Sizing synthetic

The poor adhesion of carboxymethylcellulose to synthetic fibres means that where such fibres are present, it can only be effective in combination with a synthetic size polymer (Table 10.6). This needs to be taken into account when considering suitable desizing procedures. If this cellulose derivative is to be used in conjunction with an electrolyte-sensitive acrylic acid copolymer, it is advisable to choose a salt-free carboxymethylcellulose. 

Clearly, one option to reduce the add-on is to use high-efficiency size formulations. However, there is a limit to what can be achieved by this approach. Even if the add-on is reduced to only 5%, the pollution load is still substantial. The two main options to facilitate disposal are (a) recovery of size polymers and (b) biological effluent treatment. Recovery of size polymers, particularly from water-soluble synthetic sizes, is based on extraction washing using the minimum quantity of water. Recovery rates in the region of 50% have been quoted for polyfvinyl alcohol) and carboxymethylcellulose size formulations. It is necessary to apply one of three concentration techniques precipitation, condensation or ultrafiltration [205]. 

The storage stability of these reactive synthetic size emulsions is also of practical Importance AKD sizes tend to be delivered by the manufacturer in emulsion form, whilst ASA is emulsified on site shortly before pumping it into the wet-end. This is an area where much confidential manufacturer s expertise comes into play. 

No specific information on the possible effect of the synthetic sizes on permanence is available, and they are not mentioned in the standard 04), but it seems unlikely that they would be deleterious. Presumably they have been used in comnercial grades of neutral/alkaline paper subjected to accelerated ageing tests. In terms of general effects on paper, the synthetic sizes have a tendency to reduce the surface frictional properties of paper to a greater extent than rosin. For example, this makes it more difficult to stack piles of cut sheets without slippage. However, the effect is less noticeable when high proportions of chalk filler are used, because the blocky particles increase friction. 

Synthetic sizes, such as styrene maleic anhydride (SMA) copolymer or anionic polyurethane (PU) emulsion, are often added to starch-based surface size to develop water resistance, particularly in the production of label grades. This procedure may permit reducing or eliminating the use of internal size.216... 

Synthetic Size for Filament Acetate Warps Product Description ... 

Efficient in removal and suspension of synthetic size. Excellent emulsifier of waxes and oils--anionic. 

TABLE III. POLYETHYLENE ADHESION OF SYNTHETIC SIZED PAPERS (from Fredholm and Westfelt, Reference 6)... 

Paper Friction In addition to the effect on toner fix, organic components in plain uncoated papers intended for electrophotography have other important characteristics that should be evaluated for proper machine performance. For example, chemical surface treatments tend to impact the friction characteristics. Synthetic sizes, when surface applied, may significantly decrease the overall paper-paper friction level (Figure 11), and the static friction peak or resistance towards initial movement is not developed (Figure 12). 

Figure 11. Examples of paper-paper friction traces for rosin sized (left) and synthetic sized (right).

Figure 12. Paper-paper friction traces for synthetic sized sheets. Static friction peaks were not developed.

Vikomul. [Vikon] Enuilsifier/deteigent blends for emu ficatkm waxes and oils, starch and synthetic size lemovaL... 

Most sizing problems can be related to one main problem the lack of the sizing agent, be it rosin, AKD, ASA, polymeric, or any one of the other synthetic sizes available in the paper or board. 

The two major types of synthetic size employed at the wet-end of a paper or board machine, AKD and ASA, will be dealt with jointly as in many respects the wet-end chemistry is the same. Individual problems related to tlie sizes thanselves will be dealt with later in this section. 

Many articles and papers have been written regarding the reaction (or nonreaction) of AKD and the advantages of ASA over AKD and vice versa. The advantage of synthetic sizing over rosin sizing is also well covered in these papers and articles, and no attempt will be made to justify the use of one type of size or the other, and only solutions will be offered to possible problems that may occur. 

Lack of sizing with synthetic size has, in many ways, the same causes as that for rosin sizes it is just the solutions that may be different. There are obvious differences such as pH, but other factors such as those listed below are similar ... 

The synthetic sizes operate at a different pH range to rosin sizes (cationic rosin size systems can work at higher pH), in general between pH 6.0 and 8.5. 

Anionic trash, in synthetic sizing, has a similar effect on size retention as that for rosin size, except that in this case, it is the size that carries the cationic charge, not the alum. This will mean that it is the sizing agent that will be adsorbed onto the anionic trash. If the size is adsorbed onto the anionic trash, sizing will be subject to the retention of this anionic trash and will vary accordingly. This is why mnch more emphasis is placed on the correct retention system to improve anionic trash retention, or fmes/filler retention, as much of the size can also be adsorbed on this. 

For synthetic sizes the action of the drying cylinders is different to that of rosin/ alnm, where the main function is to spread and fix the rosin. With AKD and ASA sizes, the spreading of these is not as important, as AKD is a low melting point wax, and ASA is an oily liquid. The main purpose of the drying section is to break the AKD or ASA particle, as shown in Fig. 5.7, to allow the AKD or ASA to spread and then react. 

As stated for rosin size, the drying temperature is important for synthetic sizes, but the profile is more important and as long as a profile similar to that of the ideal is used, lack of sizing should not be a problem. However, it is a case of trial and error to obtain the correct dryer profile for individual machines, to obtain the best balance of sizing performance and energy input. 

Slow cure with synthetic sizes is the same for both ASA and AKD (and all other synthetics). It can normally be related to the drying profile and the moisture of the paper or board. The paper or board has to reach a certain moisture content and temperature before the size particles will break and align/react. If they do not reach the values they will not give the true sizing effect. 

With the synthetic sizes, the problem of fugitivity came to the fore in the USA with PCC. The effect was seen initially in the USA/South America because of the quality and availability of (jCC and chalk and the process for PCC was introduced in order to allow the conversion to alkaline of fine paper machines. 

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