Published January 1974
This report is primarily concerned with synthetic printing and writing papers made from polymer fillms. Synthetic papers are being developed to reduce dependence on uncertain supplies of pulpwood. Moreover, synthetic paper has improved properties compared with those of wood-based paper: Tensile strength, folding endurance, dimensional stability, and moisture resistance are significantly improved.
Synthetic papers that readily accept writing with pencil, ball-point pen, and high-quality printing of various types are emphasized in this report. On the other hand, synthetic materials designed primarily for packaging uses are not included.
Papers composed chiefly of the less expensive polymers are most likely to be attractive contenders in the marketplace. These polymers would include polyolefins, polystyrene, and polyvinyl chloride (PVC). Polyamides or polyesters may find application for more specialized uses.
Synthetic papers may be made from either modified films or fibers, including continuous fibers. Although it has some uses as a paper substitute, a polymeric substrate composed of a compacted sheet of very fine continuous fibers (l'spun bonded") falls into the field of nonwoven fabrics. Therefore, it is considered outside the scope of this report.
Papers made from discrete fibers are becoming increasingly interesting. A synthetic pulp made from polymer fibers--alone or mixed with wood Pulp --may be converted into a paper by the use of traditional papermaking methods. A ttsecond generation" of synthetic pulps that forms a fibrous pulp slurry directly in the polymerization reactor is now being developed. Detailed evaluation of synthetic pulp processes, however, has not been included in this report.
The following sections deal with the modification of polymer films to make them more paper-like. Mainly this requires increasing opacity, stiffness, and ability to accept printing and writing. The technology entailed is therefore primarily that of the plastics-converting industry, particularly the film-making segment.
It should be noted that wood-based pulp, as produced, is not immediately suitable for making finished paper. To obtain proper strength, opacity, surface, and feel, the wood-pulp slurry must be treated--usually by beating or refining. Beating the fibers makes the paper stronger, denser, more uniform and opaque, but less porous. Filler is added to give a smoother surface, more brilliant whiteness, and improved opacity. Sizing is added to reduce penetration by liquids. Coatings may be applied to improve printability and smoothness.
These desirable properties of wood-based paper should also be present in a synthetic paper made from polymer films. In some cases, similar techniques may be used (filling, coating); in other cases, entirely different techniques are more appropriate (orienting, solvent treating), This report is organized according to these paperizing techniques, and an evaluation of typical synthetic papers made by a combination of these processes follows.
Information was compiled from patents, published articles, and discussions with manufacturers of equipment designed for producing various types of synthetic paper.