Tape unwinders

The final type of removable media drive is a tape drive (see Figure 4.6). The tape cartridge uses a long polyester ribbon coated with magnetic oxide wrapped around two spools. As the tape unwinds from one spool, it passes by a read/write head in the drive that retrieves or saves the information. It then proceeds to the other spool where it is kept until needed again. 

Vinyl backed packaging tapes are quite popular in Europe. The vinyl backing is commonly manufactured using a calendering process. Printability and smooth unwind of the tape rolls are amongst the desirable features of these tapes. 

Release coatings are important components of pressure sensitive adhesive (PSA) products such as tapes and labels [1]. Release materials are coated onto the backside of PSA tape backings (often called low adhesion backsizes or LABs in this form) to provide the desired tape roll unwind force. They are also coated onto various substrates to form release liners for PSA products such as labels and transfer tapes. Typically the thickness of the release coating is less than 1 p,m, and often times less than 0.1 jLm. Release coatings can be thought of as the PSA delivery system, providing a controlled unwind or release force and protecting the adhesive from contamination and unintentional contact until it is applied. 

Unwind some of the 13 mm wide coated PET tape and measure the thickness (0.02 mm) with callipers. A loop of tape can withstand a tensile force of about 60 N before it yields and about 80 N before it fails in tension. Check this by using a spring balance on a loop of tape, and calculate its tensile strength (approximately 150 MPa). It must bend around cylinders of diameter 5 and 6 mm (Fig. 1.4), so it must have a very low bending stiffness. It must resist wear as it is dragged over the stationary metal cylinders. It must be dimensionally stable, so that the coating is not damaged. 

The fast unwinders may work at fairly high speeds upto 50 m/min, and they may also adapt to the shapes of goods in some way. (Figs 93 and 94). All the main suppliers of PS tapes and labels 3M, Avery Dennison, TESA, SCAPA etc. supply such unwinding and application equipment. 

It is interesting here to compare the three techniques which are used in packaging for cases and cartons closing in large plants, as far as the available speeds, strength, costs, ease of application, ease of opening are concerned. In the past, cases were closed and sealed with staplers. This was a fairly slow and manual application, and it is less and less used, and only for small jobs, small production output. For the medium speed production lines upto 5 cases per minute, pressure sensitive tapes, applied by automatic unwinders, are suitable and used. 

Figure 94 Unwinding and application of a fixed tape on a fixed (non-moving) substrate. Width of the tape 10-50 mm. Length of the tape 15-100 mm (source 3M).

Pressure-sensitive tapes consist of a carrier, coated, with adhesive on one side, and wound into a roll. The back side is often coated with a release agent to control the unwind force. 

Glass and polymer fibers are used to decrease strain under the influence of unwinding stress in unsupported double sided tapes (transfer tapes). 

Release coatings are important components of pressure sensitive tapes as they enable the formulator to adjust the release force according to the application, for example, the unwinding force of tapes and the transfer of double-sided tapes to substrates. 

Considerable amounts of oriented poly(vinyl chloride) (PVC) films are used for tapes in Europe. In combination with solvent-based rubber-resin adhesives, they yield high-performance packaging tapes with smooth unwind characteristic without the need for a backsize. 

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