Paper-layering process

RPs are usually applied as laminates of several layers. Many variables are important in determining the performance of the finished product. Some of the important ones are orientation of plies of the laminate, type of plastic, fiber-plastic ratio, type or types of fibers, and directional orientation of fibers (Chapter 7). Nonwoven fabrics are fibrous sheets made without spinning, weaving, or knitting. They include felts, bonded short to long fiber febrics, and papers. The interlocking of fibers is achieved by a combination of mechanical work, chemical action, moisture, and heat by either textile or paper malting processes. 

It is important to bear in mind the conditions in the coater unit and in particular the coater nip . A good review has been provided by Brander and Thorn (29). For our purposes here, it is sufficient to note that modern paper coating processes have exceedingly high technical demands modem units run at over 1500 m/min and must produce a uniform 10 pm layer from a suspension which arrives at the blade or roll at up to 70% solids content. Blade coating, the most common implementation of the process, imposes shear rates of the order of 10 s Because of the very short residence times at the blade/roll, the coating process is therefore a low-deformation, but high-defonnation-rate process. 

In the continuous process, for example, special coating plants with blade or doctor knife systems provide the backs of high-quality web carpets with a plastic film. For automobile upholstery the fabric covers are laminated with foam material by heating up the foam and pressing the upholstery fabric against it. During the production of textile wallpapers the fabric lamination takes place, for example, as the decoration fabric is pasted automatically with a paper layer so that it can be attached by paste on walls. 

The examples in the preceding section, of the flotation of lead and copper ores by xanthates, was one in which chemical forces predominated in the adsorption of the collector. Flotation processes have been applied to a number of other minerals that are either ionic in type, such as potassium chloride, or are insoluble oxides such as quartz and iron oxide, or ink pigments [needed to be removed in waste paper processing [92]]. In the case of quartz, surfactants such as alkyl amines are used, and the situation is complicated by micelle formation (see next section), which can also occur in the adsorbed layer [93, 94]. 

The most commonly used reinforcement for high pressure decorative and industrial laminates is paper (qv). The strong substrate layers, or filler, are kraft paper. Kraft is a brown paper made from a sulfate pulp process (8). It consists of both short cellulose fibers from hardwoods and long fibers from conifers. The long fibers impart most of the wet strength required for resin saturation processes. 

Mica splittings are processed from lower quaUty blocks and from sheets too thin for blocks and unsatisfactory for producing film. The splittings are packed for sale in three ways book form, which are laminae spHt to the desired thickness from the same book of mica, then dusted with mica dust, and restacked in book form pan packed, in which splitting layers are placed evenly in a pan, and each layer separated by a thin sheet of paper then pressed together and loose packed, in which splittings are si2ed with screens then padded loosely in a wooden box for shipment. 

The initiation of development in the activator solution is more rapid than in conventional processes because the developer molecules need not diffuse into the light-sensitive layers from the processing solution. In spite of the low activity of the coated developer, some unintentional reduction sensitization may occur, which produces unwanted fog. Therefore, coating the developer in a separate layer usually is preferred. Because of simplicity, rapid access, and solution stabihty, incorporated developer papers have been used for office copying appHcations. 

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