Dielectric Polymers NT-702 Acrylic Tape is an electrical-grade pressure-sensitive adhesive tape specified for coil finishing, harness insulation, and bus bar isolation in low- and medium-voltage assemblies. The product code NT-702 is a manufacturer-specific designation; it does not by itself communicate total thickness, backing polymer, adhesive coat weight, or thermal endurance class. Those values must be confirmed against the supplier’s batch certificate before release to production. Qualification under ASTM D1000, ASTM D3330/D3330M, ASTM D3759/D3759M, ASTM D149, and ASTM D257 is required for electrical insulation purposes. Published data for the exact NT-702 configuration are limited in this document, so representative acrylic electrical tape values are identified as class data and should not replace supplier-certified NT-702 values.

Converted rolls are available in slit widths common to coil and harness insulation: 6 mm, 12 mm, 19 mm, 25 mm, and 50 mm, with width tolerance commonly maintained at ±0.2 mm when specified. The acrylic adhesive coat weight for this product class is generally between 15 g/m² and 35 g/m², while total caliper is backing-dependent. Because the adhesive system is acrylic, incoming inspection should include a residue-on-ignition check or equivalent verification of adhesive distribution across the web, particularly for rolls used in automated taping heads where edge ooze can transfer to guides and tooling.

Slot Die Coating and Roll-to-Roll Converting Limits the Usable Width and Winding Tension

Coating processes for acrylic electrical tapes are typically run on roll-to-roll lines using comma roll, reverse gravure, or slot die application heads with line speeds of 10 m/min to 60 m/min depending on coating viscosity and solvent-evaporation demand. The adhesive solution for solvent-borne acrylic systems is commonly conditioned to 1,000 mPa·s to 4,000 mPa·s at 25 °C. Drying is staged: the first zone removes low-boiling solvent at 50 °C to 70 °C, the second zone is set at 90 °C to 120 °C, and the final zone is controlled at 130 °C to 150 °C with air velocity between 2 m/s and 5 m/s. A final-zone deviation of more than ±5 °C from the validated drying profile can shift acrylic adhesive crosslink density enough to alter peel adhesion measured by ASTM D3330/D3330M and to increase edge ooze under subsequent winding tension.

Slitting is performed by circular knife, razor, or crush cutting. The selected method affects the edge character of the tape, which in turn influences dielectric weakness at the tape periphery. In production converting, tension must be held below the backing yield point as measured by ASTM D3759/D3759M. Telescoped rolls and adhesive ooze are observed on automated taping heads when unwind tension is set too high or when ambient storage rises above 38 °C. Rolls that are wound with excessive in-wound tension can develop blocking at the core and lose usable length before the first full rotation of the coil taping head.

For coil wrapping and motor lead bundling, the tape is applied with dedicated spiral wrapping heads or semi-automatic bench fixtures. Wrapping tension should not exceed 10% of the tape breaking strength recorded on the batch certificate. This prevents reduction of thickness at the overlap and preserves dielectric withstand in the finished winding. Adhesion to copper and epoxy-coated laminates is verified by ASTM D3330/D3330M. Adhesion to low-energy surfaces such as untreated polypropylene or powder-coated steel may fall below the approved value when substrate surface energy is below 38 mN/m; corona or plasma pretreatment is then required. Application at substrate temperatures below 10 °C reduces acrylic adhesive wet-out and is not recommended unless validated on the actual production substrate.

What Distinguishes NT-702 from Silicone and Rubber Adhesive Electrical Tapes?

The principal difference is chemical compatibility. Acrylic adhesive systems do not intentionally release volatile cyclic siloxane species, while silicone adhesive tapes can deposit siloxane contamination on adjacent surfaces. In paint-shop, optical assembly, oxygen-sensor, and medical-device environments, this difference drives selection of an acrylic adhesive tape unless thermal endurance above 180 °C is required. Compared with rubber adhesive electrical tapes, acrylic systems have better oxidative stability but may exhibit lower initial tack on rough or low-energy surfaces. PVC electrical tapes differ by using a plasticized vinyl backing; plasticizer migration can cause embrittlement and contamination of adjacent cable insulation, an effect measured in long-term heat aging rather than short-term adhesion.

These differences do not imply that NT-702 is limited to the lower thermal class if the dielectric backing is polyimide or aramid. However, the acrylic adhesive layer will typically impose the continuous-use limit. For applications above 155 °C, a silicone adhesive tape on polyimide is generally selected. For applications below 105 °C where plasticizer contamination is prohibited, an acrylic tape of the NT-702 category is preferred over plasticized PVC tape.

In transformer interlayer insulation, the absence of plasticizer and silicone avoids interference with subsequent varnish impregnation. Varnish compatibility is evaluated by applying the tape to a bare copper panel, curing the varnish according to the manufacturer’s cycle, and inspecting for adhesive lifting, interfacial haze, or solvent attack. Published data for NT-702 in varnish compatibility is limited; therefore a qualification coupon should be run before production release.

UL 510 Recognition and IEC 60454-3 Type Designations

Compliance for insulating tapes in North America is often evaluated under UL 510, which examines adhesion, dielectric breakdown, and thermal aging on specified substrates. In international electrical applications, IEC 60454-1 establishes general requirements, and the applicable IEC 60454-3 material specification sheet defines product-type allowances. A manufacturer’s UL file number and IEC type designation should be compared with the printed batch label; the NT-702 designation alone is not a compliance mark. Under REACH 1907/2006 and RoHS 2011/65/EU, the supplier’s declaration should confirm restricted-substance status for the acrylic adhesive and backing.

Storage of unopened rolls should follow the manufacturer’s date-code statement. Typical acrylic pressure-sensitive tape storage conditions are 10 °C to 27 °C at 45% to 60% relative humidity, away from direct UV and conductive dust. Rolls should be stored flat or suspended on cores to prevent ovalization. If the tape is conditioned below 10 °C, it should be allowed to reach 20 °C to 25 °C before application to reduce peel-force drop and die-cutting chipping.

In hermetic motor lead connections, NT-702 acrylic tape is used as a secondary insulation wrap under lacing cord or over soldered joints. The taping head should use polyacetal or anodized aluminum roll guides; steel guides without release coating can abrade the backing and create dielectric weak spots. On production lines with high-speed lacing operations, tape edges should be inspected under 10× magnification after slitting to detect adhesive stringing or nicks larger than 0.1 mm.

In capacitor winding and bus bar insulation, the tape is applied as a straight wrap or spiral wrap under controlled tension. Inspection at 10× magnification after slitting should detect edge nicks greater than 0.1 mm; such defects can lower dielectric withstand under ASTM D149. Surface contamination by silicone release liners, mold release, or plasticizer-containing films must be cleaned before application; a wipe with isopropanol and lint-free cloth is acceptable only when validated by adhesion pull tests on the actual substrate.