DD209837A1 - METHOD FOR ADJUSTING TARGETED PARTICLE SIZE DISTRIBUTIONS IN CONTINUOUS EMULSION POLYMERIZATION - Google Patents

Abstract

The method allows the benefits of continuous processes to be exploited, while eliminating the disadvantages associated with the setting of targeted particle sizes. In this process, the process sequence is designed such that two or more reaction vessels connected in parallel are preceded by the reaction vessel or series reaction vessels in which or in which the main polymerization process proceeds continuously, in which the polymerization is started continuously and carried to completion of the particle formation phase becomes. The targeted adjustment of the Teilchengroessenverteilungen for the final dispersion is carried out already by suitable formulation designs and Reaktionsfuehrungen in the main polymerization process upstream reaction vessel. The method can be used particularly advantageously in the cases where polymer dispersions with specific use values resulting from the targeted particle size distributions are to be produced continuously.

Description

Title of the invention

Method for setting specific particle size distributions in continuous emulsion polymerization

Field of application of the invention

The invention relates to a method for adjusting specific particle size distributions in continuous emulsion polymerization, which can be used particularly advantageously in the continuous preparation of polymer dispersions having specific utility values which result from the deliberately set particle size distributions.

Characteristic of the known technical solutions

As is known, the preparation of polymer dispersions in emulsion polymerization processes is carried out in the art both batchwise and by continuous processes, wherein the feed of dispersing agent, monomers, emulsifier and initiator (partially Begier and other additives) and the discharge of the final dispersions is carried out batchwise or continuously.

In addition to these processes, so-called feed processes are known in which the dispersing agent, the emulsifier and the initiator are initially introduced and the monomer is added either completely or partially only during the polymerization.

In general, the batch process as well as the feed process that desired particle sizes, especially smaller particles can not be made too wide particle size "here safer and less expensive than in continuous processes, which often undesirable smallest particles and oversized particles to draw characterized & xxB _f Use value of Final dispersion influence negatively (DE-OS 2 16O 381). From the point of view of the preparation of polymer dispersions with specifically set particle size distributions, preference should therefore be given to the discontinuous process or the feed process.

From an economic point of view, on the other hand, the continuous processes offer significant advantages, especially in the case of larger production units, since the considerable idle times for cleaning, filling, heating, cooling, printing etc. can be decisively reduced only in these processes (DE-OS 1900, 112, DE-OS 25 55 142). In addition, in addition to the better use of the heat of reaction, automated quality controls and process controls can be used much more effectively in these processes. However, these processes have the disadvantage that a targeted variation of the particle size distribution is not possible.

Goal of the Invention

The object of the invention is to produce ₉ targeted particle size distributions in continuous Bmulsionspolymerisations ™ processes by a simple and economical procedure, taking full advantage of the advantages of continuous processes * but the disadvantages are eliminated in terms of setting targeted particle size distributions.

Explanation ; of the Jffesens of the Ecfindung;

- The technical problem of the invention

The invention is based on the object of developing a method for adjusting specific particle size distribution in continuous emulsion polymerization with the aid of suitable process steps so that the final dispersions correspond to predetermined values with regard to the distribution widths of the particles, their modalities and the position of the distribution maxima.

Features of the invention

The object is achieved according to the invention in that the polymerization is started continuously in two or more reaction vessels connected in parallel and / or upstream of the polymerization vessel (s), and is conducted until completion of the particle formation phase.

The use of this process surprisingly makes it possible to control the particle size distributions of the final dispersions in a well-reproducible manner over a wide range, the control for the targeted adjustment of the particle size distributions already being carried out by suitable process designs and reaction guides in the reaction vessels preceding the main polymerization process he follows.

The advantages of the process according to the invention result from the "spatial separation of particle formation and particle growth processes." It has been found that in the reaction vessel or vessels in which or in which the main polymerization process takes place the particle counts remain constant during the main polymerization, when particle aggregations is prevented by sufficient particle stabilities and further particle formation by possible subsequent additions of surfactants

"Since these conditions can be met without difficulty, the Hauptpolymerisationsprozeß can always be performed so that only particle growth processes take place." For a specific Hauptpolymerisationsprozeß with Isorgegebenem sales is therefore the particle size distribution of the final dispersion only a function of : Particle size distribution with which the main polymerization process is fed »

The particle size distribution _s with which the main polymerization process is fed results in the superposition of all the particles formed in the reaction vessels connected in parallel and in the main polymerization process in the process according to the invention. Since the formation of these particles, ie their size and their specific number, In the individual upstream reaction vessels, the recipe design (eg type and concentration of emulsifier and initiator and monomer concentration) and the process control (eg temperature and stirring speed) make it well reproducible and can be selectively controlled within wide limits The particle size distributions of the final dispersion in terms of the distribution width, their modalities as well as fege the distribution maxima given values. The targeted adjustment of the particle size distribution is of essential importance for the application properties of the dispersions produced, eg. For example, for paints and adhesives ₉ in particular with respect to rheological behavior, film formation and adhesion to absorbent substrate en «.

As reaction vessels, which are connected in parallel upstream of the main polymerization, tube or Zellarreaktoren are particularly suitable soiirie stirred tank with low residence times »

, ^: ' ⁵

The advantage of this process compared with known solutions which describe possibilities for adjusting the particle size and its distribution in continuous emulsion polymerization (DE-OS 2 16.0-381, DE-0S 1 802 089) lies in the following points:

The method described offers the possibility not only of adjusting the distribution width and the position of the maximum of the particle size, but also of specifying the modality of the distribution, which is essential for certain application properties (slumping behavior, substrate adhesion)

- The method is arbitrarily applicable for the preparation of both surfactant and Schutzkolloidstabilisiert s dispersions in the context of a continuous polymerization process with minimal accumulation of transition products of inferior quality at type change.

embodiment

A polyvinyl acetate dispersion having a polymer content of 50 % and a bimodal particle size distribution is to be produced via a continuous emulsion polymerization process, wherein at the same particle frequency the maxima of the particle size distribution should be 200 nm and 350 nm.

The main polymerization process, which proceeds in two reaction vessels connected in series, is preceded by two parallel reaction vessels (reaction vessel I and reaction vessel II).

With the conditions: Reaction vessel I

Polymerization temperature T »80 ⁰ G mean shear rate = 90 s" ¹

Initiator concentration (K ₂ S ₂ Og) ^ s 7 · 10 °° mol / 1

Concentration of boric acid ο «3 * 10 ° * rnol / 1

(Suberosuccinic acid semi-ester) polymerized pesticide fraction e = * 2%

Reaction vessel II

polymerization T ss 80 ⁰ C mean shear rate β 90 s ~ ° ¹ initiator concentration ^c i = 7. 10 ~ ³ mol / 1 (K ₂ S ₂ O ₈ ) Bnulgatorkonzentration ^c s β 0 mol / 1 polymerized pesticide C β 2 55 proportion of

arising at the output of the reaction vessel I spezifisehe of particles of ϊΐχ = 10 cm ^J and average particle sizes of d _T = 70 mn and at the outlet of the reaction vessel II specific particle numbers of njj = 2.10 ^ cm ^J and average particle sizes of äjj = 120 nm.

If now the discharge rate of the reaction vessel II compared to that of the reaction vessel I is chosen to be five larger and the particles are mixed from the two upstream reaction vessels, then at the entrance of the main polymerization η = 39 3 "1O ¹ - ³ cm" - ³ particles with the same particle abundances for the dj-β 70 nm and the ά ^ χ ~ ^ ^{20 1} ^ particles.

Un subsequent Hauptpolymerisationsprozeß in which the polymer content is increased to 50 % , these Teil chen grow to the desired average values of dy = 200 nm and · d-pj = 350 nm.

Claims (1)

Erfindun ^ sanspruch Process for adjusting specific particle size distributions in continuous polymerization in one or more successive polymerization vessels, characterized in that the polymerization is started continuously in two or more reaction vessels connected in parallel and upstream of the polymerization vessel (s) until completion of the particle formation phase becomes.