Лако-красочные материалы — производство

For the development of cements of the glass ionomer (GI) type, features have been borrowed from both the polycarboxylates and the silicate cements. In the fundamental cementation process, polyacids, such as poly(acrylic acid) and acrylic-maleic or acrylic- itaconic acid copolymers, interact with inorganic cationic constituents of sodium aluminosilicate glass possessing a high Al content. The reaction involves a complex interplay between hydronium ions from the polyacids penetrating into the glass core and calcium and aluminum cations migrating out of the core into an outer gel phase for subsequent salt and complex formation with the polyacids. Tartaric acid is commonly added as a controlling agent of the setting characteristics. The application forms, powder-liquid and powder-water, are similar to those of the polycarboxylates. The cured cements are quite strong under compressive load, ultimate compressive strength values approximating 140 to 180 MPa, and sonication immediately after mixing of the components, resulting in void reduction, appears to have an enhancing effect on com­pressive strength. The adhesion characteristics resemble those of the polycarboxylates, provided that early moisture access is avoided, for example, by protecting the fresh lute margin with a coat of varnish. Typical shear bond strength data measured in vitro on conventional cements bonded to enamel and dentin, respectively, are 9 to 10 and 3 to 5 MPa [4,5]. Because of the rather low (ca. 12 MPa) inherent tensile strength of the glass ionomers, tensile failure is cohesive in the cement, setting a limit to overall expected bond strengths. For a novel stainless steel-reinforced GI cement, corresponding strength values of about 14 and 10 MPa, respectively, have been reported [5]. As the predominant use of the GI cements is in cavity lining, the reader is referred to Section IV. B.5 for additional details.