Coumarone-indene resins are thermoplastic copolymers of coumarone (benzofuran) and indene obtained from the heavy solvent naphtha fraction of coal tar distillation. NOVARES C10 Coumarone-Indene Resin for Rubber & Adhesives is produced by cationic polymerization of this fraction, followed by neutralization, water washing, and vacuum stripping. The designation C10 identifies the nominal ring-and-ball softening point of 10 °C, placing the material in the liquid resin class at ambient processing temperatures. The product is supplied as a viscous, amber liquid with a density of 1.06–1.08 g/cm³ at 20 °C (ISO 1183-1), an acid number below 0.1 mg KOH/g (DIN EN ISO 2114), and a Gardner color not exceeding 4 (ISO 4630-2). Gel permeation chromatography (ISO 16014-1) with polystyrene calibration places the number-average molecular weight in the 400–600 g/mol range. The low molecular weight and aromatic-polar heterocycle content lower the glass transition to below 0 °C, as measured by differential scanning calorimetry at 10 K/min (ISO 11357-2). Batch-to-batch variation in dynamic viscosity, typically 1000–2500 mPa·s at 25 °C (ISO 2555, Brookfield RVT), reflects the low molecular weight distribution and residual aromatic monomer content after stripping. Unlike higher-softening-point coumarone-indene grades, NOVARES C10 functions as a plasticizing tackifier rather than as a reinforcing hard resin.

The specifications define the product release envelope. Where incoming material falls outside the viscosity range, packaging should be inspected for air ingress and direct solar heating, because the unsaturated coumarone-indene backbone is oxidation-sensitive even before compounding.

What distinguishes NOVARES C10 from higher-softening-point coumarone-indene grades and C9 petroleum tackifiers?

Compared with NOVARES C30, which has a softening point of 28–32 °C, and NOVARES C70, which has a softening point of 68–72 °C, the C10 grade has the lowest melt viscosity and the lowest glass transition temperature. In an SBR tread compound, C30 raises compound hardness and modulus at 300% elongation, while C10 acts more like an aromatic process oil: it reduces Mooney viscosity ML(1+4) at 100 °C (ISO 289-1) and increases green tack. The distinction is critical when the required compound property is building tack rather than reinforcement. Compared with C9 aromatic petroleum tackifiers of similar aromaticity, NOVARES C10 contains polar oxygen heterocycles from coumarone units, which can modify wetting of polar surfaces. However, the unsaturated backbone causes greater susceptibility to thermo-oxidative yellowing and odor generation during high-temperature processing. Hydrogenated C9 resins exhibit lower aromaticity and lower polar wetting, but their saturated structure permits longer processing at 180 °C without Gardner color increase above 2 (ISO 4630-2).

Addition ratios in rubber compounding are typically 2–10 phr on hydrocarbon rubber, with higher loadings used in friction compounds and calendered plies. In a tangential internal mixer of 75 L net chamber volume with 0.75 fill factor and 50 rpm rotor speed, the resin is charged with carbon black and plasticizer after the rubber has achieved a coherent mastication state. Because the C10 grade is liquid, it disperses more rapidly than flake or pastille grades. Batch-to-batch variation in viscosity can nevertheless influence dosing accuracy when gravimetric oil injection is not available. Addition of 5 phr NOVARES C10 to a carbon-black-filled NR/SBR carcass compound typically reduces the Mooney viscosity ML(1+4) at 100 °C by 3–8 Mooney units (ISO 289-1), with a smaller effect on scorch time than an equivalent mass of naphthenic oil. The unsaturated indene/coumarone structure participates in sulfur vulcanization to a limited extent; cure rate and crosslink density must be checked when replacing process oil at loadings above 5 phr, using rotorless cure testing (ISO 6502) and equilibrium swelling in toluene (ISO 1817). Dynamic mechanical analysis of a crosslinked SBR compound containing 5 phr NOVARES C10 shows the loss tangent peak shifts to lower temperature by approximately 2–4 °C compared with the oil-free control (ISO 6721-7), indicating plasticizing action without suppressing the rubbery plateau modulus. In tire innerliner or carcass compounds, this improves component tack without the softening penalty of a purely aliphatic oil. However, the shift in glass transition must be accounted for in dynamic performance indices because low-temperature plasticization can alter tan δ values at 0 °C and 60 °C (ISO 4664-1). On a two-roll mill with roll temperatures of 40–60 °C, the liquid resin should be added after band formation to prevent roll slippage. If added too early, the resin can lubricate the roll surface and increase milling time by 3–5 min per batch; this effect is not observed with flake grades such as C70.

NOVARES C10 compatibility boundary in SBR and EVA hot-melt systems

Low-softening-point coumarone-indene resins are not universally compatible with all base polymers. In SBR and natural rubber, the resin is miscible at conventional processing temperatures because the solubility parameters of the resin and the diene rubber overlap; the resin’s Hildebrand solubility parameter is generally reported as 8.5–9.5 (cal/cm³)^0.5. In EVA with vinyl acetate content below 18%, macroscopic phase separation may occur if the resin is loaded above 10 wt%, visible as surface haze or exudation after aging for 7 days at 40 °C under ISO 9142 conditioning. Formulators should screen compatibility by annealing a pressed film at 40 °C for 72 h and checking for exudation under 10× magnification. In EVA hot melts, the low molecular weight fraction acts as a plasticizer and reduces the glass transition of the formulation, lowering open time and allowing lower coating temperatures. Formulation screenings are run on a heated coater with slot die at 150–170 °C, using a coating weight of 20–30 g/m²; adhesion is assessed as 180° peel per ASTM D903 and loop tack per ASTM D6195. Loadings above 22 wt% in EVA hot melts can reduce shear adhesion failure temperature below 55 °C on corrugated board (ASTM D4498).

Hot-melt adhesive compounding imposes a different set of constraints because the resin is handled at elevated temperature for prolonged residence time. A twin-screw compounding line with an L/D ratio of 32:1 and barrel temperatures from 120 °C to 170 °C can incorporate NOVARES C10 as a liquid injection at the second barrel zone after the EVA or SIS polymer has softened. Injection pressure at the gear pump inlet must be maintained below 2.0 MPa because low-viscosity resin phases can cause screw slip and feed instability in starve-fed extruders. Hot-melt formulators use nitrogen blanketing during mixing to limit thermo-oxidative darkening; a headspace oxygen concentration below 5 vol% is recommended when the melt is held above 160 °C for more than 4 h. Samples taken from the production line should be checked for Gardner color (ISO 4630-2) and viscosity stability (ISO 2555) after 24 h at 150 °C; an increase in viscosity greater than 15% indicates unsaturated backbone oxidation. When using drum melters, the maximum melt temperature should be limited to 180 °C for short residence times, and the resin should not be held above 160 °C for more than a single shift. These limits are more restrictive than those for hydrogenated tackifiers because of the unsaturated coumarone-indene backbone.

Pressure-sensitive adhesive formulations use NOVARES C10 as a secondary tackifier in combination with a high-softening-point tackifier. At 30 wt% total tackifier loading, the C10 component may be 5–10 wt% of the formulation. A typical screen uses a 100 μm coating of adhesive on PET film and measures rolling ball tack (ASTM D3121), loop tack (ASTM D6195), and 180° peel from stainless steel (ASTM D3330). The low glass transition of C10 extends the application window to lower temperatures; the same property lowers shear resistance. End-users should evaluate 24 h shear adhesion failure temperature (ASTM D4498) and static shear (ASTM D3654) before qualifying a production formula. In solvent-borne PSAs based on natural rubber at 40% solids, addition of 8 phr liquid coumarone-indene resin can reduce minimum film-forming temperature and improve tack on recycled corrugated board. The Gardner color of the resin limits use in transparent label applications; a Gardner color of ≤4 is not suitable for high-clarity facestocks requiring water-white tackifiers.

When NOVARES C10 replaces an aromatic process oil in polychloroprene contact adhesive compounding

Polychloroprene solvent-borne contact adhesives use aromatic process oils or liquid resins to control dry film tack and open time. In a two-component solvent system based on methyl ethyl ketone/toluene at 60:40 by weight, replacement of 5 phr of aromatic process oil with NOVARES C10 is evaluated by ISO 9664 lap shear on beech wood and by ASTM D903 peel from steel. Published data for this specific configuration is limited; therefore the substitution is screened over a range of 3–7 phr because the resin’s higher viscosity raises the flow time of a 50 mL sample through a 4 mm ISO flow cup at 20 °C. Airless spray equipment operating at 8–12 MPa may require nozzle size adjustment if flow time increases by more than 10 s. The unsaturated resin can modify adhesion to porous substrates, but the formulation must be checked for storage stability because free acidic residues may catalyze solvent hydrolysis. Addition of 0.5–1.0 phr of an epoxy stabilizer is often used when the contact adhesive is stored above 30 °C; compatibility with magnesium oxide/zinc oxide curatives must be confirmed by viscosity stability over 14 days at 40 °C (ISO 3219).

Storage and handling require separate verification because the liquid resin is combustible but not readily classified as flammable under CLP; the flash point is typically above 200 °C (ISO 2719). Storage should be in sealed carbon steel or stainless steel vessels with internal temperature maintained below 30 °C. Above 40 °C, viscosity decreases sufficiently for pumping, but accelerated oxidation of the unsaturated backbone becomes measurable. Heating coils should not exceed 80 °C wall temperature to avoid localized polymerization. The resin should not be stored in direct sunlight; ultraviolet exposure at 340 nm can generate color bodies and increase peroxide value. Under nitrogen blanketing and cool conditions, the product is stable for 12 months from the certificate of analysis date. Batch-to-batch variation in color and viscosity should be monitored for continuous compounding lines because liquid injection flow meters require viscosity-corrected calibration. Combination with strong Lewis acids or amine-based additives in adhesive formulations may accelerate the cationic or condensation chemistry of residual functional groups; compatibility tests are required before blending with amine-cured epoxy systems.