Aqueous polymer dispersion and process

Abstract

There is described a multi step process for preparing an aqueous dispersion of heterogeneous polymer particles by mini-emulsion polymerisation, the process comprising the steps of (I) (a) forming a mixture comprising: (i) water; (ii) at least one stabiliser (such as a surfactant and a hydrophobic co-stabliiser); (iii) at least one tackifier (such as polyterpenes, rosin resins and/or hydrocarbon resins); (iv) at least one +-,-ethylenically unsaturated monomer;, (b) applying high shear to the mixture from step (a) to form an essentially stable mini-emulsion comprising an aqueous continuous phaseand dispersed therein stabilised droplets of average diameter from about 10 to about 1000 nm, (c) polymerising the monomer(s) within the droplets in the presence of a free radical initiator; (d) adding further monomer to the dispersed phase to form a dispersion; then: (II) using the dispersion from step (I) as a seed to form a dispersion of heterogeneous polymer particles in a subsequent emulsionpolymerisation. The resultant tackified PSAs may have a core shell structure and are stable under high shear.

Description

technical field [0001] The present invention relates to the field of pressure sensitive adhesives (PSAs) comprising tackified acrylic emulsions. Background technique [0002] It is desirable for PSA emulsions to have higher adhesion to a variety of substrates such as substrates with lower surface energies such as polymeric films and other substrate types such as cardboard. One of the ways to achieve this is to add tackifiers such as polyterpenes, rosin resins and / or hydrocarbons. Addition of tackifiers to emulsions, however, can have an adverse effect on the stability of aqueous latexes, especially when the latex is subjected to high shear. [0003] Dispersions of tackifiers in water are unstable under high shear due to coagulation. For example, hydrocarbon tackifiers are usually at 4000 to 5000s -1 coagulation at higher shear rates. When this tackifier dispersion is added to a conventional acrylic PSA emulsion, the resulting mixture also coagulates under high shear. ...

AI Technical Summary

Problems solved by technology

[0022] None of the existing literature suggests the incorporation of tackifiers in the dispersed hydrophobic phase of microemulsions, and given the difficulty of simultaneously stabilizing both tackifiers and microemulsions, there is every reason not to do so

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