3M 685 Riveters Tape, also designated 3M Polyethylene Tape 685 in manufacturer technical data, is a transparent polyethylene film tape coated with a pressure-sensitive acrylic adhesive. It is supplied in common roll formats of 25.4 mm × 32.9 m (1 in × 36 yd) and 50.8 mm × 32.9 m (2 in × 36 yd). The nominal total thickness is 0.14 mm (5.5 mil); the polyethylene backing accounts for 0.11 mm (4.5 mil) and the adhesive layer for approximately 0.03 mm (1.0 mil). The principal application is temporary surface protection during drill-and-rivet operations on aircraft aluminum panels. The product is also used for edge masking, protection of tool surfaces during low-temperature debulk, and reduction of rivet-set marking on Alclad surfaces. The polyethylene backing has a nominal elongation at break near 300%, which is higher than the elongation of many biaxially oriented polyester masking tapes. The acrylic adhesive is selected because it does not rely on migrating plasticizers and can provide comparatively clean removal from metallic surfaces when the tape is used within its stated temperature and dwell boundaries.

Physical Property Baseline and Standardized Test Methods

Tape product data should be read as typical values, not specification limits. The following values are derived from manufacturer-published technical data and are determined under the cited pressure-sensitive tape test methods.

Which Backing Property Dominates the Choice Between 3M 685 and Polyester Tapes?

The decision between 3M 685 and a polyester-backed protective tape is controlled by elongation, tensile stiffness, and thermal exposure. 3M 685 has a nominal breaking strength of 2.98 N/mm (17 lb/in) and elongation at break near 300% under ASTM D3759. Polyester films used in masking tapes typically exhibit higher tensile strength because biaxially oriented polyester has a higher elastic modulus than polyethylene. The lower tensile stiffness of 3M 685 improves conformance over curved panels and rivet heads, but it means that high unwind tension can permanently deform the backing. Conversely, tapes with lower elongation may split when stretched over a raised rivet head. The thermal boundary is another differentiator: 3M 685 is rated for continuous service from -51 °C to 66 °C (-60 °F to 150 °F), whereas many polyester protective tapes can tolerate higher bake temperatures. When a process requires paint bake above 66 °C, polyester or polyimide backings are standard substitutions. For one-cycle riveting operations below 66 °C, the conformability of the polyethylene backing is usually the controlling variable.

Unwind Tension Limits and Edge Lift on Automated Applicators

Because the polyethylene backing has lower tensile modulus than polyester, unwind tension on automated tape heads must be controlled. Published manufacturer data for a specific tension limit is limited, but width reduction greater than 1% during application is a practical indicator of excessive tension. Tape heads should be set to the minimum tension that produces wrinkle-free laydown. On production masking stations, 70 durometer rubber nip rollers with pressures of 0.2 MPa to 0.4 MPa are used to improve adhesive contact without stretching the film. Edge lift has been observed on oily or silicone-contaminated substrates and when the tape is stretched during application and allowed to relax after placement. Solvent cleaning with a non-residue cleaner and application at room temperature reduce edge lift. The tape should not be applied to substrates colder than 10 °C; below this temperature the acrylic adhesive does not wet out sufficiently and peel adhesion on aluminum falls below values required for reliable masking.

On production-scale CNC gantry riveting lines, 3M 685 is applied over Alclad skin panels after cleaning and before pilot-hole drilling. The tape reduces chip smear around drill entry points and protects the panel surface from rivet-set impact marks. Application is performed with a 70 durometer rubber roller at 0.2 MPa to 0.4 MPa nip pressure. The tape is not used over holes that require orbital riveting because the film can be drawn into the hole under tool pressure. Operators should verify that the tape does not bridge over countersunk holes; bridging creates a secondary cutting interface and can affect hole diameter. On panels with heavy oxide, a solvent wipe is completed before tape application. Published data for this specific configuration is limited, so first-article trials should be run on the intended substrate and rivet pattern. Failure modes seen on production lines include adhesive transfer when the tape is left in place during prolonged sun exposure and tearing when removal is attempted after the tape has been heat-aged above 40 °C.

When Removal Windows Tighten on Anodized Surfaces

Peel adhesion of the acrylic adhesive to stainless steel is 2.2 N/10 mm (20 oz/in) under ASTM D3330 Method A. On anodized aluminum, surface energy changes can reduce peel values; therefore, the stainless-steel peel value is not a substitute for lot qualification on the intended anodized surface. Dwell times above 72 h at 23 °C increase the risk of adhesive islands after removal. The tape should be removed by pulling back at an angle below 30° to the surface to lower the probability of cohesive adhesive failure. If the substrate temperature exceeds 40 °C at removal, the dwell window shortens because the adhesive softens. Panels heated by riveting or solar load should be cooled to room temperature before removal. Adhesive transfer can be inspected under 10× magnification after removal; visible residue is a removal-window failure.

For air-dry and low-bake paint masking below 66 °C, 3M 685 is used as a narrow edge tape on aluminum and primed panels. The tape edge is burnished with a 70 durometer roller to prevent solvent intrusion. High-solids two-component polyurethane systems containing ketones or esters can undercut the adhesive edge; a tape seal test on the primer system is required before production use. The tape is removed after the paint has flashed but before full cure when the coating is less sensitive to peeling. If left in place through an extended bake or placed on a hot panel above 66 °C, the backing can shrink and expose the paint edge. The product should not be used as a paint masking tape for powder coating, where cure temperatures exceed the continuous service limit.

Chemical and Thermal Boundaries in Masking Operations

Chemical exposure limits are controlled by the polyethylene backing and the acrylic adhesive. Brief contact with aliphatic solvents and common aerospace cleaning agents is generally acceptable, but immersion or prolonged contact with ketones, esters, or chlorinated solvents can soften the backing and initiate edge lift. The tape is rated for continuous service from -51 °C to 66 °C (-60 °F to 150 °F). Above 66 °C, the backing begins to soften and shrink; this is the controlling limitation in paint bake and autoclave cycles. Autoclave conditions also combine pressure and temperature, which can press the backing into the bag side and transfer adhesive to the tool. For cure cycles of 120 °C to 180 °C, polyester or polyimide tapes are standard substitutions. In low-bake paint systems that remain below 66 °C, 3M 685 can remain through one cure cycle, but edge quality should be confirmed on a painted panel before full production.

In room-temperature composite debulk operations, 3M 685 is placed on tool flange edges and vacuum port areas where epoxy resin flash is expected. The tape is removed after debulk and before the resin reaches a tack-free condition. If resin advances to gelation, the tape can become embedded in flash and may tear during removal. Vacuum bag consolidation at room temperature is below the service temperature limit, but the tape is not a substitute for proper tool surface release. On release-coated composite tools, adhesion may be too low for reliable placement during layup compaction; published data for this specific configuration is limited and first-article qualification is required. The tape should be burnished with a 70 durometer roller before bag placement to improve wet-out.

How Does the Acrylic Adhesive Compare with Natural Rubber Adhesives?

The acrylic adhesive on 3M 685 differs from natural rubber adhesives commonly used in general-purpose masking tapes. Natural rubber adhesives typically exhibit higher initial tack on low-surface-energy substrates, while acrylic adhesives develop adhesion more slowly and require adequate dwell. The acrylic adhesive on 3M 685 is less likely to migrate into paint systems than plasticized vinyl or rubber systems, which is a key requirement in aerospace riveting where the tape may contact primer. However, the acrylic system can become more aggressive after heat exposure. Users should not extrapolate rubber-adhesive removal behavior to this product; removal windows should be established on the actual substrate. The acrylic adhesive also contributes to lower residue on aluminum after short dwell, but that benefit is lost if the tape is left in place beyond the stated dwell window or exposed to sustained heat above 40 °C.

Storage conditions affect unwind and adhesion. Rolls should be kept at 21 °C ± 3 °C and 40% to 60% relative humidity in original packaging. Storage above 30 °C for extended periods can soften the adhesive and cause edge tack, while storage below 0 °C can reduce initial tack until the roll is conditioned at room temperature. Rolls should be used within 24 months of the ship date when stored under these conditions. If a roll has been exposed to a freeze-thaw cycle, it should be conditioned at 21 °C for 24 h before application. Incoming inspection typically checks total thickness per ASTM D3652 and peel adhesion to stainless steel per ASTM D3330 Method A. Regulatory status under REACH, RoHS, and FDA 21 CFR 175.105 should be verified through the current manufacturer certificate for the intended end use.