NOVARES TM85 AS is a low-molecular-weight pure monomer resin produced from copolymerized styrene and alpha-methylstyrene. It is supplied as pastilles for hot-melt adhesive compounding and is part of the NOVARES TM series in which the numerical suffix denotes the nominal softening point. Unlike mixed C5/C9 hydrocarbon tackifiers, the resin is polymerized from selected aromatic monomers rather than from cracked petroleum fractions; the resulting composition contains no ester or acid functionality and has a narrow molecular weight distribution. Published technical data report a ring-and-ball softening point of 81–89 °C under ASTM E28, an acid number below 0.1 mg KOH/g under DIN EN ISO 2114, a Gardner colour below 2 at 50 % solids in toluene under ASTM D6166, and a Brookfield melt viscosity at 180 °C between 150 mPa·s and 350 mPa·s under ASTM D3236. Differential scanning calorimetry under DIN EN ISO 11357-2 places the glass transition temperature between 48 °C and 55 °C. Molecular weight expressed as Mw is typically 1000–1400 g/mol by gel permeation chromatography using polystyrene calibration.

The lack of acid groups in NOVARES TM85 AS reduces interaction with calcium carbonate filler and with metal surfaces in mixing vessels. In ethylene-vinyl acetate hot-melt formulations containing 18–28 % vinyl acetate, the resin is typically incorporated at 15–30 wt% of the total adhesive to raise heat resistance without shifting melt viscosity beyond the limit of a gear-pump-fed slot-die coater. The viscosity response is best monitored by ASTM D3236 using a Brookfield Thermosel with spindle 27 at 180 °C; the target application window of 800–1500 mPa·s for roll-coating equipment is generally achieved at the lower resin addition level, while the upper addition level is reserved for high-viscosity case-sealing formulas that use heated hose pressures above 40 bar. At 20 wt% loading in an EVA wax-based packaging adhesive, open time under ASTM D4497 is typically reduced by approximately 2 s relative to a rosin ester formulation of equivalent softening point, while fibre tear on corrugated board remains above 90 % at -10 °C using an internal Kraft-tear method.

How Does the Narrow Molecular Weight Distribution Affect Phase Compatibility in Styrenic Block Copolymers?

The narrow molecular weight distribution of the pure monomer resin modifies the styrene-rich phase of styrene-isoprene-styrene and styrene-butadiene-styrene triblocks differently from a broad-distribution C9 aromatic resin. Because the resin has a high aromatic content and low Mw, it solvates the styrene end blocks more effectively at melt temperature, lowering the order-disorder transition temperature of the block copolymer when formulated at 40–60 wt% total tackifier. At the same time, the glass transition temperature of the aromatic resin phase remains above 40 °C, which preserves room-temperature shear holding power. This dual effect is measurable as an increase in shear adhesion failure temperature under ASTM D4498 and a reduction in melt viscosity at 180 °C under ASTM D3236. Published data for the exact shift in order-disorder transition temperature in NOVARES TM85 AS-based formulations is limited; evaluation by dynamic mechanical analysis at 1 Hz is required for a specific SIS grade.

In a controlled-rheology evaluation using a cone-and-plate rheometer with a 25 mm cone at 170 °C, an SIS blend containing 50 wt% NOVARES TM85 AS exhibits a lower zero-shear viscosity than a comparable C9 aromatic blend but a higher crossover frequency in small-amplitude oscillatory shear. This indicates that the pure monomer resin shifts the gel-like behaviour of the styrenic network to lower temperatures while maintaining the elastic character of the cooled adhesive. The crossover frequency can be used to set coating-line start-up temperature and die pressure setpoints, reducing air entrapment in the melt at high line speed. Compared with a pentaerythritol rosin ester of similar softening point, the pure monomer resin has a lower acid number and better colour retention, but it also has lower specific adhesion to unprimed aluminium and to polyester film. Wet-out on aluminium under ASTM D2578 may require corona surface treatment or a small addition of a polar rosin ester when the resin is used above 70 wt% of the tackifier package.

When NOVARES TM85 AS Replaces a C9 Aromatic Hydrocarbon Resin in Pressure-Sensitive Assembly Adhesives

The replacement of a standard C9 aromatic hydrocarbon resin with NOVARES TM85 AS changes the failure mode of the finished adhesive from cohesive to interfacial at low addition levels. Because the pure monomer resin has a higher glass transition temperature per unit of softening point, the plateau modulus of the SIS network increases more steeply with resin loading. Formulators should reduce the total tackifier content by 5–10 wt% when performing a one-for-one replacement, unless the formulation already contains a liquid plasticizer such as paraffinic white oil or a low-molecular-weight polyisobutylene. Failure to adjust the plasticizer level can produce a brittle adhesive with low loop tack on corrugated board at 5 °C; this transition is measured as a drop in loop tack under ASTM D6195 below 1.5 N/25 mm. For low-application-temperature pressure-sensitive adhesives, NOVARES TM85 AS should not dominate the tackifier package because its glass transition temperature above 48 °C can raise the continuous-phase Tg and cause rolling-ball tack under ASTM D3121 to fall below 20 mm at 5 °C when the resin exceeds 30 wt% of the adhesive.

In continuous hot-melt mixing operations using a 70-mm co-rotating twin-screw extruder with L/D 40:1, the resin is gravimetrically fed into the first feed throat while the SIS and oil are introduced in the second barrel section. Barrel setpoints from 150 °C to 180 °C with screw speed of 250–350 rpm provide sufficient dispersion without exceeding the temperature limit at which alpha-methylstyrene sequences undergo depropagation. The pressure drop across the die plate is typically lower than for a C9 resin of equivalent softening point because of the lower high-shear viscosity of the pure monomer resin. Operators monitoring melt temperature at the die should avoid excursions above 200 °C for more than 30 min; residence-time data from production campaigns show that colour and volatile content increase when the melt temperature exceeds 200 °C even in the absence of oxygen. The material has a flash point above 200 °C under ASTM D92 Cleveland open cup, which requires hot-oil heating systems to maintain temperature control and avoid ignition hazards in the event of a spill.

Processing Boundaries, Equipment Settings, and Storage Limits

The practical processing window for NOVARES TM85 AS is bounded at the lower end by the softening point and at the upper end by thermal depropagation. In batch hot-melt mixing vessels, a jacket temperature of 165–185 °C is sufficient to dissolve the pastilles into an EVA or SIS melt within 20–40 min at moderate impeller speed. The pastilles should be stored below 30 °C in sealed containers and should not be exposed to relative humidity above 60 %; surface moisture introduced into a melt above 180 °C can generate steam and cause foaming in the finished adhesive. The resin is incompatible with high-density polyethylene and polypropylene homopolymers as primary polymers; at addition levels above 10 wt% in such systems, the aromatic resin phase can separate and reduce elongation at break under ASTM D638-14.

Compatibility with amine-functional additives and polyamide resins is not supported by published data; such additives should not be introduced into the same melt without preliminary solubility testing. In food-contact applications, the finished hot-melt adhesive must be evaluated as an article component under 21 CFR 175.105(c) or Commission Regulation (EU) No 10/2011, with migration testing conducted according to the specific food simulants and time-temperature conditions defined in those regulations. REACH registration under EC No 1907/2006 should be confirmed with the supplier for the import region before use in European production. No conclusion regarding food-contact compliance should be drawn from the resin specification alone.