GB1594971A - Non-aqueous dispersions - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO NON-AQUEOUS DISPERSIONS (71) We, VIANOVA KUNSTHARZ AKTIENGESELLSCHAFT an Austrian Body Corporate of Johannesgasse 14, A-1010 Vienna 1, Austria, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with a process for the production of a non-aqueous polymer dispersion in which monomers are polymerised in an organic liquid such as, for example, an aliphatic hydrocarbon in the presence of a stabiliser.

In British Patent Specification No. 1,450,175 there is described a process for the production of an aqueous polymer dispersion wherein a seed latex having rubber-like crosslinked dispersion particles is initially prepared and further monomers are grafted thereon without cross-linking.

In German Offenlegungsschrift 2,350,654 there is described the preparation of a non-aqueous dispersion of micro gel particles by the addition of small quantities of a melamine resin and thus cross-linking minor portions of the dispersion. In such a dispersion there are present, in addition to the usual non-crosslinked dispersion particles, small quantities of gelled particles having a size of from 1-40 iim formed by linkage of polymer particles to one another.

German Offenlegungsschrift 2,611,186 also describes the preparation of micro gel particles but, in this case, the finished dispersion particles are linked to form micro gel particles. The initial micro gel particles are not crosslinked internally and they can therefore be solubilised or swelled.

Non-aqueous polymer dispersions, in admixture with soluble polymeric resins and melamine resins, can be used for the production of stoving enamels. However, the viscosity of such systems tends to rise on storage, and in many cases the stability towards other solvents is quite unsatisfactory.

In the usual methods of producing non-aqueous dispersions either an emulsion of solvent, stabilising resin, monomers and catalyst is prepared, a portion thereof is charged to the reaction vessel, the polymerisation reaction is initiated and the major part of the emulsion is added dropwise over the course of several hours or, the solvent blend and the stabiliser are charged to the reaction vessel and the monomer blend and catalyst are added.

Other methods involve a combination of both of these procedures. The addition of crosslinking agents, with the emulsion addition method or with the combined methods, tends to result in coagulation of the dispersion or in the dispersion having an extremely high viscosity. On examination with the aid of a microscope it can be seen that the dispersed particles are not only crosslinked internally but also with each other.

We have now invented a process whereby the stability of non-aqueous dispersions to solvents such as alcohols, esters and ketones, as well as the stability of the viscosity of paints prepared from such dispersions can be substantially improved. In the process according to our invention the polymerisaion is controlled such that the dispersed polymer particles polymerise substantially intraparticularly with virtually no interparticular cross linking.

The expression "intraparticular crosslinking" as used herein refers to crosslinking which takes place within a single particle of the dispersed phase, whereas the term "interparticular crosslinking" refers to crosslinking which takes place between discrete particles in the dispersed phase.

According to the present invention therefore there is provided a process for the production of a non-aqueous dispersion by polymerisation of a,P-ethylenically unsaturated monomers in a non-aqueous medium, which process comprises (i) adding a mixture of from 20 to 80% by weight of the total monomer to be polymerised and a polymerisation catalyst to a solution of a dispersion stabiliser in a non-aqueous liquid dispersion medium and polymerising the monomer to form dispersed polymer particles and (iiU adding a mixture of crosslinking agent and the remainder of the monomer to be polymerised to the reaction mass and completing the polymerisation simultaneously with crosslinking taking place within the cores of the dispersed particles, substantially no crosslinking of the particles with each other taking place.

The blend to be added preferably comprises from 50 to 70% by weight of the total monomer.

By the process according to the invention selective intraparticular crosslinking occurs within the particles of the dispersed phase with substantially no crosslinking of the particles with each other (interparticular crosslinking). This is achieved by the addition of crosslinking agent at the optimum point during polymerisation. Before addition of crosslinking agent the polymerisation is carried on to a point where dispersed particles of polymer having a relatively thick protective layer of stabiliser are formed, which layer substantially prevents interparticular crosslinking upon addition of the crosslinker. After the optimum amount of polymerisation has occured, the crosslinker is added blended with the remainder of the monomers and, together with the monomers, can penetrate through the stabiliser layer into the swollen particle core and effect crosslinking.

The stabilisers generally used in the preparation of non-aqueous dispersions are "amphipatic" compounds. Thus they include one molecular portion which is strongly solvated by the organic liquid, and another portion which is associated with the dispersed polymer particles or chemically combined with the particle core. They are capable of stabilising dispersions in non-aqueous media. The preparation of such stabilisers is described for example, in Austrian Patent Specifications Nos. 328,186 and 320,279 and in British Patent Specifications Nos. 1,108,261 and 1,122,397.

Suitable ethylenically unsaturated monomers which can be copolymerised with the stabiliser include esters of acrylic and methacrylic acid such as the methyl, ethyl, propyl, hydroxyethyl, hydroxypropyl, hydroxybutyl and propylene glycol esters; as well as acrylic acid, methacrylic acid, styrene, p-t-butylstyrene and vinyltoluene.

Crosslinkers suitable for use in the process according to the invention include di- and tri-functional a,ss-olefinically unsaturated compounds such as butanediol diacrylate or dimethylacrylate, 1,6-hexanediol diacrylate or dimethylacrylate, allyl acrylate or methacry late, trimethylolpropane triacrylate or trimethacrylate, and pentaerythritol triacrylate or trimethacrylate. The preferred crosslinkers are the esters of methacrylic acid. Other suitable crosslinkers include divinylbenzene, and allylic compounds such as trimethylbl propane diallyl ether, pentaerythritol triallyl ether, triallylcyanurate, and N,N diallylmelamine. The quantity of crosslinkers employed may range from 0.1 to 10%, preferably 1 to 7%, by weight based on the total weight of monomers used.

Suitable organic solvents are, in particular, aliphatic and aromatic hydrocarbons. But other solvents such as alcohols, esters or ketones may also be used, if desired, as co-solvents.

Non-aqueous polymer dispersions may be prepared according to the present invention by firstly dissolving a stabilising agent in a suitable solvent or solvent blend. The solution is charged to a polymerisation reactor equipped with a stirrer and is heated to reaction temperature under a nitrogen atmosphere. The monomer blend for forming the particle nucleus is added over a period of several hours, the crosslinker being added when at least 20% of the monomer blend has been charged. Preferably the crosslinker is added to the monomers when 50 to 70% of the monomer blend has been added to the batch. The crosslinker may be added later but this is not preferred because it may promote crosslinking between the particles.

The copolymer dispersions prepared in accordance with the invention can be obtained free from coagulates and seeding. The solids content may be as high as 50%. The exhibit an outstanding stability towards most of the solvents. A dispersion prepared with at least 4% of a crosslinker, may be diluted down to a ratio of 1:1 with xylene, butanol, butyl acetate or even acetone without coagulation or precipitation occurring.

Dispersions prepared in accordance with the invention may be further processed with mill bases formed from pigments, in admixture with a blend of a suitable white spirit compatible acrylic resin and a suitable white spirit compatible melamine resin; the dispersions being added to the mill base. The acrylic and melamine resins shduld be compatible with the non-aqueous dispersion. The resin solids ratio of non-aqueous dispersion to mill base resin and melamine resin should be about 30:50:20.

The following examples illustrate the invention. Parts referred to are unless otherwise stated parts by weight.

EXAMPLE 1 Preparation of Stabiliser 678 parts of decylmethacrylate, 284 parts of glycidylmethacrylate, 39.5 parts of t-dodecyl mercaptan, 19.2 parts of azodiiso butyrodinitrile and 962 parts of monoethyleneglycol monoethylether acetate (ethylglycolacetate) are mixed and 1/3 of the blend is charged to a reaction vessel equipped with stirrer, reflux condensor, addition funnel and thermometer while the remaining 2/3 are charged to the feed supply. The reaction vessel is flushed with nitrogen, the batch is heated to 90"C and the further monomers are added over a period of 3 hours.

The batch is held at 90"C for a further 6 hours until a solids content of about 47% is obtained. 0.96 parts of hydroquinone are added to this polymer solution and it is heated to 1200C. At this temperature, a blend of 18.1 parts of methacrylic acid, 1.9 parts of dimethylbenzylamine and 40 parts of ethylglycolacetate is added over a period of 1 hour.

The reaction is continued for 6 hours whereupon, 320 parts of p-t-butylbenzoic acid are added and the batch is held at 1200C for 13 hours, while continuously being stirred. The solution of stabiliser resin obtained has a solids content of 55%.

Preparation of dispersion 77.3 Parts of stabiliser solution are dissolved in a blend of 312 parts of aliphatic white spirit (having a boiling range 100 to 1400C and a content of aromatic hydrocarbons of about 12% by volume) and 78 parts of xylene. 9 Parts of methylmethacrylate, 6 parts of styrene and 1,2 parts of dibenzoyl peroxide (50%) are added and the mass is charged to a reaction vessel as described above. -To the addition vessel a blend of 150 parts of methylmethacrylate, 45 parts of styrene, 75 parts of hydroxyethyl acrylate and 12 parts of dibenzoylperoxide (50%) are charged. To effect polymerisation the reaction batch is provided with a blanket of nitrogen heated to 900C and monomer blend is continuously added over a period of 2 hours. 55 Minutes after commencement of the addition, 11.4 parts of trimethylolpropane trimethylacrylate are added to the monomer blend. After completion of the addition a temperature of 90"C is maintained for a further 2 hours. The stable, coagulate-free and seed-free dispersion has a solids content of 46%, and a viscosity of 90 cP (Brookfield RVT, spindle no. 2, 100 rpm) or 21 s (DIN 53 211).

Comparison Example A The process of Example 1 is repeated except that trimethylolpropanetrimethylacrylate is added to the monomer blend at the beginning.

The dispersion thickens and coagulates after about 1 hour. Under the microscope a mass of connected polymer particles can be seen.

Comparison Example B Using the stabiliser resin of Example 1 a non-aqueous dispersion is prepared as follows: All ingredients mentioned in Example 1 are mixed (raw materials), 1/5 of the blend is charged to a reaction vessel, the vessel is flushed with nitrogen and the batch is heated to 90"C. After about 5 minutes the blend becomes quite turbid indicating that the polymerisation has started. Addition of the remaining 4/5 of the monomer blend is commenced. After 15 minutes the dispersion coagulates. Under the microscope again one can see a mass of polymer particles.

EXAMPLE 2 5 non-aqueous dispersions having different degrees of cross-linking were prepared using the procedure described in Example 1 except that 369 parts of the aliphatic white spirit and 92 parts of xylene were used and that the quantities of trimethylolpropane trimethacrylate are varied as follows: batch 1 2.85 parts batch 2 8.55 parts batch 3 14.25 parts batch 4 28.50 parts batch 5 42.75 parts Dispersions 1 to 3 have roughly the same viscosity and solids contents, as can be seen from the following table.

batch % by weight solids viscosity viscosity crosslinker content cp s (DIN 53 211) on total (Brookfield) monomers 1 1 42 40 14 2 3 42 40 14 3 5 42 46 14.3 4 10 42 3000 not recordable 5 15 strong coagulation agglomera tion Under the microscope, these 3 dispersions show no formation of agglomerates, i.e. there is no interparticular crosslinking, also with the use of higher quantities of crosslinkers. With 10% of crosslinker the viscosity rises to a remarkable extent although the dispersions obtained are substantially free from agglomerates (batch no. 4). At 15% cross-linker strong agglomeration is occurring and the dispersion agglomerates.

Comparison Example C The procedure of Example 2, first batch, is duplicated (1% crosslinker on total monomers), however, the trimethylolpropane trimethacrylate is added to the monomer blend in the addition funnel at the beginning (as in Comparison Example A). The dispersion has a viscosity of 150 cP (Brookfield RVT, spindle no. 3, 100 rpm) or 32 seconds (DIN 53 211) and, under the microscope it shows a strong tendency to agglomeration of the particles. The same batch, with 5.7 parts of trimethylolpropane trimethacrylate (2% on total monomers) thickness and coagulates after a time of addition of 110 minutes. Under the microscope a mass of agglomerated polymer particles can be seen.

EXAMPLE 3 The procedure of example 2 is duplicated, using 11.4 parts of trimethylolpropane trimethylacrylate (4% on total monomers). 11 dispersions are prepared, differing only in the time of addition of the cross-linker. The following table shows the effect of variation of the addition time in the resulting dispersions.

dispersion 1) 2) 3) 4) 5) 1 0 60 2 10 75 3 20 95 4 30 110 5 40 no thi- 110/26 monodisperse thickened ckening with few agglo merates 6 50 44/14 monodisperse 2 % no agglo merates 7 60 41/13 monodisperse 0 no agglo merates 8 70 28/13 slight forma- 0 tion of agglo merates 9 80 43/14 strong forma- 2 % tion of agglo merates 10 90 43/14 strong forma- 3 % tion of agglo merates 11 100 43/14 strong forma- 3 % tion of agglo merates Notes to the table 1) Addition of crosslinker after % by weight of addition 2) coagulation started during polymerisation, in minutes 3) viscosity of the dispersion cP/20 C DIN 53 211 4) observation under the microscope 5) resistance to butanol upon 1:1 dilution Recording of the resistance of the dispersions upon dilution with butanol 1:1 was chosen because butanol is one of the most aggressive solvents for this type of dispersion. The evaluation is made by recording the sedimentation after standing for 8 days.

EXAMPLE 4 Using the stabiliser resin according to Example 1, a dispersion is prepared as follows: 77.3 parts of stabiliser solution are diluted in a blend of 356 parts of the aliphatic white spirit and 89 parts of xylene. 9 parts of methylmethacrylate, 6 parts of styrene and 1.2 parts of dibenzoylperoxide (50%) are added and all is charged to a reaction bessel as described above. To the addition vessel a blend is charged consisting of 150 parts of methylmethacrylate, 45 parts of styrene, 75 parts of hydroxyethylacrylate and 12 parts of dibenzoylperoxide (50%). For polymerising, the charge is blanketed with nitrogen, heated to 90"C, and, over a period of 2 hours, the monomer blend is added continuously. 55 minutes after the commencement of the addition, 11.4 parts of butanedioldimethacrylate are added to the monomer blend in the addition vessel. When the addition is complete a temperature of 90"C is held for a further 2 hours. The stable coagulate-free and seed-free dispersion (42% solids) has a viscosity of 45 cP (Brookfield RVT, spindle no. 2, 100 rpm) or 15 seconds (DIN 53 211).

EXAMPLE 5 The procedure of Example 4 is repeated except that, as crosslinker, 11.4 parts of 1 ,6-hexanedioldiacrylate are used instead of butanedioldimethacrylate. A 42% solids dispersion, seed-free, with a viscosity of 45 cP (Brookfield RVT, spindle no. 2, 100 rpm) or 15 seconds (DIN 53 211) is obtained. Under the microscope the dispersion shows no formation of agglomerates.

EXAMPLE 6 The procedure of Example 4 is followed except that, as crosslinker, 2.85 parts of trimethylolpropanediallylether are used in place of 11.4 parts of butanedioldimethacrylate.

An about 42% solids dispersion is obtained, seed-free, with a viscosity of about 12 seconds (DIN 53 211).

EXAMPLE 7 The procedure of Example 6 is followed, except that as crosslinker, pentaerythritoltriallyl ether or N,N-diallylmelamine or divinylbenzene are used. In all three cases the same results.

are obtained as in Example 6.

Preparation of a paint 27.6 parts by weight of titantium dioxide (Rutile type) are mixed with 19.4 parts by weight of the mill base resin (71 %1)) and passed over a triple roll mill. The mill base is mixed with 11.5 parts melamine formaldehyde resin 2) and diluted with 6.8 parts of xylene, and 30 parts by weight of the dispersion are added with stirring (46%, prepared according to Example 1) together with 0.2 parts of a paint additive based on a polysiloxane modified with monoethyleneglycol. The paint thus prepared is adjusted to a viscosity of 18 to 20 seconds (DIN 53 211, 20"C) with an aromatic solvent, sprayed onto steel panels and cured at 135"C for 30 minutes.

The obtained dry film thickness with two passes of the spray gun, crosswise is about 60cm, without sagging or "cissing".

gloss: > 100% (Lange 45 ) white spirit resistance: 5 minutes Notes 1) The mill base resin used is a copolymer from 12 parts of methacrylic acid, 10 parts of methylmethacrylate, 10 parts of ethylacrylate, 10 parts of styrene, 24 parts of 2ethylhexylacrylate, 24 parts of butylacrylate, 20 parts of hydroxyethylacrylate and 2 parts of tert. dodecylmercaptan, prepared in a hydrocarbon solvent with a content of aromatic hydrocarbons of about 97% by volume (ASTM D 1319) and a boiling range of from 160 to 1800C (ASTM D 1078/86) 2) The melamine resin used is a melamine formaldehyde condensate, containing 5.2 moles of formaldehyde, 42% of which are etherified with isobutanol.

WHAT WE CLAIM IS: 1. A process for the production of a non-aqueous dispersion by polymerisation of a, -ethylenically unsaturated monomers in a non-aqueous medium, which process comprises (i) adding a mixture of from 20 to 80% by weight of the total monomer to be polymerised and a polymerisation catalyst to a solution of a dispersion stabiliser in a non-aqueous liquid dispersion medium and polymerising the monomer to form dispersed polymer particles and (ii) adding a mixture of crosslinking agent and the remainder of the monomer to be polymerised to the reaction mass and completing the polymerisation simultaneously with crosslinking taking place within the cores of the dispersed particles, substantially no crosslinking of the particles with each other taking place.

2. A process as claimed in claim 1 wherein, in step (i), from 50 to 70% by weight of the total monomer to be polymerised is added to the solution of stabiliser.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. spirit and 89 parts of xylene. 9 parts of methylmethacrylate, 6 parts of styrene and 1.2 parts of dibenzoylperoxide (50%) are added and all is charged to a reaction bessel as described above. To the addition vessel a blend is charged consisting of 150 parts of methylmethacrylate, 45 parts of styrene, 75 parts of hydroxyethylacrylate and 12 parts of dibenzoylperoxide (50%). For polymerising, the charge is blanketed with nitrogen, heated to 90"C, and, over a period of 2 hours, the monomer blend is added continuously. 55 minutes after the commencement of the addition, 11.4 parts of butanedioldimethacrylate are added to the monomer blend in the addition vessel. When the addition is complete a temperature of 90"C is held for a further 2 hours. The stable coagulate-free and seed-free dispersion (42% solids) has a viscosity of 45 cP (Brookfield RVT, spindle no. 2, 100 rpm) or 15 seconds (DIN 53 211). EXAMPLE 5 The procedure of Example 4 is repeated except that, as crosslinker, 11.4 parts of 1 ,6-hexanedioldiacrylate are used instead of butanedioldimethacrylate. A 42% solids dispersion, seed-free, with a viscosity of 45 cP (Brookfield RVT, spindle no. 2, 100 rpm) or 15 seconds (DIN 53 211) is obtained. Under the microscope the dispersion shows no formation of agglomerates. EXAMPLE 6 The procedure of Example 4 is followed except that, as crosslinker, 2.85 parts of trimethylolpropanediallylether are used in place of 11.4 parts of butanedioldimethacrylate. An about 42% solids dispersion is obtained, seed-free, with a viscosity of about 12 seconds (DIN 53 211). EXAMPLE 7 The procedure of Example 6 is followed, except that as crosslinker, pentaerythritoltriallyl ether or N,N-diallylmelamine or divinylbenzene are used. In all three cases the same results. are obtained as in Example 6. Preparation of a paint 27.6 parts by weight of titantium dioxide (Rutile type) are mixed with 19.4 parts by weight of the mill base resin (71 %1)) and passed over a triple roll mill. The mill base is mixed with 11.5 parts melamine formaldehyde resin 2) and diluted with 6.8 parts of xylene, and 30 parts by weight of the dispersion are added with stirring (46%, prepared according to Example 1) together with 0.2 parts of a paint additive based on a polysiloxane modified with monoethyleneglycol. The paint thus prepared is adjusted to a viscosity of 18 to 20 seconds (DIN 53 211, 20"C) with an aromatic solvent, sprayed onto steel panels and cured at 135"C for 30 minutes. The obtained dry film thickness with two passes of the spray gun, crosswise is about 60cm, without sagging or "cissing". gloss: > 100% (Lange 45 ) white spirit resistance: 5 minutes Notes 1) The mill base resin used is a copolymer from 12 parts of methacrylic acid, 10 parts of methylmethacrylate, 10 parts of ethylacrylate, 10 parts of styrene, 24 parts of 2ethylhexylacrylate, 24 parts of butylacrylate, 20 parts of hydroxyethylacrylate and 2 parts of tert. dodecylmercaptan, prepared in a hydrocarbon solvent with a content of aromatic hydrocarbons of about 97% by volume (ASTM D 1319) and a boiling range of from 160 to 1800C (ASTM D 1078/86) 2) The melamine resin used is a melamine formaldehyde condensate, containing 5.2 moles of formaldehyde, 42% of which are etherified with isobutanol. WHAT WE CLAIM IS:

1. A process for the production of a non-aqueous dispersion by polymerisation of a,ss-ethylenically unsaturated monomers in a non-aqueous medium, which process comprises (i) adding a mixture of from 20 to 80% by weight of the total monomer to be polymerised and a polymerisation catalyst to a solution of a dispersion stabiliser in a non-aqueous liquid dispersion medium and polymerising the monomer to form dispersed polymer particles and (ii) adding a mixture of crosslinking agent and the remainder of the monomer to be polymerised to the reaction mass and completing the polymerisation simultaneously with crosslinking taking place within the cores of the dispersed particles, substantially no crosslinking of the particles with each other taking place.

2. A process as claimed in claim 1 wherein, in step (i), from 50 to 70% by weight of the total monomer to be polymerised is added to the solution of stabiliser.

3. A process as claimed in claim 1 or claim 2 wherein the crosslinking agent is a di- or

tri-functional a,ss-olefinically unsaturated compound.

4. A process as claimed in claim 3 wherein the crosslinking agent is an ester of acrylic or methacrylic acid.

5. A process as claimed in claim 4 wherein the crosslinking agent is trimethylolpropane trimethacrylate.

6. A process as claimed in any of the preceding claims wherein from 0.1 to 10% by weight of cross-linking agent based on the total weight of monomers is employed.

7. A process as claimed in claim 6 wherein from 1 to 7% by weight of cross-linking agent are employed.

8. A process as claimed in claim 1 substantially as described herein

9. A process as claimed in claim 1 substantially as described herein with reference to Examples 1-7.

10. A non-aqueous dispersion whenever prepared by a process as claimed in any of the preceding claims.