Calendering of films

The calender, usually consisting of three or four heated steel rolls, is very simple in principle. However, in order to obtain wide thin films with narrow thickness tolerances and constant properties, numerous precautions must be taken, which make the designing and operating of a calender a skilled art.9.10.11 

The calender is used for the manufacture of many products, sheets, floor coverings, artificial leather, etc. Many types of plastics and rubbers are suitable raw materials, but in the field of thin films its use is almost restricted to plasticised and rigid homopolymers and copolymers of vinyl chloride. The output of a calender decreases with decreasing thickness of the film. Hence, only films with a thickness of approx. 0 25 mm or more can be made economically. 

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In very large volumes a roller application of a melted coating is used. This technology is closely related to the calendering of film and their lamination onto a textile carrier, as described in Section 14.4.4 in the discussions on calendering and laminating. 

Impact modifiers for PVC include methyl butadiene styrene (MBS) and acrylics. MBS modifiers improve the impact strength of PVC compounds without sacrificing the other characteristics. They are used for a variety of rigid and semirigid applications and processes, such as blow moulding of bottles, calendering of film and sheet, extrusion of profiles, and injection moulding of technical parts. Some types can also be tailored to suit specific requirements. 

Numerous techniques related to the fabrication of fibers made from UHMWPE have been described. Fibers can be fabricated from films by subsequent splitting (40,41). A process for the production of films and fibers of UHMWPE below 2 mil (=1/1000 inch) in thickness has been described (42). This process involves the calendering and drawing the tapes at a temperature above the melting point of the UHMWPE. 

Figure 3 shows the end uses, arranged in categories, of the PVC produced in the United States (5). About 35% of the PVC resin is extruded into pipe, complex forms, or flat sheets. Another 32% is calendered into film and flooring materials. About 12% is injection-molded or blow-molded into packages, records, and other forms a lesser amount is coated onto paper or fabric. Approximately 4% is exported. It is easy to see how the demand for this extraordinarily versatile material would stimulate great interest in its production. 

I. Brazinsky, H. F. Cosway, C. F. Valle, Jr., R. Jones, R. Clark, and V. Story, ATheoretical Study of Liquid-film Spread Heights in the Calendering of Newtonian and Power Law Fluids, J. Appl. Polym. Sci., 14, 2771 (1970). 

J. F. Agassant and P. Avenas, Calendering of PVC—Forecast of Stresses and Torques, paper presented at the 2nd Int. Symp. on PVC, Lyon, France, 1976 also, J. L. Bourgeois and J. F. Agassant, Calendering of PVC—Defects in Calendered PVC Films and Sheets, paper presented at the 2nd Int. Symp. on PVC, Lyon, France, 1976. 

Calendering of Polymers The Newtonian Haskell Model A 0.2-m-diameter, 1-m-wide, equal-sized-roll calender operates at a speed of 50 cm/s. At a gap separation of 0.02 cm, it produces a 0.022-cm-thick film. Assuming a Newtonian viscosity of 104 poise, calculate in the last nip (a) the maximum pressure (b) the separating force and (c) estimate the mean temperature rise. 

Starch grafts are a new class of products for use on the size press.212,213 They have high water retention and form flexible films. They are offered as a liquid, ready-to-use binder on conventional and metered size presses and on calender water boxes. Starch grafts are used in pigmented formulations for the production of film-coated offset, recycled offset, textbook and LWC (lightweight coated) grades, and as precoat for double-coated, sheet-fed offset grades. 

Creases formed in the film prior to the emboss nip will become welded into it as longitudinal faults. Such creases usually are caused by release of film from the calender roll in the form of an extreme arc, or by a total failure to control the tension between the calender and the emboss nip. Momentary contact of the film with the surface of the stripping rolls also may cause creases. 

The finish on the surfaces of the calender rolls is very important they may be highly polished or matt, and these surfaces affect behaviour during processing as well as the appearance of film or sheet produced. Unless it is grossly over-lubricated the hot material will adhere to the hotter of two similar rolls forming a nip, or to the roll running faster—except that irrespective of differences in roll speed or temperature there is a preference to adhere to a matt rather than a polished surface. 

For long runs and high outputs calendering probably is the most economical method for making thermoplastic film or sheet (in the case of conventional rubbers, as distinct from thermoplastic elastomers, it often is the only process available for making wide sheets). Speaking broadly, extrusion is the preferred method for manufacture of film and sheet in materials other than PVC. 

The 121 sample films were formulated into a replicate series. Those utilizing emulsion polymerized PVC were cast from plastisol onto glass plates and fused in a circulating hot air oven. Those incorporating suspension polymerized PVC were fluxed via a Banbury and two-roll compounding mill and finished on an inverted L 8-inch X 16-inch four-roll calender. Plastisol films were of nominal 8-mil thickness calendered film was 4 mils. 

The complete equipment usually consists of a mixer such as a Banbury mixer followed by the heated rolls, chilled rolls, and finally a windup roll.3 The windup roll controls the tension on the film or sheeting as it moves through the calender rolls. Calenders are generally designed to meet the specific needs of the customer. Once installed and operating continuously, the cost per pound of film or sheet is lower than by any other process such as extrusion. 

The characteristics of lubricants, their effects during plastics processing and their influence in the calendering process are discussed in depth. Attention is paid to the different intemal/external behaviour of lubricants, viscosity reduction by internal lubricants, fusion delay by external lubricants, shear liquefaction by lubricants and the suitability of various lubricants for the manufacture of calendered PVC films in relation to melt elasticity, release effect, flow and plate-out. 

Calendering is a popular method of rubber processing. It is also used in the production of films and in lamination of plastic film to substrates in a continuous web process. Hot-melt coating equipment is another version of calendering equipment used for production of plastic coated textile materials. 

EINECS 246-614-4 Isooctyl phosphite ((C8H170)3P) Phosphorous acid, triisooctyl ester Triisooctyl phosphite Weston TIOP. Intermediate insecticides lubricant additive specialty solvents stabilizer for acrylics, nylon, unsaturated polyester, PVC improves antiwear and antifriction properties. Stabilizer tor hot-melt adhesives. PU, polyesters used in molding, extrusion, and film applications in PP, HOPE, LDPE, PVC, and polyesters also useful for PP fiber applications and calendering of PVC. Oil d = 0.891. Albright i Wilson Americas Inc. GE Specialities Stave. 

Uses Stabilizer, lubricant for calendering of rigid pigmented film Features One-pack high efficiency additional lubricants and costabilizers may be needed Properties Solid Balab748 [WitcoSA]... 

The other methods of film manufacture, calendering and several extrusion techniques, are much more interesting from our point of view. 

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