WO2004013184A2

WO2004013184A2 - A process for preparing beads

Info

Publication number: WO2004013184A2
Application number: PCT/IB2003/003410
Authority: WO
Inventors: Silvia Banfi; Fabio Giberti; Dario Giudici; Umberto Moschetti; Giampiero Serri
Original assignee: Cray Valley SA
Current assignee: Cray Valley SA
Priority date: 2002-08-01
Filing date: 2003-07-25
Publication date: 2004-02-12
Anticipated expiration: 2005-02-01
Also published as: ITMI20021732A1; WO2004013184A3

Abstract

A polymerization process in aqueous suspension of acrylic and/or vinylic monomers to obtain beads having a diameter from about 2 micron to about 80 micron, wherein radical initiators soluble in the monomer and a suspending agent in an amount in the range 0.02%-6% by weight, with respect to the continuous phase (water), are used, wherein : the polymerization in aqueous phase is carried out in the presence of a surfactant in an amount from 1 to 10,000 ppm, with respect to the continuous phase ; the ratio between the continuous phase and the discontinuous phase (monomer mixture) is in the range 1.3:1 - 8:1.

Description

A PROCESS FOR PREPARING BEADS.

The present invention relates to a process for preparing acrylic or vinylic polymer beads, preferably acrylic, having sizes from 2 to 80 micron, to be used particularly as antireflection agents to obtain a mat effect for paints, photographic applications, inks, plastic sheets, for example calendered or extruded, or to be used as lubricating or opacifying agents in cosmetics.

More specifically, the invention relates to a process for preparing acrylic or vinylic polymer beads preferably having sizes from 2 to 60 micron and more preferably lower than 30 micron, having improved productivity and yields and lower by-products which must then be disposed, lower encrustations in industrial reactors and therefore lower plant stops for maintenance and lower content of residual monomers in the final beads .

It is known in the prior art, see EP 457 356, a polymerization process in aqueous suspension of acrylic monomers in the presence of suspending agents having formula :

R₂

CH₂ = C CO A - C - CH₂ - S0₃ M⁺ (I)

R_l R₃

wherein : Ri is H or CH₃ ; R₂ and R₃, equal or different, are H or Ci-Cs alkyl, optionally branched ; M is an alkaline or alkaline-earth metal or ammonium and A is NH, 0 or NCH₃. With said process, see the Examples ^'reported in said patent, beads having a size from 100 to 1,000 micron can be obtained. By said process, it is therefore not possible to obtain beads having sizes lower than 100 micron.

EP 683 182 describes a polymerization process in aqueous suspension of acrylic monomers in the presence of the same suspending agents of EP 457 356, wherein the aqueous phase is totally or partially formed by mother liquors coming from a previous polymerization of acrylic monomers. By the process of said patent, it is possible to obtain beads having a size from 30 to 100 micron, in function of the percentage of mother liquors with respect to the total of the aqueous phase. For example, when there is a 100% recycle, it is possible to obtain beads having average sizes from 30 to 50 micron. By working on the contrary with a percentage of mother liquors from 30 to 50% with respect to the total of the aqueous phase beads having sizes from 200 to 300 micron are obtained. Tests carried out by the Applicant have shown that it is not possible to obtain with said process beads having average sizes lower than 30 micron, even using a ratio by weight water/monomers 8:1. Besides, by using said ratio there is the drawback to reduce the process productivity and to considerably increase the residual monomer content in the final product. To obtain with said process beads having a diameter from > 50 micron to < 80 micron, the Applicant has found that it is necessary to use ratios by weight water/monomers at least of 3.5:1 or higher. With said process, by reducing the sizes of the obtained beads, there is a parallel decrease of the productivity. Furthermore, it has been found by the Applicant that the beads obtained with said process have not the sizes required for the applications in the photographic and cosmetic field. Besides, the processability of said beads in extrusion requires particular precautions since the beads contain significant amounts of residual monomers which develop vapours during the extrusion. To avoid said drawback, it is necessary to pre-treat the beads before the use or the extrusion. This has the drawback to need supplementary units in the industrial plant.

The need was felt to have available a process for the preparation of beads having sizes from 2 micron to 80, preferably from 2 to 60 micron and more preferably lower than 30 micron, by using a process having a higher productivity. More specifically, it would be desirable to have available a polymerization process in aqueous suspension having the following combination of advantages in comparison with the processes described in the prior art : substantially the same productivity but lower consumption of suspending agent ; or improved productivity, at equal consumption of the suspending agent ; - lower amount of polymerization by-products, which remain in the aqueous phase and which are removed in the successive steps to separate the final products ; said by-products are for example the following : beads having sizes lower than 1 micron, also known as the polymer fraction which remains in the mother liquors under the form of emulsified particles, suspending agents present in the aqueous phase to be removed, etc ... ; - lower encrustations in the reactors and therefore shorter times of plant stop, the product obtained being the same. An object of the invention is a polymerization process in aqueous suspension of acrylic and/or vinylic monomers to obtain beads having a diameter from about 2 micron to about 80 micron, preferably from 2 micron to 60 micron and more preferably lower than 30 micron, wherein radical initiators soluble in the monomer and a suspending agent in an amount in the range 0.02%-6% by weight, preferably 0.05%-3% by weight with respect to the continuous phase (water) , are used, wherein : - the polymerization in aqueous phase is carried out in the presence of a surfactant in an amount from 1 to 10,000 ppm, preferably from 20 to 5,000 ppm and more preferably from 100 to 4,000 ppm with respect to the continuous phase ; - the ratio between the continuous phase and the discontinuous phase (monomer mixture) is between 1.3:1 and 8:1, preferably between 1.5:1 and 5:1 and more preferably from 2/1 to 4/1.

The suspending agents which can be used are for example one or more of the following : a) homopolymers of compounds having formula :

R₂

CH₂ = C - CO - A - C - CH₂ - S0₃~ M⁺ (I)

Ri R₃

wherein : Ri is H or CH₃ ; R₂ and R₃, equal or different, are H or Ci-Cs alkyl, optionally branched ; M is an alkaline or alkaline-earth metal or ammonium and A is NH, 0 or NCH₃ ; b) copolymers of the formula (I) compounds having no more than 40% by weight of acrylic or vinyl comonomers ; c) polyvinylalcohol (PVA) or vinyl alcohol copolymers, preferably copolymer vinyl alcohol/vinylacetate in molar ratios from 75:25 to 99:1 preferably from 80:20 to 95:5 ; d) hydroxyalkylcellulose, wherein the alkyl comprised from 1 to 5 carbon atoms, preferably from 1 to 3 ; e) (meth) acrylic polyacid or ( eth) acrylic acid copolymers with other acrylic or vinyl monomers, for example methylmethacrylate and/or styrene.

The preferred suspending agents are those of the classes a) , b) and c) and more preferably compounds of class a) and c) .

As surfactants both ionic and those non ionic can be used.

As non ionic surfactants, it can be mentioned mono-, di- and trialkylphenols ethoxylated with number of ethoxy units (EO) comprised between 2 and 50 and C₄-Ci₈ alkyl chains ; ethoxylated fatty alcohols with number of EO units between 3 and 50 and C₈-Ci₈ alkyl chains, for example Disponil^® LS500 ; Cχ₂-Ci8 ethoxylated alkanols with number of EO units comprised between 4 and 50 ; polyethylenglycols having molecular weight from 350 to 2,000 polyethylenoxide esters with C₈-C₂₄ fat acids, for example polyethylglycolstearate.

Examples of anionic surfactants are the following : ammonium or alkaline metal salts of Cs-C₂ alkyl sulphates ; hemiesters of the sulphuric acid with C₈-Ci₈ ethoxylated alkanols -with number of EO units comprises between 4 and 50, for example Cι₂-C₁₄ fat alcohols ethoxylated sodium sulphate, for example Disponil^® FES 32 IS ; Cs-Cis alkylsulphonic acids such for example sodium lauryl sulphate, 2-ethylhexyl sodium sulphate ; or alkylarylsulphonic acids with 6 carbon atoms of the aromatic ring and C₉-Cι₈ alkyl chains ; alkaline, alkaline- earth metal or ammonium salts of Cg-C₂ι carboxylic acids.

Examples of cationic surfactants are the Cs-Cι₈ primary, secondary or tertiary fat amines, wherein the other alkyls are C₁-C₄ ; said amines salified with strong inorganic acids or strong organic acids ; or said amines are salified by addition to the nitrogen of alkyl halides such as for example methylchloride.

Preferably, when the suspending agents a) and/or b) are used, the surfactant is non ionic and more preferably ethoxylated fatty alcohols with number of EO units between 3 and 50 and Ce-Cis alkyl chains.

Preferably, when c) is used as only suspending agent, the surfactant is anionic.

A more preferred combination is a suspending agent of class a) with a surfactant being selected from ethoxylated fatty alcohols with number of EO units between 3 and 50 and C₈~Ci8 alkyl chains or a suspending agent of class c) with a surfactant being anionic.

The acrylic comonomers of the suspending agents mentioned in b) can be selected for example from the following : (meth) acrylamide ; (meth) acrylic acid under the form of the corresponding alkaline salts, for example sodium or potassium or alkaline-earth, for example calcium or magnesium ; esters of the (meth) acrylic acid with C₁-C₄ linear or branched aliphatic alcohol (for example ethanol, methanol, propanol) , (meth) acrylonitrile, C1-C4, linear or branched hydroxyesters of the (meth) acrylic acid such for example hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate .

Among the vinyl monomers of the suspending agents indicated in b) , the following can be mentioned : vinylaromatic monomers, as styrene and derivatives thereof obtained by substituting one or more hydrogen atoms of the aromatic ring with one hydroxyl or one methyl and/or- of vinyl with a methyl, for example α-methylstyrene ; Cι-Cι₂ alkyl vinylethers, such as methyl-, ethyl-, n-propyl-, isopropyl-, n-butyl-, isobutyl- and 2-ethylhexyl-vinyl ether ; vinyl esters of Ci-Cis aliphatic monocarboxylic acids, as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl hexanoate, vinyl 2-ethyl-hexanoate, vinyl decanoate, vinyl laurate and vinyl stearate. The monomers which can be polymerized by the present invention process can be selected from the following : acrylic monomers, for example Cι-Cχ₂ alkyl

(meth) acrylates, wherein the alkyl can be linear or branched, such for example methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl

(meth) acrylate, butyl (meth) acrylate, sec-butyl

(meth) acrylate, terbutyl (meth) acrylate, 2-ethylhexyl

(meth) acrylate, lauryl (meth) acrylate ; (meth) acrylic acid ; C₁-C4, linear or branched hydroxyesters of the (meth) acrylic acid, methacrylamide ; vinyl monomers, for example styrene and derivatives thereof, such for example methyl- and ethyl-styrene, wherein the alkyl group is in the ortho or para position ; alpha methylstyrenes ; mono-, di-, tri-, tetra-, penta-halogenstyrenes, wherein the halogen is Cl, F ; vinyl-ethers CH₂=CH-[ 0- (CH₂) _n] _m-OR wherein n is from 1 to 4, m from 1 to 10 and R is H, CH₃, for example ethylenglycolvinylether .

Mixtures of acrylic and/or vinyl monomers can also be used. It is also possible to use the invention monomers, alone or in admixture with each other, in admixture with other comonomers containing double bonds, polymerizable by radical route, the amount of said comonomers being up to

50% by weight in the monomeric mixture, such for example

(meth) acrylonitrile, n-alkyl or aryl maleimides, butadiene. ^•

The invention beads can optionally be crosslinked. To obtain crosslinked beads, the initial monomer mixture contains also crosslinking comonomers which contain more than one polymerizable group, preferably at least two double bonds, in amounts from 0.01% to 25%, preferably from 0.1% to 20% by weight with respect to the total amount of the monomers. Examples of said crosslinking comonomers are allyl (meth) acrylate, diallyl maleate, diallyl phthalate, diallyl fumarate, triallyl cyanurate, ethylenglycol di (meth) acrylate, di-, tri~, tetraethylenglycol di (meth) acrylate, 1,3- 1,4- butylenglycol di (meth) acrylate, divinylbenzene, trivinylbenzene, ^• etc ...

As radical initiators, those soluble in the monomeric organic phase can be used, such for example both aliphatic and aromatic peroxides, such for example t-butylperoxy-2- ethyl-hexanoate, dibenzoylperoxide, benzoylperoxide, laurylperoxide, t-butylperoxydiethylacetate or unstable azocompounds such for example azodiisobutyronitrile. Preferably, the polymerization aqueous phase can be at least partially formed by mother liquors obtained from a polymerization process in suspension of a monomer polymerizable by radical route, preferably an acrylic monomer, even different from those used in the process. With mother liquors obtained from a polymerization process in aqueous suspension, it is meant the aqueous phase which remains after separation of the (co) polymer beads, which is for example obtained by centrifugation or filtration.

Said aqueous phase, or polymerization mother liquors, contains in suspension an organic phase formed by the suspending agent and by polymer compounds present in the form of polymer fractions under the form of emulsified particles, not separable with the techniques usually employed to recover the polymerization product. The solid contained in the mother liquors is determined as dry residue. Said residue is generally in the range 0.05-5% by weight, preferably 0.05-1.5%. On the residue, it is possible to determine the amount of suspending agent and of polymer as indicated in the methods described hereinafter.

The mother liquors can come from a polymerization process of acrylic or vinyl monomers, therefore to the mother liquors the above surfactant amount is to be added. If the mother liquors derive from a polymerization process according to the present invention, optionally fresh surfactant is added to bring the concentration to the desired values.

In the monomer mixture, also a chain transfer agent can optionally be used. The amount of said compounds is from 0 to 3% by weight, preferably from 0 to 1% by weight with respect to the monomeric mixture. Mercaptan compounds, as mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid, mercaptopropionic acid, butylmercaptan, n-dodecylmercaptan can for example be mentioned.

The polymerization temperatures are those at which the initiator decomposition takes place and they are generally in the range 50°C-120°C.

It has been surprisingly and unexpectedly found by the Applicant that by using as aqueous phase the mother liquors of a previous acrylic polymerization process, at equal concentration of the suspending agent a) , by the process according to the present invention, it is possible to significantly reduce the aqueous phase/monomers ratio obtaining, substantially with the same yields, beads having the same sizes of the process of the prior art but with a much lower amount of encrustations in the reactor and a lower amount of residual monomers.

When a type c) suspending agent, such as for example PVA, is used to have beads with the same diameter of those obtained with the invention process, according to the processes of the prior art, it is necessary to use a more than double amount of the type c) suspending agent.

Furthermore, it has been found by the Applicant that with the same type and amount of suspending agent, of suspending phase, of monomeric phase and of suspending phase/monomeric phase ratio, by the present invention process, it is possible to obtain beads having a diameter lower than that of the beads obtained with the processes of the prior art.

As said, the beads obtained with the present invention process can be used as antireflection agents to obtain a mat effect for paints, photographic applications, inks, plastic sheets, for example calendered or extruded, or as lubricating or opacifying agents in cosmetics. As paints, the paints on the market, based both on solvent and water paints are used.

As plastics for antireflection sheets, acrylic sheets, in polycarbonate, PVC, polyesters as PET, PBT, etc... can be mentioned.

As lubricating and/or opacifying agents in cosmetics, the beads obtained with the present invention process having a diameter lower than 15 micron can be used, in formulations such as for example, lipsticks, foundation creams, face powders.

The following examples illustrate the invention for non limitative purposes.

Examples

Determination of the dry part of the mother liquors

A sample is drawn from the mother liquors having a weight between 2 g and 10 g and it is evaporated at 160 °C until a constant weight.

Determination of the suspending agent PAMS and/or PVA (+ optional surfactant) and of the polymer fraction contained in the mother liquors under the form of emulsified particles The dry extract is suspended in dichloromethane in a ratio by weight 1:50. The suspension is stirred for one hour and the soluble fraction is separated from the insoluble residue.

The insoluble residue weight corresponds to the added suspending agent amount. By evaporating the organic phase, a residue is obtained corresponding to the polymer fraction contained in the mother liquors under the emulsion form.

One attains the percentage by weight taking into account the considered weight of the mother liquors.

Determination of the encrustation amount in the reactor

At the end of the polymerization, after discharging the reactor, the reactor inside is washed with water. In the presence of encrustations on the reactor walls and/or on the stirrer and on the baffle, an organic solvent such for example acetone or dichloromethane is introduced in the reactor, after having completely removed the washing water, stirring until the encrustation detachment, the reactor is discharged, the solvent is completely evaporated and the obtained solid is weighed. The weight is referred to the initial monomeric phase weight.

Determination of the residual monomers in the obtained product

The residual monomers are determined according to the gaschromatography method by the ISO 2561:1974 standard, and the respective amounts expressed in ppm.

Example 1

Preparation of the suspending agent (PAMS)

120 parts by weight of a NaOH solution 40% by weight and 610 parts by weight of deionized water are fed into a reactor. 250 parts by weight of 2-acrylamido-2 methylpropansulphonic acid (AMPS) are slowly fed. The pH is adjusted between 7 and 8 with small amounts of soda or AMPS. After the solution has been fluxed with nitrogen to remove the oxygen and heated to 50°C, 0.075 parts by weight of K₂S₂O_g and 0.025 parts by weight of Na₂S₂0s are added. The polymerization is total in about 60 minutes. Then, it is diluted with 400 parts of deionized water obtaining a solution with a dry residue (PAMS) at 160 °C of 5.5% by weight and a Brookfield viscosity determined at 25°C of 4 Pa.s.

Example 2 Polymerization in suspension of methylmethacrylate and ethyl acrylate using as suspending agent the homopolymer of the sodic salt of the 2-acrylamido-2- methylpropansulphonic acid of Example 1.

In a 10 litre reactor, equipped with stirrer, with thermal exchange jacket and resistant to pressure,

193 parts by weight of deionized water and 5.45 parts by weight of the solution of Example 1, corresponding to

0.300 parts by weight of dry product (0.151% by weight with respect to the aqueous phase) are fed. The oxygen is removed with a nitrogen flow and the solution is heated to

80°C.

In the reactor, 100 parts by weight of a mixture, from which the oxygen has been previously removed, are fed, formed by 96 parts by weight of methylmethacrylate (MMA) , 4 parts by weight of ethyl acrylate (AE) ,

0.25 parts by weight of t-butylperoxy-2-ethylhexanoate,

0.12 parts by weight of n-butan-thiol.

The reactor is sealed and pressurized at 100 kPa.

Under continuous stirring, the mixture is gradually heated up to 110 °C in 120' . The temperature of 110 °C is maintained in the reactor for 15 minutes and then it is cooled. The obtained polymer is separated from the mother liquors by centrifugation under the form of beads, which are collected, washed with distilled water and then dried in a stove at 80 °C.

The mother liquors have a dry residue of about 0.6% by weight. The suspending agent forms the 0.15% by weight of the mother liquors. By difference, it is calculated that beads lower than 1 micron (emulsions) constitute the 0.45%.

Example 3 (comparative)

Preparation of beads having antireflection properties with a diameter of 24 μm according to the prior art, using PVA as suspending agent In the same reactor used in Example 2, a suspending solution is fed formed by 244.5 parts by weight of demineralized water, 5.5 parts by weight of polyvinyl alcohol (PVA) (2.2% by weight with respect to the aqueous phase) . The solution is put under mechanical stirring and it is stabilized at the temperature of 35 °C. Apart the monomeric mixture is prepared, formed by 96 parts by weight of MMA, 4 parts by weight of AE, 0.5 parts by weight of benzoylperoxide (BPO, radical initiator) . The aqueous phase/monomers ratio (WMR) results therefore to be be 2.5/1. The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the polymerization waters and from the emulsions, which form together the mother liquors, by centrifugation at 5,000 rp for 15 minutes. The obtained beads have a diameter of 24 μm. The reaction yield is 85.2%. The dry residue of the mother liquors (polymerization by-products to be disposed, equal to 20.4 parts by weight) is equal to 7.7%, of which 2.08% is formed by the suspending agent and 5.62% by the polymer fraction contained in the mother liquors under the emulsion form, calculated on the basis of the initial charge.

Example 4

Preparation of beads having antireflection properties with a diameter of 24 μm according to the invention, using as suspending agent PVA and an anionic surfactant.

In the same reactor used in Example 2, a suspending solution is fed, formed by 247.3 parts by weight of demineralized water, 2.5 parts by weight of PVA (1% by weight with respect to the aqueous phase). 0.2 parts by weight of Mersolat^® H (sodium dodecylsulphate) (800 ppm with respect to the aqueous phase) are added. The solution is put under mechanical stirring and it is stabilized at the temperature of 35°C. Apart a monomeric mixture equal to that of Example 3 is prepared (96 parts by weight of MMA, 4 parts by weight of AE, 0.5 parts by weight of BPO). The aqueous phase/monomers ratio (WMR) results therefore to be 2.5/1. The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the polymerization waters and from the emulsions, which form together the mother liquors, by centrifugation at 5,000 rpm for 15 minutes. The obtained beads have a diameter of 24 μm. Reaction yield : 91.8%. The dry residue of the mother liquors is equal to 4.23% (equal to 10.93 parts by weight), of which 1.05% is formed by the suspending agent + surfactant and 3.18% by the polymer fraction contained in the mother liquors under the form of emulsified particles, calculated on the basis of the initial charge. The obtained data show that, by the invention process, beads can be obtained having the same sizes as those of the process of the prior art with improved yields and lower consumption of suspending agent. Besides, the parts by weight of the polymerization by-products to be disposed result a half with respect to the comparative Example 3.

Example 5 (comparative)

Preparation of beads according to EP 683 182 (diameter 50 μm) using as polymerization aqueous phase the mother liquors of a previous polymerization (Example 2) .

400 parts by weight of the mother liquors of Example 2 (0.15% by weight of PAMS in the aqueous phase) are introduced in the same reactor used in the previous Examples. The solution is put under mechanical stirring and it is heated at 50 °C. Apart the monomeric mixture is prepared formed by 75 parts by weight of MMA, 25 parts by weight of styrene, 0.5 parts by weight of BPO (radical initiator) . The aqueous phase/monomers ratio (WMR) results therefore to be 4/1 (amount of suspending agent 0.6 parts by weight) . The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the polymerization waters by centrifugation as described in Example 4. The obtained beads have a diameter of 50 μm. Reaction yield : 95.59%, calculated by considering also the polymer fraction present in the initial mother liquors under the form of emulsified particles. The mother liquor residue is equal to 1.22% by weight (equal to 4.91 parts by weight), of which 0.15% is formed by the suspending agent and 1.07% by the polymer fraction contained in the mother liquors under the form of emulsified particles, calculated on the basis of the initial charge. The weight of the encrustations formed inside the reactor is equal to 0.2% with respect to the weight of the initial monomeric phase + the polymer fraction present in the initial mother liquors under the form of emulsified particles.

The amount of residual monomers in the obtained product is equal to 8,000 ppm.

Example 6

Preparation of beads according to the invention (diameter 50 μm) by using as polymerization aqueous phase the mother liquors of a previous polymerization (Example 2), additioned with non ionic surfactant. 199.8 parts by weight of recycle waters coming from Example 2 containing 0.15% by weight of PAMS and 0.2 parts by weight of non ionic surfactant (mixture of ethoxylated C₁₂-C₁₄ fats alcohols Disponil^® LS 500, equal to 1,000 ppm of surfactant with respect to the aqueous phase) are introduced in the reactor used in the previous Examples. Under stirring, the aqueous phase is heated to 50 °C. Apart the monomeric mixture is prepared, formed by 75 parts by weight of MMA, 25 parts by weight of styrene, 0.5 parts by weight of BPO (radical initiator) . The aqueous phase / ^• monomers ratio (WMR) is 2/1 (amount of suspending agent 0.3 parts by weight). The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation as described in Example 4. The obtained beads have a diameter of 50 μm. Reaction yield : 97.46%. The residue of the centrifugation waters is equal to 1.40% by weight (equal to 2.82 .parts by weight), of which 0.25% is formed by the suspending agent and 1.15% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

The weight of the encrustations formed inside the reactor is equal to 0.05% with respect to the weight of the initial monomeric phase + the polymer fraction present in the initial mother liquors under the form of emulsified particles.

The residual monomer amount is equal to 6,000 ppm. This Example shows that by the invention process, it is possible to reduce the water/monomers ratio, increasing the plant productivity for each polymerization batch since it is possible to increase in the reactor the monomeric phase with respect to the aqueous phase. At equal volume used for the polymerization, and considering the respective reaction yields in the Examples 5 (comparative) and 6, one can calculate that the productivity increase is higher than 60%.

Besides, both the encrustations formed in the reactor and the residual monomers in the obtained product are in lower amounts than those corresponding to the Example 5 (comparative) . The amount of the polymerization by-products which are to be disposed, is about half of that of Example 5 (comparative) , considering that the water used in Example 6 of the invention is half of that of the Example 5 (comparative) , at equal monomer feeding in polymerization.

Example 7 (comparative) 5 Preparation of beads according to EP 457 356 (diameter 80 μm) using in polymerization an aqueous solution containing PAMS as suspending agent.

In the reactor used in the previous Examples, a suspending solution is fed, formed by 256.36 parts by

10 weight of demineralized water and 43.64 parts by weight of solution of the suspending agent PAMS prepared in Example 1, equal to 2.4 parts by weight of PAMS (0.8% by weight of PAMS with respect to the aqueous phase) . Said solution is put under stirring and heated to 50 °C. Apart the monomeric

15 mixture is prepared formed by 100 parts by weight of MMA, 0.2 parts by weight of chain transfer agent (butanthiol) , 0.5 parts by weight of BPO. The aqueous phase/monomers ratio (WMR) results therefore to be 3/1. The monomeric mixture is fed to the reactor, then it is heated as

20 described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the polymerization waters by centrifugation as described in Example 4. The obtained beads have a diameter of 80 μm. Reaction yield : 99.8%. The residue of

25 the centrifugation waters is 0.86%, of which 0.8% is formed by the suspending agent and 0.06% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge. The encrustations in the reactor are insignificant.

•30 Example 8

Preparation of beads according to the invention (diameter 35 μm) wherein in the polymerization aqueous phase the solution of the suspending agent PAMS of Example 1 and a non ionic surfactant is used.

In the same reactor used in the previous Example, a suspending solution is fed, formed by 255.76 parts by weight of demineralized water and 43.64 parts by weight of solution of the suspending agent PAMS prepared in Example 1, equal to 2.4 parts by weight of PAMS (0.8% by weight of

PAMS with respect to the aqueous phase) and 0.6 parts by weight of non ionic surfactant used in Example 6

(Disponil^® LS500), equal to 2,000 ppm with respect to the aqueous phase. The solution is put under mechanical stirring and heated at 50 °C. Apart the monomeric mixture equal to that used in Example 7 (100 parts by weight of

MMA, 0.2 parts by weight of chain transfer agent

(butanthiol), 0.5 parts by weight of BPO) is prepared. The aqueous phase/monomers ratio (WMR) is 3/1. The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the polymerization mother liquors as described in Example 4. The obtained beads have a diameter of 35 micron. Reaction yield : 99.4%. The dry residue of the mother liquors is equal to 1.20% of which 1.00% is formed by PAMS + surfactant and 0.20% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge. The encrustations in the reactor are insignificant.

The Example shows that under the same conditions with the process of the prior art (Example 7 (comparative) ) by the invention process beads having notably lower sizes are obtained.

Example 9 (comparative) Preparation of antireflection PMMA beads having a diameter of 21.7 μm according to the prior art, using PVA as suspending agent

In the reactor used in the previous Examples, a suspending solution is fed, formed by 392 parts by weight of demineralized water and 8 parts by weight of PVA, equal to 2% by weight of PVA with respect to the aqueous phase. Under mechanical stirring, the temperature is brought to 35 °C. Apart the monomeric mixture formed by 100 parts by weight of MMA, 0.2 parts by weight of chain transfer agent (butanthiol), 0.5 parts by weight of BPO is prepared. The aqueous phase/monomers ratio (WMR) results therefore to be 4/1. The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation as described in Example 4. The obtained beads have a diameter of 21.7 μm. Reaction yield : 85.7%. The dry residue obtained from the mother liquors is equal to 5.40%, of which 1.93% is formed by the suspending agent and 3.47% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

Example 10 Preparation of antireflection beads according to the invention having a diameter of 13.6 μm, wherein in the polymerization aqueous phase PVA as suspending agent + an anionic surfactant is used

In the same reactor used in Example 9, a suspending solution is fed, formed by 391.6 parts by weight of demineralized water, 8 parts by weight of PVA (equal to 2% by weight of PVA with respect to the aqueous phase) and 0.4 parts by weight of anionic surfactant (mixture of ethoxylated fat alcohol sulphates sodium salt Disponil^® FES 32 IS), equal to 1,000 ppm with respect to the aqueous phase. The solution is put under mechanical stirring and it is stabilized at the temperature of 35 °C. A monomeric mixture equal to that of Example 9 (comparative) is used

(100 parts by weight of MMA, 0.2 parts by weight of chain transfer agent (butanthiol), 0.5 parts by weight of BPO). The aqueous phase/monomers ratio (WMR) results therefore to be 4/1. The monomeric structure is fed to the reactor, then it is heated and the polymerization is allowed to take place as described in Example 2. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation. The obtained beads have a diameter of 13.6 μm. Reaction yield : 83.22%. The dry residue of the mother liquors is 6.06% by weight, of which 2.02% is formed by the suspending agent + surfactant and 4.04% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

The Example shows that under the same conditions of the process of the prior art (Example 9 (comparative) ) , with the invention process, beads having lower sizes are obtained. Example 11 (comparative)

Preparation of antireflection PMMA beads having a diameter of 13.8 μm according to the prior art, using PVA as suspending agent In the reactor used in the previous Examples, a suspending solution is fed, formed by 382 parts by weight of demineralized water and 18 parts by weight of PVA, equal to 4.5% by weight of PVA with respect to the aqueous phase. Under mechanical stirring, the temperature is brought to 35 °C. Apart the monomeric mixture equal to that of Example 9 is prepared. The aqueous phase/monomers ratio (WMR) is 4/1. The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the mother liquors by^' centrifugation at 5,000 rpm in 35 minutes, since in the time of 15 minutes, used in the previous Examples, there is only a partial separation of the beads from the mother liquors. The obtained beads have a diameter of 13.8 μm. Reaction yield : 82.59%. The dry residue obtained from the mother liquors is equal to 8.50%, of which 4.31% is formed by the suspending agent and 4.19% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

Example 11 (comparative) shows that by using the process of the prior art as described in Example 9

(comparative) , to obtain beads having the same sizes as those of the previous Example 10 according to the invention, it is necessary to use a PVA amount more than double than that of the Example 9 (comparative) , with an increase of the production costs and greater difficulty of separation of the obtained beads from the mother liquors.

Example 12 (comparative) Preparation of beads according to EP 683 182 (diameter 31.5 μm) , by using as polymerization aqueous phase the mother liquors of a previous polymerization (Example 2)

In the reactor used in the previous Examples, a suspending solution is fed, formed by 800 parts by weight of mother liquors coming from Example 2, containing 0.6% by weight of PAMS. Under mechanical stirring, the temperature is brought to 50 °C. Apart the monomeric mixture formed by 75 parts by weight of MMA, 25 parts by weight of styrene and 0.5 parts by weight of BPO is prepared. The aqueous phase/monomers ratio (WMR) results therefore to be 8/1 (amount of suspending agent 1.2 parts by weight) . The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation under the conditions of Example 4. The obtained beads have a diameter of 31.5 μm. Reaction yield : 83.17%. The dry residue of the mother liquors is equal to 2.30%, of which 0.15% is formed by the suspending agent and 2.15% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge. The residual monomer amount is equal to 16,000 ppm.

Example 13

Preparation of beads according to the invention process (diameter 21.6 μm) , by using as polymerization aqueous phase the same used in Example 12 (comparative) and adding a non ionic surfactant

In the reactor, a suspending solution is fed, formed by 799.2 parts by weight of mother liquors coming from Example 2, containing 0.6% by weight of PAMS, and 0.8 parts by weight of the non ionic surfactant Disponil^® LS500 used in Example 6, equal to 1,000 ppm with respect to the mother liquors. Under mechanical stirring, the temperature is brought to 50 °C. Apart the same monomeric mixture of Example 12 (comparative) is prepared (75 parts by weight of MMA, 25 parts by weight of styrene and 0.5 parts by weight of BPO). The aqueous phase/monomers ratio (WMR) results therefore to be 8/1 (amount of suspending agent 1.2 parts by weight). The monomeric mixture is fed to the reactor, then it is heated and the polymerization is allowed to take place as described in Example 2. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation as described in Example 4. The obtained beads have a diameter of 21.6 μm. Reaction yield : 81.57%. The dry residue of the mother liquors is 2.60% by weight, of which 0.25% is formed, by the suspending agent + surfactant and 2.35% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

The residual monomer amount is equal to 16,000 ppm. This Example shows that by the invention process it is possible to decrease the particle diameter below the values obtainable by using the process described in Example 12 (comparative) according to EP 683 182.

In fact, by comparing the bead sizes and the amount of residual monomers of the beads obtained in Example 12 (comparative) with those corresponding of the Example 5 (comparative) , it is noticed that by increasing the weight ratio aqueous phase/monomers from 4:1 to 8:1, it is possible to reduce the bead diameter but not below 30 μm. However, operating at said dilution ratios, the amount of the residual monomers doubles, increasing from 8,000 to

16,000.

Example 14 Obtainment of beads having a diameter of 4.9 μm, by the invention process

In a reactor equal to that used in the previous Examples, a suspending solution is fed, formed by 381.6 parts by weight of demineralized water, 16 parts by weight of PVA, equal to 4% by weight of PVA with respect to the aqueous phase, and 0.4 parts by weight of anionic surfactant (mixture of ethoxylated fat alcohol sulphates sodium salts Disponil^® FES 32 IS), equal to 1,000 ppm with respect to the aqueous phase. Under mechanical stirring, the temperature is brought to 35 °C. Apart the monomeric mixture formed by 96 parts by weight of MMA, 4 parts by weight of AE (ethyl acrylate), 0.5 parts by weight of BPO, is prepared. The aqueous phase/monomers ratio (WMR) results therefore to be 4/1. The monomeric mixture is fed to the reactor, then it is heated as described in Example 2 and the polymerization is allowed to take place. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation as described in Example 11 (comparative) . The obtained beads have a diameter of 4.9 μm. Reaction yield : 76.8%. The dry residue of the mother liquors is 9.43% of which 3.89% is formed by the suspending agent 4- surfactant and 5.54% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

By comparing the bead sizes obtained in this Example with those of Example 11 (comparative) , it is noticed that with the same aqueous phase/monomers ratio (WMR) , by the present invention process it is possible to reduce the bead diameter even to values lower than 5 μm.

Example 15 Preparation of beads having a diameter of 46 μm, by using the PAMS aqueous suspension described in EP 457 356, additioned with a non ionic surfactant according to the present invention process

In the reactor used in the previous Examples, a suspending solution is fed, formed by 249 parts by weight of demineralized water, 0.5 parts by weight of PAMS, equal to 0.2% by weight with respect to the aqueous phase, and 0.5 parts by weight of non ionic surfactant used in Example 6 (Disponil^® LS500), equal to 2,000 ppm with respect to the aqueous phase. Under mechanical stirring, the solution is heated to 50 °C. Apart the monomeric mixture formed by 75 parts by weight of MMA, 25 parts by weight of styrene, 0.5 parts by weight of BPO, is prepared. The aqueous phase/monomers ratio (WMR) results therefore to be 2.5/1. The monomeric mixture is fed to the reactor, then it is heated and the polymerization is allowed to take place as described in Example 2. At the reaction end, the product (beads) is separated from the mother liquors by centrifugation as described in Example 4. The obtained beads have a diameter of 46 μm. Reaction yield : 97.02%. The dry residue of the mother liquors is 1.55% by weight, of which 0.35% by weight is formed by the suspending agent + surfactant and 1.20% by the polymer fraction present in the mother liquors as emulsified particles, calculated on the basis of the initial charge.

The Example shows that by using • in the present invention process the PAMS aqueous suspension described in EP 457 356, it is possible to obtain beads having sizes lower than the limit of 100 μm indicated in said patent.

Claims

1. A polymerization process in aqueous suspension of acrylic and/or vinyl monomers to obtain beads having a diameter from about 2 micron to about 80 micron, preferably from 2 micron to 60 micron, wherein radical initiators soluble in the monomer and a suspending agent in an amount in the range 0.02%-6% by weight, preferably 0.05%-3% by weight with respect to the continuous phase (water) , are used, wherein : the polymerization in aqueous phase is carried out in the presence of a surfactant in an amount from 1 to 10,000 ppm, preferably from 20 to 5,000 ppm with respect to the continuous phase ; the ratio between the continuous phase and the discontinuous phase (monomer mixture) is between 1.3:1 and 8:1, preferably between 1.5:1 and 5:1.

2. A process according to claim 1, wherein the used suspending agents are selected from the following.: a) homopolymers of compounds having formula :

R₂

CH₂ = C - CO - A - C - CH₂ - S0₃ ^~ M⁺ (I)

Ri R₃

wherein : Ri is H or CH₃ ; R₂ and R₃, equal or different, are H or Cι-C₈ alkyl, optionally branched ; M is an alkaline or alkaline-earth metal or ammonium and A is NH, 0 or NCH₃ ; b) copolymers of the formula (I) compounds having no more than 40% by weight of acrylic or vinyl comonomers ; c) polyvinylalcohol (PVA) or vinyl alcohol copolymers ; preferably vinyl alcohol/vinylacetate copolymer in molar ratios from 75:25 to 99:1 preferably from 80:20 to 95:5 ; d) hydroxyalkylcellulose, wherein the alkyl comprises from 1 to 5 carbon atoms, preferably from 1 to 3 ; e) (meth) acrylic polyacid or (meth) acrylic acid copolymers with other acrylic or vinyl monomers, for example methylmethacrylate and/or styrene.

3. A process according to claim 2, wherein the suspending agents are selected from those of the classes a) , b) and c) .

4. A process according to claims 1 to 3, wherein the used surfactants are ionic and non ionic.

5. A process according to claim 4, wherein the non ionic surfactants are selected from mono-, di- and trialkylphenols ethoxylated with number of ethoxy units

(EO) comprised between 2 and 50 and C₄-Ci8 alkyl chains ; ethoxylated fat alcohols with number of EO units between 3 and 50 and Cs-Cis alkyl chains, Cι₂-Cι₈ ethoxylated alkanols with number of EO units comprised between 4 and 50 ; polyethylenglycols having molecular weight from 350 to 2,000 ; polyethylenoxide esters with C₈-C₂₄ fat acids.

6. A process according to claim 4, wherein the ionic surfactants are anionic surfactants selected from the following : ammonium or alkaline metal salts of Cs-Cι₂ alkyl sulphates ; hemiesters of the sulphuric acid with Cs-Cis ethoxylated alkanols with number of EO units comprised between 4 and 50, Cs-Cis alkylsulphonic acids, preferably sodium lauryl sulphate, 2-ethylhexyl sodium sulphate ; alkylarylsulphonic acids with 6 carbon atoms of the aromatic ring and Cg-Cis alkyl chains ; alkaline, alkaline-earth metal or ammonium salts of C₉-C2i carboxylic acids .

7. A process according to claim 4, wherein the ionic surfactants are cationic surfactants selected from the following : C₈-Ci8 primary, secondary or tertiary fat amines, wherein the other alkyls are C₁-C4 ; salified with strong inorganic acids or strong organic acids ; or salified by addition to the nitrogen of alkyl halides preferably methylchloride .

8. A process according to claims 1 to 7, wherein when the suspending agents are a) and/or b) , when the surfactant is non ionic and when c) is the only suspending agent, the surfactant is anionic.

9. A process according to claims 2 to 8, wherein the acrylic comonomers of the suspending agents mentioned in b) are selected from the following :

(meth) acrylamide ; (meth) acrylic acid under the form of the corresponding alkaline salts, preferably sodium or potassium ; or alkaline-earth, preferably calcium or magnesium ; esters of the (meth) acrylic acid with Cι~C₄ linear or branched aliphatic alcohol (for example ethanol, methanol, propanol) , (meth) acrylonitrile, C1-C₄, linear or branched hydroxyesters of the (meth) acrylic acid such for example hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate .

10. A process according to claims 2 to 8, wherein the vinyl comonomers of the suspending agents indicated in b) are selected from the following : vinylaromatic monomers, preferably styrene and derivatives thereof obtained by substituting one or more hydrogen atoms of the aromatic ring with one hydroxyl or one methyl and/or of vinyl with one methyl, in particular - methylstyrene ; C1-C12 alkyl vinylethers, preferably methyl-, ethyl-, n-propyl-, isopropyl-, n-butyl-, isobutyl- and 2-ethylhexyl-vinyl ether ; vinyl esters of C₁-C₁8 aliphatic monocarboxylic acids, preferably vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl hexanoate, vinyl 2-ethyl-hexanoate, vinyl decanoate, vinyl laurate and vinyl stearate.

11. A process according to claims 1 to 10, wherein the monomers are selected from the following : acrylic monomers, selected from Cι-Cι₂ alkyl (meth) acrylates, wherein the alkyl is linear or branched, preferably methyl (meth) acrylate, ethyl

(meth) acrylate, propyl (meth) acrylate, isopropyl

(meth) acrylate, butyl (meth) acrylate, sec-butyl (meth) acrylate, ter-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate ; (meth) acrylic acid ; Cχ-C₄, linear or ' branched hydroxyesters of the

(meth) acrylic acid, methacrylamide ; vinyl monomers, selected from styrene and derivatives thereof, preferably methyl- and ethyl-styrene, wherein the alkyl group is in the ortho or para position ; alpha methylstyrenes ; mono-, di-, tri-, tetra-, penta-halogenstyrenes, wherein the halogen is Cl, F ; vinylethers CH₂=CH-[ 0- (CH₂) _n] _m-OR wherein n is from 1 to 4, m from 1 to 10 and R is H, CH₃, in particular ethylenglycolvinylether .

12. A process according to claim 11, wherein mixtures of acrylic and/or vinyl monomers are used.

13. A process according to claims 11 or 12, wherein the comonomers are used in admixture with other comonomers containing double bonds, in amounts up to 50% by weight in the monomeric mixture, said comonomers selected from (meth) acrylonitrile, n-alkyl or aryl maleimides, butadiene.

14. A process according to claims 1 to 13, wherein the initial monomer mixture contains also crosslinking comonomers having more than one polymerizable group, preferably containing at least two double bonds, in amounts from 0.01% to 25%, preferably from 0.1% to 20% by weight with respect to the total amount of the monomers.

15. A process according to claim 14, wherein said crosslinking comonomers are selected from allyl (meth) acrylate, diallyl maleate, diallyle phthalate, diallyl fumarate, triallyl cyanurate, ethylenglycol di (meth) acrylate, di-,tri-, tetraethylenglycol di (meth) acrylate, 1,3- 1, 4-butylenglycol di (meth) acrylate, divinylbenzene, trivinylbenzene.

16. A process according to claims 1 to 15, wherein the polymerization aqueous phase is at least partially formed by mother liquors obtained from a polymerization process in suspension of a monomer polymerizable by radical route, preferably an acrylic monomer, even different from those used in the process.

17. A process according to claim 16, wherein the dry residue of said mother liquors is generally in the range 0.05-5% by weight, preferably 0.05-1.5%.

18. A process according to claims 1 to 17, wherein in the monomer mixture a chain transfer agent is used.

19. A process according to any one of claims 1 to 18 wherein the suspending agent is of class a) with a surfactant being selected from ethoxylated fatty alcohols with number of EO units between 3 and 50 and Cs-Cis alkyl chains or the suspending agent is of class c) with a surfactant being anionic.

20. Use of the beads obtained by the process as claimed according to any one of claims 1 to 17 as antireflection agents or as matting agents for paints, photographic applications, inks, plastic sheets, or as lubricating or opacifying agents in cosmetics.

21. Use according to claim 19 as an antireflection or matting agent for plastics wherein these plastics are calendered or extruded.