Saint-Gobain CHR M855 Polyester Film Backing Natural Rubber Adhesive Pressure Sensitive Tape is a single-coated pressure-sensitive tape in which a biaxially oriented poly(ethylene terephthalate) film carries a natural rubber adhesive layer. The backing is supplied at 0.051 mm (0.002 in) and the adhesive layer at 0.038 mm (0.0015 in), producing a nominal total thickness of 0.089 mm (0.0035 in). The product is available in log rolls and slit rolls; common converting widths extend from 6.4 mm to 914 mm, although published data for this specific configuration is limited outside that interval. Under ASTM D3330/D3330M Test Method A, 180° peel adhesion to stainless steel is typically 13.7 N/25 mm (50 oz/in). Tensile strength at break is 438 N/100 mm (25 lb/in) and elongation at break is 100% when tested to ASTM D3759/D3759M. A single layer exhibits a dielectric breakdown voltage of 5000 V under ASTM D149. The continuous service envelope is -29°C to 130°C, governed by the natural rubber adhesive rather than by the polyester backing.

What processing parameters dominate peel adhesion on metal and polymer substrates?

Bond development is not instantaneous; pressure-sensitive adhesion depends on dwell time, contact pressure, temperature, surface energy, and backing stiffness. The ASTM D3330/D3330M reference bond is prepared with a 2 kg roller pass and a 20 min dwell at 23±2°C and 50±5% RH. Production lamination may deviate from that reference. Hard-nip lamination at 0.2–0.4 MPa contact pressure accelerates wet-out on low-energy films such as corona-treated polyethylene or polyethylene terephthalate. Surface energy below 38 mN/m reduces peel strength because the adhesive cannot fully wet the substrate. Silicone oil, fluorochemical release residues, and amine-based slip additives suppress wet-out and may produce peel values below 4 N/25 mm even on otherwise clean film. Plasma or corona pretreatment to 40–48 mN/m is commonly specified before splicing. The natural rubber adhesive demonstrates rapid bond build at 20–40°C; below 10°C, cold-flow decreases and dwell time should be extended. Above 60°C, shear holding is reduced until the adhesive is cooled or mechanically constrained.

Coil winding and film splicing operations utilize the backing tensile strength and dielectric properties. On a multi-axis coil winder, the tape is unwound under servo or pneumatic tension control. Because the backing yields at 438 N/100 mm and stretches 100% before break, unwind tension is typically maintained at 10–15 N/10 mm width to prevent necking and adhesive ooze at the edge. The biaxial orientation of the polyester film reduces elongation during high-speed winding and contributes dimensional stability during thermal cycling. In film splicing, the overlap length is selected so that the bond shear strength exceeds the web line tension; for 25–50 µm polyethylene terephthalate web, a 25 mm overlap is usually sufficient. The adhesive bond is strong enough to hold the splice through a festoon accumulator, but the splice should be allowed to consolidate for at least 20 min before full-speed running if the substrate is below 15°C.

Representative physical property matrix for the M855 construction

The values below are typical release values for the product and are not intended as batch specifications. They were generated under the laboratory conditions indicated by the cited methods.

Chemical resistance is controlled by both backing and adhesive. The polyester backing withstands short-term contact with aliphatic hydrocarbons, alcohols, and dilute mineral acids but is not recommended for continuous immersion in alkaline solutions above 50°C because of hydrolysis. The natural rubber adhesive swells in aromatic hydrocarbons, ketones, and esters; plasticizer migration from flexible polyvinyl chloride also softens the adhesive, producing residue transfer. If the tape is used in a sealed electrical enclosure with ester-based varnishes or amine-cured epoxy coatings, compatibility testing under ASTM D896 is required before production qualification. Storage conditions of 10–27°C and 40–60% RH preserve unwind performance; self-wound rolls exposed above 40°C may exhibit elevated unwind forces due to rubber cold flow. The product should be allowed to equilibrate for 24 h at 20–25°C before slitting to avoid condensation-induced adhesion loss.

If continuous exposure exceeds 130°C or chlorinated solvents are present

At temperatures above 130°C, the polyester backing retains mechanical strength, but the natural rubber adhesive undergoes thermo-oxidative chain scission and crosslinking; adhesion falls and residue transfer increases. The tape should not be used for sustained exposure above 130°C unless the design includes a mechanical overwrap. Chlorinated solvents such as methylene chloride and trichloroethylene attack both the adhesive and, with prolonged contact, the polyester backing. For high-temperature coil winding, a silicone adhesive polyester tape with a continuous service limit of 180–200°C is substituted. The lower initial tack of silicone adhesives, often 3–8 N/25 mm, requires more dwell or higher lamination pressure than M855. This trade-off is a primary design difference between M855 and higher-temperature polyester tape grades.

Positioning the natural rubber adhesive against silicone and acrylic coated polyester tapes

M855 is differentiated by its natural rubber adhesive. Acrylic polyester tapes typically use a crosslinked acrylic ester polymer that provides better oxidation resistance and long-term aging but slower initial pressure-sensitive wet-out. Silicone polyester tapes provide higher thermal stability and lower adhesion to low-energy release liners but tend to exhibit low peel to steel. The following matrix summarizes typical performance ranges for the three adhesive chemistries when coated on a polyester backing; values are comparative ranges from published pressure-sensitive tape literature, not batch specifications.

On a varnished coil winding, the tape is overcoated with a solventless polyester or epoxy impregnating resin. The natural rubber adhesive can absorb minor resin components during vacuum impregnation; peel retention after varnish cure should be measured with ASTM D3330/D3330M and dielectric breakdown with ASTM D149 after 24 h cure at 125°C. Published data for this specific configuration is limited, so lot qualification should include residue transfer measurement after 7 days at 50°C against the actual copper and varnish system.