Process for agglomerating a latex, agglomerated latex obtained and its application to the modification of thermoplastic matrices to make them impact-resistant

The present invention relates to a process for agglomerating a latex based on a polymer chosen from elastomers and thermoplastic resins, the latex obtained by this process, and its application to the modification of rigid thermoplastic matrices to make them impact-resistant. By way of examples, there may be mentioned the application of a polybutadiene-based latex to the preparation of acrylonitrile-butadiene-styrene (ABS) resins, or the application of multilayer acrylic latices or of SBR latices in the reinforcement of matrices based on methyl methacrylate and styrene, or, yet again, the application of multilayer acrylic latices in the reinforcement of polystyrene matrices.
It is known that latices consist of emulsions of polymers in water to which various agents have been added, such as emulsifying agents, stabilizers and the like, and that in most cases they are produced directly by emulsion polymerization. The purpose of the agglomeration process is to increase the size of the polymer particles in these emulsions.
For example, if the reaction rate of the monomers is low then, in order to avoid a waste of energy and time, particularly in the case of manufacture on industrial scale, it is advantageous to employ high polymerization rates which lead to small particle sizes, below 200 nm, and then to perform an agglomeration of these particles of intermediate size, enabling them to attain the size finally required.
Thus, to produce an ABS resin with good impact strength characteristics, it is necessary to have available a polybutadiene-based latex in which the particle sizes lie between 300 and 700 nm. Now, with the usual method of emulsion polymerization of butadiene, the particle sizes increase at a rate of only 10 nm per hour, with the result that the polymerization is carried out so as to produce latices in which the polymer particles are small in size (of the order of 80-200 nm), in order to subsequently make use of an agglomeration technique.
The principle of all the known techniques for agglomerating latices is the transition from a stable state in which the latex contains fine polymer particles to another stable state in which the latex contains large polymer particles, under the effect of a physical, chemical or physicochemical agent, it being possible for the final stable state to be ensured, if desired, by a post-stabilization of the latex.
The agglomeration methods proposed in the literature may be subdivided into two categories according to whether they do not employ a chemical agent or whether, on the contrary, they do employ one.
The first of these, among which the cooling method and the pressure gradient method may be mentioned, have the advantage of not contaminating the latices and, consequently, not interfering with subsequent processing of the latter (for example, grafting in the case where ABS is produced from a polybutadiene latex) and with the properties of the resulting products.
The second methods employ, as chemical agents, either solvents such as benzene, toluene, acetone and mixtures of the benzene-alcohol type, because of their destabilizing and swelling action, or else electrolytes, salts or acids, which act by partial destruction of the emulsifier protection, or, yet again, hydrophilic polymers: polyvinyl alcohol, polyvinyl methyl ether, polyoxyethylene, acrylic polyelectrolytes, polyurethanes, polyethylene glycol (Carbamax 20M), carboxymethyl cellulose and polyvinylacetal.
However, all these known methods present the following disadvantages:
a high energy consumption;
a more or less pronounced formation of coagulum;
a limited and rather small size of the agglomerated particles;
a high dependence of agglomeration with relation to temperature and time; and
the difficulty of controlling and the difficulty of reproducing the size distribution of the agglomerated particles.
To overcome these disadvantages, European Patent No. 29,613 has already proposed a process for the agglomeration of latices based on rubbery polymers, this process consisting of adding to the latex to be agglomerated another latex (called an agglomerating latex) containing:
(1) a polymer other than that present in the latex to be agglomerated and less lipophilic than the latter, chosen from (a) the homopolymers of C.sub.1 -C.sub.12 -alkyl acrylates and methacrylates; and (b) the copolymers of ethylenically unsaturated monomers capable of forming water-insoluble homopolymers, and
(2) a nonionic surface-active agent consisting of a product of addition of ethylene oxide to organic compounds containing reactive hydrogen atoms in their molecules.
However, this known process has a number of disadvantages and limitations.
Firstly, it may be emphasized that since, in this known process, the polymer in the latex to be agglomerated must be other than that of the agglomerating latex, and since the principal latex to be agglomerated is polybutadiene, it is not possible to employ a polybutadiene latex as an agglomerating latex.
Secondly, the synthesis of the latex which agglomerates by adsorption of the agglomerating surfactant on the initial latex involves the presence of the anionic surfactant in the latter, which reduces the size of the agglomerated latex and can lead to a preagglomeration, or even to incipient precipitation of the agglomerating latex.
Thirdly, a bimodal population is invariably obtained in this known process.
The present inventors have found, surprisingly, that when the abovementioned surface-active agent (2) in the agglomerating latex was replaced by a copolymer containing at least one polyoxyethylene block and at least one block of a vinyl, diene, acrylic and methacrylic ester polymer, this multiblock polymer being, furthermore, that in whose presence the preparation of the agglomerating latex is carried out, then it was possible to avoid the disadvantages of the known process, namely:
on the one hand, that the polymers in the latex to be agglomerated and in the agglomerating latex can be identical and that, generally, the group of the polymers to be agglomerated can be widened to the thermoplastic polymers without this making it necessary to perform the agglomeration at a temperature above the glass transition temperature of the polymer to be agglomerated, as is the case with the process described in European Patent No. 29,613, which is also limited to the use of rubbery polymers to be agglomerated;
on the other hand, that it is readily possible to produce agglomerated particles of large size;
and
lastly, that a monomodal or bimodal population may be obtained at will, according to the value of the ratio of the mass of agglomerating polymer in 100 g of final latex to the mass of the polymer to be agglomerated in 100 g of final latex, and this forms a completely unexpected feature of the present invention.
In addition, the use of the abovementioned multiblock copolymer offers the additional advantages of making it possible:
to perform the agglomeration in a wide range of temperatures and in a wide range of solids contents of the agglomerating latex and of the latex to be agglomerated (it is possible, in particular, to work at much lower values of solids contents in the agglomerating latex than in the known process); and to attain a percentage of agglomerated particles of 100%.
The subject of the present invention is therefore a process for agglomerating a latex of a polymer chosen from elastomers and thermoplastic resins, characterized in that the latex to be agglomerated is mixed with an agglomerating latex consisting of:
(A) a polymer chosen from elastomers and thermoplastic resins; and
(B) a nonionic surface-active agent consisting of a block polymer containing at least one polyoxyethylene block and at least one block of a polymer chosen from vinyl, diene and acrylic and methacrylic ester polymers,
the said agglomerating latex being produced by the synthesis of the polymer defined under (A) during which (B) has been employed as surfactant.
Among the polymers of the latices to be agglomerated and the agglomerating latices, particular mention will be made of homopolymers and copolymers of butadiene, isoprene, styrene, alpha-methylstyrene, vinyltoluenes, acrylonitrile, and alkyl esters of acrylic, methacrylic, maleic, fumaric, crotonic and itaconic acids, in which the alkyl group contains from 1 to 12 carbon atoms, it being also possible for the latices to be agglomerated to be SBR latices or multilayer (bi- or trilayer) acrylic latices of a structure known as "core-shell".
A nonionic surface-active agent (B) consisting of a triblock polymer, preferably a polymer containing two terminal polyoxyethylene blocks, will preferably be chosen. A nonionic surface-active agent (B) consisting of a diblock polymer may equally be employed.
Furthermore, a polymer in which the block(s) other than the polyoxyethylene block(s) consists (or consist) of polystyrene will be chosen in particular. Thus, there may be mentioned the surfactant B which consists of the polyoxyethylene-polystyrene-polyoxyethylene triblock copolymer, referred to hereinafter as POE-PS-POE.
In addition, the surfactant (B) will advantageously have the following characteristics:
a number average molecular mass of between 1000 and 1,000,000; and
a polyoxyethylene content ranging from 5 to 95% by weight.
The surfactants (B) employed in the process according to the present invention are generally prepared by an anionic route, and this has the advantage of resulting in practically pure products. In the case of the preparation of the POE-PS-POE copolymer, the PS block is initiated by difunctional initiators of the "alpha-methylstyrene tetramers" type in tetrahydrofuran at a temperature of -80.degree. C. The POE block is then polymerized at a temperature of 30.degree. C.
In accordance with a preferred embodiment of the present invention, the latex to be agglomerated which is employed is prepared by emulsion polymerization in the presence of an anionic surface-active agent such as potassium laurate and sodium dodecylsulphate (SDS), a free-radical initiator such as potassium persulphate and a chain transfer agent such as tert-dodecyl mercaptan, and at a temperature of the order of 40.degree. to 90.degree. C. The polymer particle diameter in the latex to be agglomerated is, in particular, between 50 and 300 nm and the solids content of the said latex is between 5 and 50% by weight.
Similarly, use will be made, in particular, of an agglomerating latex in which the particle diameter of the polymer (A) will lie between 60 and 500 nm and which has a solids content of between 1 and 40% by weight.
In accordance with the invention, the agglomerating latices are prepared by emulsion polymerization in the presence of the nonionic surface-active agent (B), which enables them to be obtained directly. The polymerization also takes place in the presence of a free-radical initiator such as potassium persulphate. The presence of a chain transfer agent, such as tert-dodecyl mercaptan, is found to be practically essential; the purpose of this agent is to limit the chain length and it also acts as an initiator in the organic phase. An alcohol, such as methanol, may also be added to the mixture, and this acts as a cosurfactant and produces a marked decrease in the particle size by significantly reducing the interfacial tension between the particles and the solvent; this enables the latex particle size to be adjusted. Another surfactant, such as sodium laurylsulphate, could, furthermore, be employed for the same purpose. The polymerization is carried out batchwise or semicontinuously, at a temperature of the order of 40.degree. to 90.degree. C. (for example 70.degree. C.). The conversion is very high and can reach 100%.
The diameter of the polymer particles in the agglomerating latices is a function of the monomers employed (thus, it appears to be lower for butyl acrylate than for butadiene and styrene), of the concentration of alcohol acting as a cosurfactant (as indicated above) and of the process employed (the semicontinuous process results in much smaller particle sizes than the batch process); furthermore, particle diameter diminishes with rising concentrations of copolymer (B), of cosurfactant alcohol and of initiator; on the other hand, an increase in the particle size is observed when the molecular mass Mn of the copolymer (B) increases.
In order to perform the agglomeration the procedure may be to add the agglomerating latex to the latex to be agglomerated, or to add the latex to be agglomerated to the agglomerating latex. It has been found, in fact, that the mixing method employed to produce the agglomeration has practically no effect on the diameter of the resulting agglomerated particles, except for special cases. In general, in practice it is preferable to follow the first method, because it is easy to add the agglomerating latex (a very small volume, in principle) to the latex to be agglomerated (a very large volume, in principle).
Furthermore, the agglomeration mixing according to the invention is performed for a period of time which, as a general rule, is between one minute and 48 hours; similarly, this mixing is carried out at a temperature which may lie between 10.degree. C. and 100.degree. C.
In accordance with the present invention, the agglomerating latex is introduced in a quantity of at least 0.05 part by weight of the solid polymer (A) and of at least 0.0001 part by weight of the surface-active agent (B) per 100 parts by weight of the polymer present in the latex to be agglomerated. In particular, the agglomerating latex may be introduced in a quantity corresponding to 0.05-20 parts by weight of the solid polymer (A) and of 0.0001-0.2 part by weight of the surface-active agent (B) per 100 parts by weight of the polymer present in the latex to be agglomerated. It should be emphasized, nevertheless, that the quantities indicated above are not critical at all.
In accordance with a feature of the present invention which is of great interest, it has become apparent that, as a general rule, all the curves representing the size of the agglomerated particles as a function of the value of the ratio of the mass of agglomerating polymer to that of the polymer to be agglomerated in 100 grams of final latex exhibit a maximum, the population obtained being bimodal or monomodal, according to whether R is lower or higher than the value corresponding to this maximum. This represents a finding which is of great interest, when compared with the agglomerations produced in the process described in the abovementioned European Patent 29,613.
The morphology of the agglomerated particles is generally spherical and the surface of these particles is smooth. Moreover, the agglomerated particles obtained are stable thermally (freezing-thawing cycle), to ultrasound, to postaddition of agglomerating latex and to shear stresses.
It has thus been possible to produce agglomerated particles which have a size of up to 1700 nm.
The present invention also relates to the agglomerated latices produced by the process just defined and to the application of these agglomerated latices to the modification of thermoplastic matrices to make them impact-resistant. These matrices consist, in particular, of rigid thermoplastic polymers of at least one monomer chosen from alkyl methacrylates in which the alkyl group contains from 1 to 4 carbon atoms, styrene, substituted styrenes, acrylonitrile and methacrylonitrile, or of polymers with more than 50% by weight of at least one of the abovementioned monomers and at least one other ethylenically monounsaturated copolymerizable monomer. Examples of application have been mentioned in the introduction to this specification. The methods for preparing these reinforced matrices are traditional methods, which are known to the specialist. In general, the agglomerated particles are subjected to a coating process before flocculation, washing and drying, the final stage being dispersion in the matrix.
Various agglomerations of latices, which have been performed using the process according to the present invention will be described below in greater detail, by way of guidance and without implying any limitation. The latices employed in these examples have been designated by LPB, LS, LPBA and LSBR in the case of latices to be agglomerated of polybutadiene, polystyrene, poly(butyl acrylate) and of butadiene-styrene copolymer respectively, and by LPBCop, LPSCop, LPBACop and LPBA-SCop, in the case of the agglomerating latices of polybutadiene, polystyrene, poly(butyl acrylate) and butyl acrylate-styrene copolymer respectively, Cop denoting the triblock POE-PS-POE copolymer which is the nonionic surfactant in the presence of which the preparation of the agglomerating latex took place. The percentages indicated in the examples which follow are given by weight.
I - PREPARATION OF THE LATICES TO BE AGGLOMERATED
1) Preparation of polybutadiene latex
The following are introduced in succession into an 8-l reactor, after the stirring has been started up gradually to run at 500 revolutions/minute: 500 g of water, 6.3 g of lauric acid dissolved beforehand in 200 g of water, 1.75 g of potassium hydroxide, 2.10 g of tert-dodecyl mercaptan (TDM), 1.40 g of potassium hydroxide dissolved in 50 g of water, and a rinse of 500 g of water. The whole reactor is deoxygenated by being subjected to vacuum and then by the introduction of nitrogen at a pressure of 3 bars. It is heated to 70.degree. C. 2.8 g of potassium persulphate, dissolved beforehand in 100 g of water, are added through an airlock and under nitrogen pressure, followed by a rinse with 50 g of water.
The polybutadiene latices LPB1 to LPB6, whose characteristics are given in Table 2 below, were successfully prepared in this manner, while the pressure was varied.
2) Preparation of the other latices to be agglomerated
a) General operating procedure
Water, the surfactant and sodium hydroxide are employed at a constant temperature of 70.degree. C., with stirring and under a nitrogen stream. After the surfactant has completely dissolved, the mixture of monomer and TDM is added. After 10 min, when the temperature has become steady again, potassium persulphate, dissolved beforehand in water, is added.
b) Preparation of polystyrene and poly(butyl acrylate) latices
The above general operating procedure was followed in order to prepare the individual latices as shown in Table 1 below, the characteristics of these latices also being given in Table 2 below.
TABLE 1______________________________________ Potas-Latex Mono- siumto be mer Surfactant hydrox- TDMagglom- mass Mass K.sub.2 S.sub.2 O.sub.8 ide mass masserated intro- intro- mass in- intro- intro-pre- duced duced troduced duced ducedpared (g) Type (g) (g) (g) (g)______________________________________LPS 100 Lauric 3.03 0.40 0.85 0.3 acidLPBA 1 100 Lauric 0.80 0.40 0.80 0.3 acidLPBA 2 160 SDS 4.85 0.39 0 0.4______________________________________
3) Characteristics of the latices to be agglomerated prepared according to 1) and 2)
TABLE 2______________________________________Type ofLatex to Mean Standard Solidsbe agglom- .phi. deviation content Surface tensionerated (nm) (nm) (%) (newton/cm)______________________________________LPB1* 203 51.5 30.6 71.3 .times. 10.sup.-5LPB2** 181 48.4 30.7 60.1 .times. 10.sup.-5LPB3 112 33.2 31.0 72.6 .times. 10.sup.-5LPB4 104 27.8 32.2 73.2 .times. 10.sup.-5LPB5 100 24.1 32.3 72.1 .times. 10.sup.-5LPS 75 25 16.9LPBA1 139 26 33.1LPBA2 125 22 32.9______________________________________ *Highly crosslinked latex **Sparsely crosslinked latex
II - PREPARATION OF AGGLOMERATING LATICES
1) POE-PS-POE triblock copolymeric surfactants
The characteristics of these surfactants are shown in Table 3, which follows:
TABLE 3______________________________________ % Mn of the Mn of each Mn of theCop PS PS block POE block Cop.______________________________________1 40.5 2400 1800 60002 16.1 2400 6300 150003 21.0 1600 3000 76004 18.4 1600 3600 88005 21.0 1800 3400 86006 17.8 1800 4200 102007 9.1 1800 9000 19800______________________________________
2) General operating procedure for preparing these agglomerating latices by the batch process
Water, the Cop surfactant and methanol are introduced into a 1-l glass reactor thermostated with a water bath at a constant temperature of 70.degree. C.; the residual air is removed by continuous bubbling of nitrogen. The reactor is stirred at a speed which will remain constant at 250 revolutions/min. After the Cop surfactant has completely dissolved and when the temperature has reached 70.degree. C., the mixture of monomer(s) and TDM is added. After 10 min, when the temperature has become steady again, potassium persulphate dissolved in 15 g of water is added, the addition of the persulphate marking the beginning of the reaction.
3) General operating procedure for preparing these agglomerating latices by the semicontinuous process
The procedure is initially as indicated in paragraph 2), except that 30% of the mixture of monomer and TDM is added and, 5 min later, all of the initiator, dissolved in water. The polymerization is then allowed to take place to 100% conversion, which results in the "seed" latex. The remaining 70% of the mixture of monomer and TDM is then added continuously at a rate of 0.3 ml/min.
4) Preparation of various agglomerating latices
The above general operating procedures were followed to prepare the individual latices as shown in Table 4 below, in which the characteristics of these latices are also given.
TABLE 4__________________________________________________________________________ POE-PS-POE Transfer Mean Standard SurfaceType of agglomer- surfactant K.sub.2 S.sub.2 O.sub.8 Monomer(s) agent MeOH diameter deviation Conversion tentionating latex mass (g) (g) mass (g) mass (g) mass (g) (nm) (nm) (%) (newton/cm)__________________________________________________________________________LPBACop1 4 0.1 65 0.4 60 197 43.1 99.8LPBACop2 4 0.1 65 0.4 60 155 37.8 90.0LPBACop3 4 0.1 65 0.0 60 117 31.2LPBACop4 -a 4 0.1 65 0.4 60 135 32.5 92.5 45.6 .times. 10.sup.-5LPBACop4 -b 4 0.1 65 0.4 0 197 64.4 69.0 46.9 .times. 10.sup.-5LPBACop4 -c 5 0.1 65 0.4 60 114 32.4 99.9 45.1 .times. 10.sup.-5LPBACop7 4 0.1 65 0.4 60 185 52.4 88.0 46.6 .times. 10.sup.-5LPSCop4 4 0.1 65 0.4 60 186 44.9 100.0 47.8 .times. 10.sup.-5LPBCop4 8 0.2 130 0.8 120 225 70.5 52.0 45.3 .times. 10.sup.-5LPBCop5 8 0.2 130 0.8 120 277 108.0 70.0 45.7 .times. 10.sup.-5LPBCop7 8 0.2 130 0.8 120 330 90.2 31.0 46.3 .times. 10.sup.-5LPBA-SCop6 4 0.5 50 (BA) 0.0 60 138 37.9 15 (S)__________________________________________________________________________
III - AGGLOMERATION PROCESSES
1) General operating procedure
Various proportions of agglomerating latices of different concentrations were added by means of a burette, with mechanical stirring, to different types of latices to be agglomerated. Unless indicated otherwise, a uniform initial mass of 30 g of latex to be agglomerated was chosen. A gentle stirring by means of a bar magnet is provided during the addition of the agglomerating latex. This stirring is continued for a few minutes after the addition of agglomerating latex, and it is then stopped.
2) Concentration units chosen
In the following text, R denotes the ratio of the mass of agglomerating polymer in 100 g of final latex to the mass of polymer to be agglomerated in 100 g of final latex. If it is assumed that:
m.sub.1 =mass of agglomerating polymer
m.sub.1.sup.L =mass of agglomerating latex
x.sub.1 =solids content of the agglomerating latex and
m.sub.2 =mass of polymer to be agglomerated
m.sub.2.sup.L =mass of latex to be agglomerated
x.sub.2 =solids content of the latex to be agglomerated,
then ##EQU1##
If C is the final solids content expressed in total mass of polymer in 100 g of latex, ##EQU2## with m.sub.1.sup.L +m.sub.2.sup.L =100 [Cop] is the mass of POE-PS-POE triblock copolymeric surfactant added per 100 g of latex to be agglomerated expressed as solids content. The ratio I=D.sub.90 /D.sub.10 has also been defined, where D.sub.90 and D.sub.10 refer to the cumulative diameters forming 90% and 10% of the particle volume respectively.
3) Agglomeration of the polybutadiene latices by POE-PS-POE triblock copolymeric acrylic agglomerating latices
a) Influence of the mixing method
Latex to be agglomerated: LPBA (.phi.=104 nm; x.sub.2 =32.2%)
Agglomerating latex: LPBACop 4a (.phi.=135 nm; x.sub.1 =4.52%)
TABLE 5______________________________________ Agglomerated latex Standard R .times. C (Cop) .times. Mean .phi. deviationTest 10.sup.+2 g/100 g 10.sup.+2 (nm) (nm)______________________________________1* 0.46 31.30 0.029 201 VB 0.92 30.47 0.058 450 172 1.17 30.07 0.072 607 VB 1.41 23.68 0.087 605 210 1.84 28.11 0.116 490 149 2.82 27.58 0.174 438 138 4.23 25.81 0.241 390 1152** 0.87 30.57 0.053 402 142 0.97 30.40 0.059 450 151 1.09 30.19 0.067 542 181 1.25 29.92 0.076 612 163 1.46 29.58 0.089 573 157 1.75 29.12 0.107 510 141 2.19 28.45 0.134 449 116 2.92 27.42 0.179 392 96 4.38 25.60 0.268 386 110 8.77 21.54 0.537 302 76______________________________________ *Agglomeration temperature: 17.degree. C. **Agglomeration temperature: 25.degree. C. VB = very large
In test 1, the agglomerating latex was added to the latex to be agglomerated and, in test 2, the latex to be agglomerated was added to the agglomerating latex.
It is found that the mixing method employed to produce the agglomeration has no particular influence in this case on the diameter of the agglomerated particles.
b) Influence of time on the agglomeration method
Latex to be agglomerated: LPB3 (x.sub.2 =31.0%)
Agglomerating latex: LPBACop 3
TABLE 6______________________________________ Agglomerated latex Agglomerating Standard latex added R .times. Time Mean .phi. deviationTest x.sub.1 (%) 10.sup.+2 (h) (nm) (nm)______________________________________3* 2.4 0.78 0.06 195 73.0 0.13 204 73.9 0.25 209 78.7 0.50 212 83.2 1.5 215 81.5 48,0 216 85.14** 4.8 3.13 0.02 264 89.3 0.2 347 126 0.4 382 99.8 0.5 372 124 0.8 400 122 1.0 446 163 1.25 461 168 1.75 476 170 2.0 476 167 48.0 493 173______________________________________ *final solids content: C = 28.40 **final solids content: C = 28.61
The time t=0, the beginning of the agglomeration, is taken from the end of the addition of the agglomerating latex to the polybutadiene latex.
Agglomeration of a latex of this type is fast, since, depending on the system under consideration, the final diameter is obtained after a few minutes to approximately one hour.
c) Influence of the respective concentrations of the latex to be agglomerated and of the agglomerating latex
1 - Variation of the particle size as a function of the total concentration C at constant R
Latex to be agglomerated: LPB5
Agglomerating latex: LPBACop4a
Agglomeration temperature: 25.degree. C.
TABLE 7__________________________________________________________________________ Test (%)x.sub.1 (%)x.sub.2 .times. 10.sup.+2R g/100 gC (h)Time (nm)Mean .phi. deviation (nm)Standard ##STR1##__________________________________________________________________________5 4.5 32.3 1.39 29.77 0.01 282 99 2.2 0.16 357 115 2.2 0.33 368 126 2.3 0.76 394 121 2.2 1.91 445 137 2.1 3.08 457 157 2.2 22.0 545 187 2.06 2.2 16.1 1.37 14.83 0.01 141 45 2.0 0.25 173 57 2.1 0.50 186 65 2.3 1.00 195 67 2.0 2.50 199 68 2.2 24.0 280 98 --7 1.1 8.0 1.38 7.37 0.01 103 22 1.8 1.00 106 22 1.8 4.00 113 26 1.8 24.0 143 42 --__________________________________________________________________________
2 - Variation in the size of the agglomerated particles as a function of R at constant C
Latex to be agglomerated: LPB3 (x.sub.2 =31%)
Agglomerating latex: LPBAcop 3
Agglomeration temperature: 17.degree. C.
TABLE 8______________________________________ Test (%)x.sub.1 .times. 10.sup.+2R g/100 gC (h)Time (nm).phi.Mean (nm)deviationStandard ##STR2##______________________________________3 2.4 0.78 28.39 0.06 195 73 2.3 0.13 204 74 2.2 0.25 209 78 2.3 0.50 212 83 2.3 1.5 215 81 2.3 48.0 216 85 2.18 4.8 1.56 28.51 1 530 185 -- 24 580 233 --4 4.8 3.13 29.05 0.02 264 89 2.1 0.2 347 126 2.1 0.4 382 99 2.2 0.5 372 124 1.7 0.8 400 122 1.9 1.0 446 163 2.1 1.25 461 168 2.1 1.75 476 170 1.8 2.0 476 167 2.2 48.0 493 173 1.9______________________________________
3 - Variation in the size of the agglomerated particles as a function of time (R and C variable)
Latex to be agglomerated: LPB4 or LPB5
Agglomerating latex: LPBCop 4a (x.sub.1 =4.5%)
Agglomeration temperature: 25.degree. C.
TABLE 9______________________________________ Test (%)x.sub.2 .times. 10.sup.+2R 100 gg/C (h)Time (nm)Mean .phi. (nm)deviationStandard ##STR3##______________________________________5 32.3 1.39 29.77 0.01 282 99 2.2 (LPB5) 0.16 357 115 2.2 0.33 368 126 2.3 0.76 394 121 2.2 1.91 445 137 2.1 3.08 457 157 2.2 22.0 545 187 2.09 16.1 0.69 15.04 0.01 175 104 2.1 (LPB5) 0.16 189 127 2.0 0.33 192 118 2.2 1.91 250 129 2.2 2.50 270 110 2.2 24.0 354 127 2.12 32.2 0.87 30.57 24.0 402 142 1.9 (LPB4) 0.97 30.40 24.0 450 151 2.0 1.09 30.19 24.0 542 181 2.0 1.25 29.92 24.0 612 163 2.0 1.46 29.58 24.0 573 157 1.9 1.75 29.12 24.0 510 141 1.8 2.19 28.45 24.0 449 116 1.8 2.92 27.42 24.0 392 96 1.8 4.38 25.60 24.0 386 110 1.9 8.77 21.54 24.0 302 76 2.0______________________________________
4 - Discussion
It is found that the change in the size of the agglomerated particles shows a strong dependence on the agglomeration time, on R and on C. In all cases, when C is high, the agglomeration process is fast and virtually immediate.
d) Effect of temperature
Latex to be agglomerated: LPB3 (x.sub.2 =31.0%)
Agglomerating latex : LPBACop3 (x.sub.1 =4.82%)
R.times.10.sup.10+2 =3.10
C (g/100 g)=26.63
TABLE 10______________________________________ Agglomerated latex Standard T Time Mean .phi. deviationTest (.degree.C.) (h) (nm) (nm)______________________________________10 65 0.02 286 103 0.18 303 102 0.20 299 109 0.50 298 105 1.00 304 114 1.50 329 121 2.00 315 113 Heating stopped 11 2.25 448 153 2.75 458 153 6.00 491 147______________________________________
It is found that the increase in agglomeration temperature results in a fairly large decrease in the diameter of the agglomerated particles. In fact, the maximum diameter reached during the agglomeration at T=17.degree. C. is 480 nm, whereas it is only 300 nm at T=65.degree. C. On the other hand, if the heating is stopped at this diameter and the agglomeration temperature is set at T=11.degree. C. as quickly as possible, a continued growth is observed in order to reach a final diameter of 490 nm, which is similar to the diameter obtained in an agglomeration at a low temperature (T=17.degree. C.).
e) Effect of the characteristics of the agglomerating latices
1 - Influence of the molecular mass of the POE blocks on the agglomeration of the polybutadiene latex LPB4 (x.sub.2 =32.2%; .phi.=104 nm).
Agglomeration temperature: 17.degree. C.
Agglomeration time: 24 h.
TABLE 11__________________________________________________________________________ Agglomerated latexAgglomerating latex Mean .phi. StandardTest Type x.sub.1 (%) R .times. 10.sup.+2 C g/100 g [Cop] .times. 10.sup.+2 (nm) deviation (nm)__________________________________________________________________________11 LPBACop1 4.81 0.74 30.89 0.043 250 VB 1.49 29.71 0.085 425 158 2.48 28.28 0.143 556 187 4.48 25.88 0.257 410 14912 LPBACop4 -a 1.13 0.35 29.37 0.021 166 58 0.70 27.02 0.042 219 VB 1.05 25.04 0.084 303 11313 2.26 0.70 29.47 0.043 244 VB 2.10 25.29 0.087 474 189 1 4.52 0.46 31.30 0.029 201 VB 0.92 30.47 0.058 450 172 1.17 30.07 0.072 607 VB 1.41 29.68 0.087 605 21014 1.41 29.68 0.087 605 220 1.41 29.68 0.087 597 VB 1 1.84 28.11 0.116 490 14914 2.82 27.58 0.174 455 137 1 2.82 27.58 0.174 438 138 4.23 25.81 0.241 390 11514 4.23 25.81 0.241 404 11715 LPBACop7 1.06 0.32 29.37 0.021 172 VB 1.09 25.01 0.084 380 VB16 4.24 0.43 31.29 0.029 191 VB 0.86 30.45 0.058 363 1.10 30.04 0.072 790 1.32 28.67 0.087 1396 2.64 27.54 0.174 766 3.96 25.74 0.241 60717 LPBACop2 1.10 0.34 29.37 0.021 170 VB18 4.41 0.45 31.30 0.029 210 0.67 30.46 0.042 263 0.90 30.10 0.058 382 1.13 30.06 0.072 635 1.35 29.61 0.087 90519 1.35 29.61 0.087 91518 1.58 28.10 0.102 700 2.71 27.56 0.174 63819 4.06 25.81 0.241 481__________________________________________________________________________ VB = very large
2 - Influence of the molecular mass of the POE blocks on the polybutadiene latices LPB2 (x.sub.2 =30.7%; .phi.=181 nm) and LPB1 (x.sub.2 =30.6%; .phi.=203 nm)
Agglomeration temperature: 17.degree. C.
Agglomeration time: 24 h.
TABLE 12__________________________________________________________________________Polybuta- Agglomerating latex Agglomerated latex diene x.sub.1 .phi. R .times. C [Cop] .times. Mean .phi. StandardTest latex Type (%) (nm) 10.sup.+2 (g/100 g) 10.sup.+2 (nm) deviation__________________________________________________________________________20 LPB2 LPBACop4 -a 1.13 135 0.37 28.01 0.022 450 161 1.10 23.87 0.066 471 15421 4.52 0.49 29.85 0.030 377 VB22 1.47 28.32 0.091 528 22921 1.47 0.091 492 VB23 2.94 26.33 0.182 373 14622 2.94 0.182 388 12423 4.41 24.65 0.273 320 9522 4.41 337 5521 4.4 391 15124 LPBACop7 1.06 185 0.35 28.00 0.022 666 VB25 4.24 1.38 28.29 0.091 4.14 24.59 0.27326 LPBA LPBACop4 -a 4.52 1.47 28.22 0.022 610 VB 4.52 2.95 26.25 0.182 450 153 4.52 4.43 24.58 0.273 385 VB__________________________________________________________________________
3 - Influence of the initial concentration of POE-PS-POE triblock copolymeric surface active agent
Latex to be agglomerated: LPB4 (x.sub.2 =32.2%; .phi.=104 nm)
Agglomeration temperature: 17.degree. C.
Agglomeration time: 24 h.
TABLE 13__________________________________________________________________________ Agglomerated latexAgglomerating latex [Cop] .times. Mean .phi. StandardTest Type x.sub.1 (%) Mean .phi. (nm) R .times. 10.sup.+2 10.sup.+2 (nm) deviation (nm)__________________________________________________________________________12 LPBACop4 -a 1.13 135 0.35 0.021 166 58 0.70 0.042 219 VB 1.05 0.084 303 113 1 4.52 0.46 0.029 201 VB 0.92 0.058 450 172 1.17 0.072 607 VB 1.41 0.087 605 210 1.84 0.116 490 149 2.82 0.174 455 137 4.23 0.241 390 11527 LPBACop4 -c 1.21 114 0.75 0.054 358 12528 4.84 0.75 0.054 268 10129 1.00 0.072 461 VB 1.25 0.109 574 VB28 1.25 0.109 544 19330 1.25 0.109 539 19229 1.75 0.145 475 164 2.00 0.182 470 142 2.50 0.218 405 104 3.00 0.255 394 13628 3.00 415 130 4.51 0.401 392 13829 4.51 365 10428 7.51 0.545 329 137__________________________________________________________________________ VB = very large
It is found that more or less extensive agglomeration is obtained depending on the type and the concentration of the POE-PS-POE triblock surfactant employed. It appears that the higher the Mn of the POE blocks, the larger the diameter of the agglomerated particles.
4 - Influence of the particle size of the agglomerating latex
Agglomerating latex: LPBACop4b (.phi.=197 nm)
Agglomeration temperature: 17.degree. C.
Agglomeration time: 24 h.
TABLE 14__________________________________________________________________________ Agglomerated latexPolybutadiene latex [Cop] .times. Mean .phi. StandardTest Type x.sub.2 (%) Mean .phi. (nm) x.sub.1 (%) R .times. 10.sup.+2 10.sup.+2 (nm) deviation (nm)__________________________________________________________________________31 LPB4 32.2 104 1.06 0.32 0.021 167 VB 0.64 0.041 247 VB 1.09 0.084 359 VB32 4.24 1.32 0.087 644 VB 2.64 0.174 623 210 3.96 0.241 658 17133 LPB2 30.7 181 1.06 0.34 0.022 365 116 1.05 0.066 461 VB34 4.24 1.41 0.091 965 VB35 4.24 0.273 1634__________________________________________________________________________ VB = very large
The sizes of the agglomerated particles obtained clearly depend on the size of the agglomerating latex particles. This effect, perceptible in the case of small-sized particles, becomes very considerable when the size of the particles to be agglomerated is large.
4 - Agglomeration of the polybutadiene latex with agglomerating latices of POE-PS-POE triblock polybutadiene copolymers
a) Influence of the molecular mass of the POE blocks
Latex to be agglomerated: LPB5 (.phi.=1000 nm; x.sub.2 =32.3%)
Agglomerating latices: LPBCop5 (.phi.=225 nm; x.sub.1 =2.5%)
Agglomerating latices: LPBCop6 (.phi.=277 nm; x.sub.1 =3.6%)
Agglomeration temperature: 25.degree. C.
TABLE 15______________________________________ Agglomerated latex Agglomer- Mean Standard- ating R .times. C [Cop] .times. .phi. deviationTest latex 10.sup.+2 (g/100 g) 10.sup.+2 (nm) (nm)______________________________________36 LPBCop5 0.67 29.92 0.074 132 47 (0.5) 135 49 (48)37 LPBCop5 1.34 27.89 0.148 173 64 (0.5) 179 66 (48)38 LPBCop5 2.58 24.85 0.285 214 81 (48)39 LPBCop5 3.09 23.78 0.342 245 92 (48)40 LPBCop5 7.73 17.40 0.856 324 95 (48)41 LPBCop5 10.31 15.27 1.142 335 109 (48)42 LPBCop6 1.1 29.69 0.085 216 79 (0.5) 227 83 (48)43 LPBCop6 2.2 27.51 0.171 275 (48)______________________________________
b) Influence of the particle size of polybutadiene
Latex to be agglomerated: LPB5 (.phi.=100 nm; x.sub.2 =32.3%)
Latex to be agglomerated: LPB2 (.phi.=181 nm; x.sub.2 =30.7%)
Agglomerating latex: LPBCop5 (.phi.225 nm; x.sub.1 =2.5%)
Agglomeration temperature: 25.degree. C.
TABLE 16______________________________________ Agglomerated latex Polybuta- Standard diene R .times. C [Cop] .times. Mean .phi. deviationTest latex 10.sup.+2 (g/100 g) 10.sup.+2 (nm) (nm)______________________________________36 LPB5 0.67 29.92 0.074 135 4937 1.34 27.89 0.148 179 6638 2.58 24.85 0.285 214 8139 3.09 23.78 0.342 245 9240 7.73 17.40 0.856 324 95 44* LPB2 0.81 28.13 0.090 232 6745 1.63 26.01 0.180 240 3546 2.44 24.00 0.270 256 6347 3.24 22.64 0.361 284 6848 8.14 16.60 0.901 323 82______________________________________ *Mixing method employed = addition of polybutadiene latex to the agglomerating latex.
According to the results obtained, it is found that the agglomeration employing the abovementioned latices is a function of the method of mixing the two latices (it is sometimes necessary to choose to add the latex to be agglomerated to the agglomerating latex), of the surfactant concentration, of the initial size of the polybutadiene latex and of the molecular mass of the POE blocks, and hence of the size of the agglomerating latex.
5 - Agglomeration of polybutacrylate latices by POE-PS-POE triblock acrylic copolymer agglomerating latices
Latex to be agglomerated: LPBA1 (.phi.=139 nm; x.sub.2 =23.1%)
Agglomerating latex: LPBACop4a (.phi.=135 nm; x.sub.1 =4.5%)
Agglomeration temperature: 25.degree. C.
TABLE 17______________________________________ Agglomerated latex Standard R .times. C [Cop] .times. Mean .phi. deviationTest 10.sup.+2 (g/100 g) 10.sup.+2 (nm) (nm)______________________________________49* 1.5 29.75 0.098 153 42 3.5 26.31 0.230 177 34 7.3 22.97 0.496 218 31 8.9 21.79 0.586 238 70 13.6 18.85 0.898 260 -- 22.6 15.22 1.496 260 64______________________________________ *LPBA1 prepared in the presence of potassium laurate as a surfactant.
6 - Other agglomerations
a) Agglomeration of polybutadiene latices by the POE-PS-POE triblock butylacrylic-styrenic copolymer agglomerating latices
Latex to be agglomerated: LPB4 (.phi.=104 nm; x.sub.2 =32.2%)
Agglomerating latex: LPBA-SCop6 (.phi.=138 nm; x.sub.1 =4.68%)
Agglomeration temperature: 25.degree. C.
Agglomeration time: 24 h.
TABLE 18______________________________________ Agglomerated latex Standard R .times. C Cop .times. Mean .phi. deviationTest 10.sup.+2 (g/100 g) 10.sup.+2 (nm) (nm)______________________________________50 0.48 31.31 0.028 191 VB 0.97 30.48 0.057 437 147 1.45 29.69 0.085 496 173 1.94 28.96 0.114 484 170 2.90 27.61 0.172 438 142 4.36 25.85 0.256 376 131______________________________________
b) Agglomeration of poly(butyl acrylate) latices by the POE-PS-POE block butadiene copolymer agglomerating latices
Latex to be agglomerated: LPBA1 (.phi.=139 nm; x.sub.2 =33.1%) or LPBA2 (.phi.=125 nm; x.sub.2 =32.9%)
Agglomerating latex: LPBCop5 (.phi.=225 nm; x.sub.1 =2.5%)
Agglomeration temperature: 25.degree. C.
Agglomeration temperature=48 h.
TABLE 19______________________________________ Agglomerated latex Standard Latex to be R .times. C Mean .phi. deviationTest agglomerated 10.sup.+2 (g/100 g) (nm) (nm)______________________________________51 LPBA1* 0.84 30.04 330 11952 LPBA2** 0.75 30.13 329 VB______________________________________ *LPBA1: surfactant: potassium laurate **LPBA2: surfactant: SDS VB = very large
c) Various agglomerations
TABLE 20______________________________________ Agglomerated latex Latex Stand- to be Agglomer- C Mean ard de- agglom- ating R .times. (g/ .phi. viationTest erated latex 10.sup.+2 100 g) (nm) (nm)______________________________________53 LPS LPBCop5 4.9 4.8 358 --54 LPB* LPSCop4 + 3.2 26.28 190 70 SDS 6.5 24.85 223 82 9.6 23.63 350 13155 LPS** LPBACop4 -a + 0.9 30.1 181 VB SDS 5.5 27.1 288 VB 8.2 25.7 390 131 13.7 23.4 280 89______________________________________ *LPB' (.phi. = 84.5 nm; x.sub.1 = 28.0%) **LPS' (.phi. = 83.5 nm; x.sub.1 = 30.9%) VB = very large
The present invention will be illustrated further by the following examples:
Two POE-PS-POE triblock polymers whose characteristics are shown in Table 21 below were used to prepare the agglomerating latices employed:
TABLE 21______________________________________ M of each POECop M of Cop* block % PS**______________________________________8 77 000 15 000 209 25 000 4 000 33.3______________________________________ *determined by gel permeation chromatography; **determined by the UV method based on the fact that ethylene oxide does not absorb at a wavelength of 258 nm, only the PS block being detectable.
A series of LPBACop agglomerating latices were prepared according to the following general operating procedure:
"Into a 2-1 reactor are introduced: water, methanol if desired, in weight percentages shown in Table 22 below, 23% by weight of butyl acrylate together with, based on the monomer, 6% by weight of triblock polymer and 0.6% by weight of TDM. The reactor is heated up to 70.degree. C., at a stirring speed of 250 revolutions/min. When the temperature reaches 70.degree. C., 0.15% by weight of K.sub.2 S.sub.2 O.sub.8, based on the monomer, is added. The synthesis time is set at 4 hours."
The above operating procedure was followed in order to prepare these various LPBACop latices, as shown in Table 22 below, in which the characteristics of these latices are also given.
Also shown in this table are the characteristics of a polystyrene latex prepared batchwise in a 2-1 reactor, the ingredients (91% by weight of water+Cop 8, 9% by weight of styrene and 1% by weight of TDM) being charged into the reactor and heated to 90.degree. C. at a stirring speed of 200 revolutions/min, potassium persulphate then being added and the synthesis time being set at 3 hours.
TABLE 22______________________________________Type ofagglomerating % % of Mean .phi. x.sub.1latex of water methanol (nm) (%)______________________________________LPBACop 8 -a 77 0 340 23LPBACop 8 -b 67 10 200 22.5LPBACop 8 -c 320 23LPBACop 9 -a 55 22 130 19LPBACop 9 -b 67 10 220 23LPSCop 8 91 25 160 25______________________________________
The characteristics of the latices to be agglomerated employed in this series of examples are shown in Table 23 below:
TABLE 23______________________________________Type of latex to Mean .phi. x.sub.2be agglomerated (nm) (%) pH______________________________________LPB6* 110 30 10LPB7 110 30 12LPB8 150 30 12LPBA3** 80 31 4.5LPBA4** 75 28 4.5LSBR 230 40 11______________________________________ *latex containing 10.sup.-2 mole of SDS per 100 g of latex. **synthesized with SDS as a surfactant.
In order to produce the agglomeration, the agglomerating latex is added batchwise to the latex to be agglomerated, to which the SDS surfactant has been added where appropriate, with mechanical stirring. The temperature, the agglomeration time and all the parameters affecting the development of the size of the agglomerated particles (measured by turbidimetry) have been studied.
a) Influence of the agglomeration time
Latex to be agglomerated: LPB6
Agglomerating latex: LPBA Cop 9a
Operating conditions: temperature: 20.degree. C.; R=2.times.10.sup.-2
TABLE 24______________________________________ Time Agglomerated latexTest (h) Mean .phi. (nm)______________________________________56 0.5 280 2 470 6 840 12 1010 24 1010______________________________________
After 12 hours' agglomeration the particle size is stable.
b) Influence of the respective concentrations of the latex to be agglomerated and the agglomerating latex
1 - Variation of the size of agglomerated particles as a function of the total concentration C at constant R
Latex to be agglomerated: LPB8
Agglomerating latex: LPBACop8a
Operating conditions: temperature: 20.degree. C.; R=2.times.10.sup.-2, pH=12.
TABLE 25______________________________________ C Time Agglomerated latexTest g/100 g (h) Mean .phi. (nm)______________________________________58 30 1 300 24 43059 50 1 660 24 1000______________________________________
2 - Variation in the size of agglomerated particles as a function of R at constant C
Latex to be agglomerated: LPB8
Agglomerating latex: LBPACop8a
Operating conditions: temperature: 20.degree. C.; time: 24 hours; pH=12
TABLE 26______________________________________ C Agglomerated latexTest R .times. 10.sup.-2 g/100 g Mean .phi. (nm)______________________________________58 1 30 43060 2 " 66061 3 " 70062 5 " 58063 8 " 58064 0.5 50 82059 1 " >100065 2 " 66066 3 " 580______________________________________
c) Influence of the characteristics of the agglomerating latices
1 - Influence of the particle size
Latex to be agglomerated: LPB8
Operating conditions: temperature: 20.degree. C.; time: 24 hours; pH=8
TABLE 27______________________________________ Agglomerating Mean .phi.Test latex R .times. 10.sup.2 (nm)______________________________________67 LPBACop8 -b 1 60068 " 2 62069 " 3 60070 " 5 550 71* " 7 480 72* LPBACop8 -a 1 640 73* " 2 >1000 74* " 3 960 75* " 5 780______________________________________ *addition of 1.5 .times. 10.sup.-4 mole of SDS/100 g of latex to be agglomerated.
2 - Influence of the molecular mass of the POE blocks in the POE-PS-POE triblock polymers
Latex to be agglomerated: LPB8+1.5 10.sub.-4 mole of SDS/100 g of latex
Operating conditions: temperature: 20.degree. C.; time 24 hours
TABLE 28______________________________________ Agglomerating Mean .phi.Test latex R .times. 10.sup.2 (nm)______________________________________76 LPBACop9 -b 1 45077 " 2 45078 " 3 50072 LPBACop8 -a 1 64073 " 2 >100074 " 3 96075 LPBACop9 -b 5 78079 " 5 70080 " 7 480______________________________________
d) Influence of the characteristics of the latices to be agglomerated
1 - Influence of the pH of the polybutadiene latices
Latex to be agglomerated: LPB8
Agglomerating latex: LPBACop8a
Operating conditions: temperature: 20.degree. C.; time: 24 hours
TABLE 29______________________________________ C SDS Agglomerated latexTest pH R .times. 10.sup.2 g/100 g mole 10.sup.4 Mean .phi. (nm)______________________________________64 12 0,5 50 0 82059 1 " " >100065 2 " " 66066 3 " " 58063 8 " " 58081 8* 1 " 1.5 60082 2 " " 62083 3 " " 70084 5 " " 100085 7 " " 82058 12 1 30 " 43060 2 " " 66061 3 " " 70062 5 " " 58063 8 " " 64072 8* 1 " 1.5 64073 2 " " >100074 3 " " 96075 5 " " 780______________________________________ *pH of the latex to be agglomerated adjusted to 8 by the addition of a dilute solution of hydrochloric acid.
2 - Influence of the degree of covering of the latex to be agglomerated
Agglomerating latex: LPBCop8a
Operating conditions: temperature: 20.degree. C.; time: 24 hours
TABLE 30______________________________________ Degree of Latex to be covering Agglomerated latexTest agglomerated % R .times. 10.sup.2 Mean .phi. (nm)______________________________________57 LPB7 >100 2 42058 LPB8 80-85 1 43060 " 2 66061 " 3 70062 " 5 58063 " 8 580______________________________________
The agglomeration is more pronounced in the case of the latex which has a lower degree of covering.
e) Other agglomerations
Operating conditions: temperature: 20.degree. C.; time: 24 hours
TABLE 31______________________________________ Agglomerated Agglomerating Latex to be latexTest latex agglomerated R .times. 10.sup.2 Mean .phi. (nm)______________________________________86 LPSCop 8 LPB8 1 42087 " " 2 45088 " " 3 70089 " " 5 55090 " " 7 46091 LPBACop8 -c LPBA3 1 18592 " " 3 20093 " " 5 42094 " " 7 55095 " " 10 84096 " " 15 80097 " " 20 545 98* LPSCop 8 LPBA4 1 230 99* " " 3 550100 LPBACop8 -c LSBR .gtoreq.0.5 >1 .mu.m______________________________________ *Addition of 10.sup.-4 mole of SDS per 100 g of latex to the latex to be agglomerated.
The attached drawing shows the interesting feature of the process according to the present invention which was referred to earlier and according to which the curves representing the size of the agglomerated particles as a function of R pass through a maximum, the population being respectively bimodal or monomodal according to whether R is lower or higher than the value corresponding to this maximum.
FIG. 1 in the attached drawing shows the curve .phi. (nm)=F (R.times.10.sup.2) corresponding to test No. 1. The morphology of the agglomerated latex particles was determined by electron transmission microscopy for five values of R, the five corresponding photographic reproductions forming the subject of FIGS. 2 to 6 respectively, the corresponding value of R being shown on each of these. The magnification is 10,000. In FIGS. 2 and 3, in the case of which R is lower than the value corresponding to the maximum, a bimodal population can be seen, and in FIGS. 4 and 6, in the case of which R is higher than the value corresponding to the maximum, a monomodal population can be seen.

Number	Name	Date	Kind
3558541	Dalton	Jan 1971
4357270	Pippa et al.	Feb 1982

Process for agglomerating a latex, agglomerated latex obtained and its application to the modification of thermoplastic matrices to make them impact-resistant

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