For conventional oil-based offset ink, keep rosin-modified phenolic resin as the primary structure-forming binder and screen C9 aromatic or suitably modified DCPD resin as a co-resin. The hydrocarbon resin can tune varnish solubility, body, tack, set, film hardness and cost, but it is not an automatic one-for-one replacement. Prove compatibility in the complete resin, oil, solvent, pigment and additive package before a press trial.
How C9 and DCPD fit an offset binder system
Rosin-modified phenolic resins are widely used as resin for offset ink because they can combine pigment wetting, gloss, gelling response and compatibility with suitable mineral distillates. One current commercial TDS describes a highly soluble phenolic-modified rosin grade for sheetfed, heatset and coldset offset, with pigment wetting, high gloss and fast setting among its stated features.1
C9 aromatic resin adds a hard, thermoplastic component with useful affinity for aromatic media and selected oil-based vehicles. DCPD-derived resins can also enter lithographic vehicles, especially after chemical modification. ASTM D5958 explicitly lists C9 aromatic, modified DCPD and phenolic-modified rosin resins among the classes used in oil-based offset and letterpress test solutions.2 Published lithographic technology also describes combinations of modified rosin esters and hydrocarbon resins.3
“DCPD resin” is not one chemistry: an unmodified DCPD petroleum resin and a rosin-, phenolic- or maleic-modified DCPD hybrid are not interchangeable. Confirm the offered grade before assuming the compatibility reported for a modified resin.
Three properties to qualify first
1. Solubility and vehicle compatibility
Prepare each candidate at the same solids, temperature and heating history. Check hot and cooled clarity, haze, separation and viscosity. For a controlled comparison, ASTM D6038 measures precipitation temperature in high-boiling ink solvent: under that method, a higher precipitation temperature means poorer resin–solvent compatibility.4 Also repeat the check in the actual varnish because alkyd, vegetable oil, gellant and co-resin can change the result.
2. Film formation and gloss
Make equal-film-weight drawdowns on the intended paper or board. Record gloss, transparency, set, rub resistance and blocking after the same conditioning time. A compatible petroleum resin printing ink can level into a clear, hard film; excess resin, poor solvent release or phase separation can instead reduce gloss.
3. Pigment wetting
Compare grind time, fineness of grind, color strength, viscosity, tack and storage stability at equal pigment loading. Faster dispersion or lower initial viscosity alone does not prove durable wetting. The pigment must remain uniformly dispersed without flooding, flocculation or unacceptable rheology drift.
Typical values — formulation-screening priorities
| Ink process | Practical petroleum-resin role | First rejection criteria |
|---|---|---|
| Conventional offset | C9 or modified DCPD co-resin with rosin-modified phenolic binder | Hazy varnish, poor water balance, excessive tack or weak set |
| Solvent gravure | Co-binder or hardness/gloss modifier where the solvent dissolves it | Slow solvent release, brittle film or poor re-solubility |
| Solvent flexo | Limited co-resin in a compatible liquid-ink vehicle | Poor plate re-solubility, film adhesion or blocking |
What high-softening-point C9 contributes
High-softening-point C9 is worth screening when an offset varnish needs more body, a harder film or stronger blocking resistance. It can also support gloss when compatibility and leveling are good. The trade-off is important: increasing softening point can raise varnish viscosity or tack and may reduce tolerance for aliphatic ink oils. It does not independently guarantee faster drying, less misting or greater press-temperature resistance.
Use a ladder trial rather than a fixed replacement claim. Compare a nominal 110°C C9 grade with a nominal 120°C grade at equal substitution levels, then measure varnish clarity, cloud point, tack, flow, set, gloss, rub and press transfer.
Gravure and flexographic ink considerations
Gravure and flexographic inks are low-viscosity liquid inks, unlike paste-like lithographic inks. A technical review published by IARC describes a historical publication-gravure formulation as 15–20 wt% resin and 60–70 wt% solvent, illustrating how strongly solvent release controls that process.5
C9 resin is therefore most plausible in solvent-borne gravure or flexo vehicles whose solvent blend actually dissolves it. In nitrocellulose, polyamide, polyurethane, acrylic, alcohol-rich or water-based systems, treat it as a candidate co-resin—not the default primary binder. Standard C9 does not become water-soluble merely because the ink is water-reducible. Test solution clarity, drying, adhesion to the actual film or paper, flexibility, heat-seal response where relevant, and re-solubility on press.
Milorez grades to screen
Typical values — first-screen Milorez options
| Grade | Typical selection point | Suggested ink screen |
|---|---|---|
| MR-C9110 | Thermal C9; nominal 110°C softening point | General offset co-resin where balanced processing is the priority |
| MR-C9120 | Thermal C9; nominal 120°C softening point | Higher-body or harder-film offset development |
| MR-C9130 | Cold-polymerized C9; confirm current specification | Lighter-color work where standard thermal C9 is too dark |
| MR-* DCPD series | Chemistry and specification confirmed per offer | Formulations already designed around a compatible DCPD resin |
Review the full C9 resin range before choosing by softening point alone. Milorez is a transparent export trading supplier in Fujian, China; the proposed source and specification are matched to the application rather than presented as Milorez-owned manufacturing.
Request a free ink-resin sample
Send Milorez your printing process, incumbent resin, binder and solvent package, target softening point, Gardner color limit, test method, annual demand and destination port. We will shortlist a C9 or DCPD option for a free laboratory sample. Commercial MOQ is 1×20’FCL. Request a sample or email [email protected].
Frequently asked questions
Which resin is best for conventional offset ink?
Rosin-modified phenolic resin is a common primary binder. Screen C9 aromatic or suitably modified DCPD resin as a co-resin when you need to adjust body, hardness, gloss, set or cost.
Can C9 resin replace rosin-modified phenolic resin?
Not universally. Partial replacement may work, but qualify solubility, tack, rheology, water balance, gloss, drying and storage stability at each level.
Why use high-softening-point C9 resin in ink?
It can add body, film hardness and blocking resistance. It can also raise viscosity or tack and reduce aliphatic-solvent tolerance, so higher is not automatically better.
Is C9 resin suitable for gravure and flexographic inks?
Yes, as a co-resin in compatible solvent-borne systems. For water-, alcohol-, NC-, polyamide- or PU-based vehicles, verify clarity, solvent release, adhesion and press re-solubility first.
What is the MOQ, and are samples free?
Samples are free for laboratory screening. The commercial MOQ is one 20-foot full-container load. Include your formulation and destination so the sample and quotation address the same requirement.
Sources
Footnotes
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Lawter, SETAPRINT 2376 E Technical Data Sheet, updated July 5, 2024. ↩
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ASTM International, ASTM D5958-99(2026): Preparation of Oil-Based Ink Resin Solutions, active revision updated June 17, 2026. ↩
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Arizona Chemical Company, US5902389A: Rosin-Based Resin Ink Vehicles. ↩
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ASTM International, ASTM D6038-21: Compatibility of Resin/Solvent Mixtures by Cloud Point. ↩
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IARC, Printing Processes and Printing Inks, in Printing Processes and Printing Inks, Carbon Black and Some Nitro Compounds. ↩
Frequently asked questions
Which resin is best for conventional offset ink?
Rosin-modified phenolic resin is a common primary binder for conventional oil-based offset ink. C9 aromatic or suitably modified DCPD resin can be screened as a co-resin to adjust body, hardness, gloss, set and cost, subject to varnish and press testing.
Can C9 resin replace rosin-modified phenolic resin in offset ink?
Usually not as a universal one-for-one replacement. C9 resin can replace or supplement part of the binder package when its solubility, tack, rheology, water balance, gloss and drying behavior are acceptable in the complete formulation.
Why use high-softening-point C9 resin in ink?
A higher-softening C9 grade can add varnish body, film hardness and blocking resistance. It may also raise viscosity or tack and narrow aliphatic-solvent compatibility, so softening point alone does not prove faster drying or better press performance.
Is C9 petroleum resin suitable for gravure and flexographic inks?
It can be useful as a co-resin in compatible solvent-borne systems. In water-based, alcohol-rich, nitrocellulose, polyamide or polyurethane systems, confirm solution clarity, solvent release, adhesion, re-solubility and storage stability before use.
What is the Milorez MOQ, and are samples free?
Milorez provides free samples for laboratory screening. The minimum commercial order is one 20-foot full-container load (1×20'FCL). Share the ink process, binder, solvent package, target softening point and destination when requesting a sample.