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OwnerDaniele Becciii, Stefano Finocchiaro +2inventors
InventorsDaniele Becciii, Stefano Finocchiaro, Mario Lugli, Leo Mario Saija
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A process for obtaining an aqueous polymer dispersion comprising the following steps:—formation of a monomer preemulsion in water by using surfactants;—transfer into the reactor of the basic charge containing a surfactant solution and a part of the preemulsion;—step C.1 polymerization start;—step C.2 polymerization of the monomeric mixture;—step C.3 removal of the residual monomers; wherein: A) from the start and up to a time in the range from −40% to +20% with respect to the instant wherein the polydispersity index of the particle sizes increases, the preemulsion is fed and the surfactant concentration in the reactor is not higher than 0.7% by weight; B) subsequently and till the polymerisation end, the remaining part of preemulsion is fed and the surfactant concentration in the dispersion is higher than that in step A) but lower than 5% by weight with respect to the dispersion weight.
1- A process to obtain an aqueous polymer dispersion having a dry content from 65% to 75% by weight and the combination of the following properties:
2- A process according to claim 1, wherein the surfactant solution used in the basic charge is formed by water containing a surfactant in an amount from 0.05 to 0.3% by weight.
3- A process according to claims 1-2, wherein the preemulsion in step C.2 is fed into the reactor with constant flow both in A) and in B).
4- A process according to claims 1-2, wherein the preemulsion in step C.2 is fed into the reactor by initially using a preemulsion feeding rate, determined as % by weight based on the total of the prepared preemulsion, initially using a preemulsion feeding rate from 0.08%/min to 0.25%/min for the first 20-40 minutes and then a feeding rate of 0.25%/min, preferably 0.32%/min-0.80%/min, until the polymerization end.
5- A process according to claims 1-4, wherein the ethylenically unsaturated monomers used are esters of C3-C10-α,β-unsaturated, mono- or di-carboxylic aliphatic acids with C1-C12, preferably C1-C8, aliphatic or C5-C8 cycloaliphatic alkanols, in admixture with C3-C10-α,β-unsaturated, mono- or di-carboxylic aliphatic acids, optionally in the presence of other ethylene monomers.
6- A process according to claim 5, wherein at least 70% by weight of the monomeric emulsion is formed by the esters optionally in the presence of C3-C10-α,β-unsaturated, mono- or di-carboxylic aliphatic acids.
7- A process according to claims 5-6, wherein the ratio by weight between the acid and the ester ranges from about 1:10 to about 1:350.
8- A process according to claims 5-7, wherein the other ethylene monomers are selected from one or more of the following:
9- A process according to claims 5-8, wherein to the monomer mixture crosslinking monomers are added in an amount not higher than 3%, preferably from 0.1% to 1% by weight with respect to the monomeric formulation.
10- A process according to claims 5-9, wherein the monomer mixture has the following composition:
11- A process according to claims 1-10, wherein the surfactants are non-ionic, and/or anionic or cationic or mixtures thereof;
12- A process according to claim 11, wherein the total amount of surfactants and optional protector colloids is lower than 5% as percentage by weight with respect to the final polymer dispersion, preferably from 0.7 to 3.5% by weight, more preferably from 1 to 2.5% by weight.
13- A process according to claims 1-12, wherein a control agent of the polymer chain length and of its molecular weight as chain transfer agent is optionally used in an amount from 0.01 to 5% by weight with respect to the monomeric mixture.
14- A process according to anyone of claims 1 to 13, wherein the aqueous polymer dispersion to be obtained has a Brookfield viscosity lower than 2,000 mPa·s, measured at 23° C. under the following conditions:
15- A process according to anyone of claims 1 to 14, wherein the aqueous polymer dispersion to be obtained has a Brookfield viscosity lower than 1,000 mPa·s when the dry content is about 68% by weight, measured at 23° C. under the following conditions:
16- Aqueous dispersions obtainable by the process according to claims 1-15.
17- Dispersions according to claim 16 containing multimodal distributions of the dispersed polymer particle sizes containing a fraction of particles of a non spherical shape having an average diameter determined by electronic transmission microscopy, comprised between 800 and 1,300 nm.
18- Dispersions according to claims 16-17, containing polymers having a Tg comprised between about −60° C. and about +40° C.