640 0.45 Fungicide Karhon LX (1.5%) 0.68 Sodium carbonate Aldrich 1.91 Rutile TiO.sub.2 (76.5% by Kronos 2310/Tronox CR 828/Ti-Pure R 112.49 weight) 902 Kaolin Polygloss 90 9.07 Water 38.28 Remainder Latex Arkema Encor 300 158.76 Latex Arkema Encor 626 68.04 Antifoaming agent Rhodaline 640 0.91 Thickening agent Coatex Rheotech 2800 9.84 Thickening agent Coatex Rheotech 4800 0.18 Water 44.45 TOTAL 486.75

[0206] The Stormer viscosity (KU) (ASTM D 562), the ICI viscosity (ASTM D 4287) and the Brookfield viscosity (ASTM D 2196) at 10 revolutions/min and 100 revolutions/min at 25 C. were measured for the three paint formulations. The results are presented in table 3.

TABLE-US-00003 TABLE 3 Dispersing copolymer 1-1 1-2 2-1 Stormer (KU) 112.2 117.2 113.2 ICI 0.555 0.495 0.475 Brookfield 10 rev/min 9560 14 600 10 400 (mPa .Math. s) Brookfield 100 rev/min 3715 4300 3660 (mPa .Math. s)

[0207] The dispersing properties of the copolymers employed were evaluated by producing deflocculation curves for different grades of TiO.sub.2 particles. The effectiveness of the dispersing agent during the suspending in water of titanium dioxide at a specific concentration is thus demonstrated.

[0208] An aqueous TiO.sub.2 slurry is prepared by introducing 190 g of water into a beaker, by then adding 612 g of rutile TiO.sub.2 (Kronos 2310, Tronox CR 828 and DuPont Ti-Pure R 902) and by slowly mixing by means of a mechanical mixer until complete homogenization is achieved. A thick paste is formed, the solids content of which is confirmed by means of a balance when dry. The solids content has to be 76.50.5%.

[0209] The initial Brookfield viscosity (ASTM D 2196) of the thick paste is measured at 100 rev/min.

[0210] A first amount of dispersing agent is then added and mixing is carried out for 5 min in order to obtain a dispersion of the TiO.sub.2 particles.

[0211] Brookfield viscosity (ASTM D 2196) of the thick paste comprising the dispersing agent is measured at 100 rev/min.

[0212] The stages of addition of slightly increasing amounts of dispersing agent, of mixing and of measuring the viscosity are repeated until, at one measurement, a viscosity value which is stabilized or which varies very slightly is obtained. The results for the different rutile TiO.sub.2 products Kronos 2310, Tronox CR 828 and DuPont Ti-Pure R 902 are presented in tables 4, 5 and 6.

TABLE-US-00004 TABLE 4 Amount of % Brookfield viscosity TiO.sub.2 dispersant (dry/dry)/ 100 rev/min Kronos 2310 (g) TiO.sub.2 (mPa .Math. s) Dispersing 1 0.060 19 360 copolymer 1-1 1.2 0.073 14 240 1.4 0.083 11 680 1.6 0.098 3800 1.9 0.117 638 2.2 0.132 208 2.5 0.148 174.4 2.9 0.176 181.4 3.5 0.212 286.2 Dispersing 1.0 0.0637 18 920 copolymer 1-2 1.4 0.0892 9150 1.7 0.1083 1260 2.0 0.1274 235 2.2 0.1401 180 2.4 0.1528 162 3.4 0.2165 118 Dispersing 1.0 0.0607 NA copolymer 2-1 1.2 0.0728 17 920 1.5 0.0910 12 480 1.8 0.1092 5800 2.0 0.1214 1700 2.3 0.1396 392 2.6 0.1578 214.4 2.8 0.1699 185.6 3.1 0.1881 177.6 4.4 0.2670 348.8

TABLE-US-00005 TABLE 5 Amount of % Brookfield viscosity TiO.sub.2 dispersant (dry/dry)/ 100 rev/min Tronox CR 828 (g) TiO.sub.2 (mPa .Math. s) Dispersing 1.5 0.092 not measurable copolymer 1-1 1.7 0.104 12 720 1.9 0.116 29 360 2.2 0.133 19 680 2.5 0.152 23 520 3.3 0.203 10 320 3.6 0.219 5230 3.9 0.238 3280 4.2 0.258 1284 4.6 0.284 604 4.9 0.297 548 5.3 0.324 454 5.82 0.356 491 Dispersing 2.7 0.170 15 000 copolymer 1-2 3.1 0.195 14 200 3.4 0.214 13 560 3.9 0.246 3180 4.2 0.265 1644 4.4 0.277 1034 4.7 0.296 780 4.9 0.309 592 5.1 0.321 491 5.3 0.324 431 6.3 0.385 374 Dispersing 1.2 0.0731 31 880 copolymer 2-1 1.4 0.0852 27 980 1.6 0.0974 27 680 1.9 0.1157 27 400 2.1 0.128 27 760 3.3 0.201 11 040 3.5 0.213 7280 3.7 0.225 3160 3.9 0.237 1246 4.3 0.262 750 4.5 0.274 534 4.9 0.298 466 5.10 0.311 376 5.80 0.353 536

TABLE-US-00006 TABLE 6 Amount of % Brookfield viscosity TiO.sub.2 dispersant (dry/dry)/ 100 rev/min DuPont Ti-Pure R 902 (g) TiO.sub.2 (mPa .Math. s) Dispersing 2.06 0.126 18 320 copolymer 1-1 2.3 0.143 7960 2.6 0.157 2890 2.9 0.175 688 3.1 0.191 408 3.4 0.208 266 3.7 0.227 275 4.4 0.267 216.4 4.8 0.293 229.2 Dispersing 2.2 0.140 18 600 copolymer 1-2 2.5 0.159 6560 2.8 0.178 836 3.0 0.191 490 3.2 0.204 286 3.4 0.216 228 3.6 0.229 197 4.5 0.286 152 Dispersing 1.7 0.1060 16 800 copolymer 2-1 2.1 0.1262 5880 2.3 0.1408 1900 2.5 0.1542 900 2.7 0.165 480 3.0 0.180 283.6 3.3 0.201 238.8 3.6 0.220 210 4.0 0.242 204.8

[0213] The different copolymers make possible good dispersion of the TiO.sub.2 particles of different grades.

[0214] The optical properties of the three paint formulations were also evaluated by measuring their gloss at 20, at 60 and at 85 by means of a Micro-Tri-Gloss reflectometer from BYK-Gardner (ASTM D3928) and their opacifying properties (ASTM D2805). The measurements were carried out 24 hours after application of the paint.

[0215] The flow-sagging compromise of these three formulations was also evaluated (respectively ASTM D4400 and ASTM D4062).

[0216] The clearness index or whiteness index of the paint film was also measured by the measurement of the L* component in the Lab (L*a*b*) colorimetric space, using a spectrophotometer (ASTM D2244).

[0217] The wet abrasion resistance of these three formulations was also evaluated (ASTM D2486 and ASTM D4213).

[0218] The combined results are presented in table 7.

TABLE-US-00007 TABLE 7 Dispersing copolymer 1-1 1-2 2-1 Gloss 20 36.5 30.4 33.3 Gloss 60 70.7 69.1 69.8 Gloss 85 93.5 91.7 94.3 Opacity 97.37 96.98 97.38 Color L 95.4 95.38 95.25 Color a 2.59 2.58 2.57 Color b 2.34 2.43 2.31 Flow 12 14 14 Sagging 7 7 7 Wet abrasion resistance (cycles) 349 742 503

[0219] The neutralized copolymers according to the invention make possible good performance qualities of dispersion of the TiO.sub.2 particles as well as very good optical properties and excellent wet abrasion resistance properties for the water-based paint formulations prepared.