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JR 3000 vs JR 3001 vs JR 3003 vs JR 3125 — which unmodified epoxy resin should you use?

When engineers, formulators and shop managers pick an unmodified epoxy resin they’re solving a set of practical problems: matching viscosity to the process, getting the required optical clarity, tuning cure behavior via an appropriate hardener, and minimizing waste and handling issues on the shop floor. The JR-series (3000, 3001, 3003, 3125) covers that spectrum. This comparative guide cuts through specs and gives a pragmatic decision map you can act on.

At-a-glance technical summary

• JR 3000 — Standard multipurpose unmodified epoxy. EEW 185–195 (typical 188). Viscosity 10,000–15,000 mPa·s (typ ~11,800). Good baseline for laminates, potting, general casting and formulations that need a dependable, industry-standard resin.
• JR 3001 — Extra-clear variant for optical work. EEW 188–199. Viscosity similar to JR-3000, but engineered for APHA < 20 (extra low tint). Best where clarity and low intrinsic colour are critical (art, decoupage, clear coatings).
• JR 3003 — High-viscosity unmodified resin. EEW 200–230. Viscosity 20,000–40,000 mPa·s. Designed where body and edge-hold matter — adhesives, thick brushable coatings and decoupage.
• JR 3125 — Very high-viscosity grade for heavy adhesive formulations. EEW 200–250. (High body / thixotropic base for structural adhesives and formulated mortars.)

All four are supplied in practical shop pack sizes (10 / 20 / 30 kg — barrels available), with long shelf life in company packaging.

Key performance trade-offs (what the numbers mean in practice)

• Viscosity: lower viscosity (JR 3000 / 3001) → better substrate wetting and faster bubble release (useful for casting, laminating and vacuum/degassed work). Higher viscosity (JR 3003 / 3125) → anti-sag, gap filling and bead retention for adhesives or vertical coatings.
• EEW & formulation: EEW sets the resin’s reactive epoxy content for stoichiometry and affects how a chosen hardener performs; cure kinetics and final properties are determined primarily by hardener chemistry and overall formulation, not by resin choice alone.
• Optical clarity: JR 3001 is the pick where APHA < 20 matters (display parts, jewel-like casts). All epoxies will tend to yellow with prolonged UV exposure — hardener and post-cure choices influence long-term colour stability.
• Handling: JR 3000/3001 are easier to pump and degas; JR 3003/3125 allow you to formulate thixotropic adhesives without additives or with less thickener.

Job-ready tips and common pitfalls

• Batch size & exotherm: even “slow” resins can overheat if batch volumes are large or additives accelerate cure — always trial the mixed mass and control batch size.
• Bubble management: for optical casts use low-viscosity resin, small batches and vacuum degassing. For thick decorative work, consider staging pours or seal coats.
• Pigments & fillers: low-viscosity grades wet pigments and coated fillers better; high-viscosity grades may need pre-dispersion. Use coated fillers to avoid colour spots.
• Hardener selection: cure behaviour (pot life, yellowing tendency, final Tg) is governed by hardener chemistry. Always validate the resin/hardener pair under your process conditions.
• Handling & inventory: 10/20/30 kg packs reduce waste and make FIFO practical; barrels give scale economies. Company packaging shows long shelf life — still rotate stock.

Troubleshooting quick reference

• Tacky or undercured parts → check mix ratio, mixing thoroughness, temperature and hardener compatibility.
• Core haze → trapped microbubbles or outgassing; reduce batch size, degas or seal porous inclusions.
• Sagging on verticals → switch to JR 3003 or JR 3125 or add thixotropy.
• Premature yellowing → evaluate hardener choice and add UV-protective topcoat if exposure expected.

Pick the JR grade to match the process objective — low-viscosity JR 3000/3001 for clarity, wetting and casting; JR 3003/3125 when body, edge hold and gap fill are the priority. Combine the right hardener, control batch size and use the practical pack sizes to keep waste down and quality consistent.