Saint-Gobain Performance Plastics supplies the CHR M788 pressure-sensitive tape as a single-coated roll product comprising a polyester film carrier and a natural rubber adhesive layer. The alphanumeric designation CHR M788 identifies the specific combination of backing and adhesive within the CHR product family; the M788 configuration is distinguished from acrylic, silicone, and thermosetting rubber adhesive tapes by its use of natural rubber chemistry on a polyester support. The polyester carrier is a biaxially oriented film whose mechanical properties are selected for tensile strength, dimensional control, and dielectric isolation. The adhesive is a compounded natural rubber system containing tackifier resins, plasticizers, and antioxidants; it is applied as a continuous layer on one side of the carrier. The product is available in log or slit-roll form and can be converted into die-cut parts for industrial assembly. Because natural rubber pressure-sensitive adhesives are highly responsive to substrate surface energy, dwell time, and temperature, any quoted peel, tack, or shear value is valid only when accompanied by the test method, panel type, and conditioning environment. The technical profile of the M788 must therefore be read against ASTM, PSTC, and IEC test frameworks.

How Does the Natural Rubber Adhesive System Influence Peel, Tack, and Shear?

Pressure-sensitive adhesion in natural rubber is not a simple surface property. The adhesive is a heterogeneous blend of high-molecular-weight cis-1,4-polyisoprene, tackifier resins, plasticizers, and stabilizers. At room temperature, the compounded system is designed to operate above its glass transition temperature; tackifier resins shift the effective T_g from approximately −60 °C for raw natural rubber to a window near −10 °C to +10 °C, which promotes rapid fibrillation and bonding under low application pressure. Peel adhesion is commonly measured according to ASTM D3330 or PSTC-101 using a stainless steel panel and a dwell time of 1 min to 24 h. Shear resistance is evaluated by ASTM D3654, with a static load typically between 0.5 kg and 1.0 kg on a 25 mm wide specimen. Loop tack may be measured by ASTM D6195, while rolling ball tack is historically described by PSTC-6. Natural rubber PSAs generally show high immediate tack and good adhesion to paper, metal, and many polar plastics, but their cohesive strength and temperature resistance are lower than crosslinked acrylic systems. In addition, natural rubber requires protection against ozone, ultraviolet radiation, and long-term thermal oxidation; the performance of the M788 tape is therefore bounded by the grade of antioxidant system compounded into the adhesive.

Within the natural rubber PSA category, the balance between peel and shear is manipulated by tackifier loading, molecular weight distribution, and crosslinking. A low crosslink density formulation may generate high loop tack and fast wet-out at 23 °C but will fail cohesively under a shear load of 0.5 kg to 1.0 kg at temperatures above 60 °C. In contrast, a more crosslinked acrylic PSA can sustain comparable shear loads at 150 °C but may require higher application pressure. The natural rubber adhesive on M788 is therefore positioned for general-purpose industrial holding and splicing where ambient or short-duration thermal conditions dominate. Users should not extrapolate room-temperature peel data to hot peeling, as natural rubber systems can transition from adhesive failure to cohesive failure above 50 °C to 70 °C, depending on formulation.

Polyester film carriers in the CHR product range provide a uniform thickness profile that supports automated roll handling. Thickness is determined by ASTM D3652, with individual readings taken across the web using a dead-weight or electronic thickness gauge. For a carrier thickness between 0.012 mm and 0.05 mm, a total calendar variation of ±10% is common in commercial film; tighter uniformity is available but must be specified. Tensile strength and elongation at break are measured according to ASTM D3759/D3759M; these values are reported in newtons per 100 mm width or pounds per inch rather than engineering stress. The polyester backing offers a high modulus and a relatively low elongation at break compared to polyethylene or polypropylene film tapes, making the product suitable for web splicing where minimal stretch under tension is required. The dielectric strength of the composite is evaluated by ASTM D1000 or IEC 60454-3; because the adhesive is an organic layer with different permittivity and conductivity, breakdown voltage depends on total thickness, electrode geometry, and humidity. Conditioning at 23 °C ± 2 °C and 50% ± 5% relative humidity is standard before electrical testing.

Slitting, Die-Cutting, and Roll-to-Roll Handling Parameters

Conversion of CHR M788 from log stock into narrow rolls is controlled by the shear and low-speed unwind characteristics of the natural rubber adhesive. The polyester backing resists necking, but edge quality in slitting depends on blade geometry, blade sharpness, and unwind tension. Narrow-web converters typically hold unwind tension between 15 N and 40 N per 100 mm of web width for polyester carrier tapes in the 0.05 mm to 0.10 mm total thickness range; excessive tension may induce adhesive deformation or telescoping in finished rolls. Die-cutting of natural rubber adhesive films requires attention to matrix stripping and adhesive flow. During hot-weather runs, natural rubber PSA may exhibit edge ooze if the converted parts are stacked under pressure; cooling or interleaving with release liners is used in production. The product has a release-coated liner or may be self-wound depending on the supplied format, but self-wound rolls rely on a release coating on the polyester film which reduces unwind force. For automated application, M788 tapes can be die-cut with tabbed liners and placed by pick-and-place equipment, but process validation should include a dwell study to detect adhesive transfer to cutting dies. On rotary shear slitters with a blade speed of 100 m/min to 250 m/min, edge quality is maintained when the incoming web tension is steady and the blade overlap is held within 10% of total thickness. Crush-cut systems require hardened anvil rolls and frequent cleaning because the adhesive can transfer to tooling. In die cutting, a hydraulic or servo press with controlled shut height is preferred to avoid cutting into the liner. Process engineers typically specify liner release force between 0.20 N and 0.60 N per 25 mm at 180° peel and 300 mm/min for pick-and-place liners, but M788 converters must confirm this against the supplied liner grade.

When the M788 Tape Is Evaluated for Electrical Insulation, the Relevant Test Matrix Includes ASTM D1000

In electrical and electronic applications, the polyester carrier provides the primary dielectric barrier. M788 may be considered for coil wrapping, transformer layer insulation, capacitor wrapping, or protective jacketing of wire harnesses only after the composite is tested to ASTM D1000 and, where applicable, IEC 60454-3. The polyester film can tolerate short excursions above 200 °C, but the natural rubber adhesive is not rated for indefinite exposure at that temperature. Varnish impregnation cycles often run between 120 °C and 135 °C; M788 may survive short excursions if the adhesive is protected from oxidative attack, but any continuous Class 130 °C or higher construction requires a recognized system evaluation. In motor coil wrapping, edge coverage and overlap must be controlled because the adhesive layer can flow away from sharp edges during bake cycles. In transformer applications, oil compatibility is a first-order concern; natural rubber PSA may swell in mineral oil unless specifically compounded for oil resistance. Published data for this specific configuration in transformer oil is limited, so qualification must include oil immersion at the design operating temperature.

Comparative selection between CHR M788 and other pressure-sensitive tapes is determined by the interaction of backing and adhesive. A polyester/natural rubber construction is generally selected when the application requires moderate tensile strength, dimensional stability, electrical isolation, and high immediate tack at room temperature, but does not expose the tape to aggressive solvents, plasticizer-rich films, ozone, or sustained temperatures above about 80 °C. In contrast, a polyester/acrylic tape from the same product family is more appropriate for outdoor exposure, glass bonding under UV, or higher continuous temperature; a polyimide/silicone tape is required for high-temperature masking above 200 °C, but it costs more and may require higher application pressure. A polyester/silicone tape is preferable for release surfaces and very high-temperature electrical insulation, although its adhesion to polar substrates is lower. If the application involves contact with plasticized PVC cable compounds, natural rubber PSA may lose peel strength as plasticizers migrate; acrylic or rubber-resin adhesives with high crosslink density and lower free volume may be specified. Published data for this specific M788 configuration is limited; therefore, substitution decisions should be supported by side-by-side evaluation on the actual production substrate.

The operational boundary is defined by solvent resistance and environmental aging, not by the polyester carrier alone

Natural rubber PSAs are swollen or degraded by many aliphatic and aromatic hydrocarbons, chlorinated solvents, ketones, and esters. In industrial wiping, cleaning, or painting operations, solvent contact must be restricted; if exposure is unavoidable, a crosslinked acrylic or silicone system should be selected. Plasticizer migration from soft PVC, neoprene, or certain polyurethane lacquers can plasticize the natural rubber adhesive, causing a measurable reduction in shear strength and an increase in adhesive transfer. Environmental aging of natural rubber involves ozone cracking and oxidative chain scission; antioxidant packages slow but do not eliminate these reactions. Storage should be in polyethylene packaging, at 15 °C to 25 °C, and below 60% relative humidity, away from ultraviolet light and ozone-generating electrical equipment. Under these conditions, many natural rubber PSA tapes retain measurable peel and tack for 12 months to 24 months from the date of manufacture, but material should be re-qualified for critical applications beyond 12 months. For bonding to low-energy surfaces such as polyethylene or polypropylene, corona discharge, plasma treatment, or primer application may be required to raise surface energy above 38 dyn/cm; natural rubber PSA alone may not wet untreated polyolefin films reliably.