Calendering material

Lustrex [Solutia], TM for styrene molding compound and extruding and calendering material. 

Emissions from semihard (Table 3.2-9) calendered materials and especially from PVC tiles are much fewer and lower. The primaiy emissions from a calendered PVC flooring are l-methyl-2-pyrrolidinone, 2-(2-butoxyethoxy)-ethanol and 1,2-propanediol. Semihard PVC flooring also frequently emits phenol, which may derive from the stabilizers (Saarela et al., 1989). 

Controlled rheology grades of PP have been used in the production of calendered PP films [29]. Compared with conventional reactor grade material, the reduced molecular weight distribution of PP provides better flow and a slow rate of crystallisation, giving better processibility and films free from surface defects. However, the optical quality of the calendered film does not reach that of extruded film. The poor thermal oxidation resistance of PP in the presence of air is the major impediment in use of PP as a calendering material. 

Take-Off n The mechanism for drawing extruded or calendered material away from the extruder or calender. The most common form of extrusion take-off is a pair of endless caterpillar belts with resilient grip pads conforming to the section being extruded, driven at a speed synchronized with that of the extrudate. 

In order to obtain reproducible results the test should be carried out with films (or sheets) and not with other finished products. In a more complex orientation, internal stress crystallinity may also be involved. For that reason samples for this kind of testing should be pressed or cast to an even thickness and not cut out from rolled or calendered materials. In the investigation of industrial products it is necessary to know and to consider the processing conditions, especially the possibilities of internal stress and anisotropy of the samples. 

Available as both film and sheet unless otherwise noted. All materials are available in PDA grades except for CTA, PVP, and PL EX = extrusion CL = calendering REG = regeneration CAST = casting BO = biaxial orientation. 

The basic methods for forming film or sheeting materials may be classified as follows melt extmsion, calendering, solution casting, and chemical regeneration. Of special note is the use of biaxial orientation as part of the critical manufacturing steps for many film and sheet products. 

In the calendering method, a PVC compound which contains plasticizers (qv) (60—120 phr), pigments (qv) (0—10 phr), fillers (qv) (20—60 phr), stabilizers (10—30 phr), and other additives, is kneaded with calender roUs at 150—200°C, followed by extmsion between clearance-adjusted roUs for bonding onto the substrate. This method is employed for products with thick PVC layers, ie, of 0.05—0.75 mm thickness. The main plasticizer used is di-2-ethylhexyl phthalate (DOP). For filler to reduce cost, calcium carbonate is mainly used. A woven or knit fabric made of cotton, rayon, nylon, polyester, and their blend fiber is used as substrate. For foamed vinyl-coated fabrics, the bonded materials are heated in an oven to decompose the foam-blowing... 

Specific terms have been designated according to the function and composition of various roUs. Steel roUs that impose pressure, transmit heat, and emboss a pattern onto the fabric are known as pattern roUs. Flexible surface roUs that transport the fabric and permit pressure transmission to the fabric are termed bowl roUs or bowls. Bowl roUs are usually larger in diameter than pattern roUs. The material used to make these types of roUs is chosen according to the depth of surface smoothness to be placed on the fabric being calendered, and must be compatible with the pattern roU. Cellulose pulp, cotton, wool, cotton—wool mixtures, com husk, and various polymer materials are used as fillers for the roU surface compound. 

Tests on raw or compounded but unvulcanized materials are chiefly concerned with rheological properties, that is, the response to the forces imposed during the operations of mixing, extmsion, calendering, and curing. 

Calendering processes, of great importance in the production of sheet materials from PVC compounds, are little used with polyethylene because of the difficulty in obtaining a smooth sheet. Commercial products have, however, been made by calendering low-density polymer containing a small amount of a peroxide such as benzoyl peroxide to give a stiff but crinkly sheet (Crinothene) which was suitable for lampshades and other decorative applications. 

The main applications for CPVC arise from the fact that the material has a softening point of about 100% and very good chemical resistance. Particular interest has been shown in waste and soil systems which may pass hot water effluents. Calendered sheet may be vacuum formed for uses where hot filling techniques are employed, for example in jam packing. 

Calendering A process by which fabric or wire is passed through a pair of heavy rolls to reduce thickness, to flatten the intersections of the threads/wires and to control air permeability. Rolls are heated when calendering synthetic materials. Carbonized threads Nylon or polyester therads that have been treated to include varrying degrees of carbon. 

Example 4.9 A calender having rolls of diameter 0.4 m produces plastic sheet 2 m wide at the rate of 1300 kg/hour. If the nip between rolls is 10 mm and the exit velocity of the sheet is 0.01 m/s estimate the position and magnitude of the maximum pressure. The density of the material is 1400 kg/m and its viscosity is 10 Ns/m. ... 

Since quite a bit of difference exists between raw materials, the recipe, and the equipment, the processing procedure and conditions vary a lot. Also, the processing procedures of commercial products are usually not available to the public. Thus, much work needs to be done to find the best procedure and condition for each individual system. In general, a good procedure is a combination of optimal processing time, temperature, and rotating speed of the screw (in the case of extruder use) or the roll nip (in the case of calender use). 

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