Size press, paper machine

On a fine paper machine, size press starch addition is typically 1.2 gsm per side. For a 70 gsm copier grade this equates to 34 kg/t. Hence if a mill is running 10% broke the returned size press starch amounts to 3.4 kg/t in the furnish. This can have considerable impact on wet-end chemistry. Size press starch is of necessity viscosity-reduced, and so contributes little to the paper strength on recycling. However, it is believed that while the starch chains are too short to bridge between fibres in the forming sheet, it may contribute to an increase in relative bonded area after pressing. 

The on-machine size press is the most common method of applying surface sizes to a base paper. The base paper is normally passed... 

Sometimes it is not possible to add the chemicals to the sliury due to negative effects on the process or final property of the paper. A size press is then the normal equipment for application. It is integrated in the paper machine. 

Though functionally and chemically similar, fillers and pigments ate distinguished from one another in that fillers are added at the wet end of the paper machine, and serve to fill the sheet pigments are added at the size press and serve to alter the surface of the sheet. The most common fillers are mineral pigments, eg, clay, titanium dioxide [13463-67-7] calcium carbonate, siUca [7631-86-9], hydrated alumina [21645-51 -2], and talc [14807-96-6]. 

The type of varnish used in the process depends on the kraft paper manufacturer and basis weight of the papers the machine, temperature, and control (scraper bars, squeeze roUs) used the method of cutting the paper to size the laminate being produced (post-forming or regular) and the press-cure cycle (see Laminated materials, plastic). 

Paper may also be colored by surface appHcation of dyestuff solutions after the paper has been formed and dried or partially dried by utilizing size-press addition, calendar staining, or coating operations on the paper machine. In addition, paper may be colored in off-machine processes by dip dyeings or absorption of dyestuff solution and subsequent drying, such as for decorative crepe papers. 

The quantity of starch transferred to paper by a size press depends on several factors concentration of dispersed starch in the surface size viscosity of the starch dispersion diameter of the size press rolls size press pond height cover hardness of the size press rolls size press nip loading pressure paper machine speeds wet-end sizing of the sheet and water content of the sheet. The concentration of starch in the surface size liquid can range from 2% to —15%, depending on product requirements. Frequently, pigments and other materials are added, which further increases total dispersed and suspended solids content. The viscosity ranges from water thin to several hundred cP (mPa-s). 

Operational problems with high water transfer to paper during surface sizing and pond instability have led to the development of pre-metered size presses. Two design options are being used in modem high-speed paper machines pre-metering rolls or short-dwell coater heads attached to the size press.186187... 

The sizes added at the size press/film press are commonly used on modem paper machines to impart a particular property to Ihe paper which cannot be achieved by wet-end size addition alone. These properties include ... 

A 1,(X)0 t/day fine paper machine changing from a cationic to a non-ionic size press stareh therefore removes 3.4 t/day cationie materials from the wet-end. This can lead to a serious charge imbalance in the wet-end. 

The number of dryers and the auxiliary equipment used in a dryer section depend on the particular grade to be produced and the speed of the machine. Up to 70 cylinders may be used in a Kraft dryer section 50-55 would be adequate for a typical newsprint or fine paper dryer section. On the other hand, although the breaker stack and size press are necessary for Kraft bag and the hot press, size press, and intercalender dryers for linerboard, none of these is used for corrugating medium [4],... 

Chem. Descrip. Vise, modified waxy corn starch CAS 9005-25-8 EINECS/ELINCS 232-679-6 Uses Film-former providing wafer holding for papermaking size press, pigmented size press, and paper coatings Features Provides machine cleanliness and runnability CMCDaicel [DaicelUSA]... 

Chem. Descrip. Cone, polymeric surfactant Uses Defoamer for wet-end, size press, coating applies., alkaline paper machine systems... 

Special surface treatment of the paper can be done on machine using a size press (starch addition) or a coater (coating color contains fillers like carbonate, clay, titanium dioxide and a latex as binder). 

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