Study On Polymerization Of Acrylate Soap-free Emulsion Used In Exterior Emulsion Coating

As the acrylic emulsion has advantages of heat-proof, bearing light and anti-ageing, it has been widely used in the coating industry.But ordinary acrylic emulsion also has many disadvantages,such as poor resistance to water, weak adhesive strength and hardness, and it bubbles easily in the process of using . Moreover ,the waste results in pollution because of containing plenty of emulsify. The coating prepared with it also has poor water and stain resistance,thus the expansion application of acrylic emulsion in exterior emulsion coating meets great trouble. So it is imperative to enhance the water resistance,bubbling ability and adhesive strength of the emulsion under the situation.The soap-free emulsion doesn't contain or only contain little(its density is small at the critical gum bunch density) emulsify, compared with ordinary emulsion, the particles of gum have ciean surface and simplex dispersion,it can avoid the adverse influences of water-close surface activity .So it is possible to make the polymer have better physics-chemistry function, machine performence and sticky ability, we can also get the high performance coating with it.In this paper, two technique methods are introduced to make high performance soap-free emulsion:(1)using self-made emulsifier: An oligomer P(BA/AANa) which has good capability of emulsification was made from soap-free emulsion polymerization using acrylic acid(AA) and butyl acrylate(BA) as polymerization monomers, Potassium Persulfate(KPS) as initiator, Dodecyl Mercaptan(DDM) as chain transportation agent and NaHCO3 as cushion. We made certain the best monomerratio BA/AA at 3/7through experiments, then used this oligomer as emulsifier to compound soap-free latex polymerization.When the dosage of oligomer P(BA/AANa) is at 2.5%, latex and its coating had the best comprehensive function.The cross-linking monomer HEMA was mixed in the shell layer improvement the water resistent of the latex, its dosage was 1.5% of shell-polymerization monomers.(2)using reactive emulsifier:The reactive emulsifiers have polymerization activity, the reactive function groups in which can participate latex polymerization, they are connected to the surface of polymer grains by covalence key.As became part of the polymer, it is easy to avoid emulsifier moving from the polymer grain or moving at the latex film, the water-close groups on surface of film decrease greatly, thus adhesive strength , water resistant and stain resistant of the coating increase.The reactive emulsifier used in this paper include HPMAS , HAPS SVS, DNS-86, SE-10N and NaUA,they were used alone,with each other or with ordinary emulsifier to make high performance soap-free latex.Through a great deal of experiment, we know that the emulsifier DNS-86, SE-10N,NaUA has good capability of emulsification, they can be used alone.Considering the comprehensive performances of latex, the best dosage of SE-10N is 1.0%～1.5%, the best dosage of NaUA is 2.7%, the best dosage of DNS-86 is 1.0%.But the DNS-86 is the best one in this 3 kind of emulsifier.Compared them with the normal regulations latex,the adhesive strength, bubbling ability, waterabsorbing rate solid content and are all obvious improved.The systems in which reactive emulsifier SE-10N, NaUA, DNS-86 used with each other are good for water resistent, waterabsorbing rate and solid content of the latex.Considering all performances, SE-10N/ DNS-86 at 0.6/0.5, SE-10N/NaUA at 0.6/1.5, NaUA/ DNS-86 at 1.0/0.7 are the best ratios. SE-10N, NaUA, DNS-86 used with the other kinds of reactive emulsifier,such as SVS, HAPS, HPMAS ,can improve water resistent and waterabsorbing rate of the latex,and the water resistent of coatings which confected with the latex are also enhanced. But too much dosage is not proper.The order of their impact on performances is SVS>HAPS>HPMAS. Mixed the reactive emulsifiers mentioned above with ordinary emulsifier OP-10, the stability of reaction system is very good, the average diameter of particles are smaller, and the single dispersion is better, but the bubbling ability,water resistent are not really perfect.In general, soap-free latex and its coating had better performances of water resistent , bubbling ability,stain resistent, adhesive strength,hardness than the ordinary one.