Oriented polypropylene films for adhesive tape

Examples 1–4

[0141]The appropriate resin mixture was fed into the feed hopper of a 4.45 cm single screw extruder manufactured from H.P.M (Mt. Gilead, Ohio) having an extruder barrel temperature adjusted to produce a stable homogeneous melt of about 250–260° C. The polypropylene melt was extruded through a 17.8 cm single manifold sheet die onto a rotating water cooled steel casting wheel which had about 50–60° C. water circulating through it. The cast sheet was next passed through a quenching water bath maintained at about 30° C. to produce a cast sheet having a thickness of about 0.16 cm.

[0142]Sequentially biaxially oriented polypropylene biaxially oriented substrates were prepared by a process known as the sequential tenter process. The cast sheet was passed over a first series of heating rolls maintained internally from about 127° C. to 136° C., and then stretched between two nipped drawing rolls rotating at different speeds to attain a first draw ratio of 5.0:1 in extrusion or castin

Examples 5–7

[0143]Simultaneously biaxially oriented polypropylene Examples 5–7 were prepared by a process known as the simultaneous tenter process. First, the appropriate resin mixture was extruded to produce a stable homogeneous melt having a melt temperature of about 257° C. The polypropylene melt was cast onto a water cooled steel casting wheel rotating at about 10 meters per minute which had about 11° C. water circulating through it. The cast sheet was next passed through a quenching water bath maintained at about 20° C. to produce a cast sheet having a thickness of about 0.15–0.2 cm.

[0144]The cast film was simultaneous stretched in longitudinal and transverse directions using a diverging spindle simultaneous biaxial orienting tenter equipped with 7:1 stretching spindles, at a line speed of 80–85 meters per minute and a stretching temperature of about 175–180° C. to a final balanced area stretching ratio of about 50:1.

Examples 8–16

[0145]Examples 8–16 were cast as described above in Examples 1–4.

[0146]Examples 8–9 were simultaneously stretched in two perpendicular directions using a laboratory two-way film stretching machine known as a frame or batch stretcher as follows. The cast film sheet of 0.16 cm thickness was cut into square tablets of 6.83 cm on a side and held in the stretching oven of the batch stretcher by edgewise gripping with a series of clips to leave a stretchable sample of 5.08 cm on a side. The tablet was pre-heated for 90 seconds at 155° C., and stretched at a rate of about 300% / second in the reference direction and about 250% / second in the direction perpendicular to the first direction to a final area stretch ratio of about 40:1. Samples were immediately removed from the stretching machine to cool. The film had a nominal thickness of about 0.030 cm. The film was slit into useful sample widths using a razor blade cutter equipped with fresh blades.

[0147]Examples 10–16 were prepa