Calendering and Lamination

Two procedures that involve the application of pressure to either a single layer of green tape or to a stack of layers of green tape are calendering and lamination. These procedures will be reviewed in this section. 

Several manufacturers have included this processing step in their tape-processing lines for one or more of these reasons. The use of calendering is not widespread in the industry, however, and very little has been disclosed about its use. 

The basis for the production of MLC and MLCC (multilayered ceramics and multilayered ceramic capacitors) is the ability to laminate together several layers of green tape to form a structure that sinters together into a monolithic solid ceramic part. This procedure for the lamination of green tape cast-sheets was invented in 1965 by W J. Gyurk of RCA.  

All of the basic parameters that must be controlled for lamination were described in that patent. These are temperature, pressure, and time. The temperature for lamination is dependent upon the organic phases present in the tapes, that is, the binder and plasticiz- 

Hold the pressure for times ranging from seconds to minutes. Usually about 3 to 4 minutes is adequate for full lamination. 

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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. 

Once the tape-cast product has been fabricated in either sheet or roll form, it is ready for evaluation and characterization before being processed into a useful shape or part. This chapter will cover the green tape characterization techniques and procedures that are used in industry as well as procedures we have instituted in our laboratory. The remainder of the chapter will address the downstream processing steps followed in the final shaping procedures to produce parts for specific products. These procedures include blanking, punching, calendering, and lamination. First we will review the tape characterization procedures and techniques. 

Model LVS-3012 Laser Via System, Pacific Trinetics Corporation, Carlsbad, CA. 5.3 Calendering and Lamination... 

Since fully cured thermoset sheets cannot be resoftened, forming is not appKcable to them. Common materials subjected to thermoforming are thermoplastics such as polystyrene, cellulose acetate, cellulose acetate butyrate, PVC, ABS, poly(methyl methacrylate), low- and high-density polyethylene, and polypropylene. The bulk of the forming is done with extruded sheets, although cast, calendered, or laminated sheets can also be formed. 

In addition to the conventional three- or four-roll calendering procedures used for the production of sheet material, two important variations are practised with TPU, namely hot-melt calendering and film lamination. 

Coated fabrics can also be made on conventional calenders in conjunction with a slit die extender, the calender in this case spreading and laminating the molten film. 

This method provides coated fabrics with good flexibility since the polyurethane does not penetrate between the weave of the fabric. The films may be made by extrusion or calendering and a variety of methods are available for bonding the film to the fabric. Solvent and latex adhesives may be used in conjunction with oven or drum laminators and the composites can be embossed and printed. 

Finishing and converting are the last operations performed on the fabric before it is delivered to the customer. Finishing includes operations such as coating and laminating, calendering, and embossing to impart particular surface properties corona... 

Thicker needle-punched webs and a broad range of coated and laminated products can be produced on a Docan line equipped with a calender. 

White pigmented, lightly filled PVC sheet was made by dryblending 100 phr of PVC resin (K= 70) with 50-60 phr of plasticizer (as indicated. Table 3), 5 phr of surface treated TiOa, 10 phr CaC03, 0.3 phr of HALS/UV absorber UV package, 2.5 phr Ca Zn heat stabilizer and 0.25 phr stearic acid. Dryblends were extruded onto a calender and processed into 0.3 or 0.5 mm sheets. Sheets of different gauge were laminated around a polyester scrim, L9P based sheet on L9P based sheet, DIDP on DIDP and L9P/DIDP on L9P/DIDP. 

In order to minimise air entrapment and blistering, the thickness of each sheet is generally limited. To build up the required thickness of the final sheet, two or more plies of calendered sheet are usually laminated on the bottom bowl of a three-bowl calender. 

A more complex form of coating calender is the four-bowl Z or L arrangement. A four-bowl calender can simultaneously apply a rubber coating onto both sides of a fabric. In effect, the No. 1 and 2 bowls and the No. 3 and 4 bowls form pairs where two rubber sheets are produced. The sheets are then laminated to a substrate between the No. 2 and 3 bowls. Very sophisticated devices are usually incorporated into the calender design to control thickness and width of the individual sheets and the resulting laminate. 

An important step in the manufacture of any plastic product is the fabrication or the shaping of the article. Most polymers used as plastics when manufactured are prepared in pellet form as they are expelled from the reactor. These are small pieces of material a couple of millimeters in size. This resin can then be heated and shaped by one of several methods. Thermoset materials are usually compression molded, cast, or laminated. Thermoplastic resins can be injection molded, extruded, or blow molded most commonly, with vacuum forming and calendering also used but to a lesser extent. 

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