Quality Control

While it can be said that a good quality paper is one that causes the printer a minimum of trouble in producing a good printed article, some means of expressing quality in terms of the physical properties of the paper must be available before paper quality can be evaluated.

Considering newsprint in particular, the printer is chiefly concerned with two characteristics — runability and printability. Runability may be defined as to how well the paper travels mechanically through the printing press, while printability may be defined as the faithfulness of reproduction of the image impressed on the paper by the ink covered form.

Printability is a complex combination of ink and paper properties and printing conditions, but provided ink and paper properties are constant or change only gradually, a good result can be consistently attained.

However, the printer cannot follow rapid fluctuations in paper properties without either losing considerable time or producing a substandard article. Hence the mill aims to produce paper with uniform printing characteristics, at as high a level as possible.

Runability is almost entirely controlled by paper strength and the presence or absence of defects. Quality control on paper machines aims to completely eliminate defects such as holes, wrinkles, checking edge tears etc., by continuous inspection, rejecting faulty paper and correcting operational faults. With a daily production of approximately 1300 miles of a twenty-two feet wide sheet of newsprint the enormity of this task can perhaps be visualised. However, the biggest problem in quality control is that most of the commonly used tests for measuring paper properties are arbitrary tests, dependent upon arbitrary instrument design and carefully defined procedures. These arbitrary tests generally measure a combination of several fundamental properties. Because of their complex nature, results based on these arbitrary tests are difficult to relate to both papermaking and printing operations without considerable experience.

With higher and higher demands being placed on paper by its users science must help the papermaker better to understand his product by developing instruments to measure the fundamental properties of paper, and to discover how these fundamental properties can be controlled to produce a uniform, high quality paper.

In the past the efforts of scientists in the New Zealand papermaking industry have been largely confined to improving the efficiency of the manufacturing processes. This will continue to be of major importance in a competitive industry.

Typical of this type of problem would be the current efforts to extend the life of the woollen felts on the paper machines. These become clogged with "pitch" (from the wood resins) and frequent changing of the felts means loss of valuable production time. Various additives are being evaluated with respect to their ability to remove this pitch.

The industry has now reached a stage where it is able and prepared to support more basic research. Taking the example above, this would involve obtaining a knowledge of the chemical and physical properties of pitch, and the mechanism which causes it to bind to the felts. When this is understood development of a more effective method of prevention would be possible.

Though New Zealand's forest reserves at present seem vast, in fact foreseeable expansions of the pulp, paper and sawmill industries will take up all available wood. Therefore research directed towards forest improvement, both with respect to wood yield and wood quality, is of increasing importance.

Thus the scientific problems facing the papermaking industry span a wide range of disciplines, with a wide variety of tasks but all with the ultimate aim of producing an inexpensive product of high quality.