Application Of Carboxylic Acid Monomer MBI And β - CEA And Curing Agent SAC - 100 In Emulsion Type Acrylate PSA

Acrylate latex has many characteristics such as excellent weather and aging resistance, low cost, environmentally friendly and safety in the process of manufacture and use. However, after film formation, the acrylate latex film showed poor water, solvent and creep resistance and adhesive properties when compared with the solvent-borne counterparts. Therefore, it is significant to undertake the modification research on the acrylate latexes in order to improve their comprehensive properties. In this dissertation, the functionalized acrylate latex and pressure sensitive adhesive (PSA) were produced with the application of the unsaturated monocarboxylic monomers, monobutyl itaconate (MBI) and β-carboxyethyl acrylate (β-CEA), into the emulsion polymerization. The theoretical basis researches about the application of these two carboxylic monomers in the latex and emulsion PSA were also studied. Moreover, the results were compared with the common carboxylic monomers, i.e. acrylic acid (AA) and methacrylic acid (MAA). On the other hand, propyleneimine external cross-linker (SAC-100) was added to modify the carboxylated acrylate PSA latex in this thesis. In the meantime, the most advanced technologies were applied into the emulsion polymerization and PSA testing, Relevant mechanisms in the cross-linking reaction were explored and comprehensive properties of the latex films before and after cross-linking were investigated. This will definitely provide some research basis for the product development in the future. The modification researches on the peel strength of the acrylate emulsion pressure sensitive adhesives were eventually studied. Main research contents and results of this dissertation are listed as follows:(1) The results obtained on the different partitioning behaviors for carboxylic acids between organic and water phases from this study are of great importance because they allow us to better understand the different carboxyl group distributions in latexes and derived films, and their resulting properties for our future works. The partitioning behaviour of different vinyl acids (AA,MAA,MBI,β-CEA) between n-butyl methacrylate (n-BMA) and the aqueous phases was studied. It was found that the partition coefficients (D) of the unsaturated carboxylic acids depended to a large extent on the acid concentration in the total comonomer mixture. Moreover, the values of the partition coefficient for these four different carboxylic acids between n-BMA and the water phase showed a decreasing order:MBI> MAA> P-CEA> AA, irrespective of the acid mass concentration in the total monomers. The larger the partition coefficient, the more hydrophobic for the carboxylic monomers. The ratio of monomer to water (M/W) does have a significant effect on the distribution of hydrophobic vinyl acids between the n-BMA and water phase, and the stronger the lipophilicity, the greater the effect. Nevertheless, the partition coefficient value for hydrophilic acid monomers were not greatly affected by M/W. The partition coefficients for MBI and β-CEA are strongly influenced by variations in pH. Besides the partition coefficient of the "strong" acids is more sensitive to pH, when compared with "weak" acids, irrespective of the water solubility of the carboxylic acids. The partition coefficients of vinyl acids appear to be independent of the temperature.(2) The research of the emulsion polymerization of n-butyl methacrylate (n-BMA) in the presence of monobutyl itaconate (MBI) and β-carboxyethyl acrylate (β-CEA) is presented. HLB values of different carboxylic monomers were calculated to determine their water solubility, which can be further confirmed by their partition coefficients between n-BMA and water phases. Besides, the effects of the functional comonomers on the final conversion, coagulation, particle size of the latexes, optical density, high-temperature stability as well as on the water absorption, TGA of the polymer films were investigated. Results were compared with those obtained when using methacrylic acid (MAA). Based on Griffin’s method, which was generally applicable for nonionic surfactants, the results of HLB values for different carboxylic monomers in the decreasing order is:β-CEA (12.36)> MAA (10.46)> MBI (9.57). The effect of the carboxylic monomers on the water absorption of the latex film was totally determined by their water solubility. The lipophilic carboxylic monomer MBI does not produce any significant effect on the particle size, while, with the incorporation of the hydrophilic acid β-CEA, the particle size of the latex decreased dramatically. The thermal stability of the three carboxylated polymers follow the order:P(n-BMA+MAA)> P(n-BMA+β-CEA)> P(n-BMA+MBI). It can be seen that with the addition of MBI and β-CEA, the thermal stability of the latex film was not improved when compared with MAA.(3) Although many research reports about the acrylate emulsion PSA appeared in the literature, most of them were confined to the exploration of the polymerization process and kinetics. Moreover, the effect of the carboxylic monomers were limited to the application research of the common vinyl acids, acrylic acid (AA) and methacrylic acid (MAA), in the PSA field. Acrylate emulsion PSAs were synthesized via starved semi-continuous emulsion polymerization processes using butyl acrylate (BA) and methyl methacrylate (MMA) as main monomers. The influences of MBI and β-CEA on the latex conversion, coagulation, stability, zeta potential, critical coagulation concentration (CCC), dynamic shear rheological property as well as on the gel content and adhesive properties (loop tack, shear strength, peel strength) of the latex film were researched. Results were compared with those obtained when using common carboxylic acids AA and MAA. It was found that different carboxylic monomers have no significant effect on the dynamic rheological property of the emulsion. The gel content of the carboxylated PSA showed decreasing order: P-CEA>AA>MBI>MAA, while the sol molecular weight exhibited opposite trend. The loop tack and peel strength of the PSA were increased, while the shear strength was decreased, with the addition of β-CEA. On the other hand, the application of MBI can improve the comprehensive properties of the acrylate emulsion PSA, leading to a good balance among the three basic mechanical properties of the PSA.(4) Propyleneimines external cross-linker (SAC-100) was added to modify the carboxylated acrylate PSA latex. The effects of curing agent contents on the gel content, molecular weight between cross-links (Mc), soluble molecular weight (Mw, Mn) and its distribution (Mw/Mn), water absorption and adhesive properties of the PSA copolymers were investigated. In addition, IR、TGA、SEM and DMA were used to characterize the latex film before and after cross-linking. With the increase of the external cross-linker (SAC-100) content, the gel content of the acrylate PSA polymer increased significantly, while molecular weight between cross-link points (Mc) and the sol molecular weight (Mw, Mn) of the polymer decreased remarkably as expected. The water resistance, film formation and heat stability of the cross-linked adhesive were enhanced when compared with the uncross-linked counterpart. Furthermore, with the addition of external cross-linker SAC-100, the storage modulus (G’) of the polymer film increased, corresponding to the increment in the cohesive strength and shear holding power, the loss modulus (G") and tan δ decreased, corresponding to the reduction in the loop tack and peel strength.(5) Pressure sensitive adhesives (PSA) were produced using latexes synthesized via starved semi-batch emulsion polymerization processes. And the modification researches on the peel strength of the PSA were studied. The results indicated that the type and content of hard monomers have significant effects on the properties of latex PSAs. With the hard monomers contents increased, gel content of the latexes decreased, the glass transition temperature (Tg) increased as expected. Peel strength increased first and then decreased with the increasing St content. On the other hand, the peel strength decreased with the increments in the proportion of MMA and SR340 contents. Peel strength of the final latex PSAs prepared with different kinds of hard monomers in the decreasing order is:St> MMA> SR340. The particle size increased with increasing amount of NaHCO3, and that a good linear relationship between particle size and the amount of NaHCO3 is observed. The particle size distribution of the latex become broader with the NaHCO3 content due to the particle coalescence. However, the stability of the latex decreased when the concentration of NaHCO3 increased. Peel strength increased with the increasing in NaHCO3 concentration when the amount of NaHCO3 is below 0.3 g, and above 0.3 g, the peel strength decreased. Different semi-batch polymerization technologies play significant roles in modifying the properties of latex PSAs. Latex particle size in the decreasing order is:monomer seeded semi-batch>unseeded semi-batch pre-emulsion seeded semi-batch.180° peel strength in the decreasing order is: pre-emulsion seeded semi-batch> unseeded semi-batch> monomer seeded semi-batch.