| Water-borne coating was the most widely used,promising and likely to replace the traditional solvent-based coating.Latex coating was the main variety of water-borne coatings.Latex coating had strong shielding,fast drying speed,wash-ability and environmental protection.The polymer in latex coatings dispersed in water by the form of spherical particles with emulsifier,which made its difficult to form a continuous film.At present,the researches on the film-formation process of water-borne latex were mainly focused on the individual stages for moisture volatilization,particle deformation and polymer molecular chain diffusion,etc..While the systematical researched on the influence of film-formation process and mechanism on the properties of latex films were less.Understanding and controlling the film-formation process was one of the key technologies to realize the final application of water-borne coatings replace the solvent-based coatings.Therefore,it had great significance to systematically study the film-formation process of water-borne latex even waterborne coatings for developing,upgrading and application of waterborne coatings in the future.In this paper,the film formation of styrene-acrylate copolymer latex was used as the research object.The effects of film-formation parameters,coalescents,filler types,self-crosslinking reactions and curing reactions on the film-formation process and the properties of latex films were studied by differential scanning calorimeter（DSC）,thermogravimetric analyzer（TG）,dynamic thermomechanical analyzer（DMA）,fourier transform infrared spectrometer（FT-IR）,laser scattering particle size analyzer,electrochemical impedance spectroscopy（EIS）,scanning electron microscope（SEM）and so on.The latex film formation mechanisms in different situations were also discussed.The main research contents and achievements of this thesis mainly included the following five aspects:Firstly,water-borne styrene-acrylate copolymer latex and solvent-based styrene-acrylate copolymer solution was respectively prepared by seed latex polymerization and solution polymerization methods by using styrene and butyl acrylate as reaction monomers.The deformation mechanism of latex particles was discussed by the parameters in latex film formation.By comparing the film-formation processes of water-borne and solvent-based styrene-acrylate copolymer systems,the basic reasons for the properties of latex film obtained by water-borne film was worse than solvent-based film were analyzed.It was found that the evaporation rate of the solvent and water were increased with the increasing of film formation temperature.The film-formation temperature could also affect the latex particles deformation mechanism.The latex particles fusion followed the dry sintering mechanism when the film-formation temperature was below the glass transition temperature(Tgp)of polymer,14.4°C.And the wet sintering mechanism was observed when the film-formation temperature was above Tgp.When the film-formation time was extended from 2h to 24h,the water-absorption rate of latex film decreased from 10%to 4%,and the solvent system decreased from 5.5%to3.5%.The performance of the latex film formed under the wet sintering mechanism is inferior to the solvent-bases polymer film because of its emulsifier.Secondly,using styrene,methyl methacrylate,and butyl acrylate as reaction monomers,styrene-acrylate copolymer latex I with Tgp of 67.4°C andⅡwith 31.3°C were prepared by seed emulsion polymerization.The influences of the coalescents of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate（CF12）and propylene glycol phenyl ether（PPH）on the latex film formation and latex films’properties were studied.It was found that the coalescent had no significant effect on the size and zeta potential of the latex particles.The coalescent could promote the diffusion of polymer chains in latex particles.With the increase of the amount of coalescent,the Tgf of the latex film decreased,and the fusion mechanism of the latex particles changed from dry sintering mechanism to wet sintering mechanism.The reason was the coalescent could promote the diffusion of latex particles polymer chains.Under the wet sintering mechanism,the polymer molecular segments of the latex particles in the latex film could diffuse among the particles to form a uniform latex film.Therefore,the addition of coalescent could make the property of the latex film closer to the solvent film.The addition of coalescent CF12 and PPH resulted in additional weightlessness in the latex film at 150°C to320°C and 180°C to 320°C,respectively.The coalescent still existed in the latex film for a period of time after the film-formation process was finished.Thirdly,filler iron red powder（Fe2O3）and titanium dioxide（Ti O2）were added into styrene-acrylate copolymer latex I andⅡ,respectively.The effects of filler on the latex film’s glass transition temperature Tgf,water absorption,hardness and film-formation mechanism were studied.The results showed that the addition of fillers had little effect on the Tgf of the films formed by styrene-acrylate copolymer latex.When the wet film of styrene-acrylate copolymer latex with fillers was dried at a temperature below the polymer Tgp,its surface was mainly covered with polymer latex particles.While the drying temperature was higher than Tgp,the filler particles would appear on the film surface.Meanwhile,the incorporation of fillers into the styrene-acrylic copolymer latex system increased the water absorption rate of the dry film.When the film was formed at a temperature lower than Tgp,the filler would increase the stress generated by the particle accumulation during the film-formation process,resulting in an increase of the crack spacing.Fourthly,using styrene,methyl methacrylate and butyl acrylate as reaction monomers,and vinyltriethoxysilane（A-151）,vinyltrimethoxysilane（A-171）orγ-methacryloxypropyl-methyldimethoxysilane（UP-571）as functional monomers,a silicone-containing styrene-acrylate copolymer latex was prepared by seed latex polymerization method.The effect of the hydrolysis and cross-linking reactions of organo-siloxane on the film-formation process and the properties of the latex films were studied.It was found that the double bond-containing organo-siloxane monomers A-151,A-171 or UP-571 could participate in the radical copolymerization reaction to form silicon-containing styrene-acrylate copolymer latex.The water evaporation rate of the polymer latex was related to the polymer Tgp,and the latex particles were fused in a dry sintering mechanism during film-formation.The absorption peak intensity of Si-O-C at 1086 cm-1 in the FT-IR spectra were gradually decreased during the film-formation,and the absorption peak intensity of-OH at 3600 cm-1 increased firstly and then decreased.Moreover,the Tgf of the latex film increased with the increase of the film-formation temperature.All these facts confirmed that there was a hydrolysis and cross-linking reaction in the film formation.EIS analysis showed that the density of the latex films increased with the hydrolysis and cross-linking reaction of organo-siloxane during latex film formation.Thus,the properties of the latex film will be closer to the solvent film.Finally,the latex of modified styrene-acrylate copolymer containing epoxy groups were prepared by seed latex polymerization method with styrene,methyl methacrylate,butyl-acrylate and bisphenol F-type epoxy resin.DSC,TG,FT-IR and SEM were used to study the effects of the curing reaction of the epoxy groups on the latex film-formation and the properties of the films.The results showed that the absorption peak intensity of the epoxy group of the polymer at 914 cm-1 in the FT-IR spectra gradually decreased during the film formation,and this absorption peak disappeared after curing for 1800s.While the intensity of the-OH absorption peak at 3310 cm-1 gradually increased.The Tgf of the cured latex film increased with the development of curing reaction between the modified styrene-acrylate copolymer containing epoxy groups and the epoxy curing agent.When the curing agent was not added,the Tgf of the latex film formed by epoxy modified styrene-acrylate copolymer latex was-8°C.The latex film Tgf increased to 45°C after adding 30%curing agent.SEM showed that there were a large number of granular latex particles on the surface of the latex film,which indicated that the cross-linking reaction between the curing agent and epoxy modified latex preceded the diffusion of copolymer molecules through the boundary of latex particles. |
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