sizing

Sizing is a process in the manufacture of paper and has nothing to do with sticking in everyday understanding. It is used to improve key properties of paper and has its origins in ancient Chinese knowledge of the 5th century.

Purpose

A papermaker mean by sizing or glue the partial waterproofing paper, to make it writable or printable with aqueous or solvent-based inks. The term therefore infers that earlier animal glue was used for this purpose. Instead of the concept of sizing can be used analogously to the term impregnation. In the English -speaking world are also used correctly sizing instead of glueing, which is derived from the main property of the sizing, namely the Hydrophilieverringerung and thus the Saugfähigkeitsbegrenzung.

On unsized paper, for example, paper towels or toilet paper, running water-based and low-viscosity materials such as ink or writing ink and the high Kapillarwerte of the paper prevent a clean typeface. Gluing the inner surface is reduced to a tension of the paper web and thus, the capillarity, the second sealing sizing and the fiber-to- fiber bond points and thus increases in marked extent the tensile strength of the paper.

Unlike often than suspected the glue of the paper maker is no adhesive in the usual understanding and thus in many issues of paper properties of different modes of action. For example, as built in the vat the free glue binding capacity of the fibers by occupying the bondable Fibrillenenden, thereby preventing linking upon drying. Breaking length and burst strength decrease with increasing Leimeinsatz.

As a measure of comparable water absorption, there is the so-called Cobb value. This value specifies how many grams of water can be taken from a square of paper under standardized conditions.

Paper with a weight of about 80 g / m² ( weighs as much of standard copy paper) takes unsized to about 100-120 g / m² water. After it was glued, the water absorption is only about 20-25 g / m². Insufficient water intake is also to be avoided because the ink / printing ink usually does not pick up fast enough and can blur. The effect of Überleimung can then perceive as beading of the writing material from the paper surface.

Methods of paper sizing

Natural strength and various mucilages were used as sizing agents in the early East Asian and Arab papers. Later, when the knowledge of papermaking came to Europe, was used animal glue or hide glue - hence the name. Both animal glue (gelatin solution ) and starch solution can be useful to use only as a surface sizing, since their intrinsic retention is too low for use in the mass. The so sized paper is very well protected against environmental influences and writing materials, but it is not erasable.

Since about 1806 we used previously modified ( by boiling with alkali saponified ) tree resins, mainly rosin, as sizes in bulk. The so-called acid precipitating the saponified resins in the paper machine or the first vat was made by the aluminum ion of potassium alum, and later by the cheaper aluminum sulfate. This corresponded to the traditional experience of the papermakers alum.

Since it must be worked in both cases to prevent free glue with an excess of free aluminum ions over the reactive colloidal Leimsubstanzen, produced during handsheet procedure a weakly acidic reaction paper product - the acid or acidic paper. This makes the presence of air humidity sulfuric acid which damages the paper from the inside out (catalytic caused Cellulosedegradation ).

The most modern and papierschonendste method is the currently common, synthetic sizing. Be used as a priority hydrophobisierend acting polymers ( for example, copolymers of styrene and acrylic acid esters ) or alkylated diketenes ( AKD sizing ) or alkylated succinic anhydride ( ASA sizing ).