Roll coaters, paper

Roll coaters can apply a coating simultaneously to both sides of the sheet, while blade coaters generally treat one side at a time and require intermediate drying. Roll and blade systems have been combined in the Billblade coater, which has found use in the production of carbonless copy papers and for paper precoating.224... 

Two areas of major interest in 1955 were paper antiskid and investment castings. Wilson (19) used colloidal silica to increase the friction between paper surfaces. In this application (Figure 2), the silica sol is typically diluted to 1-7% as silica solids and then applied to multiwall bags, corrugated boxes, and linerboards. Various methods of applying the silica sol were used. Typical applicators were sprays, segmented applicator rollers, knife blades, full roll coaters, sponges, and brushes. 

Latex adhesives are made from natural rubber latex by adding stabilizers, wetting agents, and other components. They are applied to the substrate by brush, spray, doctor knife, or reverse roll coater. The adhesive is dried to film near room temperature. The adhesive strength can be improved by vulcanizing the system. The applications of latex adhesives are to porous substances such as paper, leather, and textiles. 

Although virtually any type of roll coater may be used, reverse roll coating is the most common. This may incorporate a doctor roll, doctor blade, or Mayer bar to meter the spread rate. With tapes, adhesive is usually applied directly to the tape, which then passes through a drying station incorporating countercurrent air, usually warm. The dried tape is then rolled and slit. With label stock, adhesive is normally applied to the release paper, dried, and then transferred to the label when the label stock is united with the release paper in a nip roll. 

These roll coaters are very simple and cheap and are also easy to cleaa Suppliers for roll coaters include Hestika Germany for footwear and leatho- goods, Kolbus Germany for bookbinding (bonding of decorative paper to the cardboard of the cover). 

Table 6 shows typical paper coating for-mulations with a 50 50 SBR-to-casein ratio, for use on two types of coaters. For a multiple roll coater, water would be added to adjust to a percent total solids of 50-55, giving a coating weight of 3-4 lb per 1000 sq ft. For an air knife... 

Vinyl film, saturated paper, and fabric are bonded to plywood, chipboard, and steel to produce a variety of decorative panels, from simulated wood paneling to fabric-covered modular office sections. Generally, the adhesive is coated onto the rigid substrate via roll coater or spray application. Roll coater adhesive application to plywood and chipboard generally requires more than one pass for sufficient adhesive deposition, since the surfaces tend to absorb the adhesive. The primer or sealer coat is generally dried completely before a second coat is applied. Then, this second coat is subjected to a partial dry before nipping-some-times under heat—to the decorative surface film. When the flexible laminate is bonded to a metal surface such as office partition sections, the adhesive usually is deposited via spray application onto the metal. 

Roll coaters were first used on papermachines in the late 1920 s. Roll coaters, as their name implies, use a series of rolls to apply coating to the paper. The coating color is added to a reservoir between the first two rolls that are set to meter the amount of coating to be applied to the sheet. The next several rolls oscillate as they turn distributing the coating evenly across the whole width of the rolls. The paper web passes between the final two rolls, which transfer the coating onto the paper surface. Depending upon the specific process, both sides of the paper may be coated simultaneously or each side can be coated sequentially. A double roll coater is illustrated in... 

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... 

Paper base is supplied in roll form and together these units provide the coater with a continuous feed at the speed and tension required. 

Low-viscosity soybean briquetting adhesives are generally applied by spray. Paper and softboard laminating glues are usually applied by curtain coater, knife, or indirect roller. High-viscosity plywood and lumber assembly formulations are fairly well limited to application by spreader roll or extrusion. For very small assembly jobs, soybean glue can easily be applied by brush. 

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. 

Information is given on methods of applying coatings (air-knife coaters, lock coalers, roll coalers and blade coalers) and the development of synthetic latices from SB, NB and AN for coating paper. 24 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

Coater backing rolls give elastic support and ensure transport of the paper web without slipping of the web, which is coated on the opposite side. Elasticity and optimized deformation behavior are the crucial parameters for roll cover design. 

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