Saint-Gobain CHR M69 Polyester Film Backing Acrylic Adhesive Pressure Sensitive Tape is a pressure-sensitive adhesive laminate consisting of a biaxially oriented polyethylene terephthalate backing and an acrylic pressure-sensitive adhesive layer. The product is supplied as log rolls, precision slit spools, and die-cut components. It is commonly used for temporary masking, electrical insulation, film splicing, wire harness bundling, and general bonding where a thin polymer film with moderate continuous temperature resistance is required without a heat cure step. The acrylic adhesive distinguishes the product from rubber-resin and silicone pressure-sensitive adhesive systems through its oxidation resistance, ultraviolet aging stability, and absence of silicone adhesive transfer. The polyester backing distinguishes it from polyimide or glass cloth tapes in thickness, dielectric properties, material cost, and thermal ceiling. The values discussed in this document represent the polyester film/acrylic adhesive tape class and general industrial practice; the current Saint-Gobain CHR M69 technical datasheet and lot-specific certificate of conformance must be consulted for production qualification.

The data above are not lot-specific guarantees. Actual Saint-Gobain CHR M69 values can shift with coating batch, film source, and test method revision. For critical electrical or masking applications, incoming inspection should include thickness verification, unwind force measurement, and adhesion testing on the actual substrate.

How Does the Acrylic Adhesive System Influence Short-Range Peel, Long-Range Shear, and Adhesion Build?

The acrylic pressure sensitive adhesive on CHR M69 provides a balance between room-temperature peel adhesion and resistance to shear loading at elevated temperatures. Acrylic pressure sensitive adhesives are typically high molecular weight acrylate ester copolymers, often lightly crosslinked to improve cohesive strength. When the tape is applied to a polar substrate such as aluminum, epoxy laminate, or glass, peel adhesion under ASTM D3330/D3330M typically develops rapidly, with a measurable fraction of final adhesion within 20 min to 30 min and maximum wet-out within 24 h. Static shear resistance under ASTM D3654/D3654M is generally more stable for acrylic systems than for natural rubber-resin systems, particularly after thermal aging. The adhesive is not a structural bond; it is a pressure sensitive adhesive intended for temporary or semi-permanent retention, not load-bearing lap-shear joints.

Adhesion to low surface energy thermoplastics such as polyethylene, polypropylene, or PTFE is reduced unless the substrate is pretreated by corona, plasma, or chemical primer. On moderately rough metal surfaces, adhesive wet-out improves with firm lamination pressure, but excessive pressure above approximately 400 kPa does not further increase peel adhesion and can induce adhesive ooze at the edge. The service temperature limit is governed by the acrylic adhesive rather than the polyester backing. At sustained exposure above 130 °C, the adhesive can soften, lose shear holding power, and leave residue on the substrate during removal. Published data for low-temperature peel adhesion of the specific CHR M69 configuration are limited; acrylic pressure sensitive adhesives of this class typically show reduced tack below -10 °C to -20 °C.

The polyester backing is normally corona or primer treated on the adhesive side to improve anchorage. Adhesive transfer to the substrate after high-temperature exposure is therefore usually a cohesive or interfacial adhesive failure of the acrylic layer rather than a backing delamination. Acrylic systems also show lower outgassing of plasticizing oils than many rubber-resin adhesives, which reduces the risk of visible film on optical surfaces and electrical contacts. However, the adhesive must be evaluated under the specific process atmosphere because acrylic polymers can absorb moisture and polar solvents, temporarily reducing shear strength.

Production-scale slitting of CHR M69 is typically performed on razor or rotary shear slitting stations with precise tension control. Biaxially oriented polyester film exhibits high modulus and clean slit edge formation, but edge nicks can propagate during high-speed converting if blade sharpness is not maintained. Unwind tensions commonly used for polyester film tapes of this thickness range are in the range of 0.2 N/mm to 0.5 N/mm of web width, but converter-specific values depend on roll diameter, speed, and release characteristics. The acrylic adhesive can flow under pressure, so storage of finished slit rolls at temperature above 30 °C can cause telescoping or interlayer blocking. Edge quality is best maintained when the roll is slit rather than crush-cut, especially for electrical insulation uses where filamentary edge debris is a cleanliness concern.

Voltage Withstand, Flammability, and Dielectric Behavior in Electrical Insulation Applications

The polyester backing provides the primary dielectric barrier in CHR M69. Polyethylene terephthalate film has been used in electrical insulation because of its relatively high dielectric strength per unit thickness, moderate moisture resistance, and good tensile strength. When tested under ASTM D149, breakdown voltage is strongly dependent on film thickness, electrode geometry, and relative humidity. Thin polyester film of 25 µm to 36 µm thickness typically exhibits breakdown voltages in the range of 4 kV to 6 kV, but any scratch, fold, or foreign particle lowers the withstand voltage. The adhesive layer contributes mechanical adhesion but should not be relied upon as the primary dielectric. Air entrapment under the tape during application creates partial discharge sites in higher voltage applications.

In coil winding, interlayer insulation, and wire harness bundling, the tape is applied with controlled tension to avoid compressing the film beyond its yield point. Biaxially oriented polyester film has high tensile strength in both machine and transverse directions, which reduces splitting during tight wrapping. For electrical insulation applications, the tape is often evaluated under ASTM D1000, which includes requirements for dielectric breakdown, flammability, and low-temperature flexibility. The flammability class recognized under UL 510 applies to the full tape construction, not to the backing alone, and the rated flame-retardant classification must be confirmed on the UL recognition card before use in listed equipment.

Because polyester film is hygroscopic in comparison to some fluoropolymer films, prolonged exposure to high humidity can absorb moisture and reduce dielectric performance. Conditioning of the tape and the wound component under controlled humidity before high-voltage testing is therefore standard practice. The acrylic adhesive is non-corrosive to copper in typical indoor electrical service, but published electrolytic corrosion data for CHR M69 on specific magnet wire enamels are limited. Users should verify compatibility with wire enamel and potting compounds at the intended voltage stress and thermal class.

For printed circuit board processing, polyester/acrylic tape of this type is used as temporary masking during selective conformal coating, touch-up masking, or low-temperature bake cycles. The product is not a substitute for polyimide tapes in wave soldering or reflow operations. Polyimide backing with silicone adhesive is typically rated for short excursions up to 260 °C or higher, while polyester/acrylic constructions are limited by the acrylic adhesive and the thermal shrinkage of polyester. During infrared reflow or vapor phase soldering, the tape can shrink, lift, and leave adhesive residue. It is better suited to masking before solvent-borne conformal coating where the subsequent cure does not exceed 130 °C. Ketone, ester, or strong polar solvent exposure should be limited because the acrylic adhesive can be attacked even if the polyester backing remains intact.

In powder coating masking, the tape can serve for low-temperature cure powders but is not recommended for high-temperature powder coat cycles above 150 °C unless qualification demonstrates clean removal. The thin polyester backing is conformable around gentle radii but may crease on sharp corners. On textured or silicone-contaminated surfaces, adhesion can drop; cleaning with isopropanol or a solvent appropriate to the substrate before application improves wet-out. Masking tape must be removed after cooling to a handling-safe temperature because hot removal can leave adhesive residue and increase the risk of backing tear.

When Silicone-Free Processing or Low Surface Energy Bonding Becomes the Production Constraint

Silicone pressure sensitive adhesive tapes are often selected for high-temperature masking because of their broad service temperature range and low peel force on difficult surfaces. However, silicone adhesives can release low molecular weight cyclic siloxanes that migrate to nearby surfaces and interfere with painting, conformal coating adhesion, encapsulant wetting, or optical cleanliness. The acrylic adhesive on CHR M69 avoids silicone adhesive transfer and is therefore used in silicone-sensitive environments such as optical component handling, medical device assembly, and electronics where subsequent coating adhesion is critical. The distinction should be confirmed through adhesive transfer testing because the backing or release coating may use a silicone release system unless otherwise certified by Saint-Gobain.

Compared with rubber-resin pressure sensitive adhesive tapes, the acrylic system shows better ultraviolet aging, lower plasticizer migration, and more stable shear resistance after thermal exposure. Rubber-resin tapes often provide higher initial tack to low energy surfaces and soft films, but they can darken, harden, and lose peel adhesion after exposure to heat or sunlight. For applications requiring clean removal after outdoor weathering or after moderate bake, acrylic systems are generally preferred. For applications requiring aggressive tack to polyethylene film or rough powder-coated surfaces without pretreatment, a rubber-resin adhesive may perform better, though at the expense of aging stability.

Compared with polyimide tapes, CHR M69 has a lower continuous temperature ceiling. Polyimide backing can survive short-term exposures above 260 °C, while polyester is limited to approximately 130 °C continuous. Polyester is less expensive, easier to slit into narrow widths, and can provide a clearer or more uniform appearance. Polyimide tapes are generally selected for wave solder masking, transformer coil wrapping at high thermal class, and applications requiring extreme chemical resistance. Polyester/acrylic tape is selected where the temperature does not exceed the acrylic adhesive limit and where silicone-free operation, lower cost, or specific dielectric thickness is more important than maximum thermal endurance.

Compared with glass cloth tapes, CHR M69 is thinner, smoother, and less conformable around irregular surfaces. Glass cloth tapes provide abrasion resistance and mechanical strength, but they are bulkier and can leave fiber debris when cut. Polyester film backing provides a more uniform, pinhole-resistant dielectric surface. For wire bundling and coil wrapping, the choice depends on whether the coil needs conformability or a smooth dielectric film. For motor lead insulation, a polyester/acrylic tape may be preferred where space is limited and a thin wall is required. For heavy thermomechanical stress, a glass cloth tape with a high temperature adhesive is more appropriate.

Maximum continuous temperature for CHR M69 should be treated as an adhesive-limited parameter. The product is not recommended for continuous exposure above 130 °C or for direct immersion in aggressive polar solvents. Adhesion to low surface energy thermoplastics requires corona, plasma, or adhesion promoter pretreatment. Because the polyester backing is thin, surface scratches, nicks, or split edges reduce dielectric strength. Storage above 30 °C and 60 % relative humidity should be avoided, and roll stock should remain in original polyethylene packaging until use to prevent dust pickup and edge oxidation. Published data for long-term aged adhesion on specific powder-coated substrates are limited; prospective users should conduct qualification on actual production substrates and process conditions before committing volume.