A distinction is made between the two sheet materials named in the title and nine examples are quoted covering a wide range of both of them. A brief description is given of the method of producing such materials and surface micrographs at a magnification of 2,000 times are reproduced to show the wide difference in surface texture.
The physical test data for six of the synthetic and plastics papers are quoted in comparison with similar data for three conventional coated papers. In particular, the ink absorbency of plastics paper is far too low to permit the use of conventional printing inks that dry mainly by solvent absorption. The dimensional stability is exceptionally good and increases as the proportion of cellulose fibres in the sheet diminishes. Most plastics and synthetic papers suffer from a relatively low stiffness compared with conventional papers, but there is definite evidence that a ‘second generation’ of plastics papers is being designed to give greater stiffness by means of a multi-ply construction, in which the centure of the sheet has a low density honeycomb structure.
Generally, the plastics papers have a significantly higher resistance to the dissipation of static electricity than do conventional papers. The presence of mineral coatings considerably reduces the resistivity, as shown by some of the plastics papers that have had a surface coating. Contrary to expectations the consistency of quality of plastics papers is not better than that of conventional papers; in fact, it is often less consistent. Values of the coefficient of variation for some of the papers are given in the text.
In an appendix, a description of the physical characteristics of an unidentified Japanese second generation plastics paper are given. The plies had been separated by a manual technique and their varying grammage, thickness and density were determined.