Method of making opacifying polymer particles

Abstract

A method of preparing an aqueous dispersion of opacifying polymer particles containing inorganic pigment particles therein is disclosed. The method yields hollow polymer particles containing pigment particles therein using a non-RAFT emulsion polymerization process by free radical polymerization. The technique is much faster and simpler than known RAFT methods.

Claims

1. A method of preparing an aqueous dispersion of opacifying polymer particles containing inorganic pigment particles, the method comprising: i) dispersing an inorganic pigment in an aqueous medium in the presence of an anionic polymer dispersant of a weight average molecular weight (Mw) of at least 1000 Daltons, wherein the dispersant comprises acid moieties that are at least one of carboxyl, sulphur acid, or phosphorus acid functional moieties, and wherein the acid value of said anionic polymer dispersant is from 65 to 400 mg KOH/g non-volatile (non-vol.) dispersant, and wherein the pH during dispersion is greater than the pKa of the acid moieties and at least 0.25 pH units above or below the iso-electric point of the pigment particles, to form a stable aqueous dispersion of the pigment in the aqueous medium; ii) adjusting the pH of the stable aqueous dispersion to below the pKa of the acid moieties of a base swellable polymer while satisfying the pH criteria of i); iii) optionally polymerizing monomers to form first intermediate polymer layer having an acid value between 0 and 65 mg KOH/g polymer on the pigment; iv) forming a first layer of the base swellable polymer on the pigment particles or, if present, the first intermediate polymer layer, by polymerizing monomers comprising acid moieties; v) optionally polymerizing monomers to form a second intermediate polymer layer having an acid value between 0 and 65 mg KOH/g polymer on the first layer; vi) forming a second layer of a non-base swellable polymer on the first layer or, if present, the second intermediate polymer layer; vii) at least partially neutralizing the base-swellable-polymer, using a base, at a temperature above the Tg.sub.eff of the non-base-swellable polymer whereby the base-swellable polymer is caused to swell; and viii) cooling the dispersion of opacifying polymer particles to a temperature below the Tg.sub.eff of the non-base-swellable polymer; wherein the polymerizations are free of RAFT agents.

2. The method according to claim 1, wherein the first intermediate polymer layer is formed between the pigment and the first layer.

3. The method according to claim 2, wherein the acid value of the intermediate polymer layer is from 0.1 to 65 mg KOH/g polymer.

4. The method according to claim 2, wherein the further monomers polymerised to form the first intermediate polymer layer comprises sodium styrene sulphonate.

5. The method according to claim 1, wherein the inorganic pigment comprises titanium dioxide.

6. The method according to claim 1, wherein the inorganic pigment dispersed in i) has a mean particle diameter of from 75 to 300 nm.

7. The method according to claim 1, wherein the inorganic pigment dispersed in i) has a mean particle diameter of from 225 to 275 nm.

8. The method according to claim 1, wherein the dispersant further comprises hydroxyl moieties.

9. The method according to claim 1, wherein the dispersant comprises carboxyl moieties and the carboxyl moieties are provided by itaconic acid.

10. The method according to claim 1, wherein the base swellable polymer of iv)has an acid value of from 100 to 450 mg KOH/g of polymer.

11. The method according to claim 1, wherein the base swellable polymer of iv) has an acid value of from 130 to 260 mg KOH/g of polymer.

12. The method according to claim 1, wherein the base swellable polymer of iv) comprises one or more monomers selected from the group consisting of methacrylic acid, acrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, cinnamic acid, fumaric acid and beta carboxy ethyl acrylate.

13. The method according to claim 8, wherein the base swellable polymer of iv) comprises one or more monomers selected from the group consisting of methacrylic acid, acrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, cinnamic acid, fumaric acid and beta carboxy ethyl acrylate.

14. The method according to claim 1, wherein the Fox Tg of the non-base swellable polymer of vi) is at least 60 C.

15. The method according to claim 1, wherein the Fox Tg of the non-base swellable polymer of vi) from 90 to 140 C.

16. The method according to claim 1, wherein the non-base swellable polymer of step vi) comprises monomers selected from the group consisting of styrene, alpha methyl styrene, tert-butyl styrene, vinyl toluene, methyl methacrylate, acrylonitrile, methacrylonitrile and mixtures thereof.

17. The method according to claim 16, wherein the non-base swellable polymer of step vi) comprises at least 90 wt % styrene monomer.

Description

(1) FIG. 1 shows an idealised structure of an opacifying particle comprising the invention where (1) is a pigment particle, (2) is a layer of base-swellable polymer in its unswollen state and (3) is the layer of non-base-swellable polymer.

(2) FIG. 2 shows the same structure as in FIG. 1 at basic pH with the base-swellable polymer (2) swollen with water.

BASE SWELLABLE POLYMER

(3) The role of the base swellable layer is to react with a base once it has been overcoated with a rigid outer shell to form a hydrophilic ionomeric layer. This layer causes surrounding water to be drawn in by osmosis and to swell the polymer.

(4) This base swellable polymer layer should preferably contain sufficient acid monomer to give an acid value of from 100 to 450 mg KOH/g of polymer more preferably 130 to 260 mg KOH/g of polymer. This corresponds to from about 15 to 70 wt % and 20 to 40 wt % of methacrylic acid calculated on the total weight of base-swellable polymer.

(5) Preferably, the monomer is a carboxy acid functional monomer, although multifunctional acid monomers can also be used. Suitable examples include methacrylic acid, acrylic acid, crotonic acid, maleic acid (or anhydride), itaconic acid, cinnamic acid, fumaric acid, beta carboxy ethyl acrylate.

(6) Preferably the acid functional monomer is methacrylic acid, acrylic acid or combinations thereof.

(7) The base-swellable-polymer layer can also contain non-polymerisable acid if desired. Suitable non-polymerisable acid monomers include C.sub.6-C.sub.12 aliphatic monocarboxylic acids and aromatic acids such as benzoic acid.

(8) The base-swellable-polymer layer may optionally be crosslinked with a multifunctional unsaturated monomer such as divinyl benzene, diallyl methacryrlate, ethylene glycol dimethacrylate, butane diol dimethacrylate or allyl methacrylate. Preferably from 0.1 to 5 wt. %, based on the weight of base swellable polymer, of said multifunctional unsaturated monomer is used and more preferably from 0.1 to 1.0 wt. % is used. Allyl methacrylate is particularly preferred as a crosslinker as it promotes grafting between the different polymer layers.

(9) The Fox Tg of the base-swellable-polymer layer is preferably from 0 to 170 C. and more preferably from 20 to 150 C.

(10) The thickness of the base-swellable-layer is from 2 to 20 nm unswollen, and from 10 to 200 nm swollen. By thickness is meant the measured increase in radius of the particles.

(11) Non-Base Swellable Polymer

(12) The non-base swellable polymer of step iv) must fulfil two roles. Firstly, during the neutralisation step of the base-swellable polymer, the non-base swellable polymer must expand, without rupturing in order to accommodate the increased volumethus, it must be chosen to have an effective Tg below the temperature used during the neutralisation step. Secondly, during drying and loss of water, the non-base-swellable polymer must be rigid enough to prevent collapse of the void. The polymer should preferably have a high modulus.

(13) Preferably the non-base swellable polymer is non-film forming at ambient temperature. Non-film forming polymers have a Tg.sub.eff above ambient temperature.

(14) A good guide to modulus is the glass transition temperature, Tg. Generally, as Tg increases, modulus also increases and we have found this can be used as a useful guide to determine the Tg of the polymer which resists collapse and film formation.

(15) Preferably, the Fox Tg of the non-base swellable polymer iii) is at least 60 C., more preferably from 90 to 140 C.

(16) Furthermore, the polymer should not be significantly plasticised by water as this will cause it to soften and deform as the paint dries. Preferably it is hydrophobic as this reduces water plasticisation and has the added benefit that it improves water resistance of coatings containing the opacifying polymer particles of the present invention. More preferably, at least 90 wt. % of the monomers making up the non-base-swellable polymer should have a water solubility of less than 2 g/100 g of water at 20 C.

(17) Suitable monomers to make the non-base-swellable polymer include styrene, alpha methyl styrene (as a monomer in a copolymer), tert-butyl styrene, vinyl toluene, methyl methacrylate, acrylonitrile, methacrylonitrile and copolymers of these with lower Tg monomers.

(18) Preferably the polymer contains at least 90, more preferably 90-100 wt % styrene. It may also contain from 0 to 20% acidic moieties, more preferably from 0.1 to 10%. These are especially beneficial because it helps the non-base-swellable layer adhere to the base-swellable polymer layer. The presence of the acid moieties also helps with the swelling stage by helping to facilitate passage of the neutralising base through the rigid outer shell during the neutralisation step

(19) The thickness (i.e. the radius) of the non-base-swellable polymer layer is preferably from 15 to 150 nm, more preferably from 30 to 75 nm. Of course the thickness of the non-base-swellable polymer reduces as the base-swellable polymer swells because it has a greater area to encapsulate.

(20) The acid value of the non-base-swellable polymer is preferably less than 130, more preferably less than 100 and even more preferably less than 65 mg KOH/g non-vol polymer,

(21) Optional Intermediate Polymer

(22) The optional intermediate layer is not base swellable

(23) Preferably, the acid value of the optional intermediate polymer layer is less than 65 mg KOH/g of polymer, more preferably from 0.1 to 65 mg KOH/g of polymer and most preferably from 10 to 65 mg KOH/g of polymer. Suitable acid functional monomers are as hereinbefore described in relation to the base swellable polymer layer. Additionally, monomers comprising strong acid moieties such as sulphonate and phosphate can be used. Suitable examples include sodium styrene sulphonate.

(24) The Fox Tg of the optional intermediate polymer layer is preferably between 30 and 100 C. and more preferably between 50 and 90 C. The thickness of any intermediate polymer layer is from 5 to 50 nm before swelling of the base swellable polymer layer, more preferably 10 to 30 nm.

(25) Without being bound by this, it is thought that the optional intermediate polymer layer at least partially or preferably fully encapsulates the base swellable polymer layer in order to make it easier for the far less polar rigid outer shell to overcoat the base swellable polymer in a more uniform manner.

(26) FIG. 3 shows an idealised structure of an opacifying particle comprising the invention where (1) is a pigment particle, (2) is a layer of base-swellable polymer in its unswollen state, (3) is the layer of non-base-swellable polymer and (4) and (5) are intermediate layers.

(27) Swelling Stage

(28) The base swellable polymer layer is swollen by raising the pH using, for example, either volatile bases, including ammonia or amine, or non-volatile bases, for example alkali metal hydroxides such as sodium hydroxide. Of course, the polymer is not actually swollen by base but rather by the aqueous medium or water comprising the continuous phase of the dispersion. Following addition of the base, the neutralised acid moieties on the polymer become hydrophilic and the aqueous phase or water is drawn in by osmosis creating the driving force for swelling.

(29) In order for the water ingress to proceed unhindered, the non-base-swellable, non-film-forming polymer must be extensible during the neutralisation stage. It is necessary that the addition of the base is carried out at a temperature above the effective glass transition temperature of the non-base-swellable, non-film-forming polymer in order to accommodate the increase in volumes accompanying the water ingress without rupturing.

(30) An aqueous medium comprises at least 50 wt % of water, the remainder comprising organic solvents, preferably water compatible solvents.

(31) In the absence of a plasticising material for the polymer, the effective Tg is the same as the Fox Tg. Where a plasticiser is present the effective Fox Tg is lower than the Fox Tg.

(32) Preferably, the addition of base is at a temperature at least 5 C., more preferably from 5 to 20 C. above the effective Tg of the polymer.

(33) For example where the base swellable layer is over-coated with an intermediate polymer layer having a Tg less than the process temperature, the base can be added to the dispersion at elevated temperature (>Tg of the intermediate layer) and after the swelling is complete and the pH has dropped, a rigid hydrophobic layer of polymer is polymerised on top of this. Alternatively, the addition and polymerisation of the monomer can occur whilst the swelling is occurring.

(34) Alternatively, a rigid hydrophobic layer of polymer can be polymerised directly onto the base swellable polymer layer, followed by plasticising this polymer layer with monomer in order to reduce its effective Tg. This can be achieved by (a) stopping the addition of initiator, (b) optionally adding a free radical inhibitor (e.g. monomethyl ether hydroquinone, MEHQ), (c) using a non-homopolymerisable monomer, or (d) using a monomer with a ceiling temperature below the operating temperature (e.g. alpha methyl styrene). The base is then added to the dispersion at elevated temperature as before and after the swelling is complete and the pH has reduced, the polymerisation is continued (e.g. by adding further initiator and monomer) and a rigid hydrophobic layer of polymer is polymerised on top of this. Of course, a plasticising solvent can be also be used but is far less preferable as, depending on its boiling point, it may well contribute to VOC.

(35) Processing Conditions

(36) It is preferable to run the polymerisation under conditions that encourage control of the morphology, e.g. low free monomer levels and levels of surfactant that are adequate for giving stability but not so high as to cause nucleation and stabilisation of non pigmented latex particles.

(37) As a corollary to this, it is useful to make adjustments to lower the pH of the dispersion of inorganic pigment particles formed after step i) of the processfor instance, by the addition thereto of an acid such as hydrochloric acidand allow for pH equilibration before the polymerization of the base swellable polymer.

(38) The invention will now be illustrated by the following examples, in which the abbreviations used are defined below.

(39) The following abbreviations have the following meanings; AMA Allyl Methacrylate BA Butyl Acrylate BMA Butyl Methacrylate DI water Deionised water HEMA Hydroxyethylmethacrylate IA Itaconic Acid MAA Methacrylic Acid MAM Methacrylamide MMA Methyl Methacrylate SSS Styrenesulfonic Acid Sodium salt hydrate ST Styrene

Example 1

(40) Anionic Dispersant Solution (D-1)

(41) A solution of anionic polymer dispersant was produced according to the process described below and in Table 1, and having a monomer composition MMA:HEMA:IA:MAM of 15:45:36:4 by weight.

(42) TABLE-US-00001 TABLE 1 Dispersant Polymer (P1) Material Weight (g) Solvent (A) Iso-Propanol 15.17 DI water 5.06 Monomer (B) Methyl Methacrylate 7.05 Hydroxyethylmethacrylate 20.97 Itaconic Acid 16.68 Methacrylamide 1.91 n-Octyl Mercaptan 1.05 VAZO 67 1.46 Iso-Propanol 22.58 DI Water 7.75 Initiator (C) VAZO 67 0.11 Iso-Propanol 0.24 DI Water 0.14 Total 100.17

(43) The solvent mixture (A) was loaded to a reaction vessel. 25% of the mixture (B) was then added and the temperature increased to 65 C. under a blanket of nitrogen.

(44) The mixture was then allowed to exotherm to 82 C. and held for 15 min. The remainder of the mixture (B) was then fed over 2 hours at 85 C. The mixture (C) was then added and the mixture held at reflux temperature (80 to 85 C.) for 2 hours.

(45) A Dean Stark was then adapted to the reaction vessel and the Iso-Propanol was distilled off. As described in Table 2, (D) and (E) were then added while stirring at high speed at 75 C. to form the polymer solution (D-1) at 27.3 wt % solids.

(46) TABLE-US-00002 TABLE 2 Anionic Dispersant Solution D-1 Material Weight (g) Polymer (P1) 33.50 DI Water (D) 62.50 Ammonia (E) 4.00 Total 100.00
Aqueous Dispersion of Titanium Dioxide MB-1

(47) The anionic dispersant solution, D-1, was used to make an aqueous dispersion of titanium dioxide according to the recipe and method below.

(48) TABLE-US-00003 TABLE 3 Material Weight (g) D-1 23.01 DI Water 106.24 Tipure R-706 420.75 Total 550.00

(49) 23.01 g of the dispersant solution (D-1) were diluted in 106.24 g of water. 420.75 g of Tipure R-706 were then dispersed in the solution obtained using a high speed disperser operating at 1,500 rpm for 20 min.

(50) Aqueous Dispersion of Opacifying Polymer Particles

(51) An aqueous dispersion of opacifying polymer particles was made using the titanium dioxide dispersion prepared in Table 3. The method and ingredients used are shown in Table 4.1 and 4.2

(52) TABLE-US-00004 TABLE 4.1 TiO2 dispersion with first polymer layer (ME-1) Material Weight (g) Aqueous charge (A) MB -1 261.90 Sodium Dodecyl Benzene Sulphonate 1.46 Solids adjust (B) DI water 258.68 Initiator Catalyst (C) 0.1% Iron II Sulphate aqueous solution 1.12 1% Ethylene Diamine Tetra Acetic Acid aqueous solution 0.08 Initiator Feed (D ) Tert-Butyl Hydroperoxide (70% active) 0.37 DI water 3.27 Reductant Feed (E) Ascorbic Acid 0.20 DI water 15.04 Optional intermediate polymer layer (F) DI water 5.38 Sodium Dodecyl Benzene Sulphonate 0.64 Butyl Methacrylate 10.93 Methyl Methacrylate 6.25 Styrenesulfonic Acid Sodium salt hydrate 1.93 Total 567.69

(53) The TiO.sub.2 dispersion (A) was charged to a reaction vessel, diluted with DI (B), purged with nitrogen and the temperature raised to 50 C. The catalyst (C) was then added followed two minutes later by the initiator (D). The reductant (E) and the monomer mixture (F) were then fed in linearly over 30 min at 50 C.

(54) TABLE-US-00005 TABLE 4.2 Material Weight (g) Aqueous charge ME-1 567.69 Solids Adjust (G) DI Water 154.89 Initiator Catalyst (H) 0.1% Iron II Sulphate aqueous solution 1.48 1% Ethylene Diamine Tetra Acetic Acid aqueous solution 0.17 Sodium Dodecyl Benzene Sulphonate 4.93 Initiator Feed (I) Tert-Butyl Hydroperoxide 1.19 DI Water 11.18 Reductant Feed (J) Sodium Formaldehyde Sulfoxylate 0.42 DI Water 11.13 Base swellable layer stage (K) DI Water 7.08 Sodium Dodecyl Benzene Sulphonate 3.26 Methyl Methacrylate 16.01 Butyl Acrylate 16.01 Methacrylic Acid 16.01 Allyl Methacrylate 0.05 Solids Adjust (L) DI Water 234.84 Initiator Catalyst (M) 0.1% Iron II Sulphate aqueous solution 1.13 1% Ethylene Diamine Tetra Acetic Acid aqueous solution 0.13 Initiator Feed (N) Tert-Butyl Hydroperoxide 0.92 DI Water 8.63 Reductant Feed (O) Sodium Formaldehyde Sulfoxylate 0.32 DI Water 8.46 Optional Intermediate Polymer layer (P) Methyl Methacrylate 33.10 Butyl Acrylate 3.68 Aerosol MA80 0.87 DI Water 8.83 Non film forming outer shell (Q) Methyl Methacrylate 55.21 Aerosol MA80 1.31 DI Water 13.24

(55) ME-1 and Solids Adjust (G) were charged to a reaction vessel. The dispersion was then adjusted to pH 4.1 by addition of hydrochloric acid (1 mol/L) and stirred for 10 min to allow for pH equilibration. After addition of (I), the pH was checked again and readjusted if necessary to 4.1 by addition of hydrochloric acid (1 mol/L). The solution was purged with N.sub.2 and the temperature adjusted to 50 C. (J) and (K) were fed in linearly over 30 min, before the solid adjust (L) was added.

(56) The temperature was then kept at 50 C. while adding (M) and (N); (O) and (P) were then fed over 30 min.

(57) The dispersion was then heated up to 90 C. and (Q) and (R) were fed into the vessel.

(58) The mixture was then allowed to cool to room temperature; it was filtered to remove any grit. The filtered dispersion was then stirred at 90 C. and ammonia (S) added over 30 min. The stirring was continued for 4 hours at 90 C., before the dispersion was allowed to cool and was filtered.

Example 2

(59) As for Example 1, with the following formulation changes:

(60) TABLE-US-00006 Base swellable layer stage (K) DI Water 7.13 Sodium Dodecyl Benzene Sulphonate 3.29 Methyl Methacrylate 20.78 Butyl Acrylate 13.07 Methacrylic Acid 14.53 Allyl Methacrylate 0.05 Optional Intermediate Polymer layer (P) Styrene 36.78 Aerosol MA80 0.87 DI Water 8.83 Non film forming outer shell (Q) Styrene 55.21

(61) All other process and formulation steps remaining identical.

Example 3

(62) As for Example 1, with the following formulation changes:

(63) TABLE-US-00007 Base swellable layer stage (K) DI Water 7.02 Sodium Dodecyl Benzene Sulphonate 3.24 Methyl Methacrylate 11.84 Butyl Acrylate 16.75 Methacrylic Acid 19.06 Allyl Methacrylate 0.05 Non film forming outer shell (Q) Styrene 54.79 Aerosol MA80 1.30 DI Water 13.14

(64) All other process and formulation steps remaining identical.

Example 4

(65) As example 2, with the following formulation changes:

(66) TABLE-US-00008 Base swellable layer stage (K) DI Water 7.08 Sodium Dodecyl Benzene Sulphonate 3.26 Methyl Methacrylate 16.01 Butyl Acrylate 16.01 Methacrylic Acid 16.01 Allyl Methacrylate 0.05

(67) All other process and formulation steps remaining identical.

Example 5

(68) As for example 1, with the following formulation changes:

(69) TABLE-US-00009 Non film forming outer shell (Q) Styrene 56.18 Aerosol MA80 1.31 DI Water 13.24

(70) All other process and formulation steps remaining identical.

Example 6

(71) As for example 1, with the following formulation changes:

(72) TABLE-US-00010 Optional Intermediate Polymer layer (P) Methyl Methacrylate 31.72 Butyl Acrylate 5.06 Aerosol MA80 0.88 DI Water 8.83 Non film forming outer shell (Q) Styrene 53.44 Aerosol MA80 1.36 DI Water 12.81

(73) All other process and formulation steps remaining identical.

Example 7

(74) As for example 1, but with the following changes:

(75) TABLE-US-00011 Material Weight (g) Aqueous charge (A) MB-1 262.81 Sodium Dodecyl Benzene Sulphonate 1.47 Solids adjust (B) DI water 259.58 Initiator Catalyst (C) 0.1% Iron II Sulphate aqueous solution 1.12 1% Ethylene Diamine Tetra Acetic Acid aqueous solution 0.08 Initiator Feed (D ) Tert-Butyl Hydroperoxide (70% active) 0.37 DI water 3.28 Reductant Feed (E) Sodium Formaldehyde Sulfoxylate 0.20 DI water 15.09 Optional non base swellable polymer layer (F) DI water 5.40 Sodium Dodecyl Benzene Sulphonate 0.65 Butyl Methacrylate 11.28 Methacrylic Acid 0.39 Methyl Methacrylate 5.98 Styrenesulfonic Acid Sodium salt hydrate 1.96 Solids Adjust (G) DI Water 155.43 Initiator Catalyst (H) 0.1% Iron II Sulphate aqueous solution 1.48 1% Ethylene Diamine Tetra Acetic Acid aqueous solution 0.17 Sodium Dodecyl Benzene Sulphonate 4.95 Initiator Feed (I) Tert-Butyl Hydroperoxide 1.19 DI Water 11.22 Reductant Feed (J) Sodium Formaldehyde Sulfoxylate 0.42 DI Water 11.17 Base swellable layer stage (K) DI Water 7.10 Sodium Dodecyl Benzene Sulphonate 3.27 Methyl Methacrylate 20.70 Butyl Acrylate 13.02 Methacrylic Acid 14.47 Allyl Methacrylate 0.05 Solids Adjust (L) DI Water 235.66 Initiator Catalyst (M) 0.1% Iron II Sulphate aqueous solution 1.14 1% Ethylene Diamine Tetra Acetic Acid aqueous solution 0.13 Initiator Feed (N) Tert-Butyl Hydroperoxide 0.92 DI Water 8.66 Reductant Feed (O) Sodium Formaldehyde Sulfoxylate 0.32 DI Water 8.49 Optional intermediate Polymer layer (P) Methyl Methacylate 33.21 Butyl Acrylate 3.69 Aerosol MA80 0.87 DI water 8.86 Non film forming outer shell (Q) Styrene 55.40 Aerosol MA80 1.31 DI water 13.29 Initiator/Feed (R) Ammonium Persulphate 0.34 DI Water 19.58 Ammonia (S) Ammonia 40.81 Total 1246.98

(76) All process steps remain unchanged.

Example 8

(77) Same as example 1, but with the following formulation changes:

(78) TABLE-US-00012 Optional non base swellable polymer layer (F) DI water 5.42 Sodium Dodecyl Benzene Sulphonate 0.65 Butyl Acrylate 4.18 Methyl Methacrylate 13.54 Styrenesulfonic Acid Sodium salt hydrate 1.97 Base swellable layer stage (K) DI Water 7.13 Sodium Dodecyl Benzene Sulphonate 3.29 Methyl Methacrylate 20.78 Butyl Acrylate 13.07 Methacrylic Acid 14.53 Allyl Methacrylate 0.05 Non film forming outer shell (Q) Styrene 55.61 Aerosol MA80 1.32 DI Water 13.34 Ammonia addition (S) Ammonia 36.17

(79) All other formulation and process steps remaining unchanged.

Example 9

(80) Same as example 5, with the following formulation changes.

(81) TABLE-US-00013 Optional non base swellable polymer layer (F) DI water 5.38 Sodium Dodecyl Benzene Sulphonate 0.64 Styrene 0.39 Butyl Methacrylate 10.93 Methyl Methacrylate 6.69 Styrenesulfonic Acid Sodium salt hydrate 1.93

(82) All other formulation and process steps remaining unchanged.

(83) Spreading Rates

(84) The spreading rate to achieve a contrast ratio of 95% and 98% was evaluated by converting examples 1-3, 5-7 and 9 of the dispersion of the invention to model paints according to the formulations shown in Table A

(85) TABLE-US-00014 TABLE A Example 1 2 3 5 6 7 9 wt (g) wt (g) wt (g) wt (g) wt (g) wt (g) wt (g) Opacifying 46.72 50.01 49.19 32.85 47.26 44.66 48.90 dispersion of example as indicated above Film 35.50 34.30 33.03 33.57 32.83 33.94 33.64 forming latex VA:BA Thickener 1.50 1.50 1.49 1.48 1.51 1.51 1.50 Water 15.98 13.89 15.99 31.79 18.10 19.59 15.66 AMP 95 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 PVC 29.57 31.95 34.43 33.35 34.80 32.66 33.27 TiO.sub.2 PVC 8.09 8.72 8.74 8.64 8.84 8.53 8.62 Density 1.11 1.11 1.11 1.11 1.11 1.11 1.11 Volume 25.00 25.00 25.00 25.00 25.00 25.00 25.00 solids (vol %) Weight 32.54 32.52 32.49 32.51 32.48 32.47 32.47 solids (wt %)

(86) Table B shows the recipes of two standard paints at PVC 9 and 10%.

(87) TABLE-US-00015 TABLE B Standard A Standard B Standard TiO2 slurry A Standard TiO2 slurry B Weight (g) Weight (g) TiO2 slurry (76.5 wt % 9.30 10.30 TiO2) ASP 170 slurry (65 wt % 21.72 20.83 clay) VA-BA latex 30.18 30.08 Thickener 1.50 1.49 DI 37.00 36.99 AMP 95 0.30 0.30 100.00 100.00 34.80 34.82 TiO2 PVC % 9.00 10.00 Density 1.20 1.20 Volume solids % 25.00 25.00 Weight solids 37.51 37.70

(88) The TiO.sub.2 and clay slurry recipes as used in Standard A and B are shown below

(89) TABLE-US-00016 TiO.sub.2 slurry ASP 170 slurry wt % wt % Water 22.80 34.30 Biocide (25% solids) 0.11 Dispersant (45% solids) 0.30 0.35 (Polyacrylic acid) Antifoam 0.20 AMP 95 0.04 Biocide (22% solids) 0.23 Antifoam (60% solids) 0.19 TiO.sub.2 76.48 Hydrous Clay 65.00 Total 100.00 100.00

(90) The spreading rates are shown in Table C

(91) TABLE-US-00017 TABLE C Spreading Spreading Rate Rate TiO.sub.2 (m2/L at 95% (m2/L at 98% Run Sample PVC PVC contrast ratio) contrast ratio) 1 Example 1 8.09 29.57 7.3 4.5 2 Example 2 8.72 31.95 7.5 4.5 3 Example 3 8.74 34.43 7.3 4.2 4 Example 5 8.64 33.35 7.3 4.4 5 Example 6 8.84 34.80 7.3 4.3 6 Example 7 8.53 32.66 7.2 4.2 7 Example 9 8.62 33.27 7.3 4.3 12 Standard A 9.00 34.80 6.3 3.8 13 Standard B 10.00 34.82 7.0 4.4

(92) As can be seen, at 95% contrast ratio all of the examples containing opacifying particle of the invention have better opacity, as evidenced by the increased spreading rates, compared to standard A and B at PVC of 9 and 10%, even though the inventive compositions are at PVC significantly lower than these. Even at 98% contrast ratio all examples of the invention have a better spreading rate than the standard A at PVC of 9%.

(93) Effect of Intermediate Polymer on pH Stability of a Pigment Dispersion

(94) Onto the pigment dispersion, MB-1 (as described in Table 3) was polymerised various intermediate polymer comprising sodium styrene sulphonate.

(95) The resulting dispersions were allowed to cool and hydrochloric acid was added, whilst stirring, to reduce the pH. The minimum pH reached before flocculation was noted.

(96) Replacing sodium styrene sulphonate monomer with methacrylic acid monomer in the intermediate polymer resulted in flocculation on addition of hydrochloric acid.

(97) TABLE-US-00018 .sup.1Intermediate .sup.2SSS content of polymer/ intermediate polymer/ Minimum pH reached Example wt% wt % before flocculation 1 9.6 10.0 3.78 2 13.0 15.0 3.53 3 9.6 20.0 1.40 4 6.0 20.0 3.05 5 6.0 15.0 Flocculated at pH 4.3 6 9.6 10.0 3.05 .sup.1wt % based on pigment .sup.2SSS = sodium styrene sulphonate