Лако-красочные материалы — производство

During research for anticorrosive pigments with improved performance properties compared to zinc phosphate, the development of so-called modified polyphosphate pigments was a further focus.

Orthophosphates are manufactured using the reaction of orthophosphoric acid with basic and/or amphoteric substances. Polyphosphates are obtained by conden­sation of acidic orthophosphates at higher temperatures [5.54]:

• Orthophosphates

e. g. 3 ZnO + 2 H3PO4 ^ Zn3(PO4)2 + 3 H2O

• Polyphosphates

e. g. Al(H2PO4)3 ^ AlH2P3Ow -2 H2O

Modified polyphosphate pigments, which are of practical importance today, are predominantly reaction products of acidic aluminum tripolyphosphate with com­pounds based upon zinc, strontium, calcium, and magnesium (Table 5.7).

Development activities in conjunction with polyphosphate pigments have been focused on the high chelate building potential of acidic aluminum tripolyphosphate with metal ions [5.87].

Furthermore the accentuation of specific properties of certain substances within one product (synergistic effects) was tried [5.54]. Although the utilization of synergis­tic effects is not new for the pigment and coatings industry, it leads to very interesting results in the area of anticorrosive pigments [5.54]. Recent research work reports that special synergistic effects can be observed when using a phosphate-based pigment in combination with an organic corrosion inhibitor. Due to the utilization of such a combination, there might be the possibility to improve the substrate protection during the initial phase of exposure, resulting in improved long-term protection in special applications [5.54]. As discussed before, the development of modified or­thophosphates, and polyphosphates was possible by taking effect of synergies. A key feature of the most modified phosphate-based pigments is their compatibility with a wide range of resins. Although the modified phosphate anticorrosives show wide

compatibility, it is advisable to select those pigments, which are recommended by the pigment supplier for any particular application [5.54].

This is one of the reasons why the pigment industry has been working on the development of phosphate-based pigments for universal applications. The typical properties of two modified orthophosphate based anticorrosive pigments, which have been available on the market since 2003 for universal applications, are summarized in Table 5.8.

5.2.5.4