Laboratoire de Pharmacie Galénique et Biopharmacie, Faculté de Pharmacie, Université Paris XI, 5, rue Jean-Baptiste Clément-U.A. CNRS 1218, 92296 Chatenay-Malabry Cedex.
Int J Cosmet Sci. 1987 Dec;9(6):269-78. doi: 10.1111/j.1467-2494.1987.tb00483.x.
Synopsis In cosmetology eye shadows are often presented as pressed powders. The pressed powder studied contains about 80% of lamellar substances such as talc and titanised mica, pigments, preservatives and a liquid binder which is a mixture of lipophilic substances. Usually cohesion in compacts is obtained by establishing bonds between dry particles; on the contrary in the case of pressed powder in the presence of a liquid binder one can suppose that all particles are covered before compaction with a thin layer of liquid, so that the binding mechanism must be different to that for dry compacts. The aim of this study is to verify this hypothesis using (i) investigation of the energy of compaction by measuring the total energy balance during compaction; (ii) a resistance evaluation by a drop test; (iii) indentation hardness measurements. Among the different energy terms the network of compaction is representative of the formation of the bonds between particles and also of particle fragmentation or deformation occurring during compression. The results show that the network of compaction is influenced by the binder level, but the resistance is not proportional to the network. This indicates that the network of compaction, as it has been measured or calculated, is not able to predict the resistance of the compacts. However, a direct relation, independent of the binding level, has been found between network of compaction and indentation hardness. It means that indentation hardness is rather more indicative of the compact deformation under a low loading rate than of the resistance to rupture, which implies a high loading rate. However, the binder level is of paramount importance: the rupture resistance increases when the quantity of binder is increased. The rheological properties of the liquid binder are also important. The effect of a variation of the binder viscosity upon the compact cohesion is important, especially at low compaction pressures (<8 MPa); at higher pressures the viscosity influence is less drastic, suggesting a change of the banding mechanism. However, viscosity is only one aspect of the medogid properties of the binder. The rheological behaviwr is shown to be thixotropic so that shearing time aid relaxation time become an importnnt parameter for cohesion and resistance. This conclusion is of importance for the formulation. Those two facts throw light on the cohesion mechanism of pressed powder. The banding of the particles seems to be essentially due to the presence of the liquid binder. Capillarity forces or viscosity forces, depending on the binder rheology, am responsible for the properties exhibited by pressed powder. Finally, one can conclude that the pressed powders form damp powder-eompacted systems whose binding mechanism is very different from those involved in pharmaceutical compact cohesion, so that a good formulation must involve a complete study of the rheological properties of the binder.
概要 在化妆品中，眼影通常以压粉形式呈现。本文研究的压粉含有约 80%的层状物质，如滑石粉和钛化云母、颜料、防腐剂和一种亲脂性物质的液体结合剂。通常，在压粉中，在存在液体结合剂的情况下，所有颗粒在压实前都可能被一层薄薄的液体覆盖，因此结合机制必须与干压粉不同。本研究旨在通过以下方法验证这一假设：（i）通过测量压实过程中的总能量平衡来研究压实能量；（ii） 通过跌落试验评估阻力；（iii） 压痕硬度测量。在不同的能量项中，压实网络代表了颗粒之间的键的形成，以及颗粒在压缩过程中碎裂或变形。结果表明，结合剂水平会影响压实网络，但阻力与网络不成比例。这表明，正如已经测量或计算的那样，压实网络不能预测压块的阻力。然而，已经发现压实网络与压痕硬度之间存在直接关系，与结合剂水平无关。这意味着压痕硬度在低加载速率下更能指示压块的变形，而不是在高加载速率下的破裂阻力。然而，结合剂水平至关重要：随着结合剂数量的增加，破裂阻力增加。液体结合剂的流变性能也很重要。结合剂粘度的变化对压块内聚的影响很重要，尤其是在较低的压实压力（<8MPa）下；在较高的压力下，粘度的影响不那么剧烈，这表明结合机制发生了变化。然而，粘度只是结合剂介质性能的一个方面。流变学行为表现出触变性，因此剪切时间和松弛时间成为内聚性和阻力的重要参数。这一结论对配方很重要。这两个事实揭示了压粉内聚的机制。颗粒的结合似乎主要是由于液体结合剂的存在。取决于结合剂的流变学，毛细力或粘度力负责压粉表现出的性质。最后，可以得出结论，压粉形成潮湿的粉末压实系统，其结合机制与药物压块内聚中涉及的机制非常不同，因此良好的配方必须涉及对结合剂流变学性质的全面研究。
