Patent GB-1102296-A (GB)
Title: Pressure-sensitive adhesive tapes
IPC: C09J7/02
Filed: 1965-03-08
Abstract: A nonfibrous, finger-tearable, stretchable, pressure-sensitive, adhesive tape comprises a thin foil or film backing consisting essentially of pigmented isotactic polypropylene which has a melt flow value of 1 to 10 dispersed pigment which opacifies the film, and is melt-formed in such a manner that it is readily finger-tearable, has an elongation at break of over 100% and a tensile strength of at least 10 pounds per inch width at a 500% per minute strain rate, and an elongation at break of 10 to 50% at a 5000% per minute strain rate, and being coated with an aggressively tacky, pressure-sensitive adhesive.  The film is formed by controlled cooling or quenching of the melted polymeric mass to 120 DEG  to 190 DEG F, and cooling thereon to ambient temperature.  Mixtures of polymers of lower and higher melt flow can be used.  The film may be prepared by extrusion or calendaring.  The pigment may be titanium dioxide zinc oxide, an organic pigment or a chromatic colourant such as a mixture of iron oxide and strontium chromate and titanium dioxide pigments to produce a tape having a tan or brown coloured backing or finely-divided, solid, filler materials such as amorphous, colloidal silica. Additives to the film may be compatible polymers such as butyl rubber, chloro-sulphonated polyethylene, antioxidants, U.V. light absorbers, lubricants.  The film can be treated on one or both side sides with an electrical discharge which permits stronger anchorage of applied coatings.  The applied coatings may be low adhesion backsize to reduce the force required for unwinding a roll of pressure-sensitive tape, and a primer facesize to increase the anchorage of subsequently applied overlying, tacky, adhesive coating. The primer may be a mixture of atactic, amorphous polypropylene and butyl rubber in 1:4 ratio. Primers also exemplified are compositions containing: chloro-butadiene rubber, phenol-aldehyde resin, magnesium oxide, zinc oxide, and sodium acetate.  The backsizing exemplified is a copolymer reaction product of N-octadecyl isocyanate and polyvinyl alcohol.  The back side may also be primed and a backsize coating applied which can be printed on the back, e.g. a 1:1 copolymer of ethyl acrylate and methyl methacrylate.  The pressure sensitive adhesive coating composition exemplified consists of natural rubber, titanium dioxide pigment, zinc oxide pigment, polyterpene tackifier resin, tricresyl phosphate, rubber antioxidant, and an oil soluble, phenol-aldehyde resin.  In making films by the extrusion method, a masterbatch of pelletized, pigmented polymer may be mixed with more polymer in pelleted form, the mixture melted and the melt downwardly extruded as a flat film sheeting which drops into the nip of a pair of rolls one or both of which have a coolant such as water circulating therein which results in the cooling of the film, which can then be wound up in a jumbo roll.  A combination of a chromium plated steel roll and a steel roll covered by a silicone rubber sleeve to provide traction may be used.  Contact with the rubber surface produces a dull finish which is the adhesive-coated face side in the product, contact with the chromium plated roll produces a glossy back side. The film is then drawn around a rotatable electrically earthed, steel drum which has a semi-cylindrical shroud concentrically located from its surface and to which an A.C. potential is applied to cause a continuous electrical discharge between the shroud and the drum.  The film may then be given a back sizing, and a primer face-size followed by the overlying adhesive composition.  The pressure-sensitive adhesive tape may be used as masking tapes, label and identification tapes having back surfaces that can be written on.